Heat exchanger mechanism using capillary wipers for a thin film distiller

[0002] The present invention relates to an improvement in heat exchanger design, more particularly to thin film distillation systems.

[0003] It is well known in the art to provide a distiller which utilizes the condensation of vapor on one side of a heat conductive plate to provide the heat for evaporation of a liquid on the opposite surface of the plate. In some systems it can often be important to minimize the overall temperature difference through which the process occurs. One method which allows the process to occur without requiring a high temperature differential is to maintain a thin film of liquid on the evaporative side and a minimum film of condensate on the condensing side. This enables the thermal resistance of the films to be minimized.

[0004] Currently used methods include application of liquid with a squeegee such as in U.S. Pat. No. 5,409,576 to Tleimat or liquid application by spraying the film on a rotating disc and allowing condensate removal by centrifugal acceleration such as in U.S. Pat. No. 4,731,159 to Porter et al. Others use gravity as in U.S. Pat. Nos. 4,329,204 and 4,402,793 both to Petrek et al. Though each apparatus has its advantages, each require extensive hardware and fairly large spacing between plates. What is needed is a system which allows the use of compact simple hardware particularly suited to smaller systems.

[0005] Until the present invention, compact low energy requirement evaporative systems were not practical and thus have not been commercialized. The purpose of this invention is to enable the efficient application of a thin film of liquid to closely spaced heat exchanger surfaces without having to resort to expensive and precise mechanisms. Additionally, an apparatus meeting these requirements should also enable the removal of condensate from closely spaced surfaces without the need to rely upon rotation of the heat exchanger or to require specific orientation of the surface to enable removal of the condensate by gravity.

[0006] A new and non-obvious distillation system which accomplishes these requirements is introduced herein. In its most simplistic form, the invention comprises a pad of resilient material which can hold and move a distilland liquid to be applied by capillary action, and a means to move the pad repeatedly across an evaporator heat transfer surface to apply and renew a thin film of liquid on the surface. The pad is connected to a supply of the liquid, which is continually fed to the surface as it evaporates. In practice the pad is sized to move easily in the gap between two closely spaced corrugations of a surface thus applying liquid to each side of the gap.

[0007] In a preferred embodiment the heat transfer surface is a corrugated cylinder or bellows comprising a thin heat conductive material. A set of pads is aligned to rotate about the axis of the heat exchanger within the outer corrugations forming the heat transfer surface. These pads apply a liquid to be evaporated. Another set of pads, aligned to rotate about the center of the heat exchanger within the inner corrugation serve to remove condensate. This embodiment could be utilized as the heat transfer system of a vapor compression distiller where vapor leaving the outer surface is compressed and introduced to the inside surface which is otherwise sealed from the outside in order to maintain the required pressure differential.

[0008] As such it is an object of the present invention to provide a thin film heat exchanger system which places a thin film of liquid for evaporation on a surface by use of a capillary applicator.

[0009] Another object of the present invention is to provide a heat exchanger utilizing a capillary applicator capable of applying a thin film of liquid between two closely spaced surfaces.

[0010] Still a further object of the present invention is to provide a liquid distiller which operates efficiently and requires minimum energy input into the system to perform.

[0011] The novel features considered characteristic of the invention are set forth in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of the specific embodiments when read and understood in connection with the accompanying drawings.

[0012] FIG. 1 is a side elevation sectional view of a simplified heat exchanger with a capillary applicator array in accordance with the present invention;

[0013] FIG. 2 is a top sectional view of the apparatus of FIG. 1 taken through 2—2;

[0014] FIG. 3 is a top view of a preferred heat exchanger;

[0015] FIG. 4 is a side elevation of the FIG. 3 heat exchanger;

[0016] FIG. 5 is an isometric perspective view of a capillary applicator array used to remove condensate from the inside of the heat exchanger of FIG. 3;

[0017] FIG. 6 is a top view of a wiper support for use in the FIG. 3 device;

[0018] FIG. 7 is a side view of the FIG. 6 wiper supports;

[0019] FIG. 8 is an isometric perspective view of an assembly of wiper supports;

[0020] FIG. 9 is a top view of a wiper and wiper support in a preferred heat exchanger embodiment;

[0021] FIG. 10 is a side sectional view of an array of wipers and wire supports of FIG. 9;

[0022] FIG. 11 is a side elevation sectional view of a representative heat exchanger showing an alternative plate orientation; and

[0023] FIG. 12 is an end view of the housing of the heat exchanger of FIG. 11.

[0024] The preferred embodiments of this invention are mechanisms that allow movable contact between a capillary applicator and a heat exchanger surface with maximum effectiveness and minimum cost. A heat exchanger utilizing this invention can have plates that are more closely spaced than currently allowed with other heat exchangers. The separation between the plates is limited by two parameters. The first being the smallest dimension in which the liquid does not bridge the gap between the plates; and the second being the thickness of the applicator since it needs to accommodate liquid flow as well as physically fit between the plates.

[0025] Looking now more specifically at FIGS. 1 and 2, a simple heat exchanger system designated generally at 1 is depicted. Liquid to be evaporated enters a chamber 3 via an inlet port 5 and collects in a sump 7. The liquid is absorbed via capillary action by a central capillary 9 and distributed to any number of branch capillaries 11 where it is applied to a heat exchanger surface 13. Should the sump 7 have excess liquid, an overflow port 15 can be provided to drain said liquid. Although in each preferred embodiment of the invention the capillaries 9 and 11 are preferably wicks comprising woven or non-woven cloth or pads, for the purpose of the invention a capillary applicator could also be a brush, foam pad, a rigid yet porous material, a combination of these, or any other structure so long as the resulting structure can transport liquid by capillary attraction. As such, capillaries 9 and 11 form a capillary applicator array designed to remove liquid from the sump 7 and distribute it on the heat exchanger surface 13. To enable the applicator array to distribute the liquid, the heat exchanger surface 13 or the capillaries 11 must be moved one with respect to the other. To accommodate this requirement, a rod 17 mountably attached to the capillary applicator array 9 and driven by a driving means (not shown) is made to reciprocate causing the applicator array to move back and forth on the heat exchanger surface 13. As the liquid is evaporated, vapor can leave the evaporation chamber 3 via a vapor port 19. In a vapor compression distiller the exiting vapor would be compressed by a compressor (not shown) and then allowed to enter an inlet port 21 leading into a condensing chamber 23. The vapor entering the condensing chamber 23 now at a slightly higher pressure condenses upon the opposite face of the heat exchanger surface 13. Condensate leaves via drain port 25.

[0026] Though the above constitutes a simplified version of the present invention, a more complex version could provide a capillary array which is used in reverse to actually remove liquid from a surface. For instance, a second applicator array could be made to follow the first applicator array. The second array would be utilized to remove excess liquid film thickness after the first applicator array applied the liquid to the evaporative surface. Additionally, a capillary array could even be utilized on the condensate side of the system to remove condensate and allow it to collect in the bottom of chamber 23. It is of course desirable to utilize the capillary applicator in conjunction with treated surfaces. For instance, it is well known in the art to treat the evaporator side of heat exchanger surface 13 to make it more wettable and to treat the condensation side of heat exchanger surface 13 to reduce wettability resulting in the creation of droplets that cover less surface area and are easier to remove. Though this is a common practice it is a desirable addition from the standpoint that it would increase the efficiency of the system.

[0027] Another preferable embodiment of the present invention is depicted in FIGS. 3 and 4. These FIGS. show a preferred embodiment of a heat exchanger design 27 that is in the form of a bellow shaped cylinder or corrugated tube with outer convolution 29 and corresponding channels 31 forming the evaporator surface and inner convolutions 33 with corresponding inner channels 35 forming the condenser surface.

[0028] FIG. 5 shows a rotatable assembly of capillary applicators 37 that can be assembled inside heat exchanger 27 to remove condensate. The assembly includes two vertical capillary applicator arrays 39 and 41 positioned diametrically opposite one another. Each array has a number of capillary applicators 43 spaced to fit in every other channel 35. The two vertical arrays are coordinated so that each channel 35 has a capillary applicator associated with it. In the embodiment depicted, applicator array 39 has an applicator 43 associated with every other channel 35. Whereas applicator array 41 has an applicator 43 associated with the remaining every other channel 35. It is intended that the entire assembly 37 can be rotated generally between 10 and 30 rpm inside heat exchanger 27. This would effectively remove condensation from the surfaces of channels 35. Each capillary applicator 43 is made to contact vertical holders 45 and 47 so that condensate can be drawn from the applicators 43 to the vertical holder. Each vertical holder contains an additional capillary element which removes condensate from capillary applicators 43 and transports the condensate to a designated region such as a sump. The vertical capillaries can be designated to take advantage of gravity to assist in removing condensate.

[0029] FIG. 6 shows a capillary applicator support 49, a series of these are needed to hold applicators 43. In a preferred embodiment, each support 49 is a thin metal or plastic clip approximately 0.005 to 0.020 inch thick that can be snapped into a holder 51. These holders 51 are best illustrated in FIGS. 7 through 10. Referring to these figures, the capillary material preferably comprises a fabric wick 53 that wraps around a bridge 55 of holder 51. The wick is held in place by small projections 57 and extend on each side of support 49 until passing through suitable slots 59 in the holder 51 and wraps around cross pieces 61 to pass through another slot and wrap around another support. The wick then is formed from a single piece of material for each subassembly of supports 49 and holder 51. The support 49 is assembled into holder 51 by sliding it through slots from the back-side, the side opposite the extended support.

[0030] In mass production a suitable length of wick material can be extended across the small projection 57 and bridge 55 of the supports, allocated to a holder, at intervals corresponding to the length of wick per support. Then the supports are brought together to a spacing corresponding to the slots in holder 51 as the wick becomes pleated and folds over the supports and the array of supports is pushed through the mounting slots from the back side of holder 51 and snapped into place. This forms an assembly shown in FIG. 9 that can be mounted to a rotatable frame 63 of FIGS. 5 and 10, or frame 65 of FIG. 8.

[0031] FIG. 8 shows double sets of wicks oppositely mounted to frame 65. When the assembly is rotated in the channels 31 of heat exchanger 27 there is a leading and following wick moving in each channel 27 This can result in a better liquid film on the surface of heat exchanger 27. The lead wick can remove residual concentrate from the surface while the following wick applies a new film. An alternative method is to have the leading wick apply excess liquid whereas the following wick removes the excess and spreads a suitably thin film.

[0032] Frame 65 contains a channel 67 that can pick up liquid from a stationary source and facilitate its distribution to the capillary arrays, for example, by means of small bleed ports or by having an end of the wick material submerged in the liquid in channel 67. In fact, it is desirable to position the channel 67 vertically higher than the wick 53 to better enable flow by utilizing gravity assist.

[0033] FIGS. 11 and 12 depict an alternative heat exchanger system 69 similar to FIGS. 1 and 2 but oriented so that the channel surfaces 71 are vertical. The disadvantage of this arrangement is its requirement to individually drain each channel via ports 73 so the channels do not become filled with liquid. The advantage is that gravity assists in the flow through the capillary applicators, in this case a single piece of wicking material 75 that follows the corrugations of the heat exchanger and can be supported with structures similar to those in FIGS. 6-10. Another single piece wick 77 is shown on the under side of the heat exchanger and would serve to remove condensate, again assisted by gravity. Wick 75 supplies liquid to the evaporator side of the heat exchanger and would serve to remove condensate, again assisted by gravity. Wick 75 supplies liquid to the evaporator side of the heat exchanger and is shown with liquid container 79 that would contain liquid 81 to be picked up by the ends 83 of wick 75. Container 79 could also supply the wick 75 via small holes 85 and could be part of the wick support structure.