Experimental and numerical study of the compact heat exchanger with different microchannel shapes (original) (raw)
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Numerical analysis of heat transfer in air-water heat exchanger with microchannel coil
E3S Web of Conferences, 2019
This paper presents numerical analysis of fluid flow and heat transfer in the heat exchanger with microchannel coil (MCHX). In accordance with previously published experimental results, 3D mathematical model has been defined and appropriate numerical simulation of heat transfer has been performed. Geometry and working parameters of cross-flow air-water heat exchanger with microchannel coil, installed in an open circuit wind tunnel and used in experimental investigations, have been applied in numerical analysis in order to validate the mathematical model. 3D model with air and water fluid flow and heat transfer domains has been used, as it gives more precise results compared to models that assume constant temperatures or constant heat fluxes on the pipe walls. Developed model comprised full length of air and water flows in the heat exchanger. Due to limitations of computational capacity, domain has been divided in multiple computational blocks in the water flow direction and then solved successively using CFD solver Fluent. Good agreement between experimentally measured and numerically calculated results has been obtained. The influence of various working parameters on heat transfer in air-water heat exchanger has been studied numerically, followed with discussion and final conclusions.
Heat Transfer Analysis in Microchannel Heat Exchanger: A Review
A systematic review on the heat transfer in microchannel heat exchangers with different geometries is presented. The slip and No-slip flow are accounted in this study. The two dimensional, three dimensional studies considered with single phase convective heat transfer microchannel with different geometries. Both theoretical and experimental studies are considered and comparison made between them. From the available experimental literature friction factor, Nusselt number is measured and they compared with the conventional theory and results shows that inequality between experiment and conventional theory results. The compressibility effect, roughness effect, viscous dissipation effect, variation in properties is also considered for find out the pressure drop. The results show that the pressure drop is the function of roughness. By paralleling the experimental data on single-phase convective heat transfer through microchannels, it is manifest that additional methodical studies are ess...
Iaeng International Journal of Applied Mathematics, 2010
The influence of flow arrangement on the heat transfer behaviors was carried out for a microchannel heat exchanger. The results were obtained by both numerical simulations and experimental data. The solver of numerical simulations-COMSOL-was developed by using the finite element method. For all cases done in this study, the heat flux obtained from the counter-flow arrangement is always higher than that obtained from the parallel-flow one: the value obtained from the counter-flow is 1.1 to 1.2 times of that obtained from the parallel-flow. This means that the heat transfer behaviors of the microchanel heat exchanger with counter-flow are better than those with parallel-flow. For the case of the counter-flow, the experimental results indicated that the total heat flux of 17.81 W/cm 2 was achieved for water from the hot side of the device having the inlet temperature of 70 ºC and flow rate of 0.2321 g/s and for water from the cold side having the inlet temperature of 22.5 ºC and flow rate of 0.401 g/s. Besides, the numerically obtained profiles of the temperature and the temperature gradient were shown graphically. Furthermore, the results obtained from the numerical analyses were in good agreement with those obtained from the experiments, with the discrepancies of the heat transfer coefficient estimated to be less than 10 %.
A study on the simulation and experiment of a microchannel counter-flow heat exchanger
Applied Thermal Engineering, 2010
Numerical simulations and experimental tests were carried out to study the fluid flow and heat transfer characteristics for a rectangular-shaped microchannel heat exchanger. Moreover, influences of gravity to heat transfer and pressure drop behaviors of the microchannel heat exchanger were presented by variation of the physical inclinations of the microchannel heat exchanger system used for experiments. For experimental results, a heat flux of 17.4 W/cm 2 was achieved for the heat exchanger. Besides, the results obtained for the actual effectiveness and for the effectiveness (the so-called effectiveness-NTU method) were determined. In this study, the pressure drop decreases as the water temperature rises. As the pressure drop increases from 880 to 4400 Pa, the mass flow rate increases from 0.1812 to 0.8540 g/s. In addition, the results obtained from numerical analyses were in good agreement with those obtained from experiments, with discrepancies of the heat transfer coefficient estimated to be less than 9%.
Experimental Research and CFD Simulation of Cross Flow Microchannel Heat Exchanger
Journal of Thermal Engineering, 2021
In this study, a cross flow microchannel heat exchanger has been manufactured out of standard sizes using aluminum material. The plate dimensions of heat exchangers have been 50x50x3 (mm 3) that composed of two plates in cross flow arrangement. All evaluated geometries have been consisted of square microchannels with 490 μm width and 490 μm depth. An appropriate experimental facility has been established to perform the fluid flow and heat experiments. Moreover, heat transfer and fluid flow characteristics in microchannels have been simulated by ANSYS Fluent V15 Computer Program and experimental results have been compared with Computational Fluid Dynamics (CFD) results. Results showed that experimental heat transfer data was a very good agreement between data obtained by CFD simulation. However, the numeric pressure drop values have not been compatible with experimental ones.
International Journal of Heat and Mass Transfer, 2012
This communication documents the experimental investigation of the theoretical model for predicting the thermal performance of parallel flow microchannel heat exchangers subjected to external heat flux. The thermal model investigated in this communication is that previously developed by the authors of this communication; Mathew and Hegab [B. Mathew, H. Hegab, Application of effectiveness-NTU relationship to parallel flowmicrochannel heat exchangers subjected to external heat transfer, International Journal of Thermal Sciences 31 (2010) 76-85]. The validity of the theoretical model with respect to microchannel profile, hydraulic diameter, heat capacity ratio and degree of external heat transfer is checked. The microchannel profiles investigated are trapezoidal and triangular with hydraulic diameter of 278.5 and 279.5 lm, respectively. The influence of hydraulic diameter is analyzed using trapezoidal microchannels with hydraulic diameters of 231 and 278.5 lm. Experiments are conducted for heat capacity ratios of unity and 0.5 using the heat exchanger employing the trapezoidal microchannel with hydraulic diameter of 278.5 lm for purposes of validating the model. Experiments are done for all heat exchangers for two different levels of external heat transfer; 15% and 30% of the maximum possible heat transfer. Irrespective of the parameter that is investigated the experimental data are found to perfectly match with the theoretical predictions thereby validating the thermal model investigated in this communication.
Hydraulic and thermal design of a gas microchannel heat exchanger
Journal of Physics: Conference Series, 2012
In this paper investigations on the design of a gas flow microchannel heat exchanger are described in terms of hydrodynamic and thermal aspects. The optimal choice for thermal conductivity of the solid material is discussed by analysis of its influences on the thermal performance of a micro heat exchanger. Two numerical models are built by means of a commercial CFD code (Fluent). The simulation results provide the distribution of mass flow rate, inlet pressure and pressure loss, outlet pressure and pressure loss, subjected to various feeding pressure values. Based on the thermal and hydrodynamic analysis, a micro heat exchanger made of polymer (PEEK) is designed and manufactured for flow and heat transfer measurements in air flows. Sensors are integrated into the micro heat exchanger in order to measure the local pressure and temperature in an accurate way. Finally, combined with numerical simulation, an operating range is suggested for the present micro heat exchanger in order to guarantee uniform flow distribution and best thermal and hydraulic performances.
Study of Thermal Performance of Counter Flow Microchannel Heat Exchangers
In this paper a full numerical simulation is made to find the velocity and temperature fields for a counter flow microchannel heat exchanger (CFMCHE). Effects of entrance region and axial conduction on thermal performance of a CFMCHE are studied for various conditions. Results show that the well defined ε-NTU relation of conventional counter flow heat exchanger is remained the same but the value of U is the average along the heat exchanger taking into account the effect of entrance region and axial conduction. Analysis show that axial conduction reduced effectiveness of the heat exchanger and there is also an optimal value of wall to fluid thermal conductivity ratio which gives maximum performance of the heat exchanger.
Influence of channel geometry on the performance of a counter flow microchannel heat exchanger
International Journal of Thermal Sciences, 2009
Microchannel heat exchangers (MCHE) can be made with channels of various geometries. Their size and shape may have considerable effect on the thermal and hydraulic performance of a heat exchanger. In this paper numerical simulation is carried out to solve 3D developing flow and 3D conjugate heat transfer of a balanced counter flow microchannel heat exchanger (CFMCHE) to evaluate the effect of size and shape of channels on the performance of CFMCHE for the same volume of heat exchanger. The effect of shape of the channels on its performance is studied for different channel cross-sections such as circular, square, rectangular, iso-triangular and trapezoidal. Results show that for the same volume of a heat exchanger, increasing the number of channels lead to increase in both effectiveness and pressure drop. Moreover circular channels give the best overall performance (thermal and hydraulic) among various channel shapes. New correlations are developed to predict the value of heat exchanger effectiveness and performance index as a function of relative size of channels with overall heat exchanger volume, Reynolds number and thermal conductivity ratio.