A direct contact liquid-liquid heat exchanger for solar heated and cooled buildings
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Solar gain
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Direct-contact heat exchange (DCHX) has several advantages over conventional finned-tube heat exchangers. Without the intervening tube wall, thermal resistance is lower and fouling of the heat-exchange surface is not a problem. Intimate mixing of the two fluid streams can produce very high rates of heat transfer. The heat exchanger design can be simpler, require less construction material, and provide more flexibility in choice of materials.
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Heat transfer characteristics of water/cryogenic hydrogen heat exchanger for nuclear rocket reactor
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Heat pumps (HPs) allow for providing heat without direct combustion, in both civil and industrial applications. They are very efficient systems that, by exploiting electrical energy, greatly reduce local environmental pollution and CO2 global emissions. The fact that electricity is a partially renewable resource and because the coefficient of performance (COP) can be as high as four or more, means that HPs can be nearly carbon neutral for a full sustainable future. The proper selection of the heat source and the correct design of the heat exchangers is crucial for attaining high HP efficiencies. Heat exchangers (also in terms of HP control strategies) are hence one of the main elements of HPs, and improving their performance enhances the effectiveness of the whole system. Both the heat transfer and pressure drop have to be taken into account for the correct sizing, especially in the case of mini- and micro-geometries, for which traditional models and correlations can not be applied. New models and measurements are required for best HPs system design, including optimization strategies for energy exploitation, temperature control, and mechanical reliability. Thus, a multidisciplinary approach of the analysis is requested and become the future challenge.
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In order to solve the engineering problems of a large number of low-quality flue gas waste heat recovery and acid dew point corrosion leading to failure of the device easily, a new kind of heat transfer component named a compound hollow heat pipe was proposed. Its structure and working principle was introduced. Its internal heat transfer mechanism is analyzed, and its start-up characteristics, isothermal temperature performance and heat transfer properties were studied. The results show that compound hollow heat pipe can start and work fast while the outer tube wall temperature is 30 °C within 2 min heating time. And in the natural air convection cooling conditions, it has good isothermal characteristics. The heat transfer coefficient of the compound hollow heat pipe increases with the cooling water Reynolds number. When the heating steam temperature is below 125 °C and the cooling water Reynolds number is 6650, the heat transfer coefficient of the compound hollow heat pipe is 1350 W.m -2 .°C -1 . Experimental results of the compound hollow heat pipe provide the basis of engineering applications for heat exchanger.
Isothermal process
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Evaporative cooler
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