QUESTION

$4$

A

$50$

$$kg block of cod initially at

$14$

oC is placed in a plate freezer and frozen to

$-$

$30$

oC in

$5$

$$hours$.$

The phase change occurs at the initial freezing temperature of

$-$

$2$

oC and the latent heat of

fusion is

$280$

$$kJ

$/$

kg

$.$

$$Specific heat capacities of the unfrozen and frozen cod are

$3\mathrm{.}55$

$$and

$1\mathrm{.}85$

kJ

$/$

kgoC respectively. The plate freezer is operated with a refrigerant R

$-$

$134$

a mechanical

refrigeration system with evaporation at

$-$

$20$

oC and condensation at

$20$

oC

$.$

$$Calculate the

required compressor power

$($

in kW

$)$

$$if the compressor efficiency is

$0\mathrm{.}80$

$$and the cooling load

is

$80$

$\%$

$$of the total heat removed from the cod during the freezing process. Leave your answer

correct to two decimal places.

$[15$

$$MARKS

$]$