Abstract:

Heat transfer characteristics of multi-walled carbon nanotubes (MWCNT) -water / ethylene glycol nanofluids flowing in automotive radiators were experimentally investigated. Nanofluids with five different MWCNT particle volume fraction (0.05%, 0.1%, 0.15%, 0.3% and 0.5%) have been prepared in an 80%/20% solution of water/ethylene glycol. By studying the influence of ultrasonic oscillation time on the stability of nanofluids, it is concluded that the stability of nanofluids is better when the oscillation time is 1h. Two kinds of nanofluids with the volume fraction of 0.15% were respectively added with sodium dodecyl benzene sulfonate (SDBS) and cetyltrimethylammonium chloride (CTAC) as dispersants for stability experiments. The visual and transmissivity methods were used to evaluate the stability of the nanofluids, the better type and amount of dispersant were selected, and the stability of the three nanofluids was evaluated. The results showed that when the addition amount of CTAC was 0.05%, and the addition of SDBS was 0.1%, the dispersion effect of nanofluid was better, and the dispersion effect of CTAC was better than SDBS. The volume flow rate of hot fluids ranges from 2L/min up to 6L/min and the inlet temperature varies from 45℃ to 65℃, respectively. In this paper, the effects of nanofluid volume fraction, inlet temperature and flow rate on the heat transfer enhancement of nanofluids were analyzed using two different types of designs——The one-factor experiment design and the orthogonal experiment design. The results demonstrate that nanofluids clearly enhance the heat transfer rate compared to the base fluid and in the best conditions (0.5%, 6L/min, 65℃) of the experiment range, the heat transfer rate can be increased by 35.24%. Using the entropy method, the weights of the nanoparticles to heat transfer, pressure drop and effective pumping power are 0.626, 0.035, 0.340, respectively. Based on the multi-index comprehensive evaluation method, the adverse effects of pressure drop and pumping power are negligible in the appropriate concentration range compared with the increase of the heat transfer coefficient of the nanofluids.

Key words: nanofluid, car radiator, stability, heat transfer characteristics

摘要：

实验研究了多壁碳纳米管（MWCNT）-水/乙二醇纳米流体在汽车散热器中的传热特性。在80%/20%的水/乙二醇基液中制备了5种不同体积分数（0.05%，0.1%，0.15%，0.3%和0.5%）的MWCNT纳米流体，通过研究超声波振荡时间对纳米流体稳定性的影响得出，超声波的振荡时间为1h时，纳米流体的稳定性较为良好。将体积分数为0.15%的纳米流体分别添加十二烷基苯磺酸钠（SDBS）和十六烷基三甲基氯化铵（CTAC）作为分散剂进行稳定性实验，分别采用目测法和透射比法来评价纳米流体的稳定性，选出分散效果较好的分散剂种类和添加量并评价了两种纳米流体的稳定性，结果表明：CTAC的添加量为质量分数0.05%、SDBS的添加量为0.1%时，纳米流体的分散效果较好，并且CTAC的分散效果优于SDBS。分别使用单因素实验设计和正交实验设计对不同浓度的纳米流体在不同流速、温度下的传热特性进行分析，纳米流体的体积流量为2～6L/min，入口温度为45～65℃。结果表明，与基液相比，纳米流体的传热速率有了明显的提高，在本实验的最佳工况下（体积分数0.5％，6L/min，65℃），传热速率可提升35.24%。使用熵值法计算出纳米流体的传热速率、压降和有效泵功的权重分别为0.626、0.035、0.340。基于多指标综合评价方法得出，与纳米流体的传热速率增加相比，纳米流体浓度对压降和有效泵功的不利影响可以忽略不计。

关键词: 纳米流体, 汽车散热器, 稳定性, 传热特性