A Study On Heat Transfer Characteristics In Pool Boiling Of Nanofluids

With the rapid development of the modern industry,the issue of improving the cooling efficiency of high heat flux heat sink equipments has been of great significance.The urgent need to resolve this problem has also promoted the development of the nanofluid boiling heat treasfer.Many domestic and foreign scholars have been doing the research on this subject,and considerable amount of the achievements on this field have been applied to engineering practice.This thesis contains the research of the pool boiling heat transfer characteristics of?-Al2O3/water nanofluid under different gravity conditions.In this paper,an preparation stage and an experimental system of pool boiling have been set up successfully,and the reliability and repeatability of the experiment system are verified.The heat transfer characteristics of pool boiling on platinum wires with OD of 0.03 mm and 0.05 mm under hypergravity environment are experimentally investigated.The main purpose of the study is to obtain the pool boiling heat transfer characteristics and the influences of nanoparticle concentration and SDBS concentration,platinum wire diameter and overload on it.The experimental conditions are overload range of 0-3.0 g,the pressure of 1 bar,nanoparticles concentration of 0-0.01 wt %,SDBS concentration of 0-0.5 wt %.According to the analysis of experimental data obtained under normal gravity,the effects of nanoparticles concentration and the concentration of dispersant and platinum wire diameter on nanofluid pool boiling heat transfer characteristics are studied.The experimental results show that boiling heat transfer coefficient increases firstly and then decreases with the increase of concentration of nanoparticles,while the CHF increases with increasing concentration all along;the SDBS urges the formation of sintering layer on the heating surface to deteriorate CHF,and deterioration degree increases with the increase of the concentration;in low heat flux density,the heat transfer coefficien of small size 0.03 mm platinum is higher than 0.05 mm platinum,whlile on the contrary at high heat flux,which is associated with the disturbance characteristics of bubbles.The boiling heat transfer of nanofluids under overload experimental results show that overload has certain influence on heat transfer characteristics of nanofluids.The heat transfer properties of different concentrations of nanofluid under the same hypergravity are similar to that of normal gravity,but hypergravity reduces the best concentration of the nanofluid;the transfermation laws of the heat transfer coefficient and CHF with the increasing hypergravity between different concentration nanofluids have inconsistent conclusions,which needs futher tests.The results of verification tests show that the heating formation of the porous sintered structure on the heating surface is the main mechanism for nanofluid heat transfer.