Minichannel tubes have been successfully integrated into automotive, aerospace and HVAC due to their performance superiority and cost effectiveness. Recently, they have also been introduced in the solar thermal industry for similar reasons. Considering the indirect and limited contact area for heat exchange between absorber and fluid in a conventional solar collector, a minichannel tube has the advantage of providing an absorber surface with large heat transfer area and has less thermal resistance. Due to the method of construction, in many cases, minichannel tubes are separated by a few millimeters from each other, leaving a gap in between tubes that wastes collector area. The addition of a back plate to these minichannel-tube collectors will enhance the thermal output as they together provide a larger surface area for absorption. This effectively increases the thermal output. However, the balance between heat transfer and pumping power needs to be analyzed, thereby the need arises to optimize these geometric parameters. This paper attempts to determine these performance values while optimizing the minichannel-tube geometry and back plate width. From energy analysis, it is deduced that a back plate of 40mm width with the corresponding hydraulic diameter for a constant heat exchange width of 100mm maximizes the thermal performance. The exergy analysis further shows that when the back plate width was between 40mm–45mm, maximum of 73% exergy efficiency can be achieved.
Heat Transfer Enhancement Techniques for Solar Air Collector Hater: Review
