Sensible Cooling

During this process, the moisture content of air remains constant but its temperature decreases as it passes over a cooling coil. To keep the moisture content constant, the surface of the cooling coil should be dry and its surface temperature should be greater than the dew point temperature (DPT) of air. If the cooling coil is 100% effective, then the exit temperature of air will be equal to the coil temperature. However, in practice, the exit air temperature will be higher than the cooling coil temperature. Figure 8.8 shows the sensible cooling process 2−1 on a psychrometric chart. The heat rejection rate during this process is given by,

Figure 8.8 Sensible Cooling Process 2−1 on Psychrometric Chart

 

Q_c = m_a (h₂ − h₁) = m_ac_pm (T₂ − T₁)

Sensible Heating

During this process, the moisture content of air remains constant and its temperature increases as it flows over a heating coil. The heat addition rate during this process is given by,

 

Q_h = m_a (h₂ − h₁) = m_ac_pm (T₂ − T₁)

 

where c_pm is the humid specific heat (≈1.0216 kJ/kg dry air) and m_a is the mass flow rate of dry air (kg/s). Figure 8.9 shows the sensible heating process on a psychrometric chart.

Figure 8.9 Sensible Heating Process 1−2 on Psychrometric Chart