Properties Of Solids And Liquids Question 113
Question: In an industrial process 10 kg of water per hour is to be heated from 20°C to 80°C. To do this steam at 150°C is passed from a boiler into a copper coil immersed in water. The steam condenses in the coil and is returned to the boiler as water at 90°C. how many kg of steam is required per hour. (Specific heat of steam = 1 calorie per gm°C, Latent heat of vaporisation = 540 cal/gm)
Options:
A) 1 gm
B) 1 kg
C) 10 gm
D) 10 kg
Show Answer
Answer:
Correct Answer: B
Solution:
Suppose m kg steam required per hour Heat released by steam in following three steps (i)
When 150°C steam $ \xrightarrow[Q _{1}]{}100{}^\circ C $ steam Q1 = mcSteam Dq = m ´ 1 (150 - 100) = 50 m cal (ii)
When 150°C steam $ \xrightarrow[Q _{2}]{}100{}^\circ C $ water Q2 = mLV = m ´ 540 = 540 m cal (iii)
When 100°C water $ \xrightarrow[Q _{2}]{}90{}^\circ C $ water Q3 = mcW Dq = m ´ 1 ´ (100 - 90) = 10 m cal Hence total heat given by the steam Q = Q1 +Q2 + Q3 = 600 mcal … (i)
Heat taken by 10 kg water $ Q’=mc _{W}\Delta \theta =10\times 10^{3}\times 1\times (80-20)=600\times 10^{3}cal $
Hence Q = Q¢
therefore 600 m = 600 ´ 103
therefore m = 103 gm = 1kg.
