Flow boiling heat transfer and pressure drop in multiport tube using R134a and R32

Resumo

New environmental policies in the European Union require that emissions of ozone-depleting substances should be decreased in order to reduce the global warming. The refrigeration industry contributes direct or indirectly to those emissions, by that reason in last decades scientists and engineers associated with the refrigeration field have been working to develop more compact, efficient and environmental friendly equipment. The use of multiport aluminium tubes in compact heat exchangers present several advantages that contributes to achieve this purpose, such as high heat transfer coefficients, low mass charge requirements, compactness, and thermal efficiency. For industries, these advantages are profitable to decrease costs, energy and reduce environmental impact. The multiport tubes are considered of great interest for the manufacture of compact heat exchangers which are incorporated into the air-conditioning systems (domestic-automobile) and heat pumps. There are many international researchers working in this field, such as Karayiannis et al., Thome et al. , Garimella et al. The research group of Thermal and Energy Systems Modelling, located at the Technical University of Cartagena have designed two experimental installations to investigate the boiling and condensing flow phenomenon in multiport tubes with some publication in this field . A fundamental issue to optimise the design of compact heat exchanger is the ability to estimate pressure drop and heat transfer coefficient (HTC) for specific required conditions. The aim of this study is characterise the HTC and two-phase flow pressure drop in multiport aluminium tube with diameter of 0.715 mm using R32 and R134a as tested fluids. The experimental ranges considered are: heat flux [0.98-9.30] kWm-2, mass velocity [275-1230] kg m-2s-1, vapour quality [0-0.55] and saturation temperature [5, 7.5, 12.5] ºC. The multiport tube consists in 18 triangular parallel channels