Thesis (M.S.)--University of Nevada, Reno, 2004. / "December 2004." Includes bibliographical references (leaves 43-46). Online version available on the World Wide Web.

Thesis (M. Phil.)--University of Hong Kong, 1987.

Thesis (MEng) -- Stellenbosch University, 1991. / ENGLISH ABSTRACT: In the present study various mathematical models have been developed for the analysis of spray cooled finnned-tube heat exchangers. These models range from simplified models based on the work by Kreid et al. [78KR1], Nakayama et al. [88NA1] and Erens et al. [90ER1] to a more comprehensive model based on the work by Poppe [84P01]. Computer programs were written to evaluate the performance prediction of these models on spray cooled heat exchangers in the vertical air flow mode. Experimental tests were conducted on a four-row finned-tube heat exchanger in a vertical air /water mist flow to verify the mathematical models and it was found that the performance of this heat exchanger could be predicted within 20 per cent using the accurate model. Significant performance enhancement (up to 3.5 times the dry performance) was found by spraying relatively small amounts of water onto the heat exchanger. The spray water massflow rate was found to have a significant effect on the two phase pressure drop across the heat exchanger. The present study indicated certain important factors which have to be taken into consideration when designing spray cooled heat exchanger units. These include the geometry of the finned-tubes, the temperature difference between the process water and the optimum air and the air /spray water ratio. / AFRIKAANSE OPSOMMING: In die tesis is 'n aantal wiskundige modelle ontwikkel wat gebruik kan word vir die analise van sproei verkoelde vinbuis warmte uitruilers. Die wiskundige modelle wissel van eenvoudige modelle wat gebaseer is op die werk van Kreid et al. [78KR1 ], Nakayama et al. [88NA1] en Erens et al. [90ER1] tot 'n omvattende model wat gebaseer is op die werk van Poppe [84 PO 1]. Rekenaar programme is geskryf om die die modelle se voorspellingsvermoe van die kapasiteit van sproei verkoelde warmte uitruilers te evalueer. 'n Eksperimentele ondersoek is gedoen op 'n warmte uitruiler met vier vinbuis rye in 'n toetsseksie met vertikale lugvloei. Die toets resultate is gebruik vir die evaluasie van die wiskundige modelle en het getoon dat die akkurate model se voorspellings binne 20 per sent van die gemete kapasitiet van die uitruiler val. Die eksperirnentele werk het verder aangetoon dat deur klein hoeveelhede water op die uitruiler te sproei, 'n toename in kapasiteit tot 3.5 keer die droe werkverrigting moontlik is. Die twee-fase drukval oor die uitruiler is sterk bei:nvloed deur die sproei water massavloei. Die analitiese navorsmg wat gedoen is met behulp van die rekenaar programme het aangedui dat daar 'n paar belangrike faktore is wat in ag geneem moet word met die ontwerp van sproei verkoelde warmte uitruilers. Die faktore sluit die vinbuis geometrie, die temperatuur verskil tussen die proses water en lug en optimum lug/sproeiwater massavloei verhouding in.

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.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: High temperature heat sources are becoming an ever-increasing imperative in the process industry for the production of plastics, ammonia and fertilisers, hydrogen, coal-toliquid fuel and process heat. Currently, high temperature reactor (HTR) technology is capable of producing helium temperatures in excess of 950°C; however, at these temperatures, tritium, which is a radioactive contaminant found in the helium coolant stream, is able to diffuse though the steel retaining wall of the helium-to-steam heat exchanger. To circumvent this radioactivity problem, regulations require an intermediate heat exchange loop between the helium and the process heat streams. In this paper, the use of a uniquely designed sodium-charged heat pipe heat exchanger is considered, and has the distinct advantage of having almost zero exergy loss as it eliminates the intermediate heat exchange circuit. In order to investigate this novel heat pipe heat exchanger concept, a special intermediate-temperature (± 240°C) experimental heat pipe heat exchanger (HPHE) was designed. This experimental HPHE uses Dowtherm A as working fluid and has two glass windows to enable visual observation of the boiling and condensation two-phase flow processes. A high temperature air-burner supply simulates the high temperature stream, and the cold stream is provided by water from a constant-heat supply tank. This experimental apparatus can be used to evaluate the validity of steady-state and start-up transient theoretical models that have been developed. This paper will highlight the special design aspects of this HPHE, the theoretical model and the solution algorithm described. Experimental results will be compared with the theoretically calculated results. The theoretical model will then be used to predict the performance of a high temperature (sodium working fluid at 850°C) HPHE will be undertaken and conclusions and recommendation made. / AFRIKAANSE OPSOMMING: Hoë temperatuur hitte bronne is besig om ‘n toenemende noodsaaklikheid te raak in die proses industrie vir die vervaardiging van plastieke, ammoniak, kunsmis, waterstof, steenkool-tot-vloeibare brandstof en proses hitte. Huidige hoë temperatuur reaktor tegnologie is in staat om helium te verhit tot temperature hoër as 950°C, maar by sulke hoë temperature is die vorming van tritium, wat ‘n radioaktiewe produk is, in die helium verkoeling stroom wat deur die reaktor vloei, ‘n probleem. Die tritium is in staat om deur die staal wand van ‘n enkel fase warmte uitruiler te diffundeer. Om hierdie radioaktiewe probleem te uitoorlê, stel huidige regulasies voor dat ‘n oorgangs hitte uitruil lus gebruik raak tussen die helium en proses strome van die reaktor stelsel. In hierdie tesis word ‘n unieke natrium gevulde hitte pyp warmte uitruiler nagevors, hierdie ontwerp het die voordeel dat dit geen “exergy” verlies het omdat dit nie ‘n oorgangs hitte uitruil lus benodig nie. Hierdie unieke konsep was nagevors deur ‘n spesiale oorgangs temperatuur (± 230°C) eksperimentiële hitte pyp warmte uitruiler te ontwerp. Hierdie eksperimentiële hitte pyp warmte uitruiler gebruik Dowtherm A as oordrags medium tussen die warm en koue strome en het twee glas venters waardeur die kook en kondensasie van die oorgangs medium dop gehou kan word. ‘n Hoë temperatuur verbrander simuleer die warm stroom deur die reaktor en die koue stroom word gesimuleer deur koue water. Die eksperimentiële opstelling sal gebruik word om die tyd afhangklike en tyd onafhangklike teoretiese wiskundige modele te valideer. Hierdie tesis sal die spesiale ontwerp aspekte van die hitte pyp warmte uitruiler, teoretiese modelle en oplos algoritme te bespreek. Eksperimentiele resultate sal met die teoretiese resultate vergelyk word en dan sal die teoretiese modelle gebruik word om ‘n natrium gevulde warmte uitruiler te simuleer. Gevolgtrekkings en aanbevelings sal in die lig van die resultate verskaf word.