US2764879A - Cooler construction in a hot-gas engine - Google Patents

Description

Oct. 2, 1956 DE LANGE r. 2,764,879

COOLER CONSTRUCTION IN A HOT-GAS ENGINE Filed Dec. 30, 1954 INVENTOR LEENDERT D: LANGE AGENT United States Patent "ice 2,764,879 COOLER CONSTRUCTION IN A HOT-GAS ENGINE Leendert De Lange,

lands, assignor to Hartford.National Bank and Trust Company, Hartford, Conn., as trustee This invention relates to hot-gas reciprocatingapparatus comprising a space of low temperature anda space of high temperature, which spaces freely communicate with one another by way of a heater, a regenerator and a cooler, while their volumes may be varied by means of one or more pistonlike bodies. A gas, the so called working medium, in the apparatus performs a closed thermodynamic cycle which gas always remains in the same state of aggregation.

The term hot-gas reciprocating apparatus is to be understood in this case to mean a hot-gas reciprocating motor, a refrigerator or a heat pump, the two last-mentioned operating on the reversed hot-gas motor principle. The refrigerator is frequently also termed cold-gas refrigerator. Hot-gas reciprocating apparatus, as is wellknown, may be constructed in different ways, for example as displacer apparatus, as double-operating apparatus, as apparatus having the cylinders at an angle to one another, or as apparatus in which the working space of a cold-gas refrigerator is united with that of a hot-gas motor.

In such apparatus the heater constitutes the heat-exchanger in which heat is supplied to the working medium of the apparatus, whereas heat is dissipated from the working medium in the cooler. It is also known that different media may be utilized in the apparatus. In the case of hot-gas motors and heat pumps, use is commonly made of air as the working medium. In the case of coldgas refrigerators use may be made of air, nitrogen or oxygen, hydrogen or helium according to the purpose for which the apparatus is intended. Air may be used only if the temperature at which the refrigerator must supply cold output is not unduly low and, for example, not lower than l40 C. If a cold-gas refrigerator must supply cold production at lower temperatures, hydrogen or helium must be utilized. In this case, the refrigerator may be of a construction such that a temperature of, for example 200 C. is reached.

According to the invention it has been found that in the cooler the ratio between the length and the inner hydraulic diameter of the ducts must be located within determined limits. It was found also that if the ratio is smaller than the values specified below, the cooling action of the cooler becomes so small that the trans mission of heat from the working medium in the apparatus to the walls of the ducts becomes insuflicient. However, if the ratio is increased, the loss due to flow increases to such an extent that although the transmission of heat is considerably improved, the specific capacity of the apparatus decreases.

Furthermore, it has been found that the limits are dependent upon the kind of the gas performing a thermodynamic cycle in the apparatus.

Further in accordance with the invention, the total length L of the ducts in the cooler wherein L is at least 20 M- dh, and at the most 55 M- dn, and wherein M=the molecular weight of the gas in the apparatus and dn=the inner hydraulic cross diameter of the ducts Emmasingel, Eindhoven, Netherfor the gas in the cooler.

2,764,879 Patented oer. 2 1956 2 The hydraulic diameter is four times the quotient of the surface and the periphery of the passage of a duct. If the cooler comprises two 'or more-portions located one after another, L represents the total distance between the inlet surface of one cooler and the outlet surface of the other cooler.

It will be evident that the molecular weight differs for the different gases. Thus, the molecular weight is 2 forhydro'gen and 4 for" helium while a molecular weight of 29 m'aybe assumed for air.

The above-mentioned limits apply to different types of coolers, for example to pipe coolers and also to coolers with fins.

In order that the-invention may be readily carried into effect, it will now be described with reference to the accompanyingdrawing, which" Fig. 1 shows a cold-gas refrigerator of the displacer type and Fig. 2 shows on an enlarged scale a horizontal section of part of a cooler.

The refrigerator comprises a cylinder 1, in which a displacer 2 and a piston 3 are adapted to move up and down with a substantially constant phase difference, the displacer acting upon the volume ,of a space 4 which freely communicates with a space 8 through a freezer 5, a regenerator 6 and a cooler 7. The spaces 4 and 8 are frequently termed the freezing space and the cooled space, respectively said space 8 naturally being at a temperature higher than the temperature of space 4.

The displacer is coupled by means of a driving-rod system 9 to a crank of a crank-shaftll), whereas the piston is coupled by means of a driving-rod system 11 to cranks of the same crank-shaft 10.

The refrigerator is driven by an electric motor 12, so that the piston and the displacer are moved up and down, substantially expansion occurring in the space 4 and substantially compression occurring in the space 8. A gas to be cooled, for example air, may be led along the fins 17 provided on the outside of the freezer 5,While any condensate produced may be discharged from the apparatus. The working medium used in the apparatus itself may be, for example, hydrogen. The cooler 7 is of the type comprising fins 17. The cooling water is supplied to the cooler by way of a line 13 and discharged therefrom through a line 14.

In the refrigerator shown, the working medium used is hydrogen. If the hydraulic diameter of the duct 18 is 0.1 cm., L must be at least 20.2 .0.1 cm.=2.3 cm. and at the most 55.2- .0.1=6.3 cm.

If, however, the refrigerator is operated with air, L must be located between different limits. In this case L is at least 20.29- .0.1 cm.=3.8 cm. and at the most 55.29 .0.1 cm.=10.45 cm.

It is noted that the duct 18 having a hydraulic diameter of 0.1 cm. is obtained if the width 15:62.5 microns and the length l6=250 microns such as with a duct 18 as given by way of example, in

shown in Fig. 2. In this embodiment, in which a large number of fins is'provided, the inner cross-section may without objections be regarded as a rectangle. However, if the number of fins or the radius of curvature of the wall of the cylinder should be small, it is preferable to calculate the surface and the periphery of the actual inner section. It will be evident that in the case of pipes having a circular cross-section, the hydraulic diameter is equal to the actual diameter of the pipe.

While I have shown and described the preferred embodiment of my invention, it will be understood that the latter may be embodied otherwise than as herein specifically illustrated or described and that in the illustrated em- 3 parting from the underlying idea or principle of the invention within the scope of the appended claims.

What is claimed is:

1. A hot-gas reciprocating apparatus having a gas of invariable chemical composition therein comprising a low temperature space, a space having a temperature higher than said low temperature space, a freezer, a regenerator and a cooler having ducts therein, cylinder means, two pistons reciprocating in said cylinder meansfsaid spaces communicating with each other through said cooler, freez er and regenerator while said gas performs a closed thermodynamic cycle therein and the volume of said gas being varied in said spaces by the said reciprocating pistons, the total length L of the ducts in the cooler being at least 20 M- d11, where M =the molecularweight of the gas in the apparatus and dh=the hydraulic diameter of said ducts for the gas in the cooler.

2. A hot-gas apparatus as setfo'rth in claim 1 wherein L is between 20 M- dh and 55 M -db.

3. A hot-gas reciprocating apparatus having a gas of invariable chemical composition which is subjectto* a closed thermodynamic cyclic process in whichthe gas is invariably the same physical state comprising; at least one cylinder; a crankshaft; at least one piston in said cylinder connected to said crankshaft; said cylinder having a chamber on one side of said piston with a relatively low temperature, and a chamber on another side of said piston having a temperature higher than said first chamber; said chambers varying continuously in volume; and means connecting said chamber of relatively low temperature with said chamber of relatively high temperature; said means comprising a' freezer, a regenerator, and a cooler provided with ducts and connected in series; the total-length L of the ducts in the cooler being at least 20 M dh, where M =the molecular weight of the gas in the apparatus and dh=the hydraulic diameter of said cooler ducts.

References Cited in the file of this patent UNITED STATES PATENTS 2,011,964 Aug. 20, 1935

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