Solar thermal tube plate heat exchanger

Abstract

A combination solar absorber and atmospheric radiator in multiple embodiments, a method for constructing these embodiments, and a method for using the combination solar absorber and atmospheric radiator, the absorber / radiator has a thermally conductive sheet which serves as a back plate, tubular fluid conduit or conduits, generally rectangular thermally conductive caps, and a means for fastening the caps to the sheet, covering one or more conduits and pressing them against the sheet. The side of the sheet with the caps and conduits is exposed to the sun and atmosphere, providing two thermal pathways to and from the conduit.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS [0001] The present application claims priority to U.S. Provisional Patent Application No. 60 / 809,878, filed May 31, 2006, the teachings of which are incorporated herein by reference.BACKGROUND OF THE INVENTION [0002] The present invention relates to solar thermal tube-plate heat exchangers. [0003] The external surface of buildings receives solar energy. Most of the received solar energy is transferred passively to the building by heating up the walls, the roof and other exposed external surfaces of the building. Roofs and walls face the sky, protect against the sun, the cold and the rains, but roofs and walls make little use of the sun, the night's coolness or evaporative cooling. Some have taken advantage of the available solar energy by developing devices that actively harness the solar radiation. Solar flat-plate collectors are one example of such devices. [0004] Flat plate thermal solar collectors have been developed to take advantage of ...

AI Technical Summary

Benefits of technology

[0008] It is an unexpected advantage of the various embodiments of the apparatus that it is not necessary to use optimally thermally conductive materials for any particular embodiment of the apparatus to operate effectively. Fastening tubular fluid conduit or conduits and caps close together to a large area of a relatively poorly conductive sheet can often provide sufficient heat transfer to and from the sheet. By tightly enclosing the tubular fluid conduit or conduits and fastening them to the sheet, the contact of the tubular fluid conduit or conduits with the cap or caps and the sheet is optimized.

[0009] Although the apparatus in accordance with the embodiments of the present invention can collect or radiate the most heat from a given area of roof or wall, the demand may be less than what the building can supply. In many cases it is more economical to space the tubular fluid conduits far apart across the entire roof or wall than to place them close together on a part of it. Instead of investing in 1,000 feet of tubes or hoses or pipes which would then be spaced 6 inches apart across a roof or wall of 0.032 inch aluminum, it is more economical to use only 800 feet of tubes spaced 12 inches apart. Placement of tubular fluid conduit or conduits on metal roofs and walls is guided by getting the most energy with the least additional expense. The heat exchangers of radiator / absorbers that are described herein can use the roofs and walls of buildings and thus the investment in metal skin, back insulation and support structure has been made before using the roof or wall to give or take heat. The additional use of the wall or roof by adding metal caps, tubular fluid conduit or conduits and headers is much less expensive than the total cost of the usual solar absorbers or radiators.

[0010] The cap or caps provide numerous additional benefits to the embodiments of the apparatus. By mechanically constraining a tubular fluid conduit or conduits, they are prevented from runaway expansion if the fluid in them freezes, since a tubular fluid conduit is more prone to aneurysm if its radius has expanded; e.g., see U.S. Pat. No. 5,143,053 (Baer). Because the cap or caps can be fastened to the sheet with relative ease, such as by threaded fasteners, adhesives and epoxies, rivets, soldering, welding, nailing and snapping-on, the embodiments of the apparatus are very easy to construct or modify in the field as well as in the shop. The cap or caps improve the efficiency of the embodiments of the apparatus, for when the caps carry heat parallel to the plate below, they lessen the steep temperature gradient that afflicts other plate collectors near the tubular fluid conduit or conduits. It is not necessary for the cap or caps to be in thermal contact with the sheet; even without such thermal contact, a cap absorbs or dissipates heat that would otherwise have to be absorbed or dissipated by the area of the thermally conductive sheet in contact with the tubular fluid conduit or conduits.

[0012] Some of the benefits of using plastic or rubber tubes or hoses are that they are inexpensive, they readily conform to the cap or caps, and they can be rapidly cut to proper length on site. Polyethylene is inexpensive and thermally conductive. Because plastic and rubber tubes are sold in rolls of flat tube, they do not take up space at the work place. Rubber tubes in particular are freeze tolerant, but the tubular fluid conduit or conduits utilized generally do not need to be freeze tolerant. The inventors herein have found that the flexing of the metal or steel sheet and cap provides freeze protection where the metal is 26 gauge steel.

[0013] Some embodiments, such as those deployed on roofs, can avoid freezing, due to the drain back of the fluid; whenever a freeze threatens, the water drains out of the absorber and into storage.

Problems solved by technology

Another loss in efficiency in flat-plate collectors is due to the presence of sharp temperature gradients which afflict flat-plate collectors near the tubes.

Another disadvantage of flat-plate collectors is that the tube-plate surface needs protection from wind and rain and other elements.

As such flat-plate collectors have sturdy enclosures, which detract from their overall thermal efficiency and add to their mounting and fastening demands.

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