During forced aeration of deep grain bulks with ambient night air, the cooling front velocity through the bed is roughly:
Options:
(A) $500$ to $1000$ times slower than the interstitial air velocity because of the high heat capacity of grain relative to air
(B) Equal to the speed of air
(C) Twice the speed of air
(D) Zero
Answer Key:
A
Step-by-Step Solution & Explanation
Because the volumetric heat capacity of packed grain ($\rho_g c_g \approx 1200\text{ kJ/(m}^3\cdot\text{K)}$) is nearly 1000 times greater than that of air ($\rho_a c_a \approx 1.2\text{ kJ/(m}^3\cdot\text{K)}$), the thermal front lags vastly behind the airflow.