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• 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]

• 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]

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]

• 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]

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]

• 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]