flat tube, heat transfer intensity, aerodynamic drag, intensifier.


It is know that a heat exchange tube with a flat-oval profile has excellent thermal and aerodynamic characteristics in contrast to a round tube. Thus, with the same planes, a flat tube has a significant increase in thermal and aerodynamic efficiency compared to a round tube, which is widely used in industry. However, at present, there are a limited number of publications on the study of heat transfer and aerodynamics inside a flat pipe.

In this paper, we present the methodology and results of the study of heat transfer and aerodynamic drag in a pipe, and describe the experimental stand for such studies.

The experiments performed in a flowing wind tunnel with an internal diameter of 36 mm, operating in an open-loop circuit. The working medium is air drawn from the laboratory room. The prototype was a steel pipe with a flat-oval profile, 320 mm long, 30x15 mm cross section, and 2 mm wall thickness.

The created experimental stand allows us to study the heat transfer and aerodynamic drag of a flat pipe under the boundary condition q=const. An electric heater ensured this condition, which is a nichrome wire with a diameter of 0.6 mm wound along the entire length of the pipe and insulated from the external environment.

The experiments were carried out in the range of Reynolds numbers (10.5 - 55.0) 103 and dissipated powers (50 - 150) W. The average air temperature in the pipe was set in the range (20 - 55) 0C, and the average temperature of the pipe wall was set in the range (24 - 140) 0C in accordance with the electric power supplied to the heater.

Empirical correlations proposed for determining the intensity of heat transfer and aerodynamic drag inside a flat pipe. The data had compared with a round tube. The results had analyzed, and it had shown for the first time that the intensity of heat transfer and aerodynamic drag in a flat-oval pipe is 1.1 to 1.2 times and 1.4 to 1.7 times higher, respectively.


S.A. Burtsev, V.K. Vasil'ev, S.A. Burtsev, V.K. Vasil'ev, Yu.A. Vinogradov, N.A. Kiselev and A.A. Titov, “Experimental study of parameters of surfaces coated with regular relief,” Sciene and educacion. Scientific periodical of the Bauman MSTU, no.1, pp. 1-23, Jan. 2013.

S. Eiamsa-ard, P. Somkleang, C. Nuntadusit and C. Thianpongm, “Heat transfer enhancement in tube by inserting uniform/non-uniform twisted-tapes with alternate axes: Effect of rotated-axis length,” Applied Thermal Engineering, vol. 54, iss. 1, pp. 289–309, May 2013.

S.W. Chang, T.L. Yang and J.S. Liou, "Heat transfer and pressure drop in tube with broken twisted tape insert," Experimental Thermal and Fluide Science, vol. 32, iss. 2, pp. 489–501, Nov. 2017.

S. Eiamsa-ard and P. Promvonge, “Enhancement of heat transfer in a tube with regularly-spaced helical tape swirl generators,” Solar Energy, vol. 78, iss .4, pp. 483–494, Apr. 2005.

O. Keklikcioglu and V. Ozceyhan, “Experimental investigation on heat transfer enhancement in a circular tube with equilateral triangle cross sectioned coiled-wire inserts,” Applied Thermal Engineering, vol. 131, pp. 686–695, Fed. 2018.

S.W. Chang, J.Y. Gao and H.L. Shih, “Thermal performances of turbulent tubular flows enhanced by ribbed and grooved wire coils,” International Journal of Heat and Mass Transfer, vol. 90, pp. 1109–1124, Nov., 2015.

P. Promvonge, “Thermal performance in circular tube fitted with coiled square wires,” Energy Conversion Management, vol. 49, iss. 5, pp. 980–987, May 2008.

P. Promvonge, N. Koolnapadol, M. Pimsar and C. Thianpong, “Thermal performance enhancement in a heat exchanger tube fitted with inclined vortex rings,” Applied Thermal Engineering, vol. 62, iss. 1, pp. 285–292, Jan. 2014.

A. Acir, I. Ata and M.E. Canli, “Investigation of effect of the circular ring turbulators on heat transfer augmentation and fluid flow characteristic of solar air heater,” Experimental Thermal and Fluide Science, vol. 77, pp. 45–54, Oct. 2016.

W. Chingtuaythong and S. Chokphoemphun, “Thermal performance augmentation in heat exchanger tube with oval-pentagon rings,” Transactions of the TSME. Journal of Research and Applications in Mechanical Engineering, vol. 6, no. 1, pp. 50–62, Jul. 2018.

V. A. Rogachev, A. M. Terekh, V. D. Burley and A. V Semenyako, “Intensification of heat exchange in a round tube,” Energy: economy, technology, ecology, no. 1(22), pp. 36-42, 2008.

V. Demchuk, V.A. Rogachev, O.M. Terekh and O.I. Rudenko, “Thermal and aerodynamic efficiency of helical tubes with equidistant surface,” East European Journal of Advanced Technologies, vol. 53, no. 5/8, pp. 26-30, 2007.

S.A. Reva, “CFD modeling of flow inside helical pipes,” Energy: economy, technology, ecology, no. 4(50), pp. 119-125, 2017.

M. Kh. Abdolbaqi, W. H. Azmi, Mamat Rizalman, N. M. Z. N. Mohamed, G. Najafi, “Experimental investigation of turbulent heat transfer by counter and coswirling flow in a flat tube fitted with twin twisted tapes,” International Communications in Heat and Mass Transfer, vol. 75. pp. 295–302, Jul. 2016.

H. Pourdel, H. H. Afrouzi, O. A. Akbari, M. Miansari, D. Toghraie, A. Marzban and A. Koveiti, “Numerical investigation of turbulent flow and heat transfer in flat tube. Effect of dimples with operational goals,” Journal of Thermal Analysis and Calorimetry, pp. 3471 – 83, Jul. 2018.

E. N. Pis’mennyi, “Ways for improving the tubular heaters used in gas turbine units,” Thermal Engineering, vol. 59, no. 6, pp. 485–490, 2012.

V.S. Kulynych, V.A. Rogachev and O.M. Terekh, “Methods of experimental study of heat transfer and aerodynamic drag in a flat-oval channel with intensifiers,” In Thermal power engineering: ways of renovation and development: collection of scientific works of the XVIII international scientific and practical conference. Kyiv, 2022, pp. 239 – 243.

V.P. Isachenko, Ed., Heat transfer: textbook for universities. M: Energoizdat, 1981.