The comparison of the intensity of heat transfer and pressure drop during boiling of the refrigerants R404A and R22 in horizontal pipes

Abstract
Due to the limited use of R22 there is an issue about the choice of refrigerant for marine refrigeration units operating at the boiling temperatures of –30 ...–45 оС. Alternative refrigerant, along with other properties, must provide high intensity of heat transfer and low pressure drop during boiling in the tubes. The comparative calculations of heat transfer coefficients by the five generalized correlations and pressure drop by the five correlations during boiling R404A and R22 in horizontal pipes for different combinations of the original data are made. It is proposed to compare refrigerants for fixed values of the pipe length and full heat input as, for fixed values of the mass velocity wρ and heat flux q, unequal length evaporative area for different refrigerants are obtained. Comparison with the same pipe length shows that, with all the methods of calculation, R404A provides increased rate of heat transfer compared to R22 and pressure drops ∆РТ do not differ significantly as long as in the inlet of the tube vapor quality хн is the same. Volumetric flow rates of vapor formed during boiling R404A are smaller that suggests the possibility of increasing the cooling capacity of the compressor working on R22.