US3091120A - Thermostatic charge for motor system of expansion valve and method of charging - Google Patents

Description

INVENTORS EDWARD F'. KOUNOVSKY HAROLD T LANGE www ATTORNEYS.

E. F. KOUNOVSKY ETAL Filed July 25, 1959 THERMOSTATIC CHARGE FOR MOTOR SYSTEM OF EXPANSION VALVE AND METHOD OF CHARGING FIGI.

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O Wa mm3 May 28, 1963 United States Patent Oiitice 3,091,12() Patented May 28, 1963 THERMOSTATIC CHARGE FOR MOTOR SYSTEM F EXPANSIGN VALVE AND METHOD 0F CHARGlNG Edward F. Kounovsky, Webster Groves, and Harold T. Lange, Huntleigh Village, Mo., assigner-s to Sporlan Valve Company, inc., St. Louis, Mo., a corporation of Missouri Filed July 23, 1959, Ser. No. 829,098 4 Claims. (Cl. 73--36S.2)

This invention relates generally to improvements in a sensing system for a thermostatic expansion valve, and more particularly to a new and improved charge for the motor system of such a valve and to an improved method of charging the system.

Heretofore there have been three basic types of thermostatic charges commonly used in the motor system of the thermostatic expansion valves. The first type is a limited pressure charge employing the same iluid as used in the refrigeration system. The second type is a liquid charge employing the same iluid as used in the refrigeration system. The third type is a liquid crosscharge consisting of a volatile liquid plus a superheated vapor.

The motor system for a thermostatic expansion valve is well known, such system consisting of a sensing bulb to be located at some point in the refrigeration system, a diaphragm or bellows with its housing usually connected on the valve casing, and connecting capillary tub- The above mentioned limited pressure charge consists of a limited charge of volatile liquid, such liquid being the same as the refrigerant employed in the refrigeration system. At normal operating temperatures a portion of the charge is Vsaturated liquid and the balance of such charge exists as a saturated vapor. Above a predetermined temperature the entire charge is in a superheated vapor phase. This type of charge is described in U.S. -Patent No. 1,971,695, issued August 28, 1934, to Clyde E. Ploege-r.

An advantage of the limited pressure charge is that overloading of the compressor motor is prevented because the charge limits the evaporator pressure to `a predetermined maximum value. This maximum evaporator pressure value is known as the limiting pressure. Because the danger of overloading the compressor motor is obviated when starting up equipment at high temperatures, following defrost, or during other occasional periods of high loading, the selection of the compressor motor may be based on normal operating loads and temperatures.

Another advantage realized by the use of the limited pressure charge is that it permits the use of a thermal ballast in the sensing bulb of the motor system of the thermostatic expansion valve in order to reduce hunting, all as described and disclosed in U.S. Patent No. 2,573,- 151, issued October 30, `1951, to -Harold T. Lange, and in Reissue No. 23,706, issued September 1, 1953, to Harold T. Lange.

An inherent disadvantage of the limited pressure charge is its tendency to produce higher superheat of the refrigerant vapor leaving the evaporator as the evaporating temperature is reduced. This action results in a corresponding loss in 4the capacity of the refrigeration system. In such Va refrigeration system, the limiting pressure, or in other Words the maximum evaporator pressure determined by the motor system of the expansion valve at which the entire charge converts to a superheated vapor phase, is set somewhat above the normal operating range in order to provide as rapid a temperature pull-down as possible without overloading the compressor motor. Because of this setting of the limiting pressure land because of the increasing superheat characteristic,

there may occur a flood-back of liquid refrigerant to the compressor at some point during the pull-down period especially if the iinal superheat is required to be low. These problems Iare usually related :to commercial or low temperature equipment.

The second type or liquid charge is also the same as the refrigerant used in the system. However, the volume of the powerhead consisting of diaphragm or bellows in its housing and the volume of the bulb, together with the amount of charge are so proportioned that the liquidvapor interface is always in the sensing bulb regardless of the temperature of the powerhead. As a result, the point of control is always in the sensing bulb. This liquid charge is -always in the saturated liquid-vapor phase.

The third type or liquid cross-charge consists of a volatile liquid that can be the same as that refrigerant used in the refrigerating system or such a liquid having a lower vapor pressure and a rilatter pressure-temperature curve than that of the refrigerant in the refrigeration system, together with a superheated vapor (non-condensible gas) such as carbon dioxide, air, nitrogen and the like added to increase the total pressure in the powerhead. Similar to the straight liquid charge, the liquid crosscharge is so designed that the temperature control is basically at the sensing bulb. In other words, the volume of the powerhead, the volume of the bulb and the amount of charge are so proportioned that a liquid-vapor interface exists in the bulb at all times regardless of the temperature of the powerhead,

The liquid cross-charge overcomes two of the disadvantages of the liquid and limited pressure charges. Because of its atter pressure-temperature curve, it is less responsive, pressure-wise to changes in bulb temperature. Consequently there -is less tendency for the refrigerant expansion valve to overfeed and hence stability control is improved.

yIn addition, with the liquid cross-charge the changing superheat character-istie is reversed from that of the liquid or the limited pressure charges. For example, as the evaporating temperature is reduced, the superheat of the refrigerant vapor leaving the evaporator becomes progressively lower, thereby enabling more of the evaporator to be available for cooling action. As a result, there is no danger of iiooding liquid back to the compressor at the start of the refrigerating cycle. It Iis necessary only to establish a setting on the expansion valve which will provide for an adequate superheat at the minimum evaporator temperature for any given job application.

However, the liquid cross-charge provides only partial overload protection by its changing superheat characteristie. Normally this extent of protection is inadequate.

Heretofore in order to provide the complete load limiting protection afforded by the limited pressure charge, it has been necessary to incorporate in the valve design, a mechanical pressure-limiting device. This type of pressure-limiting device consists of a collapsing member such as a diaphragm or bellows, which is responsive to increasing evaporator pressure above a pre-set maximum limit and acts to throttle the expansion valve above such maximum value. While a mechanical pressure-limiting device is effective in providing motor overload protection, it is expensive and has various limitations as to size and range of pressures.

It is a primary object of this invention to provide a thermostatic charge for the motor unit of a refrigerant expansion valve that has the controlled stability and favorable superheat control characteristic oiered by the flat-temperature curve of the liquid crosscharge; which operates with the simplicity of the limited pressure charge in providing complete compressor motor protection during periods of overload, and which enables additional control stability by the selective use of a ther- 'mal ballast to reduce hunting as disclosed in Lange VU.S.

Patent No. 2,573,151 and Lange Reissue No. 23,706.

Another important object is -to provide a thermostatic Ycharge for -a motor system which comprises a limited Apressure lcharge of volatile liquid yand the vapor of the liquid, and aV gas which is non-condensible within the temperature and pressure ranges to which the motor system is 'subjected during use, such a charge providing the results and functional advantages mentioned previously.

IStill another important object of the invention is to provide a method of charging the motor system of the thermostatic expansion valve with th thermostatic charge.

The foregoing and numerous other objects of the invention will more clearly appear from the following detailed description of the thermostatic charge together with the method of charging the motor system, particularly when considered in connection with the accompanying drawing, in which:

FIG. 1 is a graph of .pressure-temperature curves for saturated refrigerant-500 and for a limited pressure charge of 4refrigerant-l2;

FIG. 2 is a graph illustrating a calculated curve and Van actual test curve of a limited pressure cross-charge,

and illustrating the limiting pressureof each curve, and

FIG. 3 is a graph of pressure-temperature curves for a limited pressure cross-charge showing the effect of varying amounts of air.

This invention relates to a thermostat-tic charge for a motor system of a thermostatic expansion valve which comprises a limited pressure charge of volatile liquid and the vapor of the liquid and a gas or a vapor that is superheated and non-condensible throughout the range of pressures and temperatures in which it is required to operate, such vapor and non-condensible gas raising the total pressure of the charge to a predetermined value selected to give a suitable limiting pressure at which the entire charge is in vapor phase. In this thermostatic charge the non-condensible gas is one that is chemically not reactive with the limited pressure charge.

According to ASHRAE Data Book, Design Volume,

saturated liquid or liquid at saturation is the condition for co-existence `in stable equilibrium of two or more distinct phases. For example, saturated lliquid is liquid at boiling point or liquid which is not subcooled.

It is characteristic of allsaturated liquids that those whose vapor pressures are lower than other such liquids at any given temperature also change less in pressure for a giventemperature change. As for example, FIG. 1 of the drawing shows portions of the saturated pressuretemperature curve for two such saturated liquids between Y the temperatures of zero degree and plus 60 degrees F. The two saturated liquids are refrigerant-500, an azeotrope of dichlorodiuoromethane and diuoroethane, and refrigerant-12 also known as dichlorodiuorornethane or Freon-IZ.

From FIG. 1 it is Vapparent that the pressure rise for the refrigerant-12 charge is at a lower rate than that of refrigerant-500. With these two saturated liquids, it is seen that the pressure of refrigerant-12 at any given ternperature is lower than the corresponding pressure of ree frigerant-SOO. Moreover, it is seen that the curve for refrigerant-12 is atter than the curve for refrigerant-500 which indicates a smaller pressure change for any given temperature change.

In addition, the relationship between the superheat and evaporating temperature is also indicated by the horizontal ,distance between the two curves, such as is indicated by line A-B, under the conditions whererefrigerant-SOO is employed as the system refrigerant and refrigerant-l2 is employed as the thermostatic charge of the expansion valve. For example, at an evaporating temperature of 40 degrees F., the superheat is 10 degrees F. The point C -spring that assists the pressure of the thermostatic velement and tends to open the valve or by the addition of a non-condensible gas in the thermostatic charge that raises the total pressure. The provision of a non-condensible gas in a -thermostatic charge and the particular method involved in charging the thermostatic motor system represents the present inventive features.

One method of charging the thermostatic motor system, which consists of a sensing bulb, diaphragm or bellows with its housing and connecting capillary tubing, includes the step of evacuating the system. Then, a volatile uid is introduced in vapor yform by maintaining the temperature of the entire system above the saturation ternperature corresponding to the charging pressure selected. Typical uds that can be utilized in this last described step are isobutane, methylchloride, dichlorodifluoromethane (Freon-12), monochlorodiuoromethane (Freon- 22), propane and the like. Following this last step, a non-,condensible gas is introduced into the systemto raise the total pressure of the thermostatic system to a predetermined value. 'I'he non-condensible gas that can be added may be air, carbon dioxide, nitrogen or any other gas which does not react chemically with the volatile uid. The total pressure selected for the motor system charge is Vone which will give suitable limiting pressure at which the `entire charge is in vapor phase, such asv the limiting pressure value illustrated in FIG. 2.

After the introduction of the non-condensible gas, the

system is closed and sealed. As one example of the above described method, after the thermostatic system is evacuated, such system is charged with Freon-l2 to a gauge pressure of 68 p.s.i. while the temperature is maintained at degrees F. The saturation temperature of Freon-12 at this gauge pressure is 68 degrees F. Air is then added until the total pressure equals 83 p.s.i. gauge pressure and the system is closed and sealed. The saturation pressure forthe volatile uid at the charging temperature of 90 degrees F. is 99.8 p.s.i. gauge pressure.

Another method of charging the motor system of the refrigerant expansion valve is to reverse the aboveV described procedure. In other words, after evacuation of the system, the air is introduced into the system iirst to a predetermined pressure value, as for example, t-o 15 p.s.i. absolute, and then the volatile uid, such as Freon-12, is introduced into the system with the air to raise the final pressure to 83 p.s.i. gauge pressure.

Of course, in each of the above described methods, noncondensible gases other than air can be utilized effectively.

Still another method of charging the thermostatic system, if air is used as the non-condensible gas and if the air pressure is not to exceed one atmosphere, is to evacuate the Isystem partially or not at all, as required and then the volatile Huid is introduced intoV the system in vapor form in the manner previously described to raise the total Vpressure to the predetermined value.

In the last two charging methods, the total pressure of the thermostatic system must be less than the pressure of saturated vapor for the volatile uid used at the charging temperature selected. f

Basically, the partial pressure of the non-condensible gas varies with temperature according to Charless law, while the vapor pressure of the volatile liquid charge follows the pressure-temperature curve for saturatedvapor until the point of complete vaporization occurs, such as at the limiting pressure point C of FIG. 1. At temperatures above the point of complete vaporization, which occur at a limiting pressure value, the pressure of the thermostatic system follows Charless and Daltons laws. However, these pressure-temperature characteristics are further modified because -of absorption of the non-condensible gas by the volatile liquid charge, or modied by the use of a thermal ballast in the sensing bulb.

It is well known that when a non-condensible gas is m-iXed with saturated liquid-vapor, absorption of a portion of the non-condensible gas by the liquid takes place. 'I'his absorption has been observed since 1934 in thermostatic expansion valves manufactured by Sporlan Valve Company of St. Louis, Missouri, assignee of the present application and invention.

One type of liquid cross-charge for a representative valve manufactured by Sporlan Valve Company, known as type G valve, consists of methyl chloride and air. In this particular valve, the internal bulb volume is 0.44 cubic inch, the internal volume of the diaphragm housing is 0.14 cubic inch and the internal volume of the connecting tubing is 0.09 cubic inch. The amount of liquid in the charge is suicient to fill completely the diaphragm housing Without completely depleting the bulb. In other words, in accordance with the prior disclosure, there is a liquid-vapor interface in the sensing bulb at all times.

It has long been noted that this type of charge (saturrated vapor over liquid plus a non-condensible gas) produced a pressure that was proportional to the temperature of the bulb, the capillary tubing and the diaphragm housing. The pressure effect was a resultant of all three temperatures and directly related to the volume of all three parts of the thermostatic system. The relative volume of the tubing is small and has been neglected in the following tabulation of the above elect.

From the above table, it is seen that in the first thermostatic system tested the internal bulb volume Was 0.44 cubic inch while in the second thermostatic system the internal bulb volume was 1.4 cubic inches. In each of the systems tested, the weight of methyl chloride was 5.45 grams and the partial pressure air charge was 23.6 pounds per square inch absolute. In each system, the bulb and tubing temperature was maintained at 80 degrees F. while the diaphragm case temperature was varied from 32 degrees F. to 80 degrees F. In the first system, the element pressure varied from 75 p.s.i. gauge to 90 p.s.i. gauge for a pressure change of l5 p.s.i. In the second system, the element pressure varied from 90.5 p.s.i. gauge to 97.5 p.s.i. gauge for a change in element pressure of 7 p.s.i.

It has also been found, in a thermostatic system of the type described above in which the relative volumes of the bulb, the capillary tubing and the diaphragm housing atleet the resultant pressure, that the amount of volatile liquid can be reduced to only a few drops with beneficial results. When such reduction in the amount of volatile liquid is made, there is an increased volume in the bulb available for vapor and gas mixture, and therefore the proportion of the volume of the bulb to that of the diaphragm case increases. Therefore, the pressure effect from bulb temperature predominates which is a desirable eifect. This phenomenon is shown in the following table as test results.

lst 2d 3d System System System Weight of Methyl Chloride (grams)- 5. 45 1. 8 0. 2 Bulb Volume (cu. in.) 0.44 0. 44 0. 44 Partial Air Pressure (p.s.i. absolute)- 23. 6 23. 6 23. 6 Bulb and Tubing Temperature f F. 80 80 Diaphragm Case Temperature F.) 80-32 80-32 80-32 Element Pressure (p.s.i. gauge). -75 94. 5-83. 0 104. 5-97. 5 Change in Element Pressure (p.s.i.) 15 11. 5 7

From the above table, it is seen that the thermostatic system had an internal bulb volume of 0.44 cubic inch, the partial air pressure charge was 23.6 p.s.i. absolute, and the bulb and tubing temperature was maintained at 80 degrees F. In each of the three tests of this system, the diaphragm case temperature was varied from 32 to 80 degrees F.

In the first test the weight of methyl chloride introduced into the system as a charge was 5.45 grams. Upon varying of the diaphragm case temperature within the temperature range indicated, the element pressure varied from 75 p.s.i. gauge to 90 p.s.i. gauge, thus showing a change in element pressure of l5 p.s.i.

In the second test, the weight of methyl chloride charge was 1.8 grams. The element pressure varied from 83.0 p.s.i. gauge to 94.5 p.s.i. gauge, thus indicating a change in element pressure of 11.5 p.s.i.

In the third test, the system was charged with methyl chloride having a weight of 0.2 gram. This particular charge represents one within the teaching of this invention. In other words it is a limited charge of volatile liquid and the vapor of the liquid with the addition of a superheated vapor such as air to increase the pressure. At a predetermined pressure value, called the limiting pressure, the entire charge will be in vapor phase. In this test, the element pressure varied from 97.5 p.s.i. gauge to 104.5 p.s.i. gauge for a change in element pressure of 7.0 p.s.i.

It is believed that in any thermostatic system containing a non-condensible gas plus a volatile liquid and the vapor of the liquid, absorption of =a portion of the noncondensible gas by the liquid and vapor occurs and that the volume of the component parts of the system and their temperatures effect the element pressure. The amount of such absorption varies with the temperature, pressure, the nature of the volatile liquid, and the noncondensible gas. This absorption causes a deviation from the theoretical pressures calculated according to Daltons law.

FIG. 2 of the drawing shows the comparison between a calculated curve and an actual test curve in which the bulb, tubing and diaphragm housing temperatures are varied together.

The thermostatic system `for which the test was run and on which the calculations were based for the actual test curve in FIG. 2, was charged with Freon-lZ added to air at one atmosphere to a total pressure of 83 p.s.i. gauge at 80 degrees F.

In addition, the amount of non-condensible gas affects the slope of the pressure-temperature curve. For example, increasing the amount of non-condensible gas results in a flattening of the curve. The curves illustrated in FIG. 3 of the drawing were plotted with the same 4basic charge as that described above with respect to FIG. 2, except for varying amounts of lair. These curves illustrate the eiect of flattening the pressure-temperature curve upon increasing the `amount of air.

The thermostatic charge from which the actual test curve shown in FIG. 2 was calculated is designed to produce a fairly extreme cross-charge eect when used on a refrigeration system employing refrigerant-500. If a less extreme effect should be desired, less air or a higher pressure volatile liquid, or both, could be used. Therefore, by the Yproper selection of charge components, various characteristics can be Iobtained for different refrigerants.

Although Ythe -inventionhas =been described eby making detailed reference to a single thermostatic charge and to a method of charging a thermostaticsystem, together with several modifications, such detail iis to be `understood in an instructive, rather than in `any restrictive sense, many variants lbeing possi-ble within Vthe `scope of the claims hereunto appended.

VWe claim as our invention.

1. A charge for a motor system of a thermostatic expansion valve comprising a motor system, a limited pressure charge in said motor system of volatile liquid and the vapor of the liquid, and a gas which is noncondensible throughout 'the range of temperature and Ipressures to which the motor system is to be subjected during use, the non-condensible -gas raising the total pressure of the charge to a predetermined Yvalue selected to VVgive a suitable limiting pressure at which the entire charge is in vapor phase.

2. A charge ifor a lmotor system of a thermostatic eX- pansion valve comprising a motor system, a limited pressure charge in said motor system of volatile liquid and the vapor of theliquid, and a vapor that is superheated and non-condensible throughout the range of pressure and temperature in which it is required to operate the last said superheated vapor raising the total pressure of t-he charge to a predetermined value selected to give a suitable limiting pressure at which the entire charge is in a superheated vapor phase.

3. A charge for a motor system of a thermostatic expansion valve adapted for use in a refrigeration unit comprising a motor system, a limited pressure charge Vin themotor system of volatile liquid and the vapor of the liquid, and a non-condensi-ble gas that is chemically uri-reactive with the limited pressure charge which is non-condensible throughout-the range of temperaturesand pressures to which the motor ysystem is to be subjected during use and which raises the total pressure t-o a predetermined value Aselected to give a suitable limiting pressure at which the entire charge is in a superheated Yvapor phase.

4in la 'refrigeration unit, a motor sys'tem including 'a sensing Ibulb, a flexible motor element With its housingand connectingrcapillary tubing, and a charge in said motor system comprising alimited pressure charge of volatile -liquid and the vapor ofthe liquid 4and ya gas'which is noncondensible throughout the range of temperatures and pressures to which the motor system `is subjected during use the vapor of the liquid fand the non-condensi'ble gas raising the total pressure of the charge to a -predetermined value s'elected to give 'a suitable `limiting pressure at which 'the entire chargeis in superheated 'vapor VVVphase in response to -bulb temperature.

References Cited Vin the tile Voi? this patient Y UNITED STATES PATENTS 1,629,174 Patten May 17, `1927 2,186,984 .Mccwy Jan. 16, 1940V 27,494,454 'Ritchie 1 Jan. 1o, 195o OTHER REFERENCES Gunther: Refrigeration, lAir Conditioning, and Cold Storage, pub. by Chilton Company, 1957, pp. 391 to 4. 'In a thermostatic expansion valve 'adapted for use Y

Claims (1)

1. A CHARGE FOR A MOTOR SYSTEM OF A THERMOSTATIC EXPANSION VALVE COMPRISING A MOTOR SYSTEM, A LIMITED PRESSURE CHARGE IN SAID MOTOR SYSTEM OF VOLATILE LIQUID AND THE VAPOR OF THE LIQUID, AND GAS WHICH IS NONCONDENSIBLE THROUGHOUT THE RANGE OF TEMPERATURE AND PRESSURES TO WHICH THE MOTOR SYSTEM IS TO BE SUBJECTED DURING USE, THE NON-CONDENSIBLE GAS RAISING THE TOTAL PRESSURE OF THE CHARGE TO PREDETERMINED VALUE SELECTED TO GIVE A SUITABLE LIMITING PRESSURE AT WHICH THE ENTIRE CHARGE IS IN VAPOR PHASE.

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