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Micro gas turbines are an auspicious technology for power generation because of their small size, low pollution, low maintenance, high reliability and natural fuel used. Recuperator is vital requirement in micro gas turbine unit for improve the efficiency of micro turbine unit . Heat transfer and pressure drop characteristics are important for designing an efficient recuperator. Recuperators preheat compressed air by transfer heat from exhaust gas of turbines, thus reducing fuel consumption and improving the thermal efficiency of micro gas turbine unit from 16–20% to 30%. The fundamental principles for optimization design of PSR are light weight, low pressure loss and high heat-transfer between exhaust gas to compressed air. There is many type of recuperator used in micro gas turbine like Annular CWPS recuperator , recuperator with involute-profile element , honey well , swiss-Roll etc . In this review paper is doing study of Heat transfer and pressure drop characteristics of many types recuperator.

A qualitatively new dimension has been introduced to the issue of building structures for energy-efficient buildings by the system of Active Thermal Insulation (ATI), which is already applied in the construction of such buildings. ATI are embedded pipe systems in the envelope structures of buildings, into which we supply a heat-carrying medium with adjusted temperature, so this constitutes a combined building-energy system. This introduces the concept of an internal energy source understood as an energy system integrated into the zone between the static part and the thermal insulation part of the building structure envelope. Under certain conditions, the ATI can serve as a heat recuperator or as an energy collector for a heat pump application. ATI consists of pipe systems embedded in building structures, in which the medium circulates heated by energy from any heat source. The function of the system is to reduce or eliminate heat losses through non-transparent structures in the winter and at the same time to reduce or eliminate heat gains in the summer. It is especially recommended to apply heat sources using renewable energy sources due to the required low temperatures of the heating medium and thus shorten the heating period in the building. Also recommended is to apply ATI for the use of waste heat. Buildings with a given system show low energy consumption and therefore meet the requirements of Directive no. 2018/844/EU, according to which, from 01.01.2021, all new buildings for housing and civic amenities should have energy needs close to zero.

Three major parameters for efficient liquid-fuel-fired melting-furnaces include fuel-economy, thermal efficiency and environmental friendliness of operation. These key parameters form the basis for the adoption of recuperator in the waste gas recycling released during many melting operations in furnaces. This work analysed the thermal performance of both cold and hot fluids across the length of a double-pipe recuperator coupled to a ferrous-melting furnace. The thermal analysis carried out was anchored on some basic assumptions including taking the radiant and temperature characteristics of the exiting waste gases from the exhaust of the furnace as being constant over the volume of the furnace while the temperature at various positions on metal surface is equally taken as being constant. In addition, the heat flow transferred from the waste gases to the lining of the furnace is taken to be by convection and it is equal to the heat flow that the lining gives up to the adjourning surrounding. The derived equations were thereafter analysed and subsequently solved. The obtained results were thereafter used to graphically illustrate the variation of temperature of the agents of heat transfer over the entire length of the recuperator at different instances for parallel flow of the constituent working fluids. The analysis was observed to have conformed to a very great extent to the theoretical pattern expected for similar flows.

As applications of the heat pump and refrigeration, thermally-driven absorption systems which use the lithium bromide and water pair have been widely utilized in various industrial fields since the waste heat can be used directly to obtain the desired effects. A recuperator preheats a working fluid, which enters a generator in the absorption system, decreasing the required heating load. The present study addresses the optimum design of the welded-plate-type heat exchanger as an application of the recuperator. Computational fluid dynamics (CFD) predicted the flow characteristics through chevron plate heat exchangers of different structural dimensions; based on the predictions, optimized dimensions in terms of the heat transfer rate and friction factor was selected. Then, four headers using the selected dimensions were investigated by the CFD technique for selecting the desired plate heat exchanger. Experimental investigations were conducted on the selected configuration as well, and the results were compared with those of the CFD simulation.

Introduction. The wide spread of plate heat exchangers in various fields of technology is due to the simplicity of their design and a variety of layout schemes. An area where their use is very promising is heat recovery. The effect of an air heat exchanger-recuperator consists in heating the incoming flow with the heat of the outgoing flow and is expressed in drastically reduced power consumption, which would otherwise be spent on heating. Research methodology. The object of research is a recuperator designed to heat the air entering the production room in winter. Resistance to air flow is a significant disadvantage of the plate heat exchange. The aerodynamic resistance reduces the flow rate, therefore, leads to a decrease in the flow rate of air passing through the recuperator, so the required flow rate is ensured by special fan installations. The task of designing a recuperator is to minimize the size of the flow part and prevent excessive load on the fan unit. Calculation with the use of the recuperatorТs mathematical model is applied in the research. Results. In the course of the research, a mathematical model of the recuperator has been developed, which includes a condition for limiting the pressure loss by an acceptable value. Ratios have been obtained for determining the optimal duct width between the plates, plates height, length and number. Conclusion. A simplified mathematical model has been proposed to estimate the dimensions of the flow part. The reliability of the simplified model has been confirmed by numerical calculation.

The article considers the following software tools for calculating heat losses and energy consumption: Passive House Planning Package (PHPP) and DesignPH, EcoDesigner STAR, TRNSYS, and MagiCAD Room. The calculations were carried out for one particular object — a residential house with an area of 205 m2 built in the Moscow region. The BEM packages used for the analysis are described. Their advantages and disadvantages, as well as specific features of modeling are noted. The process of interconnection between the building energy model (BEM) and its information model (BIM) is considered. Comparison of the results from modeling the power performance of the object with the same thermophysical properties of its enclosing structures has shown that several BEM-packages should simultaneously be used in designing buildings, because each package is unique in its own way and provides important information, and comparison of the calculation results makes it possible to ascertain that the modeling is correct in nature. The results from calculation of heat losses by heat transfer obtained in all packages have been found to be approximately the same. The calculated heat inputs from solar radiation estimated in EcoDesigner STAR are higher than those estimated in PHPP. The calculated internal heat releases obtained in all packages are different, because each package uses its own methods for specifying internal heat releases. The main disadvantage of the EcoDesigner STAR and TRNSYS packages is noted, namely, impossibility to specify the recuperator thermal efficiency, which leads to excessively high thermal loads on the ventilation system. The MagiCAD Room package does not take into account heat release and heat input from solar radiation; therefore, it can only be used for calculating heat losses and selecting the space heating devices.

In the supercritical CO2 recompression Brayton cycle, recuperators play an important role in cycle efficiency and operating performance. In this work, a dynamic model of the supercritical CO2 recompression Brayton cycle is developed. The effects of high-temperature and low-temperature recuperators on the dynamic characteristics of the cycle are examined. It is found that cycle parameters, including temperature, power, and cycle efficiency, exhibit sinusoidal variations like the source signal provided by the hot-side inlet temperature of recuperator. The transient responses in different locations of the cycle have different amplitudes and phases. The source signal with amplitude of 12.5 K at the hot-side inlet temperature of the high-temperature recuperator causes power variations of 10, 1, and 1.3 kW, respectively, in the turbine, main compressor, and recompressor, while the maximum variance of the cycle efficiency is within 1.57%. When the amplitude at the hot-side inlet temperature of the high-temperature recuperator is changed to 25 K, variances in the cycle efficiencies, powers, and temperatures, respectively, nearly double in the turbine, compressors, and recuperators. When two source signals are added to the cycle, the phase of the cycle efficiency well matches each phase of the two individual source signals.

There is an increasing research interest in the recovery of cooling capacity stored in cryogenic liquids (CLs) for industrial applications, especially for LNG regasification systems. In this study, a novel heat exchanger network (HEN) has been designed for cryogenic liquid regasification process to recover the released cooling capacity and develop a frozen-free heat transfer system with compact structure and high efficiency. Firstly, the specific design concept is proposed to employ the gasified CL as multiple cyclic streams to vaporize its own liquid in the evaporator, which allows a large temperature difference and a compact structure for the vaporization of the CL. Then, according to the optimization design of the flow arrangement, heat exchanger structure and flow rate control, the temperature of the heat medium can always be kept above its freezing point in the superheater and recuperator. Finally, the heat medium as the coolant extracts and transports the cryogenic cooling capacity from the CL to other refrigerated spaces, which can achieve various discharge temperatures to meet the requirements of different kinds of applications by adjusting the circulation number of the cyclic streams and the flow rates of the fluids. In the process calculation, the specific design parameters and energy balance relation of the HEN are obtained, and the cooling capacity recovery efficiency of the HEN system is analyzed using the pinch technique. A prototype of the heat exchanger network is designed and corresponding experiments are carried out for the regasification process of liquid nitrogen. The results indicate that the recovered cooling capacity and recovery efficiency of the prototype can, respectively, reach up to 17.5 kW and 90% within a 7.5% error range, which proves the feasibility of the novel HEN proposed in this paper.

Purpose Because of the appreciable application of heat recovery systems for the increment of overall efficiency of micro gas turbines, promising evaluation and optimization are crucial. This paper aims to propose a multi-factor theoretical methodology for analysis, optimization and comparison of potential plate-fin recuperators incorporated into micro gas turbines. Energetic, exergetic, economic and environmental factors are covered. Design/methodology/approach To demonstrate applicability and reliability of the methodology, detailed thermo-hydraulic analysis, sensitivity analysis and optimization are conducted on the recuperators with louver and offset-strip fins using a genetic algorithm. To assess the relationship between investment cost and profit for the recuperated systems, payback period (PBP), which incorporates all the factors is used as the universal objective function. To compare the performance of the recuperated and non-recuperated systems, exergy efficiency, exergy destruction and corresponding cost rate, fuel consumption and environmental damage cost rates, capital and operational cost rates and acquired profit rates are determined. Findings Based on the results, optimal PBP of the louvered-fin recuperator (147 days) is slightly lower than that with offset-strip fins (153 days). The highest profit rate is acquired by reduction of exergy destruction cost rate and corresponding decrements for louver and offset-strip fins are 2.3 and 3.9 times compared to simple cycle, respectively. Originality/value This mathematical study, for the first time, focuses on introducing a reliable methodology, which covers energetic, exergetic, economic and environmental points of view beneficial for design and selection of efficient plate-fin recuperators for micro gas turbine applications.

The mass flow rate inside heating, ventilation, and air-conditioning units provides important information for fault detection and diagnosis (FDD) and for performance monitoring. Most commercial units are not equipped with physical flow rate sensors, and virtual sensors (VS) offer an alternative that provides improved FDD performance. This paper presents the virtual mass flow sensor for an air handling unit with a recuperator (a fixed-plate heat exchanger). The VS is based on the heat exchange process inside the recuperator. It estimates the mass flow of air only on the basis of temperature readings from the inlet and the outlet of the recuperator. Two different approaches to the design of the VS model are described here. The first approach uses a simplified physical description of the recuperator, and the second approach uses knowledge of the recuperator performance curve. Laboratory experiments have confirmed that the proposed VS can be utilized as a substitute for a physical mass flow rate sensor for monitoring and for fault detection.

Purpose The purpose of this paper is to recommend a validated numerical model for simulation the flue gases heat recovery recuperators. Due to fulfill of this demand, the influences of ash fouling characteristics during the transient/steady-state simulation and optimization of a 3D complex heat exchanger equipped with inner plain fins and side plate fins are studied. Design/methodology/approach For the particle dispersion modeling, the discrete phase model is applied and the flow field has been solved using SIMPLE algorithm. Findings According to obtained results, for the recuperator equipped with combine inner plain and side plate fins, determination of ash fouling characteristics is really important, effective and determinative. It is clear that by underestimating the ash fouling characteristics, the achieved results are wrong and different with reality. Originality/value Finally, the configuration with inner plain fins with characteristics of: di =5 mm, do = 6 mm, dg = 2 mm, dk = 3 mm and NIPFT = 9 and side plate fins with characteristics of: TF = 3 mm, PF = 19 mm, NSPF = 17·2 = 34, WF = 10 mm, HF = 25 mm, LF = 24 mm and ß = 0° is introduced as the optimum model with the best performance among all studied configurations.

A numerical investigation into conjugate heat transfer for a double-tube heat exchanger in mini-scale was conducted, with an asynchronous intermittent laminar flow imposed at the inlets. As a basic component of the micro recuperator for a micro swing engine, a mini double-tube exchanger under the same flow conditions was chosen as the physical model with consideration of variable fluid properties. Results indicate that, for the asynchronous intermittent pulsed flow, the axial wall heat conduction is much more serious and the periodic fluctuation of the solid wall temperature further worsens the heat transfer efficiency. Two dimensionless numbers R ∗ and C ¯ ∗ are proposed to evaluate the two adverse effects. Then, two key parameters involved in the design of the micro recuperator for the micro swing engine are studied, namely, wall thickness ratio δ / D c and flow frequency. For certain flow frequencies, as the value of δ / D c increases, the axial heat conduction is enhanced while the wall temperature fluctuation is reduced. For a given δ / D c , the flow frequency dually affects the heat exchanger efficiency and the optimum frequency exists. The optimal value increases with the wall thickness ratio. These results lay a good foundation of the micro recuperator design for the micro swing engine.

Thermoelectric modules are usually sandwiched between hot-side and cold-side heat exchangers to generate electrical power. But the sandwiched structures are unsuitable for recuperators because large thermal resistance caused by the thermoelectric modules significantly reduces the heat transfer efficiency. In order to maintain heat transfer efficiency and generate more electrical power, a novel concept of a thermoelectric generator integrated recuperator is proposed, with fins made of thermoelectric materials rather than steel. A numerical model is developed using FLUENT software with User Defined Function codes. Compared with conventional plate-fin recuperators, the new recuperator has similar thermal-hydraulic performance and generates additional electrical power. The effects of Reynolds number on open circuit voltage, internal resistance, heat transfer, output power, and pumping power are studied. The optimum hot gas velocity is 1.5 m/s, which produces a temperature difference of 147.6 K, an open circuit voltage of 31.5 mV, and an output power of 0.23 mW. The Taguchi method is employed to design numerical cases for geometrical optimization. Results show that the effect order is: channel width > TE fin thickness > TE fin height. The optimum values of channel width, fin thickness, and height are 1 mm, 3 mm, and 1 mm, respectively.

An experimental Lead Lithium (PbLi) loop named DRAGON-V has been built at the Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences (INEST, CAS). The purpose of this loop is to test the technical issues of PbLi blankets for fusion reactors, such as thermal hydraulics, material corrosion, magnetohydrodynamics (MHD) effect and safety issues, etc. The main heat recovery system of the DRAGON-V loop is the Concentric Recuperator Heat Exchanger (CRHE) which was made of T91 steel. It has counter flow arrangements with PbLi as the working fluid across the tube and shell sides. In this paper, the system was analyzed in detail for thermal performance, pressure drop, pumping power, entropy generation, the effect of inlet temperature of shell side fluid on overall performance, and the temperature distribution and flow characteristics. It was found that the effectiveness and heat transfer rate of the CRHE was decreased with the inlet temperature of the PbLi across the shell side. The difference of effectiveness calculated by correlation and simulation was about 4.5%. The high pumping power of PbLi fluid circulation was required on the shell side due to its thermo-physical properties variation, which resulted in the high pressure drop across the shell side as compared to the tube side. The temperature variation across the tube and shell sides indicated that the simulation results agreed well with the design parameters within a deviation of less than ˜ 5%.

The current study aims to perform a stochastic analysis on microturbine compact recuperators to evaluate the impact of uncertainties in design parameters on their cost and volume, by using two different probabilistic approaches: Monte Carlo (MC) and Response Sensitivity Analysis (RSA). These two methods have been developed in Matlab® and then coupled with CHEOPE (Compact Heat Exchanger Optimisation and Performance Evaluation) software, which allows to analyze two different types of recuperators, used in microturbine applications: the furnace-brazed plate-fin type and the welded primary surface type. This paper focuses on an analysis of plate-fin type recuperators, for which the cost function adopted was tuned and verified in a previous study. Three main parameters of the recuperator have been considered as uncertain: effectiveness, hot side and cold side pressure drops. The uncertainties associated with these three parameters are based on industrial knowledge. The aforementioned stochastic methods have been used to propagate such uncertainties on the relevant outputs, such as cost and volume, allowing us to evaluate the least expensive and the most compact recuperator among those analysed.

High efficiency solar chemical-looping methane reforming is demonstrated in a prototype reactor operated in a high-flux solar simulator. The reactor includes six tube assemblies, which each comprise a fixed-bed of ceria particles and a gas-phase heat recuperator. The cycle was accomplished by alternating the flow to one tube assembly between CH4 and CO2. In the initial series of experiments, temperature, CH4 concentration, reduction flow rate, and cycle duration were varied to minimize carbon accumulation and maximize efficiency. In the second set of tests, the reactor was operated at optimized conditions for ten cycles at 1228 and 1274 K. Higher temperature favors better performance. At 1274 K, CH4 conversion is 0.36, H2 selectivity is 0.90, CO selectivity is 0.82, CO2 conversion is 0.69, and the energetic upgrade factor is 1.10. Heat recovery effectiveness is over 95%. Solar-to-fuel efficiency is 7% and the thermal efficiency is 25%. Projected solar-to-fuel and thermal efficiencies are 31 and 67% for the full-scale reactor and 56 and 85% for a commercial reactor with lower thermal losses. The demonstrated efficiencies are the highest reported to-date for this process. The projected scaled-up efficiencies suggest solar chemical-looping methane reforming could be a competitive approach for production of solar fuels.

Indian TBM team is developing Lead-Lithium Cooled Ceramic Breeder (IN-LLCB) Test Blanket Module (TBM) along with its associated systems for testing in ITER. The outer box of LLCB TBM is cooled by first wall helium cooling system (FWHCS) which is designed to remove the heat load of ∼300 kW. FWHCS is a high temperature high pressure closed loop which produces significant movements and propagates high stresses in the piping system. This, in turn, leads to forces and moments on the supports and equipment nozzles. FWHCS may experience a high acceleration (∼59.69 m/s2) during seismic events, the deflection of pipes in this scenario may increase the complexity in the loop operation. This paper describes pipe stress analysis, methodology and results of FWHCS. The pipe stress analysis is performed for sustained and occasional load combinations for various ITER operating states as envisaged for TBMs. FWHCS piping is subjected to category I (likely event) and IV (extremely unlikely event, SL-2) loading conditions. The Pipe stress analysis is performed in accordance with ASME B31.3. The calculated stresses are within the limits for the considered cases. The highest value of stress (about 0.65 times the allowable stress) and the maximum displacement of 23 mm (x direction), 15 mm (y direction) and 11.5 mm (z direction) is observed in recuperator to electrical heater line. The obtained reaction and moment forces are needed as an input for the selection of pipe supports, location of supports and the verification of embedded plates loading criteria. This pipe stress analysis is also used in the optimization of FWHCS layout and further these inputs would be utilized in preliminary design phase.

Following paper focuses on the application of a counter-flow indirect evaporative cooler as a heat recovery device in air conditioning systems in temperate climate (climate where temperature in summer does not exceed 32 °C and humidity ratio does not exceed 15 g/kg, which is typical for Central and Eastern Europe). The purpose of the study is to show the potential of retrofitting conventionally used recuperator exchangers by changing them into indirect evaporative coolers (IEC). Study was performed with original e-NTU-model. Proposed analysis discussed the critical operational aspects of the IEC unit operating as a heat recovery device, including detail discussion about the heat and mass transfer process with and without condensation in the product air channel and investigation of the influence of different parameters on the exchanger performance. Achieved results are additionally compared with the conventional recuperation process, which is commonly used in temperate climates, in order to show the energy savings which can be obtained by simple modification of such devices. It was found that the counter-flow indirect evaporative cooler is suitable for these climate conditions and it allows to significantly increase the temperature drop during heat recovery process in compare with the commonly used recuperators. In addition, several important operational aspects where analyzed, including analysis of pressure drops inside IEC unit and potential of water recovery from the condensation inside the unit.

The Carleton University Brayton Cycle Loop (CUBCL) is a project involving virtually all aspects of 10 MW supercritical CO2 gas turbine design. One of the concerns regarding the 10 MW S-CO2 gas turbine is recuperators degradation due to fouling. This work reveals that when the high temperature recuperator (HTR) overall heat transfer coefficient declines from 2471.65 to 1882.83 (kW/m2 K), the cold outer temperature decreases from 814.16 to 728.89 K. To offset this, the control system directs the primary heat exchanger to add 11101.14 kW of heat to compensate for the loss due to fouling, which results in a cycle efficiency decrease from 48.25 to 32.16%. The amount of heat added by the primary heat exchanger will not be absorbed in the HTR and/or the low temperature recuperator (LTR) due to fouling layers, so the LTR hot stream discharge temperature (recompressor inlet) rises. The current design of a 10 MW S-CO2 gas turbine recompressor works on fluid before heat is removed by the pre-cooler. This highlights the necessity for further protection to prevent the recompressor from overheating.

Energies : open-access journal of related scientific research, technology development and studies in policy and management 14(21), 6873 (2021). doi:10.3390/en14216873 special issue: "Special Issue "Heat Transfer Analysis and Modeling in Furnaces and Boilers" / Special Issue Editors: Dr. Giancarlo Sorrentino, Guest Editor; Dr. Pino Sabia, Guest Editor", Published by MDPI, Basel

In this paper, experimentally studies of a 1 kW-scale organic Rankine cycle (ORC) with R290 as working medium were carried out for cryogenic cold energy recovery. Specifically, a three-fluid wounded tube heat exchanger was utilized as the condenser and the recuperator, which made the system operate under the basic ORC (bORC) and the recuperative ORC (rORC) working modes. The hot water and the liquid nitrogen were respectively used as the heat source and cold source. The system performances were evaluated at 20–50 °C of the heat source, −170∼-160 °C and 60–120 kg/h of the cold source. The optimal heat source temperatures were obtained for the different cold source conditions. Moreover, the superiority of the rORC was verified. The results demonstrated that the maximum net power outputs were 0.673 kW and 0.894 kW for the bORC and rORC, respectively. For the bORC and the rORC, the maximum energy efficiency was 5.23% and 6.49%, and the maximum exergy efficiency was 21.34% and 28.99%, respectively. The cold energy efficiency varies in the range of 1.73%–14.20% and 1.16%–19.72% for the bORC and rORC, respectively. The three-fluid recuperator occupied the largest exergy loss, which varied in the range of 66.59–84.12%.

Cycle humidification applied to micro Gas Turbines (mGTs) offers a solution to overcome their limited operational flexibility in terms of variable electrical and thermal power production when used in a Combined Heat and Power (CHP) application. Although the positive impact of this cycle humidification on the performance has already been proven numerically and experimentally, very detailed modeling of the system performance remains challenging, especially the determination of the recuperator effectiveness, which has the highest impact on the final cycle performance. Indeed, the recuperator performance depends strongly on the mass flow rate of the air stream and its humidification level, two parameters that are difficult to measure accurately. Accurate modeling of the recuperator performance under both dry and humidified conditions is thus essential for correct assessment of the potential of humidified mGT cycles in Decentralized Energy Systems (DES). In this paper, we present a detailed analysis of the recuperator performance under humidified conditions using averaged experimental data, extended with the application of a Support Vector Regression (SVR) on a time series to improve noise-modeling of the output signal, and thus enhance the accuracy of the monitoring process. In a first step, the missing experimental parameters, air mass flow rate and humidity level, were obtained indirectly, using rotational speed, fuel flow rate, exhaust gas composition and pressure level measurements in combination with the compressor map. Despite the low accuracy, some general trends regarding the recuperator performance could be observed based on these experimental data, indicating that the recuperator, despite having an increased total exchanged heat flux, is actually too small to exploit the full potential of the humidification. In a second step, by means of the SVR model, a first attempt was made to improve the accuracy and reduce the scatter on the recuperator performance determination. The predicted results with the SVR indicated indeed a reduced scatter on the determinations of the air mass flow rate and the amount of introduced water, opening a pathway towards online recuperator performance prediction.

The performance models for high-temperature metallic recuperators considering one and two-dimensional heat transfer are presented. In one-dimensional model, an explicit expression to represent the effect of both the temperature and product of partial pressure and mean beam length on the emissivity is developed using emissivity charts. The effect of upstream and downstream surroundings is neglected. A two-dimensional heat transfer model is developed using zone method along with sum-of-gray-gases approximation to study the effect of upstream and downstream surroundings on performance. The results from the two models are compared. For lower values of inlet flue gas temperatures and higher mass flow rates, one-dimensional model predicts results within 5% of two-dimensional model. One-dimensional model provides a simplified solution for the assessment of recuperator performance but predicts the surface temperature distribution on a relatively lower side for higher inlet flue gas temperatures and low mass flow rates.

The current work is an analysis of the recuperated Humphrey cycle. Three cycle topologies are studied with and without turbine cooling. The study focuses on the interconnection between combustor pressure gain and heat recuperation. It is an attempt to optimize the cycle topology and configuration to achieve the maximum possible cycle efficiency. It is found that the best option to use recuperation in the Humphrey cycle is to operate the combustor at stoichiometric conditions, without preheating the air fed to it. The combustion air comes effectively form a compressor air bleed. The remaining air is further compressed at the combustor outlet pressure and is fed to a plenum between combustor and turbine once it is preheated by the recuperator. This cycle configuration results in the best performance both in terms of efficiency and specific work. Specifically, an efficiency increase between 2 and 5% points is achieved. This work concludes with a feasibility study for shockless explosion combustion (SEC) for the Humphrey cycle configurations and topologies that achieve an efficiency advantage against the Joule cycle. It is found that realistic SEC combustor lengths and efficiency gains can be simultaneously achieved, albeit not at the cycle configurations with the best performance.

Recuperator and precooler are key components of supercritical CO2 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.

Although supercritical CO2 (S–CO2) coal-fired paper generation systems have been studied broadly in recent years, there is still potential for further energy savings. A new system is proposed to efficiently use the waste heat of both the cooler and the boiler. The new system extends the air preheater surface area, uses the economizer to replace part of the heat load of the high-temperature recuperator, and both the evaporator and precooler are arranged before the cooler. The performance analysis model of the new system is built, and the effects of the economizer split ratio, the main compressor split ratio, and the operation load on the new system performance are investigated. The results show that the new system performance is much better than that of the reference system. Under the design condition, the boiler efficiency and the power generation efficiency of the new system are 96.3% and 49.5%, 1.1% and 2.6% higher than those of the reference system. There exist optimal split ratios for both the economizer and main compressor. The optimal split ratio of the economizer is 10%, and that of the main compressor is 70%. The power generation efficiency decreases with a decreasing operation load.

When the state-of-the-art supercritical CO2 cycle is applied to the marines, priority should be given to the feasibility of its component size. In this study, a thermodynamic model of the marine supercritical CO2 recompression cycle was developed. To evaluate the thermoeconomic and component size of the system, the recuperator and precooler with a microtube structure were designed. After quantitatively discussing the impact of the two-stage compression mode on the component scale, the sizes of the heat exchangers were optimized based on the maximum allowable pressure drop. The parameter analysis demonstrates that increasing the speed of the power turbine is beneficial to the system thermoeconomic. Not only can an efficiency improvement of 1.73% and a cost saving of 1.77 $/MWh be achieved, but also the implementation of two-stage compression reduces the volume of the high-temperature recuperator, low-temperature recuperator, and precooler by 4.62%, 6.33%, and 37.4%, respectively. The size optimization analysis suggests that the direction with the longest distance should be regarded as the length constraint of the heat exchanger design in the absence of multi-objective optimization. Moreover, this study has guiding significance for the size optimization of the supercritical CO2 cycle used in a limited space.

Humid Air Turbine (HAT) cycle is considered to be one of the most advanced gas turbine cycles due to its high efficiency, flexible operation, low NOX emissions, and low investment cost. The heat recovery determines the temperature field distribution of the humidification process, which is critical to the performance of the HAT cycle. However, so far, the effect of heat recovery of heat exchangers on cycle performance is still a research gap. Filling up the research gap is of great significance to the full utilization of the thermodynamic potential of the HAT cycle. This paper built a humid air turbine cycle with additional heat exchangers (aftercooler, regenerator, economizer) based on a humid air turbine test rig. A comprehensive thermodynamic analysis of the effectiveness of the heat exchanger components had been carried out. To conclude, the water–air ratio, aftercooler effectiveness and regenerator effectiveness can effectively affect the humidification performance and efficiency. The above analysis provided a theoretical reference for the actual transformation and performance enhancement of the test rig. In addition, research on the influence of the water–air ratio on the HAT cycle at different power outputs showed that the optimal water–air ratio gradually decreases with the increase of power output. The effect of the pressure ratio on the HAT cycle was clarified by comparison with a simple regenerative cycle. Finally, exergy analysis of the HAT cycle was carried out based on different optimization strategies. For the humid air turbine of 4 MW-class, increasing recuperator effectiveness is one of the effective techniques to enhance exergy recovery as well as efficiency, and improving the proportion of exergy utilized for water evaporation can augment specific work output. The maximum efficiency of 48.5% was obtained where its corresponding exergy efficiency reaches 44.4%. The maximum specific work output of 560.6 kJ/kg was achieved with an exergy efficiency of 38.0%.

Humid Air Turbine (HAT) cycle that uses a water-air mixture as a working fluid has a significant advantage in the distributed generation technologies and combined heat and power. The feature of the HAT cycle is that air humidification is carried out at a variable temperature. This cycle is considered as one of the optimal humidified gas turbine cycles to achieve the energy cascade utilization. However, most studies typically use the method of a single variable to investigate the coupled process of humidification and heat recovery, which limits the further performance improvement of the HAT cycle. Herein, we study the interactions among air humidification, heat recovery and system performance to elaborate the effects of interactive variables on the HAT cycle performance. Considering the complexity of the interaction of water-air ratio, aftercooler effectiveness and recuperator effectiveness, a thorough numerical analysis was carried out from the following perspectives: the thermodynamic correlation between components and systems was investigated by controlling a single parameter; the interaction of multiple variables was performed with identical turbine inlet temperature (TIT) and pressure ratio (PR) conditions; and the coupling relationship between interactive variables with a variation of TIT and PR conditions. A thorough analysis revealed that the variables that significantly impact the HAT cycle efficiency are successively RE, W/A, and AE. The analysis of the coupling effects of interactive variables under different TITs is consistent with the above results. As the PR increases, the W/A and AE have a more significant effect on HAT cycle efficiency and the effect of RE on the HAT cycle efficiency greatly diminishes. The HAT cycle efficiency, specific work output, and heat recovery achieved 43.9%, 556 kJ/kg, 5505.33 kW, where its corresponding TIT, PR, W/A, AE, RE values are 1280 °C, 8, 1.5,0.75, 0.9, respectively. Overall, a thorough analysis of interactive variables is of great significance to fully understand the effect of heat recovery on the efficiency enhancement and specific work output improvement from the thermodynamic perspective.

Carbon dioxide transcritical power cycle (CTPC) systems are dynamically tested on a constructed test bench using an expansion valve. Effects of external perturbations of pump speed, expansion valve opening and engine conditions on dynamic performance of the CTPC systems are investigated with step changes. Dynamic characteristics are identified with rise time, settling time and overshoot. Results show that both a basic CTPC system and a CTPC system with a recuperator (R-CTPC) behave as a second-order underdamped system with the perturbations of pump speed and expansion valve opening. Overshoot or undershoot tends to appear in pressures when pump speed changes, while overshoot or undershoot occurs more noticeably in temperatures when expansion valve opening varies. Although the CTPC systems respond slowly with the perturbations of engine conditions, they have the ability to operate safely and produce power continuously. Therefore, the CTPC systems are robust when facing narrow fluctuations of heat sources while swift when required to make adjustments, showing great potential for truck engine waste heat recovery. Overall, current research gives a full understanding of the dynamic performance of the CTPC systems, which will provide references for dynamic model validation and possible control strategy identification.

The design of a highly efficient gas generating plant with a direct­flow gas generator was proposed for gasification of low­grade fuels. The design includes a gas­air recuperator and an evaporator for preliminary preparation of air­steam mixture. The gasification process is fully controlled since operation of the evaporator is coordinated with operation of the blast gas supply system due to which humidity of the mixture fed to the gasification zone is programmed 10 mm pellets produced of rape stems were used as fuel. Two­factor experiments have been carried out to estimate the effect of volume and humidity of blast air on the lower heat value of the generator gas and the mass fuel consumption in the gasification process. The effect of air volume and humidity on temperature of the air­steam mixture required for the gasification process was also investigated. It has been established that the optimum temperature of the air­steam mixture was 550...570 o N and was achieved at the volume of blast gases entering the gas generator in the range of 37...42 m 3 /h and air humidity of 55...65 %. Under these conditions, the lower calorific value of the generator gas was 12.3 MJ/m 3 , which was 15.1 % higher than that of the gas obtained without the use of air­steam blast in the gasification process. Consumption of pellets for the gasification process was reduced by 14.7 % and the volume of gas produced from a kilogram of pellets increased by 18 % to 3.2 m 3 /kg. The total energy efficiency of using the given flowsheet in production of generator gas from pellets produced of rape stems was 23.5 %. The innovative procedure of compiling heat balance for the process of air­steam gasification of plant materials was presented. According to the results of experimental studies, a heat balance has been compiled for the developed design of the gas generating plant. This balance has demonstrated high efficiency of the process of air­steam gasification. Efficiency factor of the direct­flow gas generator was 79 % and that of the gas generating plant as a whole was 74.6 %. The presented studies can be used as a basis for modernized methodologies of thermal calculation of mobile and stationary gas generating plants

In this study, a modified refrigeration cycle (MRC) using refrigerant mixture R170/R290 was proposed for applications in low-temperature freezers. Different from traditional auto-cascade cycle (ARC), additional recuperator and expansion valve are set between condenser and separator to realize phase separation at an intermediate pressure. The MRC can significantly improve volumetric refrigeration capacity (qev) and the coefficient of performance (COP) especially in low evaporating temperature condition. As evaporating temperature is set at −60°C, using MRC system can acquire 18% and 35% COP and qev improvements, and the compression ratio in MRC reduced 23% in comparison to ARC. In general, decreasing both separating temperature and quality of condenser outlet will benefit the performance of MRC. Besides, there exist an appropriate mixture quality at evaporator outlet to obtain the best COP and qev under the given condition.

In the present work, based on half-wall thickness multi-periodic boundary conditions, a 3D fluid-solid coupled heat transfer model considering variable properties and mutual influence between high temperature hot gas and compressed cold air is established to predict the flow and heat transfer in the cross-wavy (CW) channels. The present model is verified by comparing the Nusselt numbers of the numerical results with those of experimental results. On the base of model validation, the flow and heat transfer characteristics of the different CW channels are further investigated in a wide Reynolds number range (gas side: 100–2200; air side: 100–2800). The secondary flow which is responsible for the enhancement of heat transfer and the increase of the pressure loss is successfully captured, and its influence on the thermal and flow boundary layers is analyzed. By comparing the heat transfer and pressure loss of five configurations, the effecting law of geometrical parameters is revealed. Based on a large number of simulation results, the correlations of heat transfer and Fanning friction factor involving Reynolds number, Prandtl number and geometrical parameters are proposed using the least-squares method, which are helpful to the design of CW primary surface recuperator in the microturbine.

In this work, a computational model of heat transfer and pressure drop is established for the design optimization of the annular involute-profile cross wavy primary surface (CWPS) recuperator in microturbine. The genetic algorithm method is employed to solve the optimization problem of annular CWPS recuperator with multiple design variables. Thus, an optimal design approach for this kind of recuperator is formulated. The validity of the computational model is checked by comparing the calculation results with the experimental data of C30 and C65 prototype recuperators (Capstone Turbine Corporation). With the total relative pressure loss as the optimization target, the developed method is applied to the optimal design of the recuperator in a 300 kW power-level microturbine. In comparison with the original design, the optimal design results in a significant reduction of the pressure loss in the case that all constraints are satisfied, which indicates the formulated optimal design approach is effective for the annular CWPS recuperator. By replacing the optimization target, the optimal design approach presented in this work can be also applied to the single-objective optimization for other targets (compactness, heat transfer area, weight, volume, effectiveness, etc.) and even the multi-objective optimization according to the particular requirements of different microturbines.

A 250W turbo charger comprising of a radial turbine, a centrif ugal compressor with reverse flow combustor coupled to an electric generator to produce power is under development and testing stage at the laboratory. Also a swirling reverse flow recuperator has been designed and fabricated for integration with the turbo charger to recover waste heat coming out of the radial turbine and to improve thermal efficiency of the engine cycle. This paper covers the design, analysis, fabrication and testing of radial turbine and recuperator, with the design objective of higher effectiveness and lower pressure loss.The swirling recuperator with a cylinder surface has been designed and analyzed for stresses due to thermal and structural loads. A test rig set up with compressed air lines and space heaters (combustor) has been designed and fabricated. Simulated engine design conditions such as flow, pressure and temperatures were applied and thermal effectiveness and pressure drop across the model are evaluated, validating the theoretical predictions.A full scale swirling recuperator has also been fabricated for integration with the radial turbine.

Supercritical CO2 (S-CO2) power cycles have received much attention due to their desired advantages in various applications. Due to the substantial difference in specific heat of S-CO2 at different pressure, unique characteristics inside heat exchangers, especially in the recuperator, are observed and affect the cycle design. In this research, the problem of inner pinch occurring inside the S-CO2 recuperator is identified and resolved by suggesting a new framework for the definition of heat exchanger effectiveness using the point of zero inner pinch. The design methodology of S-CO2 cycles is improved using this definition by developing a module to calculate the zero inner pinch using artificial neural network (ANN) to undergo a learning process. As a result, the computation time required for cycle analysis is reduced by an order of 10 3 in the case of simple recuperated Brayton cycle, under the accuracy of 10 - 7 error bound. As the readers gain the access to the developed module for calculating the zero inner pinch, the procedure for S-CO2 cycle optimization will become far more manageable for researchers, and as a result, this result can allow the conceptualization of even further complex layouts in S-CO2 cycle research.

For thermal systems using CO2 as a working fluid, an isobaric heat transfer in the supercritical region is a variable temperature process. When CO2 is near the pseudo-critical point, its specific heat changes clearly with temperature, which results in an increase in the average temperature difference and thus, an increase in entropy generation. A thermodynamic optimization method for a heat transfer process based on temperature glide matching is proposed in this paper. This method can allow the temperature difference to be uniform and near the minimum value. The heat transfer process in the gas cooler of a CO2 heat pump water heater and the recuperator of the supercritical CO2 (S-CO2) Brayton cycle are optimized based on this method. Using this concept, a CO2 heat pump water heater can simultaneously obtain a certain amount of warm water without simultaneously reducing the hot water output; in addition, for S-CO2 cycle, the exergy efficiency of the regenerator is improved, and the thermal efficiency of the system is thereby improved.

This paper presents a comparative analysis of thermodynamic cycles of two ship power plant systems with a high-temperature helium-cooled nuclear reactor. The first of them is a gas system with recuperator, in which classical gas chamber is substituted for a HTGR reactor (High Temperature Gas-cooled Reactor). The second of the considered cycles is a combined gas-steam system where working medium flux from gas turbine outlet is directed into waste heat boiler and its heat is utilized for production of superheated steam to drive steam turbine. Preliminary calculations of the combine cycles showed that it is necessary to expand the system by adding to its steam part an inter-stage overheat for secondary steam, owing to that a required degree of steam dryness at outlet from the turbine can be reached, ensuring its correct operational conditions. The analyzed power systems were compared to each other with regard to efficiency of their thermodynamic cycles. Also, efficiency of particular cycles were subjected to optimization in respect to such parameters as : working gas temperature at outlet from reactor in gas system as well as steam pressure at outlet from waste heat boiler and partition pressure in steam part of combined system. Advantages of nuclear power plants compared with the classical power systems dominating currently in sea transport were also discussed.

This paper presents a review of system design and analysis, and transient control and optimization of solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems for different system configurations. The main feature of SOFC power systems is production of less harmful chemical and acoustic emissions at a higher efficiency compared to conventional power production technologies. Microturbines have been shown amenable to integration with a high temperature fuel cell due to the well-matched temperature and pressure characteristics of an SOFC and microturbine in a hybrid system. Different configurations of hybrid SOFC-GT systems are briefly discussed. The main focus of this paper is investigation of different control strategies and transient performance characteristics of hybrid SOFC-GT systems in the literature. Different control strategies including variable and fixed speed operation of shaft using PI control methods are discussed. Different types of bypass valves for hybrid system control such as recuperator bypass are used to control the inlet temperature of the air entering the stack. In addition, SOFC bypass valves are used to control the mass flow through the SOFC stack. Different control methods are described to avoid stall/surge in the compressor. The main components of a hybrid system and their effects on the system performance are thoroughly discussed. Impacts of heat exchangers on a hybrid system are also determined and pressure losses between the recuperator and combustor for three different conditions are evaluated. Effects of different system parameters such as Steam-to-Carbon ratio (S/C), fuel utilization and operating pressures on system performance are determined. Net efficiencies of different hybrid system configurations are compared. Other applications of a hybrid system such as those that include CO 2 capture and sequestration are investigated. Finally, system optimization and investigation of alternative fuels are discussed.

A novel recompression supercritical CO2 Brayton cycle integrated with an absorption chiller (RSBC/AC) is proposed for air-cooled concentrated solar power (CSP) plants. The residual heat of CO2 in the cold end of the supercritical CO2 cycle is utilized to drive the absorption chiller, which chills the CO2 exiting the precooler further before it enters the main compressor. Parametric analyses and optimizations are performed for the RSBC/AC. Energy and exergy analyses and comparisons are conducted to illustrate the mechanisms of RSBC/AC performance improvement. Sensitivity analyses of pressure drop and ambient temperature are performed to investigate RSBC/AC performance under various working conditions. Economic evaluations of a CSP plant integrated with RSBC/AC are performed to investigate its feasibility as an alternative to the stand-alone supercritical CO2 cycle. Results show that the optimized thermal and exergy efficiencies of RSBC/AC are 5.19% and 6.12% higher, respectively, than those of the stand-alone supercritical CO2 cycle. The exergy destruction/loss in the high-temperature recuperator and precooler of RSBC/AC are significantly reduced. The levelized cost of electricity and payback period for the plant integrated with RSBC/AC are reduced by 0.46–0.77 ￠/kWh and 0.67–5.27 years, respectively, with an annual full-load hour ranging from 5000 to 8500.

This paper presents a baseline design and optimization approach developed in Aspen Custom Modeler (ACM) for microtube shell-and-tube exchangers (MSTEs) used for high- and low-temperature recuperation in a 10 MWe indirect supercritical carbon dioxide (sCO2) recompression closed Brayton cycle (RCBC). The MSTE-type recuperators are designed using one-dimensional models with thermal-hydraulic correlations appropriate for sCO2 and properties models that capture considerable nonlinear changes in CO2 properties near the critical and pseudo-critical points. Using the successive quadratic programming (SQP) algorithm in ACM, optimal recuperator designs are obtained for either custom or industry-standard microtubes considering constraints based on current advanced manufacturing techniques. The three decision variables are the number of tubes, tube pitch-to-diameter ratio, and tube diameter. Five different objective functions based on different key design measures are considered: minimization of total heat transfer area, heat exchanger volume, metal weight, thermal residence time, and maximization of compactness. Sensitivities studies indicate the constraint on the maximum number of tubes per shell does affect the number of parallel heat exchanger trains but not the tube selection, total number of tubes, tube length and other key design measures in the final optimal design when considering industry-standard tubes. In this study, the optimally designed high- and low-temperature recuperators have 47,000 3/32 in. tubes and 63,000 1/16 in. tubes, respectively. In addition, sensitivities to the design temperature approach and maximum allowable pressure drop are studied, since these specifications significantly impact the optimal design of the recuperators as well as the thermal efficiency and the economic performance of the entire sCO2 Brayton cycle.

Supercritical carbon dioxide (S-CO2) power cycle has been under the spotlight for years as one of the promising solutions to resolve the energy and environmental problem. The most of previous studies focused on cycle performances and applicable configuration. In this study, detailed and extensive analysis on the recompression S-CO2 power cycle was carried out to reflect more practical and desirable conditions. This study focused on the optimization of the S-CO2 cycle by evaluation of the irreversibility of the recuperators using the effectiveness analysis and pinch point temperature difference (PPTD) analysis. Split ratio from the main stream to the recompressor and compression ratio were considered as independent parameters. From the simulation, the characteristics and performance of the recompression cycle were discussed. The optimum operating conditions were determined in combinations of PPTDs of the two recuperators. With the performance curves, control strategy of the two independent parameters is ranged for desirable operation of S-CO2 power cycle.

Micro gas turbines are manufactured to have a compact structure and small volume, which makes them more vulnerable to internal leakages compared to heavy-duty gas turbines. Accordingly, precise diagnosis of the performance degradation in a micro gas turbine is important. This study investigates the characteristics of degradation. Performance maps were used for the compressor and turbine, and a multi-segment counter-flow heat exchanger model was used for the recuperator. The component models were refined using actual operation data, resulting in precise simulation of the reference operation without leakage. A performance analysis was carried out, and the results were analyzed for three types of leakage with the following paths: from the compressor outlet to the recuperator’s cold-side outlet, from the compressor outlet to the combustor outlet, and from the combustor inlet to the turbine outlet. The third path produced the largest reduction in engine efficiency. The degradations were also compared with those related to compressor fouling and turbine erosion, which are the most common causes of degradation in a gas turbine. Even when qualitatively similar performance changes were observed, the root cause could be determined by analyzing differences in performance parameters such as the fuel flow.

The current study aims to simultaneously and comprehensively investigate the performance of four types of recuperative heat exchangers applied in 200 kW microturbines by using numerical method. Different fin configurations including rectangular, triangular, louver and offset strip fins are employed in the recuperators to enhance the heat transfer rate. Additionally, the calculations are separately undertaken for both counter and cross-flow arrangements. To achieve the best performance, a three-objective optimization problem is solved using Non-dominated Sorting Genetic Algorithm (NSGA-II). Recuperator effectiveness and exergy efficiency and total cost are considered as the objective functions. The recuperator effectiveness and exergy efficiency are maximized and the recuperator total cost is minimized, simultaneously. The results of each optimization are delineated by a set of designs using three dimensional Pareto-optimal fronts. Maximum cycle thermal and exergy efficiencies and NPV occur in the counter-flow recuperator employing offset strip fin and the values are found to be 39.1275%, 36.7431% and 3088164 $, respectively. A sensitivity analysis of variation in recuperator effectiveness and exergy efficiency and total cost with changes in design parameters of the plate-fin recuperators employing louver and offset strip fins with counter-flow arrangement is performed. Finally, all the optimal designs obtained from the Pareto diagrams are compared to determine the optimum designs using normalization method and non-dominated sorting concept. According to the comparisons, offset strip fin and louver fin with counter flow arrangement show better performance.

The paper investigates whether air-water heat exchanger with longitudinal fins along the air flow direction are an appropriate means to reduce pressure loss in mechanical ventilation systems, compared to conventional heating coils. To answer this question, theoretical calculations regarding pressure loss and heat transfer are performed and the results are checked by measurements. It is found that a longitudinal fin heat exchanger with 30 radially arranged fins and an overall length of 830 mm transfers the same heat flow as a conventional heating coil (∅ 125). The pressure loss only adds up to about 60% to 70%, so a reduction of 30% to 40% can be achieved. Additionally it is expected, that the longitudinal fin heat exchanger is more suitable for efficient low temperature heating systems, because of the counter-current heat transfer. The disadvantage of its increased length can be compensated by integrating the longitudinal fin heat exchanger in a duct silencer, which is required anyway. Hence, the energy efficiency of mechanical ventilation system can be increased.

An exploratory study is presented considering the effect of eight different binary mixtures that serve as working fluid for a transcritical Rankine cycle operating with or without recuperator – the binary mixtures considered are composed by CO2, a natural fluid, and a secondary fluid (i.e., R134a, R32, R152a, R41, R161, R1234ze(E), R1234yf, R1270). The secondary component selection was based on its environmental impact (i.e., GWP

In this research, a novel hybrid thermodynamic cycle with an asynchronous buffering heat recovery process is proposed to overcome the extremely difficult problem for micro swing engine, i.e. the far too low efficiency. Firstly, the 3-arm micro swing engine is presented, which is proven to hold a better performance than the original 2-arm one. Among the 3 chambers, two are isometric and operate in four-stroke cycle while the rest has a slightly larger volume and works in two-stroke cycle. Then, depending on the reasonable structural design, a novel asynchronous buffering recuperator suitable for the 3-arm structure was designed and the hybrid thermodynamic cycle with heat recovery process was introduced. That is, the gas in the four-stroke chambers recycle all the exhaust heat while the gas in two-stroke ones do not. In the recuperator, the cold flow is intermittent and the heat exchange process is asynchronous. But CFD simulations demonstrate that this buffering recuperation method is effective in settling the problems. Finally, the performance of the hybrid cycle was analyzed. The results indicate that the efficiency of the novel engine reached as high as 11.74%, which was increased by 40.77% in comparison with the one without a recuperator.

This paper involves an exhaust gas waste heat recovery system for vehicles, which uses thermoelectric modules and a heat exchanger to produce electric power. Based on summarizing the latest research of vehicle exhaust thermo-electric generator (TEG), it presents two new fin structures for the cylindrical heat exchanger in a TEG system. It mainly studies the thermal performance of two kinds of three-dimensional cylindrical heat exchanger models including spiral-fin heat exchanger with variable pitch in a computational fluid dynamics simulation environment. In terms of interface temperature and thermal uniformity and based on an evaluation method of the temperature uniformity for the heat exchangers, the thermal characteristics of heat exchangers with different pitch angle of the twisted fins, pitch of spiral fin, fin thickness and fin height are discussed. Two new fin structures are feasible to enhance the heat transfer performance of heat exchanger.