A. The basis of thermal design

Cooling towers are designed such that a given amount of water is cooled down from a given inlet temperature by a required difference in temperature, taking into account the typical environmental conditions such as ambient pressure, temperature and humidity. In this process the heat is transferred from the cooling water to the air.

The amount of air that is required for cooling depends on the characteristics of the cooling tower packing. The outlet temperature (T_C,w,out) of the cooling water is dependent on cooling water inlet temperature (T_C,w,in), ambient air temperature (T_C,a), wet bulb temperature (T_C,wb) and atmospheric pressure (p_A) and the magnitudes (Ṁ_w and Ṁ_a) of the entering flows as well as the transfer function K of the packing:

\[T_{C,w.{\rm out}} = f{\dot{M}_{w}, T_{C/w,{\rm in}}, T_{C/a}, T_{C/wb}, p_A, \dot{M}_{a}, K}\notag\]

The transfer function K depends in different ways on operating parameters according to the packing used. Some further terms which are used in cooling tower technology shall be explained in what follows: