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Research conducted at the University of Warwick The file attached to this record is the authors final peer reviewed version. The publisher's final version can be found by following the DOI link below. Experimental studies were carried out to investigate the effects of micro-channel geometry on the thermal and hydraulic performance of absorber plates for compact (thin and light-weight) solar thermal collectors. Three plates with channel depths 0.25 mm, 0.5 mm and 1 mm were studied. Each plate had sixty channels which were 270 mm long and 2 mm wide. Experiments were run at typical operating conditions for flat plate solar collectors. The results showed a Reynolds number dependent Nusselt number; this was due to axial thermal conduction. The Nusselt number was observed to increase as the aspect ratio approached unity. Measured friction factors were similar in trend to the predictions for rectangular channels, although the overall rise in fluid temperature resulted in slightly lower friction factors. The plate with 0.25 mm deep channels was found to have best thermo-hydraulic performance; thermo-hydraulic performance reduced slightly with increase in hydraulic diameter. The results showed that thermal improvement can be achieved by increasing the fluid velocity, however, pumping the thermal fluid above a pump power per plate area of 0.3 W/m2 resulted in marginal improvement. The results are beneficial for the design of micro-channel absorber plates.

The file attached to this record is th authors final peer reviewed version. The publishers version can be found by following the DOI link below. Experimental and theoretical analyses were carried out to investigate the absorber plate temperature distribution for compact (thin and light-weight) solar thermal collectors. An analytic model combining convective heat transfer with axial conduction in the metal plate was developed. Forced convection experiments were then performed on an instrumented metal plate with micro-channels 0.5 mm × 2 mm × 270 mm long, at various flow rates; the heat transfer fluid was Tyfocor® LS. Reynolds numbers were in the range 10–100 and fluid inlet temperatures ranged from 5 to 60 °C. The predicted plate temperature profiles from the analytic model were in close agreement with the measured profiles. Thermal entry lengths were found to be significant and resulted in slight variations at the entry portion of the plate at higher flow rates. The model was used to study the effects of varying design/operating parameters and showed that axial conduction can significantly alter the temperature profile in the plate.

The file attached to this record is the authors final peer reviewed version. The publisher's final version can be found by following the DOI link. 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.