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The Finite-Element Method (FEM) is mainly used to design Compact Heat Exchanger structures. However, the narrow channel structures require fine mesh to accurately compute stress and strain. Combined with the dimensions of the overall component, this leads to an excessively large numerical model and therefore long computing time. This is especially true for transient thermal analyses, which require taking into account the full geometry. It is therefore interesting to reduce the size of the mesh. Periodic homogenization is an efficient method for achieving this goal. It can be applied to the core of the structure when periodic patterns (identified on basis of the arrangement of the channels) exist. A method based on this technique, with some improvements, is proposed in this paper for thermal loading without internal pressure. In addition to the Equivalent Homogenous Medium (EHM) replacing the periodic patterns, some explicit channels are interposed between the EHM and the cover plates. This has two advantages. The first is to smooth the transition of stiffness between the cover plates and the homogenized medium. The second one is to be able to directly compute stress and strain on the most critical channels located in this area. This paper assesses the method's effectiveness for thermal loadings in order to conduct thermal stress analyses. First, the equivalent elastic constants of the EHM are obtained with a numerical Finite Elements Method. Then, two 2D cases using EHM are compared against a 2D explicit model (i.e. explicit geometry for the core channels). These cases are chosen to validate the EHM itself and its effectiveness for a real section of the heat exchanger. Results show very good agreement with a relative difference lower than 1%. In addition, the sensitivity to the number of layers added between the EHM and the cover plates is analysed. It is recommended interposing at least two layers of patterns to obtain converged results for the considered configuration. Finally, a triangular mesh is considered to reduce the size of the model. No difference with a regular quadrangular mesh can be observed whereas the computing time is reduced. This method can be used to perform the design of any CHE under thermal loading as long as the channel arrangement shows periodicity. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of changing the bending radius of pipes on the maldistribution of velocity and turbulence of thermal fluid when flowing through a u-shaped tube bundle used in compact heat exchangers, among other applications. The study included three bending radii corresponding to successive rows of the actual tube bundle of a compact heat exchanger. Both liquid flow velocities recommended for compact heat exchangers and velocities elevated from the recommended ones were adopted. The results of the study were obtained by Computational Fluid Dynamics (CFD) and the performed experiment using the Particle Image Velocimetry (PIV) method. The limits of maldistribution were indicated by parameterizing this phenomenon with related geometric and flow values (turbulent flow intensity factor, flow velocity, pipe diameter, and bending radius). An increase in flow velocity above the recommended values did not result in a significant increase in turbulent flow intensity factor for u-tubes with large d/rg values. The shortest distance at which the return to steady-state flow conditions in a straight section of pipe downstream of an elbow took place was determined. This distance was 17d for geometry rg = 0.009 m, with velocity vp = 1.44 m/s. The localization of the areas of highest and lowest fluid velocity in the elbow element of the u-tube for extreme values of rg was opposite. This fact has an exploitable significance (non-uniform erosive effect of thermal fluid on pipes in different rows). [ABSTRACT FROM AUTHOR]

In this paper, a compact and efficient single-phase liquid cooling system is developed for the microelectronic devices with high-power dissipation, such as the high performance servers, power amplifiers, and airborne systems. The developed system includes three major components: 1) a silicon-based hybrid microcooler; 2) a customized compact liquid-to-liquid heat exchanger; and 3) a commercial micropump. Our focus in this paper is on the efficiency improvement for the full cooling system, which includes the development of the silicon-based hybrid microcooler, and the optimization of the miniaturized heat exchanger with low pressure drop, small footprint area, and high heat exchange efficiency. The following accomplishments have been obtained through this paper. The developed microcooler combines the merits of both microjet array impingement and microchannel flow cooling technologies. The optimized heat exchanger is with about 50% of pressure drop, nearly 10% of the footprint area, and around 420% of heat transfer density of a commercial heat exchanger investigated in this paper as a benchmark. The developed system has been demonstrated with the heat dissipation capability of 350 W/cm2 on a chip of 7~\textrm mm \times 7 mm (a total power of 175 W) with a low pumping power of 0.1 W. [ABSTRACT FROM AUTHOR]

Energy recovery ventilators (ERVs) are the key equipment to fresh air ventilation, which is helpful for the control of respiratory diseases like COVID-19. In this paper, design optimization of the compact heat exchanger in a proposed heat recovery ventilator of the energy efficient building has been carried out and discussed. Appropriate theoretical models are required to evaluate system performance and potential energy savings. This is challenging because of the complexity of the preferred module combining cross- and counter-flow regions. The objective of the design optimization is to maximize the heat transfer effectiveness and to minimize the pressure loss of the compact heat exchanger with limited space. In this study, the allowable dimensions, heat transfer specifications and design requirements of the proposed heat exchanger are firstly defined. Then, the flow configuration, numbers, and dimensions of the air flow channels inside the heat exchanger are identified as the design parameters. A systematic design and optimization method for heat exchanger effectiveness improvement is explored. Furthermore, a detailed mathematical modeling is conducted and validated against the experimental results using the effectiveness-NTU method. It is found that the proposed modeling method is expected to be used to design of the compact heat exchanger. Finally, guidelines for improving the heat transfer effectiveness of air-to-air heat recovery ventilator were derived. [ABSTRACT FROM AUTHOR]

This paper presents a numerical simulation to determine the air-side heat transfer and the pressure drop characteristics of a flat tube heat exchanger with offset strip fin. The effects of the fin bending ratio such as 29%, 36%, 44%, 50%, and the fin spacing such as 2.10 mm, 2.35 mm, 2.60 mm on the performance of the heat exchanger are studied by using a commercial CFD software. The air having constant viscosity, thermal conductivity, and density enters the heat exchanger at 298 K and the wall temperature of the strip fins is considered as constant at 314 K. Variations of the heat transfer coefficient and the pressure drop in the airside are presented with respect to the frontal air velocity while Colburn j-factor and the friction factor f are presented with respect to the airside Reynolds number ranging from 200 to 1200. Finally, the thermal-hydraulic performance of all investigated cases is compared by using the volume goodness factor, j/f1/3. The results show that the air-side heat transfer coefficient and the pressure drop increase when the frontal air velocity ascends. The air-side heat transfer coefficient decreases with the increase of fin spacing. The fin bending ratio does not have a significant effect on the pressure drop in the considered fin spacing. Both the Colburn j-factor and friction factor reduce with the increment of Reynolds number and fin spacing [ABSTRACT FROM AUTHOR]

In this paper, heat transfer enhancement has been numerically investigated for fin and tube compact heat exchangers with radiantly arranged rectangular winglets and has been compared with the existing structures. In the proposed structure, there are total 12 winglets, 3 on each tube arranged radiantly with an attack angle of 60° each. Investigation has been carried out on low Reynolds number from 400-800 heat transfer is compared with other structures without winglet as baseline arrangement, prevailing rectangular winglet arrangement and wavy down rectangular winglet arrangement. The simulation results show that the radiantly arranged winglet that guides the fluid from main flow to the wall creates collision and leads to turbulence behind the tube. It is found that newly proposed structure with radiantly arranged winglets has the highest heat transfer rate, as compared to the existing structures and this can replace the previous structures. The heat transfer characteristics and flow structures are numerically investigated in ANSYS. [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]

Due to the scarcity of conventional energy sources, a lot of efforts need to be taken regarding energy conservation in the buildings, including heat recovery of air ventilation systems. The present paper focuses on new methods to improve the thermal performance of the heat recovery system by investigating the heat transfer characteristics and the flow development in a flat-plate heat exchanger (FPHE) using three different rib-grooved surfaces (trapezoidal, triangle and semi-circular), the numerical simulations were carried out for uniform wall heat flux equal to 290 W/m2for air as the working fluid, the Reynolds number varies from 500 to 2000 for three different channel heights. The numerical results indicated that, rib-grooved surfaces have a significant impact on heat transfer enhancement with an increase in the pressure drop through the channel. The effect of rib-grooved patterns on the heat transfer and the fluid flow is more significant in a narrow channel especially for trapezoidal and triangle corrugated surfaces, because they have sharp edges. Based on the present research, the FPHEs with the added rib-grooved surfaces are recommended to provide an efficient and compact heat recovery system. Moreover, it was found that by applying the new design, a considerable amount of energy and power could be saved. [ABSTRACT FROM AUTHOR]

Establishing an optimal intercooled aeroengine constitutes a coupled problem where the conceptual design of the intercooler and the engine has to be considered simultaneously. The heat transfer and pressure loss characteristics will depend on the choice of the intercooler architecture. Hence, to be able to optimize the performance of an intercooled aeroengine, the performance characteristics of a given intercooler architecture has to be known in the parameter range anticipated for the aeroengine optimization. Here, the conceptual design of a tubular two-pass cross-flow intercooler architecture intended for a turbofan aeroengine application is presented. The internal flow is simulated applying a porous media model for the intercooler tubes, whereas the connecting ducts are analyzed with three-dimensional simulations allowing the assessment of a number of design solutions. The external flow is treated with two-dimensional simulations investigating the external pressure loss and heat transfer characteristics of the two elliptical tube stacks. The intercooler performance is then generalized by developing a reduced order correlation covering a parameter range anticipated for a turbofan conceptual design optimization. The paper constitutes a first effort to establish an open literature complete set of correlations for the prediction of aeroengine intercooler performance. [ABSTRACT FROM AUTHOR]

The influence of the thermal parameters of a Plain-Fin Compact Heat Exchanger on its performance is examined in this paper. The objective of this work is to analyse the effect of the different flow and geometric parameters on the output performance of a plain fin compact heat exchanger (PFCHE) designed to be used on a small-scale gas turbine and how these parameters can be used for the optimisation of PFCHEs. In this work, we examined the effects of the variation of input parameters of a plain-fin compact heat exchanger (fin length, fin height, fin thickness, mass flow rate of air and turbine exhaust gas) on the output performance of the heat exchanger (Overall heat exchanger efficiency, fin heat transfer efficiency and the outlet temperatures). The analytical expressions for the outlet temperatures and heat exchanger efficiencies were derived and analysed. Then the derived model was designed and simulated using CFD codes. Also, from the derived expressions, the performance model of the heat exchanger was programmed for analysis. From the results, it shows that the effectiveness (e-value), fin length, fin height and mass flow rates of the gases influence performance of a plain-fin compact heat exchanger. A 50% reduction in fin height can cause as much as an 18% increase in the fin efficiency of the heat exchanger. While a 50% increase in the effectiveness value can cause as much as a 40% increase in the outlet temperature. [ABSTRACT FROM AUTHOR]

• Validation of numerical models is presented by comparison with experimental results. • Influence of turbulence Prandtl number model and turbulence model is analyzed. • Effects of structural parameter on thermal hydraulic performances are discussed. • Effects of flow parameter on thermal hydraulic performances are analyzed. Sodium-cooled fast reactor coupled with supercritical CO 2 Brayton cycle has broad development prospects owing to the high thermal efficiency, smaller components and compact footprint. As one of the key components, sodium-supercritical CO 2 compact heat exchanger plays a vital role in improving the operation performance of coupled power systems. In this paper, a numerical model for coupling heat transfer of sodium-supercritical CO 2 in a straight-channel compact heat exchange channel is established and the prediction accuracy of the model is verified with experimental results. The influence of structural parameters and flow parameters on the resistance characteristics and heat transfer performance of cold and hot channels is systematically analyzed. The results show that the structure of semi-circular cross-section with an ABAB layout performs best in heat transfer performance. For the sodium channel, performance evaluation criteria gradually grow with the increase of sodium inlet velocity and slowly decline with the supercritical CO 2 inlet velocity. For the supercritical CO 2 channel, performance evaluation criteria decrease with the increase of sodium inlet velocity and increase with the supercritical CO 2 inlet velocity. Reducing the supercritical CO 2 inlet temperature could effectively improve the thermal hydraulic performance of the sodium-supercritical CO 2 compact heat exchange channel. [ABSTRACT FROM AUTHOR]

• Compound porous media model is proposed to simulate performance of U-tube HX. • The complicated U-tube bundle is divided into three porous media sections. • For each section, porous coefficients are obtained from empirical correlations. • Results of compound porous media approach are in good agreement with test results. • The proposed model shows the ability to correctly model a complex geometry HX. This paper describes a compound porous media model approach for numerical analysis to investigate the aero-thermal performance and characteristics of a flat top U-tube heat exchanger. The heat exchanger was considered as a combination of three sections; vertically straight tube section, bent tube section, and horizontally straight tube section. The porous media coefficients were obtained by using empirical correlations for the pressure drop and heat transfer for each section. The numerical results of the compound porous media model were compared to those of a conjugate heat transfer (CHT) CFD analysis, considering real tube geometry and experiments in order to validate the proposed compound porous media approach. The validation revealed that the proposed approach provides reasonable flow and heat transfer characteristics as well as the overall aero-thermal performance of the flat U-tube heat exchanger, with a considerable reduction of the required computational power. [ABSTRACT FROM AUTHOR]

This paper reports an experimental study on the heat transfer characteristics of a nanofluid consisting of ZnO/water/ethylene glycol (EG) and TiO2/water/ /ethylene glycol. In this study, the base fluids of ethylene glycol (EG):water (W) with volume fractions of 30:70, 40:60, and 50:50 were prepared, and 0.2 to 1.0 volume fractions of ZnO and TiO2 nanofluids were used as a cold side fluid. The prime objective of this study is to identify the effects of nanofluid concentration and three different hot fluid inlet temperatures viz., 55, 65 and 75 °C on the heat transfer enhancement of cold side fluid. The results are compared with base fluids and the percentage increase of the Nusselt number because of nanoparticle addition is noted both experimentally and theoretically. The results showed that at the hot fluid inlet temperature of 75 °C, the increase in the Nusselt number is maximum with volume concentrations of 0.6 and 0.8% for ZnO and TiO2 nanofluids, respectively. The corresponding maximum Nusselt number enhancements are about 11.5 and 21.4%, respectively, for the base fluid volume fraction of 30:70 (EG:W). There is good agreement between the results calculated from experimental values and the correlation. [ABSTRACT FROM AUTHOR]

In this paper a two-dimensional numerical simulation of a steady incompressible and turbulent model has been carried out to study the effects of vortex generators in a compact heat exchanger in a curvilinear coordinate system. The mesh which is applied in this study is boundary fitted and has been smoothed by a Laplace operator. Experimental data of a former study has been applied to validate the numerical results. The effects of geometrical variation are studied by adjusting vortex generators’ inclination and relative cross location. The major issue of this study is the optimal trade-off by selecting an optimal geometric, considering the opposite influences of geometrical variation on Nusselt number and pressure drop. [ABSTRACT FROM AUTHOR]

In recent years, the need for high temperature heat exchangers to improve the efficiency of power and chemical conversion systems has been growing. However, the creep design of the high temperature compact heat exchangers has been a primary concern because the working temperature can be well above the creep limit of the materials. To establish the high temperature design criterion for compact heat exchangers, creep behavior of the plate-fin structures and brazed joints are investigated in this paper. The time-dependent deformation and bending stress of the plate-fin structures are obtained analytically by simplifying the fins to elastic springs. The creep damage evolution inside the brazed joint is studied by coupling the finite element method with a damage constitutive equation. The significant effect of creep property mismatch in the brazed joint on the creep strength is demonstrated. [ABSTRACT FROM AUTHOR]

Compact heat exchangers (CHEs), including plate-fin, plate and spiral plate heat exchangers, are widely used in many thermal process systems. Under certain operating condition, the optimal heat exchanger with lowest cost and highest efficiency becomes the ultimate objective pursued by engineers and researchers. In addition, an economic evaluation can also possess a major impact on the selection of technical solution and project profitability. Therefore, it is important to use a proper techno-economic approach that may give enough references to choose an appropriate alternative. This paper gives an overview of the most common methods used in the techno-economic analysis of heat exchangers. Based on the optimum designs with the objective of minimum pressure drop, an optimal CHE is selected from the technical and economic standpoints. The material purchasing, equipment abrasion and power consumption have been considered comprehensively. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, the effects of fin height, louver length and fin-tube contact thickness on the amount of heat transfer and pressure drop in a compact louvered fin-and-tube heat exchanger were studied experimentally and numerically using the ε - NTU method. The effects of fintube contact thickness (with the variations of this thickness being more than or less than fin thickness variation) and fin height and also the relationship between Louvre length and fin height were examined. To validate the modeling, first, the numerical model was compared with an experimental prototype, and a good agreement was observed between the experimental and numerical results. The modeling results indicate that the increase in the fin-tube contact thickness, until the contact thickness becomes equal to fin thickness, leads to the improvement of heat exchanger performance; but beyond that, it is ineffective. Also, heat exchanger performance improves with the increase of louver length at a fixed fin height. According to the results, the minimum Louvre length should be 1.0 mm less than the fin height. An analytical equation relating Louvre length to fin height has been obtained, which agrees with model results by up to 98%. [ABSTRACT FROM AUTHOR]

The dynamic generation of ice slurry from subcooled water is one of the most promising ways to make ice; this process is utilized widely in ice storage air-conditioning systems. However, the random occurrence of ice blockage during the generation of subcooled water using conventional heat exchangers prevents the increase in subcooling, thereby reducing the efficiency of the release of the subcooled water and converting it into ice slurry. A more efficient approach to reducing the fluid passage time is to employ a compact heat exchanger with a highly efficient heat transfer performance, a heat transfer length of only 21.5 mm, and a hydraulic diameter of 0.32 mm. A compact heat exchanger was used to build a dynamic generation setup for subcooled water, and 40 wt% of non-freezing liquid and tap water was used as the working fluid for heat exchange to generate subcooled water. The results show that the compact heat exchanger can achieve a greater subcooling degree (3.8 K) and longer duration (108 min). This study further explored the potential for dynamic ice making from deep, subcooled water and improved the overall structure of the compact heat exchanger used. The experimental setup is recommended based on the analysis of the results. [ABSTRACT FROM AUTHOR]

• This paper proposes an approach for design and optimization of heat exchangers. • This paper discusses heat transfer enhancement of heat exchangers. • This investigates the effect of baffles and tubes in heat transfer performance. • This work studies the fluid flow behavior within a heat exchanger. • This presents on how CFD can be useful in heat exchanger design. Heat transfer is one of the key aspects of machineries, devices and industrial processes for maintaining their functionality and also for achieving better product quality. Hence, heat exchangers of different types and sizes are used in these applications with the purpose of removing the extra process/device heat to maintain the desirable working temperatures. However, the size of a heat exchanger is a major consideration for any type of process/device as it decides the space requirements (i.e., the size) of the machine/device or the processing plant. At first, this study aims to investigate the design procedure of a heat exchanger theoretically and then its performance will be analyzed and optimized using computational fluid dynamics. For the design purposes, a counter flow heat exchanger was considered and its length was theoretically calculated with the LMTD method while the pressure drop and energy consumption were also calculated with the Kern method. Afterwards, a computational model of the same heat exchanger was implemented with ANSYS and then this model was extended to six different models by altering its key design parameters for the optimization purposes. Eventually, these models were used to analyze the heat transfer behavior, mass flow rates, pressures drops, flow velocities and vortices of shell and tube flows inside the heat exchanger. Theoretical and CFD results showed only a 1.05% difference in terms of the cooling performance of the hot fluid. The axial pressure drops showed positive correlations with both the overall heat transfer coefficient and pumping power demand. Overall, the results of this study confirms that CFD modelling can be promising for design and optimization of heat exchangers and it allows testing of numerous design options without fabricating physical prototypes. [ABSTRACT FROM AUTHOR]

In the recent years some papers have dealt with heat exchangers with non-circular tube geometry and vortex generators. Parametric studies with vortex generators applied on heat exchangers models are necessary. The present work consists of an experimental investigation about the influence of combining a plate-finned elliptical tube with vortex generators mounted on the fin surface. The objective is to search for the best position to place the vortex generators just considering heat transfer enhancement. The experimental technique for Nussel tnumber determination was the naphthalene sublimation and mass transfer analogy. A visualization was implemented spreading wetted chalk on fin surface, as a color sensitive evaporation material. The better position obtained is useful for future investigations involving heat exchanger formed by a higher number of tube rows. Additionally was studied the influence of Reynolds number and angle of attack on the average Nusselt number.

• Numerical evaluation of three channel configurations of a plate and shell heat exchangers. • Validated results for internal flow for various Reynolds number. • Analysis of pressure drop, friction factor and Nusselt number for three configurations. • Analysis of the correlations present in the literature for plate heat exchangers. The Plate and Shell Heat Exchanger (PSHE) is a variation of the Plate Heat Exchanger (PHE) with a more compact and robust geometry. This paper presents the analysis of the flow in the inner channel formed by a pair of plates of a PSHE employing computational fluid dynamics to determine the hydrodynamic and thermal characteristics for three Chevron angle configurations, 15° × 15° (High/High-HH), 45° × 45° (Low/Low-LL) and 15° × 45° (High/Low-HL). The ANSYS CFX software was employed with the application of the Standard k-ε and the SST (Shear-Stress-Transport) turbulence models for comparison. Experimental pressure drop data and flow streamlines were used to validate the numerical model and to analyze simplifications in the geometric model. Pressure drop, friction factor, and Nusselt number were evaluated for the three geometries studied. A local analysis of the parameters that describe the channels was also performed in this study. [ABSTRACT FROM AUTHOR]

In the last few years, there has been considerable interest in closed-cycle gas turbine power plants due to the important contribution it can make to meeting worldwide energy demands. Closed-cycle gas turbine has the potential to serve as power conversion system for a wide range of energy sources such as fossil fuel, concentrated solar power, nuclear, biomass and waste heat. However, there is a need to provide an update on the development of closed-cycle gas turbine with a view to identifying the challenges and the opportunities for future commercialisation. This paper is a review of the research activities and studies carried out worldwide so far on closed-cycle gas turbine. The historical development in chronological order was presented first, followed by a review of some fundamental features such as heat sources, working fluids, heat exchangers and cycle layouts/configurations. Important research programmes and experimental/pilot plants as well as previous commercially operated plants were also reviewed. Moreover, various studies based on modelling and simulation of closed-cycle gas turbine were reviewed, in addition to the operation and control strategies. Based on the review studies, the challenges ahead and potential future breakthroughs were highlighted in different aspects such as heat source technologies, power conversion system and demonstration plant. [ABSTRACT FROM AUTHOR]

In the recent years some papers have dealt with heat exchangers with non-circular tube geometry and vortex generators. Parametric studies with vortex generators applied on heat exchangers models are necessary. The present work consists of an experimental investigation about the influence of combining a plate-finned elliptical tube with vortex generators mounted on the fin surface. The objective is to search for the best position to place the vortex generators just considering heat transfer enhancement. The experimental technique for Nussel tnumber determination was the naphthalene sublimation and mass transfer analogy. A visualization was implemented spreading wetted chalk on fin surface, as a color sensitive evaporation material. The better position obtained is useful for future investigations involving heat exchanger formed by a higher number of tube rows. Additionally was studied the influence of Reynolds number and angle of attack on the average Nusselt number. [ABSTRACT FROM AUTHOR]

This paper is about the thermal and hydraulic characterization of a compact heat exchanger having two row of tubes and rectangular wavy fins. The dimension of the tubes and the fin are similar to the used in the air conditioning and refrigeration area. A numerical approach was used and the computational domain was implemented using symmetry and periodic condition. Were considered extended inlet and outlet section for accuracy. The numerical procedure ant its model were certified against published literature and a good match was found. The impinging flow on the fin surface was found responsible for the differences between the heat transferred at every side of the fin. The differences disappearing when the average value was calculated. [ABSTRACT FROM AUTHOR]

Supercritical carbon dioxide (s-CO2) can be used both as a heat transfer and working fluid in solar power tower plants. The main concern in the design of a direct s-CO2 receiver is the high operating pressures, i.e., close to 20 MPa. At such high pressures, conventional receivers do not exhibit the necessary mechanical strength or thermal performance. In this paper, a receiver based on compact heat exchanger technology is developed. The receiver consists of a group of plates with square-shaped channels which are diffusion bonded together to tolerate the high operating pressure. A computational model is developed and validated against data in the literature. Inconel 625 is used as the base material because of its superior resistance against corrosion in the presence of s-CO2. The receiver heats s-CO2 with mass flow rate of / kgls from 530 °C to 700 °C under a solar flux density of 500kW/m². The influence of different parameters on the performance of the receiver is evaluated by a parametric analysis. Subsequently, a multi-objective optimization is performed to determine the optimal geometry of the heat exchanger considering the tradeoff between objective functions, such as unit thermal resistance and pressure drop. The design variables are hydraulic diameter, number of layers, and distance between the channels. The mechanical strength of the system is the constraint to the problem, which is evaluated using an ASME code for the pressure vessels. Finally, the temperature profiles inside the channels and the surface of the receiver are presented. It is shown that the fluid reaches the desired temperature while the maximum temperature of the surface remains well below the material limit. [ABSTRACT FROM AUTHOR]

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The present paper deals with a review of the nonuniformities present in compact heat exchangers in terms of temperature and flow and their effect on the performance of different energy transfer equipment. The understandings of flow distribution and flow pattern at the entrance of compact heat exchanger and prediction of the behavior of heat exchanger have also been reviewed. Different models for temperature and flow nonuniformities have been discussed. Investigations on steady state and transient thermal performance due to nonuniformity of temperature and flow have also been discussed. Focus has also been given on design aspects of the inlet headers and distributors mainly responsible for nonuniformities. Experimental studies have been cited to evaluate the effects of distributor׳s configuration parameter on the fluid flow maldistribution in the plate-fin heat exchanger. Effect of nonuniformities on both two- and three-fluid heat exchangers with phase change and with physical property variations has also been reported. The deterioration of thermal performance of a solar collector due to flow nouniformity effect has also been discussed. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the thermal performance of pressurized air solar receiver for applications in concentrating solar power (CSP) systems. The design is imagined and manufactured based on compact heat exchanger (CHE) concept. An experimental set-up has been built and a series of experiments are carried out under realistic concentrated solar irradiation conditions. The performances of the micro-channel pressurized air solar receivers have been studied in the following parameter ranges: pressure, 2–6bar; air mass flow rates, 0.431–0.862gs−1, solar flux density 170–470kWm−2 and temperature elevation, 100–360°C. Derived heat transfer coefficients reach 750Wm−2 K−1. [Copyright &y& Elsevier]

Abstract: This paper presents a robust, efficient and parameter-setting-free evolutionary approach for the optimal design of compact heat exchangers. A learning automata based particle swarm optimization (LAPSO) is developed for optimization task. Seven design parameters, including discreet and continuous ones, are considered as optimization variables. To make the constraint handling straightforward, a self-adaptive penalty function method is employed. The efficiency and the accuracy of the proposed method are demonstrated through two illustrative examples that include three objectives, namely minimum total annual cost, minimum weight and minimum number of entropy generation units. Numerical results indicate that the presented approach generates the optimum configuration with higher accuracy and a higher success rate when compared with genetic algorithms (GAs) and particle swarm optimization (PSO). [Copyright &y& Elsevier]

Abstract: This paper describes the design, fabrication and performance evaluation of a high efficiency, compact heater that uses the catalytic oxidation of hydrogen to provide heat to a hydrogen storage system. The heater was designed to transfer up to 30kW of heat from the catalytic reaction to the hydrogen storage system via a recirculating heat transfer fluid. The catalytic heater consists of three main parts: 1) the reactor, 2) the gas heat recuperator, and 3) oil and gas flow distribution manifolds. The reactor and recuperator are integrated, compact, finned-plate heat exchangers to maximize heat transfer efficiency and minimize mass and volume. Detailed, three-dimensional, multi-physics computational models were used to design and optimize the system. At full power the heater was able to catalytically combust a 10% hydrogen/air mixture flowing at over 80 cubic feet per minute and transfer 30kW of heat to a 30 gallon per minute flow of oil over a temperature range from 100°C to 220°C. The total efficiency of the catalytic heater, defined as the heat transferred to the oil divided by the inlet hydrogen chemical energy, was determined to exceed the design goal of 80% for oil temperatures from 60°C to 165°C. [Copyright &y& Elsevier]

Abstract: This paper gives a review on performances of compact heat exchangers (CHEs), including well-established devices, some relative newcomers to the market and also designs still being tested in the laboratory. The structures of the CHEs are briefly introduced, and their heat transfer enhancement mechanisms, as well as their advantages and limitations, are summarized. Then, different heat transfer enhancement technologies in CHEs are compared and their thermo-hydraulic performances are analyzed on the basis of available correlations for heat transfer and friction factor developed by various investigators quoted in the open literature. Finally, the technologies that may fit the specifications for a new generation of solar receiver, which is a critical component of the Concentrated Solar Power (CSP) system, are proposed. It is concluded, among others in the review, that solar receivers based upon CHE technology have been rarely reported, and therefore, more work is needed in this field for a comprehensive understanding and to improve the uses of new energy sources and contribute to sustainability. [Copyright &y& Elsevier]

Abstract: The miniaturization of the process equipment has lead to the development of micro-chemical and thermal systems for high tech applications. With the increase of temperature and pressure, the design of the miniature components against creep failure becomes a primary concern. However, the stress analysis of the structure is highly complicated and time-consuming by general finite element methods if a network of inter-connected dodecahedral-like cells is involved. In the present paper, the short-term mechanical properties and the viscoelastic parameters are measured by uniaxial tension experiments. Based on these parameters and small deformation theory, the time-dependent deformation and stresses of the plate-foam structures are analyzed by assuming the metal foams as elastic foundation. Using the numerical inversion of Laplace transform and the standard linear solid model, the analytic expressions of the deformation and stresses are derived. By comparison, the results show that the time-dependent deflection and bending stress along the normalized distance from the analytical method were consistent with those from the finite element method. It indicates that the proposed analytical method was feasible and accurate. Additionally the effect of the viscoelasticity on the deflection will disappear gradually if is much larger than 600GPa. [Copyright &y& Elsevier]

Abstract: An experimental and theoretical investigation of the utilization of finned tube compact heat exchanger for a heat recovery steam generator (HRSG) to recover both sensible and latent heat is presented in this paper. The heat transfer and pressure drop characteristics of the fin-and-tube heat exchanger are theoretically studied. A correlation of the combined convection–condensation heat transfer is derived by using the heat and mass transfer analogy models. The experimental results have shown that the Colburn factor (j) and the friction factor (f) for humid air, simulating the exhaust of HRSG, are larger than those for dry air. It has been also found that the f factor difference between humid air and dry air decreases as the air side Reynolds number increases and both the f factor and the j factor for humid air increase with the increase of water vapour concentration. A scheme for the design of compact heat exchanger for HRSGs is presented. [ABSTRACT FROM AUTHOR]

Very high-temperature reactors require high-temperature (900-950°C) and highintegrity heat exchangers with high effectiveness during normal and off-normal conditions. A class of compact heat exchangers, namely, the printed circuit heat exchangers (PCHEs), made of high-temperature materials and found to have these above characteristics, are being increasingly pursued for heavy duty applications. A high-temperature helium test facility, primarily aimed at investigating the heat transfer and pressure drop characteristics of the PCHEs, was designed and is being built at Ohio State University. The test facility was designed to facilitate operation at temperatures and pressures up to 900° C and 3 MPa, respectively. Owing to the high operating conditions, a detailed investigation on various high-temperature materials was carried out to aid in the design of the test facility and the heat exchangers. The study showed that alloys 617 and 230 are the leading candidate materials for high-temperature heat exchangers. Two PCHEs, each having 10 hot plates and 10 cold plates, with 12 channels in each plate, were fabricated from alloy 617 plates and will be tested once the test facility is constructed. Simultaneously, computational fluid dynamics calculations have been performed on a simplified PCHE model, and the results for three flow rate cases of 15, 40, and 80 kg/h at a system pressure of 3 MPa are discussed. In summary, this paper focuses on the study of the high-temperature materials, the design of the helium test facility, the design and fabrication of the PCHEs, and the computational modeling of a simplified PCHE model. [ABSTRACT FROM AUTHOR]

In desalinization devices and some heat exchangers making use of low-quality heat energy, both wall temperatures and wall beat fluxes of the heated tubes are generally quite low, hence they can not cause boiling in flooded tube-bundle evaporators with common large tube spacing. However, when the tube spacing is very small, the incipient boiling in restricted spaces can occur and results in higher heat transfer than that of pool boiling at the same heat flux. This paper investigated experimentally the effects of tube spacing, positions of tubes and test pressures on the boiling heat transfer of water in restricted spaces of the compact in-line bundles consisting of smooth horizontal tubes. The experimental results show that the tube spacing and tube position have significant effect on the boiling heat transfer in a compact tube bundle. There is an optimum tube spacing, which provides the largest heat transfer coefficient at the same heat flux. [ABSTRACT FROM AUTHOR]

The supercritical carbon dioxide (s-CO2) power cycles are mostly preferred due to their high thermal efficiency and power density in comparison with the conventional steam Rankine cycles. In this study, a printed circuit heat exchanger recuperator which is an important component in s-CO2 recuperative Brayton cycles is numerically and experimentally examined. Within this scope, thermal–hydraulic and structural analyses of a proposed PCHE have been carried out. The sub-heat exchanger model, which uses the output of a sub-heat exchanger as the input of the next one, is applied in the numerical thermal–hydraulic design by subdividing the printed circuit heat exchanger. From the results of this analysis, a heat exchanger is structurally designed and fabricated in compliance with ASME BPVC rules. The fabricated 25 kW printed circuit heat exchanger has reached to 1000 m2/m3 compactness value with 1 mm thickness of fin and 1.5 mm thickness of plate. The experiments were performed on a test bench working with supercritical carbon dioxide at high pressures. The results of the experimental and numerical analyses are in good agreement. The maximum difference between the heat loads and the effectiveness values is 4.9% and 5.4%, respectively. The difference between the overall heat transfer coefficients is 1.2%. It is shown that using the sub-heat exchanger model provides highly accurate printed circuit heat exchanger designs. [ABSTRACT FROM AUTHOR]

• Compact heat exchangers for S-CO 2 power cycle application are introduced. • The heat transfer mechanisms and correlations are described and summarized. • Thermal hydraulic performances of respective compact heat exchangers are compared. This paper first presents a review of compact heat exchanger technology for a supercritical carbon dioxide (S-CO 2) power cycle application to provide holistic insights for designing a power system and selecting appropriate heat exchangers. This is because a compact heat exchanger plays a key role in the S-CO 2 power system to have small footprint while maintaining structural integrity. The developments and characteristics of various compact heat exchangers are briefly described, and their heat transfer mechanisms and correlations obtained from open literatures are summarized, enabling the researchers to obtain information quickly for their needs. From the selected correlations, thermal hydraulic performances of compact heat exchangers are compared for the S-CO 2 recuperator operating region. [ABSTRACT FROM AUTHOR]

This paper reports an experimental study on the heat transfer characteristics of a nanofluid consisting of ZnO/water/ethylene glycol (EG) and TiO2/water/ /ethylene glycol. In this study, the base fluids of ethylene glycol (EG):water (W) with volume fractions of 30:70, 40:60, and 50:50 were prepared, and 0.2 to 1.0 volume fractions of ZnO and TiO2 nanofluids were used as a cold side fluid. The prime objective of this study is to identify the effects of nanofluid concentration and three different hot fluid inlet temperatures viz., 55, 65 and 75°C C on the heat transfer enhancement of cold side fluid. The results are compared with base fluids and the percentage increase of the Nusselt number because of nanoparticle addition is noted both experimentally and theoretically. The results showed that at the hot fluid inlet temperature of 75°C, the increase in the Nusselt number is maximum with volume concentrations of 0.6 and 0.8% for ZnO and TiO2 nanofluids, respectively. The corresponding maximum Nusselt number enhancements are about 11.5 and 21.4%, respectively, for the base fluid volume fraction of 30:70 (EG:W). There is good agreement between the results calculated from experimental values and the correlation.

The paper presents a study of thermal and hydraulic characteristics of porous heat exchangers in conditions of intensive heat dissipation from compact surfaces. We present a mathematical model of convective heat transfer in a porous heat exchange element for conjugate Darcy-Brinkman-Forchheimer equations with boundary conditions of the second kind. An accurate solution of hydrodynamic and thermal problems is obtained analytically by integral transformation. We obtained dependences for determining the velocity field, the length of the initial hydrodynamic area, the Fanning hydraulic friction head, the local temperature of the porous matrix and the liquid cooler, the local Nusselt numbers. We assessed the influence of porosity, permeability, Darcy and Reynolds numbers on the thermal and hydraulic condition of a compact porous heat exchanger. Reasonable ranges of thermal and hydraulic characteristics of the heat exchangers being developed are established. Critical operating modes of heat exchangers are specified. The data obtained agree well with the classical results. We developed an engineering methodology differing from the existing ones by its invariance. The methodology makes it possible to determine the design characteristics of compact porous heat-exchange elements of aerospace control systems.