Experimental heat transfer coefficients and pressure drop during refrigerant vaporisation inside plate heat exchangers

This paper presents the experimental heat transfer coefficients and pressure drop measured during refrigerant vaporisation inside plate heat exchangers (PHE). Two different plates were tested: both present the same macro-scale herringbone corrugation, whereas they have different surface roughness. The smooth plate has an arithmetic mean roughness Ra of 0.4 *m, whereas the roughened plate presents a roughness Ra of 3.6 *m. The prototypes were evaluated in vaporisation tests with refrigerant 22: a set of 34 experimental data was reported. The roughened plate shows an increase in the heat transfer coefficient around 30-40% with a penalty in friction losses around 25-30% with respect to the smooth plate. Present experimental heat transfer coefficients were compared against semi-empirical correlations for pool-boiling: a fair agreement was found with Cooper (1984) and Gorenflo (1993) equations both for smooth and roughened plates.