The directional movement, circulation path, and velocity distribution of air within refrigerated cargo space, determining temperature uniformity, cooling efficiency, and thermal stratification characteristics. Why It Matters: Airflow pattern is the single most critical factor determining whether a refrigerated vehicle achieves uniform temperature or develops hot and cold spots. Industry-standard roof-mounted evaporators discharge air downward at 90-degree angle to floor, fighting gravity and creating dead zones where warm air accumulates at ceiling level. This WWI-era approach ignores basic convection physics: warm air rises and concentrates at the ceiling precisely where standard evaporators cannot reach it. The result is ±8-12°C temperature variation within cargo space – unacceptable for frozen food quality but endemic to transport refrigeration because manufacturers prioritize installation simplicity over thermodynamic performance.
Physics Reality: Natural convection creates thermal stratification with warm air collecting at ceiling level and cold air settling at floor. Effective refrigeration airflow must:
- Capture warm air at ceiling level where it naturally accumulates
- Cool it thoroughly via evaporator coil
- Discharge cooled air downward working with gravity
- Distribute evenly to eliminate dead zones and short-circuiting
Industry standard achieves only step 3, pulling already-cold floor air through evaporator while ignoring warm ceiling air – fundamentally backwards physics.
Related Terms: Thermal Stratification, Temperature Uniformity, Evaporator, Plenum Chamber, Convection (Natural vs Forced), Heat Transfer (Thermal)