中文摘要：

为了减小瞬态热线法测量纳米流体导热系数时易受电磁干扰和自然对流等因素的影响,更好地探究新型换热工质的强化传热机理,研制了3ω法实验台,采用锁相放大器测得交流加热铂丝的3倍频电压响应,拟合算出待测液体的导热系数。先通过对常规液体蒸馏水、乙二醇以及酒精溶液的测量,验证了实验台的精度和可靠性。然后采用两步法合成了稳定性较高的多壁纳米碳管悬浮液,测得其各体积分数和各温度下的导热系数。实验结果表明,3ω法具有较好的电磁兼容性,测量时温升不超过0.5K,可以有效地减小对流传热和辐射传热的影响,且可以通过1ω电压来判断纳米流体的稳定性;纳米碳管悬浮液的导热系数比基液和Ham ilton-Crosser预测值明显提高,并且分别随纳米碳管含量的增加和温度升高而加大。

英文摘要：

In order to restrain the electromagnetic disturb and natural convection in thermal conductivity measurement of nanofluids using the transient hot wire method and explore the enhanced heat transfer mechanism of new cooling mediums, 3ω technique is introduced to measure the thermal conductivity of liquids with the third harmonic voltage response of an ac heating platinum wire. Firstly the setup is approved of high reliability and precision by testing the conventional liquids such as distilled water, glycol and alcohol solutions, then the steady muhiwalled carbon nanotube suspensions are synthesized by two step method, and the thermal conductivities of them are centrations and temperatures. The result shows that, 3ω measured by 3ω method at different volume con- method represents good electromagnetic compatibility and the temperature rise is not beyond 0.5K during the measurement, which reduce the convective and radiant influences. In addition the stability of nanofluids could be estimated by 1ω voltage. The thermal conductivities of nanotube suspensions are enhanced remarkably and much higer than the Hamilton -Crosser＇s predictions, and improve with the increasing of concentration and temperature.