Convective Boiling Heat Transfer of Pure and Mixed Refrigerants within Plain Horizontal Tubes: An Experimental Study
Pp. 216-303 (88)
An experimental study is carried out to investigate the characteristics of the evaporation heat transfer for different fluids. Namely: pure refrigerants fluids (R22 and R134a); azeotropic and quasi-azeotropic mixtures (R404A, R410A, R507). zeotropic mixtures (R407C and R417A). The test section is a smooth, horizontal, stainless steel tube (6 mm I.D., 6 m length) uniformly heated by the Joule effect. The flow boiling characteristics of the refrigerant fluids are evaluated in 250 different operating conditions. Thus, a data-base of more than 2000 data points is produced. The experimental tests are carried out varying: i) the refrigerant mass fluxes within the range 200 - 1100 kg/m2s; ii) the heat fluxes within the range 3.50 - 47.0 kW/m2; iii) the evaporating pressures within the range 3.00 - 12.0 bar. Experimental heat transfer coefficients and pressure drops are evaluated varying the influencing parameters. In this study the effect on measured heat transfer coefficient of vapour quality, mass flux, saturation temperature, imposed heat flux, thermo-physical properties are examined in detail. The effect on measured pressure drops of vapour quality, mass flux, saturation temperature and thermo-physical properties are examined. In this chapter the attention is focused also on the comparison between experimental results and theoretical results predicted with the most known correlations from literature, both for heat transfer coefficients and pressure drops.