Question

Calculate the efficiency of an ice making machine that takes in water at 10°C and produces ice at a temperature of -7°C. Water is taken in at a rate of 1 kg every 4 minutes. The input power of the machine is 400 W. 

 

The specific heat capacity of water is 4187 Jkg−1K−1 and its specific latent heat of fusion is 334 Jkg−1.

Answer 1

Mass of flow rate of water = Rate of ice making(m)=$\frac{1 kg}{4\times 60 sec}$ =4.166$\times 10^{-3}$ kg/sec

Amount of heat absorbed (Q)= Sensible Heat +latent heat=m(Cp$\Delta T+h_{fg}$ )

=4.166$\times 10^{-3}$ (4187x$17^o+334$ )=296.48 watt

Input Power(W)=400 watt

Efficiency of cooling system =$\frac{}{}$ $\frac {Desired\: Cooling \: Effect}{Input \: Power}\times 100=\frac{296.48}{400}\times 100$ =73.21 %