Single-phase and two-phase flow pressure drop in the vertical header of microchannel heat exchanger

•This paper explores single-phase and two-phase pressure drop in a vertical header.•Previous single-phase pressure drop correlation works well for single-phase vapor.•A new correlation for single-phase liquid is derived based on this study results.•Two-phase ΔPpro is related to single-phase vapor ΔPpro by a two-phase multiplier.•The multiplier is related to vapor mass flux in the header immediately upstream.

Refrigerant maldistribution among parallel microchannel tubes deteriorates the performance of microchannel heat exchanger because it creates unwanted superheated region that has lower heat transfer. Besides phase separation in the header, the pressure drop in the header causes the pressure drop in the microchannel tube to be different between each tube, also resulting in flow rate maldistribution. This paper experimentally investigates the pressure drop of single-phase and two-phase flow in the vertical header of a multi-pass microchannel heat exchanger. The overall pressure drop in the header includes four components: acceleration, gravitation, friction, and minor pressure drop due to microchannel tube protrusion. The gravitation and minor pressure drops are dominant for single-phase liquid flow and at low qualities of two-phase flow, whereas the acceleration and minor pressure drops are dominant for single-phase vapor flow and at high qualities of two-phase flow. The model to predict the overall pressure drop in the header for single-phase and two-phase flow is proposed based on the experimental results.