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 (xaxis) at which the velocity was measured. A curve fit was performed to obtain the
1
equation for the profile. The following equation was used to calculate the average
velocity:
2 R
Vave
V (r )rdrd 
V (r )dA  




dA

  rdrd
0 0
2 R
0 0
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)
2
Equipment
Figure 1 is a schematic drawing of the cooling tower used in the experiment.
Figures 2, 3, 4, 5, and
6 are pictures
the Water
cooling tower
located in EMCS 120 that was
Outlet
Air offor
Inlet
)
Flow
Rate
= 10.1
used for the experiment.
At the
water inlet,
there is(l/min
a mechanism that evenly distributes
the incoming
water=throughout
 Area
0.312 m2the system. On the side of the tower, a fan is responsible
 Volumetric Flow Rate= 1.6 m3/s
for inputting air, i.e. the air inlet.
 Temp. Dry Bulb= 23 °C= Wet Bulb Temp.
 Enthalpy = 86 kJ/kg Dry Air
Air Outlet
2
Warm
Water Inlet
3
Air Inlet
1
Cool Water
Outlet
4
Make-Up
Water
Portable Cooling Tower
Figure 1 Schematic of 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
5
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.
6
Results
Figure 7 is a graph of the outlet velocity as a function of radius
Velocity
for water inlet flowOutlet
fate = 5.1
(l/min) as a Function of Radius
for Water Inlet Flow Rate = 5.1 (l/min)
Velocity (m/s)
Air Outlet Velocities
V(r) = -438.81r3 - 111.83r2 + 78.86r + 0.0789
R2 = 0.9876
9
8
7
6
5
4
3
2
1
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Radius (m)
Figure 7 Outlet Air Velocity Profile @ 5.1 (l/min)
Figure 8 shows the graph of the outlet velocity as a function of radius
Outlet
for water inlet flow
fate = Velocity
10.1 (l/min)as a Function of Radius
for Water Inlet Flow Rate = 10.1 (l/min)
Air Outlet Velocities
3
2
Velocity (m/s)
V(r)= -395.28r - 118.74r + 76.678r + 0.0452
9
8
7
6
5
4
3
2
1
0
2
R = 0.9955
0
0.1
0.2
0.3
0.4
Radius (m)
Figure 8 Outlet Air Velocity Profile @ 10.1 (l/min)
7
Figure 9 shows the graph of the outlet velocity as a function of radius
Outlet
Velocity
for water inlet flow
fate = 40.3
(l/min) as a Function of Radius
for Water Inlet Flow Rate = 40.3 (l/min)
Air Outlet Velocities
3
2
V(r) = -318.78r - 32.419r + 41.871r + 0.0242
2
5
R = 0.9965
4.5
Velocity (m/s)
4
3.5
3
2.5
2
1.5
1
0.5
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Radius (m)
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
Inlet Temp
Outlet Temp.
Temp.
Change
Mass Flow
Rate
Tons of
Cooling
at 5.1
l/min
at 10.1
l/min
at 40.3
l/min
52.5 oC
56.3 oC
52 oC
27.7 oC
31 oC
30.4 oC
24.8 oC
25.3 oC
21.6 oC
0.085
kg/s
0.168 kg/s
0.671 kg/s
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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