Commercial Refrigeration FINAL TEST Questions With 100% Correct Answers. Guaranteed Success.

Commercial Refrigeration FINAL TEST Questions With 100% Correct Answers. Guaranteed Success. How is the cooling effect in a mechanical refrigeration system produced? - answerEvaporation of liquid refrigerant into vapor What is the primary purpose of a compressor? - answerIt circulates and pressurizes the refrigerant vapor before the vapor Is condensed for re use Name another function that must be performed by the compressor - answerIs raise the pressure and temperature of the refrigerant vapor. This allows the refrigerant to condense into a liquid as it circulates through the condenser What characteristic defines an "open" type compressor? - answerHas a drive shaft protruding from the compressor What are the two main disadvantages of a hermetic compressor? - answerIf either the motor or compressor malfunctions, the entire unit must be replaced. The motor is actually a part of the refrigerant circulation system. This means that a burnout can contaminate the entire system In a reciprocating compressor, the piston is connected to the crankshaft by a _____ - answerConnecting rod Name the three elements of performance that are the major factors in evaluating a compressor - answerEfficiency, capacity, and economy of operation If the suction gas superheat is too low, What could be the result? - answerLiquid refrigerant might enter the compressor. This causes stress on the compressor valves, wrist pins, rods, shaft, etc. It also causes excessive foaming of the oil in the crankcase and other damaging effects. The compressor will not reach its rated capacity What will happen if the suction gas temperature is too high? - answerWill cause the compressor to run hot How is compressor efficiency often judged? - answerBtu per cubic foot (Btu/ft^3) of displacement When the same model of open type compressor is used with both air cooled and water cooled condensing units, which is usually run at a slightly higher rpm? - answerWater cooled What is the equation for ratio of compression? - answerThe absolute discharge pressure (psig plus 14.7) divided by the absolute suction pressure (psig plus 14.7) What type of compressor is found in large applications up to 10000 tons? - answerCentrifugal compressors Which compressor utilizes two helical rotors to compress the refrigerant gas? - answerScrew compressor What is the most outstanding advantage of the hermetically sealed compressor over the open type? - answerHas no protruding crankshaft or shaft seal How are the disadvantages overcome in compressors that are employed in low temperature applications? - answerUse supplementary cooling How are the disadvantages overcome in water cooled hermetic compressor systems? - answerHave water jackets, or water coils around the compressor/motor shell or housing Is the condenser load greater or less for compressors designed for low temperature applications than for compressors designed for high temperature applications? - answerThe condenser load is less for the low temperature applications Name the two most widely used desiccants today - answerAlumina and zeolites Why is a drier installed in a refrigeration system? - answerThe primary property in the drier is desiccant which removes moisture and acid Why must a desiccant act rapidly? - answerBecause it must reduced moisture to a sufficiently low level in one pass through the drier What is the criterion for stability of a desiccant? - answerTo stay in its original solid state What standard determines the moisture holding capacity of a drier? - answerARI Standard 710-86 ARI Standard 710-86 specifies flow rates through a filter drier at a pressure drop of _____ - answer1 Psig Where should a moisture liquid indicator be installed? - answerInstalled in the liquid line, either upstream or downstream from the drier How many sources of heat have to be rejected from the vapor in the condenser? - answerThree, the heat absorbed in the evaporator, the heat picked up in the suction line, the additional heat of compression caused by compressor operation Name the three stages in which refrigerant in the condenser is cooled - answerThe vapor is cooled to saturation temperature (desuperheated), the vapor is condensed to a liquid (latent heat