Evaporation Heat Transfer and Pressure Drop of Refrigerant R134a in a Plate Heat Exchanger

Abstract

The characteristics of evaporation heat transfer and pressure drop for refrigerant R134a flowing in a plate heat exchanger were investigated experimentally in this study. Two vertical counter flow channels were formed in the exchanger by three plates of commercialized geometry with a corrugated sine shape of a chevron angle of 60°. Upflow boiling of refrigerant R134a in one channel receives heat from the hot downflow of water in the other channel. The effects of the heat flux, mass flux, quality and pressure of R134a on the evaporation heat transfer and pressure drop were explored. The preliminary measured data for the water to water single phase convection showed that the heat transfer coefficient in the plate heat exchanger is about 9 times of that in a circular pipe at the same Reynolds number. Even at a very low Reynolds number, the present flow visualization in a plate heat exchanger with the transparent outer plate showed that the flow in the plate heat exchanger remains turbulent. Data for the pressure drop were also examined in detail. It is found that the evaporation heat transfer coefficient of R134a in the plates is quite different from that in circular pipe, particularly in the convective evaporation dominated regime at high vapor quality. Relatively intense boiling on the corrugated surface was seen from the flow visualization. More specifically, the present data showed that both the evaporation heat transfer coefficient and pressure drop increase with the vapor quality. At a higher mass flux the pressure drop is higher for the entire range of the vapor quality but the heat transfer is only better at high quality. Raising the imposed wall heat flux was found to slightly improve the heat transfer. While at a higher system pressure the heat transfer and pressure drop are both slightly lower.

A composite heat transfer correlation for saturated flow boiling in small channels

“…However, even the best predictions showed a mean absolute error (MAE) of 40% against the large experimental database, and predicted less than half of the measured data to within a deviation of ±30%. It was also noted in [1] that most of the existing minichannel and microchannel heat transfer correlations were developed based on small data sets [13][14][15][16][17][18][19][20]. As a result, these correlations usually performed well in the parameter range over which they were fit, but did not extrapolate well beyond their often narrow operating range [1].…”

“…In recent years, a large number of well-characterized experiments with small channels have been published [13,14,16,[23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. These studies cover a wide range of operating parameters, fluids and physical dimensions, and present a good database against which to validate existing correlations and to support the formulation of new correlations.…”

Flow Boiling in an Asymmetrically Heated Single Rectangular Microchannel

“…Three flow regimes were observed: isolated bubble flow, which is similar to bubbly flow in a large channel; confined bubble flow, which involves an elongated bubble; and annular-slug flow. The heat transfer coefficient for the evaporation of R134a flowing in a small circular copper tube with an inner diameter of 2 mm was measured (Yan & Lin, 1998). It was showed that the evaporation heat transfer coefficient averaged over the entire vapor quality range was about 30-80% higher than that for a large pipe with an inner diameter of 8.0 mm.…”

“…(Mishima & Hibiki, 1996;Mishima et al, 1993;Tran et al, 2000;Yu et al, 2002; Table 2. Summary of previous studies on flow boiling heat transfer in mini/microchannels (Lazarek & Black, 1982;Tran et al, 1996;Kew & Cornwell, 1997;Yan & Lin, 1998;Warrier et al, 2002;Yu et al, 2002; 2. Experimental setup and procedure…”

Research on Spray Cooling Within Finite Volume Based on Eulerian-Lagrangian Method

“…In the model with equal inner and outer tube length, airflow collided with surface of other tubes, thus exhaust resistance increased. The ratio of total heat transfer coefficient K and pressure drop △P was defined as integrative index to compare characteristics of different models [12]. Fig.…”