Boiling Heat Transfer Of CO2 Research Articles

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.

Experimental Investigation on Flow Boiling Heat Transfer of CO2 at Low Temperatures

There is a growing use of CO2 refrigeration to achieve low temperatures, particularly in the food industry; however, very limited information is available in the open literature on its boiling heat transfer characteristics below –30°C. This paper investigates experimentally the flow boiling heat transfer of CO2 at low temperatures down to –40°C. The experimental data were collected from a novel experimental rig, specifically designed to achieve low temperatures, using a 4.5 m long horizontal stainless steel tube of 4.57 mm inner diameter. The effects of heat and mass fluxes and saturation temperature on the flow boiling heat transfer coefficient are also analyzed. Furthermore, this paper highlights the limitations of existing empirical correlations by comparing their predictions with the experimental boiling heat transfer coefficients. 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.

Flow Boiling Heat Transfer of CO2 at Low Temperatures in a Horizontal Smooth Tube

Flow boiling heat transfer coefficients of CO2 are measured in a horizontal smooth tube with inner diameter 6.1mm. The test tube is heated by a secondary fluid maintaining constant wall temperature conditions. Heat transfer coefficients are measured at evaporation temperatures of −15 and −30°C, mass flux from 100to400kg∕m2s, and heat flux from 5to15kW∕m2 for qualities (vapor mass fractions) ranging from 0.1 to 0.8. The characteristics of CO2 flow boiling are explained by CO2 properties and flow patterns. The measured CO2 heat transfer coefficients are compared to other published data. Experiments with R22 were also conducted in the same system and the results show that the heat transfer coefficients for CO2 are 40 to 150% higher than for R22 at −15°C and low mass flux of 200kg∕m2s mostly due to the characteristics of CO2 nucleate boiling. The presented CO2 heat transfer coefficients indicate the reduction of heat transfer coefficient as mass flux increases at low quality regions and also show that dryout does not occur until the high quality region of 0.8, for mass fluxes of 200 and 400kg∕m2s. The Gungor and Winterton correlation gives a relatively good agreement with measured data; however it deviates more at lower evaporation temperature and high mass flux conditions.