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IEEE T. Instrumentation and Measurement. 01/2011; 60:496-506.
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ABSTRACT: This paper deals with the design of an active heat-sink antenna for radio-frequency transmitter. The antenna achieves electromagnetic and thermal functions by offering a suitable radiating pattern for transmission as high efficiency to remove the dissipated power within the transmitter by heat exchange to the surrounding medium. A test transmitter has been performed by combining a 2 GHz MESFET power amplifier in a conductor-backed coplanar wave-guide with a wire-fed patch heat-sink antenna connected to the ground plane. The active heat-sink antenna has been investigated by measurement and simulation. As expected, it was found that the antenna exhibits desirable electromagnetic performance as achieving an efficient thermal control by offering suitable operating temperature. A heat spreader connecting the transistor to the antenna, was especially developed to cause any significant influence on transmitter performance. The amplifier can deliver an output power as high as 5 W under natural convection with air at room temperature and atmospheric pressure. According to the temperature and direction of the antenna, thermal resistance of the transmitter was found between 6 and 8 K.W <sup>-1</sup>. The transmitter can thus operate over a wide temperature range without any additional cooling device.
IEEE Transactions on Advanced Packaging 03/2010; · 1.12 Impact Factor
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ABSTRACT: Results concerning a model of vapour compression refrigeration system using R410A, a binary HFC blend, and designed to take into account the effects of the oil rejected by the compressor, are presented. These effects are negligible when the lubricant does not exceed 0.5% of the total refrigerant weight; above this value, the performances of the system decrease significantly.
International Journal of Refrigeration.
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ABSTRACT: The electrophoretic deposition (EPD) of silica nanoparticles was performed to prepare consolidated thermal insulating material. Optimal conditions were found considering the loading contents, the suspension medium, and the electric field intensity. The density and thermal conductivity were changed by applying a mechanical pressure before drying of the gel. Density ranged from 120 to 500 kg m−3 with an average porosity comprised between 0.78 and 0.95. According to the porosity, the average pores size of compressed materials was between 7 and 20 nm. Such materials exhibit a thermal conductivity as low as 0.020 W m−1 K−1 at room temperature and 1 atm pressure. Thermal conductivity ranged from 0.020 to 0.045 W m−1 K−1. Minimal conductivity exists for a certain distance between particles. Boundary resistance between adjacent particles was obtained as function of the porosity and its change interpreted as ones of conductive paths though air molecules and across direct solid–solid exchange between particles.
Materials Science and Engineering: B. 137:225-231.
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ABSTRACT: The consequences of the oil rejected by the compressor of a vapour-compression refrigeration system on the operation of the evaporator and condenser are analysed. The modelled prototype uses the mixture of HFC R410A and a synthetic polyolester (POE) oil. The rise of the amount of lubricant circulating in the system leads to a progressive change in the behaviour of the mixture of refrigerant and oil that, for the higher oil mass fraction, evolves like a zeotropic mixture. One also observes that the presence of lubricant is generally associated with a fall of the performances of the heat exchangers, except however in the evaporator where an optimum is observed when the quantity of oil is equal to 0.1% of the total mass of the mixture. Some conclusions are drawn about the choice of correlations for the calculation of the refrigerant side heat transfer coefficient in a plate evaporator.
International Journal of Refrigeration.
