Heat transfer and pressure drop during HFC refrigerant vaporisation inside a brazed plate heat exchanger

Abstract

This paper presents the experimental heat transfer coefficients and pressure drop measured during HFC refrigerant 134a, 410A and 236fa vaporisation inside a small brazed plate heat exchanger: the effects of heat flux, refrigerant mass flux, saturation temperature, outlet conditions and fluid properties are investigated. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. The heat transfer coefficients show great sensitivity to heat flux and outlet conditions and weak sensitivity to saturation temperature. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow. HFC-410A shows heat transfer coefficients 40–50% higher than HFC-134a and 50–60% higher than HFC-236fa and frictional pressure drops 40–50% lower than HFC-134a and 50–60% lower than HFC-236fa. The experimental heat transfer coefficients are compared with two well-known equations for nucleate boiling [M.G. Cooper, Heat flows rates in saturated pool boiling – a wide ranging examination using reduced properties, Advanced Heat Transfer, Academic Press, Orlando, Florida, 1984, pp. 157–239; D. Gorenflo, Pool boiling, in: E.U. Schlünder (Ed.), VDI Heat Atlas, Dusseldorf, Germany, 1993, Ha1-25] and a correlation for frictional pressure drop is proposed.