甲烷跨临界传热恶化影响因素分析

Analysis of Influence Factors for Methane Transcritical Heat Transfer Deterioration

关键词:  再生冷却  数值仿真  甲烷  跨临界  传热恶化

Key words:  Regenerative cooling  Numerical simulation  Methane  Transcritical  Heat transfer deterioration

摘要:

为了研究甲烷在跨临界条件下传热恶化现象的产生机理及影响因素，对非对称加热条件下矩形通道内甲烷的跨临界流动与传热进行了三维数值仿真计算，并就不同出口压力和壁面粗糙度对结果的影响进行了讨论。仿真结果表明，甲烷在通道中由于温度分层，使得其靠近壁面处的拟临界温度附近存在一段区域，其定压比热容处于极大值而热导率处于极小值。二者均会阻碍流体之间的传热，导致传热恶化现象的发生。此外，将出口压力从6MPa提高到10MPa和14MPa，表面平均传热系数分别增大了18.9%和6.5%，壁面平均温度分别降低了22.9%和16.3%。将壁面粗糙度从0μm提高到3.2μm和5μm，表面平均传热系数分别增大了56.3%和92.6%，壁面平均温度分别降低了29.1%和39.3%。这表明，增大出口压力与壁面粗糙度均可以抑制传热恶化，显著降低壁面温度。然而，当出口压力过大时，由于甲烷吸热能力的降低反而会导致冷却效率下降。

Abstract:

In order to study the mechanism and influence factors of the transcritical heat transfer deterioration of methane, the transcritical flow and heat transfer of methane in a rectangular channel under asymmetric heating conditions were simulated numerically in three dimensions, and the effects of different outlet pressures and wall roughness on the results were discussed. The results show that there is a region near the pseudo-critical temperature at the wall where the constant pressure specific heat capacity is at the maximum while the thermal conductivity is at the minimum due to the temperature stratification of methane in the channel. Both of them will hinder the heat transfer between fluids which will lead to the heat transfer deterioration. In addition, when the outlet pressure increases from 6MPa to 10MPa and 14MPa, the average heat transfer coefficient increases by 18.9% and 6.5%, respectively, and the average wall temperature decreases by 22.9% and 16.3%, respectively. When the wall roughness increases from 0μm to 3.2μm and 5μm, the average surface heat transfer coefficient increased by 56.3% and 92.6%, respectively, and the average wall temperature decreased by 29.1% and 39.3%, respectively. This indicates that increasing the outlet pressure and wall roughness can inhibit the heat transfer deterioration and significantly reduce the wall temperature. However, when the outlet pressure is too high, the cooling efficiency will be reduced due to the decrease of methane heat absorption capacity.