Important RGPV Question
ME 801 Refrigeration & Air Conditioning
VIII Sem, ME
UNIT 1- Introduction To Refrigeration
Q.1) Explain Boot-strap cycle and coefficient of performance or refrigerator.
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Q.2) A Carnot refrigeration cycle absorbs heat at 270 K and rejects it at 300 K.
i) Calculate the coefficient of performance of this
refrigeration cycle.
ii) If the cycle is absorbing 1130 KJ/min at 270 K, how
many KJ of work is required per second.
iii) If the Carnot heat pump operates between the same
temperatures as the above refrigeration cycle, what
is the coefficient of performance.
iv) How many kJ/min will the heat pump deliver at 300K
it at absorbs 1130 kJ/min at 270K
(RGPV May 2024)
Q.3) A refrigeration machine using R-12 as refrigerant operates between the pressures 2.5 bar and 9 bar. The compression is isentropic and there is no undercooling in the condenser. The vapour is in dry saturated condition at the beginning of the compression. Estimate the theoretical coefficient of performance. If the actual coefficient of performance is 0.65 of theoretical value, calculate the net cooling produced per hour. The refrigerant flow is 5kg per minute. Properties of refrigerant are:
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Q.5) Discuss any three natural methods of producing refrigeration.
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Q.6) A refrigerating system produces 30 kg/hr of ice at 0°C from water available at 25°C. Find the refrigerating effect per hour and tonnage capacity of unit. If it takes 1 kW of power, find COP of system.
(RGPV May 2023)
Q.7) The speed of an aircraft flying at an altitude of 8000 m where the ambient air is at 0.341 bar and 263 K temperature is 900 km/hr. The compression ratio of the air compressor is 5. The cabin pressure is 1.013 bar and temperature is 27°C. On the basis of 1 kg/sec of flow of air, determine (i) the power requirement of the aircraft for pressurization (ii) additional power requirement for refrigeration and (iii) refrigerating effect if Cp for air = 1.005 kg/kgK and γ = 1.4.
(RGPV May 2023)
Q.8) Explain the throttling processes and Joule Thomson effect for cooling.
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Q.9) The ambient air temperatures during summer and winter in a particular locality are 45°C and 15°C respectively. Find the values of Carnot COP for an air conditioner for cooling and heating, corresponding to refrigeration temperatures of 5°C for summer and heating temperature of 55°C for winter. Assume suitable temperature differences in the exchanger that exchanges heat with the surroundings. If water from the cooling tower at 30°C is used as a cooling medium with 3°C temperature differential for air-conditioning in summer, what will be the Carnot COP for cooling? Also, find the theoretical power consumption per ton of refrigeration in each case. Assume no increase in the temperature of the surrounding air or water.
(RGPV May 2022)
Q.10) A refrigerator storage is supplied with 3600 kg of fish at a temperature of 27°C. The fish has to be cooled to -23°C for preserving it for a long period without deterioration. The cooling takes place in 10 hours. The specific heat of fish is 2.0 kJ/kgK above freezing point offish and 0.5 kJ/kgK below freezing point of fish, which is-3°C. The latent heat of freezing is 230 kJ/kg. What is the power to drive the plant if the actual COP is half that of the ideal COP?
(RGPV May 2022)
UNIT 2- Vapour Compression System
Q.1) Explain the P-H chart of theoretical vapour compression refrigeration system.
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Q.2) Explain the vapour compression cycle with P-H and T-S diagrams. Discuss the effect of sub-cooling and superheating on the COP of the system.
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Q.3) Show the simple vapour compression refrigeration cycle on P-H chart and explain it.
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Q.4) Discuss the effect of change in suction and discharge pressure on the performance of refrigeration cycle.
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Q.5) Discuss advantages of vapour absorption cycle over vapour compression cycle.
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Q.6) In an ideal vapour compression refrigeration cycle, the enthalpy of the refrigerant at exit from the condenser, compressor and evaporator is 80 kJ/kg, 200 kJ/kg and 180 kJ/kg respectively. What is the coefficient of performance of the cycle? Draw the P-V, T-S and P-h Diagram for the above cycle.
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Q.7) Explain dry ice? Write a short note on production of dry ice.
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UNIT 3- Vapour Absorption System
Q.1) Explain the working of Aqua-Ammonia vapour absorption system.
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Q.2) Explain the working of steam jet refrigeration system.
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Q.3) Explain Practical vapour absorption system? Write down the properties of Ideal refrigerant-absorbent combination.
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Q.4) Write down the factors considered for the selection of refrigerant for a system. Explain R-12 and R-22 as a refrigerant.
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Q.5) Draw the T-S and H-S diagram of a steam jet refrigeration system.
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Q.6) Explain the working of a practical vapour absorption refrigeration cycle.
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Q.7) Discuss seven desirable property of an ideal refrigerant.
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Q.8) Discuss property of Ammonia and R-22 as refrigerant.
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Q.9) What is the Required Properties of Ideal Refrigerant?
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Q.10) Write down the short note on Li-Br Refrigerant Cycle with Neat Sketch.
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Q.10) Explain in brief which refrigerant/s would you choose for each of the following applications and why?
i) A cold storage of 100 TR capacities using reciprocating compressor.
ii) An 800 TR air conditioning plant using centrifugal compressor/s.
iii) A small capacity frozen food cabinet to maintain -30°C temperature.
(RGPV May 2022)
UNIT 4- Psychometric
Q.1)Using Psychrometric chart, explain the following processes:
i) Sensible heating and Sensible cooling process ii) Heating and Dehumidification process
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Q.2) In a cooling application, moist air enters a refrigeration coil at the rate of 100 kg of dry air per minute at 35°C and 50% RH. The apparatus dew point of coil is 5°C and by-pass factor is 0.15. Determine the outlet state of moist air and cooling capacity of coil in TR.
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Q.3) Define the following terms:
i) Dry bulb temp.
ii) Dew point temp.
iii) Specific Humidity
iv) Saturated Air
v) Sensible Heating Process
vi) Cooling and Dehumidification process
(RGPV May 2023)
Q.4) Air flowing at the rate of 100 m³/min at 40°C DBT and 50% RH is mixed with another stream flowing at the rate of 20 m³/min at 26° DBT and 50% RH. The mixture flows over a coil whose ADP temp. is 10°C and bypass factor is 0.2. Find DBT and RH of air leaving the coil. If this air is supplied to an air-conditioned space where DBT is 20°C and RH is 50%, estimate room sensible heat factor and cooling load capacity of coil in TR.
(RGPV May 2023)
Q.5) 39.6 cmm of a mixture of recirculated room air and outdoor air enter a cooling coil at 31°C DB and 18.5°C WB temperatures. The effective surface temperature of the coil is 4.4°C. The surface area of the coil is such as would give 12.5 kW of refrigeration with the given entering air state. Determine the dry and wet bulb temperatures of the air leaving the coil and the coil bypass factor.
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Q.6) Write down the short note on comfort air conditioning? What are the factors affecting comfort air conditioning?
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Q.7) Moist air enters a chamber at 5°C DBT and 2.5°C thermodynamic WBT at a rate of 90 cmm. The barometric pressure is 1.01325 bar. While passing through the chamber, the air absorbs sensible heat at the rate of 40.7 kW and picks up 40 kg/h of saturated steam at 110°C. Determine the dry and wet bulb temperatures of the leaving air.
(RGPV May 2022)
UNIT 5- Air Conditioning
Q.1) Explain the calculation of summer air conditioning load.
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Q.2) A small office hall of 25 persons capacity is provided with summer air conditioning system with the following data.
Outside conditions =34°C DBT and 28°C WBТ
Inside conditions =24°C DBT and 50% RH
Volume of air supplied = 0.4 m³/min/person
Sensible heat load in room= 125600 kJ/h
Latent heat load in room = 42000 kJ/h
Find the sensible heat factor of the plant.
(RGPV May 2024)
Q.3) The amount of air supplied to an air-conditioned hall is 300 m³/min. The atmosphere conditions are 35°C DBT and 55% RH. The required conditions are 20°C DBT and 60% RH. Find out the sensible heat and latent heat removed from the air per minute. Also find the sensible heat factor for the system.
(RGPV May 2024)
Extra Questions-
Q.1) Write short note on any three :
a) Grand sensible heat factor
b) Cascade system
c) Leak detection methods
d) Production of dry ice
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Q.2) Write short note on any three:
a) Advantages of Air refrigeration
b) Cascade system
c) Steam jet refrigeration
d) Calculation of summer air-conditioning load
e) Eco-friendly refrigerants
(RGPV May 2023)
— Best of Luck for Exam —
