Abstract
In this article, water and TiO2-H2O nanofluids are used as heat exchange mediums. The heat transfer and resistance coefficient of corrugated tubes with different corrugation pitches are studied by experimental method. The economy of experimental system is evaluated from the aspects of quantity and quality of energy by thermal and exergy efficiencies respectively. The heat transfer performance of nanofluids in the smooth tube can be enhanced by 2.64–16.9% compared with water under the same working conditions, while the corrugated tubes can improve the heat transfer performance by 4.8–66.3%. When the mass fraction of the nanofluid is 0.5%, the corrugated tubes with different corrugation pitches can increase the heat transfer by 36.3% (P = 6 mm), 40.3% (P = 4 mm) and 44.5% (P = 2 mm) respectively. For thermal efficiency, the results prove that when the Reynolds number is larger than 6000, the comprehensive evaluation indexes of corrugated tubes are much larger than that of smooth tube, and the maximum can reach 1.5637. For exergy efficiency, the research results show that the exergy efficiency of the smooth tube is better than that of the corrugated tubes.
Highlights
In order to optimize the heat transfer efficiency of the heat exchanger, the investigations mainly focus on two aspects
The results demonstrated that the thermal conductivity and viscosity of the nanofluids increase with the concentration
When the mass fraction of the nanofluid is 0.5%, the corrugated tubes with different corrugation pitches can increase the heat transfer by 36.3% (P=6mm), 40.3% (P=4mm) and 44.5% (P=2mm) respectively
Summary
In order to optimize the heat transfer efficiency of the heat exchanger, the investigations mainly focus on two aspects. One is to heighten the thermal conductivity of fluid and another is to optimize the surface of heat exchanger. In the aspect of improving the thermal conductivity of fluids, nanofluids, as a new kind working fluid, have been studied by many scholars and applied in many industries, such as natural convection heat transfer [1, 2], forced convection heat transfer [3, 4], solar absorption [5, 6], clean water [7], sunlight harvest and energy storage [8], photo-thermal conversion [9, 10], CPU cooling [11, 12] and so on.
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