Experimental heat transfer coefficients during refrigerant vaporisation and condensation inside herringbone-type plate heat exchangers with enhanced surfaces

This paper presents the experimental work carried out to apply ‘‘cross-grooved’’ surfaces to refrigerant vaporisation and condensation inside plate heat exchangers (PHE) with herringbone macro-scale corrugation. This paper also investigates the effect of an increase in the surface roughness of the plate on refrigerant two-phase heat transfer inside PHE. The enhanced surfaces are experimentally evaluated both in vaporisation and condensation tests with refrigerant 22, and compared against a PHE with a smooth surface. The experimental results show that the ‘‘cross-grooved’’ surface is useful both in vaporisation and condensation, whereas the increase in surface roughness is useful only in vaporisation. The ‘‘cross-grooved’’ surface gives an increase in the heat transfer coefficient from 30% to 40% in vaporisation to 60% in condensation with respect to a PHE with a smooth surface. The enhancement in heat transfer coefficient is higher than the simple increase in heat transfer surface area. A fair agreement was found between present experimental data and semi-empirical correlations both for condensation and vaporisation inside PHE.