flow boiling, minichannels, transient pressure drop, correlation, refrigerant
There is significant interest in the boiling performance of refrigerants in mini- and microchannels, especially in flow geometries relevant to compact heat exchangers for air-conditioning and refrigeration applications. Pressure drop (?P) characteristics during flow boiling of refrigerant R134a have been studied extensively over the past decade; however, in most research ?P is measured over a single channel or multiple parallel channels (manifold to manifold). There has been no work examining the individual pressure drop in each channel in multiple channel design. Moreover, correlations or relationships between the instantaneous ?P in individual minichannels operating in parallel have not been reported. In this work, an investigation of the effect of heat flux, mass flux and inlet vapor qualities on the flow patterns and pressure drop for flow boiling of R134a in 0.54 mm square parallel minichannels is reported. In particular, flow boiling experiments are conducted at flow rates between 0.1 and 0.51 g/s and heat fluxes from 0 to 36 kW/sq.m.. The heat flux input among a set of four horizontal, parallel minichannels is individually varied and controlled in each test. The focus of the work is on the investigation of correlations between flow boiling of R134a in parallel minichannels based on flow visualization and pressure drop measurements in each channel independently.