Flow and heat transfer characteristics of supercritical nitrogen in micro-channel with different cavity structures

doi:10.16085/j.issn.1000-6613.2022-2246

Abstract

Abstract:

In order to realize the efficient design of the surface structure of the micro-channel heat exchanger, the effects of cavity shapes (straight micro-channel, circular, rectangular and trapezoidal) and ovality on the flow and heat transfer performance of micro-channel were studied by means of numerical simulation and experiment, using supercritical nitrogen as the fluid medium, the mechanism of fluid efficient and low resistance heat transfer enhancement was revealed. The results showed that compared with the straight micro-channel, the entrance distance required for the SCN₂velocity on the axis of the circular cavity micro-channel to reach a stable value was shorter, which was due to the fact that the cavity can promote the fluid flow/thermal boundary layer to be in the alternate state of destruction and reconstruction all the time. The shape of the fluid vortex in the circular cavity was consistent with the cavity geometry, and its flow resistance and heat transfer performance were optimal, followed by trapezoidal cavity micro-channel and rectangular cavity micro-channel. With the increase of ovality, the overall performance of cavity micro-channel increased firstly and then decreased. When the ovality was 1, the overall performance was optimal. The research results in this paper are of great significance for improving the design and manufacturing capability of micro-channel heat exchangers.

Key words: micro-channel, supercritical nitrogen, cavity, structure, flow and heat transfer

摘要：

为了实现微通道换热器表面结构的高效设计，本文将数值模拟和实验手段相结合，以超临界氮气（supercritical nitrogen，SCN₂）为流体工质，研究了不同凹穴形状（直微通道、圆形、矩形和梯形）和椭圆度对微通道流动与传热特性的影响，揭示了SCN₂高效低阻强化换热机理。结果表明，相比于直微通道，圆形凹穴微通道中轴线上SCN₂速度达到稳定值所需入口段距离更短，这是由于凹穴能够促使流体流动/热边界层一直处于破坏与重建的交替状态。圆形凹穴内流体旋涡形状与凹穴几何结构保持一致，其流阻特性和换热性能最优，梯形凹穴微通道次之，矩形凹穴微通道最差。微通道综合性能随着凹穴椭圆度增加呈先升高后降低变化趋势，当椭圆度为1时，其综合性能最优。研究结果对提高微通道换热器设计制造能力具有重要的意义。

关键词: 微通道, 超临界氮气, 凹穴, 结构, 流动与传热

CLC Number:

TE088

HAN Changliang, HUANG Yiyan, XU Jianquan. Flow and heat transfer characteristics of supercritical nitrogen in micro-channel with different cavity structures[J]. Chemical Industry and Engineering Progress, 2023, 42(11): 5592-5601.

韩昌亮, 黄峄演, 徐建全. 不同结构凹穴微通道内超临界氮气流动与传热特性[J]. 化工进展, 2023, 42(11): 5592-5601.

Figures/Tables 15

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参数	数值
计算域总长（L）/mm	540
凹穴中心间距（L₁）/mm	78
每一侧凹穴个数（N）	6
入口截面高度（H）/mm	1
入口截面宽度（W）/mm	3
圆形凹穴半径（R）/mm	1.5
矩形凹穴宽度（W₁）/mm	3
矩形凹穴高度（W₂）/mm	3
梯形凹穴宽度（W₃）/mm	1.5
梯形凹穴高度（W₄）/mm	1.5

参数	数值
计算域总长（L）/mm	540
凹穴中心间距（L₁）/mm	78
每一侧凹穴个数（N）	6
入口截面高度（H）/mm	1
入口截面宽度（W）/mm	3
圆形凹穴半径（R）/mm	1.5
矩形凹穴宽度（W₁）/mm	3
矩形凹穴高度（W₂）/mm	3
梯形凹穴宽度（W₃）/mm	1.5
梯形凹穴高度（W₄）/mm	1.5

位置	边界类型	参数设置
微通道入口	质量流量入口边界	G_in=650~950kg/(m²·s)； T_in=113K
微通道出口	压力出口边界	P_out=7.5MPa
微通道左/右壁面	对称面边界	—
固体壁面与SCN₂交界面	无滑移边界	u=v=w=0
微通道上/下壁面	恒定热流密度边界	q=120kW/m²；δ=2mm

位置	边界类型	参数设置
微通道入口	质量流量入口边界	G_in=650~950kg/(m²·s)； T_in=113K
微通道出口	压力出口边界	P_out=7.5MPa
微通道左/右壁面	对称面边界	—
固体壁面与SCN₂交界面	无滑移边界	u=v=w=0
微通道上/下壁面	恒定热流密度边界	q=120kW/m²；δ=2mm

序号	网格数目	出口温度/K	出口速度/m·s^-1	最小单元尺寸/mm
1	2044992	196.05	4.19	0.2
2	2780601	189.57	3.52	0.17
3	3729528	177.78	3.05	0.15
4	4224407	177.62	3.02	0.14
5	5376328	177.51	3.00	0.13