Convection heat transfer research of supercritical R134a in mini-channel of tube

doi:10.16085/j.issn.1000-6613.2023-1273

Abstract

Abstract:

The supercritical organic Rankine cycle (SORC) is an ideal new power cycle technology for recovering energy using supercritical organic Rankine cycle. The energy efficiency of the system is significantly affected by the SORC, the supercritical organic working medium, low grade energy recovery, and the heat transfer characteristics of the supercritical organic working medium. At present, it has become a bottleneck that restrict the development of organic Rankine cycle technology. To address this issue, the experimental studies were conducted on the flow heat transfer characteristics of supercritical R134a in a tiny channel with an inner diameter of 2mm). The parameters considered in the study were as follows: heat flux ranging from 60—120kW/(m²·s), mass flow rate from 800—3000kg/(m²·s), pressure from 4.1—5.1MPa, and working medium inlet temperature from 20—100℃. The effects of heat flow density, mass flow velocity, pressure and fluid temperature on the heat transfer characteristics were discussed. The results showed that the heat transfer coefficient initially increased and then decreased with the increase of fluid temperature. It also increased with the increase of mass flow rate but decreased with the increase of heat flux and pressure. According to the experimental data, a prediction accuracy of ± 10% for R134a in the microchannel was achieved, demonstrating good prediction accuracy.

Key words: micro-channel, supercritical R134a, fluid flow and heat transfer, organic Rankine cycle, heat transfer correlation

摘要：

超临界有机朗肯循环（supercritical organic Rankine cycle，SORC）是回收中低品位能源较理想的新型动力循环技术之一，而超临界有机工质的传热特性严重影响了系统能效，目前已成为制约有机朗肯循环技术向前发展的瓶颈。基于此，本文实验研究了超临界R134a在2mm微小通道内的流动传热特性，参数范围为：热流密度60~120kW/(m²·s)，质量流速800~3000kg/(m²·s)，压力4.1~5.1MPa，工质进口温度20~100℃，探讨了热流密度、质量流速、压力、流体焓值等参数对传热特性的影响规律。结果表明，传热系数随流体温度的升高先增加后减小，随质量流速的增加而增加，随着热流密度和压力的增加而减小。流体焓值在拟临界值附近出现压降平缓区。根据实验数据拟合得到了微通道内R134a的传热关联式，该关联式预测误差均在±10%之内，具有良好的预测精度。

关键词: 微小通道, 超临界R134a, 流动传热, 有机朗肯循环, 传热关联式

CLC Number:

TK124

ZHANG Qiaoling, MA Zuhao, YU Ziyuan, LIU Zijun, HUANG Biyun, YANG Zhendong, MA Haoran. Convection heat transfer research of supercritical R134a in mini-channel of tube[J]. Chemical Industry and Engineering Progress, 2024, 43(4): 1667-1675.

张巧玲, 马祖浩, 于子元, 刘梓俊, 黄铋匀, 杨振东, 马浩然. 微小通道内超临界R134a流动传热特性[J]. 化工进展, 2024, 43(4): 1667-1675.

Figures/Tables 14

参数	范围	精度
高压恒流泵P1000+	0~1000mL/min	±3%
T型热电偶	0~500℃	±0.2℃
T型热电偶丝	0~1000℃	±0.2℃
CX-M5型齿轮流量计	0~1000mL/min	±0.5%
罗斯蒙特3051TG4压力传感器	0~6MPa	±0.075%
罗斯蒙特3051CD3差压变送器	0~20kPa	±0.075%

参数	不确定度
质量流速G/kg·m^-2·s	0.51%
压力p/MPa	0.11%
压差∆p/kPa	0.54%
热流密度q/kW·m^-2	2.13%
内壁温度T_w,in/℃	±0.5℃
换热系数h/W·m^-2·K^-1	7.98%

测点	外壁温T_1w,out/℃	外壁温T_2w,out/℃	外壁温T_3w,out/℃
1	48.2	48.2	48.2
2	138.4	138.2	138.2
3	133.9	133.7	133.7
4	153.6	153.7	153.9
5	150.5	151.2	151.0
6	162.9	164.1	163.5
7	159.2	160.1	159.7
8	168.6	169.9	168.9
9	164.7	165.8	164.8
10	178.8	179.7	178.7

参数	公式
电加热效率η	$η = M H b, o - H b, i U I$
热流密度q/kW·m^-2	$q = U I η π d L$
质量流量G/kg·s^-1	$G = ρ V A = 4 ρ V π d 2$
流体焓值H_b/kJ·kg^-1	$H b = H b, i + x L (H b, o - H b, i)$
内壁温度T_w,in/℃	$T w, i n = T w, o u t - d i n 2 q λ w d o 2 d o 2 - d i n 2 l n d o d i n - 12$
平均换热系数h/W·m^-2·K^-1	$h = q T ¯ w, i n - T ¯ b$
浮升力数	$B u J = G r b R e 2$ $G r b = g (ρ b - ρ w) d 3 ρ b v b 2$

参数	公式
电加热效率η	$η = M H b, o - H b, i U I$
热流密度q/kW·m^-2	$q = U I η π d L$
质量流量G/kg·s^-1	$G = ρ V A = 4 ρ V π d 2$
流体焓值H_b/kJ·kg^-1	$H b = H b, i + x L (H b, o - H b, i)$
内壁温度T_w,in/℃	$T w, i n = T w, o u t - d i n 2 q λ w d o 2 d o 2 - d i n 2 l n d o d i n - 12$
平均换热系数h/W·m^-2·K^-1	$h = q T ¯ w, i n - T ¯ b$
浮升力数	$B u J = G r b R e 2$ $G r b = g (ρ b - ρ w) d 3 ρ b v b 2$

传热关联式	公式形式	适用工质
Kang关联式	$N u = 0.0244 R e 0.762 P r b 0.552 ρ w ρ b 0.0293$	R134a
Jackson & Hall关联式	$N u = 0.0183 R e 0.82 P r b 0.5 c p c p b n r w r b 0.3$	水和CO₂
Bishop关联式	$N u = 0.0069 R e 0.9 P r b 0.5 ρ w ρ b 0.43 1 + 2.4 D x$	水和CO₂

传热关联式	公式形式	适用工质
Kang关联式	$N u = 0.0244 R e 0.762 P r b 0.552 ρ w ρ b 0.0293$	R134a
Jackson & Hall关联式	$N u = 0.0183 R e 0.82 P r b 0.5 c p c p b n r w r b 0.3$	水和CO₂
Bishop关联式	$N u = 0.0069 R e 0.9 P r b 0.5 ρ w ρ b 0.43 1 + 2.4 D x$	水和CO₂

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