Docsity
Docsity
Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity

Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips
Guidelines and tips
Sell on Docsity
Sell on Docsity
Docsity AI
Docsity AI
Log inSign up

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search for your university

Find the specific documents for your university's exams

Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents
download point icon20 Points

For each uploaded document

Answer questions
download point icon5 Points

For each given answer (max 1 per day)

All the ways to get free points
Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

Commercial Refrigeration: A Comprehensive Q&A Guide, Exams of Engineering

University of CambridgeEngineering

A valuable resource for students studying commercial refrigeration systems. it presents a series of questions and answers covering key components, operational principles, and troubleshooting techniques. The q&a format facilitates learning and self-assessment, making it ideal for exam preparation or reinforcing classroom learning. the questions delve into compressor types, condenser operation, evaporator function, and refrigerant handling, offering a practical understanding of commercial refrigeration technology.

Typology: Exams

2024/2025

Available from 05/06/2025

peter-karanja-3
peter-karanja-3 🇬🇧

5

(3)

4.1K documents

1 / 7

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Commercial Refrigeration FINAL TEST
How is the cooling effect in a mechanical refrigeration system produced? - Answers -
Evaporation of liquid refrigerant into vapor
What is the primary purpose of a compressor? - Answers -It circulates and pressurizes
the refrigerant vapor before the vapor Is condensed for re use
Name another function that must be performed by the compressor - Answers -Is 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? - Answers -Has a drive shaft
protruding from the compressor
What are the two main disadvantages of a hermetic compressor? - Answers -If 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 _____ -
Answers -Connecting rod
Name the three elements of performance that are the major factors in evaluating a
compressor - Answers -Efficiency, capacity, and economy of operation
If the suction gas superheat is too low, What could be the result? - Answers -Liquid
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? - Answers -Will cause the
compressor to run hot
How is compressor efficiency often judged? - Answers -Btu 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? - Answers -Water
cooled
What is the equation for ratio of compression? - Answers -The absolute discharge
pressure (psig plus 14.7) divided by the absolute suction pressure (psig plus 14.7)
pf3
pf4
pf5

Partial preview of the text

Download Commercial Refrigeration: A Comprehensive Q&A Guide and more Exams Engineering in PDF only on Docsity!

Commercial Refrigeration FINAL TEST

How is the cooling effect in a mechanical refrigeration system produced? - Answers - Evaporation of liquid refrigerant into vapor What is the primary purpose of a compressor? - Answers -It circulates and pressurizes the refrigerant vapor before the vapor Is condensed for re use Name another function that must be performed by the compressor - Answers -Is 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? - Answers -Has a drive shaft protruding from the compressor What are the two main disadvantages of a hermetic compressor? - Answers -If 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 _____ - Answers -Connecting rod Name the three elements of performance that are the major factors in evaluating a compressor - Answers -Efficiency, capacity, and economy of operation If the suction gas superheat is too low, What could be the result? - Answers -Liquid 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? - Answers -Will cause the compressor to run hot How is compressor efficiency often judged? - Answers -Btu 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? - Answers -Water cooled What is the equation for ratio of compression? - Answers -The 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? - Answers - Centrifugal compressors Which compressor utilizes two helical rotors to compress the refrigerant gas? - Answers -Screw compressor What is the most outstanding advantage of the hermetically sealed compressor over the open type? - Answers -Has no protruding crankshaft or shaft seal How are the disadvantages overcome in compressors that are employed in low temperature applications? - Answers -Use supplementary cooling How are the disadvantages overcome in water cooled hermetic compressor systems? - Answers -Have 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? - Answers -The condenser load is less for the low temperature applications Name the two most widely used desiccants today - Answers -Alumina and zeolites Why is a drier installed in a refrigeration system? - Answers -The primary property in the drier is desiccant which removes moisture and acid Why must a desiccant act rapidly? - Answers -Because it must reduced moisture to a sufficiently low level in one pass through the drier What is the criterion for stability of a desiccant? - Answers -To stay in its original solid state What standard determines the moisture holding capacity of a drier? - Answers -ARI Standard 710- ARI Standard 710-86 specifies flow rates through a filter drier at a pressure drop of _____ - Answers -1 Psig Where should a moisture liquid indicator be installed? - Answers -Installed 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? - Answers -Three, the heat absorbed in the evaporator, the heat picked up in the suction line, the additional heat of compression caused by compressor operation

How far away from the inlet air wall should the air opening for condensers be when condensing units are place in position? Why? - Answers -They should be located side by side, facing the wall, with the air openings at a distance of 24 to 36 inches This ensures that all units get a sufficient supply of outside air If an air cooled condensing unit room has an exhaust capability of 1000 cfm per unit horsepower and 2 1/2 ft^2 of inlet louver per unit horsepower, what will the average inlet air velocity be in feet per minute? - Answers -Less than 500 ft/min A typical low temperature rack maintains a suction temperature of ____ - Answers -- degrees F The three way heat reclaim valve directs the refrigerant either to the _____ or to a _____ - Answers -Condenser, heat reclaim coil What is the function of the flooding valve? - Answers -Maintains head pressure in low ambient conditions by reducing the available condensing area and restricts the flow of a liquid refrigerant from the condenser The branch liquid line solenoid valve shuts off refrigerant flow to the _____, but allows a backflow into the ______ - Answers -Evaporator, liquid manifold A SORIT, BEPR, or CDA valve may be used as a ____ valve - Answers -Evaporator pressure regulating (EPR) The tube surface of a blower evaporator is known as the ____ surface, and the fin surface is called the ____ surface - Answers -Primary, secondary What is a common evaporator coil face velocity in most air conditioning installations? - Answers -500 ft/min When an evaporator is designed for operation at 32 degrees F and above, how many fins per linear inch of tubing are generally used? - Answers -8 fins/inch When equipment is selected for an application, which component is commonly selected first? - Answers -Condensing unit Where are gravity fin coil units and gravity booster units generally used? - Answers -Are used in refrigerant areas that require little or no air flow. Examples meat aging rooms and beef sales coolers Name two limiting factors of the off cycle defrost method - Answers -Is generally limited to applications where temperature applications is kept at a minimum of 35 degrees F The pressure differentials required for temperature below 35 degrees F make it nearly impossible to get complete defrosting between running cycles. This method cannot be used in systems with operating temperature below 35 degrees F

What is one of the results of vapor defrost as the refrigerant leaves the evaporator? - Answers -The refrigerant gas is warmed by picking up additional heat Why must a capillary tube system evaporator have a low side accumulator? - Answers - To accept not only the high side refrigerant during the OFF cycle, but also the exes refrigerant not required by the complete low side during certain operating temperatures The heat added to vapor above the point of complete vaporization is called _____ - Answers -Superheat Name the three fundamental pressures that affect the opening and closing of a TEV - Answers -Bulb pressure, spring pressure, evaporator pressure What's does the abbreviation MOP stand for? - Answers -Maximum operating pressure It is the point at which all liquid in the remote bulb is evaporated What is the proper location for the remote bulb of a TEV? - Answers -Is on the suction line at the outlet of the evaporator, but still within the refrigerated area where the difference between suction line and ambient temperature is as close as possible When installing the remote bulb of a TEV, you must ensure good thermal contact between the ____ and the ____ - Answers -Bulb, suction pipe or tubing Where should the entrance of the equalizing line of a TEV be located in relation to the TEV remote bulb? - Answers -Immediately downstream of the remote bulb What is the first step in determining if a TEV is performing its function properly? - Answers -Measure the superheat to find out if a valve is performing its function The saturated liquid temperature of a refrigerant is called the ____. The saturated vapor temperature is called the ____. The difference between these two temperatures is known as _____ - Answers -Bubble point, dewpoint, temperature glide What type of pressure control is referred to as a safety control? - Answers -High pressure What is the operating differential of a differential pressure controller? - Answers -It is the difference in pressure or temperature required to open or close the switch contacts. It is actually the change in instrument differential from cut in to cut out for any setting What type of application is best suited for the use of a constant pressure valve? - Answers -Constant load applications What two forces are used to hold open a normally open solenoid valve? - Answers - Gravity, spring force

Pressure drop in valves and fittings is converted to "equivalent resistance" of _____ - Answers -Tubing or pipe of the same size in feet of length Suction and hot gas line selection charts are based on a pressure drop corresponding to a change in saturation temperature of ____ - Answers -2 degrees F What must you do to avoid gas binding? - Answers -A separate vent line When should you insulate a liquid line? - Answers -Sometimes, When it is exposed to the temperatures higher than the temperature of the liquid leaving the condenser, receiver, or heat exchanger. This could occur if it runs along a hot roof or other hot space The start winding and the run winding in a split phase motor are wired in ____, and are spaced ____ degrees apart - Answers -Parallel, 90