Jong-Taek Oh

Boiling heat transfer of a ternary refrigerant mixture inside a horizontal smooth tube

Abstract A theoretical model for predicting the forced convective boiling heat transfer coefficients of ternary mixtures is presented. The effect of mass diffusion near the gas-liquid interface is considered in both nucleate boiling and forced convection vaporization contributions. The predicted heat transfer coefficients are compared with experimental data, which are obtained for an HFC32: 125: 134a (23: 25: 52 wt%) mixture inside a horizontal smooth tube 6.0 mm i.d. and 4.0 m long, and in the ranges of heat flux 10–20 kW m−2 and of mass flux 150–400 kg m−2 s−1. The present predictive method shows reasonable agreement with the experimental data within an accuracy of ±30%.

The Comparison of Experiment Results and CFD Simulation in the Heat Pump System Using Thermobank and Two-Phase Ejector for Heating Room and Cold Storage

In this paper, the heat pump system has been developed by CFD simulation and experimental investigation. It studies the thermal behavior of a thermobank and COP on heat pump system and cold storage. The thermobank stores the waste heat of during refrigeration cycles and this energy is used for defrosting process and heating room. It also reduces defrosting time and condensation load so that the temperature regulation in the cold storage is constant. The system is investigated experimentally and CFD simulated under thermobank. The dimension L×W×H of cold storage is 3×1.6×1.4m, thermobank is 600×300×400mm. The temperature of ambient on CFD simulation process is 20∘C. This heat pump system can be used to keep preservation of agricultural products in cold storage warehouse together with floor panel heating for room in winter. The ejector is used in system with the aim of increasing coefficient of performance (COP) and decrease in compressor displacement. As the experimental results, its COP is increased about 38.57% when using thermobank and ejector in heat pump system.

A General Correlation to Predict The Flow Boiling Heat Transfer of R410A in Macro/Mini Channels

This study demonstrates a general correlation to predict the saturated flow boiling heat transfer of R410A in horizontal macro- and mini-channels. The experimental data were observed in various tube diameters of 1.5, 3.0, 6.61, and 7.49 mm, mass fluxes of 100–600 kg/m2s, heat fluxes of 10–40 kW/m2, saturation temperatures of 5°C–15°C, and vapor qualities from 0.2 to 1. The database was compared with numerous well-known correlations. The proposed correlation was based on the superposition model of nucleate boiling and forced convective boiling contribution. The new modified correlation showed a good prediction against the present database.

Heat Transfer Coefficient during Evaporation of R-1234yf, R-134a, and R-22 in Horizontal Circular Small Tubes

Experimental data of heat transfer coefficient during evaporation of R-1234yf, R-134a, and R-22 in horizontal circular small tubes are compared. The local heat transfer coefficient is obtained for heat fluxes ranging from 10 to 35 kW m−2, mass fluxes ranging from 100 to 650 kg m−2 s−1, saturation temperatures of 5, 10, and 15°C, and quality up to 1.0. The test sections are made of stainless steel tubes with inner diameters of 1.5 and 3.0 mm, the lengths of 1000 and 2000. Effects of heat flux, inner tube diameter, and saturation temperature on heat transfer coefficient are reported in the present study. Nucleate boiling heat transfer contribution is predominant, especially at low quality region, and laminar flow appears in the evaporative small tubes. The experimental results are compared against four existing heat transfer coefficients, and the modified correlation of heat transfer coefficient is developed with good prediction.

Flow condensing heat transfer of R410A, R22, and R32 inside a micro-fin tube

ABSTRACT An experimental study of condensation heat transfer characteristics of flow inside horizontal micro-fin tubes is carried out using R410A, R22, and R32 as the test fluids. This study especially focuses on the influence of heat transfer area upon the condensation heat transfer coefficients. The test sections were made of double tubes using the counter-flow type; the refrigerants condensation inside the test tube enabled heat to exchange with cooling water that flows from the annular side. The saturation temperature and pressure of the refrigerants were measured at the inlet and outlet of the test sections to defined state of refrigerants, and the surface temperatures of the tube were measured. A differential pressure transducer directly measured the pressure drops in the test section. The heat transfer coefficients and pressure drops were calculated using the experimental data. The condensation heat transfer coefficient was measured at the saturation temperature of 48°C with mass fluxes of 50–380 kg/(m2s) and heat fluxes of 3–12 kW/m2. The values of experimental heat transfer coefficient results are compared with the predicted values from the existing correlations in the literature, and a new condensation heat transfer coefficient correlation is proposed.

Characteristics of Two-Phase Flow Boiling Heat Transfer and Pressure Drop of NH3, C3H8 and CO2 in Horizontal Circular Small Tubes

An experimental investigation on the characteristics of two-phase boiling heat transfer of NH3 , C3 H8 and CO2 in horizontal small stainless steel tubes of 1.5 and 3.0 mm inner diameters are presented in this paper. Experimental data were obtained over a heat flux range of 5 to 70 kW/m2 , mass flux range of 50 to 600 kg/m2 s, saturation temperature range of 0 to 12°C, and quality up to 1.0. The test section was heated uniformly by applying an electric current to the tubes directly. Nucleate boiling heat transfer was the main contribution, particularly at the low quality region. Laminar flow was observed in the small tubes. The heat transfer coefficient of the present working refrigerants was compared with other correlations. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants in small tubes was developed.© 2010 ASME

Effect on Boiling Bleat Transfer of Horizontal Micro-channel Diameters for R-22 and R-407C

Boiling heat transfer coefficients and pressure drops for R-22 and R-407C were measured in horizontal micro-channels. The test section is stainless steel tube, inner tube diameters are 1.8mm and 2.8mm, and the respective lengths are 1500mm and 3000mm. The range of mass flux is 300-600kg/s and heat flux is 5-15kW/. In this results, pressure drop increased linearly for both R-22 and R-407C with increased mass flux, but the increase of heat flux did not affect the pressure. In addition, the pressure drop was fairly increased in the high quality region rather than low quality region. In the range of low quality, the mass flux had a small affect on the heat transfer coefficients, however, in high quality region, the heat transfer coefficients increased even more with increasing mass flux. Under the low quality region and low mass flux, the heat transfer coefficients increased with increasing heat flux densities. The effects of inner tube diameter were clearly observed. Namely, the measured pressure drop inside inner tube diameter 1.8 mm is higher than 2.8 mm with increasing the mass flux and heat flux. Also, the measured local heat transfer coefficient inside inner tube diameter 1.8 mm is higher than 2.8 mm in the range of high qualities. The experimental data for R-407C compared with proposed correlation using pure refrigerant. The experimental data for R-407C was more decreased than the proposed correlation for pure refrigerant up to 50% or more.