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1947-48 Theatre Catalog, 6th Edition, Page 422 (408)

1947-48 Theatre Catalog, 6th Edition
1947-48 Theatre Catalog
1947-48 Theatre Catalog, 6th Edition, Page 422
Page 422

1947-48 Theatre Catalog, 6th Edition, Page 422

which has been modified slightly from his original drawing.

A large area is covered by overlapping sheets of glass and enclosed within heat insulating walls. Solar heat impinges on the upper glass, part of it is multiply reflected back towards the sky, part is absorbed by the glass, and the remaining transmitted portion impinges on the black surface of the opaque glass where it is absorbed and changed to heat. As the black surface absorbs heat, its temperature rises, and it re-radiates in the far infra-red region to which radiation glass is opaque.

Air is drawn slowly between the glass plates. This air at base temperature picks up the solar heat energy absorbed in the glass. This air is passing counterfiow to the heat flow by conduction through and along the glass plates and by radiative heat transfer upward between them. Thus, most of the heat attempting to escape upward from the high temperature end of the opaque glass plate is picked up by the air stream which, therefore, enters the opaque glass section at an elevated temperature. Very

important is the fact that this air flow maintains the upper glass plates at a temperature not much greater than the air temperature. This re-radiation of heat energy back toward the sky from the upper glass is very materially reduced, since, quantitatively, it is proportional to the fourth power of the absolute temperature of the outer glass sur-, face.

Miller has made a mathematical analysis of the operation of the abovedescribed solar heat trap and has derived equations for use in the calculation of the possible heat recoveries and temperature levels of heat collection. The equations showed that exit air temperatures of 300 degrees Fahrenheit could easily be obtained in a unit built as shown and described in Figure 1. It was assumed, however, that no convection losses took place at the cover plate surface and that no heat loss by conduction through the sides or floor of the unit. These assumptions, along with the basic one that streamline fiow prevails, make the actual predicted numerical results questionable even though their

FIGURE 2*The indoor laboratory (experimental) unit was built to obtain design information to aid in the selection of the proper glass plate arrangement in the proposed outdoor unit. The unit consists of a well-insulated rectangular box. Air at room temperature enters at one end of tlte unit and passes through a finned tube air heater and mixer and into the duct for subsequent utility.



general order of magnitude may be correct.


The investigation of the collection and utilization of solar heat by the method which involves the use of overlapping glass plates as suggested by K. W. Miller was taken up in three phases.

The first phase consisted of building an experimental collection unit and an artificial light source indoors. Tests on this unit were to furnish such information as general workability, optimum plate spacing, optimum overlap, optimum plate length, and optimum air rate.

The data made available through the indoor unit studies were used in the design of a larger heat collection unit which was constructed on the south roof of the laboratory, and the data were checked under natural sunlight. The effect of changing solar angles was studied along with the effect of clouds and haze. Exit air temperature and over-all heat recovery were correlated with air rate and other operating variables.

These two phases being completed, the final phase of the investigation was to place a typical unit in operation in a local home and determine its usefulness in supplying heating requirements.

Indoor Experimental Unit

The indoor solar heat collection unit was built for the purpose of obtaining design information to aid in the selection of the proper glass plate arrangement in the proposed outdoor unit. Only a brief summary is given here because the work with the indoor unit yielded only preliminary design results.

The unit consists of a rectangular box 21/2 feet wide, 12 feet long, and 11/2 feet deep, well insulated against heat loss. Air at room temperature enters one end of the unit and passes through a tinned tube air heater where its temperature is adjusted to the desired value by allowing steam, or water, or a mixture of both, to flow on the inside of the tubes. After leaving the air heater, the air passes through a short section of duct of reduced cross section where it is thoroughly mixed and its temperature measured by a high-velocity ironconstantan thermocouple. The air in the mixing chamber is protected from direct radiation from the light source by partitioning the duct and drawing a stream of air through the upper half; this insulating air, after being partially heated by radiation from the source, is discarded into the room. The air leaving the mixing chamber enters the heat collection chamber through a perforated baiiie. (Figure 2.)

The heat collection chamber consists of a number of glass plates, defining a plurality of zones or passages through which the air is passed. These plates are arranged in staggered relation to each other and lie in a horizontal position. A section of the top surface of each plate adjacent to the trailing edge was made opaque by the use of black paint, and the corresponding bottom surface was coated with a layer of aluminum foil. This assembly is sealed from above by a continuous sheet of glass laid into a cover support. The construction is similar to that of the outdoor unit described in a later section where further details are presented.

An artificial source of solar energy

1947-48 Theatre Catalog, 6th Edition, Page 422