R245fa flow boiling heat transfer characteristics in horizontal tube with segmented porous coating

doi:10.11949/0438-1157.20250472

Abstract

Abstract:

A segmented micro-nano porous coating structure was fabricated on the inner wall surface of a stainless-steel heat transfer tube by a combined sintering and electroplating process. Flow boiling heat transfer experiments with R245fa as the working fluid were conducted in a horizontal tube. The experimental conditions were: saturation pressure of 0.6 MPa, mass flux ranging from 200 to 700 kg/(m²·s), heat flux ranging from 5 to 75 kW/m², and inlet vapor quality between 0.01 and 0.9. Experimental results indicate that constructing porous structures with different pore sizes along the tube flow direction can effectively enhance boiling heat transfer by adapting to flow pattern transitions. The enhanced tube exhibited a significant improvement in flow boiling heat transfer performance, with a maximum enhancement of up to 2.71 times compared to a smooth tube. The smaller pore structure at the outlet facilitates the capture of micro-droplets, enhancing their adsorption onto the heat exchange surface. This mechanism ensures efficient liquid replenishment, thereby mitigating the formation of wall dry-out. Flow visualization revealed the presence of three flow patterns during the experiments: stratified flow, annular flow, and dryout.

Key words: two-phase flow, heat transfer, microscale, wettability, flow boiling

摘要：

采用烧结与电镀耦合处理工艺，在不锈钢换热管内壁面制备一层在流向上呈分段式微-纳多孔镀层结构，入口处孔径较大，中间次之，出口处最小。以R245fa为工质进行水平管内流动沸腾换热实验。实验工况为：饱和压力0.6 MPa，质量流速200~700 kg/（m²·s），热通量5~75 kW/m²，实验段入口干度0.01~0.9。实验结果表明：实验管对流动沸腾换热有明显的强化效果，传热系数相较光滑管最大可达2.71倍。入口处较大的孔隙结构不仅具有较低的流动阻力，同时还能够有效地调控流动模式。出口处较小的孔隙结构可以更轻松捕获小液滴，促进小液滴吸附到换热表面，进而对换热面进行液体补给，减缓壁面干涸的形成。流型可视化分析表明实验中出现了三种流型，分别为分层流、环状流和干涸。

关键词: 两相流, 换热, 微尺度, 润湿性, 流动沸腾

CLC Number:

TK 172

Shuang CAO, He LIU, Jiaju GUO, Yi ZHANG, Wenpei LIU, Xuehong WU. R245fa flow boiling heat transfer characteristics in horizontal tube with segmented porous coating[J]. CIESC Journal, 2025, 76(11): 5806-5815.

曹泷, 刘贺, 郭家驹, 张义, 刘文裴, 吴学红. 水平管内分段式多孔镀层R245fa沸腾换热特性[J]. 化工学报, 2025, 76(11): 5806-5815.

Figures/Tables 12

Fig.1 Experimental system: (a) system device diagram; (b) principle diagram

Table 1 Measurement parameters and instrument type

测量参数	选用仪表	量程	精度
预热段进口压力	罗斯蒙特压力变送器	0~1 MPa	±0.1%
实验段进、出口压力	罗斯蒙特压力变送器	0~1 MPa	±0.1%
流体温度	Omega-K型铠装热电偶	0~800℃	±0.5℃
壁面温度	Omega-K型线状热电偶	0~260℃	±0.5℃

Fig.2 Experimental test section: (a) schematic diagram of the structure of the experimental section; (b) schematic diagram of the circumferential arrangement of thermocouples; (c) schematic diagram of segmented particle size

Fig.3 Microstructure characterization: (a) three-gradient surface; (b) 300 μm copper powder porous surface; (c) 150 μm copper powder porous surface; (d) 100 μm copper powder porous surface

Fig.4 Characterization of wettability and capillary force of sintered/electroplated layers: (a) wettability characterization; (b) capillary force characteristic diagram

Fig.5 Flow distribution

Fig.6 The effect of heat flux on the heat transfer coefficient

Fig.7 The effect of mass flux on the heat transfer coefficient

Fig.8 The effect of inlet vapor quality on the heat transfer coefficient

Fig.9 Analysis of the influence on frictional pressure drop

Fig.10 Analysis of EF and PEC

Fig.11 Analysis of heat transfer performance variation along the path

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