US 3602004 A
Description (OCR text may contain errors)
United States Patent Inventor Assignee James E. Peavler Maryland Heights, Mo.
Apr. 2, 1969 Aug. 311, 19711 American Air Filter Company, Inc. Louisville, Ky.
Appl, No. Filed Patented HEAT EXCHANGE DEVICE 7 Claims, 3 Drawing Figs.
References Cited UNITED STATES PATENTS 9/1966 Lindberg Primary Examiner-William F. ODea Assistant ExaminerP. O. Ferguson Attorney-Ralph 13. Brick ABSTRACT: A heat exchanger to temper a selected fluid having a first conduit adapted to receive a first fluid of selected temperature to transfer a tempering effect to the selected fluid and a second conduit disposed in heat transfer relation with the first conduit where the fluid to be tempered passes over the surface of the second conduit. A gas is selectively supplied to the second conduit to control the rate of heat transfer through the second conduit and the pressure of the gas in the annular chamber is varied to control the surface temperature of the second conduit.
PATENTEU AUGB] 1971 I INVENTOR.
James 6 Pear/er mm ATTORNEY HEAT EXCHANGE DEVICE BACKGROUND OF THE INVENTION In various applications a stream of fluid, for example air, is cooled by passing the airstream over a heat transfer surface provided by a conduit, for example an evaporator of a refrigeration circuit, where a selected cold fluid flows through the conduit. In many cases, the surface temperature of the heat exchange surface is below the freezing temperature of one component of the gas stream, for example water, and the water condenses and freezes on the heat transfer surface. The ice formed on the surface adversely affects the efliciency of the heat transfer surface and restricts the gas flow passage provided by the heat exchange device.
In some previous applications where such heat exchange devices have been provided to evaporate refrigerant to provide a cooling effect in refrigerant circuits having a cooperativc compressor, condenser, and refrigerant expansion device, in series with the evaporator, the flow of refrigerant to the evaporator has been controlled in accordance with the temperature of the airstream flowing over the evaporator in heat transfer relation to prevent freezing the condensate on the heat transfer surface.
In certain other applications, the moisture carried by the airstream has been removed prior to cooling the airstream to prevent frosting the heat exchange surfaces or alternate evaporators have been provided so that when one evaporator is frosted over, the alternate evaporator is used while the frost ing is removed from the first evaporator.
Such devices are expensive, have a generally adverse effect on the operating efficiency of the cooling system, and restrict the overall capacity of the cooling apparatus.
Moreover, in previous arrangements the surface temperature of the coil is not uniform along the length of the coil and, in particular, there is a tendency for ice to form in the area near the point where the cold refrigerant is first introduced to the conduit and for the surface temperature to increase downstream from this point so there is progressive freezing along the length of the conduit. In certain previous devices, an attempt has been made to minimize the effect by providing heat exchange devices with multiple passages so the refrigerant incoming stream of cooling fluid is divided into a number of smaller streams but even in these arrangements temperature control on the surface of the heat exchange device is not good.
SUMMARY OF THE INVENTION The present invention provides a straightforward, inexpensive apparatus to control the temperature of the heat transfer surface of a fluid cooling device to prevent frosting of the heat transfer surface and to improve the cooling efficiency of the apparatus. Likewise, the present invention provides an arrangement which provides a substantially uniform rate of heat transfer and a uniform surface temperature along the length of the heat transfer device and essentially prevents undesirable overcooling at one location in the heat exchanger and insufficient cooling in other sections of the heat exchanger.
Moreover, the present invention provides an economical heat device which can be used in various heat transfer arrangements where a very low temperature source of cooling fluid is provided to cool a fluid, for example an airstream, flowing over the surface of the heat exchange device without adversely affecting the heat transfer efficiency.
Various other features of the present invention will become obvious to those skilled in the art upon reading the disclosure set forth hereinafter.
More particularly, the present invention provides a heat exchange device for tempering a selected fluid flowing over the surface of the heat exchange device by means of a first fluid flowing through the heat exchange device which includes: a first conduit to carry the first fluid; a second conduit disposed in heat transfer relation with a portion of the first conduit where the selected fluid flows over a surface of the second conduit other' than that portion exposed to the first conduit; gas supply means to selectively supply a gas to the second conduit; and, temperature responsive means disposed to modulate the pressureof the gas in the second conduit in accordance with change in the temperature of the surface of the second conduit exposed to the selected fluid to be tempered.
It is to be understood that the example of the present invention given hereinafter is not by way of limitation and that various adaptations of the example, within the scope of the present invention, will occur to those skilled in the art upon reading the disclosure set forth hereinafter.
Referring to the Figures:
FIG. 1 is a schematic illustration of a refrigeration circuit including a heat exchange device in accordance with the present invention;
FIG. 2 is a view taken along a plane passing through line 2 2 ofFIG. ii and,
FIG. 3 is a schematic illustration of a temperature controlling means in accordance with the present invention.
The refrigerant circuit shown in FIG. ll includes a refrigerant compressor 4, communicating with a condenser 6 and with an evaporator l, as hereinafter described, by means of a conduit 3. An expansion valve 7 is located in conduit 2 which is provided to connect condenser 6 and evaporator 1. Refrigerant, for example a condensible-vaporizable a fluid, flows through the circuit and compressed, refrigerant passes through expansion valve 7 where the pressure is reduced. The expanded refrigerant is then supplied to evaporator l to cool a selected fluid, for example an airstream which flows over the surface of the evaporator in heat exchange relation. Expan sion valve 7 is operated in accordance with selected conditions to reduce the pressure of the refrigerant and to modulate the flow of refrigerant to selectively control the intensity of the cooling effect provided.
As is well-known in the art, refrigerant supplied to evaporator 1 is vaporized by the heat received from the airstream passing over the surface of the heat exchanger and the vaporized refrigerant is returned to compressor 4 by a conduit Referring now to FIG. 2, which shows a section of evaporator 1, the evaporator includes an outer tube 5 disposed in spaced relation from refrigerant carrying conduit 2 so that an annular chamber 5a is formed between shell 5 and tube 2. The expanding and vaporizing refrigerant flows through opening 2a of tube 2 while, in accordance with one feature of the present invention, a selected fluid is supplied to the annular area 5a.
In the example of the Figure, a conduit 8 is provided to communicate with annular chamber 5a and with the low-pressure side of compressor 4, for example with conduit 3 adjacent the inlet to compressor 4. Thus, depending on the characteristics of the refrigerant, the refrigeration circuit, and the operating conditions, a low, even subatmospheric, pressure can be maintained in annular chamber 5a. in accordance with another feature of the example of the present invention shown in FIG. 1, a second conduit 9 is provided. to communicate with annular chamber 5a and with the discharge side of compressor 4 which is operated at a high pressure to supply vaporized refrigerant to chamber 5a.
A temperature sensing device lll is located adjacent the surface of evaporator 1 to transmit the temperature of the surface of the evaporator to a controller 122. Controller 12 is provided to maintain a selected temperature at the surface of coil 1 as hereinafter described and is adapted to operate a valve 13 located in conduit 9 to control flow of high-pressure refrigerant through the conduit 9 and a valve 14 located in conduit 8 to control flow of low-pressure refrigerant through conduit 8.
The present invention recognizes that the characteristics and condition of the fluid in annular chamber 5a, for example the pressure within the annular chamber directly affects the overall coefficient of heat transfer from the fluid flowing through conduit 2 to the surface of conduit of evaporator 1 and therefore the temperature of the heat transfer surface. For example, by selectively controlling pressure, or other characteristics of the fluid flowing through the annular area, the surface temperature can be controlled.
In the example shown, the coefficient of heat transfer from conduit 2 to the surface of conduit 5 of evaporator l varies in direct proportion to change in pressure of the gas in annular chamber 511. Thus, by selectively controlling the refrigerant pressure in annular chamber 5a, the temperature at the surface of evaporator 1 can be maintained at, for example, freezing or just above. In such an application, controller 12 opens valve 13 to admit refrigerant from compressor 4 in response to an increase in temperature of evaporator l and opens valve 14 to decrease the pressure in chamber 5a in response to a decrease in temperature of evaporator 1.
Referring now to FIG. 3, which shows a schematic illustration of the temperature controlling means in accordance with the present invention, the controller 12 includes a bellows 21 which is responsive to temperature sensing means 11 and actuates bellows rod 24. Bellows rod 24 is adapted to open normally closed switch 23 when the pressure in bellows 21 rises and bellows 24 is adapted to open normally closed switch 24 when the pressure in bellows 21 decreases. Normally closed switches 23 and 24 are spring operated and revert to their normally closed position when the bellows pressure changes causing the rod 24 to disengage from the switch it is contacting.
The switches 23 and 24 actuate circuits which operate valves 13 and 14, these valves being of the solenoid-type in the example, and when the switches are in their normally closed position, valves 13 and 14 are also in their closed position. In operation, when the surface temperature of evaporator 1 increases above a preselected temperature, bellows 21 increases thereby movingrod 24 to a position whereby switch 23 opens breaking the circuit through the line 16 to valve 13. Valve 13 opens thereby allowing flow of refrigerant to the annular chamber 5a of evaporator 1. When the surface temperature of evaporator 1 decreases, pressure in bellows 21 decreases and rod 24 disengages switch 23. Switch 23, being spring loaded, reverts to its normally closed position energizing line 16 to valve 13 thereby closing valve 13. If the temperature on the surface of evaporator l continues to decrease bellows 21 will contract bringing bellows rod 24 in contact with switch 22. Switch 22 will then be opened thereby breaking the circuit through line 17 which in turn causes valve 14 to open. The opening of valve 14 causes the refrigerant in annular chamber 50 to flow outwardly and into compressor 4.
It will be noted that the use of refrigerant from the refrigerant from the refrigeration circuit provides a dry fluid which will generally be in the vaporous state and can be used without fouling the annular chamber between the conduits and that in other applications, other fluids can be used. Also, under conditions where vaporized refrigerant flows through annular area 5a from conduit 9 to conduit 8, the refrigerant is cooled before recompression and does not adversely affect the efficiency of the refrigeration cycle. 4
ln applications where the load to be carried by evaporator l varies widely, an adjustable restriction (not shown), for examplc a valve, can be provided in conduit 3 between the outlet of conduit 8 and the outlet from evaporator l to restrict flow through evaporator 1 and decrease the fluid pressure downstream of the restriction so the pressure in annular chamber 5a likewise reduced.
The inventionclaimed is:
1. A heat exchanger for transferring a thermal effect from a first fluid to a second fluid including: first conduit means to carry said first fluid: modulating conduit means disposed in heat transfer relation with said first conduit means so said second fluid is in heat transfer contact with a surface of said modulating conduit means; means to selectively supply a gaseous third fluid to said modulating conduit means and, temperature responsive means disposed to modulate the pressure of said third fluid in accordance with change in temperature of the surface of said modulating conduit means to affect the rate of heat transfer through said modulating conduit means.
2. A heat exchange device for transferring a thermal effect from a first fluid to a selected second fluid including: a first conduit to carry said first fluid; a second tubular conduit having a diameter greater than the diameter of said first conduit and disposed to surround said first conduit along a portion of the length thereof to define an annular chamber therebetween where said second fluid flows over the surface of said second conduit; means to selectively supply a selected gas to said annular chamber, and temperature responsive means disposed to modulate the pressure of said gas in accordance with change in temperature of the surface of said second conduit to affect the role of heat transfer through said annular chamber.
3. A heat exchange device for transferring heat from a selected first fluid to be cooled to a second low temperature fluid flowing through said heat exchange device including: a first conduit to carry said second low temperature fluid, a second tubular conduit disposed to surround a portion of said first conduit in spaced relation therefrom to define an annular chamber therebetween where said first fluid flows over the outer surface of said second conduit in heat exchange relation; means to selectively supply a gas to said annular chamber; and, temperature responsive means disposed to modulate the condition of said gas in accordance with change in temperature of the surface of said second conduit which is exposed to said selected first fluid to affect the rate of heat transfer through said annular chamber.
4. The heat exchange device of claim 1 wherein said first fluid is a vaporizable-condensible fluid which is vaporized in said first conduit by heat received from said third fluid; wherein said third fluid includes vaporized first fluid; and wherein said temperature responsive means include means to control the pressure of said vaporized first fluid in said modulating conduit means.
5. The apparatus of claim 2 including means to reduce the fluid pressure in said annular chamber to provide subatmospheric pressure in said annular chamber.
6. A refrigeration circuit comprising: a source of liquified vaporizable-condensible refrigerant to be supplied through a first conduit; expansion means disposed in said first conduit to selectively reduce the pressure of said refrigerant; a second conduit means surrounding a portion of said first conduit means downstream of said expansion means and defining an annular chamber therebetween; means to selectively supply vaporized refrigerant to said annular chamber between said first conduit and said second conduit whereby a fluid to be cooled may be passed over the surface of said second conduit in heat transfer relation so heat is transferred from said fluid to be cooled to said vaporizable-condensible fluid carried by said first conduit; and temperature responsive means to control the supply of vaporized refrigerant to said annular chamber in response to temperature adjacent the surface of said second conduit.
7. The apparatus of claim 4 including means to provide subatmospheric pressure in said modulating conduit means.