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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]

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]

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]

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]

The effect of winglet height on the thermal-hydraulic performance of finned tube heat exchanger (FTHE) is investigated numerically. The rectangular winglet pairs (RWPs) having 5° attack angle are placed in common flow up (CFU) manner adjacent to the tubes for analysis. The air-side performance evaluation has been done based on the area goodness factor (j/f). The working fluid (air) is considered as incompressible fluid. Additionally, MOORA (multi objective optimization on the basis of ratio analysis) method is employed to get the best performance order of various configurations by taking Nusselt number (Nu) and area goodness factor (j/f) as beneficial attributes and friction factor (f) as a non-beneficial attribute having equal significances. The present study reveals that the rectangular vortex generators having 60 % of the channel height provides the better thermal hydraulic performance compared to the other considered cases. [ABSTRACT FROM AUTHOR]

This study is purposed to estimate the pressure drop and thermal performance of three-dimensional heat exchanger units by the porous approximation, considering inertia effects. The full three-dimensional (3D) estimation of the thermal performance of the heat exchanger is very difficult because of the great complexity of the louvered-fin shape and lack of numerical resources. The volume grid used for this study was less than 10 million computational units. In order to verify the interpretation results, a compact heat exchanger having 9500 louver fins and 3D header tanks was tested experimentally and numerically. The simulation results for the air-side pressure drop agree well with the experimental result within 10 %, while the thermal effectiveness of the air was within 9.5 % of the experimental results. The present numerical method can be an effective tool to estimate the performance of multi-louver finned heat exchangers by using limited numerical resources. [ABSTRACT FROM AUTHOR]

This work explores the manufacturability of pyramidal fin arrays produced using the cold spray process. Near-net shaped pyramidal fin arrays of various sizes and fin densities were manufactured using masks made of commercially available steel wire mesh. The feedstock powders used to produce the fins are characterized using scanning electron microscopy. Obstruction of the masks was investigated. The standoff distances between the substrate, mesh, and nozzle were empirically determined. Fin array characterization was performed using digital microscopy. The fin arrays' heat transfer performance was assessed experimentally for a range of Reynolds number relevant to the application sought. The fins produced using the cold spray process outperform traditional straight (rectangular) fins at the same fin density and it is hypothesized that this is due to increased fluid mixing and turbulence. [ABSTRACT FROM AUTHOR]

A heat recovery system is crucial for the effective use of energy where heat rejection from production processes is unavoidable and must be reused. The response of the louvered fins to the low-Reynolds number hot gas is yet to be reported in the literature for the application of a heat exchanger on low-speed hot plume arising from heat sources in production processes. This study focuses on the effects of the louvered fin heat exchanger’s design parameters, which include the louver pitch and louver angle, on the convective heat transfer, which defines the thermal interaction between the hot, buoyant, naturally-induced air and the louvered fins. The resulting Colburn factors ( j) are compared with those derived under forced convection with a similar range of low Reynolds number (233 to 1024). All experiments are done on a 15:1 scaled-up model. The fin aspect ratios between the fin spacing and louver pitch are set at 0.75, 1, and 1.5, while the louver angles are set at 18°, 23°, 30°, 35°, and 40°. The Colburn factor strongly depends on the louver angle, especially at the lower range of the Reynolds number. The decreasing aspect ratio induces more hot buoyant air into the louver-formed channels, increasing the heat transfer rate. When the fin angle increases towards 30°, a larger Colburn factor is produced. However, the heat transfer characteristic drops as the angle goes beyond 30°. The highest j for the low speed flow is attained when the louver angle is 30° and the fin aspect ratio is 1. [ABSTRACT FROM AUTHOR]

When circulated air passes through the cooling coil in an air-conditioning system, the air is over-cooled to eliminate the moisture and decrease the temperature. The cooled air is then reheated to recover the temperature. The purpose of the present study was to evaluate the performance of a cooling/reheating system with regard to both cooling and reheating energy savings affected by exchanging heat between the cooled air and the reheated air with a compact heat exchanger. The thermal and dehumidification behaviors of the system were evaluated experimentally and then compared with simulation data. The results show that the energy saving rate was as high as 50% under the present experimental conditions and was affected by the face velocity of the heat exchanger, the inlet temperature, the inlet humidity ratio, and the effectiveness of heat exchanger. Furthermore, the experimental data were found to be in fairly good agreement with the simulation data. [ABSTRACT FROM AUTHOR]

A single-blow transient testing technique considering the effect of longitudinal heat conduction is suggested for determining the average convection heat transfer coefficient of compact heat exchanger surface. By matching the measured outlet fluid temperature variation with similar theoretical curves, the dimensionless longitudinal conduction parameter λ1, the time constant of the inlet fluid temperature τ+, and the number of heat transfer units N tu can be determined simultaneously using the Levenberg-Marquardt nonlinear parameter estimation method. Both sensitivity analysis and numerical experiments with simulated measurements containing random errors show that the method in the present investigation provides satisfactory accuracy of the estimated parameter N tu, which characterizes the heat transfer performance of compact heat exchanger surfaces. [ABSTRACT FROM AUTHOR]