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In an absorption type refrigerator, the heat is supplied to $NH$_3 generator by condensing steam at 2 bar and 90% dry

The temperature in the refrigerator is to be maintained at $ -5°C$. Find maximum possible COP. If the refrigeration load is 20 tonnes and actual COP is 70% of maximum COP, find the mass of steam required per hour. Take temperature of the atmosphere as $30°C$

Subject:- Refrigeration and Air Conditioning

Topic:- Vapor Absorption Refrigeration

Difficulty:- Low

1 Answer
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As the wet steam gives the heat in the generator it condenses and we know temperature remains constant during condensation,

∴$ T_G=T_{sat_{2 bar}}=120.2℃=393.2 K$

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So from equation (1) substituting the above values we get,

$Q ̇_G=56.82 \frac{kJ}{s}$

Using, $Q ̇_G=m ̇_s (h_a-h_b )= m ̇_s [(h_f+x.h_fg )- h_f ]$

Where $Q ̇_G$= rate at which heat is given away in the generator as it condenses Substituting,

$x=0.9,h_{fg_{2 bar}}=2201.6 $

(From steam table) and $Q ̇_G$

[Assuming the steam condenses to saturated liquid as it gives away the heat in generator]

We get, $m ̇_s=0.028 \frac{kg}{sec}=103.23 kg/hr$

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