REFRIGERATION CYCLES 741

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(ii)Mass of refrigerant. Mass of refrigerant circulated (per second per tonne of refrigera-
tion) may be calculated by dividing the amount of heat by the refrigerating effect.
∴ Mass of refrigerant circulated,

m =

14000

3600 ()hh 21 − kg/s-tonne ...(14.14)

because one tonne of refrigeration means cooling effect of 14000 kJ/h.
(iii)Theoretical piston displacement. Theoretical piston displacement (per tonne of re-
frigeration per minute) may be found by multiplying the mass of refrigerant to be circulated (per
tonne of refrigeration per sec.) by the specific volume of the refrigerant gas, (vg) 2 , at its entrance
of compressor. Thus,

Piston displacement(Theoretical) =

14000

3600 ()hh 21 − (vg)^2 m

(^3) /s-tonne ...(14.15)
(iv)Power (Theoretical) required. Theoretical power per tonne of refrigeration is the
power, theoretically required to compress the refrigerant. Here volumetric and mechanical
efficiencies are not taken into consideration. Power required may be calculated as follows :
(a) When compression is isentropic :
Work of compression = h 3 – h 2 ...(14.16)
Power required = m(h 3 – h 2 ) kW
where, m = Mass of refrigerant circulated in kg/s.
(b) When compression follows the general law pVn = constant :
Work of compression = n
n− 1
(p 3 v 3 – p 2 v 2 ) Nm/kg
Power required = m ×
n
n− 1
(p 3 v 3 – p 2 v 2 ) ×^1
103
kW (p is in N/m^2 ) ...(14.17)
(v)Heat rejected to compressor cooling water. If the compressor cylinders are jack-
eted, an appreciable amount of heat may be rejected to the cooling water during compression. If the
suction and discharge compression conditions are known, this heat can be determined as follows :
Heat rejected to compressor cooling water

n
n
pv pv hh
()
()
−
F −
HG
I
KJ
−−
L
N
M
O
Q
1 1000 P
(^332232) kJ/kg (p is in N/m (^2) )
...(14.18)
(vi)Heat removed through condenser. Heat removed through condenser includes all
heat removed through the condenser, either as latent heat, heat of superheat, or heat of liquid.
This is equivalent to the heat absorbed in the evaporator plus the work of compression.
∴ Heat removed through condenser
= m(h 3 – h 4 ) kJ/s (m = mass of refrigerant circulated in kg/s)
...(14.19)

14.4. Vapour Absorption System

14.4.1. Introduction

In a vapour absorption system the refrigerant is absorbed on leaving the evaporator, the

absorbing medium being a solid or liquid. In order that the sequence of events should be continuous

it is necessary for the refrigerant to be separated from the absorbent and subsequently condensed