UNDERGRADUATE RESEARCH

I have worked as an undergraduate researcher under PhD candidate Jingwei Zhu and Professor Elbel for the past two years. 

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The research I worked on studies removing the expansion valve in the vapor compression cycle and replacing it with an ejector. There is a significant efficiency increase with this replacement due to several things. First, that is because the ejector mixing chamber enables liquid recirculation. This can improve the evaporator performance because the ejector sends more liquid to the evaporator than is actually evaporated. As a result, dryout in the evaporator can be reduced. Second, the ejector can also improve refrigerant distribution for evaporators with inlet headers. Two phase refrigerant can result in non-homogeneous distribution of two-phase flow into the parallel channels. The ejector sends only single-phase liquid to the inlet headers. Due to these reasons, liquid recirculation results in higher evaporation pressure, and this results in higher system COP compared to a direct expansion cycle. However, the efficiency is only significantly increased with set conditions which is not ideal for an ever changing ambient environment; changing environments decreases the ejector efficiency.

The way to combat loss of efficiency due to changing conditions is to change the nozzle diameter thus controlling the mass flow out of the nozzle, depending on the condition. However, changing out the nozzle every time the conditions change is expensive and not feasible. There needs to be a way to have control over the mass flow out of the
nozzle so that the ejector system can be adaptable to all kinds of working conditions. My contribution focuses on a different way to control mass flow out of the nozzle by adding a tangential flow inlet thus creating a vortex or “swirl” effect at the nozzle inlet. This influences the mass flow out of the nozzle and gives control over nozzle restrictiveness without altering the physical geometry of the nozzle.