Le problème du réchauffement climatique actuel conduit au renforcement des règlementations environnementales. Ainsi, le domaine du génie climatique est affecté par ces évolutions réglementaires, ce qui impose le passage à une nouvelle génération de réfrigérants à plus bas impact environnemental. Dans cette thèse, ce sujet est étudié dans le cas des groupes refroidisseurs d’eau utilisant le R-410A qui est visé par la réglementation. Mais, résoudre ce problème ne s’arrête pas au simple changement du réfrigérant par un autre à plus bas GWP ; il faut que la transition soit accompagnée par une amélioration ou un maintien de la puissance frigorifique et de la performance énergétique du système par crainte d’avoir un effet environnemental inverse parce que la consommation énergétique représente un plus grand effet sur l’impact environnemental que celui du GWP du réfrigérant.Une revue de la littérature et des tests expérimentaux réalisés en remplaçant le R-410A montrent que les réfrigérants présents sur le marché et proposés par les fabricants pour remplacer le R-410A ne permettent pas d’avoir les améliorations souhaitées. Parmi ces substituants le R-32 est le plus utilisé et semble être prometteur mais avec une réduction du COP et des températures de refoulement du compresseur très élevées. Ainsi, la solution de la compression refroidie par injection d’huile de lubrification au niveau du compresseur est étudiée et modélisée. Le modèle théorique montre qu’elle permet de refroidir la compression et de réduire la consommation du compresseur à condition d’avoir des gouttes d’huile très fines avec un débit et une température de l’huile injectée contrôlables.Pour appliquer cette solution, un système d’atomisation de l’huile est conçu et testé ; les résultats montrent qu’il estpossible de créer un spray de gouttes très fines pour des pressions d’injection de l’ordre de la différence entre la haute et labasse pression du groupe refroidisseur d’eau. La compression refroidie est testée en connectant le système d’atomisationde l’huile au groupe refroidisseur d’eau. Une réduction de la température de refoulement du compresseur et de lapuissance consommée par le compresseur est mesurée, mais elle est plus faible que la réduction prévue théoriquement. Enintégrant une augmentation du diamètre des gouttes durant la compression dans le modèle théorique, les résultats de la simulation sont proches des résultats expérimentaux. / Current global warming problem leads to more stringent environmental standards. Thus the HVAC field is affected by these standard changes, which requires the transition to a new generation of refrigerants with lower environmental impact. In this thesis, this aspect is studied in the case of water chillers using R-410A that is subject to substitution due to new standards. But solving this problem doesn’t stop at mere refrigerant change by another with lower GWP. It is necessary that improvement or maintain of cooling capacity and energy efficiency of the system accompanies this transition by fear of having a reverse effect because global energy consumption represents a greater effect on the environmental impact than refrigerant GWP.A review of literature and experimental tests carried out by replacing R-410A show that refrigerants used in the market and offered by manufacturers to replace R-410A don’t allow the desired improvements. Among these substituents, R-32 is the most used and seems promising, but it causes a decrease of COP and very high compressor discharge temperatures. Thus, the solution of cooled compression by injection of lubricating oil in the compressor is studied and modeled. The theoretical model shows that this solution helps cooling the compression and reduces compressor power consumption provided that injection is characterized by very fine drops of oil with controllable flowrate and oil temperature.To implement this solution, an oil atomization system is designed and tested, the results show that it is possible to create a spray of very fine droplets for injection pressures of the order of the difference between the high and low pressures of the water chiller. Cooled compression is then tested by connecting the oil atomization system to the water chiller. Reductions of compressor discharge temperature and of compressor power consumption are measured, but measured reductions are lower than the theoretical expected reductions. By integrating an increased droplet

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The improvement of pig industry is a consequence of the technological advances. The aim of the present study is to evaluate the effect of cysteine in BTS (Beltsville Thawing Solution) and centrifugation on swine semen to increase the sperm quality and fertility. In the first experiment, different concentrations of cysteine in Beltsville Thawing Solution: BTS (control group); CYS0.1 (BTS added 0.1 mM cysteine); CYS0.5 (BTS added 0.5 mM cysteine); CYS1.0 (BTS added 1.0 mM cysteine); CYS2.5 (BTS added 2.5 mM cysteine); CYS5.0 (BTS added 5.0 mM cysteine); CYS10.0 (BTS added 10.0 mM cysteine) and CYS20.0 (BTS added 20.0 mM cysteine) were evaluated. In the second experiment, semen added to BTS were not centrifuged without (control group) or with 5.0 mM of cysteine (BTSCYS/NC). In other treatment groups, semen were centrifuged with (BTSCYS/CENT) or without (BTS/CENT) 5.0 mM cysteine. Semen were stored at 17 °C for 72 h. To assess the effect of cysteine and centrifugation on fertility, 136 females were randomly allotted in the following groups for artificial insemination with semen diluted in BTS and a) without centrifugation and cysteine (BTS/NC); b) without centrifugation and with 5.0 mM cysteine (BTSCYS/NC) or c) with centrifugation and with 5.0 mM cysteine (BTSCYS/CENT). After artificial insemination, the return to estrus rate and litter size were evaluated. In the first experiment, the quality of semen was determined by tests of sperm motility, vigor, morphology and viability (plasma and acrossomal membrane integrity and mitochondrial potential). In the second experiment, the semen were evaluated by the tests above, DNA compactation and function of plasma membrane. The treatments were evaluated at 0, 24, 48 and 72 h after dilution. In both experiments, the effect of treatments on the storage period was determined by analysis for repeated data (PROC MIXED) and the effect of treatments on the return to estrus rate and the number of piglets were analyzed by using PROC GLM of SAS software and applied the Tukey test for significant models. The percentage of morphological changes did not exceed 20% during storage for 72 h and do not differ between treatments in both experiments. However, the motility in the first experiment, vigor, integrity of plasma membrane and acrossomal well as the potential of mitochondria reduced the period of storage. The motility, vigor and viability decreased to levels below 10% in treatments CYS10.0, CYS20.0 in the first 24 hours of storage at 17 ºC. At the end of the storage period all groups had average below 65% of sperm with intact plasma membrane while the second experiment, treatment BTSCYS/CENT showed lower motility and force the other treatments, and the sperm motility below 60% from 24 hours of storage. The integrity of plasma membranes and acrossomal and the potential of mitochondria was less than 60% in treatments BTSCYS and BTSCYS/CENT. However in the field to the group BTSCYS showed lower average (8.83 ± 3.38) for infants and more return rate (86.05 ± 0.39) when compared to other groups. Therefore, the cysteine at low concentrations as well as maintains the control group the sperm quality. But despite treatment BTSCYS/NC have reached the same rates as the control group for sperm quality, was the treatment that received higher rates of return and lower number of piglets born. / O crescimento da suinocultura se deve a diversos avanços na área tecnológica. Buscando obter maior eficiência reprodutiva, foi analisado o efeito da cisteína ao diluente Beltsville Thawing Solution (BTS) e do processo de centrifugação sobre qualidade espermática. No primeiro experimento, foram avaliadas diferentes concentrações de cisteína no diluente BTS, conforme os seguintes tratamentos: BTS (grupo controle); CIS0,1 (BTS + 0,1 mM de cisteína); CIS0,5 (BTS + 0,5mM de cisteína); CIS1,0 (BTS + 1,0 mM de cisteína); CIS2,5 (BTS + 2,5 mM de cisteína); CIS5,0 (BTS + 5,0 mM de cisteína); CIS10,0 (BTS + 10,0 mM de cisteína) e CIS20,0 (BTS + 20,0 mM de cisteína). No segundo experimento, o sêmen foi dividido em: sêmen não centrifugado diluído em BTS/NC (grupo controle), sêmen não centrifugado diluído em BTS + 5,0 mM de cisteína (BTSCIS/NC), sêmen centrifugado diluído em BTS (BTS/CENT) e sêmen centrifugado diluído em BTS + 5,0 mM de cisteína (BTSCIS/CENT). Ambos os experimentos foram realizados para avaliar a influência dos diferentes tratamentos sobre a qualidade espermática quando o sêmen é armazenado a 17°C por até 72 horas. Para avaliar o efeito da cisteína e da centrifugação sobre fertilidade, 136 fêmeas foram selecionadas e inseminadas nos seguintes tratamentos: BTS/NC, BTSCIS/NC e BTSCIS/CENT. Após a inseminação artificial, as fêmeas foram avaliadas quanto a taxa de retorno e o tamanho da leitegada. A qualidade espermática no primeiro experimento foi determinada pelos testes de motilidade e vigor, alterações morfológicas e viabilidade espermática (membrana plasmática e acrossomal intactas e célula com potencial de mitocôndria). No entanto, no segundo experimento além dos testes citados anteriormente, foram realizados os testes de compactação de DNA e funcionalidade de membrana plasmática. As avaliações dos tratamentos foram realizadas 0, 24, 48 e 72 horas após a diluição do sêmen. Em ambos experimentos, o efeito dos tratamentos em relação ao período de armazenamento foi determinado através da análise para dados repetidos (PROC MIXED). O efeito dos tratamentos em relação a taxa de retorno e o número de nascidos foi analisado usando o PROC GLM, do programa estatístico SAS e aplicado o teste de Tukey quando o modelo foi significativo. A percentagem de alterações morfológicas não excedeu a 20% durante o armazenamento por 72 horas e nem diferiu entre os tratamentos, nos dois experimentos. Porém, no primeiro experimento a motilidade, o vigor, a integridade de membrana plasmática e acrossomal bem como o potencial de mitocôndria foram reduzidas ao longo do período de armazenamento. A motilidade, o vigor e a viabilidade diminuíram a níveis abaixo de 10% nos tratamentos CIS10,0 e CIS20,0 nas primeiras 24 horas de armazenamento a 17ºC. Ao final do período de armazenamento todos os grupos apresentavam média abaixo de 65% de espermatozóides com a membrana plasmática intacta. No segundo experimento, no entanto, o tratamento BTSCIS/CENT apresentou motilidade e vigor inferiores ao demais tratamentos, sendo a motilidade espermática inferior a 60% a partir de 24 horas de armazenamento. A integridade das membranas plasmática e acrossomal e o potencial de mitocôndria foram inferiores a 60% nos tratamentos BTSCIS e BTSCIS/CENT. No entanto na parte a campo, o grupo BTSCIS apresentou menor média (8,83 ± 3,38) de nascidos e maior taxa de retorno (86,05 ± 0,39) quando comparados aos outros grupos. Portanto, a cisteína em baixas concentrações mantém tão bem quanto o grupo controle a qualidade espermática. Mas, apesar do tratamento BTSCIS/NC ter atingido os mesmos índices que o grupo controle em relação qualidade espermática, foi o tratamento que obteve maior taxa de retorno e menor número de leitões nascidos.

Large air-cooled heat exchangers (ACHEs) are most popularly implemented in the petrochemical and power industries at arid locations. They operate on a simple concept of convective heat transfer, whereby air in the surrounding atmosphere is caused to flow across a tube bundle, which in turn transports a process fluid. The distribution and direction of the process fluid flow may furthermore be guided via a set of appropriately located header boxes, which essentially consist of a collection of welded flat plates and nozzle attachments. Perforations on one of the faces of these boxes serve as an interface to the tube bundle. The overall design and construction of an ACHE is commonly regulated by an American Petroleum Institute (API) standard, which is required to be used in conjunction with acceptable design codes. In spite of this, the design of certain header box configurations remains of prominent concern. It is the focus of the present study to investigate the approach adopted for a header box variant labelled as the removable cover type. In this configuration, one of the plates used to construct the header box is fastened and sealed by a collection of bolted joints and a gasket, allowing it to be removed. One appropriate design code for the header box equipment is the ASME (American Society of Mechanical Engineers) boiler and pressure vessel code. However, it provides no specific approach pertaining to the removable cover design. Instead it has been commonplace in industry for a number of aspects from this code to be synthesized, together with a collection of assumptions surrounding the header box behaviour, into an all encompassing design by rule approach. In this approach, the header box behaviour is accepted as being planar, whilst circumstances such as nozzle attachments and associated loading would suggest that a more comprehensive approach should be undertaken. The aim of the present study is therefore to critically evaluate the current practice, and establish its adequacy. To do so, a detailed three-dimensional finite element model (FEM) of an example header box design is developed. Subsequent comparisons with the stress distribution predicted via current practice show that the existing analytical model gives inaccurate and, in cases, overly conservative results. A new analytical approach developed from rigid frame theory is demonstrated to provide improved correlation with FEM. The linear elastic design by analysis approach, presented in the ASME code, is also utilised as a method for establishing design adequacy. Results obtained via design by analysis incorporating the finite element method are shown to be less conservative than those arising from design by rule methods. The design by analysis approach is also used to conduct a more detailed investigation of nozzle placement and external loading. In general, the effect of including a nozzle did not result in a significant increase in side plate stress, with failure more likely to occur within the nozzle wall. / Dissertation (MEng)--University of Pretoria, 2011. / Mechanical and Aeronautical Engineering / unrestricted

<p>The study of Surface Air Cooled Oil Coolers (SACOC) is motivated by the need for new cooling concepts for compact machinery designs with high thermal load. Installing finned heat exchangers in the bypass duct of a turbofan engine provides an additional cooling source having transonic flow as a heat sink. The characterization of the heat transfer and the aerodynamics of the design are essential to minimize the impact on the overall efficiency of the engine. In the present study, the SACOC is studied numerically and experimentally. Two geometries are tested in a high-speed linear wind tunnel where measurements are taken with multiple sensors and optical techniques. For the heat transfer characterization, an Inverse Heat Conduction Methodology (IHCM) based on a Levenberg-Marquardt Algorithm is developed. The experimental results are matched to numerical simulations using a Reynolds Averaged Navier-Stokes (RANS) solver. Finally, a multi-objective optimization algorithm is coupled <a>with the RANS solver</a> to explore new geometries that maximize the heat transfer and minimize the pressure drop across the studied domain. The 400 profiles generated allow for the identification of the features that have a higher influence on the performance of the fins and six profiles that present large improvements are chosen for further analysis.</p>

Air-cooled condensers (ACCs) are a type of dry-cooling technology that has seen an increase in implementation globally, particularly in the power generation industry, due to its low water consumption. Unfortunately, ACC performance is susceptible to changing ambient conditions, such as dry bulb temperatures, wind direction, and wind speeds. This can result in performance reduction under adverse ambient conditions, which leads to increased turbine back pressures and in turn, a decrease in generated electricity. Therefore, this creates a demand to monitor and predict ACC performance under changing ambient conditions. This study focuses on modelling a utility-scale ACC system at steady-state conditions applying a 1-D network modelling approach and using a component-level discretization approach. This approach allowed for each cell to be modelled individually, accounting for steam duct supply behaviour, and for off-design conditions to be investigated. The developed methodology was based on existing empirical correlations for condenser cells and adapted to model double-row dephlegmators. A utility-scale 64-cell ACC system based in South Africa was selected for this study. The thermofluid network model was validated using site data with agreement in results within 1%; however, due to a lack of site data, the model was not validated for off-design conditions. The thermofluid network model was also compared to the existing lumped approach and differences were observed due to the steam ducting distribution. The effect of increasing ambient air temperature from 25 35  −  C C was investigated, with a heat rejection rate decrease of 10.9 MW and a backpressure increase of 7.79 kPa across the temperature range. Condensers' heat rejection rate decreased with higher air temperatures, while dephlegmators' heat rejection rate increased due to the increased outlet vapour pressure and flow rates from condensers. Off-design conditions were simulated, including hot air recirculation and wind effects. For wind effects, the developed model predicted a decrease in heat rejection rate of 1.7 MW for higher wind speeds, while the lumped approach predicted an increase of 4.9 . MW For practicality, a data-driven surrogate model was developed through machine learning techniques using data generated by the thermofluid network model. The surrogate model predicted systemlevel ACC performance indicators such as turbine backpressure and total heat rejection rate. Multilayer perceptron neural networks were developed in the form of a regression network and binary classifier network. For the test sets, the regression network had an average relative error of 0.3%, while the binary classifier had a 99.85% classification accuracy. The surrogate model was validated to site data over a 3 week operating period, with 93.5% of backpressure predictions within 6% of site data backpressures. The surrogate model was deployed through a web-application prototype which included a forecasting tool to predict ACC performance based on a weather forecast.

The aim of diploma thesis is a processing of climate data and design of chiller. Chiller is proposed to two options: air-cooled chiller and chiller with open cooling tower.

Aggressive demands for high power density and low-cost power modules in the automotive sector pose significant challenges to the thermal management systems. These challenges necessitate adopting highly effective cooling technologies in power modules to remain competitive in the semiconductor industry. Furthermore, the thermal management strategy must be simple, easy to integrate, compact, effective, efficient, reliable, and economical. This thesis is an effort to investigate the impact of fin geometry on the overall performance of finned-type liquid-cooled power electronic modules in electrified transportation. The cooling system's performance metrics, including thermal resistance, pressure drop, pumping power, and mass, are discussed in depth. Various cooling technologies are benchmarked. The finned-type cooling technique is chosen over other methods due to simplicity and low pressure drop. Integrated cooling or direct cooling of the module’s baseplate is selected due to considerable thermal resistance reduction because of thermal grease elimination. Potential fabrication techniques are thoroughly explored and compared in terms of mass production and prototyping suitability. Four different fin shapes, including circular (baseline), drop-shaped, symmetric convex lens, and offset strip in the staggered arrangement, are studied herein. The cooling agent is Water and Ethylene Glycol 50% volumetric mixture (WEG 50%). Typical operating conditions in electrified vehicles (EVs) such as flow rate and inlet temperature are assumed for the numerical analysis. A grid convergence study is carried out to ensure numerical solutions are within an acceptable error band. The thermal performance evaluation results showed that, on average, offset strip, drop-shaped, and the convex lens performed 39%, 20%, and 6% better than the baseline design, respectively. Additionally, the design candidates are compared in terms of mass and estimated machining cost. The results of the baseline case are verified against empirical correlations from the literature. The maximum deviation is less than 1% and 1.2% for finned-surface temperature and pressure drop, respectively. The difference is attributed to the end-wall effects. / Thesis / Master of Applied Science (MASc)

No description available.

No description available.

With more restrictions regarding the use of refrigerants with high GWP-values, refrigeration systems that uses R744 (Carbon dioxide) as a refrigerant increases. Supermarkets are energy intense facilities where the refrigeration system utilize a significant part of the total utilized energy. Heat recovery have been proven beneficial and reduces the total energy utilization for the building.  This master thesis evaluates an existing R744 refrigeration system with heat recovery, for the purpose to find an optimal system configuration and control strategy that minimizes the operational costs. Today the refrigeration system uses a water-cooled condenser/gas cooler that during the period from February to November 2021 consumed 8 194 m3 of cooling water, that resulted in high water costs for the supermarket. With the development of a model that takes historical data as input can different system configurations and control strategies be tested and compered to the historical analysis of the existing refrigeration system. Four system configurations with different heat recovery solutions were evaluated.  The result of this study shows that the operational cost can be reduced by 31% (55 400 SEK) with a control strategy that adapts the discharge pressure to the facility’s heating demand. With maximized heat recovery the condenser/gas cooler load decreases and therefore the cooling water flow decreases too. With an additional heat exchanger in the supermarkets ventilation exhaust duct can the water consumption further be reduced, compared with similar system without an additional heat exchanger. The additional heat exchanger reduced the cooling water consumption by 1 400 m3 for the investigated period and reduced the total operational cost by 9 800 SEK. However, it is recommended to first apply the control strategy that adapts the discharge pressure to the heating demand, and from there evaluate the benefits of a heat exchanger in the exhaust duct. / Med ett allt strängare regelverk angående användandet av köldmedier med höga GWP-värden, ökar antalet kylanläggningar som använder R744 (Koldioxid) som köldmedium. Livsmedelsbutiker är energikrävande där kylsystemen är en stor del av den totala energimängd som nyttjas. Studier visar att värmeåtervinning för dessa system kan med fördel användas för att minska energianvändningen i fastigheten.  Detta masterexamensarbete utvärderar en befintlig R744-kylanläggning med värmeåtervinning, i syfte att finna en optimal systemkonfiguration och styr-strategi som minimerar driftkostnaderna. Idag används en vattenkyld kondensor/gaskylare som under perioden februari till november 2021 förbrukade 8 194 m3 kylvatten, vilket resulterade i höga vattenkostnader för butiken. Genom att utveckla en modell som använder historisk mätdata som indata kan olika systemlösningar och styr-strategier testas och jämföras med analysen av det befintliga kylsystemet. Fyra systemkonfigurationer med olika grad av värmeåtervinning utvärderades. Studiens resultat visar att driftkostnaderna kan reduceras genom att anpassa kylsystemens högtryck till fastighetens värmebehov. Genom att maximera värmeåtervinningen minskar nyttjandet av kondensorn/gaskylaren och därmed flödet av kylvatten. Med en extra värmeväxlare i butikens frånluftskanal kan vattenförbrukningen reduceras ytterligare jämfört med liknande system utan denna värmeväxlare. Dock rekommenderas att initialt nyttja en styrstrategi som anpassar högtrycket efter värmebehov, för att sedan utvärdera fördelarna med en värmeväxlare i ventilationens frånluftskanal.