GB2195174A

GB2195174A - Miniaturized high frequency electrically driven vapor cycle refrigeration system

Info

Publication number: GB2195174A
Application number: GB08719539A
Authority: GB
Inventors: James W Powell; Thomas A Bem
Original assignee: Williams International Corp
Current assignee: Williams International Corp
Priority date: 1986-09-15
Filing date: 1987-08-19
Publication date: 1988-03-30
Also published as: GB8719539D0; JPS6375446A; DE3728518A1

Description

1 GB2195174A 1

SPECIFICATION

Miniaturized high frequency electrically driven vapor cycle refrigeration system BACKGROUND OF THE INVENTION

Conventional D.C. or low frequency A.C. electric motors have weight and volume characteristics that cannot be tolerated in certain military and automotive applications which require that component size be minimized. Such miniaturized systems are particularly desirable for combat vehicle and aircraft applications.

SUMMARY OF THE INVENTION 80

The. refrigeration system of the present in vention utilizes a small high speed centrifugal compressor driven by a directly coupled, high frequency, three phase, induction motor. A feature of the system comprises a hot gas bypass line that extends from the compressor outlet to the inlet side of the evaporator whereby hot gas flows directly from the com pressor to the evaporator for the purpose of maintaining relatively constant compressor 90 flow over a range of conditions.

The refrigeration subsystem is a reverse Rankine vapor cycle, operating primarily within the two-phase (liquid-vapor) of the Rl 13 working fluid. In the refrigeration subsystem, working fluid leaves the receiver as a high pressure, saturated liquid and passes through a dryer unit before entering the expansion valve. The expansion valve throttles the work ing fluid to the evaporator pressure. As a re sult, the fluid entering the evaporator is in a two-phase condition. In the evaporator, the liquid phase is vaporized at constant pressure and temperature, and the latent heat of vapor ization cools the incoming ambient air. The saturated vapor which leaves the evaporator is then compressed to condenser pressure by the refrigerant compressor. The fluid leaving the compressor is a slightly superheated va por. The working fluid is then condensed at constant pressure to the saturated liquid con dition in the condenser using ambient air to remove the heat of condensation. The cycle is then completed as saturated liquid from the condenser enters the receiver/reservoir. This cycle absorbs heat at low temperature in the evaporator and rejects this heat plus the refri gerant compressor power at high temperature in the condenser.

The high frequency refrigerant compressor 120 induction motor is driven either directly from a high speed permanent magnet alternator or from an appropriate inverter.

R1 13 was selected as the refrigerant work- ing fluid for the vapor cycle because of its special suitability for use with centrifugal compressors. The relatively high specific volume of R1 13 permits acceptable compressor rotational speeds and reasonable aerodynamic and mechanical design criteria.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a schematic of a reverse Rankine vapor compressionrefrigeration sys- tem in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

As seen in the drawing, a refrigeration systern 10, in accordance with a constructed embodiment of the instant invention, comprises a high-speed, high-frequency, three phase, brushless, A.C. electric induction motor 12, capable of driving a directly coupled two-stage centrifugal compressor 14 at, for example, 112,000 RPM. The compressor 14 utilizes a centrifugal impeller operating at a design pressure ratio of 5.4:1. The impeller embodies an eight-splitter/vane, 50 degree lean-back confi- guration operating at an actual 111,375 RPM.

In, for example, a combat vehicle environmental protection system application, a sixpole power subsystem turboalternator 15 may be utilized having an output frequency of 3750 Hz. The alterntor 15 is rotated at 75, 000 RPM, a 6:4 pole ratio establishing a nominal motor speed of 112,500 RPM and, therefore, a nominal compressor rotor speed of 112,500 revolutions per minute.

The direct A.C. motor drive makes it possible to eliminate the shaft seal common with belt driven compressors, and to assemble the unit as a hermetically sealed assembly. Combination of the high speed/high frequency induc- tion motor, having a minimum speed of 70,000 RPM, powering the centrifugal compressor results in an overall package that is smaller and lighter than comparable low speed piston or vane-type systems. Analysis indi- cates system volume and weight savings in the 30% to 50% range.

The refrigerant selected for the system 10 is Freon R1 13 due to its suitability for use with centrifugal compressors. When compared to comparable refrigerant fluorocarbons the higher specific volume characteristics of Freon R1 13 results in reasonable acrodynamic and mechanical design criteria. Although Freon R1 13 exhibits a relatively high freezing point, its boiling point is elevated as well meaning that it can be shipped in unpressurized containers. A relatively low density in the solid state, as opposed to the liquid state, acts to prevent damage to the refrigeration system evaporator in the event of a freeze-up.

In accordance with one feature of the instant invention, a bypass valve 16 is disposed in a line 17 that forms a first fluid flow circuit from the compressor 14 to an evaporator 18.

The hot gas bypass valve 16 controls flow of hot gas from the compressor outlet directly to the evaporator 18 whereby a small amount of superheated vapor acts to maintain constant compressor flow over a range of conditions and eliminates evaporator icing.

2 GB2195174A 2 A second parallel fluid flow path from the compressor 14 to the evaporator 18 comprises a line 19 having a condenser 20, Freon R1 13 reservoir 22, filter 24 and expansion valve 26 therein. In operation, saturated vapor is compressed isentropically to a superheated vapor by the motor driven compressor 14. As the Freon 113 passes through the compressor 14, oil may be added to aid in the lubrication thereof. The oil is separated out in the compressor diffuser stage and circulated back to the compressor inlet preventing residual lubricant in the remainder of the system. Superheated vapor from the compressor 14 flows through both the first flow path comprising the line 17 and valve 16 and through the second flow path, comprising the line 19 to the condenser 20 which acts to remove heat at constant pressure, turning the vapor into a saturated liquid. As a liquid, the refrigerant flows to the expansion valve 26 with minimum loss of enthalpy. Thereafter, the refrigerant passes at constant pressure through the evaporator 18. Ambient heat entering the evaporator 18 vaporizes the working fluid into the saturated vapor state, for return to the compressor 14 thus, completing the cycle. While the preferred embodiment of the in- vention has been disclosed, it should be appreciated that the- invention is susceptible of modification without departing from the scope of the following claims.

Claims

1. A miniaturized refrigeration system com prising:

a source of high frequency alternating cur rent, a high speed high frequency induction mo tor, a centrifugal refrigerant compressor directly coupled to said motor, an evaporator having an outlet connected to an inlet on said compressor, a first fluid flow path from an outlet on said compressor to an inlet of said evaporator having a valve therein for controlling the flow of superheated vapor from said com pressor to said eyaporator thereby to main tain relatively constant compressor flow over a relatively wide range of conditions, and a second fluid flow path from the outlet on said compressor to the inlet of said evapo rator comprising a condenser and an expan sion valve.

2. A refrigeration system in accordance with claim 1 wherein the operating speed of said induction motor and compressor is over 70,000 revolutions per minute.

3. A refrigeration system constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Published 1988atThe Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.

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