Stoves and furnaces – Tool having fluid fuel burner – Curling iron
Patent
1981-06-17
1984-02-21
O'Connor, Daniel J.
Stoves and furnaces
Tool having fluid fuel burner
Curling iron
126449, 165170, F24J 302
Patent
active
044323468
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a solar collector having an improved radiation and convection-suppressing structure.
The heat losses from a planar or moderately concentrating solar collector mainly take place through the front surface or window of the solar collector, and may be separated into three different components, viz. radiation losses, convection losses and conduction losses. The losses through conduction as a rule are small and may often be neglected in comparison with the two others. Great efforts are therefore made to suppress heat losses through convection and radiation.
In order to reduce the radiation losses several transparent layers may be placed in front of the sunlight absorbing surface. Indeed, it is more difficult for the sunlight to pass, if the number of transparent layers are increased, but since the latter as a rule absorb the heat radiation from the sunlit and warm absorber, the radiation losses may be reduced to such an extent that they more than balance the transmission losses. Simultaneously the convection losses, i.e. the losses due to the air of gas flow between the absorber and the transparent layers, between the transparent layers, and between the outer layer and the surrounding, are decreased if the number of transparent layers in front of the absorber are increased.
The radiation losses may be further reduced, if the absorber is provided with a specific surface coating making the absorber surface radiate heat to a lesser extent than if the absorber is painted with "ordinary" black colour. Such so-called wavelength selective surfaces will, due to the low heat radiation emitted from the surface, be heated to much higher temperatures than a non-selective absorber surface. Since the temperature difference between the absorber surface and an above located glass, or equivalent, hereby is greater, the heat flow or convection is also increased, but the total heat losses at a certain temperature level are reduced with a selective absorber surface. The heat losses may also be reduced by coating the transparent layers in front of the absorber with a heat reflecting film which is transparent to sunlight. By combining the above described measures the heat losses can be minimized in a suitable manner. One must, however, always weigh these measures against their effect on the transmission and absorbed proportion of the incident sunlight.
An ideal plane solar collector could be described as having, in addition to a good insulation backwards and along the sides, a transparent sheeting of mineral wool in front of and in contact with the absorber as well as with an outer transparent plane layer, e.g. a glass pane. In such a way both heat radiation and convection losses from the absorber are efficiently prevented. Sufficiently transparent mineral wool sheetings do, however, not exist. As a substitute plastic or glass tube structures have been placed between and in direct contact with the absorber and the outer transparent cover, or only against the absorber without any outer cover, the tubes or cavities of said structures extending perpendicularly to the absorber and the outer glass or plastic window in parallel to the absorber. Such structures may have the form of a honeycomb like structure (see FIG. 1) which is placed on the absorber. An outer glass or plastic cover is then placed against the plane outer face of the honeycomb structure. Since the ducts, which thus extend from said window and essentially perpendicularly towards the absorber, are designed with a high ratio between the length and effective diameter of the ducts, typically greater than 5, the convection is efficiently suppressed. A complication is, however, that either the absorber or the outer transparent cover must connect closely against the convection suppressing structure to make the intended convection suppression efficient. Since the absorber usually is easier to manufacture and can be made more effective, if the liquid or gas filled heat transport ducts are placed centrally in the absorber, such that the tubes or ducts
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Karlsson Arne V.
Westerstrandh Bjorn V.
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