REFRIGERANT INJECTION INTO OIL FOR SOUND REDUCTION

Abstract: In a low side hermetic compressor, a small portion of the compressed refrigerant gas is diverted and dis­ charged into the oil sump (60) through an orifice body (30) into the upper level of the oil in the sump (60). This results in a supersaturated solution of refrigerant in oil in the upper level which drives the refrigerant out of the oil, thereby creating froth which provides sound reduction without disturbing the lower level which remains stratified.

Description: The radiated sound level of hermetic compressors, is of extreme importance since, in residential applications, they are typically located in a window opening or the yard. Of additional importance, is high performance of the compressor, however, as compressor performance increases, the sound sources and paths are often altered resulting in unacceptable radiated sound levels. As a result, the twin goals of high performance and acceptable radiated sound levels are generally in conflict. Conventional sound reduction techniques such as the use of paddles on the oil pickup tube to generate a froth are often inadequate for high performance compressors. It has already been proposed to reduce the radiated sound levels in low side hermetic compressors by injecting pressurized refrigerant into the oil sump for foam generation. This has the advantage that oil agitation by the stirring action of paddles is not required. An example of reducing radiated sound levels in low side hermetic compressors by injecting pressurized refrigerant into the oil in the oil sump for froth generation is described in US-A-3 066 857 which discloses a method according to the precharacterizing portion of claim 1 and or apparatus according to the precharacterizing portion of claim 4. In US-A-3 066 857 refrigerant that bypasses the piston on the compression stroke enters the crankcase and is then injected into the oil in the oil sump. The object of the invention is to provide an improved method and apparatus for the generation of foam or froth to reduce radiated sound levels in low side hermetic compressors. To achieve this, according to the invention, there is provided a method for reducing radiated sound levels in low side hermetic compressors having a muffler for receiving refrigerant at compressor discharge pressure, comprising injecting pressurized refrigerant into an oil sump at a point beneath the surface of the oil to create froth on the oil surface, characterized by diverting a small portion of refrigerant at compressor discharge pressure from refrigerant supplied to the muffler; and injecting the diverted pressurized refrigerant into the oil sump whereby a supersaturated solution of refrigerant in oil is created in the upper level of the oil in the sump which drives the refrigerant out of the oil in the upper level to create a froth without disturbing the lower level of the oil in the sump. In further accordance with the invention there is provided an apparatus for foam generation in a low side hermetic compressor having an oil sump comprising muffler means having header structure for delivering compressed refrigerant at compressor discharge pressure to said muffler means and a discharge line for conveying compressed refrigerant from said muffler means; and orifice means for discharging pressurized refrigerant beneath the surface of said oil sump to generate foam, characterized by diverting means for diverting a small portion of the refrigerant under compressor discharge pressure from the muffler means to said orifice means. In a low side hermetic compressor the refrigerant at compressor discharge pressure is directed from the cylinder to a muffler and then to the discharge line leading from the compressor. By diverting a small portion of the refrigerant gas at compressor discharge pressure from a muffler body into the compressor oil, the oil is foamed which results in an attenuated path through which the sound must travel and a reduced radiated sound level. The high pressure refrigerant is injected into the upper level of the oil without disturbing the lower level which remains stratified. This results in a supersaturated solution of refrigerant in oil in the upper level which drives the refrigerant out of the oil, thereby creating froth, since the inside of the shell of the compressor is at suction pressure. The lower level is undisturbed by all of this and remains a stable, saturated solution which is in equilibrium. Additionally, the upper level serves to dampen the effects of pressure drops on the lower level. The pressure drops are a normal consequence of compressor operation but can cause outgassing when the pressure is lowered. The dampening effect is because the froth is more sensitive to pressure changes than the lower level. The length and placement of the orifice body as well as the size of the orifice are important. The orifice body should be vertically located in the lower portion of the muffler body with the refrigerant gas escaping downward. The orifice body should be of a sufficient length to extend a sufficient depth into the oil sump to permit the supersaturation of the oil with refrigerant. Also, the orifice body should provide a flow path of a sufficient length and relatively small cross section to shield the orifice from the pressure oscillations in the muffler body. The orifice itself should be of such a dimension as to prevent the discharge of too much refrigerant from the muffler while permitting sufficient foam generation. These combined design parameters allow proper sound attenuation without a significant loss in compressor performance. For a further understanding of the present invention, reference should now be made to the following detailed description thereof taken in conjunction with the accompanying drawings, wherein: Figure 1 is a partially cutaway view of a muffler assembly; Figure 2 is a sectional view taken along line 2-2 of Figure 1; and Figure 3 is an enlarged sectional view of the orifice body and screen assembly shown in Figure 2. In Figures 1 and 2, the numeral 10 generally designates a muffler assembly for use in a hermetic compressor including a top portion 11 and a bottom portion 12 which are brazed or otherwise suitably joined together in a fluid tight manner to form chamber 13. Collars 14, 15 and 16 are formed in top portion 11 for respectively receiving header 17, discharge line 18 and header 19. Threaded collar 20 is formed in bottom portion 12 for threadably receiving orifice body 30. Referring now to Figure 3, orifice body 30 has a threaded portion 32 for threadably engaging threaded collar 20. A first bore 34, a second bore 36 of a lesser diameter than bore 34 are serially formed in orifice body 30 and terminate at end wall 38. An orifice 40 extends through wall 38. A typical thickness for wall 38 is 1.52 to 1.77 mm (0.06 to 0.07 inches) and a typical diameter for orifice 40 is 0.33 to 0.40 mm (0.013 to 0.016 inches). As illustrated, one or both ends 40 a and b of orifice 40 may be counterbored or tapered to a depth of 0.25 mm (0.01 inches). A strainer assembly 50 is located in bore 34 and is made up of a screen material portion 52 and a ring portion 54 secured to the screen portion 52. The ring portion 54 is force fit into bore 34. The pores of the screen portion 52 are about half the size of the orifice 40 so as to prevent its being clogged. In operation, as best shown in Figure 1, the orifice body 30 extends vertically into the oil sump 60 for a distance of approximately 25.4 mm (one inch). In the illustrated two-cylinder configuration, compressed refrigerant from each of the compressor cylinders (not illustrated) is delivered to chamber 13 of muffler assembly 10 via headers 17 and 19, respectively. Most of the compressed refrigerant passes from chamber 13 via discharge line 18 which delivers the refrigerant to the condenser (not illustrated) of a refrigeration system. According to the teachings of this invention, a small portion of the compressed refrigerant passes from chamber 13 via orifice body 30. Specifically, refrigerant from chamber 13 passes into orifice body 30 and serially passes through screen material 52 which acts as a filter and into the chamber defined by bores 34 and 36 and passes through orifice 40 into the oil sump 60. Since the refrigerant entering orifice 40 is at compressor discharge pressure while the refrigerant vapor above the oil sump 60 is at compressor suction pressure, the refrigerant discharged into the oil sump is injected into the upper level of the oil in sump 60 without disturbing the lower level. This results in a supersaturated solution of refrigerant in oil in the upper level of the oil in sump 60 which drives the refrigerant out of the oil and produces sound reducing froth due to the presence of suction pressure over the oil sump 60. The lower level is undisturbed by the injection of refrigerant and remains a stable saturated solution which is in equilibrium and dampened by the upper level from the effects of normal pressure fluctuations in operation.

Claims: A method for reducing radiated sound levels in low side hermetic compressors having a muffler (10) for receiving refrigerant at compressor discharge pressure, comprising: injecting pressurized refrigerant into an oil sump (60) at a point beneath the surface of the oil to create froth on the oil surface, characterized by: diverting a small portion of refrigerant at compressor discharge pressure from refrigerant supplied to the muffler (10); and injecting the diverted pressurized refrigerant into the oil sump (60) whereby a supersaturated solution of refrigerant in oil is created in the upper level of the oil in the sump (60) which drives the refrigerant out of the oil in the upper level to create a froth without disturbing the lower level of the oil in the sump (60). Method according to claim 1, characterized in that the step of injecting the diverted refrigerant takes place by discharging the diverted refrigerant downwardly in the sump (60) at a distance of approximately 25.4 mm (one inch) beneath the surface of the oil. Method according to claim 1, characterized in that the step of injecting the diverted refrigerant passes the diverted refrigerant through an orifice of 0.33 to 0.40 mm (0.013 to 0.016 inches) in diameter. Refrigerant injection apparatus for foam generation in a low side hermetic compressor having an oil sump (60) comprising: muffler means (10) having header structure (17, 19) for delivering compressed refrigerant at compressor discharge pressure to said muffler means (10) and a discharge line (18) for conveying compressed refrigerant from said muffler means (10); and orifice means (40) for discharging pressurized refrigerant beneath the surface of said oil sump (60) to generate foam, characterized by diverting means for diverting a small portion of the refrigerant under compressor discharge pressure from the muffler means (10) to said orifice means (40). Apparatus according to claim 4, characterized in that said orifice means (40) is 0.33 to 0.40 mm (0.013 to 0.016 inches) in diameter. Apparatus according to claim 4, characterized in that said orifice means (40) discharges approximately 25.4 mm (one inch) below the surface of said oil sump. Apparatus according to claim 4, characterized in that said orifice means (40) is 0.33 to 0.40 mm (0.013 to 0.016 inches) in diameter and 1.52 to 1.77 mm (0.06 to 0.07 inches) long.

Inventors: BAYYOUK, JACOB A., FRASER, HOWARD H., JR.
Applicants: CARRIER CORPORATION
Application year: 1987
Main classification: F04B39
IPC codes: F04B39