Three Dimensional Velocity Measurements in an Automotive-Size Evaporator Using Particle Image Velocimetry

The flow distribution inside of an evaporator is important to fully understand in order to optimize the design of the evaporator. A stereoscopic particle image velocimetry (PIV) system was used to measure single-phase water flow in a Plexiglas model of an automotive-sized evaporator. The evaporator is a “U-shape” type. Flow enters the inlet header and travels through a series of 26 parallel rectangular tubes. The tubes have a width of 15.5-mm, a flow gap (thickness) of 0.9-mm, and a length of 231-mm. The flow then enters the upper header and flows through another series of 26 parallel tubes to the outlet header. PIV measurements were only made within the headers due to the small size of the tubes, however detailed results were observed. In addition to the single-phase experimental results, computational fluid dynamics (CFD) simulations were conducted using the commercially available software Fluent, and the results compare well to the experimental results. Further work was conducted by injecting nitrogen into the flow to obtain two-phase flow under adiabatic conditions. Due to high vapor volume fractions, PIV could not be used for flow measurement, but a volume collection method was used to measure the flow of water through each tube. Significantly different flow distributions were observed at different inlet volume fractions of nitrogen and further investigation is underway.