Selected Papers in ISME KOBE 2011

Abstract

In this study, we conduct an experimental study on condensation heat transfer and pressure drop using a horizontal smooth and internally helical-grooved small-diameter tube with an outside diameter of 4.00 mm. The experimental apparatus is a vapor compression heat pump system, which consists of a compressor, a pre-condenser, test sections, a rear-condenser, a receiver, an electronic expansion valve, an evaporator, and heat-source systems. In the experiments, R410A was used as the refrigerant; the ranges of refrigerant mass flux varied from around 215 to 1290 kg/(m 2 s), and the condensation saturated temperatures were maintained at 35°C and 40°C. From the experimental results, the local heat transfer coefficients of the internally helical-grooved tube were about 1.2-2.0 times larger than those of the smooth tube. In addition, we compared the experimental values of the local condensation heat transfer coefficient and pressure drop with the empirical correlation we proposed. Using smooth and internally helical-grooved small-diameter tube, the experimental values of the local condensation heat transfer coefficient were larger than the empirical correlation proposed by the authors. In addition, the experimental values for pressure drop in a smooth and internally helical-grooved small-diameter tube were larger than the predicted value throughout the entire mass flux range.Keywords: Condensation, Heat transfer, Pressure drop, Small-diameter tube, Grooved tube, R410A INTRODUCTIONIn recent years, the development of more efficient, smaller air-conditioning heat exchangers is expected. In particular, the development of high efficiency in the heat-exchanger tube through the use of small diameter tubes is important. Most air conditioning equipment has a heat-exchanger tube with an outside diameter greater than 6.35 mm, therefore, there have been several studies on the correlation for estimating condensation heat transfer and pressure drop inside a horizontal smooth tube, such as those by Cavallini et al (1) , Haraguchi et al (2) , Shikazono et al (3) , Miyara et al (4) , Dobson et al (5) and Inoue et al (6) . However, there have been no studies on the effect on heat transfer and pressure drop of the groove shape inside an internally helical-grooved small-diameter tube, and small-diameter tubes with an outside diameter of 3.00-5.00 mm.In this study, we conducted experiments to obtain data on condensation heat transfer and pressure drop using a smooth and internally helical-grooved small-diameter tube with an outside diameter of 4.00 mm and using R410A as a refrigerant. From the experimental results, we compared the experimental values of the local condensation heat transfer coefficient and pressure drop with the empirical correlations we proposed. In addition, we compared the experimental data with the empirical correlation using the friction factor for small-diameter tube with an outside diameter of 4.00 mm on single-phase flow. Figure 1 shows a schematic diagram of the experimental apparatus, which is a vapor ...