Thesis (M.S.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains xiv, 152 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 133-136).

Thesis (M.S.)--University of Wisconsin--Madison, 1983. / Typescript. Title from title screen (viewed Aug. 14, 2007). Includes bibliographical references (leaves 152-154). Online version of the print original.

Made available in DSpace on 2014-06-11T19:30:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-07-07Bitstream added on 2014-06-13T20:39:48Z : No. of bitstreams: 1 moreira_rs_me_guara.pdf: 1015481 bytes, checksum: 6083704ea441f414182fe9b27a70777b (MD5) / Eletrobras / Neste estudo são apresentados os resultados de um trabalho realizado em uma bancada de testes, onde se constatou a diferença de potência elétrica de acionamento e do coeficiente de performance no funcionamento de dois diferentes tipos de compressores: um hermético a pistão e outro rotativo do tipo scroll, operando com inversor de frequência. No estudo variou-se a vazão do fluido refrigerante, e consequentemente o efeito frigorífico, por dois procedimentos distintos: restrição da passagem do refrigerante através de uma válvula de estrangulamento, mantendo-se a rotação do compressor a pistão constante, e por meio de variação de rotação do compressor scroll com aplicação de um inversor de frequência, mantendo-se a válvula de estrangulamento em uma posição fixa. Observou-se também a influência do inversor de frequência no controle da vazão de ar do sistema através de um conjunto motor-ventilador axial. Esse controle ora era realizado por uma válvula de controle “DAMPER”, ora por meio da rotação do motor através do emprego do inversor de frequência, com o qual foi possível economizar até 87 % de potência elétrica requerida pelo ventilador. O estudo ainda demonstrou que existe uma faixa de trabalho na qual o inversor de frequência é capaz de economizar até 56 % da potência exigida pelo compressor para uma mesma carga térmica em relação ao compressor desprovido do inversor de frequência, no qual o controle da vazão de refrigerante ocorre através da válvula de estrangulamento. Conclui-se que a utilização do inversor de frequência, em sistemas onde a carga térmica requerida (efeito refrigerante) varia, pode resultar em uma significante economia de energia. / This study presents the results of a work carried out on a test bench, where it was verified the difference of the electrical startup power and the performance coefficient of two different types of compressors, namely: a hermetic piston type compressor and a rotating scroll type compressor operating with a frequency inverter. In this study, the refrigerant flow rate was varied and, consequently, the cooling capacity obtained by two distinct procedures: one, by the restriction of the refrigerating flow while maintaining rotation of the piston compressor constant and the other, by varying the scroll compressor rotation through a frequency inverter while keeping the restrictive valve in a fixed position. Is showed also, the influence of frequency inverter in order to control the air flow rate system by employed with fan engine and afterwards compare with method which air flow rate is controlled by DAMPER valve, where until 87 % to fan actuation power was saved. Besides, the study demonstrated that there is a range where the frequency inverter is capable of savings up to 56% of the compressor demanding power for a defined cooling capacity in relation to a compressor without the frequency inverter, in which the refrigerating flow rate control occurs through the restrictive valve. Therefore, it is conclusive that the use of frequency inverters in systems where the required cooling capacity varies, it can result in an appreciated economy of energy.

M.Ing. / A steady-state model was developed to predict the performance of the highpressure side' of vapour-compression air-conditioning systems. The model consists of two segments; the compressor model and condenser model. The compressor model consists of a single empirical equation, for reciprocating compressors, operating with R-22, and having a cooling capacity from 2.6 to 3.5 kW. An important advantage of the approach is that the compressor performance indexes are based on operating conditions. The condenser model displays an exact method to determine physical dimensions of heat exchangers, and a simple, accurate manner to calculate the heat transfer variables. The correctness of the condensing temperature is obtained by an iterative procedure, using terms from both the compressor and condenser studies. The feasibility of the proposed model is demonstrated via a comparison with experimental data and a simulation study. Results indicate a good correlation between the mathematical model and its counterparts.

The air conditioning system in a car is, in addition to the heating system, installed to increase the comfort in the passenger compartment. Comfort is not the only reason for automotive air conditioning systems, as road safety also improves with the comfort of the driver, as a pleasant environment reduces driver fatigue. The rising environmental problems and, hence, resulting stringent legislation are forcing the automobile industry to develop cars with ever decreasing fuel consumptions. The question of better fuel consumption and energy utilisation does not stop with the engine and aerodynamics, but is required of the air-conditioning system as well. Thus, incessantly innovative technologies are developed to decrease the energy required by the air-conditioning systems. The interaction of the refrigerant cycle components and the rapidly changing operating conditions of the car (speed, revolutions per minute, etc.) places extensive demands on the control system. In addition, the air-conditioning system is also designed for high ambient temperatures (cool down), but is mostly used in fairly moderate conditions. This operation allows for energy saving control strategies such as externally controlled compressors, blower motor control, etc. The experimental comparison of different air-conditioning systems, components or control strategies is very time consuming and extensive, and the use of an air-conditioned wind tunnel is inevitable when experiments need to be done with reproducible ambient conditions.This, combined with the high costs of installation and operation of a wind tunnel is a major problem. Furthermore, the effect of component or control strategy enhancements should be available as soon as possible in the early stages of design. The above considerations have prompted the rapid development of new powerful simulation tools, but in most cases the simulation tools are focused on one specific component or problem only. A more holistic approach would be to combine the calculations of two or more programs. This implies the adaptation of the model to more programs which leads to a lack of transparency. Obviously, the entire development work cannot be done entirely by simulation, especially in the later phases of the development where it would still be necessary to build prototypes to evaluate the done work experimentally. However, in the early stages of development, it would be advantagous to work without expensive prototypes.

M.Ing. / Wet compression versus dry compression in refrigeration cycles working with pure refrigerants or non-azeotropic mixtures is investigated in this paper. In total 34 pure refrigerants as well as 31 non-azeotropic binary mixtures are considered. This resulted in approximately 300 different mixtures being analysed. The pure refrigerants and refrigerant mixtures were analysed for one cooling application, namely that of spatial air conditioning at an evaporating temperature of 7°C, and a condensing temperature of 50°C. The investigation was conducted with cycle analyses calculating performances at different wet and dry compressor inlet values. Use was made of thermodynamic refrigerant properties calculated from a computer database. It was concluded that for both pure and non-azeotropic refrigerants analysed, all those with re-entrant saturation vapour lines produce better cooling COP's when the refrigerant is superheated before entering the compressor. Only a few of the refrigerants with bell-shaped T-s curves consistently produce higher cooling COP's when wet compression is used. However, their cooling capacities decreased while the compressor displacement rates increased. It was concluded that in general dry compression is more favourable than wet compression. From the exceptions that do exist, some manage to produce relatively high COP c 's while retaining competitive cooling capacities. A by-product of this study is that, from the vast amount of refrigerant mixtures analysed, valuable knowledge was gathered regarding refrigerants not commonly used in the applications considered.

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