CEBU INSTITUTE OF TECHNOLOGY - UNIVERSITY
Cebu City
DEPARTMENT OF MECHANICAL ENGINEERING
ME LABORATORY 3
EXPERIMENT NO. 1
PERFORMANCE TEST OF INDUCED DRAFT COOLING TOWER
OBJECTIVE:
To evaluate the performance and conduct psychrometric analysis of a mechanical induced
draft type cooling tower.
Note: Your input must be of different text color. You can add additional diagrams, charts,
picture, etc.
LEARNING OUTCOMES:
At the end of the experiment the student will be able to:
1. Demonstrate the operation of an induced - draft cooling tower.
2. Conduct mass and energy balances of the cooling tower.
3. Plot the cooling tower characteristic curve based on enthalpy -wet bulb temperature
variation.
THEORY:
A cooling tower is a heat exchanger of a particular type that discharges heat in the
surrounding air in the form of both sensible heat and latent heat due to the increase of its
moisture. Water cooling towers are an integral part of the process industry, power plant,
and large air-conditioning and refrigeration system. Cooling towers are used as an
inexpensive means of transferring waste heat from a process to the atmosphere. Towers
consist of feeding water in at the top of the column and allowing it to cascade down over a
large number of slats while air is forced up through the tower in an opposing direction. The
purpose of the slats is to increase the surface area of the water, while at the same time
creating turbulence in the water flow and increasing the time the water is contacted with
the air. Slats are usually constructed from hydroscopic materials helping to increase water
cooling time in the tower. This therefore allows for greater cooling of the warm water.
There are two main types of cooling towers, called direct contact or open-cycle, and indirect
contact or closed-cycle ( see figure below ).
In a direct contact tower, hot water is cooled in contact with ambient air either by spraying
fine droplets, or by runoff along flow surfaces. Both fluids being in contact, heat is
exchanged by convection, and part of the water vaporizes, thereby increasing the humidity.
If it is not saturated, it starts to cool in an almost adiabatic process, before warming up along
the saturation curve. Therefore water may come out at a temperature lower than ambient
air.
An indirect contact tower involves two circuits known as external and internal. In the latter,
the cooling fluid, which can be arbitrary, remains confined in a tube bundle around which
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the external cooling circuit water runs. It warms on contact, then is cooled by exchange with
ambient air by the same mechanism as in a direct contact tower.
Direct Contact Cooling Towers
Indirect Contact Cooling Towers
Cooling towers may also classified according to the method adopted to circulate the air:
1. Natural draft cooling towers
2. Mechanical draft cooling towers.
Natural Draft Cooling Tower
As the name indicates, the air is circulated inside the cooling tower by natural convection as
shown in FIGURE A & B.
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FIGURE A - NATURAL DRAFT COOLING TOWERS
FIGURE B - HYPERBOLIC COOLING TOWER
Mechanical Draft Cooling Towers
The mechanical draft cooling towers are very much similar to that of the natural draft
cooling towers. As the name indicates, air is circulated inside the tower mechanically instead
of natural circulation. Propeller fans or centrifugal fans may be used.
Advantages of mechanical draft cooling towers over natural draft cooling towers:
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•
•
•
For the same capacity used, the mechanical draft cooling towers are much smaller
than the natural draft cooling towers. This is because of the increase in cooling
capacity due to increase in volume of the air being forced out by fan.
Capacity control is possible in mechanical draft cooling tower. By controlling the
speed of the fan, the volume of air can be controlled, which in turn controls the
capacity.
The natural draft cooling towers can be located only in open space. As they do not
depend upon the atmospheric air, the mechanical draft cooling towers shall be
located even inside the building.
Disadvantages of using mechanical draft cooling towers:
• More power is required to run the system.
• Increased running cost due to increase in maintenance of the fans, motors and its
associated controls.
According to the location of the fan, they are further classified as Forced Draft cooling
towers and Induced Draft cooling towers.
Forced Draft Cooling Towers
In this system, fan is located near the bottom and on the side. This fan forces the air from
bottom to top. An eliminator is used to prevent loss of water droplets along with the forced
air (FIGURE C).
FIGURE C - FORCED DRAFT TOWER
Induced Draft Cooling Towers
In this system, a centrally located fan at the top, takes suction from the tower and
discharges it to the atmosphere. The only between the induced draft cooling tower and
forced draft cooling tower is that the fan is located at the top in the induced draft cooling
tower (FIGURE D).
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FIGURE D - INDUCED DRAFT TOWER
Induced Draft Cooling Tower
1. Add additional information
2. Demonstrate the operation of an induced - draft cooling tower
from the Law of Conservation of Energy, applying on Whole System (Boundary 1):
q + Wp + mM hwM = ma (h2 – h1)
considering the Cooling Tower (Boundary 2) under steady state steady flow process and
from the Law of Conservation of Mass:
mWA + ma W1 + mM = mWB + ma W2
mM = ma ( W2 – W1 )
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Make - Up Water = Water Absorbed by Air
from the Law of Conservation of Energy with ΔKE and ΔPE negligible:
mWA hWA + ma h1 + mM hwM = mWB hWB + ma h2
mW ( hWA – hWB ) + mM hwM = ma ( h2 – h1 )
ma ( h2 – h1 ) – mW ( hWA – hWB ) = mM hwM
qa – qw = mM hwM = 0 ( if mM hwM is negligible )
where:
ma
mW
mM
h
= air flow rate, kg/s
= water circulated flow rate, kg/s
= make-up water flow rate, kg/s
= air enthalpy , kJ/kg
= 1.0 ( tdb ) + W ( hgw ) or from High Temp Psychrometric Chart
W = humidity ratio , kg w/kga from High Temp Psychrometric Chart
hgw = sat vapor water enthalpy at tdb , kJ/kg from Steam Table
qa & qw = heat transferred from water to air, kW
3. Explain briefly the derivation of equations
INSTRUMENTATION AND SPECIFICATION:
4. The group/team should identify the apparatuses and equipment to be used, and include
the equipment technical specification if possible.
PROCEDURE:
5. The group/team will have to formulate procedure on how to gather data. Initial values will
be provided by the instructor and must be filled out and completed by the group/team
RESULTS AND OBSERVATION SHEET:
Group#
Water flow
Dry bulb temp., C
Wet bulb temp., C
1
3200 liters/hr
29
19
2
3200 liters/hr
30
20
3
3300 liters/hr
31
21
4
3400 liters/hr
32
20
5
3500 liters/hr
33
21
6
3600 liters/hr
34
20
7
3700 liters/hr
35
21
6
8
3800 liters/hr
36
20
9
3900 liters/hr
37
23
10
4000 liters/hr
38
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Cooling Load,
qw
: _____
kW
Operation Time: ___ minute
Water
Entering
Condition
Leaving
Condition
( In )
( Out )
Temperature, C
Enthalpy, kJ/kg
Dry Bulb Temperature, C
Group
Trial
Air
Wet Bulb Temperature, C
Air Enthalpy, kJ/kg
Air Ave. Velocity, m/s
Flow Rate
kg/s
Mass Flow
Rate
Water Flow rate, kg/s
Make-Up
Water
Make-Up Water Flow rate, kg/s
Enthalpy In
kJ/kg
Air Flow rate, kg/s
Make-Up Water Temperature, C
Enthalpy Out
kJ/kg
Heat
Transferred
kW
% Diff
Make-Up
Water
kg/s
Water Absorbed
by Air
kg/.s
% Diff
Water
Air
DISCUSSION AND INTERPRETATION OF RESULTS:
6. Include a discussion on the result noting trends in measured data, and comparing
measurements with theoretical predictions when possible, physical interpretation of the
result, graphical plotting showing the relation between vital variables, and the reasons on
deviations of your findings from expected results.
CONCLUSION:
7. Make an overall conclusion by referring to experiment objective and on data of the result.
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8. Definition of Terms (you can provide illustrations exclusive of cooling towers only) ACFM,
air rate, air travel, approach, basin curb, blowdown, blowout, bleed off, capacity, cell,
collection basin, drift, driver, evaluation, height, fill deck, louvers, make up, module, packing,
plenum chamber, riser, shell, sump, total water rate, windage
9. Provide additional references
REFERENCE: (retrieve December 2018)
A)
B)
https://www.studocu.com/en/document/university-of-newcastle-australia/transferprocesses-laboratory/mandatory-assignments/exp-7-cooling-tower-reportfinal/1117688/view
https://www.brighthubengineering.com/hvac/100882-hvacr-cooling-towers-and-theirtypes/
GRAPHICS REFERENCE: (retrieve December 2018)
A) https://www.google.com/search?biw=1366&bih=657&tbm=isch&sa=1&ei=PY7oXMzFFs
b7wAPqiL2wDw&q=FORCED+DRAFT+COOLING+TOWER
B) https://www.google.com/search?biw=1366&bih=657&tbm=isch&sa=1&ei=spDoXJaECM
aHoASe_YWQCg&q=NATURAL+DRAFT+COOLING+TOWER
C) https://www.google.com/search?biw=1366&bih=657&tbm=isch&sa=1&ei=ao7oXMWO
OdWHoATfs5KoCg&q=INDUCED+DRAFT+COOLING+TOWER
VIDEO REFERENCE: (retrieve December 2018)
A) https://www.youtube.com/watch?v=ZzEHoMvzErY
B) https://www.youtube.com/watch?v=kASLz29cU1g
INDUCED DRAFT TOWER: (retrieve December 2018)
A) https://www.youtube.com/watch?v=zgzre5Agwmo
B) https://www.youtube.com/watch?v=G7Y3l16ywd0
C) https://www.youtube.com/watch?v=w9sDZSJ9XNc
D) https://www.youtube.com/watch?v=YIDH1FGWWKA
E) https://www.youtube.com/watch?v=UzHJWNL2OtM
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