The application of thermoacoustic phenomena for cooling purposes has a comparatively short history. However, recent experiments have shown that thermoacoustic refrigeration can achieve practical significance for both every day cooling in households and cryocooling for scientific purposes due to its high reliability, environmental safety and functioning under extreme conditions. We build a thermoacoustic refrigerator driven by a commercial loudspeaker. It was equipped with a vacuum pump and an entrance port for introducing different gases under different pressures as working fluids. It contained two thermocouples and a pressure transducer for quantitative measurements of the basic performance. The resonance frequency of the tube for different gases has been determined and compared to the theoretical value. The temperatures of the hot and the cold heat exchanger have been measured. Also, a simple thermoacoustic oscillator for demonstration purposes was built. After immersing one end in liquid nitrogen or heating up the other end with a bunsen burner it started to oscillate and emit a sound.

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Orientador: André Luiz Seixlack / Banca: Elaine Maria Cardoso / Banca: Henor Artur de Souza / Resumo: Neste trabalho apresenta-se um modelo numérico para simular o escoamento e a transferência de calor entre o fluido refrigerante e ar externo em regime permanente e transiente ao longo de evaporadores de tubos aletados comumente usados em refrigeradores domésticos do tipo frost-free e sistemas de ar condicionado. O escoamento do fluido refrigerante é dividido em duas regiões: uma de escoamento bifásico e outra de vapor superaquecido. Considera-se a queda de pressão do escoamento no interior dos tubos e a condensação do vapor d'água do ar úmido que escoa em fluxo cruzado na parte externa dos tubos. O escoamento bifásico é analisado segundo o modelo homogêneo. As equações fundamentais de conservação da massa, da quantidade de movimento e de conservação da energia que governam o escoamento do refrigerante são resolvidas, respectivamente, para o cálculo da velocidade, da pressão e da entalpia específica do fluido refrigerante. Para o escoamento de ar, são resolvidas as equações de conservação da energia e de conservação da massa (umidade). Resolve-se, também, a equação da conservação da energia para a parede do tubo, para obter sua distribuição de temperatura. O modelo necessita ainda de equações constitutivas para o cálculo dos: fatores de atrito, coeficientes de transferência de calor para o ar e para o refrigerante, do coeficiente transferência de massa para a água e das propriedades termofísicas do refrigerante, do ar e da água. As equações governantes são integradas numericamente usando o método de Euler e o sistema de equações algébricas resultante é solucionado pelo método de Newton-Raphson. O modelo pode ser usado para: (a) determinar os parâmetros de desempenho do evaporador, tais como: capacidade de refrigeração, temperaturas de saída do refrigerante e do ar, dentre outros, desde que as condições de operação e os parâmetros geométricos... / Abstract: This work presents a numerical model to simulate the steady and transient flow and heat transfer between the refrigerant fluid and outside air along tube-fin evaporators commonly used in 'no-frost' household refrigerators. The refrigerant flow inside the tube is taken as one- dimensional and divided in a two-phase flow region and a superheated vapor flow region. The refrigerant pressure drop and the moisture condensation on the airflow crossing the outside of the tubes are taken into account. The homogeneous flow model is employed for the two-phase flow region. The fundamental equations of mass conservation, momentum and energy conservation governing the refrigerant flow are solved in order to evaluate the velocity, pressure and specific enthalpy of the refrigerant fluid. The energy and mass (humidity) conservation equations for the air flow are solved in order to evaluate the temperature and absolute humidity of the air crossing the evaporator, respectively. The energy conservation equation for the evaporator tube wall is also solved to obtain the wall temperature distribution. Furthermore, the model needs closer constitutive equations to calculate the friction coefficients, the refrigerant and air heat transfer coefficients, the water mass transfer coefficient and the refrigerant, air and water thermo-physical properties. The governing equations are integrated numerically using Euler's method and the resulting algebraic system of equations is solved by Newton-Raphson's method. The model could be used to: (a) determine evaporator performance parameters, such as: refrigeration load; outlet refrigerant and air temperatures; among others, since the evaporator operating conditions and dimensions are known. In this case a direct problem is solved from a set of inlet conditions for the refrigerant and also for the air; (b) determine the refrigerant mass flow rate along evaporator tubes, once its ... / Mestre

Made available in DSpace on 2015-09-17T15:26:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-06-29. Added 1 bitstream(s) on 2015-09-17T15:45:12Z : No. of bitstreams: 1 000847749.pdf: 3178546 bytes, checksum: df9a1fe5199988861e46d4041fa84d9a (MD5) / Neste trabalho apresenta-se um modelo numérico para simular o escoamento e a transferência de calor entre o fluido refrigerante e ar externo em regime permanente e transiente ao longo de evaporadores de tubos aletados comumente usados em refrigeradores domésticos do tipo frost-free e sistemas de ar condicionado. O escoamento do fluido refrigerante é dividido em duas regiões: uma de escoamento bifásico e outra de vapor superaquecido. Considera-se a queda de pressão do escoamento no interior dos tubos e a condensação do vapor d'água do ar úmido que escoa em fluxo cruzado na parte externa dos tubos. O escoamento bifásico é analisado segundo o modelo homogêneo. As equações fundamentais de conservação da massa, da quantidade de movimento e de conservação da energia que governam o escoamento do refrigerante são resolvidas, respectivamente, para o cálculo da velocidade, da pressão e da entalpia específica do fluido refrigerante. Para o escoamento de ar, são resolvidas as equações de conservação da energia e de conservação da massa (umidade). Resolve-se, também, a equação da conservação da energia para a parede do tubo, para obter sua distribuição de temperatura. O modelo necessita ainda de equações constitutivas para o cálculo dos: fatores de atrito, coeficientes de transferência de calor para o ar e para o refrigerante, do coeficiente transferência de massa para a água e das propriedades termofísicas do refrigerante, do ar e da água. As equações governantes são integradas numericamente usando o método de Euler e o sistema de equações algébricas resultante é solucionado pelo método de Newton-Raphson. O modelo pode ser usado para: (a) determinar os parâmetros de desempenho do evaporador, tais como: capacidade de refrigeração, temperaturas de saída do refrigerante e do ar, dentre outros, desde que as condições de operação e os parâmetros geométricos... / This work presents a numerical model to simulate the steady and transient flow and heat transfer between the refrigerant fluid and outside air along tube-fin evaporators commonly used in 'no-frost' household refrigerators. The refrigerant flow inside the tube is taken as one- dimensional and divided in a two-phase flow region and a superheated vapor flow region. The refrigerant pressure drop and the moisture condensation on the airflow crossing the outside of the tubes are taken into account. The homogeneous flow model is employed for the two-phase flow region. The fundamental equations of mass conservation, momentum and energy conservation governing the refrigerant flow are solved in order to evaluate the velocity, pressure and specific enthalpy of the refrigerant fluid. The energy and mass (humidity) conservation equations for the air flow are solved in order to evaluate the temperature and absolute humidity of the air crossing the evaporator, respectively. The energy conservation equation for the evaporator tube wall is also solved to obtain the wall temperature distribution. Furthermore, the model needs closer constitutive equations to calculate the friction coefficients, the refrigerant and air heat transfer coefficients, the water mass transfer coefficient and the refrigerant, air and water thermo-physical properties. The governing equations are integrated numerically using Euler's method and the resulting algebraic system of equations is solved by Newton-Raphson's method. The model could be used to: (a) determine evaporator performance parameters, such as: refrigeration load; outlet refrigerant and air temperatures; among others, since the evaporator operating conditions and dimensions are known. In this case a direct problem is solved from a set of inlet conditions for the refrigerant and also for the air; (b) determine the refrigerant mass flow rate along evaporator tubes, once its ...

This work was concerned with the aerodynamic and acoustic performance of small axial flow refrigerator fans. Relevant literature focusing on the principles of fan noise generation and fan system elements that contribute to noise generation was identified and discussed. A plenum chamber test rig was designed and constructed following ISO 10302-1. A range of 200 mm diameter pressed aluminium Air-Drive fans, commonly used in commercial refrigerator systems, were evaluated using the test rig. It was found that the performance of these fans was highly dependent upon the impedance of the system in which they are installed. Indications of rotating stall under high load were observed and shown to significantly increase the noise output of the fan without greatly affecting the air moving capability. A series of novel colour map plots are presented, which allow for a visual interpretation of fan performance over a wide range of operating conditions. A fanpack developed by Wellington Drive Technologies Ltd was evaluated. This fanpack was found to generate significant tonal noise. The design of the fanpack was evaluated and improvements are suggested. Prototype fans were developed from the fanpack based on promising concepts presented in the literature. The performance of four prototype fans was evaluated. The results were disappointing, but proof of concept was demonstrated.

This study was designed to measure the effect of selected consumer practices on energy consumption of refrigerators. Seven tests designed to simulate consumer practices were performed three times each on four refrigerators. Four tests involving variations in temperature control setting, frequency and duration of door openings, and placement of the refrigerator near a heat source were each performed on a manual-defrost refrigerator, a cycle-defrost refrigerator-freezer, and a no-frost refrigerator-freezer. A test involving the use of an energy-saver switch was performed on a no-frost refrigerator-freezer, and two tests related to the effect of frost accumulation on energy consumption were performed on a manual-defrost refrigerator. Watt-hour consumption and interior cabinet temperature were recorded for all tests. Increasing the temperature control setting, frequency of door openings, and duration of door openings; the use of an energy-saver switch; and the defrosting process all increased the energy consumption of the refrigerators. Operating the refrigerator near a heat source did not affect energy consumption to the extent of the other tests. Due to inconsistent results, the effect of frost accumulation on energy consumption needs further investigation. / Master of Science

Thesis (MTech. degree in Mechanical Engineering)--Tshwane University of Technology, 2008. / The sun is known to be the main source of energy to earth. It is further more outstanding since it is clean and comes to the earth with no costs. However, mankind does not utilize most of this precious energy effectively. In South Africa, emerging farmers need their agricultural products preserved in storage or in transit. Solar adsorption cooling machines would be of benefit to these farmers as they do not require any additional source of energy and are completely autonomous. This study presents a theoretical and experimental analysis of a solar assisted adsorption fridge, as well as the cost effectiveness when compared with the vapour compression method. The cooling machine was designed, developed and tested. It does not contain any moving part; nor consume any mechanical energy. The results show that the refrigerator can chill 25 litres of water from 35 to 5 °C per day. Vegetables and fruits with preservation temperatures in the range 4 -10 °C are within the scope of the present system. The best useful cooling obtained was 1785 kJ per day, and the best coefficient of performance was 0.058.

The performance of regenerative miniature refrigerators is governed by heat transfer and pressure drop losses, particularly in the regenerator. Steady flow experiments have been performed on various regenerator matrices at cryogenic temperatures and heat transfer from helium gas to the matrix, and pressure drop across the matrix have been determined. These data have been found to be in reasonable agreement with data obtained by other workers using transient flow techniques. In order to determine the applicability of such data to the performance of a cooling engine, experimental methods have been developed to measure the performance and losses in a working Stirling-cycle miniature refrigerator. These techniques have led to the analysis of pressure drop and shuttle heat transfer losses, regenerator efficiency, and to the measurement of other losses in the refrigerator. An energy balance is performed on the machine. These novel techniques, which allow the factors determining poor performance of a working refrigerator to be measured in situ, may be applied profitably to other cyclic machines.

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