A new parabolic trough receiver design is tested. In this design, the annulus of the receiver is bifurcated such that the half facing away from the parabolic mirror, and receives minimal concentrated sunlight, is filled with an insulating material, whereas the half receiving the majority of the concentrated sunlight is allowed to be filled with air. By insulating the outward facing half of the annulus, heat loss by radiation is minimized. In the mean time, heat loss by natural convection due to the presence of air in the lower half of the annulus is expected to be significantly subdued, since the hotter air will be closer to the heat collection element, which is at a generally higher position than the glass envelope. Experimental tests were performed on roof-mounted troughs which utilize receivers with air-filled annuli. The system consists of two identical but independent rows. The receivers in the first row have normally air-filled annuli, while the receivers in the second row have annuli that are half-filled with an insulating material and half-filled with air. The results have shown that the thermal performance of the modified receiver was indeed superior to conventional receivers with air-filled annuli.

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