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Ex/ME/T/414/21/09 (S)

BACHELOR OF MECHANICAL ENGINEERING FINAL

EXAMINATION, 2009

( 4th Year, 1st Semester, Supplementary )

REFRIGERATION AND AIRCONDITIONING

Time : Three hours Full Marks : 100

Answer any five questions.

All questions carry equal marks. Use of tables & charts permitted.

Assume any missing data consistent with the problem.

Parts of the same question must be answered together.

1. a) Define 1 TR.

b) Sketch an ideal vapour compression cycle on p - h diagram

and name the components.

c) A carnot refrigerator operates between temperatures of

40oC & + 40

oC. Find the COP. It is desired to make the

COP equal to 3.5 by changing temperatures. The increase or

decrease in uppe temp. is to equal the decrease or increase in

lower temperature. Find the new temps. 4+6+10=20

2. a) Sketch a Bell-coleman cycle on P-V & T-S planes & derive

its thermal effy.

b) A refrigerator working on Bell-coleman cycle takes air from

the cold chamber at 10oC & compresses it from 1 bar to

6.5 bars with index of compression being 1.2. The

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compressed air is cooled to a temp. of 5oC above ambient

teamp. of 25oC before it is expanded in the expander where

the index of expansion is 1.35. Determine the COP and the

quantity of air circulated per minute for producing 2000 kgof ice/day at 0oC from water at 20oC. 10+10

3. a) Draw the schematic layout of a two stage vapour

compression refrigeration cycle using flash chamber and

plot it on a T-s diagram.

b) A refrigerator uses Refrigerant 134a as the working fluid

and operates on an ideal vapour compression cycle between

0.14 & 0.8 MPa. If the mass flow of the refrigerant is 0 .05

kg/s, find (i) the rate of heat removed from the refrigerated

space and power input to the compressor (ii) the rate of heat

rejection to the environment and (iii) the COP of the

refrigerator. 8+12=20

4. a) Find the expression for COP for an ideal vapour absorption

refrigeration system.

b) Find the flowrate of refrigerant through the condenser and

evaporator of a standard hi-Br vapour absorption cycle. The

pump delivers 0.6 kg/s and the following temperatures

preval: generator, 100oC ; condenser, 40

oC ; evaporator,

10oC and absorber, 30oC. 8+12=20

5. a) State the function of the capillary tube in a domestic

refrigeration system.

b) A six cylinder refrigerant -22 compressor operation at 29

RPS has a refrigerating capacity of 96 kW and a power

requirement of 28.9 kW at an evaporation temp. of 5oC and

a condensing temp. of 50oC. There is 3

oC of liquid

subscooling and 8oC of a superheating of the suction gas

entering the compressor. The cyclinder bore is 67 mm and

the piston stroke 57 mm. Calculate (i) the volumetric effy. if

the clearance vol. is 4.8% of the stroke vol. and (ii) the

compression isentropic effy. 4+16=20

6. a) Consider a room that contains air at one atmosphere, 35oC

and 40% relative humidity. Use a skeleton pychrometric

chart and find and mark the :

(i) sp. humidity (ii) enthalpy, (iii) wb temp. (iv) dp. temp. &

(v) the sp. vol. of air.

b) Sketch an adiabatic saturator. Define Adiabatic saturation

temp. Deduce how sp. humidity is obtained during the

process. 10+10=20

7. a) Define (i) Bypass factor (ii) Apparatus Dew point

b) Sketch and explain a double zone airconditioning system.

10+10=20

8. Write notes onany two of the following :

a) Diff. between ideal and actual vapour compression cycle.

b) Disadvantage of Air refrigeration system.

c) Aqua-ammonia absorption refrigeration system. 25 10=20

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