Abstract
The aim of the paper is to supply updated air convective coefficients
1 Introduction
The attempts to investigate energy exchange by convection in circular and cylindrical bodies wherein the determination of power losses, energy rate, the thermal behavior among a system and its surroundings and the development of thermal models for specific industrial applications are of utmost relevance. Taking into consideration the importance of accurately creating thermal models, convection must be analyzed at a certain level of fidelity. It could appear that heat convection is merely obtained by multiplying an average convection coefficient
Based on the information contained in the preceding paragraph, this article presents an analysis to determine the average convection coefficient of air
2 Materials and methods
Explicitly, flow forced convection is generated by external means wherewith air velocity is changed. By the application of three correlations stated by [4–6] the average convection coefficient is determined when air particles are in contact with the surface wall of a steel cylindrical rod as it is shown in Fig. 1.
2.1 Heat transfer in a single tube in air cross-flow
As it is previously mentioned, heat is influenced by several factors that are cumbersome to perform analytically. However, on account of the work by Zukauskas, Churchill et al. and Hilpert, [4–6] empirical correlations to determine the Nusselt number were established, thereby average convective coefficients can be calculated.
2.1.1 Zukauskas's correlation
2.1.2 Churchill and Bernstein's correlation
2.1.3 Hilpert's correlation
A range of Reynolds numbers were determined for air flow speeds of
2.2 Lumped heat capacity model LHC
3 Results
The average heat convection coefficient of air
Heat convection coefficient,
0.5 | 12.31 | 13.57 | 11.60 |
1.0 | 18.65 | 19.32 | 16.03 |
1.5 | 23.79 | 23.85 | 19.37 |
2.0 | 28.28 | 27.75 | 22.23 |
2.5 | 32.33 | 31.24 | 25.52 |
3.0 | 36.07 | 34.45 | 28.56 |
3.5 | 39.56 | 37.44 | 31.42 |
4.0 | 42.86 | 40.26 | 34.12 |
4.5 | 46.00 | 42.95 | 36.70 |
5.0 | 49.01 | 45.52 | 39.17 |
LHC analysis was performed during a period of time t = 30 min until steady state conditions were obtained, i.e.,
As it is illustrated in the previous figures, the steady state temperature was reached at the maximum air speed of v = 5 m s−1. The final temperature for the three different correlations were compared and evaluated by FEA.
3.1 FEA simulation
Finite element analysis using ANSYS Fluent code was performed in a 2D geometry field considering that air velocity
To illustrate, the isothermal behavior at maximum air velocity
Analytical and FEA solutions using edge sizing feature with quadrilateral dominant method performed during a simulation time of
Analytical and FEA comparison a
T(t) [ | T(t) [ | sd | T(t) [ | T(t) [ | sd | T(t) [ | T(t) [ | sd | |
1) Zukauskas C. | 2) Churchill C. | 3) Hilpert C. | |||||||
1.00 | 37.33 | 37.34 | 0.00 | 36.90 | 36.91 | 0.30 | 39.21 | 39.22 | 1.30 |
2.00 | 32.49 | 32.49 | 0.00 | 32.69 | 32.69 | 0.14 | 35.19 | 35.21 | 1.92 |
3.00 | 30.16 | 30.16 | 0.00 | 30.56 | 30.56 | 0.28 | 32.37 | 32.42 | 1.59 |
4.00 | 28.84 | 28.87 | 0.02 | 29.28 | 29.29 | 0.29 | 30.60 | 30.65 | 1.25 |
5.00 | 28.02 | 28.05 | 0.02 | 28.45 | 28.47 | 0.29 | 29.48 | 29.51 | 1.03 |
From Table 2 it is clear that more accurate results are obtained using the first correlation since the Standard Deviation
4 Conclusions
The determination of sundry convective coefficients of air
The most accurate correlation that can be applied in phenomena with air in cross-flow over cylindrical bodies is Zukauskas correlation since the standard deviation
is lower than the two other correlations; The applicability of the presented average convective coefficients of air are suitable under phenomena with Reynolds numbers in the range from
. It occurs due to the characteristics of the geometry in study and the air velocity conditions; The findings of this study hold important implications for convective analysis in mechanical systems featuring cylindrical components. Specifically, the insights gained from the present work can be readily applied to a wide range of rotary machinery, including shafts, gears, roller bearings, seals, and other components where heat transfer occurs between the solid body and the surrounding air. This revision provides a clearer explanation of the relevance and scope of the research, and offers a more specific and engaging description of the types of mechanical elements to which the results can be applied.
References
- [1]↑
L. T. Bergman and S. A. Lavine, Fundamentals of Heat and Mass Transfer. John Wiley & Sons, 2017.
- [2]
W. D. Hahn and M. N. Özisik, Heat Conduction. John Wiley & Sons, 2012.
- [3]
H. Herwig and A. Moschallski, Heat Transfer (in German). Springer Vieweg, 2014.
- [4]↑
A. Zukauskas, “Heat transfer from tubes in cross-flow,” Adv. Heat Tran., vol. 8, pp. 93–160, 1972.
- [5]↑
S. Churchill and M. Bernstein, “A correlating equation for forced convection from gases and liquids to a circular cylinder in cross-flow,” J. Heat Mass Tran., vol. 99, no. 2, pp. 300–306, 1997.
- [6]↑
R. Hilpert, “Heat dissipation of hot wires and tubes in air flow” (in German). Forshung auf dem Gebiet des Ingeniurwesens, vol. 4, pp. 215–224, 1993.
- [7]↑
M. Petrik, G. Szepesi, and K. Jármai, “CFD analysis and heat transfer characteristics of finned tube heat exchangers,” Pollack Period., vol. 14, no. 3, pp. 165–176, 2019.
- [8]↑
A. Farhana and M. A. R. Sharif, “Numerical study of cross-flow around a circular cylinder with differently shaped spanwise surface grooves at low Reynolds number,” Eur. J. Mech./B Fluid., vol. 91, pp. 203–218, 2022.
- [9]↑
C. Canpolat and S. Besir, “Influence of single rectangular groove on the flow past a circular cylinder,” Int. J. Heat Fluid Flow., vol. 64, pp. 79–88, 2017.
- [10]↑
A. B. Khaoula and F. B. Nemja, “Impact of grooved cylinder on heat transfer by numerical convection in cylindrical geometry,” Adv. Mech. Eng., vol. 14, no. 8, pp. 1–16, 2022.
- [11]↑
I. Haber and I. Farkas, “Analysis of the air-flow at photovoltaic modules for cooling purposes,” Pollack Period., vol. 7, no. 1, pp. 113–121, 2012.
- [12]↑
P. Bencs, Sz. Szábó, and D. Oertel, “Simultaneous measurement of velocity and temperature field in the downstream region of a heated cylinder,” Eng. Rev., vol. 34, no. 1, pp. 7–13, 2014.
- [13]↑
K. D. Cole, J. V. Beck, A. Haji-Sheikh, and B. Litkouhi, Heat Conduction Using Green’s Functions. CRC Press. Taylor & Francis Group, 2011.