Subtopic: Drying and milling of cereals, pulses and oilseeds
Question Statement:
A cross-flow grain dryer receives ambient air at $30^\circ\text{C}$ and heats it to $60^\circ\text{C}$ before passing through the grain bed. If the airflow rate is $120\text{ kg dry air / min}$ and humid heat of air is $1.02\text{ kJ/(kg}\cdot\text{K)}$, the heat energy supplied by the burner in $\text{kW}$ is ________ (round off to 1 decimal place).
Answer Key:
61.2
Step-by-Step Solution & Explanation
1. Mass flow rate of air $\dot{m}_a = \frac{120\text{ kg/min}}{60\text{ s/min}} = 2.0\text{ kg/s}$.
2. Temperature rise $\Delta T = 60 - 30 = 30^\circ\text{C} = 30\text{ K}$.
3. Heat supply rate $Q$:
$Q = \dot{m}_a c_s \Delta T = 2.0\text{ kg/s} \times 1.02\text{ kJ/(kg}\cdot\text{K)} \times 30\text{ K} = 61.2\text{ kW}$