{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,4]],"date-time":"2026-07-04T13:35:22Z","timestamp":1783172122866,"version":"3.54.6"},"reference-count":35,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2020,7,23]],"date-time":"2020-07-23T00:00:00Z","timestamp":1595462400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Collaborative Innovation Team Project of Gansu Province","award":["2018C-13"],"award-info":[{"award-number":["2018C-13"]}]},{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["51866007"],"award-info":[{"award-number":["51866007"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>The thermal-hydraulic performance in a novel annular tube formed by outer straight and inner twisted oval tubes is numerically investigated. An annular tube formed by two straight oval tubes is also studied for comparison. Inner twisted oval tubes with different aspect ratios and twist ratios are studied. The heat transfer is well improved by the symmetrical secondary flow in the annulus. The Nusselt number generally increases when the inner oval tube becomes flatter and the twists stronger in the studied range of geometrical parameters. The largest Nusselt number Nu of the inner twisted tube increases by 116% while the friction factor f increases by only 46% compared with that of the inner straight tube, and the largest value of the thermal performance factor (JF) can be up to 1.9. Correlations of the Nusselt number and friction factor are proposed for laminar and turbulent flows, and the deviations of the correlations are within \u00b15% and \u00b14% for Nu and f, respectively.<\/jats:p>","DOI":"10.3390\/sym12081213","type":"journal-article","created":{"date-parts":[[2020,7,23]],"date-time":"2020-07-23T11:26:01Z","timestamp":1595503561000},"page":"1213","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":28,"title":["Heat Transfer Enhancement in a Novel Annular Tube with Outer Straight and Inner Twisted Oval Tubes"],"prefix":"10.3390","volume":"12","author":[{"given":"Chao","family":"Luo","sequence":"first","affiliation":[{"name":"School of Mechanical Engineering, Key Laboratory of Railway Vehicle Thermal Engineering of MOE, Lanzhou Jiaotong University, Lanzhou 730070, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"KeWei","family":"Song","sequence":"additional","affiliation":[{"name":"School of Mechanical Engineering, Key Laboratory of Railway Vehicle Thermal Engineering of MOE, Lanzhou Jiaotong University, Lanzhou 730070, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9046-337X","authenticated-orcid":false,"given":"Toshio","family":"Tagawa","sequence":"additional","affiliation":[{"name":"Department of Aeronautics and Astronautics, Tokyo Metropolitan University, Hino, Tokyo 191-0065, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"TengFei","family":"Liu","sequence":"additional","affiliation":[{"name":"School of Mechanical Engineering, Key Laboratory of Railway Vehicle Thermal Engineering of MOE, Lanzhou Jiaotong University, Lanzhou 730070, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2020,7,23]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1075","DOI":"10.1016\/j.applthermaleng.2016.09.027","article-title":"A comprehensive review on double pipe heat exchangers","volume":"110","author":"Omidi","year":"2017","journal-title":"Appl. Therm. Eng."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"113867","DOI":"10.1016\/j.applthermaleng.2019.113867","article-title":"Experimental and numerical study on heat transfer enhancement using ultrasonic vibration in a double-pipe heat exchanger","volume":"159","author":"Setareh","year":"2019","journal-title":"Appl. Therm. Eng."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1125","DOI":"10.1016\/j.enconman.2013.09.008","article-title":"Investigating the efficacy of magnetic nanofluid as a coolant in double-pipe heat exchanger in the presence of magnetic field","volume":"76","author":"Bahiraei","year":"2013","journal-title":"Energy Convers. Manag."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"112","DOI":"10.1016\/j.cherd.2016.07.009","article-title":"The Influence of magnetic field on heat transfer of magnetic nanofluid in a sinusoidal double pipe heat exchanger","volume":"113","author":"Mousavi","year":"2016","journal-title":"Chem. Eng. Res. Des."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"114801","DOI":"10.1016\/j.applthermaleng.2019.114801","article-title":"Convective heat transfer enhancement in a double pipe mini heat exchanger by magnetic field induced swirling flow","volume":"167","author":"Bezaatpour","year":"2020","journal-title":"Appl. Therm. Eng."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"114296","DOI":"10.1016\/j.applthermaleng.2019.114296","article-title":"Thermal characteristics of perforated self-rotating twisted tapes in a double-pipe heat exchanger","volume":"162","author":"Zhang","year":"2019","journal-title":"Appl. Therm. Eng."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"161","DOI":"10.1016\/j.csite.2017.06.001","article-title":"Study the effect of axially perforated twisted tapes on the thermal performance enhancement factor of a double tube heat exchanger","volume":"10","author":"Mashoofi","year":"2017","journal-title":"Case Stud. Therm. Eng."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"112","DOI":"10.1016\/j.enconman.2016.08.090","article-title":"Heat transfer improvement in a double pipe heat exchanger by means of perforated turbulators","volume":"127","author":"Sheikholeslami","year":"2016","journal-title":"Energy Convers. Manag."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"355","DOI":"10.1016\/j.ijthermalsci.2018.06.011","article-title":"The optimal arrangement of vortex generators for best heat transfer enhancement in flat-tube-fin heat exchanger","volume":"132","author":"Song","year":"2018","journal-title":"Int. J. Therm. Sci."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"8","DOI":"10.1016\/j.expthermflusci.2016.11.002","article-title":"Effect of geometric size of curved delta winglet vortex generators and tube pitch on heat transfer characteristics of fin-tube heat exchanger","volume":"82","author":"Song","year":"2017","journal-title":"Exp. Therm. Fluid Sci."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Song, K.W., Wang, L., Hu, Y.J., and Liu, Q. (2020). Flow symmetry and heat transfer characteristics of winglet vortex generators arranged in common flow up configuration. Symmetry, 12.","DOI":"10.3390\/sym12020247"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"143","DOI":"10.1016\/j.ijheatmasstransfer.2014.11.054","article-title":"Experimental and numerical study of fluid flow and heat transfer in a twisted square duct","volume":"82","author":"Bhadouriya","year":"2015","journal-title":"Int. J. Heat Mass Transf."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"2981","DOI":"10.1016\/j.applthermaleng.2011.05.030","article-title":"Experimental study on convective heat transfer and flow resistance characteristics of water flow in twisted elliptical tubes","volume":"31","author":"Yang","year":"2011","journal-title":"Appl. Therm. Eng."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"761","DOI":"10.1016\/j.ijheatmasstransfer.2017.02.061","article-title":"Analysis of heat transfer and flow resistance of twisted oval tube in low Reynolds number flow","volume":"109","author":"Cheng","year":"2017","journal-title":"Int. J. Heat Mass Transf."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"496","DOI":"10.1504\/PCFD.2008.021327","article-title":"Relationship between heat transfer intensity and absolute vorticity flux intensity in flat tube bank fin channels with Vortex Generators","volume":"8","author":"Song","year":"2008","journal-title":"Prog. Comput. Fluid Dyn. Int. J."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"041902","DOI":"10.1115\/1.4023037","article-title":"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","volume":"135","author":"Song","year":"2013","journal-title":"J. Heat Transf."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"620","DOI":"10.1016\/j.ijheatmasstransfer.2013.03.011","article-title":"Secondary flow intensity determines Nusselt number on the fin surfaces of circle tube bank fin heat exchanger","volume":"62","author":"Hu","year":"2013","journal-title":"Int. J. Heat Mass Transf."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"349","DOI":"10.1016\/j.ijheatmasstransfer.2015.10.001","article-title":"Interaction of counter rotating longitudinal vortices and the effect on fluid flow and heat transfer","volume":"93","author":"Song","year":"2016","journal-title":"Int. J. Heat Mass Transf."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1064","DOI":"10.1016\/j.applthermaleng.2016.05.022","article-title":"Quantitative relationship between secondary flow intensity and heat transfer intensity in flat-tube-and-fin air heat exchanger with vortex generators","volume":"103","author":"Song","year":"2016","journal-title":"Appl. Therm. Eng."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"72","DOI":"10.1016\/j.ijthermalsci.2014.03.005","article-title":"Study on heat transfer and friction factor characteristics of \u03b3-Al2O3\/water through circular tube with twisted tape inserts with different thicknesses","volume":"82","author":"Esmaeilzadeh","year":"2014","journal-title":"Int. J. Therm. Sci."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"124","DOI":"10.1016\/j.icheatmasstransfer.2016.04.003","article-title":"The experimental study on the heat transfer and friction factor characteristics in tube with a new kind of twisted tape insert","volume":"75","author":"Man","year":"2016","journal-title":"Int. Commun. Heat Mass Transf."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"462","DOI":"10.1016\/j.enconman.2016.06.063","article-title":"Effectiveness-NTU analyses in a double tube heat exchanger equipped with wavy strip considering various angles","volume":"123","author":"Pourahmad","year":"2016","journal-title":"Energy Convers. Manag."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"26","DOI":"10.1016\/j.cep.2012.06.003","article-title":"Heat transfer enhancement in double-pipe heat exchanger by means of rotor-assembled strands","volume":"60","author":"Zhang","year":"2012","journal-title":"Chem. Eng. Process. Process Intensif."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"96","DOI":"10.1016\/j.ijthermalsci.2015.02.019","article-title":"Experimental and numerical study of fluid flow and heat transfer in an annulus of inner twisted square duct and outer circular pipe","volume":"94","author":"Bhadouriya","year":"2015","journal-title":"Int. J. Therm. Sci."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"113886","DOI":"10.1016\/j.applthermaleng.2019.113886","article-title":"\u03b5-NTU analysis of turbulent flow in a corrugated double pipe heat exchanger: A numerical investigation","volume":"159","author":"Bashtani","year":"2019","journal-title":"Appl. Therm. Eng."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"286","DOI":"10.1016\/j.applthermaleng.2015.06.091","article-title":"The effect of successive alternating wall deformation on the performance of an annular heat exchanger","volume":"90","author":"Zambaux","year":"2015","journal-title":"Appl. Therm. Eng."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"706","DOI":"10.1016\/j.ijheatmasstransfer.2019.01.115","article-title":"Optimal design of a double pipe heat exchanger based on the outward helically corrugated tube","volume":"135","author":"Wang","year":"2019","journal-title":"Int. J. Heat Mass Transf."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"194","DOI":"10.1016\/j.applthermaleng.2016.06.134","article-title":"Thermal and fluid flow first-principles numerical design of an enhanced double pipe heat exchanger","volume":"107","author":"Gorman","year":"2016","journal-title":"Appl. Therm. Eng."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"111877","DOI":"10.1016\/j.enconman.2019.111877","article-title":"Experimental study on the flow and heat transfer characteristics of nanofluids in double-tube heat exchangers based on thermal efficiency assessment","volume":"197","author":"Qi","year":"2019","journal-title":"Energy Convers. Manag."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"135","DOI":"10.1016\/j.ijthermalsci.2018.03.002","article-title":"Developed correlations for heat transfer and flow friction characteristics of louvered finned tube heat exchangers","volume":"129","author":"Sadeghianjahromi","year":"2018","journal-title":"Int. J. Therm. Sci."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"114343","DOI":"10.1016\/j.applthermaleng.2019.114343","article-title":"Thermo-hydraulic performance optimization of wavy fin heat exchanger by combining delta winglet vortex generators","volume":"163","author":"Luo","year":"2019","journal-title":"Appl. Therm. Eng."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"106361","DOI":"10.1016\/j.ijthermalsci.2020.106361","article-title":"Thermal performance of a zig-zag channel formed by two wavy fins mounted with vortex generators","volume":"153","author":"Luo","year":"2020","journal-title":"Int. J. Therm. Sci."},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Song, K.W., Shi, W.N., Wu, X., and Wang, L.B. (2020). Characteristics of flow symmetry and heat transfer of winglet pair in common flow down configuration. Symmetry, 12.","DOI":"10.3390\/sym12020209"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"215","DOI":"10.1016\/j.ijthermalsci.2018.11.002","article-title":"Heat transfer characteristics of concave and convex curved vortex generators in the channel of plate heat exchanger under laminar flow","volume":"137","author":"Song","year":"2019","journal-title":"Int. J. Therm. Sci."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"206","DOI":"10.1016\/j.ijthermalsci.2016.06.011","article-title":"Effects of longitudinal vortex interaction on periodically developed flow and heat transfer of fin-and-tube heat exchanger","volume":"109","author":"Song","year":"2016","journal-title":"Int. J. Therm. Sci."}],"container-title":["Symmetry"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-8994\/12\/8\/1213\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T09:51:14Z","timestamp":1760176274000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-8994\/12\/8\/1213"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,7,23]]},"references-count":35,"journal-issue":{"issue":"8","published-online":{"date-parts":[[2020,8]]}},"alternative-id":["sym12081213"],"URL":"https:\/\/doi.org\/10.3390\/sym12081213","relation":{},"ISSN":["2073-8994"],"issn-type":[{"value":"2073-8994","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,7,23]]}}}