Refrigeration – Automatic control – Preventing – removing or handling atmospheric condensate
Reexamination Certificate
2001-05-16
2003-02-18
Tanner, Harry B. (Department: 3744)
Refrigeration
Automatic control
Preventing, removing or handling atmospheric condensate
C062S196400, C062S278000
Reexamination Certificate
active
06519956
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the fields of mechanics, thermodynamics, fluidics, refrigeration, dehumidification and water collection and purification. In particular, it relates to a device and method for preventing ice formation on the evaporator of a device operating in a refrigeration cycle, particularly at low ambient air temperatures.
BACKGROUND OF THE INVENTION
The refrigeration cycle has numerous uses. One, of course, is refrigeration, the cooling of ambient air in an enclosure to a temperature at or below freezing for the purpose of preventing the spoilage of comestibles such as meat, fresh fruit and fresh produce. Another is building air conditioning. A further use for the refrigeration cycle is removing water from moist air. The purpose may simply be to dry the air as in the case of household dehumidifiers, industrial scale fruit and vegetable dryers and the like. Or the purpose may be to produce potable water for personal household use, camping, public water conservation and the like or for use during emergencies such as earthquakes, floods, fire and other natural disasters or man-made disasters such as war, when the normal water supply is compromised. In any event, the device and method employed is essentially the same and is schematically depicted in FIG.
1
.
In
FIG. 1
, compressor
1
receives a refrigerant gas, such as ammonia, sulfur dioxide, Freon®, and the like, and compresses it, i.e., raises its pressure. As the result of being compressed, the gas heats up, becoming a hot, high pressure gas. The hot, high pressure gas is then received by condenser
2
, which consists of a heat exchanger having a large surface area that is in contact with circulating ambient air. The hot, high pressure gas surrenders some of its heat content to the circulating air and, as a result, is condensed to a liquid which, while still warm, is cooler than the hot gas entering the condenser. The warm, high pressure liquid then travels to metering device
3
, which can be a simple orifice, a capillary tube or a thermostatic expansion valve, and which forces the liquid to expand and thereby cool further. The cool liquid then travels to evaporator
4
, which, like the condenser, consists of a large surface area over which moisture-containing air can be circulated. The evaporator can be merely a length of tubing which has been folded over on itself in a serpentine manner as depicted in FIG.
1
. Or the tubing can be flattened to provide more surface area when it is folded into a given volume of space. The tubing may also have vanes attached to provide more surface area. The evaporator can also be an interconnected hollow core honeycomb such as the radiator of an automobile. These and many other evaporator designs are well-known in the art. In any event, the cool liquid passing through evaporator
4
absorbs heat from the air in contact with the exterior surface of the evaporator and, when enough heat energy, called the heat of vaporization, has been absorbed, converts back into a gas, which is at approximately the same temperature as the cool liquid entering the evaporator, the heat absorbed having been used in the vaporization process. When the device is being used as a dehumidifier, the operating parameter of metering device
3
is such that the temperature of the cool, low pressure liquid circulating through the evaporator
4
is below the dew point of the air in contact with the exterior surface of the evaporator. The dew point is the temperature at which water vapor in air will condense. Thus, as the cool liquid circulates through the evaporator, absorbs heat from the surrounding air through the surface of the evaporator and vaporizes, water vapor-containing air in contact with the evaporator is cooled to below its dew point. Water vapor in the air then condenses on the evaporator and flows out of the system. The cool gas returns to the compressor to begin another cycle. A receiver is sometimes placed in the system between the condenser and the metering device to store the warm, high pressure refrigerant liquid until it is called for by the metering device.
When the purpose of the device shown in
FIG. 1
is merely to cool and/or dry air, the water condensing on the evaporator is allowed to simply drain away. When the purpose is to collect potable water, a reservoir is placed beneath the evaporator. Care must be taken to assure that the water is obtained in potable condition and that it remains so after collection. This is accomplished by manufacturing the evaporator, the reservoir and any other parts of the device that come in contact with the moist air or the condensed water, from non-contaminating materials or to coat or line potentially contaminating materials with the non-contaminating kind. Examples of such materials are stainless steel, glass and a broad range of polymeric materials such as PVC, Teflon® and the like. To ensure that collected water remains potable, such procedures as irradiating the water with ultraviolet light, bubbling ozone through it, adding iodine or other chemical anti-microbial agents, etc., are often used.
The device described above works reasonably well at ambient air temperatures above about 55° F. A problem arises, however, when the air temperature is below about 55° F. such as might be encountered in refrigeration units, fruit and vegetable produce drying rooms and meat storage lockers or when potable water is needed and the ambient temperature is less than about 55° F., such as at night or in winter. The problem is that, as water vapor, which is at about 55° F. or below, is condensed on the evaporator surface of the device in
FIG. 1
, it is rapidly cooled further because the evaporator surface is usually at a temperature substantially below 32° F. due to the thermodynamic characteristics of commonly used refrigerants and the normal operating modes of such devices. At 32° F. or below, the condensate freezes, forming ice on the evaporator. At ambient air temperatures below about 55° F., air that is in contact with the water on the surface of the evaporator cannot supply sufficient additional heat to counteract this freezing condition. As a result, ice builds up on the evaporator surface and acts as an insulator, isolating the evaporator surface from the moisture-laden air and thereby interfering with the operation of the device. When this occurs, the usual remedy is to turn off the compressor, shutting down the device, until the ice melts. The result is that the device of
FIG. 1
is extremely inefficient at ambient air temperatures below about 55° F.
One approach that is employed to avoid evaporator icing is to simply run the device at higher refrigerant temperatures. This, however, limits the cooling capability of the device. Furthermore, if the goal is to remove water from the ambient air, it is preferred that the device be run as cold as possible so that the air is cooled to as close to the freezing point of water as possible since the colder the air, the less water it can retain. Running the device at a higher refrigerant temperature is thus inefficient since it leaves water in the air.
An approach employed to reduce inefficiency due to down time is to use multiple devices and to alternate use so that when the evaporator of one device has iced up, it can be shut down and another device started up. This, however, is an expensive, not to mention space-consuming, resolution.
What is needed is a device and method that performs a refrigeration cycle, in particular at temperatures below about 55° F., without evaporator icing. The present invention provides such a device.
SUMMARY OF THE INVENTION
The present invention relates to a device that operates in a refrigeration cycle at temperatures below about 55° F. while avoiding ice formation on its evaporator assembly. Of course, the device and method herein will work equally well at any ambient air temperature but it is at temperatures below about 55° F. that icing is particularly problematic and the device herein is of the greatest utility.
A presently preferred embodiment o
Gregory Smith & Associates
Tanner Harry B.
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