GATE 2020 AG – Question 44
Steam at121°C sterilizes pineapple juice by direct injection. Juice enters80°C and diluted juice exits95°C; cp=3.9 kJ/(kg °C), no heat loss. At95°C: hf397.9,hg2668.1,hfg2270.2 kJ/kg. At121°C: hf507.7,hg2707.1,hfg2205.2. Find juice/steam mass ratio.
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Correct answer: (C) 39.47
Explanation
Each kilogram of injected steam releases hg(121)−hf(95)=2707.1−397.9=2309.2 kJ on condensing and cooling to the outlet. Each kilogram of original juice needs cpΔT=3.9(15)=58.5 kJ. Thus mj/ms=2309.2/58.5=39.47, C.