US2116958A - Means for circulating fluids - Google Patents

Description

May 10, 1938. K. P. BRACE Er AL 2,116,958

MEANS FOR CIRCULATING FLUIDS Filed April 19, 1935 2 Sheets-Sheet l 3nventor4 ffemperPBrace RObertBPQr'a 0rd 5 W (Ittomeg May 10, 1938. BRAE ET AL 2,116,958

1 MEANS FOR CIRCULATING FLUIDS Filed April 19, 1935 2 Sheets-Sheet 2 3nnentoud ffemperPBrace Zfioberfli POmwfard Gttorneg Patented May 10, 1938 PATENT OFFICE MEANS FOR CIROULATING FLUIDS Kemper l. Brace and Robert B. P. Crawford, Washington, D. 0.

Application April 19, 1935, Serial No. 17,368

This invention deals with the forced circulation of fluids and more particularly with the propulsion of one liquid into another under a higher pressure without the employment of pumps or other mechanical moving parts. An object of the invention is to provide a method and apparatus for continuously concentrating a solun For solutions, of non-electrolytes such as cane equal to the prestion.

sure of any solution depends upon the co'ncenv tion which is being continuously diluted and for continuously diluting a solution which is being continuously concentrated thereby maintaining the degree of concentration substantially con-. stant.

A further more specific object is to provide a method and means for. supplying liquid to a boiler without the use of a pump or other mechanical moving mechanism.

A still further more specific object is to provide a method and apparatus for pumping the liquid in an absorber type of refrigerator from the absorber into the boiler without the use of mechanical pumps and without the use 01' hydrogen or other gases commonly used to balance the pressures in systems of this kind.

Further objects and advantages will become apparent as the description proceeds.

Referring to the accompanying drawings which are made a part hereof and on which similar are used to denote the same reference characters part thruout,

Figure 1 is a view in elevation of one of the simplest forms of apparatus embodying the invention,

Figure 21s a view in elevation of a refrigerating system of the absorber type showing the application of the invention,

Figures 3 and 4 are modified forms of refrigerating apparatus showing the invention.

It is well known that if a pure solvent is separated from a solution of a solute in the same solvent by a semi-permeable membrane, there will be a flow of solvent thru the membrane into the solution. This flow will occur even when the pressure upon the solution is much greater than the pressure upon the solvent. The pressure necessary to be applied to the solution to prevent.

this fiow is called the osmotic pressure of the solu- As would be expected, the osmotic prestration of the solution, that. is, the higher the concentration, the higher the osmotic pressure.

sugar, the osmotic pressure is sure which an equivalent gram molecular volume of the solute would exert if confined to the space occupied by the solution. Due to the eflfect of ionization, the osmotic pressure of electrolytes such as NaCl, NaOH, LiC'l, etc., is as a rule considerably higher than that of non-electrolytes of the same concentration. It hasibeen found that for any substance, whether it is an electrolyte or From the above formula it can be readily seen that the osmotic pressure of any solution which is of suflicient concentration to lower the vapor pressure appreciably of the solvent is very high. For example, the. osmotic pressure of a six molar (67%) sugar solution is 232 atmospheres or 3410 lbs. per square inch whereas the vapor pressure lowering of a six molar sugar solution L L'L pc is only 20% at 70 degrees F.

The fact that the osmotic pressure of a six molar sugar solution is equal to 3410 lbs. per square inch means that if a semi-permeable membrane separates the solution from pure solvent, that is, frompure water, a pressure of 3410 lbs. per square inch would have to be appliedto the solution to prevent water from passing thru the membrane into the solution.

11' instead of separating a solution from a pure solvent, a solution is separated from a stronger solution by meansoi' a semi-permeable membrane, there will be a flow of pure solvent from the weakersolution to the stronger and the pressure causing the flow is equal to the difference between the osmotic vpressures of the two solutions. The flow will continue until the concentration of the two solutions is the same, that is until both solutions have the same osmotic pressure.

Now if the stronger solution is continually concentrated by boiling oil? the solvent and the weaker solution dition of pure solvent, then the flow of pure solvent" thru the membrane from the weaker solution to the strong solution will continue as long as there is a difference in concentration.

Figure 1 shows one of the simplest embodiments of the invention in the form of apparatus for continuously concentrating a solution which is being continuously diluted and for diluting a solution which is being continuously concentrated. Vessels Ill and l l contain weak solution I 2- and strong solution l3 respectively of some non-volatile solute in a suitable solvent, such for is continually diluted by the adexample as cane sugar in water. The solutions are separated by a semi-permeable membrane 15. Pure solvent may be boiled ofi from the strong solution I3 by heating element 14, thereby concentrating the solution and pure solveht'may be supplied by pipe [8 to the solution 12 to dilute this weak solution. So long as the concentration of the solution 13 is greater than the concentration of the solution 12 there will be a flow of pure solvent thru the semi-permeable membrane from chamber 18 into. chamber ll.

We may assume that the solution 12 is a 1.0 molar solution of cane sugar in water and that the solution 13 is a six molar solution of cane sugar in water. The osmotic pressure of a six molar solution is 3410 lbs. per square inch. The osmotic pressure of a 1.0 molar solution is 397 lbs. per square inch. Therefore, the force driving pure solvent (water) from the weak solution 12 into the strong solution 13 is 3410 minus 397 lbs. per square inch or3013 lbs. per square inch, and nothing will stop the flow of solvent from the weak into the strongsolution except an external pressure on the strong solution of 3013 lbs. per square inch. It is apparent from the foregoing that a semi-permeable membrane provides means for causing a solvent to flow from a weak solution under a low pressure to a strong solution under a. high pressure without the aid of a mechanical pump. Pressure may be built up in the boiler by providing a throttling valve 11.

From the structure described it will be apparent that the device may have many possibilities in its adaptation to useful purposes. For example, if the vapor under pressure from the boiler is conducted to a fluid motor the device may serve as a boiler for an engine in which the boiler is fed without the use of mechanical pumps or injectors.

Figure 2 shows the invention adapted to a refrigerating system of the absorber type. In this form of refrigerator a vapor is absorbed into a solution. As here shown numeral 18 indicates an evaporator, 19 an absorber, 20 a boiler, 2i a condenser, 22 a vapor conducting connectionfrom the boiler to the condenser and 123 a connection from the condenser to the evaporator. v Vapor is boiled ofi by a heater 2 1. A cooling coil 25 cools the liquid in the absorber. This cooling coil may be supplied with cooling water which passes thru 'pipe 26 to the condenser after leaving coils 25. If

preferred both the cooler 25 and the condenser may be air cooled; :such cooling systems are well known and therefore need not be here described;

Before starting, the boiler will be partially filled with a suitablesolntion. .This may be a solution of cane sugar and water asstated in the description of the system shown of any suitable non-volatile solute, such as NaOH,

.LiCl, H2804, Lil, ZnCl, etc., in a solvent.

Numeral 21 indicates the strong solution in the boiler, 28 a weak solution in the absorber and 29 the pure solvent in the evaporator. There will be a body of solvent'vapor 30 above the body .of solvent in the evaporator. The upper portion of the evaporator communicates with the upper portion of the absorber thru a passage 3|. A semipermeable membrane 32 separates the strong solution 21 in the boiler from the weak solution 28 in" the absorber. Suitable examples of such membranes are collodion, parchment, animal intestine, animal bladder, fish skin, rubber,-copper ferrocyanide precipitated in porous earthenware, porcelain, ground glass, gelatine, etc.

After filling the system to the desired levels hfFigure 1, or a solution with the solutions and solvent, all air and other foreign gases are evacuated from the system and the system closed. The evaporator will be surrounded by or in heat exchange relation with the media to be cooled. Heat extracted from this medium will evaporate the refrigerant. Now the vapor pressure above the pure solvent 28 is greater than the vapor pressure above the weak solution 28. There will therefore be a flow of vapor from chamber 18 thru channel 8| into chamber 19, this vapor being absorbed into the solution 28. This evaporation of vapor from the solvent body 28 and absorption into 28 will cause the temperature in 18 to fall and the temperature in IS to rise. The added heat in solution 28 may be carried ofl by'the cooling coil 25. The addition of pure solvent to the weak solution 28 will tend to dilute this solution. But the solution in the boiler 20 is stronger than the solution 28. There will, therefore, be a flow of pure solvent thru the semi-permeable membrane 82 from the body of solution 28 into the solution 21. The heater 24 continuously boiling of! pure solvent from the solution 21 continuously concentrates this solution. The addition of pure solvent from absorber 19 will tend to keep the solution at the same degree of concentration.

The rate of flow of pure solvent from I8 to 28 is directly proportional to the difierenoe between the osmotic pressures of the solutions 21 and 28 minus the difference in total pressure in vessels i9 and 211. Thus if the solution 28 is a 1.0 molar sugar solution having an osmotic pressure of 397 lbs. per square inch and solution 21 is a 6 molar sugar solution having an osmotic pressure of 3410 lbs. per square inch and if the pressure above the two liquids be ignored for the present, there will be a difference in pressures of 3410 minus 397, or 3013 lbs. per square inch and this will represent the force driving the pure solvent from solution 28 intosolution 21.

For practical purposes a solution of sodium bycane sugar solution. Let us assume, therefore,

. that water and NaOH are the solvent and 'the solute-respectively. Let us assume that the temperature desired in the evaporator is 40 degrees F. and that the temperature of the tap water for cooling coil 25 is '10 degrees. Now the vapor pres sure of water at 40 degrees is 6.4 mm. of Hg'and therefore in order for the-water 29 in the evaporator 18 to boil at 40, the vapor pressure of the solution 28 in the-absorber 19 must be less'than' 6.4 mm. of Hg at a temperature slightly in ex- "cess of 70 degrees (say perhaps degrees). Ex-

perimental data show that the vapor pressure of a 40% solution of NaOH in water exerts a vapor pressure of 5.3 mm. of Hg. at 80. Y Therefore, we can assimie that the concentration of the solution 28 is 40% and that the driving force causing solvent vapor (water) to pass from l8 to'l9 as 6.4-5.3,that is as 1.1 mm. of mercury. Withan unrestricted passage 31 between the chamber 18 and the chamber 19 water vapor will pass at a rapid rate from 29 to 28 and the temperature of 29 will be maintained at 40 degrees as long as the temperature of the solution 28 is kept at 80 degrees and the concentration at 40%.

greater than'28. Let us assume that the concen- 7 sorber and the concentrator or boiler.

permeable membraneous material tration of 21 is 50% by weight. By the formula given, the osmotic pressure of a 40% solution 28 at 80 degrees F. is 28,300 lbs. per square inch. The osmotic pressure of a 50% solution 21 at 165 degrees F. (B. P. at 36 mm. Hg) is 35,750 lbs. per square inch. The difl'erencebetween the osmotic pressure of solution 21 and solution 28 is 7,450 lbs. per square inch. Experimental data indicate that the amount of semi-permeable membrane required for a 100 lb. ice box is five square feet.

Figure 3 showsa form of the invention in which an interchanger 40 is positioned between the concentrator and the absorber. It will be noted that there is a temperature difference of about 85 degrees between the concentrator and the absorber. It is advisable to prevent a loss of heat from the concentrator to the absorber. The interchanger is designed to reduce the heat loss as far as possible, and thereby increase the emciency of the system. Numerals 4|, 42, 48 and 44 denote the condenser, the evaporator, the ag- T e evaporator contains pure solvent 45, the absorber contains weak solution 46 and the boiler a strong solution 41. Solvent is boiled off by heater 48. Cooling water for the cooler 48 is supplied thru pipe 50 the water leaving thru pipe after passing thru the condenser 4| to condense the vapor from the boiler. Both cooler 48 and condenser 4| may be air cooled if desired.

The upper portion of the evaporator chamber is connected by pipe 52 with a pipe 58 which extends down into the weak solution 46 and terminates in a header 54 which is perforated to permit vapor to pass into the solution 46 and be absorbed therein. The absorber is connected by pipes 55 and 56 with a chamber 51 thru which the weak solution is circulated by convection.

A chamber 58 is positioned within the chamber- 51 and its walls are formed partially from semi- 59. The strong solution in the boiler is circulated thru the chamber 58 passing from the boiler thru pipe 63 thence thru the interchanger 40, pipe 60, pipe 61, back thru the interchanger 40 and pipe 62 into the boiler. A water jacket 64 may be placed about the pipe 60 to cool the strong solution before it enters the chamber 58. This jacket may be supplied with water from the coil or water cooling jacket 48.

The heater may include a flue 61 which passes up thru the boiler to effect better heating.

Refrigerant vapor driven oi the boiler passes thru pipe '65, condenser 4| and into receiver 66. In order to insure that only liquid refrigerant shall pass from the receiver to the evaporator a valve 68 operated by a float 69 controls passage of refrigerant to the evaporator.

Any suitable refrigerant may be used. For domestic refrigerators requiring evaporator temperature of 20 degrees or lower it is believed the most satisfactory solution would be a solution of ammonium thiocyanate (NHiCNS) in liquid ammonia (NH:). v

Let us assume that the temperature desired in the evaporator is 15 degrees F. and that the temperature of the tap water or cooling air, when air is used, is 90 degrees. We will assume that the cooler 48 is large enough to maintain a temperature of 100 degrees in the weak solution 46. We will assume also that the cooling water in passing thru the cooler 48 is heated to approximately 100 degrees and that it is eflective to condense the ammonia in the condenser at a temperature of 110 degrees.

Now the vapor pressure of pure ammonia 45 in the evaporator 42 at 15 degrees F. is 2100 mm. of Hg. In order to have a flow of vapor from the evaporator to the absorber the vapor pressure of the weak absorbing solution must be less than the vapor pressure of the pure solution. The vapor pressure of a 60% solution of NHCNS in ammonia at 100 degrees F. is approximately 2000 mm. of Hg. This gives us a vapor pressure diiference between the evaporator and the absorber of 100 mm. of Hg. We may therefore assume that the weak solution 46 is a 60% solution of NH4CNS in NH3. According to the formula the osmotic pressure of a 60% solution of NH4CNS in NH; at 100 degrees F. is 40,719 lbs. per square inch. Assume that the strong solution 41 in the boiler is an 80% solution of NH4CNS in NHa. From the formula we note that the osmotic pressure of an 80% solution of NHiCNS in NH: at 100 degrees F. is 49,677 lbs. per square inch. It should be noted that the strong solution which is circulated from the boiler is cooled by the jacket 64 and by the body of weak solution at 100 degrees temperature which surrounds the chamber 58.

Now as we have stated above, the vapor pressure above the weak solution 46 is 2000 mm. of Hg or about 38 lbs. per square inch. The vapor pressure above the strong solution is the vapor pressure of pure ammonia at condenser tempera- .ture, which as we-have stated is 110 degrees F.

This vapor pressure is about 250 lbs. per square inch. The force tending to drive pure ammonia liquid from the weak solution into the strong is (49,677+38) (40,719+250) =8746 lbs. per square inch It is therefore apparent that in spite of the pressure difference of 212 lbs. in the boiler and the absorber pure liquid will flow from the absorber into the boiler at a rapid rate thru the semipermeable membrane due to osmotic force.

Figure 4 shows another embodiment of the invention. Numerals 10, 1| and 12 represent the evaporator, the boiler and the absorber. The absorber consists of a plurality of tubes having walls of semi-permeable membraneous material connecting headers!!! and 82. This absorber is positioned in a chamber 13 where it is enveloped in vapor passing from the evaporator thru passage 14. The solution circulating by convection thru the absorber is cooled by air cooler 15 of any suitable sort. Pure solvent vapor in chamber 13 will be absorbed thru the walls of the tubes and will tend to dilute the solution therein. To maintain the proper degree of concentration in the tubes, a portion of the solution is circulated thru the boiler thru pipes 11,18 and interchanger 18. This circulating solution is cooled by air cooler 16. This pipe 18 may be coiled around the flue 80 to effect better heating.

The boiler will be partially filled with a suitable solution. This may be a solution of NHACNS in NHa. The pure solvent in the evaporator may be liquid ammonia 82. Ammonia vapor boiled ofi from the boiler will pass thru pipe 93, be condensed by air condenser 83 and delivered to receiver 84. A valve 85 controlled by bellows 86 will control passage of liquid from pipe 81 to pipe 88 so .as to prevent the passage of gas to the evaporator- Pressure in the bellows and pressure below the valve will be equal since both are subject to the pressure in the condenser thru pipes 81 and 88 so that'the valve 85 will be closed by gravity. When liquid accumulates in the leg 88 of the U-tube this will unbalance the valve and permit liquid refrigerant to pass thru the valve into the line 89.

Instead of the pressure operated valve Just described we may use the float controlled valve shown in Figure 3.

Assume that a temperature of 15 degrees F. is desired in the evaporator and that the cooling media for the absorber is at a 90 degree temperature and that the coolers are sufflciently large to maintain a temperature of 100 degrees in the absorption solution and a temperature of 110 degrees in the condenser. We will assume, as stated above, that the solution Si is a 60% solution of NHlCNS in NIB. Now, as we have stated, the

vapor pressure of pure ammonia at 15 degrees is 2100 mm. of Hg. The vapor pressure of a 60% solution of NH4CNS in NH: at 100 degrees F. is 2000 mm. of Hg. The osmotic pressure of a 60% solution of NHrCNS in NH: is 40,719 lbs. per square inch. Since there is a pressure in the absorber chamber 13 outside the tubes of about '38 lbs. per square inch the total force tending to drive the pure solvent into the solution thru the semi-permeable membrane is I 40,757 lbs. per square inch. But the vapor pressure of the pure ammonia in the condenser is the vapor pressure at a temperature of 110 degrees which is about 250 lbs. per square inch. Taking this from the pressure indicated above, since this is a pressure acting against the flow of solvent into the strong solution, we have a total pressure acting to drive solvent vapor into the solution of 40,507 lbs. per square inch. 8

From the foregoing it will be apparent that we have a system in which the solvent will be automatically supplied to the boiler and that the system will operate continuously without the necessity of a pump or the presence of an inert gas to balance pressures.

It will be obvious to those skilled in the art that various changes may be made in the invention without departing from the spirit thereof. We, therefore, do not limit ourselves to the invention as shown in the drawings andas described in the specification but only asset forth in the appended claims.

What we claim is:

1. A device of the kind described comprising a vessel having a compartment therein having a solution of a pure solvent and a nonvolatile solute dissolved therein, a second compartment having a body of pure-solvent therein under a pressure less than that in the first named compartment,

a semi-permeable membrane separating the two bodies of liquid to-cause a flow of solvent by osmosis into the solution, means for boiling ofl solvent from the solution and means for supplying pure liquid solvent to the body of pure solvent.

2. A device of the kind described comprising a vessel divided into two chambers by a semi-permeable membrane, a concentrated solution of, a solvent and a nonvolatile solute in one chamber, a less concentrated solution of the composition in the other chamber, and a third chamber having a body of-pure solvent therein, the space above said last named solvent being opento the space above the weaker solution to permit passage of vapor from said solvent to the said solution to be absorbed therein, the semi-permeable membrane causing osmotic flow of pure solvent from the weaker to the stronger solution.

3. A refrigerator of the absorber type comprising a boiler, an absorber, an evaporator, a condenser and heater, the boiler having therein a strong solution of a solvent and a non-volatile solute, the absorber having therein a weaker solution of the same solvent and solute, means for conducting vapor from the evaporator into the weaker solution to have it absorbed therein, means for circulating said weak solution and for cooling it, a semi-permeable membrane separating the weak from the strong solution, means for circulating said strong solution in surface contact with said membrane to circulate the pure solvent absorbed from the weaker solution and bring it into the boiler to dilute the solution therein which is being continuously concentrated by boiling oif pure solvent therefrom.

4. A refrigerator of the absorber type comprising. a boiler, an evaporator, an absorber, a plurality of tubes positioned in the said absorber, said tubes being filled with a solution of a solute and a solvent, said tubes being exposed to solvent vapor from the evaporator, said tubes having walls of semi-permeable membranes to cause the solvent to flow by osmosis from the absorber to the solution, means for carrying. of! heat from the solution, and means for circulating said solution thru the boiler, and means for boiling of! pure solvent from the solution, for condensing it and returning it in liquid form to the evaporator.

5. A refrigerating system of the absorber type comprising a still, an absorber, an evaporator, a condenser, and a semi-permeable membrane separating vapor of the pure solvent in the evaporator from solution circulated from the still, a liquid trap between the condenser and evaporator, and a pressure controlled balanced valve operable upon a rise of liquid in the trap for returning only liquid refrigerant to the evaporator.

.6. A device of the kind described comprising a pair of chambers, one containing a solution of a volatile solvent and a non-volatile solute, the other containing a body of the solvent substan-, tially free of the solute and under a pressure less than the pressure in the first named chamber, a semi-permeable membrane separating the solution from vapor of the body of pure solvent, and means for vaporizing solvent from the solution in the first named chamber, condensing it, and delivering it to the body of solvent in the other chamber, the said membrane causing pure solvent to flow by osmosis from the body ofpure solvent to the solution. r

'1. A refrigerating system of the kind described comprising a boiler containing a solution of a solute and a volatile solvent, a chamber, having walls of semi-permeable membraneous material, in communication with the solution in the boiler, thermal means for circulating the solution from the boiler thru the said chamber, an evaporator, means for boiling off vapor from the solution, condensing it and delivering it to the said evaporator, means for conducting refrigerantvapor from said evaporator into surface contact with said semipermeable membraneous walls while maintaining said vapor under pressure appreciably lower than the pressure in said chamber, the solvent vapor being caused to flow by osmosis only thru the semi-permeable membraneous walls of the said chamber into the solution in said chamber.

KEMPER P. BRACE. ROBERT B. P. CRAWFORD.

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