Introduction

The objectives of the experiment conducted were to determine air outlet velocities

& flow rates, air inlet velocities and flow rates, and water inlet and outlet data and to

compare of data at different water inlet flow rates. Cooling towers are used in water

treatment processes, sewage systems, and heating and cooling systems. The type of

cooling tower that was used for the experiment was a counter-flow tower. The air

stream and water stream flow opposite of each other.

Theory

The calculations for this experiment were based on the following two equations.

Assuming Steady State Operation [IN = OUT], the following balances can be used:

Overall Mass Balance

MAO + MWO = MAI + MWI

Overall Energy Balance

hAO*MAO + hWO*MWO = hAI*MAI+ hWI*MWI

Where M=Mass, h=enthalpy, AO=Air Outlet, AI=Air Inlet, WO=Water Outlet, and

WI=Water Inlet. Wet bulb and dry bulb temperatures of the air inlets and outlets were

and used to look up enthalpy data on the psychometric chart. Also, software to calculate

psychometric chart information was used. In order to calculate air outlet velocities, the

profile is needed. The profile can be found by plotting velocity (y-axis) versus radius (x-

axis) at which the velocity was measured. A curve fit was performed to obtain the

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equation for the profile. The following equation was used to calculate the average

velocity:

Where V(r) is the velocity profile and r is the radius. The volumetric flow rate is

determined by:

(Volumetric flow rate) = Vave*Area

Using the volumetric flow rate, the mass flow rate of the air outlet can be calculated by

the following equation:

(Mass flow rate) = (density)*(volumetric flow rate)

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Equipment

Figure 1 is a schematic drawing of the cooling tower used in the experiment.

Figures 2, 3, 4, 5, and 6 are pictures of the cooling tower located in EMCS 120 that was

used for the experiment. At the water inlet, there is a mechanism that evenly distributes

the incoming water throughout the system. On the side of the tower, a fan is responsible

for inputting air, i.e. the air inlet.

Outlet Air for Water Inlet Flow Rate = 10.1 (l/min)

Area = 0.312 m2

Volumetric Flow Rate= 1.6 m3/s Temp. Dry Bulb= 23 °C= Wet Bulb Temp. Enthalpy = 86 kJ/kg Dry Air

Air Outlet2

Warm Water Inlet

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Make-Up Water

Air Inlet1 Cool Water

Outlet4

Figure 1 Schematic of Cooling TowerPortable Cooling Tower

Figure 2 Cooling Tower

3

Air Inlet

Figure 3 Air Inlet

Air Outlet and Water Inlet

Figure 4 Water Inlet and Air Outlet

4

Portable Cooling Tower

Figure 5 Cooling tower

Water Spraying Upward

Figure 6 Air Outlet and Water Inlet

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Procedure

The experiment began by filling the bottom of the cooling tower with water in

order to prevent splashing. Once the bottom was filled, the tower was plugged into a

power supply. Temperature measurements are taken for the water inlet first. Next, air

inlet wet bulb and dry bulb temperatures are taken at the 3 regions of the inlet location.

They were averaged together. As the system is running, air outlet temperatures are taken

at the same 3 radii with the 3 sections at the outlet region as shown in Figure 6. Finally,

the water outlet temperature is taken at the bottom of the cooling tower.

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Results

Figure 7 is a graph of the outlet velocity as a function of radius

for water inlet flow fate = 5.1 (l/min)Outlet Velocity as a Function of Radiusfor Water Inlet Flow Rate = 5.1 (l/min)

Air Outlet VelocitiesV(r) = -438.81r3 - 111.83r2 + 78.86r + 0.0789

R2 = 0.9876

0123456789

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Radius (m)

Velo

city

(m/s

)

Figure 7 Outlet Air Velocity Profile @ 5.1 (l/min)

Figure 8 shows the graph of the outlet velocity as a function of radius

for water inlet flow fate = 10.1 (l/min)Outlet Velocity as a Function of Radiusfor Water Inlet Flow Rate = 10.1 (l/min)

Air Outlet VelocitiesV(r)= -395.28r3 - 118.74r2 + 76.678r + 0.0452

R2 = 0.9955

0123456789

0 0.1 0.2 0.3 0.4

Radius (m)

Velo

city

(m/s

)

Figure 8 Outlet Air Velocity Profile @ 10.1 (l/min)

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Figure 9 shows the graph of the outlet velocity as a function of radius

for water inlet flow fate = 40.3 (l/min)Outlet Velocity as a Function of Radiusfor Water Inlet Flow Rate = 40.3 (l/min)

Air Outlet VelocitiesV(r) = -318.78r3 - 32.419r2 + 41.871r + 0.0242

R2 = 0.9965

0

0.5

1

1.5

2

2.53

3.5

4

4.5

5

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Radius (m)

Velo

city

(m/s

)

Figure 9 Outlet Air Velocity Profile @ 40.3 (l/min)

Table 1 shows a comparison of data from calculations and measurements at different

water inlet flow rates

 

Water Inlet Flow Rates  

at 5.1 l/min

at 10.1 l/min

at 40.3 l/min

Inlet Temp 52.5 oC 56.3 oC 52 oCOutlet Temp. 27.7 oC 31 oC 30.4 oC

Temp. Change 24.8 oC 25.3 oC 21.6 oC

Mass Flow Rate

0.085 kg/s 0.168 kg/s 0.671 kg/s

Tons of Cooling 2.5 5.1 17

Figure 10 Comparison Table

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Discussion of Results

There were different velocity profiles found at each inlet water flow rate. The

profiles were all of a third order polynomial. The Tons of Cooling increased as the inlet

water flow rate increased. The greatest change in temperature occurred when the water

inlet flow rate was at 10.1 (l/min).

Conclusions

Through the conduction of this experiment, a cooling tower analysis was able to

be completed. Measurements for inlet and out data for air and water were made with

relative ease… allowing for calculations of data for the system a success. All data

reported was an average of at least 3 data points in order to provide better accuracy as

opposed to using a relative measurement (at just one point).

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Appendix

Sample Calculation

(Volumetric flow rate) = Vave*Area

(Volumetric flow rate) = (8.56 m/s) * (0.0380 m2)

(Volumetric flow rate) = 0.325 m3/s

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