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Experiment No #2: Objective

Experiment no. 2 aimed to determine the height of packing and number of transfer units (NOG) in a cooling tower, and approach temperature range for cooling. The cooling tower uses convection and evaporation to transfer heat from water to air. Calculations determined the tower's effectiveness was 33.33%, NOG was 40, and approach temperature range was 4°F. Key applications of cooling towers include use in power plants, oil refineries, and other industrial processes to reject waste heat to the atmosphere.

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58 views5 pages

Experiment No #2: Objective

Experiment no. 2 aimed to determine the height of packing and number of transfer units (NOG) in a cooling tower, and approach temperature range for cooling. The cooling tower uses convection and evaporation to transfer heat from water to air. Calculations determined the tower's effectiveness was 33.33%, NOG was 40, and approach temperature range was 4°F. Key applications of cooling towers include use in power plants, oil refineries, and other industrial processes to reject waste heat to the atmosphere.

Uploaded by

mjunaid
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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Experiment no #2:

Objective:
To determine height of packing and Nog & temperature range and
approach for cooling tower

Apparatus:
Cooling tower apparatus & water

Working principle:
Dry cooling towers operate by heat the transfer through a surface that
separate the working fluid from ambient air, such as in a tube to air heat
exchanges utilizing convective heat transfer. They do not use evaporation
Wet cooling towers operate on the principle o evaporation cooling.

Theory:
What is a cooling tower?
A cooling tower is a heat rejection device that rejects waste heat to the
atmosphere through the cooling of a water stream to a lower temperature.

Industrial cooling towers:


A large volume of air is constantly moving along the fill courtesy of large
fans in the tower. As evaporation takes place, the water loses heat. It eventually
enters the tower sump at the bottom. The cool water then goes back to cool the
initial heat source and the cycle repeats. For the sake of system dilution, of
portion of the system water goes to the drain through a bleed-off valve. The
makeup line feeds the cooling tower with fresh water for replenishment.

Types of Cooling Towers:


 Mechanical draft cooling tower
 Atmospheric cooling tower
 Hybrid draft cooling tower
 Air flow-characterised cooling tower
 Construction-characterised cooling tower

Air flow generations:


 Natural draft
 Mechanical draft
 Fan assisted natural draft

Air to water flow:


 Cross-flow
 Counter-flow
 Cross and counter flow with natural or mechanical draft

Applications:
The prime use of the cooling tower is to block out the heat absorbed in the
moving cooling water system. The application of cooling tower is as follows,

 Natural gas processing plants


 Power plants
 Food processing plants
 Petrochemical plants
 Semiconductor plants
 Petroleum refineries

Observations and calculations:


Air calculations:

Inlet Outlet
T=85oF T=102oF
Humidity=55% Humidity=75%
Tsat=72oF Tsat=93oF
Hsat=0.018lbH2O/lbAir Hsat=0.035lbH2O/lbAir
H=0.015lbH2O/lbAir H=0.033lbH2O/lbAir

Enthalpies:
1.
Tin=85oF hin=0.015
H1=(1.005+1.88h)T+2501h
H1=12.5 btu/lb
2.
Tout=102oF hout=0.0033
H2=173btu/lb
3.
Tsat,in=72oF hsat,in=0.018
H3=13.33 btu/lb

4.
Tsat,out=93oF hsat,in=1.035
H3=18.7 btu/lb

Water calculations:
Inlet Outlet
T=105oF T=99oF
From Graph
H1=64.5 H2=26.5 Hm=42
f∆Hm= Hm/H2 – Hm/H1
= 0.93

NOG= (H2-H1)/(f∆Hm)
= 40
Hog= z/Nog = 0.772/40 = 0.103m
K= G/M*P*Hog
= 84/18*1*0.103
K= 45
Temp. Range= T1-T2=41-37=4OF
Temp. approach= 37-29 = 8oF
Effectiveness = range/range+ approach
= 4/4+8 = 0.333= 33.33%

Precautions:
 Don’t let packing over-flood
 Don’t heat water more than 100oC

Results:
Effectiveness of cooling tower is 33.33%.

References:
 www.qoura.com
 www.wikipedia.com
Line flow diagram: Water
Temp.
Out

Container
for Water
desiccant storage
with
heater

Pump

Water
Temp. Out
Blower

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