Heat transfer mechanisms in cooling towers (theory and calculation methods)

Cooling towers are high-intensity mixing heat exchangers. In them, heat exchange occurs at direct contact (contact) of heat carriers, i.e. in heat exchangers there is no thermal resistance of the wall. When circulating water is cooled by air, part of the heat is transferred due to surface evaporation of water - transformation of water into vapor with subsequent transfer of vapor by diffusion into the air stream. The other part is due to the temperature difference between water and air, i.e. heat transfer by contact (conduction and convection). Heat transfer by direct contact between air and inlet is always accompanied by a process of mass transfer from one phase to the other. This is a typical process of conjugate heat and mass transfer. In our case, evaporation refers to the process of water transition from liquid to vapor state at a temperature lower than the boiling point of water at a given pressure. Since water is cooled in the process of evaporation, the source of energy is water itself. Adiabatic evaporation takes place and the water is cooled to the wet-bulb temperature. Evaporation always takes place in a cooling tower. It is found that heat transfer by evaporation dominates over heat transfer by contact. A heat balance equation is written to determine the air flow rate for cooling water. An equation for calculating the temperature of a wet thermometer is given. A method for calculating the average enthalpy difference of air in a cooling tower is given. The aerodynamic calculation of fan cooling towers is to determine whether the total aerodynamic drag of the cooling tower corresponds to the head developed by the fan. The total aerodynamic resistance is the sum of the resistances of its elements. Formulas for calculating the drag coefficients are written. Water losses due to evaporation, droplet entrainment, filtration, and blowdown are considered.