Question

In an industrial process $10kg$ of water per hour is to be heated from ${20}^{\circ }C$ to ${80}^{\circ }C$. To do this steam at ${150}^{\circ }C$ 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 ${90}^{\circ }C$. How many $kg$ of steam is required per hour.
(Specific heat of steam = $1calorie$ per $g{m}^{\circ }C$, Latent heat of vaporisation = $540cal/gm$

• A. $1gm$
• B. $1kg$
• C. $10gm$
• D. $10kg$

Answer 1

The correct option is B $1kg$

Solution Let $\Delta H$ be the heat required to

raise temperature. Then,

$\Delta H$ = mass of water $\times$ specific heat $\times$

change in temp

$\Delta H$ $=\left(10\right)\left({10}^3\right)\left(1\right)({80}^{\circ }c-{20}^{\circ }c)$

$={10}^4\times 60=6\times {10}^{5}cal$

Heat given by the steam per her,

$\Delta H$ mass of steam [Latent heat of

vaporization + specific heat $\times$| temp changed]

$\Delta H=[540+(1\left)\right[|{90}^{\circ }C-{150}^{\circ }C\left]\right]$

$\Rightarrow 6\times {10}^5=x[540+60]$

$\Rightarrow 6\times {10}^5=x\left(600\right)$

$\Rightarrow {10}^{3}g=x$

$\Rightarrow x=1kg$

Option - B is correct