Heat transfer characteristic of molten salt in transverse corrugated tube with semi-circumference heating

doi:10.11949/0438-1157.20190685

Abstract

Abstract:

The semi-circumferential heating of the solar heat absorber tube has an effect on the convective heat transfer coefficient in the tube. Base on this, convection heat transfer experimental system and mathematical model of transverse corrugated tube are established to analyze the heat transfer performance of molten salt with different groove width and height. The results show that the circumferentially temperature of inner wall increases, and the circumferentially local Nusselt number decreases first and then increases to stability with transverse corrugated tube from adiabatic side to heated side. The axial temperature of inner wall with groove obviously lower than that of smooth section, the axial local Nusselt number of groove in transverse corrugated tube is relatively large, and the convergence of after groove and smooth section is minimal. The axial local Nusselt number of heated side and the average Nusselt number in transverse corrugated tube decrease with the groove width increases, while the PEC(comprehensive performance evaluation factor) rises. The axial local Nusselt number, the average Nusselt number and Nu/Nu _ST (enhanced heat transfer ratio) increase with the groove height increment. The PEC of transverse corrugated tube is obvious affected by groove width, while the Nu/Nu _ST is remarkable affected by groove height. The Nusselt number rule equation of molten salt in transverse corrugated tube with circumferentially non-uniform heat flux is obtained, and the maximum deviation of Nu between calculated and simulated value is within ±7%.

Key words: semi-circumference heating, transverse corrugated tube, molten salt, heat transfer, solar energy, convection

摘要：

半周加热太阳能吸热器管给管内对流传热系数带来影响，基于此，建立半周加热横纹管内熔盐对流传热的实验台和数值计算模型，分析横纹管槽宽、槽深对管内熔盐传热性能的影响规律，结果表明：从横纹管绝热侧到加热侧，周向管内壁温度逐渐升高，周向管内局部Nusselt数先减小后缓慢增大至稳定。横纹管凹槽处轴向管内壁温度明显低于平滑段，凹槽处轴向管内局部Nu较大，凹槽后与平滑段交界处管内局部Nu最小。横纹管槽越宽，加热侧轴向管内局部Nu越小，管内平均Nu越小，传热综合性能评价因子PEC越大。横纹管槽越深，轴向管内局部Nu越大，管内平均Nu越大，传热强化倍数Nu/Nu _ST越大。槽宽对横纹管PEC的影响比槽深明显，槽深对横纹管内Nu/Nu _ST影响比槽宽大。通过线性拟合得到半周加热横纹管内熔盐传热Nu的关联式，其计算Nu与模拟值最大偏差在±7%以内。

关键词: 半周加热, 横纹管, 熔盐, 传热, 太阳能, 对流

CLC Number:

TK 124

Xiangyang SHEN, Jing DING, Jianfeng LU. Heat transfer characteristic of molten salt in transverse corrugated tube with semi-circumference heating[J]. CIESC Journal, 2019, 70(12): 4546-4555.

沈向阳, 丁静, 陆建峰. 半周加热横纹管内熔盐强化传热特性[J]. 化工学报, 2019, 70(12): 4546-4555.

Figures/Tables 17

Fig.1 Physical model of transverse corrugated tube with semi-circumference heating

Fig.2 Grid of transverse corrugated tube

Fig.3 Experimental system

Fig.4 Nusselt number in transverse corrugated tube with simulation and experimental value

Table 1 Structural parameters of transverse corrugated tube

管	槽宽(P ₁)/mm	槽深(e)/mm
管1(TC1)	4.3	0.95
管2(TC2)	5.8	0.95
管3(TC3)	7.3	0.95
管4(TC4)	5.8	0.73
管5(TC5)	5.8	1.15

Fig.5 Circumference temperature and circumference local Nusselt number

Fig.6 Axial temperature and axial local Nusselt number

Fig.7 Velocity vector in transverse corrugated tube

Fig.8 Axial local Nusselt number with different groove width

Fig.9 Nusselt number with different groove width

Fig.10 Nu/Nu ST and PEC with different groove width

Fig.11 Axial local Nusselt number with different groove depth

Fig.12 Nusselt number with different groove depth

Fig.13 Nu/Nu ST and PEC with different groove depth

Fig.14 Influence of groove width and depth on Nu/Nu ST and PEC

Fig.15 Comparison of simulation value and equations

Fig.16 Comparison of simulation value and Eq. (22)

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