Solar Collector Performance- Test of My Dryer
Solar radiation received by the solar collector during the tests was measured by the pyranometer located next to the collector at the same pitch. The pyranometer output was connected to the data logger and recorded every 10 minutes. However, it was difficult to obtain steady radiation levels due to intermittent cloud cover and frequent movement of clouds. The ambient temperature was measured with a probe located in the inlet of the collector and was assumed to be equal to inlet air temperature.
Preliminary tests conducted indicated that the temperature profile across the width of the collector was uniform. In the test, therefore, the temperature was measured just in the centerline along the length of the collector at three points. The measurement points were located at 10 cm from the inlet side, at the center, and at 10 cm from outlet side of the collector, respectively. The temperature measurements were also measured at the bottom plate, in the air stream, and at the absorber plate.
The experimental results of the diurnal variation of temperatures of the solar collector outlet air, absorber, ambient, and solar radiation are presented in Figures 6.5 and 6.6. Data for a typical day-June 28, 2005 - is shown in Figure 6.5. During the day the solar radiation was relatively low, varying from 200 – 900 W/m², and fluctuated considerably due to moving cloud. However, the rise in air temperature due to the generated air flow rate in the collector was sufficient for the purpose of drying most agricultural products. For the inlet air temperature (ambient temperature) of 40oC, the maximum outlet air temperature was recorded as 56oC at the solar radiation level of 960 W/m2.
Figure 6.6 shows another data for one typical day of February 8, 2005, one of the early days of the dry season in the region and the solar radiation was less fluctuating. The maximum outlet air temperature recorded was 76oC at the solar radiation level of 1000 W/m2 and an ambient temperature of 40oC. Comparison between Figure 6.5 and Figure 6.6, shows that the low and modestly fluctuating solar radiation due to moving clouds, as is typical for the tests in February-March, significantly effects the air temperature at the collector out let
