Effectiveness of actively adjusting vapour-liquid in the evaporator for heat transfer enhancement

Abstract

• Active vapor–liquid adjustment is proposed to improve flow boiling heat transfer. • Principles and configuration of vapor–liquid adjustment evaporator are introduced. • Improved heat transfer and reduced pressure drop are simultaneously obtained. • Total temperature penalization ( TTP ) can be reduced by 14.4%. • Enhancement mechanisms of the novel evaporator are clarified. Vapor quality and mass flux are crucial parameters for heat transfer coefficient and pressure drop of flow boiling. In this paper, they are actively adjusted by means of draining and refilling liquid refrigerant in the paths for evaporator performance enhancement. Principles of the vapor–liquid adjustment evaporator are introduced and its corresponding configuration is proposed. The mathematical model of this novel evaporator is established and validated by experiment data. Under different separation efficiencies, inlet vapor qualities and inlet mass flowrates, the vapor–liquid adjustment evaporator (AE) is investigated and compared to the conventional evaporator without vapor–liquid adjustment (CE) from the perspectives of overall performance and local behaviors. At the studied conditions, the improved heat transfer coefficient and reduced pressure drop are simultaneously obtained at a separation efficiency of 40%. Its superiority over the conventional evaporator is generally confirmed in terms of total temperature penalization. However, the excessive separation efficiency leads to the deteriorated performance due to the appearance of superheating. The major differences of local heat transfer coefficient and pressure drop between the vapor–liquid adjustment evaporator and conventional evaporator take place in the first and second paths, which are the consequences of the competition of the enhanced vapor quality and decreased mass flux. The stratified wave flow is mostly encountered for both evaporators. The vapor–liquid adjustment evaporator can be further enhanced by optimization. This study offers an innovative approach for flow boiling heat transfer enhancements.