Counter Flow Microchannel Heat Exchanger Research Articles

Numerical investigation of counter flow microchannel heat exchanger with MEPCM suspension

Abstract The aim of this paper is to study the flow and heat transfer of microencapsulated phase change material (MEPCM) suspension in counter flow microchannel heat exchanger (CFMCHE) and it’s effect of the performance of this heat exchanger when using this suspension as a coolant instead of pure fluid. The hydrodynamic and thermal characteristics of this suspension flows in microchannels of CFMCHE is numerically investigated. The MEPCM suspension used in this paper consists of microcapsules constructed from n -octadecane as a phase change material (PCM) and the shell material is polymethylmethacrylate, these capsules are suspended in water in a concentration of (0–20)%. From the results, using of MEPCM suspensions as a cooling fluid lead to modify thermal performance of a CFMCHE by increasing its effectiveness but it also lead to increase the pressure drop. From heat transfer (thermal performance) point of view it is better to use this type of fluid to increase cooling efficiency of a CFMCHE, but due to extra increase in pressure drop it leads to reduce the overall performance compared with pure fluids. Therefore its use depends on the application at which this heat exchanger is used.

Using of Microencapsulated Phase Change Material Suspension to Enhance the Performance of Microchannel Heat Exchanger

The aim of this paper is to improve thermal performance of a counter flow microchannel heat exchanger (CFMCHE) by using microencapsulated phase change material slurry (MEPCM suspension) as a cooling fluid instead of pure fluid. The MEPCM suspension used in this paper consists of microcapsules constructed from n-octadecane as a phase change material (PCM) and the shell material is Polymethylmethacrylat, these capsules are suspended in water in a concentration of (0 – 20) %. From the results, using of MEPCM suspensions as a cooling fluid leads to modify thermal performance of a CFMCHE by increasing its effectiveness but it also leads to increase the pressure drop. From heat transfer (thermal performance) point of view it is better to use this type of fluid to increase cooling efficiency of a CFMCHE, but due to extra increase in pressure drop it leads to reduce the overall performance compared with pure fluids. Therefore its application depends on the conditions at which this heat exchanger is used.

Experimental Investigation on Heat Transfer Characteristics of a Gas-to-Gas Counterflow Microchannel Heat Exchanger

Heat transfer characteristics of a gas-to-gas counterflow microchannel heat exchanger have been experimentally investigated. Temperatures and pressures at inlets and outlets of the heat exchanger have been measured to obtain heat transfer rates and pressure drops. The heat transfer and the pressure drop characteristics are discussed. Since the partition wall of the heat exchanger is thick compared with the microchannel dimensions, a simple heat exchange model with constant wall temperature is proposed to predict the heat transfer rate. The predicted heat transfer rate using the constant wall temperature model agrees well with the experimental results.

Performance of Counterflow Microchannel Heat Exchangers Subjected to External Heat Transfer

This article analyzes the effect of external heat transfer on the thermal performance of counterflow microchannel heat exchangers. Equations for predicting the axial temperature and the effectiveness of both fluids as well as the heat transferred between the fluids, while operating under external heating or cooling conditions, are provided in this article. External heating may decrease and increase the effectiveness of the hot and cold fluids, respectively. External cooling may improve and degrade the effectiveness of the hot and cold fluids, respectively. For unbalanced flows, the thermal performance of the microchannel heat exchanger subjected to external heat transfer depends on the fluid with the lowest heat capacity. At a particular number of transfer units (NTU), the effectiveness of both the fluids increased with decrease in heat capacity ratio when the hot fluid had the lowest heat capacity. When the cold fluid had the lowest heat capacity, the effectiveness of both fluids increased with decrease in heat capacity ratio at low values of NTU but at high values of NTU the effectiveness increased with increase in heat capacity ratio. A term called the “performance factor” has been introduced in this article to assess the relative change in effectiveness due to external heat transfer.

Influence of channel geometry on the performance of a counter flow microchannel heat exchanger

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.