【摘要】 为研究Al2O3-HITEC熔盐基纳米流体在恒热流加热管内流动换热特性,采用计算流体力学的研究方法,利用单相流热扩散模型进行了数值模拟。分析了不同质量分数的纳米颗粒对熔盐换热性能的影响,并从流体热物性的角度探讨了换热性能改变的原因。对比结果说明热扩散模型可以用于模拟熔盐基纳米流体管内流动换热。模拟结果表明:与纯熔盐管内温度分布相比,采用纳米流体降低了管内温度,且质量分数为0.063%时温度降低最明显; 4个截面处的温度分布表明在壁面热流的作用下,熔盐和熔盐基纳米流体的温度沿径向升高,而熔盐基纳米流体的温度比纯熔盐低,说明纳米流体吸收和带走了更多的能量;与纯熔盐相比,熔盐基纳米流体的换热性能提高了,证明了添加纳米颗粒具有强化熔盐换热的效果,但强化效果并非随纳米颗粒的浓度增大而线性变化,而是0.063%(质量分数)的纳米流体换热强化程度最大,其在充分发展区换热系数比纯熔盐提高了6.5%。最后通过分析熔盐与熔盐基纳米流体物性变化,发现了比热容的剧烈变化是导致换热性能变化的主要原因。更多还原

【Abstract】 To study the flow heat transfer characteristics of Al2 O3-HITEC molten salt-based nanofluids in heating tubes with constant heat flux,a computational fluid dynamics( CFD) simulation was carried out with the singlephase thermal dispersion model. The effects of nanoparticle additions with different mass fractions on the heat transfer performance of molten salt were analyzed,and the heat transfer performance variations were discussed from the respect of the thermal physical properties of the fluid. Comparisons of results show that the thermal dispersion model can be used to simulate the heat transfer performance of molten salt-based nanofluids. Simulations show that the temperature inside the tube with various nanofluids is lower than that with pure molten salt,and the temperature drop is the most obvious with the particle concentration of 0. 063%. The temperature distributions at the four sections show that under the wall heat flux boundary,the temperature of molten salt with or without nanoparticles increases radially,while the temperature of molten salt-based nanofluids is lower than that of the pure molten salt,indicating nanofluids absorb and take away more heat energy. Moreover,compared with that of pure molten salt,the heat transfer performance of molten salt-based nanofluids increases,proving that the nanoparticle additions can improve the heat transfer performance of molten salt. However,the improvement is not proportional to the increase of nanoparticle concentration. Instead,the nanofluids with a mass fraction of 0. 063% show the greatest heat transfer enhancement,and the heat transfer coefficient in the fully developed region is 6. 5% higher than that of pure molten salt. Finally,the drastic change of specific heat capacity is found playing a key role in the change of heat transfer performance through analyzing the physical properties of molten salt and molten salt-based nanofluids.更多还原