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A nanofluid is a solution of nanoparticles with diameters fewer than 100 nanometers suspended in a base fluid such as water, ethylene glycol, or oil. In the nanofluid, these nanoparticles are suspended. The goal of this research is to look at the functioning of a twin-pipe heat exchanger that uses counter flow arrangements and two different nanofluids as cooling fluids. Alkaline water is a basic fluid made up of silicon carbide (SiC) and carbon nanotubes (CNT). The goal of this research was to see how different compositions of SiC and CNT nanoparticles dispersed in water affected the heat transfer capacities of a twin pipe heat exchanger developed with a counterflow arrangement. The flow rate of the nanofluid and the particle volume concentration of alkaline water were (0.02) and (0.04), respectively. Fluids with constant intake temperatures of 60°C for water and 30°C for nanofluid flow at the same input velocity via a heat exchanger. Both fluids are traveling at the same rate. According to the findings, nanofluid absorbs more heat than water at a range of flow speeds. Because of the improved thermal properties of nanoscale fluids, this results in increased thermal efficiency in heat exchangers. [ABSTRACT FROM AUTHOR]

This paper presents a comparative analysis of a finned heat exchanger fed with synthetic refrigerant R410a and environmentally friendly refrigerant R290. Analyses of the performance of the heat exchanger operating as an evaporator in a refrigeration system were carried out. Simulation studies were performed using SOLIDWORKS software with the Flow Simulation library. The analysis was conducted for various design parameters of the device. The performance of the exchanger was examined for different fin materials (aluminium alloys: alloy 1060, 1060-H12, alloy 2014, alloy 2024), number of fins (78 and 39), and fin spacings (2.5 mm and 5 mm). The studies were conducted under various operational parameters of the exchanger (varying volume flow of air and refrigerant mass flow). Based on the results obtained, it was found that the material of the exchanger does not significantly affect its performance. The next conclusion is that when the heat exchanger is fed with an environmentally friendly refrigerant, the heat transfer surface area can be reduced by 50%. As a result, the reduction in heat transfer surface area can be achieved by increasing the fin spacing, which will reduce the electricity consumed in the defrost process under operating conditions, or by reducing the size of the exchanger, which will positively translate into a reduction in the weight of the refrigerant in the system. The possibility of reducing the dimensions of the heat exchanger by up to 50% indicates that replacing R410a refrigerant with environmentally friendly R290 is a promising direction for development. It advocates for ongoing investigations to refine these systems and maximize the operational advantages presented by natural refrigerants. [ABSTRACT FROM AUTHOR]

Thermal storage technology has received increasing attention under the policy of encouraging the development of renewable energy and new clean energy. Optimizing the heat exchange system of phase change thermal storage heat exchangers to obtain better performance has become increasingly urgent. This study comprehensively investigated the actual process of heat transfer and assessed the heat transfer correlation laws between the heat transfer fluids, heat exchange tubes, fins, and phase change materials. Taking the heat exchange efficiency of the heat exchanger as a guide, a simulation was conducted on the effect of the presence and quantity of fins as well as the flow rate of the cooling liquid on the heat exchange efficiency of the heat exchanger. The simulation results showed that too many or too few fins were not conducive to improving heat transfer efficiency. In addition, no positive correlation was observed between the flow rate of the cooling liquid in the heat exchanger and the heat transfer efficiency of the heat exchanger. Specifically, models with slightly slower cooling liquid flow rates had a higher heat transfer efficiency. After a sensitivity analysis, it was found that the number of fins had a more significant effect on the heat transfer efficiency of the heat exchanger than the flow rate of the cooling liquid. The heat exchanger with five fins and a cooling liquid flow rate of 0.1 m/s demonstrated the best heat transfer effect, achieving a temperature drop of 14.76% within 5 min. [ABSTRACT FROM AUTHOR]

The primary objective of this study is to conduct a practical investigation of heat transfer (HT) and friction factor (f) characteristics within a double pipe heat exchanger (DPHE) configured in a counter-flow arrangement. To achieve this, a novel approach involving twisted tape (TT) with dimple inserts accompanied by adjacent holes working fluid is water implemented. This dimples, characterized by their concave geometry, are strategically employed to augment the heat exchange process while concurrently mitigating any adverse impact on fluid pressure. A pivotal facet of this study centered on examining the influence of dimple diameter, as well as a consistent dimple-to-depth ratio (D/H), on both heat transfer efficiency and friction factor. The performance of TT inserts featuring diverse diameter (D) = 2, 4 and 6 mm is meticulously scrutinized in terms of their impact on heat transfer and friction factor characteristics. The outcomes of the study furnished intriguing insights. It is observed that the diameter of the dimples wielded a discernible encouragement on friction factor, revealing a direct correlation. The maximum rate of friction factor is recorded at a 2 mm dimple diameter configuration. When evaluating Nusselt number (Nu) and performance evaluation criteria (PEC), it is revealed that the most favorable results is achieved with the 4 mm dimple diameter configuration. Drawing upon these empirical findings, a significant conclusion can be drawn. Utilization of twisted tape inserts adorned at dimples is a practical, efficient and economically viable approach to heighten HT efficiency within heat exchangers. By optimizing dimple diameter and adhering to a consistent diameter-to-depth ratio, substantial improvements in HT capabilities can be harnessed without disproportionately compromising fluid pressure. This innovative methodology holds the potential to revolutionize heat exchanger design, offering an avenue to enhance HT efficiency with practical and cost-effective solutions. [ABSTRACT FROM AUTHOR]

The utilization of nanoentities in common fluids has opened new opportunities in the area of heat transportation. The rising requirements to enhance the efficiency of compact heat exchangers can be achieved by using various nanofluids. In this article, the thermal output of Maxwell and Williamson nanofluids transport over a prolonging sheet with bioconvection of self‐motivated organisms is scrutinized. A magnetic flux and the porous effects of a medium influence the flow of fluids. The fundamental principles for conservation of mass, concentration, momentum, and energy yield a nonlinear set of partial differential equations that can then be altered into ordinary differential form. A heat transfer flux is presented along with temperature boundary conditions, PST, and PHF (prescribed surface temperature and prescribed heat flux). The numerical results are acquired by executing the Runge–Kutta method with a shooting procedure in MATLAB coding. By fluctuating the inputs of influential variables of the dependent functions, a precise overview of the scheme is acquired. It can be seen that velocity decreases with the rising values of buoyancy ratio, magnetic force, Raleigh number, and porosity. Also, the temperature of the fluids begins to rise directly with the rising values of thermophoresis and Brownian motion parameters. The present study addresses bioconvection, non‐Fourier heat flow, and thermal radiations while combining the special properties of Williamson and Maxwell nanofluids. The field of biomedical engineering may benefit from this study, particularly with regard to therapies for hyperthermia and drug delivery systems. This study can be useful in cutting‐edge cooling systems, bioengineering, solar energy conversion and biotechnology. [ABSTRACT FROM AUTHOR]

A novel BHEs is proposed that can overcome the problems associated with the low heat-transfer efficiency of borehole heat exchangers (BHEs) that are connected in series (BHEs-S) and the low heat-transfer temperature differences of BHEs that are connected in parallel (BHEs-P). The new BHE uses a combined series and parallel connection (BHEs-CSP), which can further be classified into individual in-series and in-parallel zones. A numerical model of the new BHEs-CSP is then developed to optimize the key design parameters such as borehole spacing, number of series stages, and heat-extraction methods. The results show that, with the optimal configuration, the average soil temperature with a BHEs-CSP is 6.70°C higher than for a BHE that is connected in parallel. Furthermore, the heat-transfer efficiency can be improved by 4.1% compared to BHEs that are connected in series. It is recommended that the distance between buried pipes in the series area and parallel area should be 5.25 m, and the series number of buried pipe groups should be 4. To study the overall performance of the solar-assisted ground-source heat-pump with a BHEs-CSP (SAGSHP-CSP), a TRNSYS model is developed. The results show that the optimal area- and heat-storage-ratios (for in-series zone to inparallel zone), using SAGSHP-CSP, are 1:4 and 3:2, respectively. Under these conditions, the system coefficient of performance (SCOP) is over 5.2 and the COP and SCOP is improved by 9.8% and 13.0% compared to GSHP systems with BHEs-P. Furthermore, an improvement by 18.4% and 18.2%, compared to the GSHP system with BHEs-S, is reported. [ABSTRACT FROM AUTHOR]

The purpose of this research is to investigate in depth the effect of system geometry on the performance of coil-and-tube heat exchangers. This work investigates the use of direct evaporative cooling (DEC) to improve the efficiency of air conditioning systems in extremely hot weather. DEC systems must be sized and constructed properly for the particular building and climate in which they are going to be installed. The ultimate goal is to reduce energy usage while producing affordable, green cooling options for regions with exceptionally hot temperatures. For simulation, we used computational fluid dynamics with ANSYS software. We purposefully varied the quantity of nozzles and the number of turns in the cooling tubes to see how they affected the effectiveness of the system. The temperature and velocity plot findings revealed a substantial difference, demonstrating that these engineering elements had an impact on the heat exchange process. According to the results, setups with 35 nozzles and 13 nozzle turns had a maximum coefficient of performance of 4.537 at an entry velocity of 2 m/s, showing that this configuration is ideal in the investigated conditions. The findings emphasize the need for strategically modifying some engineering parameters to increase heat exchanger performance and offer exciting prospects for the design and optimization of such systems. More research is needed to better understand these complicated interactions, including the investigation of different fluids, channel diameters, pressure conditions, and performance in the transient state. [ABSTRACT FROM AUTHOR]

In the present study, using a combination of theoretical discussions, practical examples, and case studies, we sought to gain a comprehensive understanding of how numerical solutions could be used to improve the design and optimize the thermal efficiency of a heat exchanger that utilizes wastewater to reduce the domestic consumption of hot water. To this end, we developed a validated numerical model. We also carried out simulations and experiments, the results of which are presented in this paper. The novelty of this work derives from our use of a new heat exchanger design for a domestic shower, and from the presented experimental–numerical evidence that proves its efficiency. We found that use of our newly designed appliance improved thermal efficiency from 14% to 27%. Moreover, we estimated that the cost of manufacturing and installing such a device did not exceed that of a widely available drain grid. Using our newly designed exchanger, a family of four living in Poland could save EUR 38 (at 2022 values) and reduce CO2 emissions by 192 kg. An average European family could save EUR 68 and reduce CO2 emissions by 76 kg. [ABSTRACT FROM AUTHOR]

One way to increase the thermal efficiency of heat exchangers is to structure the heat transfer surfaces with dimples, resulting in an enlarged surface area and intensified turbulence in the fluid flow. The increased turbulence also causes higher wall shear stress, which potentially suppresses the deposition of particles and supports a self-cleaning of the surface. For a deeper understanding of these phenomena, the flow dynamics inside the dimple were observed experimentally with Stereoscopic Micro-Particle Image Velocimetry (Stereo µPIV). The formation of an unsteady oscillating vortex, which leads to an asymmetric trail downstream of the dimple, is visualized. The significant influence of the dimple geometry on heat transfer enhancement is shown, and the most beneficial geometric ratio of the spherical dimple regarding its ability to increase turbulence is identified. A comparison of the local flow velocities with the results of the numerically and experimentally observed patterns of the deposited particles caused by the dimple's self-cleaning effect shows a good match. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the heat flow in a plate heat exchanger located at a building heat exchange station. The plate heat exchanger is the main source of heat for the building system based on microsubstations in the building apartments. The co-operation of the heat exchange station with the substations in the apartments is also described. Such microstations are intended for both domestic hot water preparation and apartment heating. The method of calculating the product of the heat transfer coefficient k and the heat exchange surface area A is presented. In order to verify the correctness of the measured values of the temperatures of hot and cold water at the heat exchange station inlet and outlet, they were compared to the values calculated using the ε-NTU method. Good agreement was found between the results of the calculations and the measurements. Recommendations were made for the temperature of return water to the heating station. The cost of operating the district heating network could be reduced by increasing the surface area of central heating radiators in apartments, so that the temperature of return water to the heating station could be lowered. [ABSTRACT FROM AUTHOR]

Heat exchangers make it possible to utilize energy efficiently, reducing the cost of energy production or consumption. For example, they can be used to improve the efficiency of gas turbines. Improving the efficiency of a heat exchanger directly affects the efficiency of the device for which it is used. One of the most effective ways to intensify heat exchange in a heat exchanger without a significant increase in mass-dimensional characteristics and changes in the input parameters of the flows is the introduction of turbulators into the heat exchangers. This article investigates the increase in efficiency of heat exchanger apparatuses by introducing turbulent lattice structures manufactured with the use of additive technologies into their design. The study is carried out by numerical modeling of the heat transfer process for two sections of the heat exchanger: with and without the lattice structure inside. It was found that lattice structures intensify the heat exchange by creating vortex flow structures, as well as by increasing the heat exchange area. Thus, the ratio of convection in thermal conductivity increases to 3.03 times. Also in the article, a comparative analysis of the results obtained with the results of heat transfer intensification using classical flow turbulators is carried out. According to the results of the analysis, it was determined that the investigated turbulators are more effective than classical ones, however, the pressure losses in the investigated turbulators are much higher. [ABSTRACT FROM AUTHOR]

This paper studies the optimization design of capillary heat exchangers and their innovative engineering applications in buildings. The purpose of this study is to use a capillary heat exchanger as the front-end device of the heat pump in coastal areas to extract energy to facilitate the application of renewable energy in buildings. Firstly, in this paper, the main factors of capillary heat transfer efficiency were explored in areas near the coast. Secondly, for the sake of improve the heat transfer efficiency of the capillary heat exchanger, numerical calculations were carried out on the heat transfer of the capillary in the case of inconsistent operating patterns in the summer and winter months, respectively. The results showed that when the daily working time of the capillary heat exchanger was 8 hours, the temperature difference of the capillary inlet and outlet was 2.1 ℃. And the heat transfer rate was 87.1 W/m² . In summer, the temperature difference of the capillary inlet and outlet was 2.6 ℃. And the heat transfer rate was 107.8 W/m² . This article helps to promote innovative and sustainable technologies in coastland development, such as capillary heat exchangers and heat pumps, which could used in renewable energy extraction and building utilization in near coastal areas. [ABSTRACT FROM AUTHOR]

The heat transfer improvement and the increase of heat exchangers’ efficiency represent a very important issue in the energy field. Many research projects have focused on the use of fluids with high thermal conductivity such as nanofluids. In this case, hybrid nanofluids, are a new class of nanofluids with good heat transfer characteristics. The present work falls within this framework and involves a numerical study to examine the influence of two oil-based hybrid nanofluids, Al2O3-MWCNT and MgOMWCNT, with different volume concentrations and inlet flow rates. More to the point, the impact of different nanoparticle ratio and the location of hybrid nanofluid in a laminar flow of two-pipe counter-current heat exchanger have been investigated. In virtue of which, the results illustrate that increasing the volume concentration of nanoparticles and the flow rate of the hybrid nanofluid has a positive impact on improving the heat transfer rate. Therefore, the improvement in heat transfer rate reached 77.8% for Al2O3-MWCNT/oil hybrid nanofluid and 59.5% for MgO-MWCNT/oil hybrid nanofluid. Similarly, the study has also revealed that the preferred nanoparticles ratio for Al2O3-MWCNT/oil hybrid nanofluid is in the order of (25:75) and its circulation in the inner tube as a hot fluid makes it possible to improve the thermal performance of the considered two-tube heat exchanger to a greater advantage. [ABSTRACT FROM AUTHOR]

Preservation of perishable food produce is a major concern in the cold chain supply system. Development of an energy-efficient on-farm cold storage facility, hence, becomes essential. Integration of thermal storage into a vapor compression refrigeration (VCR)-driven cold room is a promising technology that can reduce power consumption and act as a thermal backup. However, designing a latent heat energy storage heat exchanger encounters challenges, such as low thermal conductivity of phase change materials (PCMs) and poor heat exchanger efficiencies, leading to ineffective charging–discharging cycles. The current study investigates the effect of the integration of a Phase Change Material (PCM) in terms of the selection of the PCM, the optimal positioning of the PCM heat exchanger, and the selection of heat exchanger encapsulation material. Numerical analysis was undertaken using 3D Experience software (version: 2024x.D31.R426rel.202403212040) by creating a 3D model of a 3.4 m3 micro-cold storage unit to understand the inner temperature distribution profile. Further, the experimental setup was developed, and tests were conducted, during which the energy consumption of 1.1 kWh was recorded for the total compressor run time of 1 h. Results indicated that an improved cooling effect was achieved by positioning the PCM trays on the wall opposite the evaporator. It is seen that a temperature difference in the range of 5 to 7 °C exists between the phase change temperature of PCM and the optimal storage temperature depending on the encapsulation material. Hence, PCM selection for thermal storage applications would have an important bearing on the material and configuration of the PCM encapsulation. [ABSTRACT FROM AUTHOR]

The heat exchanger is a core component of all thermal systems. Thus, high-efficiency heat exchangers that can save energy and material are required. Heat transfer improvement in heat exchangers by applying the newly designed fin configuration increases the heat exchanger efficiency. Moreover, the newly designed finned heat exchanger improved heat transfer, resulting in a significant reduction in the heat exchanger size. A compact countercurrent water–water heat exchanger with a high rate of heat transfer while using the least amount of space was achieved. The newly designed finned tube on the outer surface of the inner tube in this study increased the heat transfer characteristics of the double-pipe heat exchanger. An insulated Perspex shell with an inner diameter of 54 mm, 2000 mm in length, and 3 mm thick. Copper tubes with and without rectangular copper fins are studied and compared. The smooth copper tube was 2250 mm in length with 20 mm and 22 mm inner and outer diameters, respectively. The experimental results showed that the Nusselt number and effectiveness of the newly proposed finned tube increased by 95% and 127%, respectively, compared to those of the smooth tube at the same Reynolds number, while the heat transfer coefficient increased by 53% over a smooth tube. [ABSTRACT FROM AUTHOR]

The present study demonstrates the successful application of the grasshopper optimization algorithm (GOA) to the thermodynamic and economic modeling and optimization of cross-flow plate-fin heat exchangers with offset strip fins. To this end, the e - NTU method was played to determine the efficiency and pressure drop. Seven parameters, namely the exchanger length at hot and cold sides, number of hot-side layers, fin frequency, fin-strip length, fin thickness, and fin height, constitute the design parameters for the optimization of the heat exchanger. The efficiency of the heat exchanger, the entropy generation, and the total annual system cost were considered the objective functions. Accordingly, the optimization of each objective function was investigated separately. The efficiency and accuracy of the proposed algorithm were validated using two examples from the literature. Comparison between the obtained results and those in the previous studies indicates that GOA performed better in minimizing total annual cost and entropy generation and maximizing efficiency. [ABSTRACT FROM AUTHOR]

This paper proposes a solution to address the challenges of high storage and transport costs associated with using hydrogen ( H 2 ) as an energy source. It suggests utilizing ammonia ( N H 3 ) as a hydrogen carrier to produce H 2 onsite for hydrogen gas turbines. N H 3 offers higher volumetric hydrogen density compared to liquid H 2 , potentially reducing shipping costs by 40%. The process involves N H 3 pyrolysis, which utilizes the heat waste from exhaust gas generated by gas turbines to produce H 2 and nitrogen ( N 2 ). Numerical simulations were conducted to design and understand the behaviour of the heat recapture N H 3 decomposition system. The design considerations included the concept of the number of transfer units and heat exchanger efficiency, achieving a heat recapture system efficiency of up to 91%. The simulation of N H 3 decomposition was performed using ANSYS, a commercial simulation software, considering wall surface reactions, turbulent flow, and chemical reaction. Parameters such as activation energy and pre-exponential factor were provided by a study utilizing a nickel wire for N H 3 decomposition experiments. The conversion of N H 3 reached up to 94% via a nickel-based catalyst within a temperature range of 823 K to 923 K which is the exhaust gas temperature range. Various factors were considered to compare the efficiency of the system, including the mass flow of N H 3 , operating gauge pressure, mass flow of exhaust gas, among others. Result showed that pressure would not affect the conversion of N H 3 at temperatures above 800 K, thus a lower amount of energy is required for a compression purpose in this approach. The conversion is maintained at 94% to 97% when lower activation energy is applied via a ruthenium-based catalyst. Overall, this study showed the feasibility of utilizing convective heat transfer from exhaust gas in hydrogen production by N H 3 pyrolysis, and this will further enhance the development of N H 3 as the potential H 2 carrier for onsite production in hydrogen power generation. [ABSTRACT FROM AUTHOR]

This article addresses the design of a compact heat exchanger for the cooling of electronic systems. The Quality Function Deployment (QFD) method is used to identify crucial product features to improve device performance and key customer requirements. The QFD simplifies management processes, allowing modifications to device components, such as design parameters (dimensions and materials) and operating conditions (flow type and preferred temperature range). The study was applied to analyse the fundamental features of a compact heat exchanger, assessing their impact on enhancing heat transfer intensity during fluid flow through mini-channels. The thermal efficiency of the compact heat exchanger was tested experimentally. The results allow to verify the results obtained from the numerical simulations due to Simcenter STAR-CCM+. Consequently, the experimental part was reduced in favour of numerical simulations conducted using this commercial CFD software version 2020.2.1 Build 15.04.01. The numerical simulations performed with the aid of CFD showed increases in the heat transfer coefficient of up to 180% compared to the case treated as a reference. The application of the QFD matrix significantly reduces the time required to develop suitable design and material solutions and determine the operating parameters for the cooling of miniature electronic devices. [ABSTRACT FROM AUTHOR]

To demonstrate the rationalization of multi-longitudinal swirls in heat exchanger tubes, this paper investigates the thermohydraulic performance of heat exchanger tube with rectangular vortex generator using numerical simulation. Comparative analyses of rectangular vortex generators and their different slotted structures are conducted, along with the investigation of the effect of the longitudinal pitch (P = 0.1 m, 0.2 m and 0.3 m) of the rectangular vortex generators on the thermohydraulic performance. The research reveals that the multi-longitudinal swirls induced by the vortex generator inside the tube accelerate the exchange of cold and hot fluids, improve the field synergies of velocity vectors and temperature gradients, and enhance the heat transfer efficiency of the heat exchanger tube. The slotted structure reduces the flow resistance and lowers the degree of disturbance to the fluid, which reduces the strength of the multi-longitudinal swirls, thus weakening the overall performance of the heat exchanger. The strength of the multi-longitudinal swirls has a direct influence on the overall performance of the heat exchanger tube. With the increase of P, the performance evaluation criteria (PEC) of the heat exchanger tubes decreases, and the maximum PEC = 1.44 is obtained for P = 100 mm at the studied Reynolds number range. [ABSTRACT FROM AUTHOR]

The high energy consumption of water bath heaters in city gate stations due to heating the passing gas is always a significant concern. A suggested approach is to apply a shell and tube heat exchanger to raise efficiency or utilize heat losses. This study first examined the impact of the geometrical parameters of a heat exchanger, e.g., baffle cut, baffle number, tube pitch, and tube diameter, on heat transfer, pressure drop, and exchanger price as objective functions and estimated the optimal point of the exchanger's geometry based on the TOPSIS algorithm. Then, the feasibility of replacing a shell and tube exchanger with a water bath heater in city gate stations was probed. The shell and tube exchanger was simulated and analyzed by Ansys Fluent software. The results showed that increases in the baffle cut from 20 to 50%, tube pitch from 1.3 to 1.9, and tube diameter from 21.3 mm to 42.2 mm reduced heat transfer by 10, 3, and 7% and pressure drop by 9, 10 and 11%, respectively, while a surge in the number of baffles from 2 to 5 raised pressure drop and heat transfer by 14 and 12%, respectively. The outcomes associated with the economic analysis of replacing an exchanger revealed that this replacement decreased fuel consumption and led to reduced contamination, on the one hand, and cost conservation, on the other hand, such that the net present value index zeroed in less than 5 years. [ABSTRACT FROM AUTHOR]

High‐field magnets have been used in a wide range of scientific and industrial areas. REBCO (REBa2Cu3Ox, where RE = Rare Earth) coated superconductors (CCs) have been gaining increasing interest due to the potentialities of using them in high‐field magnets. However, the thermal stability of the REBCO CCs coils is limited by longitudinal heat conduction inside the coils and bubbles generated by evaporating helium. So as to enhance the heat transfer in REBCO coil, a cooling system based on GM/JT cycle was designed. In this paper, the design, thermodynamic calculation, and analysis of the cooling system for the REBCO coil are provided systematically. It is found that when the mass flow rate is 0.75 g/s at a pressure of 10 bar, the cooling capacity of the system is up to 10.16 W. Meanwhile, the inlet pressure and counterflow heat exchangers efficiency are key factors for significantly improving the cooling capacity of the system. An open loop experiment also has been carried out and the cooling capacity of 0.79 W at 4.5 K is obtained finally when He mass flow rate is 0.1 g/s. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

This research introduces an Artificial Intelligence (AI) based model designed to concurrently optimize energy supply management, biocide dosing, and maintenance scheduling for heat exchangers. This optimization considers energetic, technical, economic, and environmental considerations. The impact of biofilm on heat exchangers is assessed, revealing a 41% reduction in thermal efficiency and a 113% increase in flow frictional resistance of the fluid compared to the initial state. Consequently, the pump's power consumption, required to maintain hydraulic conditions, rises by 9%. The newly developed AI model detects the point at which the heat exchanger's performance begins to decline due to accumulating dirt, marking day 44 of experimentation as the threshold to commence the antifouling biocide dosing. Leveraging this AI model to monitor heat exchanger efficiency represents an innovative approach to optimizing antifouling biocide dosing and reduce the environmental impact stemming from industrial plants. [ABSTRACT FROM AUTHOR]

Nanofluids represent a novel category of advanced heat transfer fluids composed of nanoparticles within a size range of 1-20 nm dispersed in a base fluid such as water. Contemporary research predominantly focuses on incorporating nanoparticles like Al2O3 and ZnO into the water at a 0.1% volume fraction to create nanofluids. Recent investigations aim to optimize thermal performance by introducing nanoparticles into the base fluids and inducing turbulence through various macro-inserts. Key factors influencing heat exchanger efficiency enhancement include geometric parameters, thermal conductivity and volume fraction. This study endeavours to analyse the thermal and fluid flow characteristics of a proposed nanofluid, augmenting thermal transfer through computational simulations and experimental validation, achieving an error margin of 3%-5%. The impact of rectangular micro inserts, with dimensions of 4 cm in height and longitudinal spacings of 5 cm and 11.5 cm, on the heat transfer rate is examined to enhance fluid flow turbulence. Results indicate that among different geometric profiles, the insert with a spacing of 11.5 cm demonstrates superior performance, yielding higher heat transfer rates and Nusselt numbers. This research holds significant implications for various industries including thermal, power, aviation, space and automotive sectors, particularly in the utilization of concentric tube heat exchangers across diverse applications. By exploring novel geometrical and fluid domains within heat exchangers, this study unveils promising avenues for enhancing the heat transfer efficiency compared to conventional methods, highlighting the potential for further investigation into alternative materials and configurations for heat elimination enhancement. [ABSTRACT FROM AUTHOR]

To improve the efficiency of the heat exchanger tube, one smooth tube and four doubly enhanced tubes (EX1, EX2, EX3 and EX4) have been investigated for the pool boiling heat transfer experiments in this paper. The indicate that the pool boiling heat transfer coefficient of the doubly enhanced tubes increased visibly with the augmentation of heat flux through the bubble behavior. Heat transfer reinforcement effect of the doubly enhanced tubes are significantly better than that of the smooth tube. Additionally, pool boiling heat transfer coefficient can be further enhanced by raising the saturate temperature. Entropy generation minimization analysis demonstrates that the heat transfer characteristics of like T-shaped tubes (EX1 and EX2) are superior to that of low fin tubes (EX3 and EX4). Particularly, tube EX1 exhibits higher pool boiling heat transfer efficiency. It is observed that a reasonable fin pitch is more advantageous for improving heat transfer characteristics. The utilization of entropy generation minimization analysis provides theoretical support for the design and optimization of doubly enhanced tubes. [ABSTRACT FROM AUTHOR]

Hybrid nanofluids are emerging as an alternative to conventional heat transfer fluids and nanofluids for improving the thermal efficiency of heat exchanging devices synergistically due to their outstanding thermophysical properties associated because of the dispersion of different types of nanoparticles as compared to mono nanofluids. This will help in optimizing fluid characteristics in different flow regimes for several applications. However, enhancing the thermal energy efficiency of heat exchangers is challenging owing to the deprived stability of hybrid nanofluids at greater volume concentrations. This work concentrated on the synthesizing, thermophysical depiction, and thermal performance estimation of stable water-based Cu-graphene hybrid nanofluids using very low volume concentrations of Cu and graphene hybrid nanostructures. Cu-graphene hybrid nanofluid was successfully synthesized by dispersing the synthesized Cu and graphene nanostructures (keeping the Cu concentration constant at 0.04 vol % and varying the graphene concentration from 0.01 to 0.1 vol %) in water. Hybrid nanofluids display excellent stability against aggregation for up to 7 weeks, as proven by higher zeta potential values. Thermophysical characteristics of the prepared hybrid nanofluids were effectively measured. The thermal conductivity of Cu-graphene hybrid nanofluids shows exceptional enrichment (~ 35%) at minimal concentrations of hybrid nanostructures. Viscosity of the water-based hybrid nanofluids shows remarkable enhancement as compared to water and represents the increasing trend in viscosity of the base fluid with respect to the increase in concentration of hybrid nanostructures. The thermal and rheological properties of hybrid nanofluids are effectively validated with existing theoretical models. In addition, the specific heat and pumping power of Cu-graphene hybrid nanofluids with respect to the volume concentration of hybrid nanostructures are calculated using the existing theoretical equations. A figure of merit (FOM) analysis was conducted for the synthesized hybrid nanofluids to gauge thermal efficiency and evaluate the applicability of these hybrid nanofluids under laminar and turbulent flow conditions. [ABSTRACT FROM AUTHOR]

Purpose: Addition of fins on tube surface enhances thermal efficiency of the heat exchanger by providing more heat transfer area. However, the effect on vibrations response of the tube due to fins has been little understood and requires further research. To further extend the understanding, the current study is designed to analyze the flow-induced vibrations response of finned tube bundle in cross flow with various effective pitch ratios and tube-to-tube vibration interaction. This study helps to improve the structural design of industrial finned heat exchangers. Method: In current paper, the flow-induced vibrations response of spiral finned tubes has been investigated through experimentation in parallel triangular tube bundles with different effective pitch ratios of 1.37, 1.60 and 1.83. Experiments were designed to perform in depth study of the coupling between finned tubes and its relationship with fluidelastic instability. The vibration responses of the monitored finned tube have been captured using the tri-axial wireless accelerometer. The free stream velocity varies from 0 to 10 m/s and the associated Reynolds number ranges from 0 to 9300. Results: The analysis shows that the behavior of the finned tube is more complex than bare tube results. It has been observed that amplitude response of monitored finned tube is strongly influenced by effective pitch ratios as well as surrounding tube locations. The fluidelastic instability occurs strongly in finned tube bundles with low effective pitch ratios mainly due to stiffness mechanism. The different surrounding flexible finned tube locations in the tube bundle seems to be critical in triggering instability in monitored finned tube. Conclusion: The surrounding tube locations T2, T5 and T6 have major contribution in triggering the fluidelastic instability in these tube bundles. Moreover, this behavior is more significant in small effective pitch ratio (1.37). [ABSTRACT FROM AUTHOR]

Autostrainer is used for the purpose of debris removal in order to increase the efficiency of the heat exchanger by taking the required raw water as a heat source for the pre-cooling hydrothermal system. During the operation of the autostrainer, a pressure drop occurs due to the blockage of the screen in the autostrainer. As a result, the resistance of the pipe network for the intake system is changed, and the operating efficiency point of the pump, valve, heat exchanger, etc., is altered. By calculating the system resistance taking into account the pressure drop caused by the blockage rate of the screen in the autostrainer, the optimum operating efficiency can be expected when the intake system such as a pump, valve or heat exchanger, etc. is constructed. In this study, Computational Fluid Dynamics (CFD) was used to construct a scenario in which screen blockage may occur, predicting pressure drop for the slot cross-section of the screen in the autostrainer to derive a resistance coefficient value. The resistance coefficient value was applied to the porous region corresponding to the screen in the autostrainer's 3D shape and compared with the experimental value for the pressure drop and headloss coefficient. By predicting the pressure drop for the autostrainer's screen blockage rate of 0% to 50%, the coefficient of headloss required for the design of the intake system was calculated. Additionally, in order to predict the debris removal rate, which is the original role of the autostrainer, the debris was assumed to be particles, and sedimentation rate was predicted according to the size and weight of the particles. Building on this, when introducing the autostrainer used in pre-cooling into the membrane filtration process, due to the pressure loss caused by the inflow of debris during the use of the autostrainer, this study aims to utilize Computational Fluid Dynamics (CFD) to derive the head loss coefficients according to the screen blockage rate, and use these coefficients to calculate the system's resistance curve. Additionally, in this study, the term "autostrainer" is used instead of the term "membrane strainer" to align with more popular terminology. [ABSTRACT FROM AUTHOR]

Researchers and engineers are actively working on enhancing the efficiency of heat exchangers in engineering applications by developing novel designs, exploring new materials, and utilizing nanofluids. Three kinds of nanofluids with varying concentrations are investigated in this paper. The objective is to assess the performance of N‐shaped double‐pipe heat exchanger used in thermoelectric power plants. The performance has been evaluated using COMSOL Multiphysics software. The findings show that higher nanofluid concentrations resulted in elevated heat transfer coefficients and improved efficiency of N‐shape double pipe heat exchanger. The analysis revealed that a mere 1% rise in the volume fraction of nanofluids enhanced the efficiency of the heat exchanger on average 23% when compared to the base fluid (water). In comparison to the N‐shape double pipe (Inconel 625) heat exchangers, the N‐shape double pipe (copper) heat exchangers appear to be more efficient. The introduction of nanoparticles has a notable impact on the heat transfer coefficients. Specifically, within an N‐shaped double pipe (copper) heat exchanger, the inclusion of a 1% volume fraction results in a 2.09% enhancement in the heat transfer coefficient for Al2O3/water, a 1.3% improvement for Fe3O4/water, and a 1.15% increase for TiO2/water. It also exposed that adding 1% Al2O3/water led to a significant 0.623% increase in effectiveness, while TiO2/water showed a 0.259% rise, and Fe3O4/water exhibited a 0.375% improvement. Moreover, increasing the Reynolds number enhances the Nusselt number for Al2O3/water and Fe3O4/water nanofluids by 55.22%, and for TiO2/water by 54.60% at a 6% volume concentration, leading to additional increases in exchanger efficiency. Therefore, the augmentation in nanofluid concentration leads to a reduction in the temperature pinch points both at the intake and outflow. This observation suggests that nanofluids exhibit a superior ability compared to conventional fluids when it comes to effectively lowering temperatures. [ABSTRACT FROM AUTHOR]

To achieve carbon neutrality and address global energy supply issues by 2050, there is active progress in the industrial sector for waste energy recovery and commercialization projects. It is necessary to consider both the energy recovery efficiency and economic feasibility based on the production volume for the resource utilization of waste energy, along with eco-friendly processing methods. In this study, a waste heat recovery system was designed to recover a large amount of thermal energy from high-temperature exhaust gases of gas engines for power generation by using biogas produced from organic waste in industrial complexes. Types and sizes of components for a waste heat recovery system that were suitable for various engine sizes depending on biogas production were designed, and the energy recovery efficiency was analyzed. The waste heat recovery system consisted of a smoke tube boiler that generated superheated steam at 161 °C under 490 kPa of pressure from the exhaust gas as the heat source, along with two economizers for heating both supply water and hot water. Heat exchangers that were suitable for three different engine sizes were configured, and their performance and energy flow were calculated. In particular, when operating two engines with a power output of 100 kW, the boiler showed the highest steam production efficiency, and the superheated steam production from high-temperature exhaust gas at 600 °C was designed to be 191 kg/h, while hot water at 58 °C was designed to be produced at 1000 kg/h. In addition, further research on the heat exchanger capacity ratio confirmed that it was within a certain range despite the difference in heat exchanger capacity and efficiency depending on the engine size. It was confirmed that the heat exchange capacity ratio of the boiler was important as an optimal-capacity design value for the entire system, as it ranged from 46% to 47% of the total heat exchanger size. [ABSTRACT FROM AUTHOR]

Absorption cooling technology is an environmentally friendly method to generate continuous chilled water making use of multiple thermal sources, such as waste heat and renewable thermal energy. In this study, two absorption chillers (nominal capacity of 400 kW) with series and parallel connections are evaluated. To research the ideal configuration of chillers after thermodynamic analysis, the structures of the chillers are optimized using the particle swarm optimization algorithm by considering the heat transfer area (HTA), exergy efficiency and total annual cost as single-objective functions. The impact of temperature differences between external and internal flows, heat exchanger efficiencies and the solution allocation ratio is estimated. The optimized HTA, coefficient of performance, exergy efficiency and total annual cost are 149.0 m2, 1.56, 29.44% and $229 119 for the series-connected chiller, and 146.7 m2, 1.59, 31.45% and $234 562 for the parallel-connected type, respectively. Under the lowest HTA condition, compared with the reference simulation results, the energy and exergy performances are improved, while the annual total cost is higher. The annual total cost is highest when maximizing the exergy efficiency, which is attributed to the increase in the HTA. The operating cost accounts for 27.42% (series type) and 26.54% (parallel type) when the annual cost is the lowest. [ABSTRACT FROM AUTHOR]

The present paper presents a numerical investigation of heat transfer in an exchanger fitted with a modified conical-shaped turbulator containing water/Fe2O3 nanofluid. The study aims to address the critical need for improved heat exchanger efficiency, a vital component in various industries, including the chemical, power generation, and food industries. The work focuses on achieving enhanced heat transfer performance within a smaller volume, a primary goal of modern technology and industrial processes. The innovation in this study lies in the design and analysis of a novel conical turbulator, which has not been explored extensively in the context of heat exchangers fitted with nanofluids. Unlike traditional methods, which often rely on active or semi-active means to enhance heat transfer, this research introduces a passive approach through the incorporation of turbulators. Specifically, the study investigates the use of perforated cone-shaped turbulators in conjunction with nanofluids to boost heat transfer performance. The research employs state-of-the-art computational fluid dynamics (CFD) models, allowing for a comprehensive evaluation of the turbulator's performance across a wide range of Reynolds numbers (Re = 4000–20,000). It further examines the influence of various turbulator parameters, nanoparticle content, and geometry on heat transfer efficiency. Key findings indicate that the modified turbulator exhibits exceptional performance, increasing Nusselt numbers by 3.4–5.4 times and friction coefficients by 2.3–1.8 times compared to smooth pipes. Particularly noteworthy is the 92 % increase in the Nusselt number achieved with a mere 2 % increase in the Fe2O3 nanoparticle content. The present study introduces a novel passive heat transfer enhancement method using perforated cone-shaped turbulators and nanofluids, filling a significant gap in existing research. The innovative turbulator design and its substantial performance improvements offer promising prospects for achieving higher heat exchanger efficiency, making it a valuable contribution to thermal systems and heat transfer engineering. [ABSTRACT FROM AUTHOR]

This paper studies how the correlation with the Nusselt number affects the final result of the efficiency, ε, and exergy efficiency, ηex, of a chevron-type gasketed plate heat exchanger, which is installed in a typical small solar installation dedicated to single-family housing; the solar fluid is a TiO2:SiO2/EG:DI hybrid nanofluid with concentrations from 0% to 1.5% vol. The experimental model assumes constant flow of the solar fluid and varies on the domestic hot water side—from 3 lpm to 6 lpm. The inlet temperatures are 30 °C and 60 °C on the cold and hot sides of the heat exchanger, respectively. Of the six analysed correlations that showed similar trends, it is concluded that for the assumed flow conditions, geometry, and chevron angle of the plate heat exchanger, one model is the most accurate. The largest difference between the ηex values for a given concentration is 3.4%, so the exergy efficiency is not affected by the chosen Nusselt model by very much. However, the choice of correlation with the Nusselt number significantly affects the efficiency, ε; the difference between the values obtained within a given concentration is more than 40% and depends on the Reynolds number and flow. Most research discusses the scenario with the nanofluid as a coolant. This paper considers the opposite situation in which the solar fluid is a hotter working medium that transfers heat to domestic hot water installation. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study on the application and optimization of automotive thermoelectric generators (ATEGs), focusing on the crucial role of heat exchangers in enhancing energy conversion efficiency. Recognizing the substantial waste of thermal energy in internal combustion engines, our research delves into the potential of TEGs to convert engine waste heat into electrical energy, thereby improving fuel efficiency and reducing environmental impact. We meticulously analyze various heat exchanger designs, assessing their influence on the TEG's output power under different exhaust gas flow rates and temperatures. Furthermore, we explore the impact of TEG material properties on the overall energy conversion effectiveness. Our findings reveal that specific heat exchanger designs significantly enhance the efficiency of waste gas heat exchange, leading to an improved performance of the TEG system. We also highlight the importance of thermal insulation in maximizing TEG output. This study not only contributes to the ongoing efforts to develop more sustainable and efficient vehicles but also provides valuable insights into the practical application of thermoelectric technology in automotive engineering. Through this research, we aim to pave the way for more environmentally friendly transportation solutions, aligning with global efforts to reduce fossil fuel dependence and mitigate environmental pollution. [ABSTRACT FROM AUTHOR]

In this study, we aim to investigate the heat transfer and flow characteristics of diverse hybrid nanofluids (CuO-ZnO-Water, EG-Water, CuO-EG-Water, SiO2-EG-Water, and Al2O3-EG-Water) as coolants across eight discrete inlet velocities in a shell and tube heat exchanger. Various materials (copper, stainless steel, titanium, and carbon steel) have been employed for the tubing to optimize system performance. The impact of Reynolds number concerning hybrid nanofluids on Nusselt number and friction factor was assessed in this research. The results of the numerical simulations are found to agree well with experimental results within an average deviation of 1.8%. The results indicated the superior heat transfer capabilities of the hybrid nanofluid compared to the base fluid across all conditions. The outcomes revealed the superior heat transfer capabilities of the CuO-ZnO-Water hybrid nanofluid under all tested conditions. When employing CuO-ZnO-Water as a coolant, a substantial increase of over 9% in temperature reduction was observed, as opposed to the approximately 6% attained by other hybrid nanofluids at a lower velocity of 0.5 m/s. Notably, higher Reynolds numbers corresponded to increased Nusselt numbers and decreased friction factors. The decline percentage of the friction factor was 43% at Reynolds number ranging between 10,000 to 40,000. We emphasize the imperative need to optimize nanoparticle types for crafting hybrid nanofluids to enhance the performance of industrial heat exchangers and their coolant efficiency. Ultimately, the utilization of hybrid nanofluids in conjunction with shell and tube heat exchanger systems has yielded a notable enhancement in the overall thermal efficiency of these systems. [ABSTRACT FROM AUTHOR]

ORC cycle is one of the most efficient technologies for the utilization of low-grade heat. ORC systems cover a wide range of heat sources and power outputs. Apart from increasing the overall efficiency, CHP systems contribute to the decentralization of energy production, the conservation of primary fuel, the reduction of the emission of greenhouse gasses and the reduction of the cost to the final consumer. This justifies the research activity around CHP-ORC systems. In the present paper, a steady-state thermodynamic model for a 50 kWel biomass microCHP-ORC was developed and four candidate fluids were selected: R124, isobutane, R245fa and isopentane. The multi-objective optimization under supercritical conditions was performed using the genetic algorithm. The thermal efficiency, the exergy efficiency and the total heat exchanger surface were selected as single objectives. The evaporation temperature and pressure and the pinch point temperature differences at the heat exchangers were selected as decision variables. Careful examination of the optimal results revealed a systematic tendency for high evaporation temperatures and pressures and low recuperator pinch point temperature differences. Recuperation was found beneficial in many aspects, especially at higher evaporation temperatures. Also, the use of cogeneration leads to overall system efficiencies that surpass 90%, while simultaneously saving at least 20% fuel. Lastly, isopentane was found to be the best-performing fluid. [ABSTRACT FROM AUTHOR]

Numerical analysis has been performed to evaluate the heat transfer characteristics and performance of a circular pipe with geometrical dimple patterns. Using computational fluid dynamics (CFD) codes, we examine the effects of geometrical configurations on the flow and thermal behavior of circular pipes with concavity (dimple) diameters. Fluid mixing and flow perturbation are facilitated by perforations across the pipe core and wall regions, thereby improving thermal efficiency. In addition, a concavity with a diameter of 4 mm enhances heat transfer. Based on the results of the study, the disrupted pipe wall and pipe core region produce swirls and transverse vortices in the flow that provide superior heat transfer compared to conventional (smooth) pipes. In an increasing Reynolds number (Re), mixing, secondary, and separation flows become larger. Performance evaluation factor (PEF) values increased at low Reynolds numbers when dimple diameter was 1mm. As a result of these improved pipes, heat exchanger efficiency may improve in industrial applications, a key factor for energy conservation. [ABSTRACT FROM AUTHOR]

In view of the current global energy situation, increasing the efficiency of heat exchangers can contribute significantly to reducing energy consumption and greenhouse gas emissions. In this study, the effects of nanofluids (SiO2/Water) prepared at different fluid flow rates and different volumetric concentrations (vol.%0.1-0.2-0.3) on three heat exchangers (Shell and Tube, Double Pipe, Plate) with the same capacity were investigated experimentally and statistically. It was concluded that there was an increase of 47% in effectiveness and 87.3% in NTU value with the increase in the volumetric concentrations of nanofluids and fluid flow rate. With the use of nanofluids, it was observed that entropy production decreased by up to 56.08%. The results obtained were analyzed using Response Surface Methodology (RSM) and mathematical models were created and the prediction capabilities of the models were 98% and above. Entropy minimization was performed using statistical methods and it was statistically determined that plate heat exchangers give better results among heat exchangers with the same capacity. It is concluded that the entropy production is minimum when the fluid flow rate is 2 lpm, the volumetric concentration is 0.3% and a plate heat exchanger is used. This study has provided a different and comprehensive perspective on heat exchangers, and it is thought that it will give many ideas to researchers working in this field. [ABSTRACT FROM AUTHOR]

Heat exchangers enable processing plants to maintain maximum performance over time when handling variable process conditions. The most frequent heat exchanger issues, however, can occasionally be far more challenging to fix, resulting in high capital expenses and rising running costs. Consequently, there is a crucial need to redesign the current heat exchanger for improved performance. In this work, a shell and tube-type heat exchanger is designed with the help of CREO 8.0 parametric software. Transient thermal analysis is done to the designed model using ANSYS 2022 R2 software to investigate different shell and tube heat exchanger materials and assess the heat exchanger for its efficiency and temperature gradient. These results can be used to design appropriate heat exchangers in stationary energy systems, including power plants and fuel cell systems. [ABSTRACT FROM AUTHOR]

Improvements in heat exchanger thermal efficiency are crucial for achieving energy use and cost reductions. The use of nanofluids and the rotation of the exchanger inner tube may enhance heat transfer and exchanger efficiency. In this work, after having performed experiments on such a heat exchanger, a three dimensional numerical model was developed to simulate the transitional forced convection flow of a horizontal double-tube heat exchanger, with the aim of obtaining insight into the effects of the inner tube rotation, fluid flow rate and type of nanofluid employed. It was found that an increase in the nanoparticle concentration up to 3% increased the exchanger efficiency. Al2O3, Al2O3-Cu and Cu-water nanofluids were studied, with the Cu-water being the fluid with the best performance (19.33% improvement). Heat transfer was enhanced with inner tube rotation up to 500 rpm (41.2%). Nevertheless, pressure drop and friction values were increased due to both phenomena, leading to higher pumping power values for the operation of the heat exchanger. Hence, a balance between the performance and pumping power increase must be considered when modifications are made on a heat exchanger. The development of the numerical model might help in further optimizing, redesigning and scaling up heat exchangers. [ABSTRACT FROM AUTHOR]

Spiral heat exchangers are designed to meet the most difficult heat transfer challenges. Whether it's frequent dirt removal or limitations related to pressure drop and installation space, they are the ideal solution to problems for liquid-liquid and two-phase loads. Robust, efficient and compact models keep installation and maintenance costs extremely low. Compared to other heat exchangers commonly used in similar applications, spiral designs offer a compact footprint and increased thermal efficiency. Built with unique features that prevent fouling, they can handle the toughest heat transfer challenges while ensuring the most reliable performance. They work consistently, with extremely low installation and maintenance costs. [ABSTRACT FROM AUTHOR]

Here, to resolve the open problem of the second-law efficiency evaluation for heat exchangers, an efficiency-effectiveness method is developed from pure convection theory, where the entropy transfer efficiency defined as the outlet temperature ratio of cold and hot fluids exchanging entropy and local entropy generation number can measure the global and local irreversibilities of heat transfer. The efficiency and effectiveness are related by the inlet temperature ratio τ and capacity rate ratio φ , and their maxima subject to the local entropy generation number are determined for different flow arrangements. When τ = φ 2, the effectiveness maxima are 0.5/(1 + φ) and 1/(1 + φ) while the highest efficiencies are φ and unity for parallelflow and counterflow arrangements, respectively. The optimum operating points of counterflow exchangers, at which the equal outlet temperature τ T 1 ∞ (T 1∞ represents the hot inlet temperature) of two fluids with a critical capacity rate ratio τ induces uniform irreversibility, the effectiveness limit of 1 / (1 + τ) , and the efficiency limit of unity, are obtained. A linear temperature difference method is also developed based on the redefined convective and overall heat transfer coefficients, invariably yielding an effectiveness equal to the number of heat transfer units. This method has potentials to be extended to wet heat exchangers with phase-change flows. • The open question of second-law efficiency evaluation of a heat exchanger is resolved. • The heat transfer effectiveness and entropy transfer efficiency limits are presented. • The global and local irreversibilities of exchangers are measured by N S and N S,l. • Two optimum design criteria of exchangers are obtained subject to N S,l. [ABSTRACT FROM AUTHOR]

• Chemical equilibrium was introduced and a novel two-stage in-cylinder steam thermodynamic model was proposed. • A theoretical thermodynamic model considering in-cylinder steam assist and exhaust gases waste heat recovery was established. • The effects of the different working fluids on the in-cylinder steam assist cycle were revealed. • The effects of in-cylinder steam assist on thermal efficiency optimization under different working fluids were evaluated. Improving efficiency and reducing emissions are essential to achieving carbon peaking and carbon neutrality in transportation sector. As a carbon neutral fuel, hydrogen is widely considered the most promising fuel for future zero-carbon internal combustion power, while iso -octane, represented by gasoline, symbolizes the current hydrocarbon fuel utilized in modern internal combustion engines. In this study, the maximum indicated thermal efficiency of both hydrogen and iso -octane utilizing air (blending O 2 and N 2), oxy-fuel (blending O 2 and CO 2) and argon power cycle (blending O 2 and Ar) were investigated theoretically based on in-cylinder steam assist cycle. A theoretical thermodynamic model combining in-cylinder steam assist and exhaust gases waste heat recovery was established to explore the thermodynamic process of in-cylinder steam assist and systematically analyze the effects of different working fluids. Results show that the utilization of in-cylinder steam assist improves thermal efficiency under O 2 , N 2, and CO 2 working fluids, but limits the improvement of thermal efficiency under Ar. In addition, the maximum achievable steam temperature and mass are limited by the exhaust gases temperature and heat exchanger efficiency. When running with H 2 under 400 K steam temperature, the optimized water-to-gas ratios were 1.58, 1.13, 1.62, and 1.13 for O 2 , Ar, N 2 , and CO 2 , respectively, the maximum thermal efficiencies increased by 35.80 %, 0.28 %, 28.21 %, and 62.79 % compared with baseline condition. Meanwhile, the competition of overall specific heat ratio and working fluid mass under different working fluids leads to different thermal efficiency enhancement, such as Ar, the decrement of overall specific heat ratio under limited steam mass leads to thermal efficiency deterioration, which can be further improved as steam mass increased. [ABSTRACT FROM AUTHOR]

To address the issue of low efficiency in cooling heat exchangers at the deeper ends of mine fans, we propose a micro-unit approach for arranging the cooling water flow path within the heat exchanger. This method involves subdividing the heat exchanger into micro heat transfer units and determining the heat transfer characteristics of each individual unit through theoretical calculations and software simulations. Utilizing a computer program, these micro units are systematically arranged and combined to exhaust all possible cooling water flow paths. The ultimate objective is to derive the optimal structural arrangement of the cooling water flow path within the heat exchanger, with the goal of achieving the most efficient heat transfer effect. The findings reveal that the optimized structure, obtained through the micro-unit optimization method, achieves an average air outlet temperature of 311.65 K. This temperature is lower than that of the typical current-flow structure (311.88 K) and the typical counter-flow structure (311.68 K), indicating a superior heat transfer effect. Further examination demonstrates that the average air outlet temperature across all counter-flow structures is 311.68 K, which is notably lower than the average air outlet temperature of 311.90 K observed in the current-flow structure. This highlights the enhanced heat transfer effectiveness of the counter-flow structure. This novel method for optimizing the heat exchanger flow path applies the concept of finite element analysis to the optimization process, reducing computational and experimental costs. This approach is significant for improving the efficiency of heat exchangers. [ABSTRACT FROM AUTHOR]

The present research utilizes an inverse 3D CFD technique, coupled with the least squares approach and laboratory temperature readings, to predict the suitable turbulence flow model and unknown heat transfer rates within a cubic hot box. This enclosure features four cylindrical horizontal tubes arranged in a diamond configuration, functioning as heaters to generate heat within the space. Furthermore, the heat dissipation from each tube, flow field and temperature contours are also established. The energy equation for tubes and the governing equations for air are solved by coupling. The present estimates are obtained assuming a constant heat transfer rate. The range of the Rayleigh number is from 60,294 to 76,824. Testing various turbulence models revealed that the zero-equation turbulence model reduces the root mean square discrepancy between the simulated thermal behavior and laboratory outcomes compared to other methodologies. To verify the chosen flow model’s accuracy, the Nusselt numbers and flow field distributions aress compared with existing correlations and interferometer photographs. The maximum errors between the estimates of heat loss and heat transfer rate and the corresponding values from previous studies are 44 and 28% for St = 0.036, 34 and 3% for St = 0.045, and 37 and 18% for St = 0.054. To assess the impact of tube surface and spacing on the flow field model, calculation results are compared with those from four square-arranged tubes, revealing a lack of existing studies on this specific investigation. [ABSTRACT FROM AUTHOR]

• First and second law analyses of newly oval-CGHEs are introduced. • Oval CGHEs exhibit superior heat transfer with a trading-off in irreversibility. • The irreversibility distribution pinpoints the irreversibility of the studied CGHEs. • The results show reduced irreversibility at the oval-CGHEs sidewalls. • Sensitivity analysis highlights key factors influencing the CGHE's irreversibility. Optimizing the heat transfer and thermodynamic efficiency of Ground Heat Exchangers (GHE) is crucial for maximizing the energy efficiency of Ground-coupled Heat Pump (GCHP) systems utilized in building heating and cooling applications. This study pioneers an effective approach of both the first and second laws of thermodynamics of the newly oval-shaped coaxial GHEs (oval-CGHEs), assessing heat transfer, thermohydraulic performance, and local entropy generation rate to explore the optimum design and operational conditions for heat exchange maximization and entropy generation minimization. Utilizing a three-dimensional numerical model validated by experimental results, this study examines the trade-offs between heat transfer improvements and entropy generation rate intensification of the oval-CGHEs in comparison to the typical circular-shaped CGHE (circle-CGHE) further than exploring the effect of key operational and design parameters and performing sensitivity analysis. The results reveal that oval-CGHEs exhibit higher irreversibility as a penalty for their superior heat transfer capabilities compared to traditional circular-shaped CGHEs (circle-CGHE), which can be mitigated by optimizing the position of the inner tube. Moreover, the study underscores the criticality of maintaining a balance between enhanced heat transfer and the associated rise in irreversibility, particularly concerning the factors of mass flow rates and installation depths. [ABSTRACT FROM AUTHOR]

This study examines the turbulent heat transfer characteristics of Al2O3–Cu hybrid nanofluids in circular ducts with triangular rib configurations. Numerical simulations were conducted for a 25 cm long, -cm high duct with walls maintained at 313 K. Hybrid nanofluids enter at 298 K, with triangular ribs on the internal surface at three attack angles (45°, 60°, and 90°) spaced 20 mm apart. Al2O3–Cu/H2O hybrid nanofluids at concentrations of 0.1–2 vol.% were investigated for Reynolds numbers between 20,000 and 60,000. The study aimed to determine the optimal rib configuration and nanofluid concentration for enhancing heat transfer while minimizing friction losses. Key findings include: (1) the 60° rib configuration produced the highest local heat transfer coefficient, with the maximum occurring at the rib centers. (2) Increasing nanofluid concentration and Reynolds number enhanced heat transfer but reduced skin friction. (3) The optimal performance was achieved with 2 vol.% Al2O3–Cu at Re = 60,000. (4) Velocity contours revealed larger recirculation zones for 60° ribs compared to 45° and 90° configurations. (5) Turbulent kinetic energy was highest for 60° ribs, contributing to enhanced thermal performance. These findings have implications for improving the efficiency of heat exchangers, cooling systems, and other thermal management applications. [ABSTRACT FROM AUTHOR]