本模擬研究探討管內設置數根扭旋片熱傳與熱性能增益之研究，由連續、能量和動量控制的方程式在管壁處施加恆定的熱通量。在入口處，指定了水的流速和溫度。在出口處，使用壓力出口條件。邊界條件求解器的類型是基於壓力的穩態模式，然後在紊流模型中使用RNG k-ε模式。扭旋片扭率為2.5，雷諾數範圍為8000-14000。工作流體為水，普朗特數為6.9892。首先進行光滑管驗證數值模擬，並將其結果與從Dittus-Boelter獲得的結果進行比較；並與Vashista等人的實驗數據相互比較，發現兩者結果一致且相近。

研究結果顯示: 放置扭旋片於圓管中可有效改善管內之熱傳現象，在雷諾數為8000-14000時，在管內放入四根具孔洞扭旋片(C6)的平均紐賽數最高，且相較於平滑四根扭旋片(C5)之平均紐賽數也有提高，最大平均紐賽數增加率為13.3% ;而在管內放入兩根具孔洞之扭旋片(C4)，相較於平滑兩根扭旋片(C3)之平均紐賽數也有提高，最大平均紐賽數增加率為8.34%。在雷諾數為8000-14000時，C6相較於C4的平均紐賽數增加率為39.6%。而C5相較於C3平均紐賽數增加率為42.39%。渦流強度與平均紐賽數隨紐旋片增加而增加，且大於穿孔所帶來的效應。

The research of simulation studies the heat transfer and thermal performance enhancement of multiple twisted tapes in the tube. The flow of a fluid and heat transfer through a tube with a constant heat flux is controlled by the continuity equation, energy equation, and momentum equation. The water of velocity and temperature are designated at the inlet. At outlet, the condition of the pressure outlet is used. The solver type is pressure based with steady and RNG in k-epsilon model. The twisted ratio of twisted tape is 2.5. The twisted tape worked in the Reynolds number (Re) range of 8000-14000, and it is investigated numerically using water as working fluid with Prandtl number of 6.9892. According to the results got from Dittus-Boelter, the numerical simulation was first verified using a smooth tube. In addition, the current results of twisted tape inserts are compared with the experimental data of other article, and the results of the comparison are quite consistent.

The results of the research showed that placing the twisted tape inserts in the circular tube can effectively improve the heat transfer performance. At Re=8000-14000, the average Nusselt number (Nu) of 4CTst-hole(C6) is highest. 4CTst-hole is improved compared with 4CTst(C5), and the maximum increase rate is 8.322%. At Re of 8000-14000, 2CTst-hole(C4) is improved compared with 2CTst(C3), and the maximum increase rate is 7.38%. At Re of 8000-14000, C6 is improved compared with C4, and the maximum increase rate is 42.99%. At Re of 8000-14000, C5 is improved compared with C3, and the maximum increase rate is 42.39%. The swirl intensity and the average Nusselt number increase with an increase in the number of twisted tapes are greater than in the number of perforation.

[1] S. Eiamsa-ard , C. Thianpong , P. Eiamsa-ard and P. Promvonge ,“Thermal characteristics in a heat exchanger tube fitted with dual twisted tape elements in tandem” , Intl. Comm. in Heat and Mass Transfer, Vol.37, pp.39–46 , 2010
[2] F.Bazdidi-Tehrani, S. M. Khanmohamadi and S. I. Vasefi, “Evaluation of turbulent forced convection of non-Newtonian aqueous solution of CMC/CuO nanofluid in a tube with twisted tape inserts” ,Adv. Powder Tecnol.,In Press, 2020
[3] M. Farnam , M. Khoshvaght-Aliabadi and M.J.Asadollahzadeh ,“Heat transfer intensification of agitated U-tube heat exchanger using twisted-tube and twisted-tape as passive techniques” , Chem. Eng. Process. - Process Intensif , Vol.133, pp.137-147 , 2018
[4] C. Thianpong, P. Eiamsa-ard, K. Wongcharee and S. Eiamsa-ard, “Compound heat transfer enhancement of a dimpled tube with a twisted tape swirl generator,” Intl. Comm. in Heat and Mass Transfer, vol. 36, no. 7, pp. 698-704, 2009
[5] S. Alzahrani and S. Usman, “CFD simulations of the effect of in-tube twisted tape design on heat transfer and pressure drop in natural circulation,” Therm. Sci. Eng. Prog, vol. 11, pp. 325–333, 2019.
[6] C. Vashistha, A.K. Patil and M. Kumar,“Experimental investigation of heat transfer and pressure drop in a circular tube with multiple inserts” , Appl. Therm. Eng., vol. 96, pp. 117–129, 2016.
[7] S. Zhang, L. Lu , C. Dong and S.H. Cha,“Thermal characteristics of perforated self-rotating twisted tapes in a double-pipe heat exchanger”,Appl. Therm. Eng., vol.162, Article 114296, 2019
[8] A.S. Dalkilic, O.A. Türk, H. Mercan , S. Nallaew and S. Wongwises,“An experimental investigation on heat transfer characteristics of graphite-SiO2/water hybrid nanofluid flow in horizontal tube with various quad-channel twisted tape inserts”,Intl. Comm. in Heat and Mass Transfer, vol.107, pp.1-13, 2019
[9] A. Saysroy and S. Eiamsa-ard,“Periodically fully-developed heat and fluid flow behaviors in a turbulent tube flow with square-cut twisted tape inserts”, Appl. Therm. Eng., vol.112, pp895-910, 2017
[10] S.Chokphoemphun, M. Pimsarn, C. Thianpong and P. Promvonge.“Thermal performance of tubular heat exchanger with multiple twisted-tape inserts”,Chin. J. Chem. Eng.,vol.23, pp755-762, 2015
[11] Y. X. Hong , J.Du and S. F. Wang,“Turbulent thermal, fluid flow and thermodynamic characteristics in a plain tube fitted with overlapped multiple twisted tapes”, Int.J.Heat Mass Transf, vol.115,pp.551-565, 2017
[12] B. Kumar, G. P. Srivastava, M. Kumar, and A. K. Patil, “A review of heat transfer and fluid flow mechanism in heat exchanger tube with inserts,” Chem. Eng. Processing-Process Intensif., vol. 123, pp. 126–137, 2018.
[13] L. Zheng, Y. Xie, D. Zhang, “Numerical investigation on heat transfer performance and flow characteristics in circular tubes with dimpled twisted tapes using Al2O3-water nanofluid,” Int. J. Heat Mass Transf, vol. 111, pp. 962–981, 2017.
[14] S. Eiamsa-Ard and P. Promvonge, “Thermal characteristics in round tube fitted with serrated twisted tape,” Appl. Therm. Eng., vol. 30, no. 13, pp. 1673–1682, 2010.
[15] Z.Han and Z.Xu, “Experimental and numerical investigation on particulate fouling characteristics of vortex generators with a hole”, Int.J.Heat Mass Transf, vol.148, Article 119130, 2020
[16] Y. Yoon, S. -J. Park, D. R. Kim and K. -S. Lee, “Thermal performance improvement based on the partial heating position of a heat sink”, Int.J.Heat Mass Transf , Vol.124, pp.752-760, 2018.
[17] H. Huisseune, C. T'Joen, P. De Jaegar, B.Ameel, S. De Schampheleire and M. De Paep, “Performance enhancement of a louvered fin heat exchanger by using delta winglet vortex generators”, Int.J.Heat Mass Transf , Vol.56, pp.475-487, 2013.
[18] S. W. Chang, H. W. Wu, D. Y. Guo, J. jie Shi, and T. H. Chen, “Heat transfer enhancement of vertical dimpled fin array in natural convection,” Int. J. Heat Mass Transf., vol. 106, pp. 781–792, 2017.
[19] C. Chen and J.-T. Teng, “A study on fluid flow and heat transfer in rectangular microchannels with various longitudinal vortex generators”, Int. J. Heat Mass Transf. ,vol.69, pp.203-214, 2014.
[20] X. Li, C. Li, B. Li, “Net heat gain assessment on a glazed transpired solar air collector with slit-like perforations”, Appl. Therm. Eng., vol. 99, pp.1-10, 2016.
[21] M. Dastmalchi, A. Arefmanesh, G. A. Sheikhzadeh, “Numerical investigation of heat transfer and pressure drop of heat transfer oil in smooth and micro-finned tubes”, Int. J. Therm. Sci. , Vol.121, pp.294-304, 2017.
[22] N.Satish and K.Venkatasubbaiah,“Conjugate heat transfer analysis of turbulent forced convection of moving plate in a channel flow”, Appl. Therm. Eng., vol.100, pp.987-998, 2016
[23] T. Alam and M.H. Kim, “Numerical study on thermal hydraulic performance improvement in solar air heater duct with semi ellipse shaped obstacles”, Energy, vol.112, pp.588-598 , 2016
[24] X. Zhang, Y. Wang, P. Cang and R. Wang,“ Experimental investigation of thermal hydraulic performance of heat exchangers with different Reynolds numbers on both air-side and water-side”, Appl. Therm. Eng., vol.99, pp.1331-1339, 2016
[25] Y. Lei, F. Zheng, C. Song and Y. Lyu,“Improving the thermal hydraulic performance of a circular tube by using punched delta-winglet vortex generators”, Int. J. Heat Mass Transf. ,vol.111, pp.299-311 , 2017
[26] Z. Zhang, C. Zhao, X. Yang, P. X. Jiang , J. Tu and S. Jiang,“ Numerical study of the heat transfer and flow stability of water at supercritical pressures in a vertical tube”, Nucl. Eng. Des., vol.325, pp.1-11, 2017
[27] S. Ebrahim Ghasemi and A. Akbar Ranjbar ,“Numerical thermal study on effect of porous rings on performance of solar parabolic trough collector” , Appl. Therm. Eng.vol.118, pp.807-816 ,2017
[28] J. Guo, A. Fan, X. Zhang, and W. Liu ,“A numerical study on heat transfer and friction factor characteristics of laminar flow in a circular tube fitted with center-cleared twisted tape”, Int. J. Therm. Sci. , vol.50, pp.1263-1270, 2011
[29] P. Promvonge, S. Suwannapan, M. Pimsarn and C. Thianpong,“Experimental study on heat transfer in square duct with combined twisted-tape and winglet vortex generators”, Intl. Comm. in Heat and Mass Transfer, vol.59, pp.158-165, 2014
[30] K.Wongcharee and S.Eiamsa-ard,“Friction and heat transfer characteristics of laminar swirl flow through the round tubes inserted with alternate clockwise and counter-clockwise twisted-tapes”, Intl. Comm. in Heat and Mass Transfer, vol.38 ,pp.348-352, 2011
[31] A.R.S. Suri , A. Kumar and R. Maithani ,“Heat transfer enhancement of heat exchanger tube with multiple square perforated twisted tape inserts: Experimental investigation and correlation development”, Chem Eng Process - Process Intensif, vol.116, pp. 249-270,2017
[32]S. Ponnada, T. Subrahmanyam and S.V. Naidu ,“A comparative study on the thermal performance of water in a circular tube with twisted tapes, perforated twisted tapes and perforated twisted tapes with alternate axis”, Int. J. Therm. Sci. , Vol.136, pp.530-538, 2019.
[33]M.M.K.Bhuiya, M.S.U.Chowdhury, M.Saha, and M.T.Islame,“Heat transfer and friction factor characteristics in turbulent flow through a tube fitted with perforated twisted tape inserts”, Intl. Comm. in Heat and Mass Transfer, vol.46 ,pp.49-57, 2013
[34] S.V. Patankar, “Numerical Heat Transfer and Fluid Flow”, McGraw-Hill, New York, 1980.
[35] H. Tennekes and J. L. Lumley, “A First Course in Turbulence”, Cambridge: MIT Press, 1972.
[36] A. Sahay and K. R. Sreenivasan, “The wall-normal position in pipe and channel flows at which viscous and turbulent shear stresses are equal,” Phys. Fluids, vol. 11, no. 10, pp. 3186–3188, 1999.
[37] M. W. Frank, “Fluid mechanics (seventh ed.)”, McGraw-Hill, New York, 1979.
[38]ANSYS Inc.Ansys Fluent 12.0: Users Guide ; ANSYS Inc.:Canonsburg, PA, USA , January 2009.
[39] C. Yunus A and G. Afshin J, “Heat and mass transfer fundamentals & applications” Mc Graw-Hill. New York. pp. 424 , 2015.
[40] I. Frank P, D. David P, B. Theodore L, and L. Adrienne S, “Fundamentals of momentum, heat and mass transfer”, Sixth ed., John Wiley & Sons, Inc, New York, pp. 669, 2005.
[41] M. Bahiraei, N. Mazaheri, F. Aliee and M. R. Safaei ,“Thermo-hydraulic performance of a biological nanofluid containing graphene nanoplatelets within a tube enhanced with rotating twisted tape”, Powder Tecnol. ,vol. 355, pp.278-288, 2019
[42] P. S. Kathait and A. K. Patil, “Thermo-hydraulic performance of a heat exchanger tube with discrete corrugations,” Appl. Therm. Eng., vol. 66, no. 1–2, pp. 162–170, 2014.