FIELD OF THE INVENTION

This invention relates to a plate type heat transfer device having a number of rectangular or oval cavities(or cells) in its cross-section which can be operated as a thermal rectifier or a plate of a uniform surface temperature. A certain amount of a working fluid is charged in each of the cavities as the heat transfer medium. The fluid transfers heat from the lower surface of the plate to the upper surface of the heat transfer device.

BACKGROUND OF THE INVENTION

The principle of this invention is that the fluid in the lower part of the cavities is vaporized by heat conducted through the lower surface of the heat transfer device. The vapor which moves up to the upper part of the cavities is then condensed by cooling at the upper surface of the heat transfer device and consequently the latent heat of vaporization is transferred to the outside through the upper surface of the cavities.

Heat is, therefore, transferred from the lower surface of the cavities by the evaporation of the working fluid to the upper surface of the cavities by the condensation of the vapor in the presence of gravity. Since heat can not be transferred from the upper surface of the heat transfer device to the lower surface of the device, it can act as a thermal diode.

When the fluid is condensed, it flows down along the walls of the cavities to the lower part of the cavities in the presence of a force field such as gravity because the density of the liquid phase of the working fluid is heavier than that of the vapor phase of the working fluid.

Therefore, when the plate type heat transfer device produced according to the present invention is installed in a place, heat is transferred only from the lower side to the upper side of the device and can not be transferred effectively

in the reverse direction.

The heat transfer mechanism in the present invention employing the latent heat of vaporization of a working fluid is similar to that of the thermosyphon as described in U.S. Patent 2,350,348.

5 However, because the structure of the heat transfer device by the present invention is quite different from that of the thermosyphon, the heat transfer route is different from that of the conventional thermosyphon. Conventional thermosyphons are made from tubings which have a relatively small area in the direction of heat flow due to the small diameter of the tubings used. In such i c conventional thermosyphons, heat is transferred into the tube through the side wall of the lower part of the tube containing the fluid and heat is removed through the side wall of the condensing part located in the upper part of the thermosyphon. Therefore, the conventional thermosyphon has disadvantages if it is to be applied to the situation where the area of heat transfer or the area is which has to be maintained at a uniform temperature is relatively large irr comparison to the area of the thermosyphon in the direction of heat flow.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a plate type heat transfer

:-c device which absorbs heat at its lower surface and transfers heat out through its upper surface. The heat transfer device can be applied to a wide area of engineering practice with a high thermal efficiency.

One of the application of the proposed heat transfer device is a plate type "thermal diode" to be used for stabilization or protection of foundation for pipes is lines, roads, airport runway, structures etc. by keeping the foundation frozen in extremely cold regions. With a conventional thermosyphon, it requires a large number to achieve the same degree of thermal effectiveness as with the plate type heat transfer device of the present invention. Furthermore, for conventional thermosyphons. it is also required to have a part of the

thermosyphon be exposed to the atmosphere.

With the plate type heat transfer device of the present invention which is completely buried in the ground, one plate can cover a large area of the road or the air field to keep the foundation frozen in extremely cold regions. Since

5 there is no exposed part of the heat transfer device, the problem of the damage to the condensing section of the device, due to any number of causes, can be completely eliminated and thus the complete loss of heat transfer performance of the device can be avoided.

Another example for the application of the plate type heat transfer device t o of the present invention is to apply the device to the ceilings or floors of relatively large spaces, such as office buildings, manufacturing factories, storage buildings, or even to the roofs of refrigerator cars where the temperature control is required. The operating cost of the device in such application will be almost negligible compared to the conventional systems. i s The present plate type heat transfer device can be manufactured by extrusion or rolling process which is known to yield a high productivity. The conventional thermosyphon is generally made individually from metallic tubing but the materials for the device by the present invention are not confined only to metals but also can be of many types of plastics.

2C As verified in International Journal of Heat and Mass Transfer, Vol. 15, p.p. 1695-1707, the main thermal resistance which determines the thermal efficiency of a heat transfer system such as a thermosyphon which transfers heat utilizing the latent heat of vaporization of the working fluid is the heat transfer coefficients at the outer surface of the thermosyphon. Therefore, even when

25 the device of the present invention is made of such plastics as polyethylene, polypropylene etc. which have relatively low thermal conductivities compared to those of metals, the thermal efficiency of the device will suffer very little.

When plastics are to be used, the manufacturing process of the device of the present invention can be very similar to the extrusion process of metallic

tubing production which is a superior process to that of the present manufacturing method employed for the production of conventional thermosyphons. If the present device is to be made of metallic materials, the roll forming, which is similar to that of the extrusion process employed for

5 plastics, can be applied.

The working fluid to be charged in the present device can be such single component fluid as water, Freon 11, carbon dioxide, ammonium, ethanol etc, depending on the practical condition of application.

For certain occasions, a two-component mixture of two fluids may show a i c superior engineering quality over that of single pure fluid. For example, a working fluid of water and ethanol, or water and ethyleneglycol in the heat transfer device of the present invention may suit better for cold region applications. _

It has been the practice with the conventional thermosyphon to use water 15 as the working fluid for the range of temperature above the freezing point at the pressure near the atmospher. For the temperature range below the freezing point, a single component fluid such as Freon 1 1, carbon dioxide, ammonium or ethanol which are relatively expensive in comparison to water is used. In the heat transfer device of the present invention, a mixture of water and ethanol, or :c water and ethyleneglycol will be used as the working fluid for the application in cold regions, instead of such expensive single component fluids as mentioned above which makes the device further cost effective.

BRIEF DESCRIPTION OF THE DRAWINGS 25 The present invention will now be described with the help of the accompanying drawings which are : Figurel is an exploded perspective view of the heat transfer device of the present invention. Figure 2A is an assembled perspective view of Figure 1 with a cut-off view to

show the inner construction of the present heat transfer device.

Figure 2B is an enlarged view of the section "A" designated in Figure 2A.

Figure 3 illustrates the charging process of working fluid into a cavity which makes up a cell in the present heat transfer device. 5 Figure 4 illustrates a cross-sectional view of the heat transfer cell based on a different design concept by the present invention. Figure 5 is a cross-sectional view of the assembly example for a practical application of the heat transfer device of the present invention.

i c DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings (Figs. 1 and 2) wherein reference numbers refer to elements and parts, the plate type heat transfer device 1 of this invention is comprised of the main plate 2 having a number of heat transfer cells(cavities) 3 which are extended in parallel along the main plate 2, and two end plates 4a and 15 4b which close off the heat transfer cells 3 in the main plate 2 by covering the left and right ends of the main plate 2.

Each heat transfer cell 3 is separated by the vertical partitions 5 which extend between the upper wall 2a of the main plate 2 and the lower wall 2b of the main plate 2. C A predetermined amount of a working fluid 6 is charged under vacuum into the heat transfer cell 3 through the charging ports 7 located on the upper wall 2a of the main plate 2.

The working fluid 6 is charged into the heat transfer cell 3 by means of the working fluid charging apparatus 8 which has a vacuum line 9 and a working 25 fluid charging line 10 as shown in Fig. 3. The inert gas or air in the cell 3 is evacuated through the vacuum line 9 of the working fluid charging apparatus 8 which is connected to the charging ports 7. The vacuum line 9 is then closed and the working fluid charging line 10 is opened so that the working fluid is sucked into the cells 3. The workinc fluid 6 of a fraction of the volume of the

heat transfer cell 3 is charged in each cell 3. Consequently, the liquid phase 3a and the gas phase 3b of the working fluid 6 coexist in the cell 3.

When the charging process of the working fluid 6 is completed, the working fluid charging apparatus 8 is removed from the charging port 7 which is 5 then sealed.

The working fluid 6 charged in the cells 3 can be either such single component fluid as water, Freon 11, carbon dioxide, ammonium, ethanol etc. or a two-component mixture of two fluids such as water and ethanol, or water and ethyleneglycol, depending on the condition of application. l c The main plate 2 can be produced by extrusion process from plastics and by roll forming process from metallic materials. The width and length of the main plate 2 will be determined by the application of the device.

The plate type heat transfer device 1 of the present invention transfers heat from the lower wall 2b to the upper wall 2a of the main plate 2. The i s working fluid in the lower part is vaporized by heat from the lower wall 2b of the main plate 2. The vapor moves up through the cell 3 and is then condensed by cooling in the upper wall 2a of the cell 3 and the latent heat of vaporization of the working fluid is transferred to the outside through the upper wall 2a of the cell 3. The condensate returns to the lower part of the cell 3 and the process 2C repeats continuously and heat is, therefore, transferred from the lower part of the plate 1 to the upper part of the plate 1 without any additional or external aid to transfer heat.

Since the plate 1 is modular structurally, the plate 1 can be so manufactured that a wide area such as highway or air-port runway can be 25 covered by simply connecting these modules in tandem or in parallel.

Figure 4 is the cross-sectional view of the heat transfer cell 3 of the present invention based on a different design concept. The wick 11 is vertically placed in the cell 3 from the upper wall 2a to the lower wall 2b. The use of the wick 1 1 in the present cell 3 is based on the principle of the

conventional heat pipes and the cell 3 with the wick 11 can be used even in the situation where there is no force field such as gravity.

Figure 5 is a cross-sectional view of an assembly for another example of practical application of the present heat transfer device. The fins 12 are attached on the upper outer surface of the heat transfer plate 1 so as to increase the thermal efficiency of the heat plate 1 when the fins 12 are exposed to air.