Abstract
AbstractThe heat pipe is a passive cooling device that transfers heat from a hot source to a heat sink using fluids as a working medium. Working medium evaporation and condensation are key factors for designing an efficient heat pipe. Many researchers highlight nanofluids, a mixture of base fluid and nanoparticles, as a new working medium for more efficient heat pipes. The present research aimed to investigate heat pipe long-term performance using water-based nanofluids as working medium. Nanofluids with 1 and 3 vol% Al2O3 of 20–70 nm particle diameter in water were prepared and characterized. It has been seen in our previous study that the heat pipe performance is enhanced by an average of 26%; however, this enhancement was not sustained over long use and raised a concern about the long-life homogeneity of the nanofluid due to the liquid evaporation. Therefore, we investigated used nanofluid characteristics to determine whether it stays suspended in the base fluid as dispersed particles, or it agglomerat...
Highlights
Background and introductionHeat pipe is a passive heat transfer device that works based on working medium phase change to increase the device thermal conductivity compared to solids
Water-gold nanofluids showed a significant reduction in the heat pipe (HP) thermal resistance as investigated by Tsai et al (2004). 50–80% reduction in the thermal resistance is reported by Zhou (2004), using particle sizes of 10 and 35 nm in water-copper nanofluids in a grooved HP evaporator
Do the particles stick to a given HP wall surface? Do particles agglomerate and/or aggregate due to base-liquid evaporation? Do particles block the porous medium and affect the wick capillarity? To our knowledge, a gap of relevant studies explains the transient changes occurring between the heat pipe and nanofluid need to be fulfilled
Summary
As it can be seen from the plots, the temperature versus time curve slope T∕ t is elevated by introducing nanoparticles, and more elevation is shown by increasing nanoparticles’ concentration These results indicate the enhancement in the boiling heat transfer coefficient as previously observed by Wen and Ding (2005). The first subsection of the experimental results will explain the heat pipe performance versus the evaporator temperature over one year of operation, and the second subsection will present and discuss the ANOVA SEM microscopy imaging for the nanoparticles structure in the heat pipe porous medium
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