To show how different water flow rates e ffect on the performance of mechanical draught cooling tower.

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EXPERIMENT NO.1
The effect of varying water flow rate on the performance of
mechanical draught cooling tower
Aim:
To show how different water flow rates effect on the performance of mechanical
draught cooling tower.
1. Theory & procedure
An apparatus include a vertical glassy tower with packing plate inside, the main uses
of cooling tower is to cool the water by forced convection process using centrifugal
fan located under the tower, from basin (tank) which collect the water, by small heater
the water heated to 50⸰c, we can control the heater by electronic thermostat inside the
tank, through a tube the hot water pumped to the top of tower, the hot water get spray
by orifices to drop on the fill and packing plate that used to increase contact area
between water and air, so that the rate of heat transfer will increase.
By flow meter valve we can record flow and control the hot water flow rate, after
water get cold so will remain under the tower then returned to the hot water tank.
Fig. 1 PID Control of cooling tower [1]

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(I) Main software operation possibilities
(II) Sensors displays, real time values, and extra output parameters
(III) Actuators controls
(IV) Channel selection and other plot parameters
(V) Real time graphics displays
The Bench Top Water Cooing Tower (Figure 2) has been designed to give students an
appreciation of cooling construction, design and operational characteristics of modern
evaporative cooling system. The unit is also an excellent example of an ‘open system’
through which two stream of fluid flow (water and air) and in which there is a mass
transfer from one stream to other. Convincing energy and mass balance are obtained,
and student can quickly investigate the effects of air flowrate, water flowrate, water
temperature and cooling loads on the performance of a cooling tower. You will
measure the performance of cooling tower and determine the errors of your sensors
and uncertainties of your measurements [1]
.
2. Reading table & calculation
The performance of cooling towers is evaluated to assess present levels of approach and
range against their design values, identify areas of energy wastage and to suggest
improvements.
Fig. 2 Mechanical draught cooling tower scheme [1]

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During the performance evaluation, portable monitoring instruments are used to
measure the following parameters:
• Cooling tower inlet water temperature [ST-2] ºC
• Cooling tower outlet water temperature [ST-7] ºC
• Wet bulb temperature of air [ST-3] ºC
• Dry bulb temperature of air [ST-4] ºC
• Water flow rate [SC-1] L/Min
• Electrical switch of heater [AR-1]
• Electrical switch of pump [AB-1]
• Electrical readings of fan motors [AVE-1]
• Water level alarm [AN-1]
• Differential pressure sensor [SPD]mmH2O
Table 1 Cooling tower parameter
Range = water inlet temp. [ST-2] – water outlet temp. [ST-7] (higher range good
performance)
Approach = water outlet temp. [ST-7] – wet bulb ambient temp. [ST-3]
(Higher approach lower performance)
Effectiveness % = Range /range + approach (higher good performance)
Cooling capacity [QR] = mw.cpw.(Tw.in-Tw.out) (higher good performance)
3. Discussion questions
1. Write your result.
2. What are the parameters that effect on the cooling tower performance? Why?
3. Use Psychrometric chart below to identify relative humidity and humidity
ratio.
No. of
Experiment
SC-1 ST-2 ST-7 ST-3 ST-4 Ambient
temperature
1
2
3

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Fig. 3 Psychrometric chart [2]
4. Draw a simple temperature chart.
References
1. Edibon, The Computer Controlled Bench Top Cooling Tower, "TTEC", 2021.
2. Perry, R.H. and D.W. Green (eds.), Chemical Engineer’s Handbook, 7th ed.,
McGraw-Hill, 1997.
Barhm Abdullah Mohamad
Erbil Polytechnic University
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