火灾环境下含炸药结构传热问题的数值模拟

为了解火灾环境下含炸药结构的热响应行为，针对其涉及的主要传热学问题，建立了池火灾火焰温升数值模型，碳/酚醛烧蚀层高温热解吸热数值模型，空气夹层复合传热数值模型，以及炸药受热分解放热数值模型。用所建数值模型，计算并获得了含炸药结构在不同温升条件下（恒定值1073 K、1273 K 及本研究所提的火焰实测温升曲线）、不同火焰辐射率（0．1～0．9）和不同空气夹层间壳体表面辐射率（0．1～0．9）下的温度响应和热点火延滞时间。结果表明：火烧30 min 情况下，火焰温度为1273 K 时，内部炸药在28．92 min 已经发生热点火现象。火焰温度为1073 K 和实测温升曲线时，内部炸药最高温度分别为448 K 和535 K。火焰辐射率从0．9降低到0．1时，内部炸药最高温度由535．4 K 降低到344．6 K，热点火延滞时间由1917 s 增加到3520 s。空气夹层间壳体表面辐射率由0．9降低到0．1时，内部炸药最高温度由535．4 K 降低到329．0 K，热点火延滞时间由1917 s 增加到3739 s。

Simulation of alumina dissolution and temperature response under different feeding quantities in aluminum reduction cell

In the feeding process of aluminum electrolytic, feeding quantity of alumina affects eventually dissolved quantity at the end of a feeding cycle. Based on the OpenFOAM platform, dissolution model coupled with heat and mass transfer was established. Applying the Rosin-Rammler function, alumina particle size distribution under different feeding quantities was obtained. The temperature response of electrolyte after feeding was included and calculated, and the dissolution processes of alumina with different feeding quantities (0.6, 0.8, 1.0, 1.2, 1.4, 1.6 kg) after feeding were simulated in 300 kA aluminum reduction cell. The results show that with the increase of feeding quantity, accumulated mass fraction of dissolved alumina decreases, and the time required for the rapid dissolution stage extends. When the feeding quantity is 0.6 kg and 1.2 kg, it takes the shortest time for the electrolyte temperature dropping before rebounding back. With the increase of feeding quantity, the dissolution rate in the rapid dissolution stage increases at first and then decreases gradually. The most suitable feeding quantity is 1.2 kg. The fitting equation of alumina dissolution curve under different feeding quantities is obtained, which can be used to evaluate the alumina dissolution and guide the feeding quantity and feeding cycle.

Numerical simulation for thermal response test performance in closed-loop vertical ground heat exchanger

In this study, a series of numerical analyses was performed in order to evaluate the performance of full-scale closed-loop vertical ground heat exchangers constructed in Wonju, South Korea. The circulating HDPE pipe, borehole and surrounding ground formation were modeled using FLUENT, a finite-volume method (FVM) program, for analyzing the heat transfer process of the ground heat exchanger system. Two user-defined functions (UDFs) accounting for the difference in the temperature of the circulating inflow and outflow fluid and the variation of ground temperature with depth were adopted in the FLUENT modeling. The thermal conductivities of grouts (cement vs. bentonite) measured in laboratory were used as input values in the numerical analyses to compare the thermal efficiency of the cement and bentonite grouts used for installing the closed-loop vertical ground heat exchanger. A series of numerical analyses was carried out to simulate in-situ thermal response tests performed in the construction site. From the comparison between the in-situ thermal response test results and numerical simulations, the average thermal conductivity of the ground formation in the construction site is back-calculated as approximately 4 W/mK. This value can be used in evaluating the long-term performance of the closed-loop vertical ground heat ex changer.