Chapter 1 Introduction - Top Engineering Colleg P… · Darshan Institute of Engineering &...

GTU Paper Analysis (New Syllabus)

Refrigeration & Air conditioning (216908) Department of Mechanical Engineering Darshan Institute of Engineering & Technology

Chapter 1 – Introduction

Sr. No. Questions

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Oct

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Theory

1. Explain in brief the Ice Making plant with neat sketch. 04 04

2. List out applications of refrigeration. 03

3. Define refrigeration, air conditioning and COP. 03

Examples

Not asked in GTU



Chapter 2 – Refrigerants

Sr. No. Questions

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Theory

1. Explain Thermodynamic, Chemical and Physical properties of an Ideal Refrigerant. 07

2. Explain the term: (i) secondary refrigerant. 01

3. Classify refrigerants briefly and explain four thermodynamic properties of refrigerants. 07

4. Explain the method of designation of refrigerant with example. 04

Examples

Not asked in GTU



Chapter 3 – Air refrigeration

Sr. No. Questions

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Oct

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Theory

1. Define refrigeration, State the Name of different types of system used for cooling of aircraft cabin, Also

Explain with schematic diagram Bootstrap air Refrigeration system. 07 07

2. Explain with neat schematic diagram simple air refrigeration system also draws its T-s plot. 07

3. Why aircrafts require cooling? 03

Examples

1.

A dense air refrigeration machine operating on Bell-Coleman cycle works between 3.4 bar and 7 bar. The

temperature of air after the cooler is 15oC and after refrigeration is 6oC, for a refrigeration capacity of 6

tons calculate: 1. Temperature after compression and expansion, 2. Air circulation required in cycle per

minute, 3. Work of compression and expansion, 4. Theoretical COP, 5. Rate of water circulation required

in the cooler in Kg/min if rate of temperature rise is limited to 30oC. For air take Cp=1.005 kJ/kg K, γ = 1.4.

for water Cp = 4.18 kJ/kg K.

07

2.

A dense air refrigerator operating on Bell-Coleman cycle works between 3 bar and 15 bar. The temperature of air after the evaporator and after cooler is 5OC and 20OC respectively. The evaporator extracts 2000 kg/min of heat from the space to be cooled. Calculate (1) amount of air required in the cycle per minute, (2) power required to run the system, (3) COP and (4) mass flow rate of water per minute in cooler if rise in temperature of water is 200C. Assume isentropic compression and expansion, Cp = 1.008 kJ/kg K, γ =1.4 for air and for water Cp = 4.18 kJ/kg K.

07



Chapter 4 – Vapour compression system

Sr. No. Questions

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Oct

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No

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Theory

1. Explain the effect of evaporator pressure, condenser pressure and liquid sub-cooling on performance of

vapour compressor refrigeration system using P-H diagram. 07

2. Explain with neat sketch the Cascade refrigeration system. 07

3. Explain following terms: (i) flash chamber 01

4. Explain with neat schematic diagram, working of two stage compression system with water intercooler, liquid subcooler and flash intercooler. Also draw p-h diagram.

07

5. Explain standard VCR cycle with T-S and P-H diagrams. 07

6. Differentiate dry and wet compression. 04

7. Discuss the effect of suction pressure and sub-cooling on the performance of a vapour compression system.

07

8. Briefly explain the working of Two stage vapour compression system with water intercooler and liquid sub-cooler.

07

Examples

1.

A R22 vapour compression refrigeration system operates between -100C and 450C. The refrigerant is

subcooled by 50C before entering the expansion valve and vapour is superheated by 50C before entering

the compressor. By using Pressure-enthalpy chart, Calculate (i) Refrigeration effect per kg (ii) Mass flow

rate of refrigerant for 5 TR capacity and iii) COP of the system.

07



2.

A refrigeration machine is required to produce ice at 0oC from water at 20oC. The machine has a condenser temperature of 25oC while evaporator temperature is -50C. The relative efficiency of the machine is 50% and 6 kg of Freon-12 is circulated through the system per minute. The refrigerant enters in the compressor with dryness fraction of 0.6. Calculate the amount of ice produced in 24 hrs. Take latent heat of ice 335 kJ/kg.

Temperature

(0C)

Liquid heat

(KJ/kg)

Latent heat

(KJ/kg)

Entropy of liquid

(KJ/kg-K)

25 59.7 138 0.2232

-5 31.4 154 0.1251

07

3.

A food storage requires a refrigeration capacity of 12 TR and works between the evaporative temperature of -8OC and condensing temperature of 30OC. The refrigerant R-12 is sub cooled by 5OC before entering expansion device and vapour is superheated to -2OC before leaving to evaporator coil. (1) Draw p-h diagram for the process and find out (2) C.O.P. (3) power required in kW/TR. Take specific heat of liquid R-12 as 1.235 kJ/kg K and vapour R-12 as 0.733 kJ/kg K.

Saturation

Temperature

(⁰C)

Saturation

Pressure

(bar)

Specific Enthalpy

(kJ/kg)

Specific Entropy

(kJ/kg K)

Liquid Vapour Liquid Vapour

-8 2.354 28.72 184.07 0.1149 0.7007

30 7.451 64.59 199.62 0.24 0.6853

07



4.

An NH3 refrigerator produces 30 tonnes of ice from and at 00C. The temperature range in the compressor is from 260C to -140C. the vapour is dry saturated at the end of the compression. Actual C.O.P. is 60 % of the theoretical. Calculate the power required for the compressor. The latent heat of ice = 335 kJ/kg. Use following table.

Saturation

Temperature

(⁰C)

Specific Enthalpy

(kJ/kg)

Specific Entropy

(kJ/kg K)

Vapour Liquid Liquid Vapour

26 1483.72 322.73 1.4257 5.3066

-14 1445.47 135.82 0.7599 4.8137

07



Chapter 5 – Absorption refrigeration system

Sr. No. Questions

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Oct

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Theory

1. Explain with neat sketch working of ammonia-hydrogen refrigerator also explain significance of

Hydrogen used in system. 07

2. Explain working of Li-Br vapour absorption refrigeration system with neat sketch. 07

3. Explain working of theoretical aqua ammonia vapour absorption refrigeration system with neat sketch. Also state few selection criteria for vapor absorption refrigeration system.

07

4. Explain working of Electrolux VAR system with neat sketch. 03

5. Enlist properties required for an ideal refrigerant-absorbent combination. 03

Examples

Not asked in GTU



Chapter 6 – Refrigeration system components

Sr. No. Questions

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Oct

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No

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Theory

1. Explain construction, working, advantages and disadvantages of Thermostatic Expansion valve with neat

sketch. 07

04

2. Explain the term: Hermetically sealed compressor 01 04

3. What is the function of expansion device? Explain automatic expansion valve with neat sketch. 07

Examples

Not asked in GTU



Chapter 7 – Psychrometry

Sr. No. Questions

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Oct

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No

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Theory

1. Define following term related to psychrometry (i) wet bulb temperature (ii) psychrometry (iii) Relative humidity (iv) By pass factor (v) dew point temperature (vi) apparatus dew point temperature (vii) sensible heat factor.

07

2. Define following terms: (1) Grand Sensible Heat Factor, (2) Humidity ratio, (3) Dew point temperature 03

3. Explain Adiabatic saturation process with neat sketch. 04

4. Explain cooling and dehumidification process. 03

5. Explain air washer. 03

6. Explain construction and working of any one type humidifier with neat sketch. 04

Examples

1.

The barometer for air reads 750 mm of Hg. The DBT and WBT measured using sling psychrometer is 33OC

and 23OC respectively. Calculate (1) Vapor pressure (2) Relative humidity (3) Humidity ratio (4) Dew

point temperature (5) specific enthalpy (6) wet bulb depression and (7) dew point depression.

07

2.

Air at 30OC DBT and 60% RH enters over cooling coil at rate 250m3/min. If effective surface temperature

of coil is 12OC and bypass factor is 0.1 then name the process undergone by air and calculate temperature

of air leaving coil, refrigerating effect in TR, mass of water vapor condensed and SHF.

07

3. 50 m3/min of air at 270C DBT and 200C WBT flows through a cooing coil and leaves the coil at 120C DBT

and 8 gm/kg of moisture content. Determine: (i) Apparatus dew point (ii) Contact factor (iii) Cooling load. 07



Chapter 8 – Human Comfort

Sr. No. Questions

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Oct

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No

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Theory

1. Explain in brief the effective temperature. 03

2. List out factors governing human comfort. Define Effective Temperature. Explain five factors governing optimum effective temperature.

07 07

3. Explain human comfort. 03

Examples

Not asked in GTU



Chapter 9 – Load Analysis

Sr. No. Questions

Ma

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6

Oct

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No

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Theory

1. State and explain various heat loads to be considered for cooling load calculation of typical building. 07

2. What are IHG and ICL? Explain flywheel effect of building material on peak load and time lag of heat load with neat sketch.

07 03

3. Explain flywheel effect as applied to cooling load calculation with neat labeled diagram. 04

Examples

1.

Explain ventilation and infiltration in brief. Also calculate total infiltration air in m3/min and load due to outside air for the restaurant. Take Inside design condition 26OC DBT, specific humidity 11.1 gm/kg of dry air and Outside design condition 42OC DBT, specific humidity 16.4 gm/kg of dry air. Size of room is 18x18x4 meter, No. of air changes required/hr is 1.5, No. of occupants 100, door open/hr/occupant is 3 and usage factor for swinging door is 3.

07



Chapter 10 – Duct design & Air distribution

Sr. No. Questions

Ma

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Oct

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No

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Theory

1. Explain various methods used for design of the duct. 07

2. Explain the term: (i) Aspect ratio 01

3. Derive the formula of equivalent diameter of circular duct for rectangular duct when (1) the quantity of air carries in both the ducts is same and (2) the velocity of air in both the ducts is same.

07

4. List out methods for duct design and explain equal friction loss method with its advantages and disadvantages.

07 07

Examples

1.

A circular duct of 40 cm is selected to carry air in an air conditioned space at a velocity of 440 m/min to keep the noise level at desired level. If this duct is replaced by a rectangular duct of aspect ratio of 1.5, find out the size of rectangular duct for equal friction method when (a) the velocity of air in two ducts is same, (b) the discharge rate of air in two ducts is same.

07



Chapter 11 – Air conditioning systems

Sr. No. Questions

Ma

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Oct

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No

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Theory

1. Classify air conditioning systems. Explain Central air conditioning system with a neat sketch. 07 04

2. Classify Fan used in air-conditioning system. Explain selection of the fan using fan characteristic curve. 07

3. Classify air conditioning systems and explain summer air conditioning system with neat sketch. 07

4. Explain all air system. 07

Examples

Not asked in GTU

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Chapter 1 Introduction - Top Engineering Colleg P… · Darshan Institute of Engineering &...

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