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Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Bioconversion of hydrocarbons to value-added intermediates and products has significant industrial potential using both prokaryotic and eukaryotic organisms. In particular, alkanes can be converted to an expansive range of commercially important products using aerobic bioprocesses under mild process conditions. Coupled with the relative abundance of alkanes derived from gas to liquid (GTL) technologies, such as those employed by SASOL, South Africa, the commercial potential for bioconverison of alkanes is large. However, unlike carbohydrate substrates, alkane feedstocks are devoid of oxygen in their molecular structure. This means that the entire oxygen demand needs to be met by oxygen transfer. Furthermore, a decline in oxygen transfer in aqueous-hydrocarbon dispersions with increasing alkane concentration has been observed to result from depression of the overall volumetric oxygen transfer coefficient (KLa). Therefore, understanding KLa and the fundamental parameters underpinning its behaviour is critical to ensuring the bioprocess is kinetically, rather than transport, limited in terms of both operation and scale-up. Previous studies have examined KLa in aerated-alkane-aqueous systems. In light of the importance of oxygen transfer in bioprocesses, this study expands on the KLa understanding in 3-phase studies by including a fourth solid phase, thus more closely representing a hydrocarbonbased bioprocess. The project aimed to determine the impact of agitation, alkane concentration and solid loading on the Sauter mean bubble diameter (DSM), gas hold-up and specific interfacial area (a) and correlate these parameters to KLa. This ultimately determined which parameter was dominant over a range of process conditions. Furthermore, concurrent measurement of the KLa and interfacial area meant the behaviour of the liquid side oxygen transfer coefficient (KL) could be defined, providing further insight into how changes in the process conditions impact on KLa. Experiments were conducted in a 5 litre stirred tank bioreactor containing n-C14-20 straight chain alkane, sparged with air at 0.8 vvm. In line with process conditions typical of a hydrocarbonbased bioprocess, KLa and a were measured for agitation rates from 450 to 1000 RPM, alkane concentrations from 2 to 20% v/v and yeast solids from 1 to 10 g/l. KLa was measured using the gassing out procedure using a dissolved oxygen (DO) probe which measured the response of the system to a step change in the sparge gas oxygen pressure. The probe response lag ( P), equal to the time taken for the probe to reach 63.2% of the saturation DO concentration, was determined for every set of process conditions. The inverse of P, KP was taken into account when calculating KLa from the DO probe response. The area was calculated from DSM and gas hold-up. DSM was quantified using high speed photography and image analysis was performed in Matlab® using bespoke routines. Elimination of optical distortion and the development of an adequate light source was key to acquiring clear images. Both KLa and interfacial area were found to be affected by changes in agitation, alkane concentration and yeast loading. An increase in agitation increased the KLa over the entire range of alkane concentration and yeast loading. Similarly, an increase in agitation resulted in an increase in interfacial area, underpinned by a decrease in the DSM. It is therefore likely that the interfacial area plays a dominant role in defining KLa when considering an increase in agitation. Increases in alkane concentration resulted in a peak in KLa between 2.5 and 5% alkane concentration while further increases in alkane concentration depressed KLa. This peak was not observed in interfacial area, where an increase in alkane concentration resulted only in a decrease in interfacial area, thus indicating a positive influence of KL on KLa at low alkane concentrations. Further increases in alkane concentration beyond those creating the peak KLa resulted in KLa depression, suggesting that the increasing viscosity imparted by the alkane decreases both KL and interfacial area. Increased yeast loading had opposing effects at low and high agitation rates. At low agitation rates, increased loadings were observed to increase KLa, while increased loadings at high agitation rates caused a decrease in KLa. This behaviour was also evident in interfacial area, suggesting that in this regime KLa was defined by interfacial area behaviour. Increased yeast loading was observed to depress the KLa for all alkane concentrations when examined at a constant midpoint agitation rate. This trend was not evident in interfacial area, which increased with increasing yeast loading at the same agitation rate. The positive influence of yeast on interfacial area was likely caused by adhesion of the yeast particles to the bubble surface, lowering the DSM by preventing coalescence. The disagreement between the KLa and interfacial area results suggested that yeast loading impacted negatively on KL, which had an over-riding negative impact on KLa. The use of reliable methods for the determination of both interfacial area and KLa were demonstrated for application in model hydrocarbon-based bioprocesses. The combined results offer a unique insight into how changes in the process conditions impact independently on KL and interfacial area, which when combined ultimately defined the KLa behaviour. Quantification of the relative magnitude of the impact each parameter had on KLa contributed toward a fundamental understanding of oxygen transfer in model hydrocarbon-based bioprocesses. / AFRIKAANSE OPSOMMING: Biologiese omsetting van koolwaterstowwe na produkte met finansiële waarde het beduidende industriële potensiaal met behulp van beide prokariotiese en eukariotiese organismes. In die besonder, kan alkane omgeskakel word na ’n uitgebreide reeks van kommersieel belangrike produkte met behulp van aerobiese bioprosesse onder ligte proses voorwaardes. Tesame met die relatiewe oorvloed van alkane afgelei van GTL tegnologie, soos dié van Sasol, Suid-Afrika, die kommersiële potensiaal vir bioconverison van alkane is groot. Maar, in teenstelling koolhidrate substrate, alkaan voerstowwe is beroof van suurstof in hul molekulêre struktuur. Dit beteken dat die hele suurstof vereiste moet nagekom word deur suurstof oordrag. Verder het ’n afname in suurstof oordrag in waterige-koolwaterstof dispersies met toenemende alkaan konsentrasie waargeneem te lei van depressie van die algehele volumetriese suurstofoordragkoëffisiënt (KLa). Daarom verstaan KLa en die fundamentele parameters onderliggend sy gedrag is van kritieke belang om te verseker dat die bioprocess is kineties, eerder as vervoer, beperk in terme van beide werking en skaal-up van bioprosesse. Vorige studies het KLa in deurlug-alkaan-waterige stelsels ondersoek. In die lig van die belangrikheid van suurstof oordrag in bioprosesse hierdie studie brei uit op die KLa begrip in driefase studies deur die insluiting van ’n vierde soliede fase, dus meer nou wat ’n koolwaterstofgebaseerde bioprocess. Die doel van die projek is om die impak van vermengingstempo, alkaan konsentrasie en soliede inhout op die Sauter gemiddelde borrel deursnee (DSM), gas-vasvanging en spesifieke gas-vloistof oppervlakarea (a) te kwantifiseer en korreleer met KLa gedrag. Dit sou defineer die dominante parameter oor ’n verskeidenheid van proses voorwaardes. Verder, gelyktydige meting van die KLa en oppervlakarea kan die gedrag van die vloeistof-kant suurstofoordragkoëffisiënt (KL) gedefinieer. Dit sal verskaf verdere insig in hoe die veranderinge in die proses voorwaardes impak op KLa. Eksperimente was uitgevoer in ’n 5 liter belugte geroerde tenk bioreaktor bevat n - C14-20 reguitketting alkane, met lug met lug deurgeborrel by 0.8 VVM. In lyn met die proses voorwaardes tipies van ’n koolwaterstof-gebaseerde bioprocess, KLa en a was gemeet vir vermengignstempos van 450-1000 RPM, alkaan konsentrasies van 2-20 % v/v en gis vastestowwe van 1 tot 10 g / l. KLa is gemeet deur die vergassinguit prosedure met behulp van ’n suurstofmeter wat die reaksie van die stelsel na ’n stap verandering in die voer gas suurstof druk gemeet het. Die suurstofmeter reaksie vertraging ( P), gelyk aan die tyd wat dit neem vir die suurstofmeter 63.2 % van die versadiging DO konsentrasie te bereik, is bepaal vir elke procesopset. Die inverse van P, KP is in ag geneem by die berekening van KLa uit die suurstofmeter reaksie. Die gas-vloistof oppervlak is bereken vanaf DSM en gas hold-up. DSM is gekwantifiseer met behulp van hoë spoed fotografie en beeld analise is uitgevoer in Matlab ® roetines. Uitskakeling van optiese vervorming en die ontwikkeling van ’n voldoende ligbron was die sleutel tot die verkryging van helder beelde. Beide KLa en grens oppervlakarea gevind geraak word deur veranderinge in vermengignstempo, alkaan konsentrasie en gis laai. ’N toename in geroer het die KLa verbeter oor die hele reeks van alkaan konsentrasie en gis laai. Net so, ’n toename in geroer het gelei tot ’n toename in grens oppervlak, ondersteun deur ’n afname in die DSM. Dit is dus waarskynlik dat die grens oppervlak speel ’n dominante rol in die definisie van KLa by die oorweging van ’n toename in roering. Stygings in alkaan konsentrasie gelei tot ’n hoogtepunt in KLa tussen 2.5 en 5 % alkaan konsentrasie terwyl verdere verhogings in alkaan konsentrasie druk die KLa af. Die piek was nie in oppervlakarea duidelik, waar ’n toename in alkaan konsentrasie gelei net tot ’n afname in oppervlakarea, dus dui op ’n positiewe invloed van KL op KLa teen lae alkaan konsentrasies waargeneem. Verdere stygings in alkaan konsentrasie verder as die skep van die piek KLa gelei tot KLa depressie, wat daarop dui dat die toenemende viskositeit meegedeel deur die alkaan verminder beide KL en grens oppervlak. Verhoogde gis laai het opponerende effekte teen ’n lae en hoë vermengingstempo. By lae vermengingstempo, ’n verhoging in gis laai waargeneem KLa te verhoog, terwyl ’n verhoging in gis laai op ’n hoë vermengingstempo veroorsaak ’n afname in KLa . Hierdie gedrag was ook duidelik in grens oppervlak, wat daarop dui dat daar in hierdie regime KLa gedefinieer deur grens oppervlak gedrag. Verhoogde gis laai waargeneem die KLa te onderdruk vir alle alkaan konsentrasies wanneer ondersoek teen ’n konstante middelpunt vermengingstempo. Hierdie tendens was nie duidelik in tussenvlak gebied, wat verhoog met toenemende gis laai op dieselfde geroer koers. Die positiewe invloed van gis op grens oppervlak is waarskynlik veroorsaak deur adhesie van die gis deeltjies aan die borrel oppervlak, die verlaging van die DSM deur die voorkoming van die saamsmelting van gasborrels. Die meningsverskil tussen die KLa en grens oppervlakarea resultate voorgestel dat gis laai negatiewe uitwerking op KL, met ’n dominante negatiewe impak op KLa. Die gebruik van ’n betroubare metodes vir die bepaling van beide oppervlakarea en KLa gedemonstreer vir toepassing in model koolwaterstof-gebaseerde bioprosesse. Die gekombineerde resultate bied ’n unieke insig in hoe die veranderinge in die proses voorwaardes impak onafhanklik op KL en oppervlakarea, wat wanneer gekombineer gedefinieer die KLa gedrag. Kwantifisering van die relatiewe grootte van die impak elke parameter het op KLa bygedra tot ’n fundamentele begrip van suurstof oordrag in model koolwaterstof-gebaseerde bioprosesse.

Gas quench technology has been rapidly developed recently with the intent to replace water and oil quench for medium and high hardenability steel. One of the significant advantages is to reduce the distortion and stress, compared to water and oil quench. However, not like liquid quench, no gas quench steel hardenability test standard exists. The fundamental difference between liquid quench and gas quench is heat transfer coefficient. The workpiece with the same hardness after liquid and gas quench process may have different microstructure due to different cooling curves. The concept of equivalent gas quench heat transfer coefficient (HTC) is proposed to have the same cooling curve, microstructure and hardness when compared with liquid quench. Several influencing factors on steel hardenability have been discussed, such as austenizing temperature, heating rate, holding time, composition variation and grain size difference. The phase quantification by X-ray Diffraction and Rietveld Refinement method is developed to measure phase percentage for steel microstructure, including martensite, ferrite and carbides. The limitations and improvements of modified Jominy gas quench test are discussed. The fundamental limitation of Jominy gas quench test is that one gas quench condition cannot be used for both low hardenability steel and high hardenability steel at the same time. The same steel grade would have different hardenability curves under different gas quench conditions, which made it difficult to compare the hardenability among different steels. The critical HTC test based on Grossmann test is proposed to overcome the limitations. In the test, different gas quench HTC conditions are applied to the sample with the same geometry. After sectioning each bar at mid-length, the bar that has 50% martensite at its center is selected, and the applied gas quench HTC of this bar is designated as the critical HTC. This test has many advantages to take the place of modified Jominy gas quench test. Since one of the advantages of gas quench is greater process flexibility to vary cooling rates, gas marquenching technology is proposed to obtain martensite with less sever cooling rate and reduce the distortion and stress.

SuperCritical-Water-cooled Reactors (SCWRs) are being developed as one of the Generation-IV nuclear-reactor concepts. Main objectives of the development are to increase thermal efficiency of a Nuclear Power Plant (NPP) and to decrease capital and operational costs. The first objective can be achieved by introducing nuclear steam reheat inside a reactor and utilizing regenerative feedwater heaters. The second objective can be achieved by designing a steam cycle that closely matches that of the mature supercritical fossil-fuelled power plants. The feasibility of these objectives is discussed. As a part of this discussion, heat-transfer calculations have been performed and analyzed for SuperCritical-Water (SCW) and SuperHeated-Steam (SHS) channels of the proposed reactor concept. In the calculations a uniform and three non-uniform Axial Heat Flux Profiles (AHFPs) were considered for six different fuels (UO2, ThO2, MOX, UC2, UC, and UN) and at average and maximum channel power. Bulk-fluid, sheath, and fuel centerline temperatures as well as the Heat Transfer Coefficient (HTC) profiles were obtained along the fuel-channel length. The HTC values are within a range of 4.7 – 20 kW/m2⋅K and 9.7 – 10 kW/m2⋅K for the SCW and SHS channels respectively. The main conclusion is that while all the mentioned fuels may be used for the SHS channel, only UC2, UC, or UN are suitable for a SCW channel, because their fuel centerline temperatures are at least 1000°C below melting point, while that of UO2, ThO2, and MOX may reach melting point. / UOIT

A novel approach to geologic CO₂ sequestration is the surface dissolution method. This method involves lifting native brine from an aquifer, dissolution of CO₂ into the brine using pressurized mixing and injection of the CO₂ saturated brine back into the aquifer. This approach has several advantages over the conventional approach, including minimization of the risk of buoyancy driven leakage and dramatic reduction in the extent of pressure elevation in the storage structure. The mass transfer coefficient for the CO₂/brine two-phase system and associated transport calculations allow efficient design of the surface equipment required to dissolve CO₂ under pressure. This data was not previously available in the literature. Original experimental data on the rate of dissolution of CO₂ into Na-Ca-Cl brines across a range of temperatures and wet CO₂ densities are presented. From this data, the intrinsic mass transfer coefficient between CO₂-rich and aqueous phases has been calculated. The statistically significant variation in the mass transfer coefficient was evaluated and compared with the variation caused by the experimental method. An empirical correlation was developed that demonstrates that the mass transfer coefficient is a function of the NaCl salinity, temperature and wet CO₂ density. For the conditions tested, the value of the coefficient is in the range of 0.015 to 0.056 cm/s. Greater temperature and smaller NaCl salinity increases the mass transfer coefficient. There is an interaction effect between temperature and wet CO₂ density, which increases or decreases the mass transfer coefficient depending on the value of each. CaCl₂ salinity does not have a statistically significant effect on the mass transfer coefficient. The transport calculations demonstrate that wellhead co-injection of CO₂ and brine is feasible, providing the same technical outcome at lower cost. For example, assuming a 2000 ft deep well and typical aquifer injection conditions, complete dissolution of the bulk COv phase can be achieved at 670 ft for bubbles of 0.16 cm initial radius. Using a horizontal pipe or mixing tank was also shown to be feasible. Gas entrainment was shown to provide a marked reduction in size of mixing apparatus required. / text

Accurate values of thermophysical transport properties of particle beds are necessary to accurately model heat and mass transfer processes in particle beds that under-go preferred processes and changes. The objective of this study is to use a proven analytical/numerical methodology to estimate the unknown transport properties within test cells filled with silicagel particles and compare the results with the previously published data. An experimental test cell was designed and constructed to carry out transient heat transfer tests for both step change conduction and convection heat transfer within a packed bed of silicagel particles. For a known step change in the test cell temperature boundary condition, the temporal temperature distribution within the bed during heat conduction depends only on the effective heat conduction coefficient and the thermal capacity of the particle bed. The central problem is to, using only the boundary conditions and a few time-varying temperature sensors in the test cell of particles, determine the effective thermal conductivity of the test bed and specify the resulting measurement uncertainty. A similar problem occurs when the heat convection coefficient is sought after a step change in the airflow inlet temperature for the test cell. These types of problems are known as inverse heat transfer problems (IHTP). In this thesis, IHTP method was used to estimate the convective heat transfer coefficient. Good agreement was seen in experimental and numerical temperature profiles, which were modeled by using the estimated convective heat transfer coefficient. The same methodology was used to estimate the effective thermal conductivity of the particle bed. Comparison between the experimental temperature distribution and numerical temperature distribution, which was modeled by using the estimated effective conductivity, illustrated good agreement. On the other side, applying the effective thermal conductivity, obtained from a direct steady state measurement, in the numerical simulation could not present agreement between the numerical and experimental results. It was concluded that the IHTP methodology was a successful approach to find the thermophysical properties of the particle beds, which were hard to measure directly.

An average heat transfer coefficient, h_bar, is often used to solve heat transfer problems. It should be understood that this is an approximation and may provide inaccurate results, especially when the temperature field is of interest. The proper method to solve heat transfer problems is with a conjugate approach. However, there seems to be a lack of clear explanations of conjugate heat transfer in literature. The objective of this work is to provide a clear explanation of conjugate heat transfer and to determine the discrepancy in the temperature field when the interface boundary condition is approximated using h_bar compared to a local, or variable, heat transfer coefficient, h(x). Simple one-dimensional problems are presented and solved analytically using both h(x) and h_bar. Due to the one-dimensional assumption, h(x) appears in the governing equation for which the common methods to solve the differential equations with an average coefficient are no longer valid. Two methods, the integral equation and generalized Bessel methods are presented to handle the variable coefficient. The generalized Bessel method has previously only been used with homogeneous governing equations. This work extends the use of the generalized Bessel method to non-homogeneous problems by developing a relation for the Wronskian of the general solution to the generalized Bessel equation. The solution methods are applied to three problems: an external flow past a flat plate, a conjugate interface between two solids and a conjugate interface between a fluid and a solid. The main parameter that is varied is a combination of the Biot number and a geometric aspect ratio, A_1^2 = Bi*L^2/d_1^2. The Biot number is assumed small since the problems are one-dimensional and thus variation in A_1^2 is mostly due to a change in the aspect ratio. A large A_1^2 represents a long and thin solid whereas a small A_1^2 represents a short and thick solid. It is found that a larger A_1^2 leads to less problem conjugation. This means that use of h_bar has a lesser effect on the temperature field for a long and thin solid. Also, use of ¯ over h(x) tends to generally under predict the solid temperature. In addition is was found that A_2^2, the A^2 value for the second subdomain, tends to have more effect on the shape of the temperature profile of solid 1 and A_1^2 has a greater effect on the magnitude of the difference in temperature profiles between the use of h(x) and h_bar. In general increasing the A^2 values reduced conjugation.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The expansion of the global fuels industry has caused an increase in the quantity of hydrocarbons produced as a by-product of refinery gas-to-liquid processes. Conversion of hydrocarbons to higher value products is possible using bioprocesses, which are sustainable and environmentally benign. Due to the deficiency of oxygen in the alkane molecule, the supply of sufficient oxygen through aeration is a major obstacle for the optimization of hydrocarbon bioprocesses. While the oxygen solubility is increased in the presence of hydrocarbons, under certain process conditions, the enhanced solubility is outweighed by an increase in viscosity, causing a depression in overall volumetric oxygen transfer coefficient (KLa). The rate at which oxygen is transferred is defined in terms of a concentration driving force (oxygen solubility) and the overall volumetric oxygen transfer coefficient (KLa). The KLa term comprises an oxygen transfer coefficient (KL) and the gas-liquid interfacial area (a), which are dependent on the uid properties and system hydrodynamics. This behaviour is not well understood for hydrocarbon bioprocesses and in a bubble column reactor (BCR). To provide an understanding of oxygen transfer behaviour, a model hydrocarbon bioprocess was developed using a BCR with a porous sparger. To evaluate the interfacial area, the Sauter mean bubble diameter (D32) was measured using an image analysis algorithm and gas holdup (ϵG) was measured by the change in liquid height in the column. Together the D32 and ϵG were used in the calculation of interfacial area in the column. The KLa was evaluated with incorporation of the probe response lag, allowing more accurate representation of the KLa behaviour. The probe response lag was measured at all experimental conditions to ensure accuracy and reliability of data. The model hydrocarbon bioprocess employed C14-20 alkane-aqueous dispersions (2.5 - 20 vol% hydrocarbon) with suspended solids (0.5 - 6 g/l) at discrete super ficial gas velocity (uG) (1 - 3 cm/s). For systems with inert solids (corn our, dp = 13.36 m), the interfacial area and KLa were measured and the behaviour of KLa was described by separation of the in uences of interfacial area and oxygen transfer coefficient (KL). To further the understanding of oxygen transfer behaviour, non-viable yeast cells (dp = 5.059 m) were used as the dispersed solid phase and interfacial area behaviour was determined. This interfacial area behaviour was compared with the behaviour of systems with inert solids to understand the differences with change in solids type. In systems using inert solids, a linear relationship was found between G and uG. An empirical correlation fo rthe prediction of this behaviour showed an accuracy of 83.34% across the experimental range. The interfacial area showed a similar relationship with uG and the empirical correlation provided an accuracy of 78.8% for prediction across the experimental range. In inert solids dispersions, the KLa increased with uG as the result of an increase in interfacial area as well as increases in KL. An increase in solids loading indicated an initial increase in KLa, due to the in uence of liquid-film penetration on KL, followed by a decrease in KL at solids loading greater than 2.5 g/l, due to diffusion blocking effects. In systems with yeast dispersions, the presence of surfactant molecules in the media inhibited coalescence up to a yeast loading of about 3.5 g/l, and resulted in a decrease in D32. Above this yeast loading, the fine yeast particles increased the apparent viscosity of the dispersion sufficiently to overcome the in uence of surfactant and increase the D32. The behaviour of G in yeast dispersions was similar to that found with inert solids and demonstrated a linear increase with uG. However, in yeast dispersions, the interaction between alkane concentration and yeast loading caused a slight increase in dispersion viscosity and therefore G. An empirical correlation to predict G behaviour with increased uG was developed with an accuracy of 72.55% for the experimental range considered. Comparison of yeast and inert solids dispersions indicated a 37.5% lower G in yeast dispersions compared to inert solids as a result of the apparent viscosity introduced by finer solid particles. This G and D32 data resulted in a linear increase in interfacial area with uG with no significant in uence of alkane concentration and yeast loading. This interfacial area was on average 6.7% lower than interfacial area found in inert solid dispersions as a likely consequence of the apparent viscosity with finer particles. This study provides a fundamental understanding of the parameters which underpin oxygen transfer in a model hydrocarbon bioprocess BCR under discrete hydrodynamic conditions. This fundamental understanding provides a basis for further investigation of hydrocarbon bioprocesses and the prediction of KLa behaviour in these systems. / AFRIKAANSE OPSOMMING: Die uitbreiding van die internasionale brandstofbedryf het 'n toename veroorsaak in die hoeveelheid koolwaterstowwe geproduseer as 'n deur-produk van raffinadery gas-tot-vloeistof prosesse. Omskakeling van koolwaterstowwe na hoër waarde produkte is moontlik met behulp van bioprosesse, wat volhoubaar en omgewingsvriendelik is. As gevolg van die tekort aan suurstof in die alkaan molekule, is die verskaffing van voldoende suurstof deur deurlugting 'n groot uitdaging vir die optimalisering van koolwaterstof bioprosesse. Terwyl die suurstof oplosbaarheid verhoog in die teenwoordigheid van koolwaterstowwe, onder sekere proses voorwaardes is die verhoogde oplosbaarheid oortref deur 'n toename in viskositeit, wat 'n depressive veroorsaak in die algehele volumetriese suurstofoordragkoëffisiënt (KLa). Die suurstof oordrag tempo word gedefinieer in terme van 'n konsentrasie dryfkrag (suurstof oplosbaarheid) en KLa. Die KLa term behels 'n suurstofoordragkoëffisiënt (KL) en die gas-vloeistof oppervlakarea (a), wat afhanklik is van die vloeistof eienskappe en stelsel hidrodinamika. Hierdie gedrag is nie goed verstaan vir koolwaterstof bioprosesse nie, asook in kolom reaktors (BCR). Om 'n begrip van suurstof oordrag gedrag te voorsien, is 'n model koolwaterstof bioproses ontwikkel met 'n BCR met 'n poreuse besproeier. Om die oppervlakarea te evalueer, is die gemiddelde Sauter deursnit (D32) gemeet deur 'n foto-analise algoritme en gas vasvanging ( G) is gemeet deur die verandering in vloeibare hoogte in die kolom. Saam is die D32 en G gebruik in die berekening van die oppervlakarea in die kolom. Die KLa is geëvalueer met insluiting van die meter se reaksie sloering, om n meer akkurate voorstelling van die KLa gedrag te bereken. Die meter reaksie sloering was gemeet op alle eksperimentele toestande om die akkuraatheid en betroubaarheid van data te verseker. Die model koolwaterstof bioproses gebruik n-C14-20 alkaan-water dispersies (2.5 - 20 vol% koolwaterstof) solide partikels (0.5 - 6 g/l) op diskrete oppervlakkige gas snelhede (1 - 3 cm/s). Vir stelsels met inerte solides (koring meel, dp = 13.36 m), is die oppervlakarea en KLa gemeet en die gedrag van KLa beskryf deur skeiding van die invloede van oppervlakarea en KL. Om die begrip van suurstof oordrag se gedrag te bevorder, is nie-lewensvatbare gisselle (dp = 5.059 m) gebruik as die verspreide solide fase en oppervlakarea is bepaal. Hierdie oppervlakarea gedrag is vergelyk met die van stelsels met inerte solides om die verskille met verandering in solide tipes te verstaan. In stelsels met inerte solides, is 'n line^ere verwantskap gevind tussen G en uG. 'n Empiriese korrelasie vir die voorspelling van hierdie gedrag is opgestel met 'n akkuraatheid van 83.34% in die eksperimentele reeks. Die oppervlakarea het 'n soortgelyke verhouding met uG en die empiriese korrelasie verskaf 'n akkuraatheid van 78,8% vir die voorspelling van oppervlakarea oor die eksperimentele reeks. In inerte solide dispersies, het die KLa toegeneem met uG as die gevolg van 'n toename in grens oppervlak asook stygings in KL. 'n Toename in solides belading het n aanvanklike styging in KLa aangedui, as gevolg van die invloed van die vloeistof-film penetrasie op KL, gevolg deur 'n afname in KL op vastestowwe ladings groter as 2.5 g/l, te danke aan diffusie blokkeer effekte. In stelsels met gis dispersies, het die teenwoordigheid van benattings molekules in die media samesmelting geïnhibeer tot 'n gis lading van ongeveer 3.5 g/l, en het gelei tot 'n afname in D32. Bo hierdie gis lading, het die fyn gis partikels die skynbare viskositeit van die verspreiding verhoog genoegsaam om die invloed van benattings molekules te oorkom en die D32 te verhoog. Die gedrag van G in gis dispersies was soortgelyk aan die van inerte solides en dui op 'n lineêre toename met uG. Maar in gis dispersies, het die interaksie tussen alkaan konsentrasie en gis lading 'n effense toename veroorsaak in die verstrooiing viskositeit en dus in G. 'n Empiriese korrelasie is ontwikkel om G gedrag te voorspel en het 'n akkuraatheid van 72,55% vir die eksperimentele verskeidenheid beskou. Vergelyking van gis en inerte patrikel dispersies wys 'n 37.5% laer G in gis dispersies in vergelyking met inerte vaste stowwe as 'n gevolg van die skynbare viskositeit bekendgestel deur fyner vastestowwe partikels. Hierdie G en D32 data het gelei tot 'n linere toename in grens oppervlak met uG met geen beduidende invloed van alkaan konsentrasie en gis lading nie. Die oppervlakarea was gemiddeld 6.7% laer as oppervlakarea gevind in inerte partikel dispersies as 'n waarskynlike gevolg van die skynbare viskositeit met fyner partikels. Hierdie studie bied 'n fundamentele begrip van die veranderlikes wat die suurstof oordrag definieer in 'n model koolwaterstof bioproses BCR onder diskrete hidrodinamiese voorwaardes. Hierdie fundamentele begrip bied n basis vir verdere ondersoek van koolwaterstof bioprosesse en en die voorspelling van KLa gedrag in hierdie stelsels.

Approved for public release; distribution is unlimited / Heat-transfer measurements were made for condensation of R-113 and steam on a smooth tube and on three finned tubes with rectangular shape fins. These tubes had a fin height and width of 1.0 mm and spacings of 0.25, 1.5, and 4.0 mm (tubes A, B, and C respectively) . Data were taken by increasing the vapor velocity from 0.4 to 1.9 m/s for R-113 and 4.8 to 31.3 m/s for steam. For both fluids, the improvement of the condensing heat-transfer coefficient with vapor velocity was smaller for the finned tubes than for the smooth tube. For R-113, the smooth tube experienced a 32 percent improvement with vapor velocity, where the finned tubes (tubes A, B and C respectively) experienced improvements of only 0, 5 and 10 percent. For steam, the smooth tube experienced a 62 percent improvement, whereas the finned tubes (tubes A, B, and C respectively) experienced improvements of only 31, 11, and 9 percent. These test results show that, although finned tubes can provide significant heat transfer enhancement over smooth tubes at low vapor velocities, the degree of enhancement becomes smaller as vapor velocity increases. / CBT-8603582 (NSF) / http://archive.org/details/effectofvaporvel00hopk / National Science Foundation / Lieutenant Commander, United States Navy

The primary purpose of this investigation was to experimentally determine the effect of operational parameters on the onset of flow instability (OFI) in narrow, uniformly heated, vertical, rectangular channels. The geometry investigated was a 9.0 cm long rectangular channel with a 1.0mm by 1.3cm cross section. This geometry closely matches the coolant channel geometry in an accelerator target. Nitrogen-saturated subcooled water was used as the coolant, with mass fluxes ranging from 250 to 1336 kg/m^2 s, and an inlet temperature of 26ºC for the OFI experiments. The exit pressures investigated ranged from 275kPa to 620kPa, while the heat flux ranged from 0.729 to 2.236 MW/m^2. The primary data collected from these experiments were used to develop two correlations for the heat flux and mass flux at OFI. Wall temperature data were also collected in order to develop a Nusselt number correlation for the single-phase regime. This correlation is valid for the Reynolds number range of 6x103 to 1.7x104. The data obtained in this investigation will aid designers of high-power-density systems establish design limits to prevent over heating and possible damage due to the onset of flow instability. The data obtained in this investigation will aid designers of high-power-density systems establish design limits to prevent over heating and possible damage due to the onset of flow instability.