Refrigeration – Refrigeration producer – With lubricant handling means
Reexamination Certificate
1999-07-09
2001-01-09
Tanner, Harry B. (Department: 3744)
Refrigeration
Refrigeration producer
With lubricant handling means
C062S084000, C062S113000, C062S513000
Reexamination Certificate
active
06170286
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to refrigeration systems. More particularly, the present invention relates to compressor-driven refrigeration chillers in which at least some lubricant tends to make its way from the system compressor to the system evaporator during the course of chiller operation. With still more particularity, the present invention relates to apparatus and a method by which to return oil from the evaporator to the compressor in a refrigeration chiller using hot compressor oil as the motive force for accomplishing oil return.
The migration of lubricant from the compressor to the evaporator in a compressor-driven refrigeration chiller is an age old problem. A very large number of systems, apparatus, methods and schemes have been used and/or suggested to accomplish the return of such oil from the evaporator of a chiller, where it settles on or into the liquid refrigerant pool found therein, back to the chiller's compressor, where it is needed for lubrication. Many of such systems/schemes employ the use of an eductor which draws oil-rich liquid from the system evaporator using a pressurized fluid sourced from elsewhere within the chiller system as the motive force by which the eductor is powered.
More recently, evaporators of the so-called falling film type have begun to be employed in refrigeration chillers, such evaporators being more efficient in terms of the vaporization process that occurs therein. Falling film evaporators operate such a large majority of the refrigerant that enters the evaporator is vaporized within the evaporator shell before having a chance to pool in liquid form in the bottom thereof. This results in the development of a more concentrated and homogenous oil-rich pool of fluid at the bottom of the evaporator shell, such pool being relatively much shallower than the liquid pools in so-called flooded evaporators where the majority of the tubes in the evaporator's tube bundle are bathed in liquid refrigerant at the top of which an oil-rich mixture is found.
One oil return arrangement employed in refrigeration chillers having falling film evaporators is the one described in U.S. Pat. No. 5,761,914, assigned to the assignee of the present invention and incorporated herein by reference, which teaches the use of a so-called “flush”-type oil return system. Other than eductors/ejectors and flush-type systems, mechanical arrangements of still other and different kinds have been employed to induce or accomplish oil return from the evaporator to the compressor in a refrigeration chiller system. Many such systems are relatively difficult and/or expensive to manufacture and/or control but accomplish oil return nonetheless. Each of such systems brings with it various negative attributes, difficulties, failure modes and expense that detract from their attractiveness with respect to the oil return process.
The need continues to exist for an improved lubricant return system in a refrigeration chiller which efficiently returns lubricant from the system evaporator to the system compressor in a reliable yet simple and inexpensive manner.
SUMMARY OF THE INVENTION
It is an object of the present invention to cause the return of oil from an evaporator to the compressor in a refrigeration chiller.
It is another object of the present invention to provide for the return of system lubricant from the evaporator to the compressor in a refrigeration chiller by the use of heat which exists in the chiller system.
It is a still further object of the present invention to provide for the return of lubricant from the evaporator to the compressor in a refrigeration chiller by the transfer of heat from a first substance within the chiller to the mixture of oil and liquid refrigerant found within the system evaporator when the chiller is in operation, the addition of such heat to the oil-rich mixture causing, in turn, the beneficial cooling of the substance which is the source of such heat.
It is another object of the present invention to provide for the return of lubricant from the evaporator to the compressor in a refrigeration chiller by the method of percolation.
It is an additional object of the present invention to return oil to the compressor in a refrigeration chiller from the location or locations within the chiller's evaporator where the concentration of oil in the pooled mixture of oil and liquid refrigerant found therein is highest.
It is still another object of the present invention to provide for the return of lubricant from the evaporator to the compressor in a refrigeration chiller using a process/methodology which is generally fail-safe and is a byproduct of system operation, yet which does not require the use of mechanical or electromechanical apparatus, valving or controls dedicated to or associated with the oil return process.
Finally, it is a specific object of the present invention to induce the return of the oil-rich mixture found in the evaporator of a refrigeration chiller to the chiller's compressor and/or its sump by placing hot oil, sourced from the chiller's oil sump, in heat exchange contact with the oil-rich mixture found in the system evaporator so as to induce the percolation thereof, the rejection of heat from the hot oil to the oil-rich evaporator mixture beneficially cooling the oil enroute to its use to lubricate the bearing surfaces of the chiller's compressor.
These and other objects of the present invention, which will be appreciated when the following Description of the Preferred Embodiment and attached Drawing Figures are considered, are accomplished by bringing hot system lubricant, pumped from the oil sump of the compressor of a refrigeration chiller in the normal process of its delivery to compressor bearing surfaces, into heat exchange contact with (i) the oil-rich mixture found generally at the surface of the liquid pool in a flooded evaporator or (ii) with the oil-rich mixture that resides at the bottom of an evaporator of the falling film type. The heat of the compressor lubricant pumped from the chiller's oil sump is rejected to the oil-rich evaporator mixture at a location exterior of the evaporator. The heating of the evaporator mixture at such location causes a portion of the refrigerant within the oil-rich mixture to vaporize/boil which, in turn, causes the mixture to percolate. Percolation of the mixture has the effect of raising slugs of the oil-rich evaporator mixture from the location of heat exchange into the compressor's oil sump, the net result being the return of lubricant from the evaporator to the chiller's oil sump where it becomes available for re-use in the lubrication of the chiller's compressor. The rejection of heat from the oil which is pumped from the oil sump into the oil-rich evaporator mixture not only causes percolation of the oil-rich mixture to accomplish oil return but cools the oil enroute to the bearings of the system compressor which is beneficial in terms of the ability of such oil to reliably carry out its compressor bearing lubrication function.
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patent: 5606872 (1997-03-01), Terasaki
patent: 5890374 (1999-04-01), Lee
American Standard Inc.
Berer William J.
Ferguson Peter D.
O'Driscoll William
Tanner Harry B.
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