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| Abstract |
Experimental results of the condensation and evaporation of non-azeotropic refrigerant mixtures of R22 and R114 inside a horizontal tube with internal spiral grooves are presented. The test condenser ...and evaporator, which are of the same shape, are tube-in-tube counter flow type heat exchangers. The inner tube is made of copper with a geometry as follows: outer diameter 9.52mm, mean wall thickness 0.60mm, mean inner diameter 8.32mm, groove depth 0.15mm, number of grooves 60, lead angle of grooves 30°. Pure refrigerants of R22 and R114 and three kinds of their mixtures containing about 25, 50 and 75% bulk molar fractions of R114 are tested in the range of refrigerant mass flow rate of 30 to 70kg/s, condensing pressure of 3 to 21 bar, and evaporating pressure of 1 to 7 bar. For the condensation and evaporation of pure R22 and R114 and three kinds of their mixtures, axial distributions of refrigerant, tube wall and cooling water temperatures, wall heat flux, heat transfer coefficient and vapor quality are graphically shown. Circumferential distributions of the condenser tube wall temperature are also shown for pure and mixed refrigerants. The local Nusselt numbers for condensation of pure refrigerants R22 and R114 are higher than those predicted from the previous empirical equation for pure refrigerants in a horizontal smooth tube by 40-70% and 50-80%, respectively. The local Nuseelt numbers of the mixtures are lower than those of pure refrigerants, and the magnitude depends on molar fraction and mass flow rate. The average Nusselt numbers for condensation can be correlated well by the following equation: [numerical formula] where <Nu>^^- is the average Nusselt number, f_y is the function of the bulk molar fraction, l is the total condensing length, d_i is the inner diameter of the tube, H is the phase change number, Re_l is the Reynolds number, Pr_L is the Prandtl number and R is the ρ-μ ratio. The local heat transfer coefficients for evaporation of pure refrigerants R22 and R114 are higher than those predicted from the previous empirical equation for a pure refrigerant R22 in a horizontal smooth tube by 120% and 90%, respectively. The local heat transfer coefficients of the mixtures are lower than those of pure refrigerants, and the magnitude depends mainly on molar fraction.show more
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KJ00004507474