Refrigeration & Air Conditioning (ME-801) - Important Questions

Calculate the COP of a Carnot refrigerator and Carnot heat pump (and heat engine / work input) operating between two given temperatures for a given heat absorbed.

State the limitations that prevent building a practical Carnot refrigeration system.

Explain the term tonne of refrigeration and discuss the advantages of dense air refrigeration system over open air refrigeration system.

Determine the mass of ice produced per day and power required for a reversed Carnot refrigerator of given TR capacity operating between given temperatures.

Explain the applications of refrigeration for food preservation and how refrigeration controls food spoilage.

Explain Boot-strap cycle and coefficient of performance or refrigerator.

Determine power for aircraft cabin pressurization, additional power for refrigeration, and refrigerating effect given altitude conditions, compressor ratio, cabin conditions and air properties.

Write short notes on selected refrigeration and air-conditioning topics such as air refrigeration advantages, cascade system, steam jet refrigeration, summer cooling load calculation, and eco-friendly refrigerants.

Discuss any three natural methods of producing refrigeration.

Calculate refrigerating effect per hour, tonnage capacity, and COP from ice production rate and power input.

Explain the throttling processes and Joule Thomson effect for cooling.

Find Carnot COP for cooling/heating and theoretical power per ton with heat-exchanger temperature differences using ambient air or cooling-tower water as surroundings.

Discuss the effect of change in suction and discharge pressure on the performance of refrigeration cycle.

Explain dry ice? Write a short note on production of dry ice.

Estimate the theoretical COP of a vapour compression refrigeration cycle operating between given temperature/pressure limits with dry saturated vapour compression and no undercooling using refrigerant property tables, and determine refrigerating effect if required.

Explain the theoretical/simple vapour compression refrigeration cycle on a P-H chart.

Explain the function liquid intercooler in multistage compression system.

What is multi-stage vapour compression refrigeration system? Compare it with cascade refrigeration system.

Calculate the COP of an ideal vapour compression refrigeration cycle from given enthalpies at condenser exit, compressor exit and evaporator exit, and draw the P-V, T-s and P-h diagrams.

Explain the desirable thermodynamic, chemical, physical and other favourable properties of an ideal refrigerant.

Explain the working of steam jet refrigeration system with neat sketch.

Properties of Ammonia and R-22 as refrigerants.

Write a short note on the Li-Br vapour absorption refrigeration cycle with a neat sketch.

Explain the working of a practical aqua-ammonia vapour absorption refrigeration system with a neat diagram, including properties of an ideal refrigerant-absorbent pair.

Write short notes on steam jet refrigeration along with other refrigeration topics such as environment friendly refrigerants, leak detection methods and bypass factor of coil.

What is the basic function of the compressor in a vapour compression system and how is that function achieved in a vapour absorption system?

Define primary refrigerant, list desirable properties of a primary refrigerant, and give refrigerant numbers for $CHClF_{2}$, $CH_{2}F-CF_{3}$ and $NH_{3}$.

Explain classification of refrigerants and list desirable properties of an ideal refrigerant.

Factors considered for selection of a refrigerant and properties of R-12 and R-22 as refrigerants.

Draw the T-S and H-S diagram of a steam jet refrigeration system.

Discuss the advantages of vapour absorption cycle over vapour compression cycle.

For $300\,m^3/min$ of air cooled from $35^{\circ}C$ DBT, $55\%\,RH$ to $20^{\circ}C$ DBT, $60\%\,RH$, find the sensible heat removed per minute, latent heat removed per minute, and sensible heat factor.

Moist air at $5^{\circ}C$ DBT, $2.5^{\circ}C$ WBT, $90$ cmm absorbs $40.7$ kW sensible heat and $40$ kg/h saturated steam at $110^{\circ}C$: determine leaving dry-bulb and wet-bulb temperatures.

Write a short note on comfort air conditioning and explain the factors affecting comfort.

Air heated and humidified from $16^{\circ}C$, 25% RH to $30^{\circ}C$, 50% RH: find heat added, moisture added, and sensible heat factor.

What is fog? Show on the psychometric chart when two air streams yield fogged state of air.

Compare the requirements for comfort air conditioning versus industrial air conditioning.

An air conditioning plant is required to supply 60 $m^{3}$ of air per minute at a DBT of $21^{\circ}C$ and 55% RH. The outside air is at DBT of $28^{\circ}C$ and 60% RH. Determine the mass of water drained and capacity of the cooling coil. Assume the air conditioning plant first to dehumidify and then to cool the air.

Define sensible heating and sensible cooling process and cooling and dehumidification process.

Explain sensible heating and sensible cooling process and heating and dehumidification process using the psychrometric chart.

Define the following terms :

Write a short note on any three:

Given inlet DBT/WBT or RH and coil ADP/effective surface temperature, with either bypass factor or cooling capacity known, determine the air outlet state (DBT/WBT/RH) and the bypass factor or cooling capacity in kW/TR.

Write short notes on refrigeration/air-conditioning topics such as Grand sensible heat factor, Cascade system, Leak detection methods, Air refrigeration advantages, Electrolux system, Production of dry ice

Numerical problem to find the (grand) sensible heat factor of an air-conditioning plant from room sensible/latent loads and ventilation data

Mix two moist air streams, pass the mixture over a cooling coil with given ADP and bypass factor, find the coil outlet DBT and RH, and for supply to a room at given condition estimate the room sensible heat factor and coil cooling load.

The air-handling unit of an air-conditioning plant supplies a total of $4500\text{ cmm}$ of dry air which comprises by weight $20$ percent fresh air at $40^{\circ}C$ DBT and $27^{\circ}C$ WBT, and $80$ percent recirculated air at $25^{\circ}C$ DBT and $50$ percent RH. The air leaves the cooling coil at $13^{\circ}C$ saturated state. Calculate the total cooling load and room heat gain.