14.3 Exercise 30

In some countries, liquid nitrogen is used on dairy trucks instead of mechanical refrigerators. A 3.00-hour delivery trip requires 200 L of liquid nitrogen, which has a density of $\text{808} \textrm{ }\text{kg}/\text{m}^{3}$.

(a) Calculate the heat transfer necessary to evaporate this amount of liquid nitrogen and raise its temperature to $3 . \text{00}º \text{C}$. (Use $c_{p}$ and assume it is constant over the temperature range.) This value is the amount of cooling the liquid nitrogen supplies.

(b) What is this heat transfer rate in kilowatt-hours?

(c) Compare the amount of cooling obtained from melting an identical mass of $0º \text{C}$ ice with that from evaporating the liquid nitrogen.