Experimental Study on Air Side Heat Transfer and Fluid Flow Characteristics of Microchannel Heat Exchanger 2011-01-1166

Microchannel heat exchangers are taken as a great area of research interest for their elevated heat transfer characteristics, higher heating surface area to volume ratio, smaller size, lighter weight, lower fluid inventory and energy efficiency compared to conventional heat exchangers with same heat exchange capacity. Though several investigations have been conducted to find out the air side heat transfer and flow characteristics of common compact cross-flow heat exchangers with various tube and fin geometries, the studies on air side thermal and hydraulic performances of microchannel heat exchangers are rare in open literature. In the present study, the air side heat transfer and fluid flow characteristics of a multiport microchannel heat exchanger in liquid-to-air crossflow orientation were investigated experimentally. Experimental setup is consisted of a closed-loop thermal wind tunnel with a test section of microchannel heat exchanger in crossflow orientation and numbers of measuring instruments with data acquisition system. The microchannel heat exchanger is made up of fifteen extruded aluminum slabs with 68 circular channels in each slab. Slab channels have the inner circular diameters set at 1mm, and the airside frontal area is 304mm × 304mm. Hot water and ethylene glycol 50:50 mixture at a constant temperature of 74°C was cooled by the cold air at different temperatures (23°C, 33°C and 43°C) flowing through the wavy fins of microchannel heat exchanger. The mass flow rate and temperature of the liquid were maintained at a constant level by using a gear pump and an inline circulation heater respectively. The inlet air velocities through microchannel heat exchanger were varied at different temperature levels. The air side Reynolds number, Nusselt number, overall thermal resistance, pressure drop and other key parameters were examined in the region of the air side Reynolds number 750-3165, at a constant liquid side Reynolds number of 200. The heat balance was observed less than 3% for all experimental runs, and the air side thermal resistance range was 74% to 83% of overall thermal resistance. The air side Nusselt number correlation with the Reynolds number was obtained. The air side Nusselt number was found higher in comparison with other studies.