Heat Transfer Characteristics Of CO2 Research Articles

Flow boiling heat transfer analysis of new experimental data of CO2 in a micro-fin tube at −30 °C

This paper presents an experimental investigation of the flow boiling heat transfer characteristics of CO2 in a horizontal micro-fin tube at saturation temperature of −30 °C. The test tube, made of copper, with outer diameter of 7.94 mm, was uniformly heated ohmically by high electric current through a transformer. The tests were conducted at mass and heat fluxes, ranging from 100 to 250 kg m−2 s−1 and 10–25 kW m−2, respectively. The new experimental data from these tests for varying conditions is provided in Appendix 1 for future research. The experimental data shows that htp increases with vapour quality until dryout, and decreases with saturation temperature, while heat flux has more pronounced effect on htp, suggesting the dominance of nucleate boiling. Furthermore, predictions from several empirical correlations disagree with the current CO2 experimental data in the micro-fin tube. [11] and [4] correlations predict with deviations of up to ±50%.

Condensation heat transfer characteristics of CO2 in a horizontal smooth- and microfin-tube at high saturation temperatures

Abstract The condensation heat transfer characteristics for CO2 at high saturation temperatures in a horizontal smooth- and microfin-tube were investigated by experiment with respect to condensation temperature and mass flux. The test sections consist of 2400 mm length with a horizontal copper tube of 4.6 mm (smooth) and 4.95 mm (microfin) inner diameter. The experiments were conducted at refrigerant mass flux of 400–800 kg/(m2s), and saturation temperature of 20–30 °C. The main experimental results showed that annular flow almost dominated the major of condensation flow in the horizontal smooth- and microfin-tube. The condensation heat transfer coefficients for the smooth- and microfin-tube increase with the decreasing saturation temperature and increasing mass flux. The average heat transfer enhancement factor (EF) for the microfin tube is approximately from 1.006 to 1.48, and penalty factor (PF) varies from 1.14 to 1.23. The experimental data in the smooth- and microfin-tube were compared against previous heat transfer correlations. Most of correlations failed to predict the experimental data. However, the correlations by Kondou and Hrnjak [1] and Cavallini et al. [4] showed relatively good agreement with experimental data in the smooth- and microfin-tube, respectively. But it is necessary to develop accurate and reliable correlation to predict condensation heat transfer coefficient at high saturation temperatures in the horizontal smooth- and microfin- tube.

Cooling Heat Transfer Characteristics of CO2 and CO2-Oil Mixtures at Supercritical Pressure Conditions

Cooling Heat Transfer Characteristics of CO2 and CO2-Oil Mixtures at Supercritical Pressure Conditions

Design and Experimental Research of Gas Cooler for CO<sub>2</sub> Heat Pump Water Heater

The advantages of CO2 Heat Pump water heater include: CO2 is one of natural refrigerants and does not affect the global environment as many other HFCs refrigerants; CO2 heat pump water heater can produce hot water up to 90 ,which is higher than HFCs heat pump water heater(about 55 ).So the application of CO2 Heat Pump water heater is potential. But the Working pressure of CO2 Heat Pump Water Heater is about 9~12Mpa and is 3-5times of HFCs heat pump water heater’. Gas cooler is one of important part for CO2 heat pump water heater, and it must meet the needs of not only pressurization but also heat transfer. So it is important to design gas cooler correctly. In the paper, one system of CO2 Trans-critical Cycle Heat Pump Water Heater is designed, and double-pipe gas cooler is designed The heat transfer characteristics of CO2 in gas cooler with water in double-pipe heat exchanger was experimentally investigated. Experimental results showed that the gas cooler can meet the need of trans-critical CO2 cycle heat pump water heater. All the work is valuable for the application of CO2 heat pump water heater.

Subcooled Boiling Heat Transfer of CO2 in A Horizontal Tube at Low Temperatures

This article presents an experimental investigation on the subcooled flow boiling heat transfer characteristics of CO2 in a horizontal tube with inner diameter of 6.16 mm below −30°C. The effects of mass and heat fluxes and saturation temperature on the heat transfer coefficient are discussed. Large deviations are noted between the predictions from previous empirical correlations and the current CO2 experimental data. Hence a new empirical correlation is developed, which agrees within ±30% with the current CO2 experimental data. It is expected that the data presented in this study would be beneficial to industry and designers of compact heat exchangers for CO2 at low temperatures.