2,454 research outputs found
Experimental Measurements Of Air Forced Convection Through Copper Foams
No full textThis paper aims at investigating the air heat transfer and fluid flow through open-cells copper foam samples with different number of pores per unit of length (PPI) with constant porosity (ε=0.93) and foam core height of 40 mm. The experimental heat transfer coefficient and pressure drop measurements were carried out during air forced convection through electrically heated copper foams; the data points are collected in a dedicated test rig. The experimental measurements permit to understand the effects of the pore density on the heat transfer and fluid flow performance of the foams. Present data relative to copper foam samples are compared against present authors experimental measurements for 40 mm high aluminum foams at the same operative test conditions. The paper presents experimental heat transfer coefficients, pressure gradients, permeability, inertia and drag coefficients; moreover, it also reports two meaningful parameters: the normalized mean wall temperature and the pumping power per area density that permit to compare different enhanced surfaces, which can be considered suitable for electronic thermal management
Circulating lubricant and its effects on the energetic efficiency of refrigeration circuits: state of the art and perspectives
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Sustainability with prospective refrigerants: a thermodynamic perspective for systems design
No full textEffects of lubricant on carbon dioxide heat transfer in transcritical refrigerating cycles
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Carbon dioxide as a natural refrigerant
No full textIn the beginnings of mechanical refrigeration, at the end of the nineteenth century, carbon dioxide was one of the first refrigerants to be used in compression-type refrigerating machines, later gaining widespread application mainly onboard refrigerated ships, but common in other sectors of refrigeration as well. It was only immediately after World War II that CO2 was rapidly eclipsed as a refrigerant, due to the advent of the synthesised halogenated working fluids, addressed as safe and ideal refrigerants at that time. Because of the stratospheric Ozone depletion environmental issue, CFC and HCFC working fluids are now in the process of being phased out of use under the Montreal Protocol. The Global Warming environmental issue casts concern over the use of the new HFC fluids as substitute refrigerants, because of their high GWP values, which make them subject to regulations under the Kyoto Protocol. In this mixed situation, CO2 is being revisited as a fully environmentally friendly and safe refrigerant. An intense research activity on its prospective applications is underway in many research establishments in Europe, Japan and North America, and important results have already been reached in exploiting the peculiar characteristics of this high-pressure fluid operated with a transcritical cycle. In some applications CO2 systems have already been commercialised; this applies to heat pump water heaters, as a brine in indirect systems and in the low temperature stage of cascade systems. The paper critically analyses the prospects for the future return of CO2 as a working fluid, or sometimes as a brine with change of phase, in important application areas. These include air conditioning and heat pump systems in the residential and commercial sectors, commercial and transport refrigeration and mobile air conditioning
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