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

$Pt = mc_w∆T + mL + mc_i∆T\\$

$\begin{aligned} P(4×60s)= &\ ( 1)(4187)(10) + (1)(334) +\\& \ (1)(4187)(7)\\ =&\ 297.97W \end{aligned}$

Efficiency = $\dfrac{297.97}{400 }× 100\% =74.49\%$