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Analysis of evaporative coolers and condensersDreyer, Andre Alexis January 1988 (has links)
Thesis (MEng.) -- Stellenbosch University, 1988. / ENGLISH ABSTRACT: In this report various mathematical models for the thermal evaluation of
evaporative coolers and condensers are presented. These models range from
the exact model based on the work by Poppe [84P01] to the simplified
logarithmic models based on the work of McAdams [54Mcl] and Mizushina
et al. [67MI1], [68MI1].
Various computer programs were written to perform rating and selection
calculations on cross-flow and counterflow evaporative coolers and
condensers.
Experimental tests were conducted on a cross-flow evaporative cooler to
determine the governing heat and mass transfer coefficients. The
experimentally determined coefficients were cqrrelated and these
correlations are compared to the existing correlations. The two-phase
pressure drop across the tube bundle was also measured and a correlation
for two-phase pressure drop across a tube bundle is presented.
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Evaluation and performance enhancement of cooling tower spray zonesRoux, Daniel 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The performance of wet cooling towers can be improved by installing spray
nozzles that distribute the cooling water uniformly onto the fill whilst operating at
a low pressure head. In this thesis, three commercial spray nozzles are
experimentally evaluated in terms of flow and pressure loss characteristics as well
as water distribution patterns. The results of the evaluation process highlight the
need for spray nozzles with enhanced performance characteristics. The theory
required to implement the results of the evaluation process in the design of a
cooling tower is presented and discussed. A systematic approach to enhance the
performance of a spray nozzle through minor alterations is applied to one of the
commercial spray nozzles that was evaluated. The fluid dynamics of an orifice
nozzle, such as the effect of a change in pressure head, spray angle, spray height,
orifice diameter and wall thickness on drop diameter and spray distance, is
experimentally investigated and a model with which a spray nozzle can be
designed is finally presented. Two prototype spray nozzles show that it is possible
to enhance the performance of spray nozzles and thus wet cooling towers by
means of the methods presented. / AFRIKAANSE OPSOMMING: Die werkverrigting van natkoeltorings kan verbeter word deur sproeiers te
installeer wat die verkoelingswater uniform versprei op die pakking teen 'n lae
pomp drukhoogte. In hierdie tesis word drie kommersiële sproeiers
eksperimenteel geëvalueer in terme van vloei en drukverlies eienskappe sowel as
water verdelings patrone. Die resultate van die evaluasie proses beklemtoon die
behoefte aan sproeiers met verbeterde werkverrigtingseienskappe. Die teorie wat
benodig word om die resultate van die evaluasie proses te implementeer in die
ontwerp van 'n natkoeltoring word bespreek. 'n Stelselmatige benadering om die
werkverrigtings van 'n sproeier te verhoog deur klein veranderinge aan die
ontwerp aan te bring, word toegepas op een van die sproeiers wat getoets is. Die
vloeidinamika van 'n plaatmondstuk, soos die effek van 'n verandering in
drukhoogte, sproeihoek, sproeihoogte, gatdiameter en wanddikte op druppel
diameter en sproeiafstand, is eksperimenteel ondersoek en 'n model word
aangebied waarmee 'n sproeier ontwerp kan word. Twee prototipe sproeiers wys
dat dit moontlik is om die werkverrigting van sproeiers, en dus ook
natkoeltorings, te verbeter deur die metodes wat in die tesis aangebied word, toe
te pas.
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The influence of cross-winds on the performance of natural draft dry-cooling towers.Du Preez, Abraham Francois 12 1900 (has links)
Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 1992. / The effect of cross-winds on the performance of natural draft dry-cooling towers is studied by
means of isothermal model tests, a numerical simulation and full scale measurements. The
action of the wind on such towers is found to be complex and is influenced by a number of
different parameters including the wind speed, the shape of the approaching wind profile, the
inlet diameter to the inlet height ratio of the tower, the tower height, the shape of the tower
shell, the pressure loss coefficient of the heat exchangers and the amount of heat rejected by the
tower. For a horizontal arrangement of the heat exchangers the wind effect on the tower is
shown to be strongly dependent on both the shape and pressure loss coefficient of the tower
supports.
In practical cooling towers the heat exchangers are either arranged horizontally in the inlet
cross-section of the tower or vertically around the circumference of the tower and the wind
effect is found to be dependent on the particular layout. The wind effect on a tower is
furthermore found to increase if the heat exchangers are arranged in the form of A-frames.
Additional reductions in the heat rejection rate of the tower are caused by a non-uniform air
temperature distribution inside the tower and flow distortions through the heat exchanger.
Significant reductions in the wind effect on a cooling tower can be achieved by installing
windbreak walls below the heat exchangers if the latter are arranged horizontally in the tower
inlet.
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Evaluation of drop break-up after impingement on horizontal slat grids and the effect of drop size of cooling tower rain zone performanceTerblanche, Riaan 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Natural draught wet-cooling tower rain zone performance can be significantly
enhanced by reducing the mean drop size in the rain zone with the installation of
specially designed grids below the cooling tower fill. Drops enter the rain zone in the
form of a polydisperse drop distribution, dripping from below the cooling tower fill,
comprising relatively large drops. In order to design and optimize a grid for breaking
up these drops, the mechanisms of drop break-up after impingement on the grid
surface, referred to as splashing, straddling and dripping, need to be clearly
understood. Two of these mechanisms, splashing and straddling, are therefore
investigated experimentally using high speed video cameras to measure initial drop
sizes, mass fractions and drop size distributions after impingement on different
horizontal slats covered with a thin layer of water. The following parameters are
varied independently for these experiments: drop fall distance, initial drop size, slat
width and the water film thickness on the slats. Dripping from below the grid, is
investigated theoretically. The effect of drop interaction on the drop size distribution
in the rain zone is also investigated experimentally by measuring the drop distributions
at the top and bottom of rain zones with a height of approximately 7.05 m to 7.65 m
for different inlet distributions. The experimental drop break-up data, numerically
obtained splash drop trajectory data and drop interaction data found in literature are
used to develop a theoretical model of a purely counter flow cooling tower rain zone
with and without installed grids. The model is compared to experimental data and
theoretical data from literature and the predicted thermal and dynamic behaviour of the
rain zone are generally found to be in good agreement with these results. Ultimately,
this model is used for the optimization of the grid layout in terms of variables such as
distance between the grid and the fill, slat width, slat spacing and slat height. It is
found that the best drop break-up is achieved for grids comprising narrower slats with
lower grid porosities as opposed to grids comprising wider slats. For the determined
optimal grid layout it is found that a significant improvement in cooling tower
performance can be achieved. / AFRIKAANSE OPSOMMING: Nat-koeltoringreënsonevermoë kan aansienlik verhoog word deur die druppelgrootte
in hierdie gebied te verklein deur roosters, wat spesifiek vir hierdie doel ontwerp is,
onder die pakkingsmateriaal te installeer. Die inlaatdruppelverdeling aan die bokant
van die reënsone bestaan uit ‘n verdeling van relatief groot druppels wat drip van die
onderkant van die pakkingsmateriaal. Ten einde ‘n rooster te ontwerp en te optimeer
wat hierdie druppels kan opbreek moet die meganismes van druppelopbreking, bekend
as spatting, vurking en drip goed verstaan word. Spatting en vurking is om hierdie rede
eksperimenteel ondersoek, met behulp van hoëspoed videokameras. Die volgende
veranderlikes is onafhanklik verander tydens hierdie eksperimente: valafstand van die
druppel, aanvanklike druppelgrootte, latwydte en die dikte van die lagie water bo-op
die lat. Die dripmeganisme aan die onderkant van die rooster is slegs teoreties
ondersoek. Die effek wat druppelinteraksie in die reënsone het op die druppelgrootte is
ondersoek deur die druppelgroottes aan die bo- en onderkant van ‘n 7.05 m tot 7.65 m
reënsone te meet vir verskillende druppelinlaatverdelings. Die eksperimentele
druppeldata, sowel as numeries berekende data wat die snelheid en trajek van
spatdruppels beskryf, tesame met data vir druppelinteraksies wat uit die literatuur
verkry is word gebruik om ‘n teoretiese model te ontwikkel vir ‘n suiwer teenvloei
koeltoringreënsone met en sonder roosters. Hierdie model word vergelyk met
eksperimentele data en data wat uit die literatuur verkry is en daar is gevind dat daar
oor die algemeen ‘n goeie ooreenstemming is tussen die voorspelde en gemete
termiese en dinamiese gedrag van die reënsone. Uiteindelik word die model gebruik
vir die optimering van die rooster in terme van die volgende veranderlikes: afstand
tussen rooster en pakkingsmateriaal, latwydte, latspasiëring en lathoogte. Daar word
gevind dat beter druppelopbreking verkry word deur gebruik te maak van smaller latte
en ‘n laer roosterporeusiteit. Daar is gevind dat die bepaalde optimale roosteruitleg in
die reënsone van ‘n koeltoring ‘n wesenlike verbetering in koeltoringvermoë tot
gevolg kan hê.
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Performance optimization of engineering systems with particular reference to dry-cooled power plants /Conradie, Antonie Eduard. January 1995 (has links)
Dissertation (PhD)--University of Stellenbosch, 1995. / Bibliography. Also available via the Internet.
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Power plant heat rejection in an arid climateScofield, Frederic Cook, 1942- January 1971 (has links)
No description available.
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Spirulina production in brine effluent from cooling towersChoonawala, Bilkis Banu January 2007 (has links)
Thesis (M.Tech.:Biotechnology)-Dept. of Biotechnology, Durban University of Technology, 2007
xvi, 185 leaves / Spirulina is a blue-green, multicellular, filamentous cyanobacterium that can grow to sizes of 0.5 millimetres in length. It is an obligate photoautotroph and has a pH growth range from 8.3 to 11.0.The large-scale production of Spirulina biomass depends on many factors, the most important of which are nutrient availability, temperature and light. These factors can influence the growth of Spirulina and the composition of the biomass produced by changes in metabolism. Brine effluent from cooling towers of electricity generating plants may provide an ideal growth medium for Spirulina based on its growth requirements, i.e. high alkalinity and salinity. The aim of this research was to optimise brine effluent from cooling towers by supplementing it with salts, in order to use this optimised effluent in a small open laboratory raceway pond in an attempt to increase the biomass production of Spirulina.
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Functional and structural diversity of the microbial communities associated with the use of Fischer–Tropsch GTL Primary Column Bottoms as process cooling water / van Niekerk B.F.Van Niekerk, Bertina Freda January 2011 (has links)
Despite emerging water shortages, most water is only used once, and often with low efficiency. However, with appropriate treatment, water can be re–used to reduce the demand on freshwater sources. The Department of Water Affairs, South Africa, promotes industries to reduce discharges into water resources in order to sustain an overall good water quality of all water systems. All of this ultimately leads to industries striving towards zero effluent discharge. Primary Column Bottoms (PCBs) is a wastewater stream derived from the Fischer–Tropsch Gas to Liquid process and consists mainly of organic acids, but no nitrogen or phosphorous, which by implication excludes possible biodegradation. In the operation of cooling towers in industrial processes, cooling water quality has a direct impact on the cooling performance of the system, where nutrient levels may affect fouling, scaling and corrosion observed in the cooling towers. Fouling, scaling and corrosion affect the operating efficiency of cooling water systems and may necessitate the addition of chemical agents to control these phenomena. This has a financial and labour time impact on the operation of these systems.
In this study a mini cooling tower test rig was operated with a synthetic PCB effluent as cooling water and various cycles of concentration, pH and linear flow velocities (LFVs). A constant delta temperature of 10 °C was maintained. Cycles of concentration (COC) evaluated included 2, 4 and 6 cycles of concentration and linear flow velocities evaluated was 0.6 m/s, 0.9 m/s and 1.2 m/s. Fouling, scaling and corrosion rates were determined using corrosion coupons and heat exchanger tubes for mild steel and stainless steel. Besides the evaluation of the various operational parameters for fouling, scaling and corrosion, the possibility for chemical oxygen demand (COD) removal by operating the cooling tower as a bioreactor was also evaluated. To this end nutrient correction was applied to the reactor to allow for a CNP ratio of 100:10:1.
With regard to fouling, scaling and corrosion, mild steel was more affected by fouling, scaling and corrosion compared to stainless steel where almost no fouling, scaling and corrosion was observed. Overall increased linear flow velocities resulted in higher fouling and scaling rates, whereas lower linear flow velocities resulted in decreased corrosion rates. In terms of cycles of concentration, increased COC resulted in higher fouling, scaling and corrosion rates. Despite the high nutrient removal levels, the accompanying fouling, scaling and corrosion was still below the particular industry’s guidelines.
Besides physical–chemical evaluation of the towers under the various operational conditions, culture–dependent and culture–independent methods were also employed. Concerning culture–dependent approaches the study demonstrated that aerobic and anaerobic organisms are present in both the planktonic and sessile phase of the cooling tower reactors. Heterotrophic aerobes were found to be the most abundant under all the operating conditions. Sulphate reducing bacteria were more abundant in the sessile phase of the cooling towers, and the presence of high sulphate levels in the experiments could be indicative of the sulphate reducing bacteria actively participating in the microbial community. Lower than expected corrosion levels, however, suggest that a combination of the organisms in the biofilm rather than sulphate reducing bacteria alone, contributed to the corrosion rates observed. Culture–independent methods, specifically phospholipid fatty acid analysis supported the results from the culture–dependent methods. Furthermore results demonstrated that linear flow velocity had a greater effect on the community structure than cycles of concentration. Finally molecular methods, specifically denaturing gradient gel electrophoresis, found that increasing cycles of concentration resulted in increased microbial community diversity, while increasing linear flow velocity resulted in decreased microbial community diversity.
Regarding COD removal, nutrient correction of the synthetic PCB effluent achieved 89.35 % COD removal at 2 COC and 1.2 m/s LFV, while 80.85 % COD removal was achieved at 4 COC at 1.2 m/s LFV. From these results it was recommended that the operation of the cooling tower should be at 4 COC and 1.2 m/s, which despite slightly lower % COD removal, were characterised by fouling, scaling and corrosion rates well within guidelines. / Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2012.
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Functional and structural diversity of the microbial communities associated with the use of Fischer–Tropsch GTL Primary Column Bottoms as process cooling water / van Niekerk B.F.Van Niekerk, Bertina Freda January 2011 (has links)
Despite emerging water shortages, most water is only used once, and often with low efficiency. However, with appropriate treatment, water can be re–used to reduce the demand on freshwater sources. The Department of Water Affairs, South Africa, promotes industries to reduce discharges into water resources in order to sustain an overall good water quality of all water systems. All of this ultimately leads to industries striving towards zero effluent discharge. Primary Column Bottoms (PCBs) is a wastewater stream derived from the Fischer–Tropsch Gas to Liquid process and consists mainly of organic acids, but no nitrogen or phosphorous, which by implication excludes possible biodegradation. In the operation of cooling towers in industrial processes, cooling water quality has a direct impact on the cooling performance of the system, where nutrient levels may affect fouling, scaling and corrosion observed in the cooling towers. Fouling, scaling and corrosion affect the operating efficiency of cooling water systems and may necessitate the addition of chemical agents to control these phenomena. This has a financial and labour time impact on the operation of these systems.
In this study a mini cooling tower test rig was operated with a synthetic PCB effluent as cooling water and various cycles of concentration, pH and linear flow velocities (LFVs). A constant delta temperature of 10 °C was maintained. Cycles of concentration (COC) evaluated included 2, 4 and 6 cycles of concentration and linear flow velocities evaluated was 0.6 m/s, 0.9 m/s and 1.2 m/s. Fouling, scaling and corrosion rates were determined using corrosion coupons and heat exchanger tubes for mild steel and stainless steel. Besides the evaluation of the various operational parameters for fouling, scaling and corrosion, the possibility for chemical oxygen demand (COD) removal by operating the cooling tower as a bioreactor was also evaluated. To this end nutrient correction was applied to the reactor to allow for a CNP ratio of 100:10:1.
With regard to fouling, scaling and corrosion, mild steel was more affected by fouling, scaling and corrosion compared to stainless steel where almost no fouling, scaling and corrosion was observed. Overall increased linear flow velocities resulted in higher fouling and scaling rates, whereas lower linear flow velocities resulted in decreased corrosion rates. In terms of cycles of concentration, increased COC resulted in higher fouling, scaling and corrosion rates. Despite the high nutrient removal levels, the accompanying fouling, scaling and corrosion was still below the particular industry’s guidelines.
Besides physical–chemical evaluation of the towers under the various operational conditions, culture–dependent and culture–independent methods were also employed. Concerning culture–dependent approaches the study demonstrated that aerobic and anaerobic organisms are present in both the planktonic and sessile phase of the cooling tower reactors. Heterotrophic aerobes were found to be the most abundant under all the operating conditions. Sulphate reducing bacteria were more abundant in the sessile phase of the cooling towers, and the presence of high sulphate levels in the experiments could be indicative of the sulphate reducing bacteria actively participating in the microbial community. Lower than expected corrosion levels, however, suggest that a combination of the organisms in the biofilm rather than sulphate reducing bacteria alone, contributed to the corrosion rates observed. Culture–independent methods, specifically phospholipid fatty acid analysis supported the results from the culture–dependent methods. Furthermore results demonstrated that linear flow velocity had a greater effect on the community structure than cycles of concentration. Finally molecular methods, specifically denaturing gradient gel electrophoresis, found that increasing cycles of concentration resulted in increased microbial community diversity, while increasing linear flow velocity resulted in decreased microbial community diversity.
Regarding COD removal, nutrient correction of the synthetic PCB effluent achieved 89.35 % COD removal at 2 COC and 1.2 m/s LFV, while 80.85 % COD removal was achieved at 4 COC at 1.2 m/s LFV. From these results it was recommended that the operation of the cooling tower should be at 4 COC and 1.2 m/s, which despite slightly lower % COD removal, were characterised by fouling, scaling and corrosion rates well within guidelines. / Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2012.
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Development of a unified mass and heat integration framework for sustainable design an automated approach /Moodley, Anand. January 2007 (has links)
Thesis (M.Eng. (Chemical Engineering)) -- Universiteit van Pretoria, 2007. / Includes bibliographical references.
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