TITLE.PM5

REFRIGERATION CYCLES 729

dharm

\M-therm\Th14-2.pm5

(ii)Mass of air in circulation :

Refrigerating effect per kg of air

= cp (T 3 – T 2 ) = 1.003 (289 – 196.25) = 93.03 kJ/kg.

Refrigerating effect produced by the refrigerating machine

= 6 × 14000 = 84000 kJ/h.

Hence mass of air in circulation

=

84000

93 03 60.×

= 15.05 kg/min. (Ans.)

(iii), (iv) Piston displacement of compressor

= Volume corresponding to point 3 i.e., V 3

∴ V 3 =

mRT

p

3

2

= ×××

×

15.05 0.287 1000 289

1.0 10^5

= 12.48 m^3 /min. (Ans.)

∴ Swept volume per stroke

= 12 48

2240

.

×

= 0.026 m^3

If, dc = Dia. of compressor cylinder, and

l = Length of stroke,

then

π

4

d^2

c× l = 0.026

or
π
4

200

1000

d^2

c ×

F

HG

I

KJ = 0.026

∴ dc = 0 026 1000 4

200

12

.

/

××

×

F

HG

I

π KJ

= 0.407 m or 407 mm

i.e., Diameter or bore of the compressor cylinder = 407 mm. (Ans.)

Piston displacement of expander

= Volume corresponding to point 2 i.e., V 2

∴ V 2 =

mRT

p

2

2

= ×××

×

15.05 0.287 1000 196.25

1105

= 8.476 m^3 /min. (Ans.)

∴ Swept volume per stroke

=^8476

2240

.

×

= 0.0176 m^3.

If de = dia. of the expander, and

l = length of stroke,

then

π

4

d^2

e × l = 0.0176

or
π
4

200

1000

d^2

e ×

F

HG

I

KJ = 0.0176

∴ de = 0 0176 1000 4

200

12

.

/

××

×

F

HG

I

π KJ

= 0.335 m or 335 mm

i.e., Diameter or bore of the expander cylinder = 335 mm. (Ans.)