Heat Transfer During Air-Water Two Phase Flow

The effects of air injection on the heat transfer coefficient for the liquid flow in two-phase in microchannels are studied. Different manifolds and microchannel configurations are used for studying the effects of air injection. The manifold has a uniform gap of 400μm between the heater chip and the cover. A manifold is designed and manufactured to provide different air water flow patterns for different combinations of liquid and air flow rates. The effect of these flow rates on the heat transfer coefficient are studied. The flow rate for air injected is kept very small with respect to the flow rate of liquid to create small, uniformly dispersed bubbles in the flow. The air is injected using a syringe pump for regulated and controlled flow of air. The effects of air injected in the form of smaller bubbles distributed throughout the flow are also studied. The effects of air injection on the pressure drop and flow patterns are also studied. The results indicate that the heat transfer performance improves with increasing air flow rates but decreases at higher air flow rates. Area coverage ratio, defined as the time-averaged area covered by liquid on the heated surface is identified as an important parameter and its variation is analyzed for different air and water flow rates.