Question 5 Solar thermal power plants usually work by concentrating the sun\'s r
ID: 1766637 • Letter: Q
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Question 5 Solar thermal power plants usually work by concentrating the sun's radiation onto a central collector. To reduce loss the receiver must be of a small area so as not to radiate too much heat away. This causes problems as a huge amount of heat needs to be transferred from a small area. A novel way around this problem is to use a small opening or aperture as shown in the figure below. A mirror farm focuses beams through a small opening into a large enclosure. This allows a large area for heat transfer to a working fluid to take place but only allows a small opening where heat can radiate away from. You may assume the aperture opening radiates back to the surroundings as this area is large compared to the mirrors. You may assume that the available incoming solar radiation is 1000 [W/m]. The enclosure is to be kept at 1000 [eC] while the surroundings are at 30 [oc]. The enclosure is to deliver a final 200 [MW1 of heat to the power plant after all losses i) What can a hole with a small opening and large volume behind it be treatedstorage as (radiatively)? Cross section and heate Turbine air out Compresor air in Inlet aperture Mirror farmExplanation / Answer
The small opening and the large volume behind it can be treated as a Black Body (radiatively).
The reason for this is that we require minimum heat to be lost and escaped form the opening. The inner surface of the enclosure are lined with heat absorbing material so heat radiation once entering from the apperture would keep reflecting in the enclosure and a very small part of it will escape from the aperture.
This system as the whole accepts large heat quantities and radiates back almost negligible amount of heat which is a characteristic feature of a Black Body - absorbtivity = 100%
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