Effect of non-uniform air velocity distribution on evaporator performance and its improvement on a residential air conditioner

Abstract

The effect of non-uniform air velocity distribution on performance of a multi-circuit evaporator was studied numerically and experimentally. The non-uniform air velocity distribution on evaporator was measured experimentally, and its corresponding evaporator performance was tested and approximated numerically. The evaporator performance was also investigated numerically at the equal airflow rate but under uniform air distribution. The results showed that the evaporator capacity under non-uniform air distribution was decreased by 7.78% than that under uniform air distribution. The decrease in evaporator capacity was mainly attributed to smaller overall heat transfer coefficient of lower tubes with smaller air velocity in first row because overall tube heat transfer coefficient varied remarkably at smaller air velocity and gently at greater air velocity. Two triangle air guide plates were installed on sheet backing of evaporator to deflect part of airflow towards evaporator bottom to increase air velocity of lower tubes and to decrease the area that smaller air velocity covered. The experimental results showed air guide plates decreased blend loss of high temperature air leaving upper circuits and low temperature air leaving lower circuits, thus decreasing outlet air dry and wet temperatures. Finally, the cooling capacity and EER were increased by 3.02% and 5.1%, respectively. ► Evaporator performance between non-uniform and uniform air distributions are compared. ► Evaporator capacity under non-uniform air distribution decreased by 7.78%. ► Overall heat transfer coefficient was a dominant factor of evaporator capacity decrease. ► Air guide plates on sheet backing of evaporator could improve evaporator performance.