Relationship between longitudinal vortex intensity and heat transfer intensity of flat tube heat exchanger

doi:10.11949/j.issn.0438-1157.20151231

Abstract

Abstract:

The longitudinal vortices can potentially enhance heat transfer with small pressure loss penalty. Vortex generators (VGs) which can generate longitudinal vortices are widely used in fin-and-tube heat exchangers for heat transfer enhancement. But for a long time, researches are carried out focusing on the effect of the shape and parameters of VGs on heat transfer and the relationship between the longitudinal vortices intensity and heat transfer intensity is analyzed qualitatively. The quantitative relationship between the longitudinal vortices intensity and heat transfer intensity is seldom reported. Longitudinal vortex is a typical secondary flow, and thus the longitudinal vortex intensity can be defined using the secondary flow intensity parameter. In this paper, the numerical models of flat tube bank fin heat exchanger with VGs mounted on the fin surfaces are studied for different fin and VGs parameters. The longitudinal vortices intensity is quantitatively defined using the nondimensional secondary flow intensity parameter Se. The relationship between the longitudinal vortices intensity and the heat transfer intensity and that between the increment values of Se and Nu caused by the longitudinal vortices are quantitatively studied. The results show that there is no corresponding relationships neither between Nu and Re, nor between Se and Re. Similarly, no linear relationship exists between the friction factor f and the values of Re and Se. But the corresponding relationship exists not only between Se and Nu but also ΔSe and ΔNu. The longitudinal vortices intensity determines the heat transfer intensity in the flat tube fin heat exchanger.

Key words: vortex generator, longitudinal vortices intensity, heat transfer intensity, quantitative relationship, heat transfer, numerical analysis

摘要：

纵向涡强化传热技术在管翅式换热器中得到了广泛的应用。但是一直以来对纵向涡强化传热的研究主要停留在涡产生器结构参数及布置方式对换热的影响方面,文献对纵向涡强度与换热强度之间定量关系的研究鲜有报道。建立了采用纵向涡强化传热的扁管管翅换热器数值模型,采用二次流强度参数Se分析了翅片及涡产生器结构参数变化时,通道内纵向涡强度与换热强度之间的定量关系;并定量分析了通道中涡产生器引起的纵向涡强度增量与传热强化量之间的定量关系。结果表明:翅片及涡产生器结构参数变化时,Nu、Se与Re之间,以及阻力系数f与Re及Se之间均不存在定量对应关系,但Se与Nu以及ΔSe与ΔNu之间存在对应关系。这表明,在布置有纵向涡产生器的扁管管翅换热器翅侧通道内,纵向涡强度决定了通道内的换热强度。

关键词: 涡产生器, 纵向涡强度, 换热强度, 定量关系, 传热, 数值分析

CLC Number:

TK121

SONG Kewei, LIU Song, WANG Liangbi. Relationship between longitudinal vortex intensity and heat transfer intensity of flat tube heat exchanger[J]. CIESC Journal, 2016, 67(5): 1858-1867.

宋克伟, 刘松, 王良璧. 扁管换热器内纵向涡强度与换热强度对应关系[J]. 化工学报, 2016, 67(5): 1858-1867.

References 22

[1]	FIEBIG M. Vortices and heat transfer [J]. Z. Angew. Math. Mech., 1997, 77: 3-18.
[2]	WU J M, TAO W Q. Impact of delta winglet vortex generators on the performance of a novel fin-tube surfaces with two rows of tubes in different diameters [J]. Energy Convers. Manage, 2011, 52(8/9): 2895-2901.
[3]	WANG Q W, CHEN Q Y, WANG L. Experimental study of heat transfer enhancement in narrow rectangular channel with longitudinal vortex generators [J]. Nucl. Eng. Des., 2007, 237: 686-693.
[4]	BISWAS G, DEB P, BISWAS S. Generation of longitudinal streamwise vortices — a device for improving heat exchanger design [J]. J. Heat Transfer, 1994, 116: 588-597.
[5]	FIEBIG M. Embedded vortices in internal flow: heat transfer and pressure loss enhancement [J]. Int. J. Heat Fluid Flow, 1998, 16: 376-388.
[6]	LEI Y G, HE Y L, TIAN L T, et al. Hydrodynamics and heat transfer characteristics of a novel heat exchanger with delta-winglet vortex generators [J]. Chem. Eng. Sci., 2010, 65: 1551-1562.
[7]	CHEN Y, FIEBIG M, MITRA N K. Heat transfer enhancement of finned oval tubes with staggered punched longitudinal vortex generators [J]. Int. J. Heat Mass Transfer, 2000, 43: 417-435.
[8]	SONG K W, WANG L B, FAN J F, et al. Numerical study of heat transfer enhancement of finned flat tube bank fin with vortex generators mounted on both surfaces of the fin [J]. Heat Mass Transfer, 2008, 44: 959-967.
[9]	TORRI K, KWAK K, NISHINO K. Heat transfer enhancement accompanying pressure-loss reduction with winglet-type vortex generators for fin tube heat exchangers [J]. Int. J Heat Mass Transfer, 2002, 45: 3795-3810.
[10]	TIAN L T, HE Y L, LEI Y G, et al. Numerical study of fluid flow and heat transfer in a flat-plate channel with longitudinal vortex generators by applying fluid synergy principles analysis [J]. Int. Commun. Heat Mass Transfer, 2009, 36: 111-120.
[11]	汉京晓, 周国兵. 平直和柱面小翼涡发生器诱发流动特性PIV实验研究[J]. 化工学报, 2013, 64(8): 2774-2780. DOI: 10.3969/j.issn. 0438-1157.2013.08.010. HAN J X, ZHOU G B. PIV investigation on induced flow characteristics in cylindrical winglet vortex generators [J]. CIESC Journal, 2013, 64(8): 2774-2780. DOI: 10.3969/j.issn. 0438-1157. 2013.08.010.
[12]	LEI Y G, HE Y L, TIAN L T, et al. Hydrodynamics and heat transfer characteristics of a novel heat exchanger with delta-winglet vortex generators [J]. Chem. Eng. Sci., 2010, 65: 1551-1562.
[13]	周国兵, 张于峰, 齐承英, 等.几种翼型涡流发生器强化换热及流阻性能的实验研究[J]. 天津大学学报, 2003, 36(6): 735-738. ZHOU G B, ZHANG Y F, QI C Y, et al.Experimental investigation of heat transfer enhancement and pressure drop of some wing-type vortex generators [J]. Transactions of Tianjin University, 2003, 36(6): 735-738
[14]	GENTRY M C, JACOBI A M. Heat transfer enhancement by delta-wing vortex generators on a flat plate: vortex interactions with the boundary layer [J]. Exp. Therm Fluid Sci., 1997, 14(3): 231-242.
[15]	KE F, WANG L B, HUA L, et al. The optimum angle of attack of delta winglet vortex generators on heat transfer performance of finned flat tube bank with considering nonuniform fin temperature [J]. Exp. Heat Transfer, 2006, 19: 227-249
[16]	YANG J S, HONG C H, CHOI G M. Heat transfer measurement using thermochromatic liquid crystal [J]. Curr. Appl. Phys., 2007, 7: 413-420.
[17]	吕静, 马济成, 杜雅萍. 纵向涡旋发生元LVG强化换热的实验研究[J]. 上海理工大学学报, 2001, 23(3): 283-285. DOI: 10.3969/j.issn. 1007-6735.2001.03.025. LÜ J, MA J C, DU Y P. Experimental study on heat transfer enhancement by using delta-winglet longitudinal vortex generators [J]. J. University of Shanghai for Science and Technology, 2001, 23(3): 283-285.DOI: 10.3969/j.issn.1007-6735.2001.03.025.
[18]	何雅玲, 楚攀, 谢涛. 纵向涡发生器在管翅式换热器中的应用及优化[J]. 化工学报, 2012, 63(3): 746-760. DOI: 10.3969/j.issn. 0438-1157. 2012.03.011. HE Y L, CHU P, XIE T. Application and optimization of fin-and-tube heat exchangers with longitudinal vortex generators [J]. CIESC Journal, 2012, 63(3): 746-760. DOI: 10.3969/j.issn.0438-1157. 2012.03.011.
[19]	宋克伟, 刘松, 王良璧. 换热器通道内反向旋转纵向涡间的干涉特性[J]. 化工学报, 2016, 67(4): 1233-1243. DOI: 10.11949/j.issn. 0438-1157.20150618. SONG K W, LIU S, WANG L B. Interaction characteristics between longitudinal vortices with counter-rotating directions in heat exchanger channel [J]. CIESC Journal, 2016, 67(4): 1233-1243. DOI: 10.11949/j.issn.0438-1157. 20150618.
[20]	SONG K W, WANG L B. The effectiveness of secondary flow produced by vortex generators mounted on both surfaces of the fin to enhance heat transfer in a flat tube bank fin heat exchanger [J]. J. Heat Transfer, 2013, 135: 041902.
[21]	CHEN Y Y, SONG K W, WANG L B, et al. Comparisons of local experimental results with numerical results of heat transfer enhancement of a flat tube bank fin with vortex generators [J]. Numer. Heat Transfer, Part A, 2009, 55: 144-162.
[22]	SONG K W, WANG L B. Effects of the interaction of longitudinal vortices on the flow field and heat transfer over a flat-tube-and-fin heat exchanger [J]. J. Enhanced Heat Transfer, 2014, 21(6): 439-462.