The South African gold mining sector consumes 47% of the mining industry’s electricity. On a deep level gold mine, 20% of the energy is consumed by the refrigeration system. The refrigeration system cools 67 ˚C virgin rock temperatures underground. Underground cooling demand increases significantly with deeper mining activities. Various cooling systems are available for underground cooling. This study focuses on the electricity usage of an ice storage system versus a chilled water system for underground cooling. An energy-savings approach was developed to determine possible power savings on the surface refrigeration system of Mine M. The savings approach involved converting an ice storage system to a chilled water system and varying the water flow through the system. The water flow was varied by installing variable speed drives on the evaporator and condenser water pumps. The feasibility of the energy-efficiency approach was simulated with a verified simulation model. Simulation results indicated the feasibility of converting the thermal ice storage to a chilled water system and implementing the energy-efficiency approach on Mine M. Simulated results indicated a 9% electricity saving when using a chilled water system. Various problems encountered by the mine were also a motivation to convert the thermal ice storage system. Converting an ice storage facility to a chilled water system for energy efficiency on a deep level gold mine Energy management is achieved through the monitoring, controlling and reporting of the implemented savings approach. Converting the glycol plant and recommissioning the chilled water plant gave the mine an additional chiller as backup to sufficiently meet underground demand. An annual summer power saving of 1.5 MW was achieved through the conversion and control strategy. It is concluded that conversion of the thermal ice storage system on Mine M results in an energy- and cost saving. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015

The South African gold mining sector consumes 47% of the mining industry’s electricity. On a deep level gold mine, 20% of the energy is consumed by the refrigeration system. The refrigeration system cools 67 ˚C virgin rock temperatures underground. Underground cooling demand increases significantly with deeper mining activities. Various cooling systems are available for underground cooling. This study focuses on the electricity usage of an ice storage system versus a chilled water system for underground cooling. An energy-savings approach was developed to determine possible power savings on the surface refrigeration system of Mine M. The savings approach involved converting an ice storage system to a chilled water system and varying the water flow through the system. The water flow was varied by installing variable speed drives on the evaporator and condenser water pumps. The feasibility of the energy-efficiency approach was simulated with a verified simulation model. Simulation results indicated the feasibility of converting the thermal ice storage to a chilled water system and implementing the energy-efficiency approach on Mine M. Simulated results indicated a 9% electricity saving when using a chilled water system. Various problems encountered by the mine were also a motivation to convert the thermal ice storage system. Converting an ice storage facility to a chilled water system for energy efficiency on a deep level gold mine Energy management is achieved through the monitoring, controlling and reporting of the implemented savings approach. Converting the glycol plant and recommissioning the chilled water plant gave the mine an additional chiller as backup to sufficiently meet underground demand. An annual summer power saving of 1.5 MW was achieved through the conversion and control strategy. It is concluded that conversion of the thermal ice storage system on Mine M results in an energy- and cost saving. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015

No presente trabalho são apresentados resultados de simulação numérica transiente de um sistema de refrigeração doméstico de compressão a vapor considerando o procedimento descrito por JAKOBSEN (1995). O modelo matemático empregado se baseia num sistema de equações algébrico-diferenciais (EAD) de primeira ordem, obtido a partir do balanço de energia nos diferentes componentes do sistema de refrigeração, e de algumas outras relações necessárias para simular o comportamento global do sistema de refrigeração. O sistema de equações resultante é resolvido numericamente no software livre WinDali, da Universidade Técnica de Dinamarca. Dito software permite resolver sistemas de EADs que apresentam descontinuidades matemáticas usando o método de Runge- Kutta de quarta ordem. O modelo matemático empregado permite calcular a eficiência do sistema de refrigeração, predizer o consumo de energia, caracterizar termodinamicamente o sistema de refrigeração e suas interações, e descrever quantitativamente as perdas termodinâmicas (geração de entropia) do sistema funcionando em regime de operação. Esses resultados são obtidos em função da estratégia de controle do compressor, eficiência do compressor e do dimensionamento dos diferentes componentes do sistema de refrigeração. Os resultados comprovam que o modelo matemático e o programa computacional empregados permitem descrever corretamente o comportamento de um sistema de refrigeração doméstico, resultando numa ferramenta muito útil para otimização de refrigeradores domésticos. / In the present work are presented transient numerical simulation results of a vapor compression domestic refrigeration system considering the procedure described by JAKOBSEN (1995). The employed mathematical model is based on first order differential-algebraic equation (DAE) systems, obtained from energy balance in the different components of the refrigeration system, and from others relations that are necessary to simulate the global behavior of a refrigeration system. The resulting equation system is solved numerically in the free software WinDali developed at Technical University of Denmark. This software allows solving DAE systems that present mathematical discontinuities, using the Runge-Kutta method of fourth order. The employed mathematical model allows calculating the refrigeration system efficiency, predict the energy consumption, thermodynamically characterize the refrigeration system and its interactions and quantitatively describe the thermodynamic losses (entropy generation) of the system running in the operation regime. These results are obtained as a function of the compressor control strategy, compressor efficiency, and sizing of different components of the refrigeration system. The results confirm that the mathematical model and the computational program allow describing correctly the behavior of a domestic refrigeration system, resulting in a very useful tool for optimization of domestic refrigerators.

The main objective of this study is to propose and to validate simplified models to simulate the performance of refrigeration systems. The proposed modelling approach of the system is modular: the compressor is modelled by a simple and physical model that takes into account the heat transfers and the un-matching of internal and external pressure ratio for the scroll compressors. The evaporator is modelled as a two zones heat exchanger on the refrigeration side (one for the two phases zone and the other one for superheated gas) and finally the condenser is assumed to be divided into three zones (de-superheating, two-phase and the sub-cooling). The compressor model was already developed by other author; here it is only validated using three scroll compressors and two reciprocating ones. The main differences are the conditions at which these compressors are tested: 20 bar at the supply and 40 at the exhaust. The condenser and evaporator models are the main contribution of this study. These models use the geometry and the correlation from the literature to calculate the global heat transfer coefficient on each zone. In the case of the condenser, a mean void fraction model is used to determinate the condenser subcooling as function of the refrigerant charge or vice-versa. The refrigeration system model is validated with experimental results obtained on each component and the whole system in five different test benches. The results show a very good agreement between the measured and predicted main outputs of the system.

Refrigeration systems, air-conditioning units and heat pumps have been recognized as indispensable machines in human life, and are used for e.g. food storage, provision of thermal comfort. These machines are dominated by the vapor compression refrigeration system and consume a large percentage of world-wide electricity output. Moreover, CO2 emissions related to the heating and cooling processes contribute significantly to the total amount of CO2 emission from energy use. The ejector refrigeration system (ERS) has been considered as a quite interesting system that can be driven by sustainable and renewable thermal energy, like solar energy, and low-grade waste heat, consequently, reducing the electricity use. The system has some other remarkable merits, such as being simple and reliable, having low initial and running cost with long lifetime, and providing the possibility of using environmentally-friendly refrigerants, which make it very attractive. The ERS has received extensive attention theoretically and experimentally. This thesis describes in-depth investigations of vapor ejectors in the ERS to discover more details. An ejector model is proposed to determine the system performance and obtain the required area ratio of the ejector by introducing three ejector efficiencies. Based on this ejector model, the characteristics of the vapor ejector and the ERS are investigated from different perspectives. The working fluid significantly influences the ejector behavior and system performance as well as the ejector design. No perfect working fluid that satisfies all the criteria of the ERS can be found. The performance of nine refrigerants has been parametrically compared in the ERS. Based on the slope of the vapor saturation curve in a T-s diagram, the working fluids can be divided into three categories: wet, dry and isentropic. A wet fluid has a negative slope of the vapor saturation curve in the T-s diagram. An isentropic expansion process from a saturated vapor state will make the state after the expansion to fall inside the liquid-vapor area of the T-s diagram which will result in droplet formation. Generally, an isentropic expansion for a dry fluid will not occur inside the liquid-vapor area, and consequently no droplets will form. An isentropic fluid has a vertical slope of the vapor saturation curve in the T-s diagram and an isentropic expansion process will hence follow the vapor saturation curve in the T-s diagram, ideally without any droplet formation. However, when the saturation condition is close to the critical point, it is possible that the isentropic expansion process of a dry fluid and an isentropic fluid occurs inside the liquid-vapor area of the T-s diagram, resulting in formation of droplets. In order to avoid droplet formation during the expansion, a minimum required superheat of the primary flow has been introduced before the nozzle inlet. Results show that the dry fluids have generally better performance than the wet fluids and the isentropic fluid. Hence the thesis mostly focuses on the features of vapor ejectors and the ERS using dry fluids. Exergy analysis has been proven to be very useful to identify the location, magnitude, and sources of exergy destruction and exergy loss, and to determine the possibilities of system performance improvement. This method is applied to the ejector and the ERS. The ejector parameters are closely interacting. The operating condition and the ejector area ratio have a great impact on the ejector overall efficiency and system COP. The ejector efficiencies are sensitive to the operating conditions, and they significantly influence the system performance. A so-called advanced exergy analysis is adopted to quantify the interactions among the ERS components and to evaluate the realistic potential of improvement. The results indicate that, at the studied operating condition, the ejector should have the highest priority to be improved, followed by the condenser, and then the generator. Thermoeconomics, which combines the thermodynamic analysis and economic principles, is applied to reveal new terms of interest of the ERS. The economic costs of the brine side fluids (fluids that supply heat to the generator and evaporator and remove heat from the condenser) play very essential roles in the thermoeconomic optimization of the ERS. Depending on different economic conditions, the system improvement from a thermodynamic point of view could be quite different from the thermoeconomic optimization. The ERS is economically sound when using free heat sources and heat sink. An ejector test bench has been built to test the entrainment ratio of different ejectors. Although the experiments do not achieve the desired results, they could still be discussed. The insignificant effect of the superheat of the secondary flow found in the theoretical study is validated. The assumption of neglecting the velocities at the ejector inlets and outlet are confirmed. The quantification of the ejector efficiencies shows that they largely depend on the operating conditions and the ejector dimensions. / <p>QC 20141102</p>

Made available in DSpace on 2014-06-11T19:25:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-06-27Bitstream added on 2014-06-13T19:32:34Z : No. of bitstreams: 1 souza_lmp_me_bauru.pdf: 1572366 bytes, checksum: b4f3b5bc0ddb17fad3e39f5f59ec6a72 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No estudo de reaproveitamento de energia térmica, os refrigeradores domésticos dissipam calor para o meio ambiente, através do seu condensador, e esse calor pode ser reciclado, ou seja, recuperado através de escoamento de água, como fluido refrigerante escoando pelo condensador e armazenada em um reservatório. Para isto, construi-se um aparato experimental contendo um refrigerador doméstico, duplex com capacidade de 263 litros para o gabinete de refrigeração e 74 litros para o gabinete de congelamento. O refrigerador tem seu condensador acrescido por um trocador de calor tipo tubos concêntricos em contra corrente, cuja fruição é condensar o fluido refrigente utilizando água em circulação. Dessa forma, caso ocorra o carregamento térmico total do tanque de armazenagem, o calor será originalmente dissipado para o meio ambiente, através do condensador aletado. A água aquecida é então armazenada em um reservatório térmico via estratificação térmica. Assim calculou-se as vazões de água aquecida e fluido refrigerante, como também o coeficiente de desempenho do sistema acumulado. Os resultados mostraram que a vazão de água bem como o coeficiente de desempenho do sistema aumenta de acordo com o aumento da pressão hidrostática. Desta maneira, dos resultados obtidos pode-se concluir que a otimização do experimento se dá de forma eficaz e que, o reaproveitamento da água quente proveniente do condensador é perfeitamente possível, reduzindoo consumo de energia elétrica com aquecedores de água e ainda, minimizando a dissipação de calor para o meio ambiente, sem alterar o funcionamento do refrigerador / In the study of recycling thermal energy it is know that domestic refrigerators dissipate heat to environment through the condenser. This heat can be recycled by a water flow, as a coolant in a modified condenser, and stored in a Domestic Hot Water Storage Tanks (DHWST). Thereby, an experimental apparatus was built containing one domestic refrigerator, each one with capacity of 263 liters in the cooling cabinet and 74 liters in the freezing cabinet. The refrigerators had the condenser increase by a type heat exchanger concentric tubes with a counter-current flow, which has the function of replace the original finned exchanger, condensing the coolant with water flow. Thus, in case the total thermal loading of the storage tank, the heat is dissipated to the original environment through the condenser finned. The heated water is then stored in a thermal reservoir via thermal stratification. In these conditions, the flow of heated water and refrigerant was calculated, as well as the coefficient of performance of the system. The results show that the water flow rate and the coefficient of performance of the system increases with the increase in hydrostatic pressure. According to these results, the experiment optimization is effective and it is totally possible to reuse the warm from modified condenser system, what could reduce the electric energy consumption in water beater and minimize the heat dissipation to environment, without modifying the refrigerator operation

No presente trabalho são apresentados resultados de simulação numérica transiente de um sistema de refrigeração doméstico de compressão a vapor considerando o procedimento descrito por JAKOBSEN (1995). O modelo matemático empregado se baseia num sistema de equações algébrico-diferenciais (EAD) de primeira ordem, obtido a partir do balanço de energia nos diferentes componentes do sistema de refrigeração, e de algumas outras relações necessárias para simular o comportamento global do sistema de refrigeração. O sistema de equações resultante é resolvido numericamente no software livre WinDali, da Universidade Técnica de Dinamarca. Dito software permite resolver sistemas de EADs que apresentam descontinuidades matemáticas usando o método de Runge- Kutta de quarta ordem. O modelo matemático empregado permite calcular a eficiência do sistema de refrigeração, predizer o consumo de energia, caracterizar termodinamicamente o sistema de refrigeração e suas interações, e descrever quantitativamente as perdas termodinâmicas (geração de entropia) do sistema funcionando em regime de operação. Esses resultados são obtidos em função da estratégia de controle do compressor, eficiência do compressor e do dimensionamento dos diferentes componentes do sistema de refrigeração. Os resultados comprovam que o modelo matemático e o programa computacional empregados permitem descrever corretamente o comportamento de um sistema de refrigeração doméstico, resultando numa ferramenta muito útil para otimização de refrigeradores domésticos. / In the present work are presented transient numerical simulation results of a vapor compression domestic refrigeration system considering the procedure described by JAKOBSEN (1995). The employed mathematical model is based on first order differential-algebraic equation (DAE) systems, obtained from energy balance in the different components of the refrigeration system, and from others relations that are necessary to simulate the global behavior of a refrigeration system. The resulting equation system is solved numerically in the free software WinDali developed at Technical University of Denmark. This software allows solving DAE systems that present mathematical discontinuities, using the Runge-Kutta method of fourth order. The employed mathematical model allows calculating the refrigeration system efficiency, predict the energy consumption, thermodynamically characterize the refrigeration system and its interactions and quantitatively describe the thermodynamic losses (entropy generation) of the system running in the operation regime. These results are obtained as a function of the compressor control strategy, compressor efficiency, and sizing of different components of the refrigeration system. The results confirm that the mathematical model and the computational program allow describing correctly the behavior of a domestic refrigeration system, resulting in a very useful tool for optimization of domestic refrigerators.

The diploma thesis is consisting of three parts. The first part is a theoretical overview. It discusses the basic types of refrigeration systems and addresses used by air conditioners. The theoretical part contains describes the basic terms of the proposed refrigeration system, air filtration technology. In the second part of the project design air conditioning systems for offices three-story office building. Following heat balance the budget, the air conditioning system. Numerical solution is completed drawings and bill of material. The third part is experimental. Objective measurement is to determine the heat loss of the pipe without insulation, with normal insulation, new insulation and determine the applicability of a new type of insulation.

Vortex tube (VT) is a mechanical device with no moving parts. The fundamental principle of Vortex Tube is that it can split an incoming fluid flow of a constant pressure and constant temperature gas stream into two separate low pressure streams, one having higher enthalpy and the other having lower enthalpy than the inlet flow. So this device essentially works as a temperature separator. On separation from the device, a warmer flow exits through a terminal which is called the “hot end” and a low temperature stream comes out from another terminal known as the “cold end”. Just with a few bar pressure of compressed air at room temperature can produce a hot stream temperature of about 150°C and a cold stream temperature of about - 40°C. This temperature separation scheme allows us to get cooling and heating effect simultaneously using the same device which makes the Vortex tube one of the popular mechanical equipment and is used in many fields of engineering. The cooling or heating effect produced by this device is largely dependent on geometric parameters of the device itself. Since no exact theoretical correlation is there between the geometric parameters and the cooling (or heating) effect produced, VT design is solely based on empirical relations. There are quite a few geometric parameters which affect the cooling effect of this device and all the empirical correlation are needed to design the optimum VT for maximum cooling/heating effect. These relations can be derived in two ways, either by numerical methods or by experimental investigations. The first part of the thesis important geometric parameter of the VT namely the ratio of the “cold end” diameter (to the “tube diameter” , which has been numerically optimized in this work to achieve maximum temperature separation. In our efforts to design a VT based refrigeration system, optimization of the VT itself is not enough. A suitable heat exchanger (HX) which can extract the cold enthalpy from the VT also needs to be designed and cascaded with the VT to get the complete refrigeration system. The second part of the thesis is solely dedicated to the design of a suitable HX that can be used alongside a VT to produce refrigeration. The HXs design can be approached from two directions, dimensional aspect and material aspect. Rather than focusing on the dimensional aspect in this work we have concentrated of the material aspect of HX design. It is fairly obvious that the thermal conductivity (TC) of the HX material will play a crucial role on the cooling effect of the refrigeration system. Conventional metals with high TC can be used to design HXs but the downsides of using pure metals such as Copper, Iron are that they are heavy, quite expensive and highly reactive to corrosive fluids. Because of this, high TC ceramic material such as Aluminium Nitride (AlN) is quite often used to fabricate HXs and they are used for spot cooling in electronic systems. AlN has TC of 160 W/m-K which is high but not as high as of Copper or Iron. TC of AlN can be increased by mixing the right volume fraction of metal powder (such as pure Aluminium) with it to a great extent. So in a nutshell, instead of using pure AlN, if we use the particle reinforced binary composite [AlN + Al (powder)] to design a HX, we would achieve the benefits of having high TC as well as properties such as anti-corrosiveness, cost effectiveness and weight reduction. In the above context, prediction of TC of particle reinforced composite materials containing a base material of low TC and a filler material of high TC is of utmost importance. Till now a very few analytical heat transfer models are available in the literature that can accurately predict the TC value of such composites especially when high volume fraction of filler particles is added to the base material or if more than one type of filler particles are added. So in this thesis, three analytical heat transfer models have been developed that can predict the TC of binary as well as tertiary particle reinforced composites. The third and the final segment of the thesis deals with the performance study of a refrigeration system comprised of the optimized VT cascaded with a suitable HX made out of a particle reinforced composite material. The numerical results show how the HX effectiveness improves as the volume fraction of the filler particles in the composite increases. The key results of the works described in the thesis are as follows: • Through extensive numerical simulations it is shown that for = 0.5, the temperature separation in a VT is maximum. • The heat transfer models developed to predict the thermal conductivity of binary composites, shows the trend of how thermal conductivity varies with increasing volume fraction of filler. It has been shown that initially the thermal conductivity increases linearly with a small slope, then after a critical volume fraction an abrupt increment of slope is observed due to the formation of continuous heat conduction paths within the composite. Further increase in volume fraction shows linear increment of thermal conductivity with lesser slope as before. • The heat transfer model developed to predict the thermal conductivity of tertiary composites is suitable for low volume fraction (< 20 %). The model shows the addition of one component into the base matrix affects the distribution of the other component which is observed through the covariance. • The last part of the thesis shows that compared to a pure AlN heat exchanger, a heat exchanger made of AlN + 30 % volume fraction of pure Aluminium powder, has increased heat exchanger effectiveness by more than 50 %. Thesis outline is as follows: • Chapter 1 is a brief introduction to Vortex Tube. • Chapter 2 deals with the necessary literature review related to Vortex Tube as well as presently available heat transfer models that are equipped to handle composite materials to predict their TC. • Chapter 3 elaborates numerical modeling and optimization of a critical parameter ( to achieve maximum temperature separation in a VT. • Chapter 4 presents a stochastic heat transfer model to estimate the TC of Binary particle reinforced composites containing low volume fraction of filler particles. • Chapter 5 describes the development of a computational heat transfer model to predict the TC of Particle Reinforced Binary Composite materials containing high volume fraction of filler element. • Chapter 6 deals with a stochastic heat transfer model to calculate TC of Particle Reinforced Tertiary Composite materials containing low volume fractions of filler elements. • Chapter 7 consolidates all the necessary concepts and data from previous chapters to design the final cascaded VT based refrigeration system and presents a performance study. • The last chapter summarizes the entire work along with scope for future work.

Orientador: Alcides Padilha / Banca: Enio Pedone Bandarra Filho / Banca: Celso Luiz da Silva / Resumo: No estudo de reaproveitamento de energia térmica, os refrigeradores domésticos dissipam calor para o meio ambiente, através do seu condensador, e esse calor pode ser reciclado, ou seja, recuperado através de escoamento de água, como fluido refrigerante escoando pelo condensador e armazenada em um reservatório. Para isto, construi-se um aparato experimental contendo um refrigerador doméstico, duplex com capacidade de 263 litros para o gabinete de refrigeração e 74 litros para o gabinete de congelamento. O refrigerador tem seu condensador acrescido por um trocador de calor tipo tubos concêntricos em contra corrente, cuja fruição é condensar o fluido refrigente utilizando água em circulação. Dessa forma, caso ocorra o carregamento térmico total do tanque de armazenagem, o calor será originalmente dissipado para o meio ambiente, através do condensador aletado. A água aquecida é então armazenada em um reservatório térmico via estratificação térmica. Assim calculou-se as vazões de água aquecida e fluido refrigerante, como também o coeficiente de desempenho do sistema acumulado. Os resultados mostraram que a vazão de água bem como o coeficiente de desempenho do sistema aumenta de acordo com o aumento da pressão hidrostática. Desta maneira, dos resultados obtidos pode-se concluir que a otimização do experimento se dá de forma eficaz e que, o reaproveitamento da água quente proveniente do condensador é perfeitamente possível, reduzindoo consumo de energia elétrica com aquecedores de água e ainda, minimizando a dissipação de calor para o meio ambiente, sem alterar o funcionamento do refrigerador / Abstract: In the study of recycling thermal energy it is know that domestic refrigerators dissipate heat to environment through the condenser. This heat can be recycled by a water flow, as a coolant in a modified condenser, and stored in a Domestic Hot Water Storage Tanks (DHWST). Thereby, an experimental apparatus was built containing one domestic refrigerator, each one with capacity of 263 liters in the cooling cabinet and 74 liters in the freezing cabinet. The refrigerators had the condenser increase by a type heat exchanger concentric tubes with a counter-current flow, which has the function of replace the original finned exchanger, condensing the coolant with water flow. Thus, in case the total thermal loading of the storage tank, the heat is dissipated to the original environment through the condenser finned. The heated water is then stored in a thermal reservoir via thermal stratification. In these conditions, the flow of heated water and refrigerant was calculated, as well as the coefficient of performance of the system. The results show that the water flow rate and the coefficient of performance of the system increases with the increase in hydrostatic pressure. According to these results, the experiment optimization is effective and it is totally possible to reuse the warm from modified condenser system, what could reduce the electric energy consumption in water beater and minimize the heat dissipation to environment, without modifying the refrigerator operation / Mestre