US 3083546 A
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Description (OCR text may contain errors)
April 2, I1963 R. F. TUREK ANTI-ICE CONTROL SYSTEM Filed Sept. 14, 1961 lll l||||| |I /NVE/VTUR nog? E Tune/r AGEN',
United States Patent O 3,683,546 ANTE-ICE CNTRGL SYSTEM Robert F. Tarek, Windsor Locks, Conn., assigner to United Aircraft Corporation, Sagt Hartford, Conn., a corporation of Belaware Filed Sept. 14, 19161, Ser. No. 138,644 8 Claims. (Ci. 62-15l) This invention relates to control mechanism and more particularly to a control for preventing the accretion of ice within a water separator.
A water separator deicing control is disclosed and claimed in U.S. Patent 2,867,989 to Thomas l. McDut wherein icing is prevented from accreting in the water separator by allowing the back pressure of the cooling turbine to increase which, in essence, increases the temperature of the air leaving the turbine, thereby melting any ice accreted in the moisture separator. While this method of deicing affords the advantage of being relatively simple, it also affords the disadvantage of not being able to provide a sufficient cooling flow for a wide range of aircraft llight conditions. This becomes particularly important in view of the advent of high altitude ying aircraft.
A system for obviating this disadvantage includes means for the addition of warm air to mix with the cold air, thereby preventing the resultant temperature from falling below the reezing point of water, 32 F. While `this does not provide cooler air than the back pressure deicing means, it increases the air weight flow, thereby providing increased cooling capacity. Various means for controlling the addition of said warm air .are well known in the art, but adord several disadvantages as will be noted herein below. A simple temperature control which admits the warm air to limit said resultant temperature to a minimum slightly above the freezing point of water, may be one of such devices. This affords the disadvantage however, of providing a deicing function during certain conditions when it is not needed, i.e., when the moisture content of the air is so low as not -to cause freezing even at air temperatures below 32 F. This unnecessarily reduces the cooling capacity which is the function of tem erature and air weight flow during this condition.
A second means for admitting said ywarm air includes an anti-.icing control which responds solely to the pressure drop across the moisture separator. Said pressure drop is indicative of the ice accreted in the moisture separator. This method affords the advantage of admitting warm air only when needed. This has the disadvantages enumerated below.
As will be realized by one skilled in the art, the pressure drop across the moisture separator varies substantially as the weight diow squared. The usual pressure drop control which solely measures the pressure drop admits warm air to limit the moisture separator pressure drop to a constant value. This has the disadvantage that as the weight flow varies due to changes in the aircraft ight conditions, different amounts of ice build up within the moisture separator occur before warm air is admitted to limit further ice accumulations. Thus the differential pressure signals for different weight ows may vary substantially. As example, at low weight flows a large increase in pressure drop occurs, thereby allowing a high amount of ice formation, while at high weight ows only a small increase in pressure drop occurs, thereby allowin g only a small amount of ice formation.
It is, therefore, an object of this invention to obviate this disadvantage by providing for a moisture separator an anti-icing control that responds to the pressure drop across the moisture separator in a manner which is substantially independent of the air weight flow.
Again referring to the usual pressure drop control, whenever warm air is admitted to the moisture separator resulting from an increase in pressure drop due to the formation of ice within the moisture separator, the admitted flow further increases the pressure drop temporarily. The 4result of this response would introduce a positive feedback signal to the control resulting in a destabilizing effect.
It is, therefore, a further object of this invention to substantially eliminate the positive feedback effect in order to achieve a more stable system.
Other additional objects will be apparent 4from the following speciiication and the attached drawings in which:
FIG. l schematically illustrates the general arrangement of an airplane air conditioning system including a Water separator with its anti-icing control.
FIG. 2 is a modification of the anti-icing control.
FIG. 3 is a graphic illustration showing the pressure drop plotted against weight flow squared through the moisture separator.
As is exemplified in the above referred to Patent 2,867,989, water separators for air conditioning systems have been a necessary incident with .the advent of present day aircraft. While the environmental control system serves to maintain the cabin of the aircraft at a predetermined temperature level, suihcient air weight flow is necessary to assure that the cabin has suflicient air for pressurization purposes. The air conditioning system not only must maintain these requirements, it must also provide humidity control while at the same time preventing ice or snow from being injected into -the cabin. It has thus become a practice to provide a turbine for reducing the temperature of the air substantially below the temperature required in the cabin or compartments and to mix this cool air with warmer air so that the mixed air will provide the required temperature Iand environmental conditions.
Since the dew point of the cool air is substantially below the cabin temperature, it thus becomes a necessity to remove moisture from the super saturated turbine discharge air so that the mixture of the warm and cool air introduced into the cabin will exhibit a relative humidity substantially below a hundred percent. Since this invention primarily is concerned with the prevention of ice from accreting in the water separator, a preferred embodiment to which this invention may be practiced will only be briefly referred to. For further details of an air cycle system, reference is hereby made to the above-referred-to U.S. Patent 2,867,989 and U.S. Patent 2,870,698, granted to Stanley G. Best.
Referring to FIG. l, the specific embodiment chosen to illustrate the invention for the purpose of explanation, but not limitation, comprises a -source of compressed air which may be the compressor l@ of a jet or turbine engine. The air is delivered to heat exchanger 12 by way of passage 14 and then passed through turbine 14 wherein the temperature is substantially reduced. After passing through the turbine, the air is then delivered to the moisture separator 16 and next delivered to the aircraft cabin or compartment generally indicated by numeral 18. It is to be understood that the terminology cabin or cornq partments hereinafter referred to as cabin is all inclusive of any of the areas of the aircraft to which air conditioning is supplied. The turbine is coupled by shaft 22 to fan 2t) which serves to load the turbine for cooling air as a result of the substantial adiabatic expansion thereof. Fan 2li may be subiected to ram air issuing from duct 26 which is rst delivered to the heat exchanger 12 where it is in indirect heat transfer relationship with the compressor bleed air. The ram air may then be discharged overboard through duct 24. Since the temperature of the ram air is substantially lower than the bleed air, a lower temperature in response to the temperaturesignal generated by a. suitable sensorY3-2 located in the cabin. A selector control generally indicated by numeral 34 serves to compare actual temperature with a selected temperature for maintaining.V
theproper )temperature level. What has just been described is an air conditioning syste-m shown in its simple form described to exemplify an embodiment that employs a moisture separator. A suitable moisture separator is shown in the McDuif et al. U.S. Patent 2,835,340 and in U.S. patent application` S.N. 71,605, filed on November 25, 1960, by. Herbert E. Taylor and assigned to the same assignee.
In accordancewith this invention, an anti-icing control comprising a pressure differential type of control generally indicated by numeral 36 and simulator restricted now line 48 is shown in FIGURE l. Aswill be noted on the drawing, branch line 44 is interposed between the moisture separator and fixedv restriction 46 for conducting fluid to control 36. It should be understood that'the restriction may be eliminated if sufiicient pressure losses-due to the friction of fluid iow in the ducting is available. Simulator line 48V bypasses the moisture separator and as will be more fully described hereinbelow serves to simulate the conditions in the line y12 when ice is not present. The ducting 48 is substantially smaller than duct-l ing 12A and has disposed therein a pair of adjustable restrictions 50 and 52. The restrictions are adjusted so that the pressure drop across each restriction is made substantially equal to the pressure drop .across the mois-2` ture separator. and restriction 46 respectively.
It will be realized that thek areas of restrictions 50 and 52 and 46 are iixed so that the restriction to the air passing therethrough is also iixed while'the ow'passing through the moisture separator varies as a function of the formation of ice. Thus ice accumulating in the moisture-separator reduces the flow area causing the pressure drop thereacross to vary. In selecting the sizes ofthe duct, it-v will be realized that line 48 is substantially smaller than the size of duct 12 sothatl the-fluid issuing into the cabin will not disturbthe environmental conditions therein.
Diaphragm 38 forming a pair of opposing variable volume chambers 40 and 42 is disposed in control 3 6, Fluid conducting passage 51 is interposed between restrictions 50 and 52` for conducting pressure to chamber 42 of control 36. Thus it is apparent from the foregoing that the diaphragm is subjected to intermediate pressure between restriction 50` and 52, the intermediate between the moisture separator and restriction 46 and the low rate spring 54. Upon the selection of the properV sizes of restrictions 50 and 52, the resultant pressure force o n the diaphragm will be substantially zero at the control point in the no-icing condition. This is owing to the fact that the ratio of theareas of restrictions 50 and 52 is made substantially equal to the ratio of the moisture separator area and the area of restriction 46 respectively, thus forming a bridge type pneumatic circuit; hence the pressure in chambers 42 and 40 will also be substantially equal during a no-ice condition. It will be realized that the pressure in chamber 40 relative to cabin pressure is va function of the weight flow ofthe airstream through the separator while the pressure in chamber 421 (relative to cabin pressure) is a function of the same weight iiow and the icing condition. Since the diaphragm acts as a subtractor, the weight now effect therefore is substantially eliminated, hence the position of the diaphragm becomes sensitive solely to the pressure dropattendant the accretion of ice in the moisture separator. That is to say that the diaphragm is insensitive'to the weight ow of the air stream. Adjusting spring 53 sets the value a-t which the control limits the increase in pressure drop due to ice formation. It is to be understood that reversing of the position of moisture separator and restriction 46 together 4 with the proper piping connections to control 36 wil product identical results.
Thus, it becomes apparent Vfrom the foregoing that the position of the diaphragm is responsive to the icing condition within the moisture separator independent of the air weight ow.
If ice should accumulate within the moisture separator, the pressure immediately upstream thereof will increase. The increased pressure is reflected in the simulatorline '48. Since the ow restrictions are fixed, the pressure immediately downstream of restriction 50' will also reect an increase in pressure. Since the pressure drop across the moisture separator will Vary due to the restriction causedv by the accumulation of ice, the pressure downstream of` the moisture separatory will remain substantially unchanged. The' now increased pressure intermediate restrictions 50 and- 52 is admitted into chamber 42, ywhere it causes diaphragrnSS to translate. Thus, it becomes apparent that the position of diaphragm is a function of the increased pressure drop across the moisture -separatorresulting from accumulation of ice therein. Flapper member 68 is carried by diaphragm 38 and moves with respect to the discharging orice 56. While'thisdescription deals with the utilization of a pneumatic servo device for transmitting the anti-ice signal for controlling the position of valve 166, it will be understood that any other force' transmitting mechanism may be employed for accomplishing thisfeature.
Continuing with the explanation of the servo mechanism, the servo control system may comprise the variable restriction 56, iixed restriction 62, and branch line 64 interposed therebetween which conducts regulated servo pressure .to actuator 69. When at the null or balanced position in the no ice condition, the apper 68 will be positioned with respect to orifice 56 to hold valve 66 in the closed position. When the flapper moves toward oriiice 56 for varying its area' and hence restrict the ow passing therethrough the pressure drop across restriction 46 is caused to rise and hence passage 64 reilecting this risedelivers an increased pressure signal to actuator 68; While any suitable pneumatic actuator may -be employed with the servo system the one selected is merely described for illustration purposes and will only be briefly referred to. The actuator comprises a pair of opposing diaphragms wherein diaphragm 72 has an eective area larger than theVV area of diaphragm 70. Pressurized iluid is continuously appliedto diaphragm 70 while servo control uid is applied to diaphragm 72. The pressure introduced to diaphragm 72 is selectedto matchV the opposing forces creat ed by diaphragm 70 so that valve 66 is held closed when control36 is in the null position. By increasing the pressure in line 64 which is conducted to diaphragm `72, -valv'e 66 operatively connected to the diaphragm bythe linkagermembers 76 and 78 schematically illustrated will be caused to o pen.
FIGURE 2 illustrates the modification of theY anti-ice control and comprises a sensor and actuator combination Vgenerally indicated by numeral 100. The sensor 100 yfunctions substantially similar to the simulator and control device describedin the foregoing. In this arrangement, a pair of opposing diaphragms 114 and 116. are ,subjected to the pressure drop across .the moisture separator and the pressure drop across the xed restriction 46. The diaphragm forms four huid-receiving chambers 102, 104, 106 and 10,8. 'I'he pressure upstream and downstream ofthe moistureseparator is admitted'to chambers 104 and 102 respectively, and the pressure upstream and downstream of restriction 46 is admitted into chambers 106 arid 108, respectively. A linkage member 110 cooperates with linkage member 112 for rotating valve 66 and admitting warm air to the moisture separator inthe event-that ice should accumulate therein. The areas of the diaphragm are selected so that they will be in a proper relationship when the moisture separator is in the no-icing condition so as -to produce a zero resultant force on the diaphragm. The diaphragm 114 serves to produce a signal which is a function of ice formation and weight ow and diaphragm 116 serves to produce as signal which is a function of air weight ilow only. The latter-mentioned signal is a biasing signal which continuously bucks the water separator pressure drop signal so that the resultant signal measures the pressure drop due solely to ice formation. It will be realized that chambers 1% and itin are sealed from each other in any suitable manner to prevent the introduction of errors in pressures in these adjacent chambers.
Curve A represents the pressure drop across the moisture separator when in the no-icing condition. Curve B is shown to illustrate the control obtained by the usual type of diderential pressure drop regulator not employing my invention. As a result of my invention, the difference between the no-icing condition, i.e. curve A, and the control line achieved by my anti-icing control, i.e. curve C, is substantially constant at all weight flow values.
Since the etfect due to weight ilow is substantially eliminated in the anti-icing controls shown in FIGS. 1 and 2, the errors arising due to variations in weight ilow through the moisture separator are eliminated. Also, due to weight llow changes, the positive feedback eect is substantially eliminated and hence improving the stability characteristics of the control.
lt is to be understood that the invention is not limited to the specic embodiment herein illustrated and described, but may be used in other ways without departing from its spirit.
1. In combination with a water separator susceptible to the accretion of ice caused by moisture laden air owing therethrough, a supply of warm air, means for regulating the now of warm air from said supply to the moisture separator for preventing ice from forming in the moisture separator, means for controlling said regulating means comprising a bypass passage having a pair of spaced restrictions and connected to the airstream at a point away from the moisture separator, a pressure responsive element subjected to the pressure downstream of the moisture pressure and the pressure intermediate the restrictions.
2. In the combination as dened in claim 1 including a spring acting on the pressure responsive element in opposition to the pressure intermediate the restriction.
3. In the combination as defined in claim 1 wherein the restrictions are mechanically adjustable.
4. In the combination as dened in claim 1 including a passage for conducting the airstream through the moisture separator including a fixed restriction disposed therein.
5. In an anti-icing control for a moisture separator subjected to a moisure laden airstream Whose .temperature -i's below freezing, a passage connecting the moisture separator for delivering the moisture separator discharge air to or from a point remote therefrom, a simulator line for simulating the pressure conditions across the moisture separator when ice is not present therein, said simulator line being substantially smaller in diameter than the connecting passage and having a pair of restrictions sized so that the ratio of the pressure drops across said pair of restrictions is proportional to the ratio of the pressure drop across the moisture separator and the pressure loss in said passage respectively, means -for measuring the difference between the pressure intermediate the pair of restrictions and the pressure 4between the moisture separator :and said passage for producing a signal, means responsive to said signal for dumping warm air into the airstream to prevent the further accumulation of ice in the moisture separator.
6. In an anti-icing control for a moisture separator subjected to a moisture laden airstream whose temperature is below the freezing point of water, a source of warmair whose temperature lis above the freezing point of Water, a passage for conducting the discharge air from the moisture separator to or from a point remote therefrom yand having a restriction formed therein, means for regulating the ilow of warm air to mix with the colder air for preventing ice from accumulating in the water separator, means for sensing when ice accumulates in the water separator for oontrolling said regulating means, said sensing means comprising a housing having a pair of cooperating diaphragms for dening four fluid receiving chambers, one of said diaphragms subjected to the pressure drop across the mois. ture separator and the other of said diaphragms subjected to the pressure drop across the restriction, means responsive to the position of said cooperating diaphragms for controlling said regulating means.
7. In an anti-icing control for a water separating device which is subjected to blocking caused by freezing of the moisture carried by a moving airstream, a passage having a irst restriction in series relation with ysaid water separating device, a supply of air lwhose temperature is above the freezing point of water, a conduit for directing the ow of warm air from the :supply to the water separating device, a normally closed valve disposed in the conduit, means responsive to iluid pressure for opening the valve in response to ice forming inthe Water separating device, said means comprising a housing, a diaphragm mounted in the housing and defining a pair of opposed chambers, a high pressure receiving conduit terminating in a discharge orifice extending into the housing and mounted in close proximity to the diaphragm together therewith forming a variable orice, a xed restriction formed in the conduit, a branch line disposed between the fixed tand variable restrictions, a simulator ilow line connected to the airstream and having a second .and third serially spaced restriction mounted in parallel relation to the Water separating device and said rst restriction, said diaphragm subjected to the pressure downstream or" the moisture separator for varying the area of the variable oriiice for establishing the pressure to the responsive means for opening said normally closed valve upon reaching a predetermined value.
8. In an anti-icing control system for a liquid separator susceptible to accumulating frozen matter from a moisture laden airstream, said anti-icing control system adapted to introduce warmer air to the airstream for raising the tempera-ture of the liquid and prevent the freezing in the moisture separator, means including a valve responsive to an icing condition in the separator for regulating the flow of warmer air, said means comprising a pressure sensing device having a pair of cooperating Vdiaph-ragms, one of said diaphragms subjected to the pressure differential of the Huid across the moisture separator and the other diaphragm subjected to the pressure differential of `the ilud across a restriction formed in series relation with the moisture separator, said diaphragms characterized by having their areas when exposed to said pressure diierentials during the no-icing condition of the separator producing a resultant signal to maintain said valve in the closed position when ice accretes in the moisture separator, said Iresultant signal opens said valve upon reaching a predetermined value.
References Cited in the le of this patent UNITED STATES PATENTS 2,809,714 Sims Oct. 15, 1957 2,829,505 Oates Apr. 8, 1958 2,992,542 Arthur July 18, 1961