US2131782A - Cooling fluids to low temperatures and diffusion refrigerating machines therefor - Google Patents

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Oct. 4, 1938. G, MAlURl 2,131,782

COOLING FLUIDS TO LOW TEMPERATURES AND DIFFUSION REFRIGERATING MACHINES THEREFOR I Filed Sept. 29, 1936 v 3 Sheets-Sheet l FHURI HTTORNEY Oct. 4, 1938. G MA|UR| 2,131,782

COOLING FLUIDS TO LOW TEMPERATURES AND DIFFUSION REFRIGERATING MACHINES THEREFOR Filed Sept. 29, 1936 5 Sheets-Sheet 2 Inw or: mp0 mum FITTORNE y Oct. 4, 1938. MAIUR] 2,131,782

COOLING FLUIDS To LOW TEMPERATURES AND DIFFUSION I REFRIGERATING MACHINES THEREFOR Filed Sept. 29, 1936, 3 Sheets-Sheet 3 RTTORNEY Patented on. 4, was 2,131,782

UNITEDISTATES PATENT OFFICE I COOLING FLUIDS TO LOW TEIVIPERATURES AND DIFFUSION REFRIGERATING MA- CHINES THEREFOR Guido Maiuri, London, England Application September 29, 1936, Serial No. 103,088 In Great Britain August 28, 1936 3 Claims. (Cl. 62-1195) This invention relates to cooling fluids to low gas atmosphere and thereby prevents such a low temperatures and diffusion refrigerating matemperature being obtained as could be obtained chines for effecting such cooling. if the gas and refrigerant entered the evaporator By diffusion refrigerating machine is meant an already cooled to the low temperature. ,1

5 absorption or resorption refrigerating machine The limiting of the low temperature obtainable, 5 wherein the refrigerant evaporates into and is by the pre-cooling of the inert gas and liquid absorbed from an atmosphere of inert gas. refrigerant on entering the evaporator is still Diffusion refrigerating machines as hitherto -more pronounced when refrigerating mediums for constructed have been arranged to produce cold obtaining low temperatures, such as propane,

at or within close range of a single temperature. ethane or ethylene with suitable organic liquid 10 There are, however, some applications of refrigabsorbents, are employed, as the latent heats of-- eration, for instance the pre-cooling of air to low evaporation of such mediums is much smaller temperatures in the production of liquid air and than that of ammonia, and therefore the partial rectification therefrom of oxygen, where it is pressures thereof are increased at a greater rate.

5 advantageous to produce cold over a wide range The object of the invention is to enable fluids to of temperatures, starting at a high refrigerating be economically cooled to low temperatures and temperature, almost atmospheric temperature, to provide therefor a. diffusion refrigerating maand ending at a very low temperature. In such c i e cap e efieci'ling Such Cooling Simulan application the refrigeration temperatures eously a o a W e range temperaturesshould conform as closely as possible to the cool-- According to the invention fl Which 20 ing of a gas, by providing a temperature gradient be gases o q are cooled to low at s of only a few degrees difference throughout the y producing d ppl i l t e fl id al n cooling, instead of the refrigeration being obliged a wide range of temp u es w t Small temper-J 'to produce and supply all the cold at the lowest atti difference from the fluid throughout the temperature attained. range of temperatures. 25

A characteristic of a diffusion refrigerating ma- :1 a diffusion refrigerating m h n according chine is the possibility of producing cold over a to the present invention, th in r s and the wide range of temperatures, by evaporating the e e a t are o d y e-fl w a -exrefrigerant vunder increasing partial pressure. change w th t p at refrigerant before However, in a diffusion refrigerating machine as entering th o t Thus a th th n rt 30 ordinarily constructed, the lowest temperature gas and the refrigerant ent the evaporator in a obtainable is limited. The inert gas can in the Cooled condition, the partial Pressure of absorber be sufficiently freed from refrigerant frigerant is low at the commencement of ev pvapour until there is a sufficiently low partial oration. and therefore a 10W minimum p 5 pressure for the refrigerant to evaporate at a low hire i obtainable- The evaporation can be 0ntemperature. However, without a heat-exchangtinued along the evaporator until the partial preser, the inert gas and the liquid refrigerant enter Sure Of the refrigerant in t e e t gas has SO the evaporator at the temperature of the medium, incr h t the temperature f refri er i n such as water or air, used to cool the absorber l y appr hes atmospheric peratureand condenser of the machine. Even if a heats simultaneously cold is p e along a 40 exchange is effected between the gas going into Wide range 0f temperaturesand the gas coming out of the evaporator, a sub- A s, Such as h e liquefied, can e oo ed stantial difference of temperature cannot be in Contra-110Wheet-exehangewithiihe p a or avoided because the temperature at the outlet giving the range of temp r r from pp from the evaporator is always definitely higher metely atmospheric downwards to the lower min- 45 than at the inlet, due to the increasing partial lm te p and throughout the Cooling pressure of the refrigerant in the inert gas as it there need be only a slight temperature difference passes through the evaporator. The inert gas or gradient, although ultimately a very low miniand the liquid refrigerant therefore both require mum temperature is attained.

cooling in the evaporator, and this cooling in- The pre-cooling of the inert gas has the fur- 50 volves the evaporation of an appreciable amount ther effect of condensing some of the vapour of of the refrigerant. This evaporation of refrigthe refrigerant and vapour of the absorbent with erant to effectvcooling of the inert gas and liquid which the inert gas is always charged on leaving refrigerant within the evaporator raises the parthe absorber. Thus the inert gas will reach the tial pressure of the refrigerant vapour in the inert evaporator relieved ofthe refrigerant absorbed by 55 the absorbent condensed by the pre-cooling, and the partial pressure of the refrigerant vapour will be correspondingly reduced, to the advantage of obtaining a low minimum temperature. To utilize this effect a somewhat volatile absorbent may be used. For example alcohol used as the absorbent with ammonia as the refrigerant will for the above reason give a lower temperature than water and ammonia.

It is desirable that the composition of the liquor supplied by the boiler to the absorber be as weak as possible, in order that in the absorber the inert gas may be freed as much as possible from refrigerant vapour. For this reason it is highly desirable that the boiler be of the kind in which practically complete rectification of the liquor can take place. For instance, the boilershould be constructed like a rectifying column, or have a liquid space in which convection is prevented or greatly restricted, for instance by the presence of beads or baffles, so that the liquor drawn off at the bottom is practically pure'absorption liquid whereas at the top it is strong liquor. In this kind of boiler the heating can be applied along a gradient of temperatures utilizing for instance the hot compressed air of an air compressor before cooling the same by water, or the exhaust of a Diesel engine, or a mixture of steam and inert gas, so that in a liquid air or similar plant the production of cold can be obtained by utilization of waste heat.

The contra-flow cooling can with advantage be adopted also in the absorber, by conducting the cold inert gas together with anyunevaporated refrigerant in contra-flow heat-exchange with the absorber, before entering the absorber.

Inthe case of aresorption machine, a range of evaporation temperatures is given owing to the progressively changing composition of the strong liquor in the evaporator. Theoretically therefore it is only necessary to pre-cool the refrigerant liquor by contra-flow with the evaporating refrigerant, prior to entering the evaporator. In practice, however, the almost impossibility of obtaining a sufhciently low degree of vacuum to obtain evaporation giving the desired low temperature, necessitates the employment of an inert gas so that only a sufficiently low partial pressure of the refrigerant is required, as distinguished from a low total pressure.

The resorption machine can also be employed in order to reach a temperature under the triple point of the refrigerant. For instance with aquaammonia,'whereas the freezing point of pure ammonia is 77 C., aqua-ammonia containing 35% of ammonia freezes at -10 5 C. With ethyl alcohol and ammonia the freezing point of the mixture is still lower and the liquor freezes as low as --108' C. so that this mixture would enable a temperature of l0'0 C. or lower to be reached without stoppage by freezing up of the machine.

Although an inert gas is employed in order to obtain a range of partial pressures of the refrigerant, the inert gas is notutilized to equalize the total pressures throughout the machine. On the contrary it is advantageous to have different pressuresin the several parts of the machine, so

that the total pressure in the evaporator is only slightly greater than the maximum partial pressure of the refrigerant, as this reduces the amount of inert gas circulated and therefore to be cooled. The difference in total pressures can be maintained by a fan for the gas and a pump for the liquor.

Representative examples of difl'usion refrigeratmama:

ing machines embodying the invention are illus trated on the accompanying drawings, in which:--

Fig. l is a diagrammatic sectional elevation of an absorption machine, and

Fig. 2 is a section on the line 22 of Fig. 1.

Fig. 3 is a sectional elevation of an alternative construction of evaporator.

Fig. 4 is a diagrammatic sectional elevation of a resorption machine.

a is the boiler of the refrigerating machine, heated by a steam coil a located in the liquor space thereof. Convection of the liquor is restricted by baille plates a, so that the weak liquor at the bottom of the liquor space and from which the refrigerant vapour has been driven off by the heat, is restrained from mixing with the stronger liquor at the top of the liquor space.

The vapour ascends into the upper portion of the boiler where it is rectified by a water-cooled coil a and baflle plates 0 From the top of the boiler a the rectified refrigerant vapour passes by a pipe b to a condenser b cooled by a water-cooled coil b From the bottom of the condenser 17 the condensed refrigerant passes by a pipe 0, past an expansion valve c to the inlet end of an evaporator d.

The evaporator d is shown in Fig. 1 as being an elongated horizontal chamber wherein liquid refrigerant is retained by a weir d at the outlet end of the evaporator.

e is an absorber, connected at the top by a pipe I to the inlet end of the evaporator d, and at the bottom by a pipe g to the outlet end thereof.

The absorber e is cooled by a water-cooled coil e The evaporator d and absorber e contain an atmosphere of inert gas, which is circulated by a fan h, driven by a motor h from the top of the absorber e through the pipe I, evaporator d, pipe 0 and up through the absorber e.

A sump at the bottom of the absorber e is connected by a pipe 1', in which is included a pump 9', to a heat-exchanger k, and thence by a pipe I to the boiler a, wherein strong liquor from the absorber is delivered by a rose m.

Weak liquor from the bottom of the boiler a, is driven under the boiler pressure up a pipe 11 to the heat-exchanger k and thence by a pipe 0 past an expansion valve 0 to the absorber e, into the upper part of which the weak liquor is delivered by a rose 12.

The'inert gas leaves the absorber e and the liquid refrigerant leaves the condenser b approximately at the temperature of the cooling water flowing in the coils e and,b'-', and as explained above, would preclude a low partial pressure of the refrigerant vapour and therefore a very low refrigerating temperature at the inlet end of the evaporator 11, if admitted to the latter at the relatively high temperature of the cooling water. It is therefore arranged for the inert gas and the liquid refrigerant to become cooled by the evaporator before entering the evaporator d. For this purpose the inert gas admission pipe I and the liquid refrigerant supply pipe 0 both extend in heat-exchange proximity with the evaporator d from the outlet end to the inlet end thereof. As the partial pressure of the refrigerant vapour diffusing more and more into the inert gas progressively inceases from the inlet end to the outlet end of the evaporator d, the temperature of evaporation of the refrigerant likewise progressively increases from the inlet end to the outlet end of the evaporator d. The inert gas arriving in the pipe f and the liquid refrigerant arriving in the pipe are therefore cooled in contra-flow with the inert gas and vapour in the evaporator d, the hottest gas in the pipe'f and the hottest liquid refrigerant in the pipe 0, namely approximately at the temperature of the cooling water, being cooled by the refrigerant evaporating at the highest partial pressure and at a temperature which may be near to that of the fluids (inert gas and liquid refrigerant) to be cooled. The cooling of the gas in the pipe I andliquid refrigerant in the pipec proceeds progressively as they flow along these pipes in heat-exchange with the evaporator, with only a slight temperature diflerence between them and the evaporator it, until they reach the inlet end of the latter already cooled approximately to the low temperature which reigns at the inlet end. The low partial pressure of the refrigerant vapour necessary for obtaining a low temperature of evaporation at the inlet end of the evaporator d, is therefore not prevented by the evaporation of refrigerant solely to cool the arriving gas and liquid refrigerant.

To adapt the evaporator to the progressive cooling of a gas, such as the pre-cooling of air in liquid air and oxygen rectifying plants, the evaporator d is shrouded by a tubular casing q. The

gas to be cooled is admitted to the casing 41 by an inlet 1 located at the outlet end of the evaporator d where the cooling temperature is highest, and leaves by an outlet s located at the inlet end of the evaporator d where the cooling temperature is lowest. Cold revert gas from the liquid air and oxygen plant may be passed in contra-flow heatexchange with the evaporator d and pipes f and c, along another casing (not shown). Thus the evaporation of refrigerant along a wide range of temperatures can be used to compensate deflciency, due to reduced calorific capacity, of contra-flowing revert gas or to inward heat leakage, in regenerative heat-exchange systems.

In an alternative construction of evaporator illustrated by Fig. 3, the evaporator is in the form of an upright casing t. The inert gas supply pipe 1, the liquid refrigerant supply pipe c and a pipe u traversed by the gas to be cooled, are intercoiled helically about a vertical axis within the I casing t. The liquid refrigerant is delivered by the pipe c to an annular trough t at the top of the casing t, and drips from this trough by a wick v on to the intercoiled pipes f, c, u. The inert gas supply pipe terminates at 1 above a diverting fairing w, whereby the inert gas is diverted towards the dripping and evaporating liquid refrigerant.

The inert gas, the liquid refrigerant and the gas to be cooled ascend their respective pipes I, c, u in contra-flow with the descending evaporating refrigerant in the casing t.

In the case of a resorption machine, as shown in Fig.4, a sump :1: wherein the weak liquor from the evaporator d is collected, is connected by a pipe 1;, including a pump z, to a rose in the vessel b, which in such case is, a resorber and not a condenser. I claim:

1. In a diffusion refrigerating machine, a boiler, a refrigerant receiver connected to said boiler, an evaporator charged with inert gas, a refrigerant inlet conduit interconnecting said refrigerant receiver and said evaporator and supplying refrigerant in contra-flow heat-exchange proximity with refrigerant evaporating in and inert gas circulating through said evaporator, an absorber charged with inert gas and connected to said boiler, an inlet conduit interconnecting said absorber and said evaporator and providing circulation of said inert gas from said absorber to said evaporator and extending in contra-flow heatexchange proximity with refrigerant evaporating in and inert gas circulating through said evaporator, an outlet conduit interconnecting said evaporator and said absorber and providing circulation of said inert gas from said evaporator to said absorber, and a fluid-conveying conduit extending in contra-flow heat-exchange proximity with refrigerant evaporating in and inert gas circulating through said evaporator.

2. In a diffusion refrigerating machine, a boiler, a condenser connected to said boiler, an evaporator charged with inert gas, a refrigerant inlet conduit interconnecting said condenser and said evaporator and supplying refrigerant in contraflow heat-exchange proximity with refrigerant evaporating in and inert gas circulating through said evaporator, an absorber charged with inert gas and connected to said boiler, an inlet conduit interconnecting said absorber and said evaporator and providing circulation of said inert gas from said absorber to said evaporator and extending in contra-flow heat-exchange proximity with refrigerant evaporating in and inert gas circulating through said evaporator, an outlet conduit interconnecting said evaporator and said absorber and providing circulation of said inert gas from said evaporator to said absorber, and a fluid-conveying conduit extending in contra-flow heatexchange proximity with refrigerant evaporating in and inert gas circulating through said evaporator.

3. A method of enabling a wide range of temperatures to a low temperature to be-simultaneously obtained in a diffusion refrigerating machine and cooling fluids therewith, consisting in pre-cooling by contra-flow heat-exchange with refrigerant evaporating in said machine inert gas and refrigerant liquid in said machine prior to admission of said inert gas to said refrigerant liquid, evaporating said refrigerant in said inert gas under increasing partial pressures of the refrigerant and a total pressure of the inert gas and the refrigerant only slightly greater than the maximum partial pressure of the refrigerant, and applying said so-produced cold along said wide range of temperatures to the fluid to be cooled by contra-flow exchange of heat between said fluid and said inert gas and evaporating refrigerant.

GUIDO MAIURI.

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