Experimental analysis of flow boiling heat transfer in multimicrochannel evaporators

This paper provides an experimental analysis of flow boiling heat transfer in multichannel evaporators. This technology is an emerging cooling solution for high heat flux applications, which has raised a rapidly growing interest in recent years in the field of thermal management, especially for power electronics devices. In fact, it has numerous advantages compared to traditional cooling systems, allowing the use of lower fluid flow rates and a more efficient heat transfer, also guaranteeing a high degree of isothermality over the cooled surfaces. In the present study four finned evaporators with different aspect ratio and heated length have been tested. R245fa was the refrigerant chosen as working fluid for its good thermal characteristics. The imposed heat flux at the footprint covered a range from 30 to 330 kW/m2, while the fluid mass fluxes within the channel varied in a range between 17 and 225 kg/m2 s. The hydraulic diameters of the investigated evaporators were 1.15 mm and 2.09 mm, with aspect ratio (channel width/channel height) respectively of 0.3 and 0.72. Thanks to the measuring apparatus, heat transfer data were collected and then processed to calculate the local heat transfer coefficients, using the fin array heat transfer model. These local values of the heat transfer coefficient were then compared with those calculated from existing correlations for mini-micro channels flow boiling and the Mean Absolute Percent Error was finally assessed.