铝制错列锯齿型板翅式换热器内低温氦气流动传热特性研究

Study on the flow and heat transfer characteristics of low-temperaturehelium gas in aluminum plate-fin heat exchangers

板翅式换热器具有传热系数高、适应性强、结构紧凑等特点,在大规模氦液化/制冷系统中得到广泛应用.文中通过数值研究了低温氦气流经锯齿型翅片通道的热工水力特性,通过对比实验获得了翅片型号65JC1403-03在室温(300 K)和液氮温区(77 K)下翅片表面低温氦气的传热摩擦性能数据,验证了文中数值模拟结果的可靠性.为进一步获得不同低温条件和翅片规格下的性能关联式,基于L25(54)正交设计展开了诸多数值仿真,系统研究了不同温区下的氦气流经不同规格锯齿型翅片表面的热工水力特性,提出了考虑氦气和铝制翅片热物性变化的传热和摩擦关联式.由于锯齿型翅片表面性能不仅受低温氦气热物性、金属热导率的影响,而且还受到低温运行条件的影响,因此在传热系数j和摩擦系数f关联式拟合过程中引入了无量纲Pr数和翅片效率ηf,以扩展低温下关联式的预测能力.结果表明与仿真数据相比,该预测关联式具有较高的预测精度,j和f预测值的均方根误差分别为10.49%和12.77%,所提出的关联式能够精确预测低温氦气在锯齿型翅片通道内的流动传热性能.

The plate-fin heat exchangers are widely used in large-scale helium liquefaction/refrigeration systems due to their high heat transfer coefficient, adaptability and compact structure. This paper firstly investigates numerically the thermodynamic characteristics of cryogenic helium flowing through the serrated fin channels, and then obtains comparative experimental data on the heat transfer friction performance of cryogenic helium on the fin surface for fin model 65 JC1403-03 at room temperature(300 K) and liquid nitrogen temperature region(77 K) to verify the reliability of the numerical simulation results in this paper. In order to obtain further performance correlations for different cryogenic conditions and fin sizes, numerous numerical simulations based on the L25(54) orthogonal design have been carried out to systematically investigate the thermal-hydraulic properties of helium flowing over the surface of serrated fins of different sizes at different temperature zones, and to propose heat transfer and friction correlations that take into account changes in the thermal properties of helium and aluminium fins. As the surface properties of the serrated fins are influenced not only by the thermal properties of the helium at low temperatures and the thermal conductivity of the metal, but also by the low temperature operating conditions, the dimensionless Pr number and the fin efficiency ηare introduced into the fitting of the correlation between the heat transfer coefficient j and the friction coefficient f to extend the predictive capability of the correlation at low temperatures. The results show that the prediction correlation has a high prediction accuracy compared to the simulation data, with the root mean square error of 10.49% for j and 12.77% for f. The correlation proposed in this paper is able to accurately predict the heat transfer performance of cryogenic helium flow in a serrated fin channel.