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ABSTRACT
To enhance heat transfer and reduce fouling of the finned-tube surface in economizers of coal-fired power plants, heat transfer and pressure drop characteristics for H-type finned oval tube with longitudinal vortex generators (LVG) and dimples, both in-line and staggered arrangements, are studied experimentally under flue dust condition. In addition, the ash samples and heat exchanger surfaces after the test are analyzed to help understanding the ash fouling and tube wear mechanisms. Compared to the original H-type finned oval tube, the Nusselt number of H-type finned oval tube bank with longitudinal vortex generators and dimples is improved by 34.5–41.7% (in-line arrangement) and 28.1–31.7% (staggered arrangement) within the studied Reynolds numbers, while the Euler number is increased by 21.9–28.3% (in-line arrangement) and 19% (staggered arrangement) in the clean finned-tube surface state. In the stable fouling state, the Nusselt number is improved by 37.7–42.3% (in-line arrangement) and 27.8–45.1% (staggered arrangement), while the Euler number is increased by 22.9–25.2% (in-line arrangement) and 33.3–42% (staggered arrangement). The results show that the novel fin structures can both inhibit fouling and enhance heat transfer effectively.
Nomenclature
| A | = | flow cross-section area (m2) |
| Am | = | minimum flow cross-section area (m2) |
| a | = | length of the oval tube major radius (m) |
| b | = | length of the oval tube minor radius (m) |
| am | = | width of the rectangle punching (m) |
| bm | = | length of the rectangle punching (m) |
| CFB | = | circulating fluidized bed |
| D | = | equivalent diameter (m) |
| Eu | = | Euler number, dimensionless |
| Fm | = | spanwise winglet pitch (m) |
| Fi, Fn | = | spanwise dimple pitch (m) |
| Ft | = | fin pitch (m) |
| Fp | = | fin thickness (m) |
| H | = | fin height (m) |
| Hm | = | height of the rectangle winglet (m) |
| h | = | heat transfer coefficient (W·m−2·K−1) |
| LVG | = | longitudinal vortex generators |
| K | = | total heat transfer coefficient (W·m−2·K−1) |
| m | = | slit width (m) |
| Nu | = | Nusselt number, dimensionless |
| P | = | pressure (Pa) |
| Re | = | Reynolds number, dimensionless |
| r1 | = | radius of the dimple (m) |
| r2 | = | radius of the bleeding hole (m) |
| rn | = | fouling resistance inside the tube (m2·K/W) |
| rw | = | thermal resistance of tube wall (m2·K/W) |
| S1 | = | spanwise tube pitch (m) |
| S2 | = | longitudinal tube pitch (m) |
| SEM | = | scanning electron microscope |
| u | = | velocity (m·s−1) |
| W | = | length of the dimple to center (m) |
| w | = | fin width (m) |
| XPS | = | X-ray photoelectron spectroscopy |
| XRD | = | X-ray diffraction |
| z | = | tube bank number |
Greek symbols
| ρ | = | density (kg·m−3) |
| λ | = | thermal conductivity (W·m−1·K−1) |
| μ | = | dynamic viscosity (Pa·s) |
| β | = | fin effect coefficient |
Subscripts
| g | = | gas |
| m | = | minimum |
| w | = | wall |
Acknowledgments
This work was supported by the National Basic Research Program of China (973 Program) under Grant No. 2011CB710702, the National Natural Science Foundation of China under Grant No. 51222604 and the 111 project under Grant No. B16038.
Additional information
Notes on contributors
Xuebin Zhao
Xuebin Zhao is a Ph.D. candidate in the Department of Thermo-Fluid Science and Engineering, School of Energy and Power Engineering at Xi'an Jiaotong University, China. He received his B.S. degree in Thermal Energy and Power Engineering from Shandong University. His areas of specialty are heat transfer enhancement, erosion mechanism of particle impact to targets and mitigation fouling of particles adherence to targets.
Guihua Tang
Guihua Tang is a full Professor in the Department of Thermo-Fluid Science and Engineering, School of Energy and Power Engineering at Xi'an Jiaotong University, China. He received his Ph.D. in Engineering Thermophysics from Xi'an Jiaotong University in 2004. He worked as the Higher Scientific Officer in STFC Daresbury Laboratory, UK from April 2007 to August 2009, and as the Visiting Scholar in University of Strathclyde UK from March 2008 to August 2008. His research interests include heat design and management, multiphase and non-Newtonian fluid flow, microscale and nanoscale heat transfer, and lattice Boltzmann method. He and his co-workers have published over 80 peer reviewed international journal papers. He has received several outstanding research/teaching awards, such as the Chung-Hua Wu Award by the Chinese Society of Engineering Thermophysics, Youth Science and Technology Rising Stars of Shaanxi Province in China, New Century Excellent Talents in University of China, and KC Wong Award for Education. He currently serves as the Associate Editor for the ASME Journal of Heat Transfer.
Yuetao Shi
Yuetao Shi is an Associate Professor in the School of Energy and Power Engineering at Shandong University, China. He received his Ph.D. in Engineering Thermophysics from Xi'an Jiaotong University in 2009. He worked as a Visiting Scholar in Rutgers, The State University of New Jersey USA from May 2015to April 2016. He mainly engaged in thermal system optimization, energy saving analysis, and numerical analysis of multiphase fluid flow in complex channels. His research interests include heat and mass transfer process in thermal power plants, nuclear power plants, chemical industry, metallurgical industry and other fields. He has won the second prize of Scientific and Technological Progress in Shandong Province for three times.
Yongkuan Li
Yongkuan Li is the boiler workshop director in Jinan Minghu Thermal Power Plant, China. He received his Bachelor's degree in Economics and Management at Party School of the Communist Party of Shandong Province, China. He worked in Jinan Minghu Thermal Power Plant since 1985, and now is the principal of boilers safety operation. He is mainly engaged in management of boiler and environment protection, equipment operation and energy conservation.