| dc.description |
At first, the author expresses his heartiest thanks to the Almighty Allah for giving the
patience and potentiality to complete the thesis work. I also express my appreciation to
all the people who have given their hearts whelming full support in preparing and
completing the study.
I am highly pleased to express my sincere and profound gratitude to my supervisor Dr.
Mohammad Ali, Professor, Department of Mechanical Engineering, Bangladesh
University of Engineering & Technology (BUET), Dhaka, Bangladesh for providing me
the opportunity to conduct research on nanofluids for cooling tower. I wish to express
my deepest thanks to him for his continuous with patience guidance, suggestions,
inspiring advice, constructive suggestions with enthusiastic supervision and
wholehearted help throughout the course of the work.
I am also thankful to Lt Col Md. Altab Hossain, PhD, Associate Professor, Dept of
Nuclear Science and Engineering (NSE), Military Institute of Science and Technology
(MIST), Dhaka for his continuous guidance to shape my research work. I am also
grateful to Head and all Faculty Members, Dept of Mechanical Engineering for their
dedicated and relentless support both for literature and experimental work.
I would also express my deepest gratitude to my wife, my beloved sons and other
family members for their support and encouragement.
Finally, I am grateful to almighty Allah for enabling me to complete the thesis. |
en_US |
| dc.description.abstract |
Cooling towers are evaporative heat transfer devices in which atmospheric air cools
warm water with direct contact between the air and the water by evaporating cooling of
water. The main objective of this study is to analysis the cooling tower performance,
with induced draft cooling tower and finding out the effect of adding nanofluids of Al
Oxide (Al2O3), Zn Oxide (ZnO), and Ti Oxide (Ti2O3) with base fluid as water. This
was done by establishing experimental set up supported with computer program and
varying the quality of circulating fluids by adding together at different ratio. Recently
large numbers of experiments have been carried out to evaluate the effect of nanofluid
in enhancement of the heat transfer rate in various heat exchangers. The heat transfer
enhancement using nanofluid mainly depends on type of nanoparticles, size of
nanoparticles, shape of nanoparticles, and type of base fluid and concentration of
nanoparticles in the base fluid. Therefore, this study deals with several experimental
investigation of the thermal performance of a prototype mechanical wet cooling tower
with a counter flow arrangement. Different volume concentrations ranging from 0.18 to
0.50 vol. % of stable Al Oxide (Al2O3), Zn Oxide (ZnO), and Ti Oxide (Ti2O3)
nanoparticles of 80, 35, and 70 nm diameter were considered. Water was taken as a
base fluid, and the experiment was carried out at 60, 70, and 80 °C, respectively, in
laboratory conditions. The study revealed that an increase in the volume concentration
of the nanofluids increased the cooling range, cooling efficiency, convective heat
transfer coefficient, tower characteristic called number of transfer unit (NTU), and
effectiveness of the cooling tower compared with water at the same mass flow rate and
inlet temperature. However, increasing the volume concentration increased the viscosity
of the nanofluids, leading to an increase in friction factor. From the result it has been
obtained a comparative study on terms of tower characteristics (kav/L), water to air
flow ratio (L/G), efficiency, range, percentage of make-up water and evaporation heat
loss are presented in graphical form. The graph shows that the performance of cooling
tower is affected by the type of cooling tower and the quality of circulating fluids. The
graphical analysis shows the cooling tower characteristics and efficiency decreases with
an increase in (L/G), the induced draft cooling tower shows better performance than
natural draft cooling tower. It is revealed that at higher volume concentration of
nanofluid, cooling range would increase by 29% at low flow rates which is also
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accompanied by the heat lost by water, and thereby, average increase in efficiency is
27% at temperature 80°C. This happens more significantly with Al2O3 and ZnO
nanoparticles when they are added in base fluid with different ratios. For instance, for
0.18% volume concentration of ZnO, at an inlet water temperature of 66.4 °C and
water/air (L/G) flow ratio of 1.93, the cooling range increased by 3.62%, cooling
efficiency increased by 33.3%, and NTU increased by 50.5% compared with fresh
water (FW).
Prediction of thermal performance is necessary for thermo-fluid engineering
applications as well as manufacturing industries. Hence, the validation of the developed
mathematical model in this study has been carried out by making comparison of the
measured and predicted thermal performance. This study presents an intelligent
approach based on fuzzy expert system (FES) of a cooling tower. FES links between
volumetric concentration (VC), mass flow rate of liquid to air ratio (L/G) and flow rate
(FR) and cooling efficiency (CE) and range (CR). To validate the mathematical model,
the thermal performance in terms of cooling efficiency (CE) and cooling range (CR),
L/G and liquid flow rate are measured on the developed cooling tower and compared
with the predicted ones. Values are obtained from experiments on an induced draft
cooling tower with nanofluids in different VC of 0%, 0.06%, 0.18% and 0.30%,
respectively. The efficiency of nanofluids slightly increases about 5.04–8.82% with the
growth of VC related to water at the highest value of L/G. Whereas, the efficiency
significantly increased about 11–50% with the increase of VC at the lowest value of
L/G. FES model has been developed for the prediction of cooling efficiency and range
with nanofluid in different VC. For instance, in case of CE, the mean of measured
(experiment) and predicted (FES) values have been found as 15.84% and 15.90%,
respectively. Similarly, for CR, the values have been found as 3.30°C and 3.28°C,
respectively. The correlation coefficients of cooling efficiency and cooling range are
found as 0.961, and 0.997, respectively. The mean relative error of measured and
predicted values from the FES model on cooling efficiency and cooling range are found
as 9.0 % and 5.87 %, respectively. For all parameters, the relative error of predicted
values are found to be less than the acceptable limits of 10 %. The goodness of fit of the
prediction values from the FES model on cooling efficiency and cooling range are
found as 0.960 and 0.987, respectively, which are found to be close to 1.0 as projected.
The results indicate that there is less variability of the measured data and predicted data
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of the counter flow induced draft cooling tower with water and with nanofluids in
different volume concentration. It also indicates that the predicted data over the
measured data has a good agreement and thus substantiates the validity of the
mathematical model. In this study, according to assessment principles of predicted
performance of the developed fuzzy expert system based intelligent model has been
found to be valid. It is an innovative adaption leading to technological capacity building
which has a remarkable contribution to enhance the machine life, better-efficient
outcome and friendly to the aquatic and environmental system. |
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