Refrigeration – Processes – Compressing – condensing and evaporating
Utility Patent
1999-03-12
2001-01-02
Capossela, Ronald (Department: 3744)
Refrigeration
Processes
Compressing, condensing and evaporating
C165S160000, C165SDIG001, C062S525000
Utility Patent
active
06167713
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the distribution of a two-phase refrigerant mixture in the evaporator of a refrigeration system. More particularly, the present invention relates to the uniform distribution of saturated two-phase refrigerant over and onto the tube bundle in a falling film evaporator used in a refrigeration chiller.
The primary components of a refrigeration chiller include a compressor, a condenser, an expansion device and an evaporator. High pressure refrigerant gas is delivered from the compressor to the condenser where the refrigerant gas is cooled and condensed to the liquid state. The condensed refrigerant passes from the condenser to and through the expansion device. Passage of the refrigerant through the expansion device causes a pressure drop therein and the further cooling thereof. As a result, the refrigerant delivered from the expansion device to the evaporator is a relatively cool, saturated two-phase mixture.
The two-phase refrigerant mixture delivered to the evaporator is brought into contact with a tube bundle disposed therein and through which a relatively warmer heat transfer medium, such as water, flows. That medium will have been warmed by heat exchange contact with the heat load which it is the purpose of the refrigeration chiller to cool. Heat exchange contact between the relatively cool refrigerant and the relatively warm heat transfer medium flowing through the tube bundle causes the refrigerant to vaporize and the heat transfer medium to be cooled. The now cooled medium is returned to the heat load to further cool the load while the heated and now vaporized refrigerant is directed out of the evaporator and is drawn into the compressor for recompression and delivery to the condenser in a continuous process.
More recently, environmental, efficiency and other similar issues and concerns have resulted in a need to re-think evaporator design in refrigeration chillers in view of making such evaporators more efficient from a heat exchange efficiency standpoint and in view of reducing the size of the refrigerant charge needed in such chillers. In that regard, environmental circumstances relating to ozone depletion and environmental warming have taken on significant importance in the past several years. Those issues and the ramifications thereof have driven both a need to reduce the amount and change the nature of the refrigerant used in refrigeration chillers.
So-called falling film evaporators, which are known in the industry, but which are not in widespread use, have for some time been identified as appropriate for use in refrigeration chillers to address efficiency, environmental and other issues and concerns in the nature of those referred to above. While the use and application of evaporators of a falling film design in refrigeration chillers is theoretically beneficial, their design, manufacture and incorporation into chiller systems has proven challenging, particularly with respect to the need to uniformly distribute refrigerant across the tube bundles therein. Uniform distribution of the refrigerant delivered into such evaporators in a refrigeration chiller application is critical to the efficient operation of both the evaporator and the chiller as a whole, to the structural design of the apparatus by which such distribution is accomplished and to reducing the size of the chiller's refrigerant charge without compromising chiller reliability. Achieving the uniform distribution of refrigerant is also a determining factor in the success and efficiency of the process by which oil, which migrates into the evaporator, is returned thereoutof to the chiller's compressor. The efficiency of the process by which oil is returned from a chiller's evaporator affects both the quantity of oil that must be available within the chiller and chiller efficiency. U.S. Pat. No. 5,761,914, assigned to the assignee of the present invention, may be referred to in that regard.
Exemplary of the current use of falling film evaporators in refrigeration chillers is the relatively new, so-called RTHC chiller manufactured by the assignee of the present invention. In addition to the '914 patent referred to above, reference may be had to U.S. Pat. Nos. 5,645,124; 5,638,691 and 5,588,596, likewise assigned to the assignee of the present invention and all of which derive from a single U.S. patent application, for their description of early efforts as they relate to the design of falling film evaporators for use in refrigeration chillers and refrigerant distribution systems therefor. Reference may also be had to U.S. Pat. No. 5,561,987, likewise assigned to the assignee of the present invention, which similarly relates to a chiller and chiller system that makes use of a falling film evaporator.
In the RTHC chiller, which is currently state of the art in the industry, the refrigerant delivered to the falling film evaporator is not a two-phase mixture but is in the liquid state only. As will be apparent to those skilled in the art, uniform distribution of liquid-only refrigerant is much more easily achieved than is distribution of a two-phase refrigerant mixture. The delivery of liquid-only refrigerant for distribution over the tube bundle in the falling film evaporator in the RTHC chiller, while making uniform refrigerant distribution easier to achieve, is achieved at the cost and expense of needing to incorporate a separate vapor-liquid separator component in the chiller upstream of the evaporator's refrigerant distributor. The separate vapor-liquid separator component in the RTHC chiller adds significant expense thereto, in the form of material and chiller fabrication costs, such vapor-liquid separator component being a so-called ASME pressure vessel which is relatively expensive to fabricate and incorporate into a chiller system.
While the RTHC chiller is a screw-compressor based chiller, it is to be understood that it is but one example of the kinds of chiller systems with which falling film evaporators can be used. The immediate prospects for use of such evaporators in centrifugal and other chillers is therefore contemplated as will be appreciated from the Description of the Preferred Embodiment which follows.
The need exists for a falling film evaporator for use in refrigeration chiller systems and for a refrigerant distributor therefor which, irrespective of the nature of the compressor by which the chiller is driven, achieves the uniform distribution of two-phase refrigerant to the chiller's evaporator tube bundle without the need for apparatus the purpose of which is to separate the two-phase refrigerant mixture into vapor and liquid components prior to the delivery thereof into the evaporator and/or into the refrigerant distribution apparatus therein.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a falling film evaporator for use in a refrigeration chiller in which a two-phase mixture of refrigerant delivered into the evaporator is uniformly distributed into heat exchange contact with the evaporator's tube bundle.
It is also an object of the present invention to eliminate the need for separate apparatus or methodology by which to achieve vapor-liquid separation in the refrigerant delivered from an expansion device to a falling film evaporator in a refrigeration chiller prior to receipt of such refrigerant in the evaporator's refrigerant distributor.
It is another object of the present invention to provide a refrigerant distributor for use in a falling film evaporator which, by the use of staged steps of flow, results in the controlled and/or uniform expression of refrigerant thereoutof along the length and across the width of the tube bundle in the evaporator.
It is also object of the present invention to provide a distributor for a falling film evaporator in a refrigeration chiller which minimizes the pressure drop in the distributed refrigerant which is attributable to the distribution process and/or apparatus.
It is, in the same vein, an object of the present inven
Hartfield Jon P.
Larson James W.
Moeykens Shane A.
American Standard Inc.
Beres William J.
Capossela Ronald
Ferguson Peter D.
O'Driscoll William
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