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,
= 40^oC

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

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

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

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,
= 12.68^oC

Temperature of air out,
= 21.07^oC

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. Tw_in, (ii) Approach vs. Tw_in, (iii) Effective vs. Tw_in, and (iv) Cooling load vs. Tw_in.

1. Range vs. Tw_in

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

2. Approach value vs.
   Tw_in

Figure 1(b): Graph of Approach vs. Tw_in

3. Cooling load vs. Tw_in

Figure 1(c): Graph of cooling load vs. Tw_in

4. Effectiveness vs. Tw_in

Figure 1(d): Graph of effectiveness vs. Tw_in

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 30^oC and 45.2^oC 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

2. Approach vs. airflow rate

Figure 2(b): Approach vs. airflow rate

3. Cooling load vs. airflow rate

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

4. Effectiveness vs. airflow rate

Figure 2(d): Effectiveness vs. Airflow rate

5. Approach vs. cooling load

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