Experimental measurements and numerical analyses of an automotive evaporator

Flow distribution within heat exchangers such as evaporators is important to understand in order to optimize the design of the evaporator. Maldistribution (non-uniform flow) can lead to problems such as dry-out which negatively impacts performance, therefore a uniform distribution of flow is needed. A full-scale evaporator model was used in this research to measure flow distribution in single-phase and two-phase adiabatic flow within the evaporator geometry. A stereoscopic particle image velocimetry (PIV) system was used to measure flow velocity for single-phase flow and a volume collection technique was used to measure two-phase flow. Distinctly different and often mal-distributed flows were observed experimentally for two-phase flow. Along with the experimental measurements, single-phase and two-phase computational fluid dynamics (CFD) simulations were carried out using commercial software FLUENT. The Algebraic Slip Mixture (ASM) model was used for two-phase flow. Also, analytical single-phase and two-phase models were developed to predict the flow distribution within the evaporator and the results were compared to the experimental results and CFD simulations. Overall, good agreement was found between the experimental measurements and analytical models for single-phase flow and for two-phase flow with a flow quality greater than 1%. The two-phase CFD results using the ASM model did not compare well to the experimental results, instead the two-phase simulation results predicted a nearly identical flow distribution to the single-phase results.;Along with the evaporator research, additional two-phase research was carried out by measuring two-phase velocity profiles in a narrow rectangular channel using PIV. The geometry had similarities to the inlet header of the evaporator and this testing was conducted to develop a two-phase PIV measurement method that could be used for the full evaporator geometry in future testing. A method of seeding the air phase of a two-phase air/water system is described using fluorescent powder paint as the PIV seed particle. Along with experimental measurements in the channel, a different two-phase CFD model, the Volume of Fluid (VOF) model was used to simulate the flow in the same geometry. Wavy two-phase air/water flow was measured and simulated in the channel. Comparison of the experimental measurements and simulation results were generally favorable; however, the VOF model over predicted the velocity of water in the system, likely due to the effective no-slip condition for the VOF model.