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In this study, the effect of gradient and multi-layered porous media is assessed for the optimized properties and arrangement in the tested novel baffle design arrangement, which results in further enhancement in its thermo-hydraulic performance. The computational study is carried out using ANSYS FLUENT; wherein the permeability and porosity for each layer is varied. It's executed in two steps: case 1 – porous layers with variations implemented (constant, linear/stepwise, increasing/decreasing) and case 2 – porosity varied over the length. The findings show that the linear/stepwise increments in both cases give almost similar performance evaluation criteria (PEC) values. The increase in heat transfer rate and pressure drop can be compared using PEC, for better evaluation of the performance of different arrangements. With the simulation data genetic algorithm optimization model is used to find the optimal arrangement of the porous layers for both cases to maximize PEC further. The optimal arrangement for case 1 and case 2 taken individually, gives PEC of 2.425 and 2.401 respectively. And their simultaneous optimization gives highest PEC of 2.508. Additionally, to improve the heat transfer rate further, Al2O3 (5 w/v %) nanoparticles in water is tested with optimized conditions, which improves the PEC by almost double magnitude. [ABSTRACT FROM AUTHOR]

The enhancement with porous media involvement is estimated and compared for three varieties of shell and tube heat exchangers (STHXs), with helical, segmental and clamping anti-vibration baffles, with two variations, viz., porosity value and dimension of this media (radius). In this study, further improvement in the thermo-hydraulic performance of the anti-vibration baffles design of STHX was investigated using simulation, with porous media inclusion. The inclusion of porous medium in the shell side is in a way that the whole tube bundle is wrapped by it; inside the tubes, porous media are located in two ways: (1) at the center of tubes and (2) fixed to the inner lining of the tubes. The findings suggest that the porous media improve the heat transfer with the expense of pressure drop; it is also noted, of all the cases, the pressure drop is minimum in anti-vibrational baffles. The analysis showed that using porous media with specific porosity and dimension can increase heat transfer rate along with less pressure drop. For the clamping anti-vibration baffles STHX, enhanced and overall effective performance was found with porous media inclusion of 0.6 porous radius ratio and porosity of 0.6. [ABSTRACT FROM AUTHOR]

In the present study, the recent research of three kinds of surface heat exchangers, i.e., shell-and-tube heat exchangers with helical baffles, air-cooled heat exchangers used in large air-cooled systems, and primary surface heat exchangers are reviewed. They are used in the energy conversion and utilization for liquid to liquid, gas to gas and liquid to gas heat exchange, respectively. It can be concluded that the helical baffled shell-and-tube heat exchangers (STHXs) should be used to replace the conventional segmental baffled STHXs in industries, despite there are a lot of research work have to be done, especially on the novel combined helical baffles. The primary surface gas to gas heat exchangers are developing towards to the more complex 3D CC primary surfaces, such as the double-wave CC primary surface, offset-bubble primary surface and 3D anti-phase secondary corrugation. The whole performance for the air-cooled heat exchangers in the air cooling system and the multi-objectives optimization for air-cooled heat exchangers should be paid more attention, considering the heat transfer, pumper power, space usage and other economic influence factors. [ABSTRACT FROM AUTHOR]

Abstract: A combined multiple shell-pass shell-and-tube heat exchanger (CMSP-STHX) with continuous helical baffles in outer shell pass has been invented to improve the heat transfer performance and simplify the manufacture process. The CMSP-STHX is compared with the conventional shell-and-tube heat exchanger with segmental baffles (SG-STHX) by means of computational fluid dynamics (CFD) method. The numerical results show that, under the same mass flow rate M and overall heat transfer rate Q m, the average overall pressure drop Δp m of the CMSP-STHX is lower than that of conventional SG-STHX by 13% on average. Under the same overall pressure drop Δp m in the shell side, the overall heat transfer rate Q m of the CMSP-STHX is nearly 5.6% higher than that of SG-STHX and the mass flow rate in the CMSP-STHX is about 6.6% higher than that in the SG-STHX. The CMSP-STHX might be used to replace the SG-STHX in industrial applications to save energy, reduce cost and prolong the service life. [Copyright &y& Elsevier]

In recent years, the genetic algorithm (GA) technique has gotten much attention in solving real-world problems. This technique has a strong ability for global searching and optimization based on various objectives for their optimal parameters. The technique may be applied to complicated heat exchangers and is particularly useful for new types. It is important to optimize the heat exchanger, for minimum volume/weight, to save fabrication cost or for improved effectiveness to save energy consumption, under the requirement of allowable pressure drop; simultaneously it is mandatory to optimize geometry parameters of heating plate from technical and economic standpoints. In this paper, GA is used to optimize the cross wavy primary surface (CWPS) and cross corrugated primary surface (CCPS) geometry characteristic of recuperator in a 100 kW microturbine, in order to get more compactness and minimum volume and weight. Two kinds of fitness assignment methods are considered. Furthermore, GA parameters are set optimally to yield smoother and faster fitness convergence. The comparison shows the superiority of GA and confirms its potential to solve the objective problem. When the rectangular recuperator core size and corrugated geometries are evaluated, in the CWPS the weight of the recuperator decreases by 12% or more; the coefficient of compactness increases by up to 19%, with an increase of total pressure drop by 0.84% compared to the original design data; and the total pressure drop versus the operating pressure is controlled to be less than 3%. In the CCPS area compactness is increased to 70% of the initial data by decreasing pitch and relatively high height of the passage, the weight decreases by 17-36%, depending on the inclination angle (θ). Comparatively the CCPS shows superior performance for use in compact recuperators in the future. The GA technique chooses from a variety of geometry characters, optimizes them and picks out the one which provides the closest fit to the recuperator for microturbine. [ABSTRACT FROM AUTHOR]

The metals are the most popular materials for the plate heat exchangers due to high thermal conductivity. The thermal performance of the metallic plate heat exchanger is degraded by longitudinal heat conduction in the plate. For the cabinet cooling system and ventilator, the metallic plate heat exchanger can be replaced by the plastic plate heat exchanger. In this article, the longitudinal heat conduction in the plastic heat exchanger is studied by using the heat transfer models with and without longitudinal heat conduction, which were proposed in our previous work. The effects of both transverse heat conduction and longitudinal heat conduction can be considered. The thermal performances of the plastic plate heat exchanger and metallic plate heat exchanger are compared. We find out that in the plastic plate, both the transverse heat conduction and longitudinal heat conduction are weakened because of the low thermal conductivity. The high-density polyethylene plastic plate heat exchanger has better thermal performance than that of the aluminum plate heat exchanger. [ABSTRACT FROM AUTHOR]

The most extensively used heat exchanger in numerous research fields and industrial processes is the shell and tube heat exchanger. The selection of the baffle plays a vital role to regulate and increase the thermohydraulic performance and also to decrease fluid-induced vibrations due to shell side flow. 3-D computational fluid dynamics (CFD) and fluid-structure interaction (FSI) have been done to analyze the pressure drop, heat transfer coefficient, vortex shedding, and tube deformation due to induced vibrations among the recently developed clamping antivibration baffles with square twisted tubes, helical baffles with cylindrical tubes, and conventional segmental baffles with cylindrical tubes at different shell side flow rates by using commercial software ANSYS. Complete heat exchangers are modeled for numerical comparison; the thermohydraulic performance of the numerical model shows the suitable agreement by validating it with already published results and Esso method for single segmental baffles. It is then used to compare the performance of the same heat exchangers with CBSTT and HBCT. Thermohydraulic performance of CBSTT-STHX is better than SGCT-STHX. The heat transfer coefficient of heat exchangers with tube-to-baffle-hole clearance is higher and there is a reduction in the pressure drop compared to the results of STHXs without tube-to-baffle-hole clearance. The deformation in the tubes and vortex-induced vibrations are minimum in STHX with CBSTT than in STHXs with HBCT and SGCT. [ABSTRACT FROM AUTHOR]

A novel structure for a shell-and-tube heat exchanger (STHX) with triple-layer flower baffles consisting of three blades is proposed in this article. This study also compares the performance of three heat exchangers with triple-layer flower baffles, double-layer flower baffles, and segmental baffles. In order to compare the hydrodynamics and heat transfer characteristics of the three heat exchangers, a water–water heat transfer experiment is designed. The experiment is carried out in a counter-current flow pattern with hot water in the shell and cold water in the tube. Based on the experimental data, at the same flow rate, the shell-side heat transfer coefficients of the STHXs with triple-layer flower baffles and double-layer flower baffles are 31.7% and 14.3% higher than those of traditional segmental baffles, respectively. With an increased number of blades, the STHX with triple-layer flower baffles achieves a comprehensive performance that is 23.7% improved over the STHX with double-layer flower baffles. Finally, an experimental correlative formula is fitted for the heat exchanger with flower baffles and an optimal design scheme for shell-side heat transfer enhancement is proposed. [ABSTRACT FROM AUTHOR]

Thermoelectric power generators (TEGs) have received considerable attention in the vehicular waste heat recovery. Large temperature difference between hot-side end and cold-side end of TE modules should be maintained to keep large power generation. However, the scaling-up problem of inevitably temperature drop of exhaust gas along the flow direction of vehicles is introduced when multiple TE modules are assembled. In this work, a three-dimensional fluid–thermal–electric multiphysics model with equivalent properties of TE modules is established. The influencing mechanism of longitudinal vortex generator (LVG) pair number and distribution in the hot-side heat exchanger on the local power generation performance of the TEGs is examined. It is found that the extent of the local power generation enhancement gets smaller or even deteriorates at the downstream TE modules by uniformly increasing the LVG pair number along the flow direction. Hence, to make the heat flux efficiently utilized, a nonuniform segmented enhancement method is used for the hot-side heat exchanger. The results show that compared with the TEG with a uniform heat exchanger or a downstream-denser heat exchanger, the total Seebeck voltage generated by the TEG with an upstream-denser heat exchanger is 28% higher, and its output power is 64.4% higher at the matched load resistance. The TEG with the upstream-denser heat exchanger significantly improves the overall power generation performance without additional pumping power. [ABSTRACT FROM AUTHOR]

As a new type of heat exchanger, the printed circuit heat exchanger (PCHE) with high compactness can work under high pressure and high temperature, and can be applied to the very high temperature gas nuclear reactors. The chemical etching technology is one of main processes during PCHE fabrication, which determines whether PCHE flow channels can be properly produced according to design. However, many factors can affect the etching quality and the poor etching process can cause a great deal of uncertainty on the precision of stainless steel flow channels. In this paper, a two-dimensional (2-D) cellular automata model (CA) is used to simulate the etching process on stainless steel to examine the change of channel features varying with time under certain etching rates. Moreover, the simulation results are compared with our previous experimental etching data. On the one hand, from the comparison of the simulation results with channels data by spray etching, 2-D CA model can realize the simulation of etching process and display channel features under different etching rates and lateral erosion rates in every time period. On the other hand, from the comparison of the simulation results with channels data by immersion etching under different FeCl3 concentration and etching liquid temperature, 2-D CA model vividly presents channel features under different factors, which can easily and clearly explain the influence of factors on the etching quality, puddling effect and so on. Therefore, the simulation result strengthens the understanding of the etching mechanism and is helpful to realize an efficient and precise PCHE fabrication. [ABSTRACT FROM AUTHOR]

Sustainability has become a broad societal goal, aiming to ensure that human beings coexist safely and harmoniously with nature over a longer time. The influence of the COVID-19 pandemic on the global economy is coming to an end. The development and merits of sustainable energy supply, advanced technology, and economic features have received significant attention over the last few decades. However, significant gaps still exist with respect to how to design, construct, and implement hybrid and optimal energy systems with the lowest investment and cost. Since 2002, the Sustainable Development of Energy, Water, and Environment Systems (SDEWES) conferences have become a significant meeting venue for researchers to introduce, discuss, share, and disseminate novel concepts and ideas. This paper presents an overview of published articles in the Special Issues (SIs) dedicated by the series SDEWES conferences, especially those published in Energies recommended by the 16th SDEWES Conference, which was held on 10–15 October 2021 in Dubrovnik, Croatia. This SI in Energies focused on four main topics, including the application of renewable bioenergy, component enhancement in renewable systems, sustainable development for buildings and economic analysis and evaluation for sustainability. The collected papers provide insight into the topics related to recent advances in improving sustainable efficiency, including studies on waste-to-wealth techniques, utilization of hybrid bioenergy systems, heat exchangers and other components for performance enhancement, energy supply and demand analysis, low-temperature DHC systems, techno-economic assessment, and environmental evaluation. [ABSTRACT FROM AUTHOR]

A three-dimensional CFD numerical simulation is successfully carried out on thermo-hydraulic characteristics of a new smooth wavy fin-and-elliptical tube (SWFET) heat exchanger with three new types of vortex generators (VGs), namely – rectangular trapezoidal winglet (RTW), angle rectangular winglet (ARW) and curved angle rectangular winglet (CARW). Several parameters have been examined in this study. There have a pronounced effect on the thermo-hydraulic performance. In addition the results are analyzed from the viewpoint of the field synergy principle which emphasizes that the reduction of the synergy angle between velocity and fluid temperature gradient is the principal mechanism for enhancement of heat transfer performance. These parameters include: Reynolds number (based on the hydraulic diameter, Re D h = 500 – 3000 ), geometric shape of VGs, attack angle of VGs ( α VG = 15–75°), placement of VG pairs (up- or/and downstream), tube ellipticity ratio ( e = 0.65–1.0) and wavy fin height ( H = 0.8–1.6 mm). The results demonstrate that with increasing Reynolds number and wavy fin height, decreasing the tube ellipticity ratio, the heat transfer performance of the SWFET heat exchanger is enhanced. The SWFET heat exchanger with the advantages of using CARW VGs and RTW VGs at smaller and larger attack angles, respectively, presents good thermo-hydraulic performance enhancement. Finally, new correlations are proposed to estimate the values of the average Nusselt number Nu , friction factor f and synergy angle θ based on the Reynolds number, attack angle of VGs, tube ellipticity ratio and wavy fin height. [ABSTRACT FROM AUTHOR]

This study analyzed the acoustic energy transfer process in expanded pipe of heat exchangers based on the field synergy principle. The synergy between the flow field and the acoustic field was deduced theoretically based on the energy and momentum equations pertaining to the acoustic field. The synergy angle of the flow field and the acoustic field was calculated numerically. The noise propagation process in the expanded pipe was measured experimentally. The results show that the sound pressure level and synergy angle both increase with the increase in flow velocity, whereas the acoustic energy transfer process decreased with the increase in synergy angle. An extended outlet of the expanded pipe segment can reduce the flow noise magnitude with a lower pressure drop. The flow noise can reach 123 dB and the pressure drop is 37.3％ and 24.7％ less than other cases. In conclusion, the theoretical analysis, experimental tests, and numerical simulation method are developed to study the acoustic energy transfer process in segments of expanded pipe based on synergy principle of flow and acoustic fields. [ABSTRACT FROM AUTHOR]

In this study numerical analysis was carried out for four different types of fins namely rectangular, triangular, inverted bolt fins and ripsaw fins and three different types of arrangements namely straight, staggered and top and bottom arrangement. The obtained results were compared with each other and the design with the highest decomposition percentage of sulfur trioxide was selected. The working fluids used in the model were sulfur trioxide, sulfur dioxide, oxygen and water vapor. The operating pressure was 1.5 MPa and the operating temperature ranges from 973 K to 1223 K. From the results it was found that the ripsaw fin design with thickness of 0.05 mm gives the highest decomposition percentage of sulfur trioxide. The inverted bolt fins gives a good heat transfer rate but due to the fin arrangement and the flow disturbances caused by the arrangement the pressure drop was the highest compared to the other fins. The pressure drop and heat transfer obtained for the rectangular and triangular fins were similar to each other. The obtained decomposition percentage of sulfur trioxide for straight, staggered and top and bottom arrangement were 17.60%, 16.74% and 20.55%. The obtained decomposition percentage increased from 16.74% to 85.15% when the channel length of the heat exchanger was increased ten times. [ABSTRACT FROM AUTHOR]

In this study three-dimensional model of ceramic plate-fin high temperature heat exchanger with different fin designs and arrangements is analyzed numerically using ANSYS FLUENT and ANSYS structural module. The ability of ceramics to withstand high temperature and corrosion makes silicon carbide (SiC) suitable candidate material to be used in high temperature heat exchanger. The operating temperature of heat exchanger is 950 °C and the operating pressure is 1.5 MPa. The working fluids are helium, sulfur trioxide, sulfur dioxide, oxygen and the water vapor. Fluid flow and heat transfer analysis are carried out for steady and transient state in FLUENT. The obtained thermal and pressure load for the steady and transient state from ANSYS FLUENT are imported to ANSYS structural module to obtain the principal stress and the factor of safety. Different arrangements of rectangular fins, triangular fins, inverted bolt fins and ripsaw fins are studied. From the results it is found that the minimum stress and the maximum safety factor are obtained for inverted bolt fins. The triangular fins have the maximum principal stress and minimum factor of safety. However, the fluid flow and heat transfer analysis show inverted bolt fins and triangular fins produce higher pressure drop and friction factor. The steady state maximum principal stress is 10.08 MPa, 9.90 MPa and 11.43 MPa for straight, staggered and top and bottom ripsaw fin arrangement. The corresponding safety factors are 21.80, 21.95 and 19.01, respectively. The ripsaw fin design is chosen to be the best design since it gives less stress, more safety factor, less pressure drop, friction factor and reasonable heat transfer rate. From the results it is also found that thermal stress is more significant than the mechanical stress. [ABSTRACT FROM AUTHOR]

As a newly developed industry, refuse incinerating power plants with air-cooled heat exchanger (ACHE) systems benefit both environment and energy savings. Since the exhaust steam of power plant is cooled in the atmosphere, the pressure of the exhaust steam fluctuates with variation of air temperature. As a result, the generated electric power of a power plant with an ACHE system is considerably influenced by meteorological conditions in the region where this type of power plant is built. The present work studies three different designs of a refuse-incinerating power plant with ACHE for a real project. Under the local meteorological conditions, the overall flow and temperature fields of the air in the whole power plant, especially around the air-cooled heat exchanger, are numerically investigated with the commercial computational fluid dynamics (CFD) code FLUENT and the feasibility of the project is then evaluated. In addition, a comparison of these three designs is also provided, including the performance of the exchangers and the fans, the collocation of the exhaust gas pipe, and the costs of the ACHE system. [ABSTRACT FROM AUTHOR]

The air inlet flow direction is not orthogonal to the heat exchanger surface in many cases. To study the performance of the heat transfer and pressure drop of a heat exchanger with different air inlet angles, this paper shows the experimental system about a finned oval-tube heat exchanger inclined toward the air incoming flow direction. The heat transfer and pressure drop characteristics of four air inlet angles (90°, 60°, 45°, and 30°) are studied separately for the Reynolds number ranging from 1300 to 13000 in this study. The experimental correlations of Nusselt number and resistance coefficient of the air side are acquired. The results show that the overall heat transfer coefficients become smaller and smaller with the decrease of the air inlet angles, while the pressure drops have significant changes. The heat transfer performances of the heat exchanger under the three inclined air inlet angles are worse than that at 90°. Among the three inclined angles, the performance at 45° is the best under identical mass flow rate criterion and at low Reynolds number under identical pressure drop criterion; that at 60° is the best at large Reynolds under identical pressure drop criterion. Finally, some conclusions are attained about the effects of the air inlet angles on the heat transfer and pressure drop performance of the finned oval-tube heat exchanger. [ABSTRACT FROM AUTHOR]

Particle-based moving bed heat exchangers are increasingly playing a significant role in industrial energy conservation and solar energy utilization. However, the moving bed heat exchanger used for cohesive granular materials still needs to be developed. This paper investigates the feasibility of indirect heat transfer of cohesive granular materials through a moving bed heat exchanger. A vibrating moving bed heat exchanger is developed for the metallurgical slag of vanadium-titanium (MSVT) from industry. The experiment demonstrates that the vibrating moving bed heat exchanger can establish an approximate mass flow regime of MSVT in the experimental section. The vibration device designed for the experimental and discharge section effectively resolves bridging and the intermittent collapse of arching in cohesive granular materials. The outer side of the tube is tightly wrapped by MSVT with vibration. Significant differences are observed in the flow and heat transfer behavior of MSVT between the aligned and staggered tubes. The local heat transfer coefficient at the top and bottom of the aligned tubes exhibits much lower sensitivity to flow velocity compared to the staggered tubes. The relationship between Nu −1 and Pe −0.5 or MSVT around the aligned and staggered tubes follows a linear correlation. Compared to aligned tubes, Nu −1 for MSVT in staggered tubes shows an average reduction of 28%. [Display omitted] • A vibrating moving bed heat exchanger is developed for cohesive granular materials. • Special experimental design can resolve bridging and arching between tubes. • Rheological properties of vanadium-titanium granular are quantitatively evaluated. • The heat transfer of granular flow is tested around different tube arrangements. • The heat transfer correlations are built to predict the heat transfer. [ABSTRACT FROM AUTHOR]

An elliptical-like combined tube (ELCT) is proposed for the shell-and-tube moving packed bed heat exchanger. The heat transfer of particle flow around the ELCT is numerical studied. The kinetic energy ratio, contact number, contact time and heat transfer coefficient are analyzed. It is found that, the heat transfer performance of the ELCT is similar to that of the elliptical tube (ET) and better than the circular tube (CT). Compared with the CT, the ELCT significantly reduces the stagnation zone and the cavity zone, and improves the heat transfer at the top and the bottom of the tube (average increase of 42% and 53%). Furthermore, compared with the ET and the CT, the ELCT has better inside-tube heat transfer performance (average increase of 5% and 29%), various inside-tube heat transfer enhancement techniques (same with the CT) and better flexural capacity (average increase of 8% and 36% under same mass). [Display omitted] • A new tube is proposed for the shell-and-tube moving packed bed heat exchanger. • The outside tube heat transfer of the new tube is simlar to the elliptical tube. • The new tube improves the heat transfer at the top and bottom of the tube. • The new tube has better inside tube heat transfer and flexural capacity. • The new tube includes some advantages of the circular tube and the elliptical tube. [ABSTRACT FROM AUTHOR]

• A prediction model is developed for shell-and-plate moving bed heat exchangers. • The penetration thermal resistance plays vital roles on the overall heat transfer. • The equivalent heat diffusion should be improved for heat transfer enhancement. • The velocity control with relaxation coefficients has good dynamic performances. To realize the heat transfer between granular flow and sCO 2 cycle, moving bed heat exchangers have been widely applied in Concentrating Solar Power systems. This work developed a prediction model for heat transfer enhancements and dynamic control strategies in a shell-and-plate moving bed heat exchanger. For fast evaluation of heat transfer performances in granular flow, the continuum model was adopted with different thermal resistances. The wall effect of near-wall region was modified by contact thermal resistance, and the equivalent heat diffusion in bulk region was reflected by penetration thermal resistance. The results showed that, the decrement of penetration thermal resistance can improve heat transfer effectively. To weaken the penetration thermal resistance, the thinner thermal boundary layer and the higher effective thermal conductivity are urgently required. The staggered arrangement is a valid way to limit the development of thermal boundary layer. The bank of heat exchanger plates offset horizontally from the previous bank, and the re-evolution of temperature distributions is equal to the equivalent thermal mixing between different banks. Meanwhile, the effective thermal conductivity can be improved by particle self-diffusions perpendicular to the major flow direction. For the particle migrations, the local disturbances can be applied. The relatively decrement of penetration thermal resistance can achieve 45.7% at a disturbance intensity of 5 × 10−7 m2/s. The outlet temperature of sCO 2 can be well controlled by the transient temperature–velocity feedback method with relaxation coefficients. The relatively decrement of temperature fluctuation is larger than 80% with a relaxation coefficient of 40. [ABSTRACT FROM AUTHOR]

Abstract: In this work an artificial neural network (ANN) is used to correlate experimentally determined and numerically computed Nusselt numbers and friction factors of three kinds of fin-and-tube heat exchangers having plain fins, slit fins and fins with longitudinal delta-winglet vortex generators with large tube-diameter and large the number of tube rows. First the experimental data for training the network was picked up from the database of nine samples with tube outside diameter of 18mm, number of tube rows of six, nine, twelve, and Reynolds number between 4000 and 10,000. The artificial neural network configuration under consideration has twelve inputs of geometrical parameters and two outputs of heat transfer Nusselt number and fluid flow friction factor. The commonly-implemented feed-forward back propagation algorithm was used to train the neural network and modify weights. Different networks with various numbers of hidden neurons and layers were assessed to find the best architecture for predicting heat transfer and flow friction. The deviation between the predictions and experimental data was less than 4%. Compared to correlations for prediction, the performance of the ANN-based prediction exhibits ANN superiority. Then the ANN training database was expanded to include experimental data and numerical data of other similar geometries by computational fluid dynamics (CFD) for turbulent and laminar cases with the Reynolds number of 1000–10,000. This in turn indicated the prediction has a good agreement with the combined database. The satisfactory results suggest that the developed ANN model is generalized to predict the turbulent or/and laminar heat transfer and fluid flow of such three kinds of heat exchangers with large tube-diameter and large number of tube rows. Also in this paper the weights and biases corresponding to the neural network architecture are provided so that future research can be carried out. It is recommended that ANNs might be used to predict the performances of thermal systems in engineering applications, especially to model heat exchangers for heat transfer analysis. [Copyright &y& Elsevier]

Printed circuit heat exchanger (PCHE) is a promising candidate of coolers used for SCO2 Brayton cycle. The thermal-hydraulic performance of SCO2 in a PCHE depends on the PCHE structure as well as the operating conditions of SCO2 due to its dramatic variation of thermal physical properties near the pseudo-critical point. This work experimentally investigated the thermal-hydraulic characteristics of zigzag-channel PCHEs between SCO2 and water at pressures that ranged from 8.0 to 11.0 MPa. Results showed that increasing the flow rate of SCO2 might affect the PCHE more pronouncedly in comparison with changing the flow rate of water, indicating that the major convective thermal resistance is on the SCO2 side. When increasing the operating pressure from 8.0 MPa to 11.0 MPa, the Nusselt numbers of PCHEs with zigzag angles of 0°, 15°, and 25° averagely decrease by 63.3%, 62.1%, and 54.0%, and the friction factors averagely decrease by 28.6%, 27.4%, and 21.0% respectively. Meanwhile, it is found that the buoyancy force is non-negligible during SCO2 cooling process in PCHEs. In this regard, Nusselt number and friction factor correlations considering the buoyancy effect are proposed with applicable ranges. [ABSTRACT FROM AUTHOR]

An efficient intermediate heat exchanger is crucial for ensuring the safe operation, lifespan and energy efficiency of the advanced nuclear systems. Benefiting from the development of additive manufacturing technology, it is possible to design and optimize heat exchangers by introducing triply periodic minimal surface (TPMS) structures. With the excellent mechanical and thermal performance of TPMS, further improvements in the energy efficiency of advanced nuclear systems are achievable. In this study, I-WP surface, Primitive surface based heat exchangers and a printed circuit heat exchanger for accelerator driven subcritical systems are constructed in three dimensions. In order to obtain the potential enhancement of thermal performance of TPMS-based heat exchangers, the fluid flow and conjugate heat transfer characteristics in TPMS heat exchangers, especially for the specific working medium of lead-bismuth eutectic (LBE) are investigated. A parametric analysis is conducted on the key design variables including the solid volume fraction and hydraulic diameter. The results indicate that TPMS-based heat exchangers could achieve about 2–3 times the total heat transfer rate with half the volume of a printed circuit heat exchanger. The TPMS topologies contribute greater heat transfer enhancement on the Helium side than the LBE side, which helps to optimize the thermal resistance allocation in Helium-LBE heat exchangers. An increase of solid volume fraction enhances the convective heat transfer of Helium in I-WP heat exchanger, while homogenizing the local thermal performance. This study provides a database for the design and optimization of TPMS-based heat exchangers, which contributes to the sustainable future target. • Heat transfer enhancement mechanisms of TPMS heat exchangers are identified. • Effects of design variables on TPMS heat exchangers performance are studied. • TPMS heat exchangers achieve 2–3 times total heat transfer rate than PCHE. • Vortex structures and periodic acceleration/deceleration enhance the heat transfer. • TPMS optimizes the thermal resistance allocation in helium-LBE heat exchangers. [ABSTRACT FROM AUTHOR]

• A simplified model of PCHE based on equivalent-homogeneous-solid concept is proposed. • Equivalent mechanical properties of PCHE channels are obtained by asymptotic homogenization method. • The maximum deviation in mechanical deformations is less than 2.4%. • The maximum deviation in thermal deformations is less than 1‰. • The computation time is significantly reduced by the equivalent model. Printed circuit heat exchanger (PCHE) is a critical component to transfer heat from the primary loop to the secondary loop in supercritical carbon dioxide (SCO 2) Brayton cycle system used for Generation IV nuclear reactors. The PCHE is operated at high temperature and high pressure, and thus the thermo-mechanical analysis is essential to its structural safety. However, it is difficult to directly model the whole PCHE by the finite element method because the PCHE is composed of large amounts of mini-channels. The simplified approach based on equivalent-homogeneous-solid concept was used by many researchers, but accurate method to calculate the equivalent mechanical properties of PCHE mini-channels is lacking. In this paper, an asymptotic homogenization method is proposed to calculate the equivalent mechanical properties of PCHE mini-channels. Firstly, the periodicity of mini-channels is considered as a small parameter, and the statement of equivalent elasticity matrix of mini-channels is derived in the form of stain energy of the unit cells. Secondly, numerical implementation of asymptotic homogenization method for a unit cell in the PCHE mini-channels is conducted. The equivalent Young's modulus, Poisson's ratio and shear modulus of mini-channels are fitted as functions of temperature. Finally, the thermo-mechanical performance of the equivalent PCHE core model is compared with the actual model. The results show that the maximum deviations in mechanical and thermal deformations between the equivalent and actual PCHE core models are less than 2.4% and 1% respectively. However, the computation time of the equivalent model is a factor of 45–190 below the value of actual model. [ABSTRACT FROM AUTHOR]

Highlights • Fabrication of printed circuit heat exchanger channels is studied. • Orthogonal array testing strategy is adopted to study the chemical spray etching. • Etching parameters greatly affect etching rate, lateral erosion and roughness. • Optimal spray pressure, etching temperature and concentration are obtained. Abstract Nuclear power is considered as the most promising energy for power generation due to low carbon emission, small fuel cost, high efficiency and reliability. As a new type of heat exchanger, printed circuit heat exchanger (PCHE) with high compactness and efficiency can be used for the supercritical carbon dioxide (SCO 2) Brayton power cycle in the Gen IV nuclear reactor systems to transfer great amount of heat from nuclear reactors. The chemical etching technology plays an important role in production of heat transfer channels for PCHEs from micron level to millimeter level. In order to produce high-quality heat transfer channels, the chemical spray etching method is used in the manufacturing process. In this work, a chemical spray etching experiment was carried out to analyse the etching phenomenon on the PCHE channels. The influences of etching parameters, such as etching rate, lateral erosion, surface roughness, etc., are investigated. The results showed that the etching parameters significantly affected the etching quality, which provided comprehensive view of details for the etching process. Besides, an orthogonal array testing strategy (OATS) was adopted for chemical spray etching to synthetically study the influences of FeCl 3 and H 3 PO 4 concentrations, etching temperature, spray pressure on the etching rate, the lateral erosion and the surface roughness. The optimal combination of etching parameters in the setting level was investigated and obtained, which is in the condition with spray gage pressure of 0.15 MPa, etching temperature of 35 °C, FeCl 3 concentration of 400 g·L−1 and H 3 PO 4 concentration of 1.5 M. The present work is of significance to realize the low-cost, high-efficiency and controllable manufacturing process of PCHEs. [ABSTRACT FROM AUTHOR]

• Heat transfer enhancement mechanisms of TPMSs are identified. • Empirical correlations for turbulent flow in TPMS channels are established. • The effects of mass flow rate and volume share on TPMS performance are studied. • Periodic acceleration/deceleration and secondary flows enhance the heat transfer. • F-KS topology obtains optimal performance at given mass flow rates. Heat exchangers are one of the key components to ensure the safe and efficient operation of nuclear energy systems. Additive manufacturing offers the processing solutions of advanced heat exchangers based on triply periodic minimal surfaces (TPMS). TPMS has superior mechanical and thermal–hydraulic performance that provides excellent energy-saving potential in the energy systems. In this study, I-WP, Neovius, Fischer-Koch S, Primitive surface-based heat transfer channels with different volume shares are constructed in three dimensions. The enhanced heat transfer mechanisms of TPMS topologies are identified and parametric analysis on the thermal–hydraulic performance is performed. The results indicate that the secondary flows, periodic flow acceleration/deceleration and constant changes in flow directions play key roles in convective heat transfer of TPMS topologies. Based on a large amount of simulation data, empirical correlations for Nusselt number and friction factor in the turbulent regime are established. This study provides a database for the design and application of TPMS-based heat exchangers, which contributes to the energy-saving and sustainable future target. [ABSTRACT FROM AUTHOR]

In typical gas-to-liquid thermoelectric generators for waste heat recovery, the stream-wise gas temperature drop in the hot-side heat exchanger leads to the decrease of power output of the whole system. Denser fins are usually arranged on the downstream of the hot-side heat exchanger to improve the uniformity of temperature field and thus the total power output performance of thermoelectric generators when the steam-wise temperature drop is small, but it is not benificial when the steam-wise temperature drop is large. This work investigates the effect of configuration of winglet vortex generators on the performance of thermoelectric generator system. Three sets of hot-side heat exchangers, including a heat exchanger with smooth channel, a heat exchanger with uniform configuration of winglet vortex generators and a heat exchanger with non-uniform configuration of winglet vortex generators, are tested in a gas-to-liquid thermoelectric generators experimental system. The hot-side Reynolds number ranges from 3000 to 6400 and the hot-side inlet temperature is within 523–553 K. The experimental results show that the total and net power output of thermoelectric generator under matched load resistance with uniform heat exchanger can respectively outperform that with smooth heat exchanger by 97.5% and 77.7% in average, whereas that with non-uniform heat exchanger by 189.1% and 177.4% in average. Since the uniform and non-uniform heat exchangers have the same number but different configuration of winglet vortex generators, this kind of active cascade control of heat transfer enhancement elements is proved to be effective in improving the power output of thermoelectric generator system without increasing pumping power. [ABSTRACT FROM AUTHOR]

Hydrogen cooler is a key equipment of the precooling unit in hydrogen refueling stations with the requirement of high heat transfer efficiency, high compactness and high pressure resistance. Printed circuit heat exchanger is a promising candidate for the hydrogen cooler due to its great performance on extremely high pressure and high temperature working environment. In this paper, a hydrogen cooler with a thermal load of 72 kW is firstly designed by using the segmented thermal design method and logarithmic mean temperature difference method. Then, the capital model of the hydrogen cooler is established to evaluate the performance using the exergoeconomic method. The results show that the operating cost, which is related to exergy destruction, accounts for 94.5% of the total cost of the hydrogen cooler. The thermal exergy destruction accounts for 92.4% of the total exergy destruction. Finally, the geometrical parameters of the channel are optimized by using the multi-objective optimization. The channel radius shows the most significant impact on the construction cost and operating cost among the three geometrical parameters. Compared with the coaxial tube evaporators, the printed circuit heat exchanger has better performance on the volume and total cost, which are reduced by 88.0% and 4.0% respectively. • PCHE used for hydrogen cooler is estimated by segmental thermal design method. • Geometrical parameters are optimized by multi-objective optimization method. • Heat transfer performance and capital of PCHE hydrogen cooler are analyzed. • PCHE shows superior performance on volume and total cost than conventional coolers. • PCHE hydrogen cooler reduces cost of producing hydrogen per kilogram. [ABSTRACT FROM AUTHOR]

Heat exchanger network synthesis (HENS) is an effective tool for heat recovery in chemical and petrochemical industries. This study aims to show a method for HENS with the consideration of different shell-side flow arrangements in shell-and-tube heat exchangers. The proposed MINLP model is modified from the stage-wise superstructure model, incorporating newly developed correlations for shell-side pressure drop calculation for the helical baffle. The objective is to minimise the total annual cost (TAC) with a trade-off between the cost of different shell-side heat exchangers, utility cost, and pumping cost. The selection of baffle design is decided by the saved pumping cost and the increased area cost. The proposed model is tested from different points of view: with/without utility constraints and different statuses of the streams. Three case studies are presented and compared with the results from the literature. The proposed method with different shell-side baffles can reduce the heat transfer area and pressure drop. For fixed utility consumptions, the TAC in a case study is decreased by 8.9% with mixed baffle types. Although the unit per area cost of the helical baffle is higher than the segmental baffle, the increased investment cost could be compensated by the reduced operation cost, especially for plants with high viscosity streams and long-term cost-saving. [ABSTRACT FROM AUTHOR]

Heat exchanger network synthesis is an essential optimisation tool for Process Integration, particularly in energy-intensive industries. Proper design or retrofit of heat exchanger network can enable energy conservation, efficiency improvement, and process debottlenecking. Many earlier pieces of research have focused on the impact of the network structure and process features such as network topology, temperature intervals, continuous/batch processes, and so on. As the major device in heat exchanger networks, heat exchangers research has always been a hot topic. However, the individual heat exchanger research is different from the number of heat exchangers in a network. Various performance aspects of the heat exchangers, e.g., pressure drop, fouling, and thermal performance, could influence the whole network and the passive responses between each heat exchanger. Besides, integrating those aspects of individual heat exchangers into the network synthesis is still an open problem, especially for cases that demand simultaneous optimisations. This work presents a thorough assessment of research into those aspects in heat exchanger networks, as well as the state-of-the-art of current approaches for heat exchanger networks optimisation that take heat exchanger performance into account. The essential coupling among fouling, pressure drop and thermal design is explored, and the nexus between them and the heat exchanger network is analysed. Researchers will benefit from this overview of heat exchanger network synthesis retrofitting methods and applications. • The impact of heat exchanger performance on the heat exchanger network is discussed. • Progress of model and approach for heat exchanger network synthesis is reviewed. • Influence factors: fouling, pressure drop, thermal design and intensified heat transfer. [ABSTRACT FROM AUTHOR]

Printed circuit heat exchanger (PCHE) is considered a promising candidate for accelerator driven systems (ADS) due to its high compactness and efficiency. The preeminent high-temperature, high-pressure and corrosion resistance enables it to withstand the severe conditions of ADS and ensure the safe and efficient operation. In this paper, a PCHE applied to the ADS is proposed, adopting helium as the cold source and lead-bismuth eutectic (LBE) as the heat source. On this basis, a three-dimensional model is established and the flow and heat transfer characteristics of the PCHE are numerically investigated. The thermal performance is further improved by optimizing structural and operating parameters. The results indicate that the high thermal conductivity and superior field synergy degree of LBE ensures a strong heat transfer performance of PCHE. The velocity disturbance and double-vortex secondary flow generated in modified channels, which intensify the fluid mixing and improve the field synergy level, help to further enhance the overall heat transfer coefficient. Structural and operating parameters of the helium side are more critical to the thermal-hydraulic performance, an increase of helium mass flow rate within allowable pressure drop is conducive to the comprehensive performance. • A printed circuit heat exchanger for accelerator driven system (ADS) is proposed. • The field synergy degree in cold and hot channels is compared. • Double-vortex secondary flow enhances the fluid mixing and heat transfer. • Modified channels increase the overall heat transfer coefficient of PCHE by 35.4%. • Increase of helium mass flow rate can improve the comprehensive performance. [ABSTRACT FROM AUTHOR]

The discontinuous airfoil-fin printed circuit heat exchanger is a leading candidate due to its high compactness, high efficiency, and ability to endure extreme conditions. In this paper, an unusual asymmetric airfoil-fin heat exchanger is experimentally investigated using the supercritical carbon dioxide and water experimental system. The effects of working parameters and flow direction on the heat transfer performance are analyzed based on the average thermal-resistance ratio. Meanwhile, the effects of flow directions on the comprehensive performance are quantitatively evaluated. Compared with the overall thermal resistance, the average thermal-resistance ratio is more sensitive in evaluating the heat transfer performance. The reverse flow hardly improves the heat transfer, while significantly amplifies the pressure drop. Compared with the reverse flow, when the bulk temperature of CO 2 is 38 °C, 41 °C and 47 °C, the comprehensive performance of forward flow increases by 6.1%, 4% and 1.8%, respectively. Finally, the unified heat transfer correlation for two opposite flow directions is proposed within applicable ranges. • One type of asymmetric airfoil-fin heat exchanger is proposed and tested. • Average thermal-resistance ratio is sensitive to the heat transfer. • Effect of flow direction on the comprehensive performance is evaluated. • Unified heat transfer correlation for two opposite flow directions is proposed. [ABSTRACT FROM AUTHOR]

The heat exchanger is an essential component of the supercritical CO 2 Brayton cycle. To attenuate the temperature fluctuations in the cycle, this study proposes a new structure with phase change materials embedded in the printed circuit heat exchanger. This structure package can contain a variety of phase change materials in a stepwise arrangement and a composite phase change material with expanded graphene. The effects of different flow directions, the number of layers in the phase change material ladder, whether the phase change material is compounded with expanded graphene or not, and the thickness of the phase change material were numerically compared. The results show that the PCM layer with 0.45 mm thickness has a smaller amplitude of both temperature fluctuations and liquid fraction fluctuations than that of 0.25 mm. Relative to the case without PCM, the outlet of hot side' temperature fluctuation amplitude of PCM/EG-3 and PCM/EG-5 with 0.45 mm thickness decreased by 17.11% and 22.37%, and the outlet of cold side' temperature fluctuation amplitude decreased by 36.84% and 38.16%, while the heat exchange decreased by only 2.28% and 1.78%, respectively. • A new structure for PCM embedded in PCHE is designed. • The effects of flow direction on the performance of PCHE-PCM are compared. • The effects of a multi-layer PCM ladder arrangement on PCHE-PCM are investigated. • The composite structure of PCM/EG significantly reduces the heat loss of PCHE. • The effects of different PCM layer thickness on PCHE-PCM are investigated. [ABSTRACT FROM AUTHOR]

A heat transfer model based on the discrete element method was developed to investigate the effect of the trapezoidal corrugated plate on heat transfer. Particles flow along a trapezoidal corrugated plate unit (TCPU) were compared with that along a flat plate, and the appropriate base angles of the trapezoidal bulge were searched. In the upstream region of the trapezoidal bulge, the contact resistance of the TCPU decreases by 44% compared with that of the PLATE. In the side and downstream regions, the trapezoidal bulge enhances the mixing between particles, destroys the development of the temperature boundary layer and strengthens the heat transfer (average heat transfer rate increased by 14%). The heat transfer rate of adding the trapezoidal bulge is better than reducing the channel width at higher mass flow rates (> 1.07 g/s). When outlet velocity is 1 mm/s, base angles between 45°- 60° are beneficial for the heat transfer. [Display omitted] • Particles flowing along the trapezoidal corrugated plate is investigated by DEM. • The trapezoidal bulge can significantly enhance the heat transfer of the plate. • The trapezoidal bulge can reduce the contact resistance in its upstream region. • The trapezoidal bulge enhances mixing and destroys the temperature boundary layer. • The base angle of the trapezoidal bulge is suggested between 45°- 60°. [ABSTRACT FROM AUTHOR]

The spiral-wound heat exchangers are widely used in chemical industrial applications, but the mechanism of flow and heat transfer in shell side has not been clarified yet. A three-dimensional model is developed based on the FLUENT software in this study, with emphasis on quantifying the effects of the main geometry parameters, such as the number of tube bundles, the number of tube layers, the thickness of space bars, the number of tubes per circle in the first layer, the tube external diameter, the central cylinder diameter, and the tube pitch in the first layer, on the flow and heat transfer. Based on the numerical simulation results, the Taguchi method is used to estimate the effect of these geometrical factors on flow and heat transfer and the contribution rate of every factor is obtained. Meanwhile, the multivariate correlation is developed by MATLAB software to calculate the Nusselt number and friction factor in the shell side. [ABSTRACT FROM PUBLISHER]

3D computational analysis was performed to investigate heat transfer and pressure drop characteristics of flow in SWFET (Smooth Wavy Fin-and-Elliptical Tube) heat exchanger with four new VGs (vortex generators), RTW (rectangular trapezoidal winglet), ARW (angle rectangular winglet), CARW (curved angle rectangular winglet) and WW (Wheeler wishbone). The numerical model was well validated with the available experimental results. Numerical results illustrate that vortex generators can bring about further heat transfer enhancement through careful adjustment of the position with respect to the elliptical tube, type and attack angle of vortex generators. The influences of the geometrical factors including attack angles of the winglets (αVG = 15∘,30∘,45∘,60∘ and 75°) and width/length aspect ratio (w/l = 0.5,1.0) of the Wheeler wishbones on enhancing the heat transfer performance of a smooth wavy fin heat exchanger with a three-row staggered elliptical tube bundle are investigated. A parametric study on the winglet vortex generators indicated that for the small attack angle, CARW vortex generators gives better thermohydraulic performance under the present conditions. The best thermal performance with winglet VGs in larger attack angle, was obtained at RTW VGs arrangement. For the SWFET heat exchangers, the WW VGs with w/l = 0.5 provide the best heat transfer performance. [ABSTRACT FROM AUTHOR]

Recuperator and precooler are key components of supercritical CO 2 Brayton cycle. One of promising candidates is printed circuit heat exchanger (PCHE) due to its high compactness and heat transfer performance. However, both of them operate at high pressure, which is a great challenge for their safety. Therefore, accurate and quick mechanical stress analysis is important for PCHE design. In this work, a simplified mechanical stress method based on homogenization method is proposed for PCHE. An optimized rectangular channel, which has the same mechanical characteristics with a semicircular channel is proposed. Then the PCHE numerical model is constructed, and the mechanical stress of PCHEs with semicircular and rectangular channels is examined by elastic stress analysis. The results show that the maximum stresses of the semicircular channel, simplified rectangular channel and optimized rectangular channel are 151.6 MPa, 253.0 MPa and 184.3 MPa, respectively. The mechanical characteristics of the optimized rectangular channel are close to the corresponding semicircular channel, which can improve the design accuracy and is benefit for the weight and volume reduction of PCHE. • A simplified stress method based on equivalent homogenization method is proposed. • Optimized rectangular channel has similar stress value with semicircular channel. • The simplified stress method can improve design accuracy of PCHE. [ABSTRACT FROM AUTHOR]

The growth of global energy demand during the 21st century, combined with the necessity to master greenhouse gas emissions, has led to the introduction of a new and universal energy carrier: hydrogen. The Department of Energy (DOE) proposed using a bayonet-type heat exchanger as a silicon carbide integrated decomposer (SID) to produce the sulfuric acid decomposition product sulfur dioxide, which can be used for hydrogen production within a sulfur–iodine thermochemical cycle. A two-dimensional computational model of SID having a boiler, superheater and decomposer was developed using GAMBIT and fluid. The thermal and chemical reaction analyses were carried out in FLUENT. The main purpose of this study is to obtain the decomposition percentage of sulfur trioxide for the integrated unit. Sulfuric acid (H2SO4), sulfur trioxide (SO3), sulfur dioxide (SO2), oxygen (O2), and water vapor (H2O) are the working fluids used in the model. Concentrated sulfuric acid liquid of 40 mol% was pumped into the inlet of the boiler and the mass fraction of concentrated sulfuric acid vapor obtained was then fed into the superheater to obtain sulfur trioxide. The decomposer region, which houses the pellets, placed on the top of the bayonet heat exchanger acts as the porous medium. As the decomposition takes place, the mass fraction of SO3is reduced and mass fractions of SO2and O2are increased. The percentage of SO3obtained from the integrated decomposer was compared with the experimental results obtained from Sandia National Laboratories (SNL). Further, effects of various pressures, flow rates, and acid concentrations on the decomposition percentage of sulfur trioxide were studied. [ABSTRACT FROM PUBLISHER]

Printed circuit heat exchangers with high heat transfer efficiency, small volume and high pressure resistance are usually chosen as a precooler for the supercritical carbon dioxide Brayton cycle. The supercritical carbon dioxide channel has high pressure and small mass flow rate, but the water channel has low pressure and large mass flow rate. The conventional printed circuit heat exchanger does not consider the difference between the two-side channels, and thus the weight is large. In this work, a diffusion-bonded hybrid printed circuit heat exchanger is put forward as the precooler used for supercritical carbon dioxide Brayton cycle. The new structure uses chemical-etching channels for the supercritical carbon dioxide side and plate-fin channels for the water side. Thermal design of the hybrid printed circuit heat exchanger based on a segmented Log-Mean Temperature Difference method is conducted. The results indicate that the hybrid printed circuit heat exchanger can effectively improve the heat transfer performance. Compared with the conventional printed circuit heat exchanger, the core volume of the optimized hybrid printed circuit heat exchanger is reduced by 49%, and the heat transfer rate per unit volume is increased by 145%. The optimized hybrid printed circuit heat exchanger in both channels can satisfy the mechanical stress requirement. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a novel bayonet tube high temperature heat exchanger (HTHE) with inner and outer fins is presented. It can be used in the ultra high temperature environment, such as hydrogen production, very high temperature reactor and externally fired combined cycle. Numerical investigation of heat transfer performance on the inside of bayonet element has been conducted for structure design. The numerical results suggest that the inner fin and inner tube should not be welded together. It is recommended that the air enters from the inner tube and exits from the annular space in the high temperature zone. A high temperature experimental system has been established to test the heat transfer and pressure drop characteristics of the HTHE. The surface area density of the tested HTHE is 6 times higher than that of the bare bayonet tube heat exchanger. The experimental results indicate that the mass flow rate on both sides and inlet temperature on the fuel gas side have a significant effect on the heat transfer rate and effectiveness, while the pressure drop ratios are mainly affected by the mass flow rate rather than the inlet temperature. Comparison between the tested HTHE and the similar HTHE without fins indicates that the proposed HTHE has a significant potential to improve the comprehensive heat transfer performance. [Copyright &y& Elsevier]

• A novel sector structure precooler breaking cuboid structure layout is proposed. • The novel precooler adopts flexible modular layout and convenient maintenance. • Segmented thermal design is combined with genetic algorithm for optimization. • The novel precooler has higher compactness and volumetric power. The rapid change in the amount of carbon dioxide released into the atmosphere stimulates the advancement of advanced space launchers. Liquefied air cycle engine is a pollution-free space launcher and attracts much attention in recent years. Air-hydrogen precooler is an important component in the liquefied air cycle engines. The thermal–hydraulic performance of the precooler significantly affects the efficiency of the engine. This paper proposes a novel annular air-hydrogen precooler based on printed circuit heat exchanger. To prove the thermal–hydraulic performance of the novel precooler design, three types of precoolers are selected for comparison of volumetric power, power per mass unit and compactness. Segmented thermal design method and genetic algorithm are used for structure optimization. The results indicate that the novel precooler has higher compactness and volumetric power. The compactness of annular air-hydrogen precooler is 682% larger than that of shell-and-tube heat exchanger. The volumetric power of annular air-hydrogen precooler is 206% larger than that of plate-fin heat exchanger. The volumetric power of annular air-hydrogen precooler is 24% larger than that of the printed circuit heat exchanger. The study concludes that the air-hydrogen precooler has a better comprehensive performance. [ABSTRACT FROM AUTHOR]

Printed circuit heat exchanger is considered a promising candidate for floating natural gas liquefaction because of its high compactness, high pressure resistance, and high efficiency. In this work, a numerical model is established to study the thermal-hydraulic characteristics of transcritical natural gas in the printed circuit heat exchanger in rolling conditions. The results show that the rolling condition has few effect on the total heat transfer rate, but significantly affects the local friction factor and heat transfer characteristics. The rolling condition enhances the local heat transfer performance of transcritical natural gas, but also increases the pressure drop, in which the influences of rolling are the greatest at 1/4 and 3/4 of the rolling period. The tangential force and Coriolis force caused by the rolling motion increase the heat transfer of the natural gas. In the subcritical zone, where the rolling condition has the greatest influence on the heat transfer of the natural gas, the maximum instantaneous Nusselt number is increased by 40%. The rolling condition shows minor effect on the pseudocritical zone, in which the maximum instantaneous Nusselt number is increased by 15%. The rolling condition has almost no effect on the heat transfer performance of natural gas in the supercritical zone. The effect of the rolling condition on the flow characteristics of natural gas is the greatest in the pseudocritical zone, where the friction factor and local pressure drop are increased by approximately 30% compared to those in the steady condition. • Good performance of PCHE makes it a promising candidate in floating natural gas liquefaction. • A numerical model is proposed for transcritical natural gas in PCHE in rolling conditions. • Rolling condition has few effect on the total heat transfer rate of PCHE. • Rolling condition has greatest influence on heat transfer of natural gas in subcritical zone. • Rolling condition on flow characteristics of natural gas is greatest in pseudocritical zone. [ABSTRACT FROM AUTHOR]

Supercritical carbon dioxide (SCO 2) Brayton cycle is widely known as highly potential bottoming cycle among energy conversion systems in the future due to its low requirement to heat source, high efficiency and small volume. Recently, SCO 2 Brayton cycle has been considered utilized in marine industry. In marine environment, unstable disturbance due to the oscillating condition driven by wind and waves makes an impact to on the dynamic performance of SCO 2 Brayton cycle. In this study, we proposed a novel type of compact heat exchanger coupled with phase change material (PCM) based on the concept of printed circuit heat exchanger (PCHE) as a transient controlling method in order to stabilize the dynamic performance of main compressor, re-compressor and turbine in the SCO 2 recompression Brayton cycle system. In this paper, dynamic modelling of the SCO 2 recompression Brayton cycle system with designed PCM based heat exchanger is developed and its dynamic performance is tested. The result of the transient simulation shows that with the effect of PCM based heat exchanger, the disturbing ranges of compression and expanding power of the main compressor, re-compressor and turbine decrease at most by 84%, 75%, and 95% respectively, and the disturbing range of efficiency is reduced by 94%. The PCM based heat exchangers are proved to have great effect on reducing disturbing amplitude of performance of turbo machineries and cycle parameters. • A novel type of PCM based heat exchanger which fits SCO 2 cycle is proposed. • The thermal design and dynamic numerical modeling of PCM-PCHE are developed. • Designed PCM-PCHEs highly reduce disturbing response range of working parameters. • PCM-PCHE in front of turbine impact most on cycle efficiency and output power. [ABSTRACT FROM AUTHOR]

In this paper, the gravity-driven granular flow was investigated by discrete element method (DEM) in the moving bed heat exchanger with tube oscillation. The particle update, the particle contact and the heat transfer were all discussed around tube out-wall. Moreover, the heat resistance analysis was developed to reveal the heat transfer mechanisms. It was found that, tube oscillation can significantly improve heat transfer coefficients (h). The relative growth of locally optimal h varies from 59.2% to 22.6%, when the outlet velocity (u) ranges from 0.65 mm/s to 6 mm/s. In details, the heat transfer can be enhanced by tube oscillation due to the smoother flow in the upstream, the denser contact in the downstream and the more particle mixing inside the flow. However, the particle separation aside the tube has a negative effect simultaneously. Therefore, there is a best frequency (f) to optimize h. The frequency is inversely proportional to the amplitude (D A) and decreases with u. Furthermore, the larger D A can increase the best h. In the present study, the optimal h was obtained as f locates between 3 and 5 Hz at D A > 1 mm. [ABSTRACT FROM AUTHOR]

In the present work, the effect of the baffle pattern on the heat transfer and fluid flow characteristics of shell-and-tube heat exchangers are experimentally investigated, including tri-flower baffle, pore plate baffle, rod baffle, segmental & pore baffle and segmental baffle. In order to compare the hydrodynamics and heat transfer characteristics of the five heat exchangers, a water-water heat transfer experiment system is built. Based on the experimental data, and at the same flow rate, comparison with segmental baffle, the h s of tri-flower baffle and pore plate baffle augment 33.8% and 17.7%. The pressure drop of the rod baffle, tri-flower baffle and segmental & pore baffle decrease are 70.1%, 19.5% and 31.1% lower than that of the segmental baffle. The comprehensive performances h s /Δ p of the rod baffle, tri-flower baffle and pore plate baffle are all superior to that of the segmental baffle. Finally, the experimental correlative formula is raised for the four heat exchangers, and an optimal design scheme for shell side heat transfer enhancement is proposed. • Four types of baffle pattern of heat exchangers are experimentally compared. • Pressure drop and heat transfer performance are experimentally investigated. • Experimental correlative formula is fitted for the four heat exchangers. • An optimal design scheme for shell side heat transfer enhancement is proposed. [ABSTRACT FROM AUTHOR]

Printed circuit heat exchangers (PCHEs) have attracted wide attention in the nuclear energy field owing to their high compactness, strong pressure endurance, and high heat transfer capacity. In situations where corrosion resistance or light weight is required, PCHEs made of titanium exhibit obvious advantages. However, the corrosion resistance of titanium is so high that it is hard to machining titanium using common chemical etching method. Also, etching methods to fabricate fluid channels on titanium plates for microchannel plate heat exchangers such as PCHEs have not been reported in the open literature, therefore the research of producing fluid channels on titanium plates using etching method for PCHEs is demanded. In this work, an electrochemical etching experimental system was established, and the electrolytic machining process using NaCl-containing ethylene glycol as an electrolyte for preparing PCHE fluid channels on titanium plates was studied. To improve the corrosion rate, ultrasonic transducers were added to the experimental system. The influences of the etching temperature and ultrasonic exposure were examined with respect to the etching rate and surface topography. The results showed that ultrasonic transducers with a rated power of 120 W and a frequency of 50 kHz can enhance the corrosion rate by a factor of 4–5 and that the growth trend of the etching rate can be improved with increasing etching temperature. An etching temperature of 45 °C leads to the best comprehensive performance under ultrasonic exposure in terms of etching rate, roughness, and etching factor. Two improved methods including secondary polishing method and pulsed electrode method are proposed to maintain the quality of the surface profile when the etching rate is enhanced. [ABSTRACT FROM AUTHOR]

In this study, diverse baffled longitudinal flow shell-and-tube heat exchangers (STHX) are contrasted with segmental baffle shell-and-tube heat exchanger (SG-STHX). Experimental data are obtained with municipal water served as the working fluid, and the shell-side volume flow rate ranges from 1.79 m3/h to 7.42 m3/h. The components of the shell-side pressure drop are discussed stand on different flow patterns. The maximum proportion of pressure drop in tube bundle section of rod baffle shell-and-tube heat exchanger (RB-STHX) is 12%, while it has nearly taken up 70% shell-side pressure drop for both SG-STHX and large-and-small hole baffle shell-and-tube heat exchanger (LSHB-STHX). The energy efficiency of three tested STHXs is deliberated from three perspectives, including entropy generation, exergy destruction, and efficiency evaluation criterion. The longitudinal flow pattern performed superior energy efficiency, particularly for RB-STHX with the least irreversible energy loss and the most available work. Grounded on the energy-saving potential of RB-STHX, further numerical simulations on the shell-side thermo-hydraulic performance of RB-STHX are conducted. The nexus between geometrical parameters of RB-STHX and its thermal-hydraulic performance are studied. The thermal-hydraulic performance and energy efficiency discussed in this study support further design and application of longitudinal flow STHX to retain inherent superiorities with advanced performance. • Only 12% of the total pressure drop in the shell-side of RB-STHX is derived from the tube bundle section. • RB-STHX performs 173%∼223% higher EEC than LSHB-STHX with the least irreversible energy loss. • Rod baffle shell-and-tube heat exchanger shows the best comprehensive performance. • Numerical investigation of the heat transfer enhancement. • Factors: tube arrangement, rod shape, baffle arrangement, and baffle number. [ABSTRACT FROM AUTHOR]

• Cross-flow plate heat exchangers are applied in cabinet cooling system. • Cross-flow heat transfer could enhance cooling performance in small dimensions. • Counter-flow heat transfer is recommended when system is limited in width. • Thermal resistance can be used to characterize irreversibility of heat transfer. Gas-gas plate heat exchanger is an important component to remove heat generated from electronic devices in the cabinet cooling system. The counter-flow plate heat exchanger is usually used due to its higher heat transfer performance than the cross-flow plate heat exchanger. However, in the cabinet cooling system, the overall dimensions for the heat exchanger is limited. Therefore, it is necessary to consider the overall dimensions of the system during heat exchanger design, but the traditional thermal design method of heat exchanger doesn't consider the effect of system parameters. In this paper, a cross-flow plate heat exchanger is proposed to improve the cooling performance of cabinet cooling system, and is compared with the counter-flow plate heat exchanger. The ε -NTU method and effectiveness-thermal resistance method are applied to evaluate the performance. It is found that for large width of cabinet cooling system, the system with cross-flow plate heat exchanger has higher cooling performance and lower thermal resistance than the system with counter-flow plate heat exchanger. When the width is 700 mm, the cooling capacity of the two systems are 176.13 W/K and 138.95 W/K, respectively. The dimensionless thermal resistance can characterize the irreversibility of the heat transfer at constant mass flow rate. [ABSTRACT FROM AUTHOR]