# Basic Water Cooling Tower Essay Example

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Basic Water Cooling Tower

Exercise A: Observation of the processes occurring within a forced draught cooling tower

The variables are measured as below:

Temperature of water entering at the top of packing, = 40oC

Temperature of water leaving at the bottom of packing, = 27.4oC

Temperature of air leaving at the top of packing (dry bulb), = 23.1oC

Temperature of air entering the bottom of packing (dry bulb), = 21.4oC

Relative humidity of air entering at the bottom, RH2 = 40.6%

Relative humidity of air leaving at the bottom, RH1 = 97.3%

Power required to heat water (cooling load) = 1.0 kW

Temperature of air in, = 12.68oC

Temperature of air out, = 21.07oC

Calculations:       = Exercise B: Effect of water inlet temperature on the performance of the cooling tower

The measured values, and calculated values of Approach, Range, and Effectiveness are shown in the table below:

Table 1(a): Effect of water inlet temperature on effectiveness

 Water inlet temperature ( ) T2 = Tw out T4 = Ta out RH1 = Rh out (%) RH2 = Rh in Cooling load (kW)

Table 1(b): Comparing performance at each water temperature

 Water inlet temperature ( ) Range ( ) Approach value Cooling load kW Effectiveness %

The graph of (i) Range vs. Twin, (ii) Approach vs. Twin, (iii) Effective vs. Twin, and (iv) Cooling load vs. Twin.

1. Range vs. Twin Figure 1 (a): Graph of Range vs. Twin

1. Approach value vs.
Twin Figure 1(b): Graph of Approach vs. Twin Figure 1(c): Graph of cooling load vs. Twin

1. Effectiveness vs. Twin Figure 1(d): Graph of effectiveness vs. Twin Figure 1(e): Graph of cooling load vs. approach

In figure 1(a), 1(b) and 1(c), range, approach and cooling load increases with increase in the temperature of inlet water. Increasing the temperature of the water inlet means that more energy will be used to raise the temperature of the water, and a larger temperature difference is created between the cooling air and the water, which increases the rate of heat transfer. From figure 1(d), effectiveness is maximum at 30oC and 45.2oC respectively, but minimum at temperatures between the two values. This can be attributed to the temperature difference created between cooling air and water. In figure 1(e), a higher cooling load is required for a higher approach. Increase in approach means increase in range, which in turn needs more energy to raise the temperature of water.

Exercise C: Effect of air flow rate on the performance of the cooling tower

The measured values, and calculated values of Approach, Range, and Effectiveness are shown in the table below:

Table 2 (a): Effect of air flow rate on effectiveness

 Air flow l/sec T2 = Tw out T3 = Ta out RH1 = Rh out (%) RH2 = Rh in

Table 1(b): Comparing performance at each Air flow rate

 Air flow l/sec Approach value Range Cooling load kW Effectiveness %
1. Range vs. airflow rate Figure 2(a): Range vs. airflow rate

1. Approach vs. airflow rate Figure 2(b): Approach vs. airflow rate

1. Cooling load vs. airflow rate Figure 2(c): Cooling load vs. airflow rate

1. Effectiveness vs. airflow rate Figure 2(d): Effectiveness vs. Airflow rate Figure 2(e): Approach vs. cooling load

From the graph in figure 2(a), 2(c) and 2(d), range, cooling load and effectiveness increases with increase in the rate of airflow. In figure 2(b) and 2(e), approach decreases with the rate of air flow rate and decrease in the cooling load respectively. Increase in the range increases effectiveness of the cooling tower, while decrease in the approach increases the effectiveness. Thus, the decrease in approach with increasing airflow increases the performance of the cooling tower. As more air passes through the fills, the cooling effect is increased.

Reference

Armfield Ltd. Basic Water Cooling Tower Instruction Manual (UOP6-MKII). Vol. Issue 3. United Kingdom, July 2015.