Meco cooling tower selection formula

September 30 18:02:24, 2018

Cooling tower selection formula: The function of the cooling tower is to cool a certain amount of water Q from water temperature t1 to t2, or to cool Î”t=t1-t2. Therefore, to design a cooling tower of the appropriate size, or to calculate the cooling capacity of an existing cooling tower, we must do the thermal calculation of the cooling tower.
For ease of calculation, we make the following simplifying assumptions for the thermal process in the cooling tower:
1: The heat dissipation coefficient, the mass coefficient, and the specific heat of the wet air are considered constant throughout the cooling process and do not vary with air temperature and water temperature.
2: In the cooling tower, since the partial pressure of water vapor is small, the influence on the pressure change in the tower is also small, so the pressure in the calculation takes the average atmospheric pressure value.
3: It is considered that the surface temperature of the water film or water droplet is consistent with the internal temperature, that is, the thermal resistance of the water side is not considered.
4: In the heat balance calculation, the amount of evaporated water can be neglected because the amount of evaporated water is not large.
5: The relationship between the saturated water vapor partial pressure and the saturated air and water temperature can be assumed to be linear in the range where the water temperature does not change much.
The thermal calculation methods of the cooling tower include the enthalpy difference method, the wet difference method and the differential pressure method. The most commonly used method is the enthalpy difference method proposed by Michael. The following is a brief introduction to the enthalpy method thermal calculation of the cooling tower.
The enthalpy method proposed by Michael unifies the heat transfer formula that was driven by temperature difference and concentration difference into a heat transfer formula based on coma. In the equation, Michael leads into the Lewis relation and derives the heat dissipation equation based on coma.

The left end of the above formula indicates the cooling capacity of the cooling tower under certain water-filling packing and grid type. It is related to the characteristics, structure, geometric size and cooling water quantity of the water-filling packing. The number of characteristics of the cooling tower is indicated by the symbol. which is:

Since the water temperature is not a direct function of air enthalpy, direct integration is difficult. Therefore, when solving the cooling number, the approximate integration method is generally used. There are many ways to integrate, including Simpson's integral method, average driving force method, Chebyshev integral method, logarithmic and arithmetic mean difference method, and many empirical curves and graphs. Only the American Cooling Tower Association (CTI) is introduced here. The recommended Chebyshev integration method.
The Chebyshev integration method is recommended by the American Cooling Tower Association (CTI) and is used in the United States and Japan. This integration method is to obtain an integral equation, and obtain a predetermined y value between a and b on the x-axis. The sum of a certain y value is multiplied by a constant value b-a, which is the integral value sought. The points are 0.102673 times, 0.406204 times, 0.593796 times and 0.897327 times of b-a. Find the corresponding y value for its four points. For calculation simplification, one bit after the decimal point is 0.1 times, 0.4 times, 0.6 times and 0.9 times of b-a. Its calculation formula is:

If the temperature difference is small, the points can also be divided according to the above multiples. The water temperature difference t can be divided into four equal parts, and the enthalpy difference of each midpoint is obtained, and then substituted into the formula. If divided by multiples, the corresponding coma for each point is shown in the table below.
The above is a complete cooling tower thermal calculation process, which can be used for both cooling tower design calculations and existing cooling tower accounting.
When calculating the existing cooling tower, the size and internal components of the tower, the amount of water Q, the inlet water temperature t1, the atmospheric pressure pa, the dry bulb temperature Î¸1, and the wet bulb temperature Ï„1 are known. Then it is required to calculate: the outlet water temperature t2, the ventilation amount G, the tower air dry bulb temperature Î¸2, and the tower air wet bulb temperature Ï„2.
The design of the cooling tower is a trial calculation process, that is, according to the given conditions, the size and internal components of the tower are selected, and then the water temperature t2 is calculated to meet the design requirements. Therefore, the thermal calculation of the cooling tower is to calculate the tower water temperature t2, and also calculate the ventilation and exhaust temperature.