The significance of scaling effects in a solar absorber plate with micro-channels

This paper investigates the significance of some micro scaling effects in micro-channel absorber plates. These plates are to be used in a proposed compact (thin and light-weight) solar thermal flat plate collector (FPC). Forced convection experiments were performed on an instrumented metal plate with micro-channels. Reynolds numbers were in the range 10-100 and fluid inlet temperatures ranged from 5 to 40 °C. Scaling effects such as viscous dissipation and entrance effects had insignificant impact on the measured average Nusselt number. However, conjugate heat transfer and measurement uncertainties were significant. Conjugate heat transfer was found to reduce the Nusselt number which agrees with the literature, this also resulted in a Peclet number dependent Nusselt number. The local Nusselt number was observed to vary axially despite satisfying the criteria for neglecting entrance effects; this variation increased with the Graetz number. It was observed that the position of the thermocouples can result in an under-estimation of the Nusselt number. The results are beneficial for the design and operation of micro-channel absorber plates.