Micro-channel evaporator with frost detection and control

Abstract

A refrigerant vapor compression system includes an evaporator having a plurality of longitudinally extending, flattened heat exchange tubes disposed in parallel, spaced relationship. Each of the heat exchange tubes has a flattened cross-section and defining a plurality of discrete, longitudinally extending refrigerant flow passages. One or more frost detection sensor(s) is / are installed in operative association with the evaporator for detecting a presence of frost / ice formation on at one of the flattened heat exchange tubes and associated heat transfer fins. A defrost system is provided and operatively associated with the evaporator heat exchanger A controller, operatively coupled to the frost detection sensor(s) and to the defrost system, selectively activates the defrost system to initiate a defrost cycle of the evaporator in response to the signal indicative of the presence of frost formation on the flattened heat exchange tubes and heat transfer fins.

Description

FIELD OF THE INVENTION[0001]This invention relates generally to evaporator heat exchangers and, more particularly, to providing for improved control of frost accumulation on the external surfaces of evaporator heat exchangers having a plurality of parallel, flattened heat exchange tubes.BACKGROUND OF THE INVENTION[0002]Air conditioners and heat pumps employing refrigerant vapor compression cycles are commonly used for cooling or cooling / heating air supplied to a climate controlled comfort zone within a residence, office building, hospital, school, restaurant or other facility. Refrigerant vapor compression systems are also commonly used for cooling air, or other secondary media such as water or glycol solution, to provide a refrigerated environment for food items and beverage products within display cases, bottle coolers or other similar equipment in supermarkets, convenience stores, groceries, cafeterias, restaurants and other food service establishments.[0003]Conventionally, these...

AI Technical Summary

Problems solved by technology

Additionally, if the frost build-up between the fins becomes excessive, the air-side pressure drop through the evaporator increases, resulting in a decrease in airflow delivered by an air-moving device, thereby further deteriorating the overall performance of the evaporator heat exchanger.

Further, unlike the larger diameter round heat exchange tubes with relatively large spaces between the tubes, commonly used in conventional refrigerant evaporators, flattened, multi-channel tubes defining a plurality of small cross-sectional area flow passages are subject and more susceptible to damage from the accumulation of frost or ice on the external surfaces of the heat exchange tubes and associated heat transfer fins.

However, on flattened tubes, the condensing water tends to accumulate rather than drain off the tubes.

Since water expands upon freezing, repeated freezing and thawing of the accumulated condensate, particularly in the confined spaces between the heat transfer fins and the flattened heat exchange tubes (e.g., in the region where the fins contact the flattened tubes), can damage the heat exchanger by deforming or cracking the tube and causing separation of the fins from the tubes.

Furthermore, during sequential defrost cycles, more ice may accumulate on external surfaces of the heat exchange tubes and heat transfer fins of the evaporator heat exchanger and may even completely block airflow passages, forcing the evaporator to run outside of a specified operational envelope (in terms of suction pressure) and compromising refrigerant system reliability or causing nuisance shutdowns, both of which are obviously highly undesirable events.

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