Heat insulating window

July 6, 1965

3,192,575

M. D. ROSEN AU, JR., ETAL

HEAT INSULATING WINDOW Filed July 25, 1962

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INVENTORS.

Rliiion J). Ro sett ou, Jr.

Roderic //. Seo 11 ^BY Pau I F. For near

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attorney:

3,192,575

Patented July 6, 196S

United States Patent Office

192 575 HEAT INSULATING WINDOW Milton D. Rosenau, Jr., Georgetown, Roderic M. Scott, Stamford, and Paul F. Forman, Ridgefield, Conn., assignors to The Perldn-Eimer Corporation, Norwalk, Conn., a corporation of New York

Filed July 25, 1962, Ser. No. 212,350

Claims. (Cl. 20—56.5)

This invention relates to a window which insulates one side thereof from the heat energy present on the other side. More specifically, the invention provides a transparent window which, by means of selective reflection, vacuum insulation, and forced fluid cooling, is able to maintain the area behind the window comparatively cool even though the other surface of the window is exposed to extremely high temperatures and intense infrared radiation.

Generally, the device comprises a plurality of transparent panes, v/hich are in spaced parallel relation. A vacuum may be maintained between one pair of these panes while forced fluid cooling may be utilized to cool one or more of the surfaces of these panes. The fluid utilized for this cooling, which is preferably a gas (e.g., air), is maintained between a pair of surfaces of these panes, which pair are preferably positioned on the side of the vacuum remote from the hot side of the window. In addition, means for filtering out infrared radiation are utilized. Preferably, this last mentioned means is a thin coating (for example, of gold) which has the property of reflecting much of the infrared radiation while transmitting most of the radiation in the visible range.

An object of the inventon is the provision of a window which has the property of insulating the area on one side from the intense heat and infrared radiation which may be present on the other side in a more efficient manner than prior art windows, while still remaining highly transparent to visible light.

Other objects and advantages will be apparent to those skilled in the art upon reading the following specification and the accompanying drawing in which:

The sole figure is a cross section through a specific embodiment of a window illustrating the invention and showing the mounting means therefor.

In the drawing the window of the invention is shown as being composed of three spaced panes 10, 20, and 30. Pane 10 is the outer pane, that is the one exposed to the intense heat and radiation existing on the exterior of the lowermost surface 12 thereof. The intense heat may be caused, for example, by the air friction when the window of the invention is utilized as part of the surface of a supersonic airplane or other flying craft. Of course, the window may be utilized in many other applications in which it is desired to insulate one area from intense heat and radiation caused by any means while still allowing viewing therethrough. In order to enable this first pane 10 to withstand high temperatures, a material which is resistant to such temperatures should of course be used. For example, pane 10 may be made of fused silica.

Between the inner surface 14 of this first pane 10 and the adjacent surface 22 of the second pane 20 an evacuated area 16 is maintained. Because of the vacuum 16 existing between panes 10 and 20, pane 20 is shielded from the heat of outer pane 10 which might otherwise reach it by either conduction or convection. The entire surface of pane 20 adjacent to the vacuum is coated with a material which is highly reflective of infrared radiation, as shown at 22. This coating 22 may be a thin layer of gold formed on pane 20 by means, for example, of evaporation techniques. Between the inner surface 24 of the second pane and the outer surface 32 of the third or innermost pane 30, a flow of fluid, such as air or other gas is maintained, as schematically represented by arrows 28. This gas flow cools intermediate pane 20 and may be caused by pressurized air or other gas emanating from nozzle 40 of pressure tube 42. In order to assist in causing this air to flow over upper surface 24 of pane 20 in a laminar manner, an exhaust or outlet tube 44 is preferably provided at the end of space 26 remote from air pressure nozzle 40. This exhaust tube 44 may have a funnel-shaped entrance as shown at 46. Intermediate pane 20 is preferably made of fused silica or other heatresistant material while inner pane 30 may be fused silica or ordinary glass.

Although the means for mounting the three spaced panes is not critical, one of the possible holding devices which may be utilized for this purpose is illustrated in the figure. This mounting means may comprise a peripheral gasket 50 composed of a comparatively resilient and heat insulating material such as a moderately soft synthetic resin or rubber. Where the overall shape of the window is circular, this gasket 50 would normally be made in one piece; however, where the window is square or rectangular, gasket 50 may be either one integral piece or made in four separate straight pieces joined together at the corners of the window. This gasket 50 seals both the outer surface 12 of pane 10 and the two facing surfaces 14, 22 of panes 10 and 20 which contain the vacuum 16 in a hermetic manner. It is not necessary that the gasket be this tight against the inner surface 24 of the intermediate pane 20 or either surface 32 or 34 of the inner pane, since isolation of the exterior air and of the vacuum is accomplished by the above-mentioned hermetic sealing. The element which contains this gasket is shown at 52 and may comprise either the existing wall of the airplane or other structure or may instead be a mounting or clamp ring installed in an opening in the outer surface of the plane.

The gas flow 28 in the space 26 is preferably laminar, as mentioned above, since any turbulence would tend to cause a certain amount of adverse effect on the view provided when looking through this window. Since one of the primary uses of the invention is to provide a window which is suitable for the taking of photographic pictures therethrough, it is quite important that the turbulence in the gas flow be minimized in order to avoid any degradation in the photographic image. When the invention is utilized as the outer window in a supersonic airplane, the area immediately inside this window (i.e., above the inner surface 34 of the inside window pane 30) may be maintained substantially at room temperature even though the outer surface 12 of the outer pane 10 may be raised to tempeartures as high as 1000° F. by air friction.

The window operates so as to effect this high degree of insulation between the area outside (i.e., below outer pane 10) and the interior side (i.e., above inner pane 30) in the following manner. Friction and incident radiation will tend to heat the outer pane 10 to extremely high temperatures when the window is utilized in supersonic aircraft. In time not only will the outer surface 12 of the first pane 10 be heated by friction with the atmosphere, but the entire pane including its inner surface 14 will become very hot from this heat as it is conducted through the pane. The vacuum 16 therefore acts to inhibit the transfer of heat from outer pane 10 to any part of the intermediate pane 20 which would otherwise occur by either conduction or convection. The gold or other metallic coating 22 on the outer surface of the intermediate pane 20 reflects most of the infrared radiation reaching this surface either directly from the outside or as re-radiated by outer window 10. However, this gold coating is sufficiently thin so as to allow the transmission

3,192,575 therethrough of most of the radiation in the visible part of the spectrum. Although most of the heat is therefore isolated from the main body of pane 2®, nevertheless this pane will tend to reach a temperature substantially above room temperature even though much lower than the temperatures of the outer pane 1®. One of the causes of this moderate heating of middle pane 2® is the partial absorption of infrared and other rays by the gold coating. Since this pane 20 will, therefore, eventually become somewhat warm even at its inner surface 24, the forced air draft along this surface will maintain the entire pane at comparatively low temperature by dissipating this heat. Therefore, the inner pane 30 will be maintained quite cool. This is caused by two factors. First, the temperature of the intermediate pane 20 is thereby maintained at a much lower temperature than it would be without the air cooling; and second, any of the residual heat of the intermediate pane which would otherwise be transmitted to inner pane 3® by either conduction or convection is actually carried away by the air fiow. By maintaining this cooling gas flow in a laminar manner no adverse effect on the images received at the inside of the window will be caused.

As previously stated, one of the main uses contemplated for the invention is as a photographic window in a high speed aircraft. By maintaining a temperature difference which may be as great as the difference between 1000° F. and 70° F. between its two most remote surfaces while still allowing transmission of most of the visible light without any variable refraction thereof, the device is especially suited for this use. . However, the window may be utilized wherever it is desirable to maintain a large temperature differential while still allowing an optically true viewing therethrough. Thus, other uses of the device would include it being used as a furnace window, particularly in laboratory or similar scientific environment where an undistorted view of the furnace interior is desirable.

Because of these various other uses and the changes in detail which may be made by one skilled in the art to adapt the illustrated preferred embodiment to varying conditions, the particular window described and illustrated is intended to represent only one manner in which the invention may be utilized. For example, the number of panes may be increased from three to any reasonable number to allow repetition of either fluid cooling, similar to that occurring between panes 20 and 3®, or vacuum isolation, similar to that occurring between panes 1® and 20. Similarly, more than one reflective coating (like 22) may be used, either on the other intermediate surfaces of the illustrated three-pane embodiment or on one or more of the surfaces of the additional intermediate panes that may be utilized in an embodiment having four or more panes. The invention is therefore not intended, nor should it be, limited to any of the details of the preferred embodiment specifically described, but rather is defined solely by the scope of the appended claims.