Abstract
Laminar free convection heat transfer from a heated cylinder and tube arrays is studied numerically to obtain the local and average Nusselt numbers. To verify the numerical simulations, the Nusselt numbers for a single cylinder were compared to other authors for the Rayleigh numbers of 103 and 104. Furthermore, the vertically arranged heated tube arrays 4 × 1 and 4 × 2 with the tube ratio spacing SV/D = 2 were considered, and obtained average Nusselt numbers were compared to the existing correlating equations. A good agreement of the average Nusselt numbers for the single cylinder and the bottom tube of the 4 × 1 tube array is proved. On the other hand, the bottom tubes of the 4 × 2 tube array affect each other, and the Nusselt numbers have a different course compared to the single cylinder. The temperature fields for the tube array 4 × 4 in basic, concave, and convex configurations are studied, and new correlating equations were determined. The simulations were done for the Rayleigh numbers in the range of 1.3 × 104 to 3.7 × 104 with a tube ratio spacing S/D of 2, 2.5, and 3. On the basis of the results, the average Nusselt numbers increase with the Rayleigh numbers and tube spacing increasing. The average Nusselt number and total heat flux density for the convex configuration increase compared to the base one; on the other hand, the average Nusselt number decreases for the concave one. The results are applicable to the tube heaters constructional design in order to heat the ambient air effectively.
Highlights
Laminar free convection heat transfer from heated tubes to air has been used in various technical applications such as heat exchangers, electronic components, heat storage equipment, and waste heat recovery systems
We have studied the laminar free convection heat transfer from the vertical array of four
We have studied the laminar free convection heat transfer from the vertical array of four courses of the local Nusselt numbers Nuφ for the individual tubes in the array are shown in Figure isothermal circular tubes with a diameter of 20 mm
Summary
Laminar free convection heat transfer from heated tubes to air has been used in various technical applications such as heat exchangers, electronic components, heat storage equipment, and waste heat recovery systems. The advantage of free convection heat transfer is a creation of thermal comfort without a draft and dust fragments swirling in the space. This energy-saving way of heat transfer is reliable and the operation without fans is cost-effective and noise reducing. Several authors have dealt with the numerical calculations of heat transfer from a heated cylinder or tubes array at free convection. Kuehn and Goldstein [3] studied laminar free convection heat transfer from the horizontal cylinder by solving the Navier–Stokes and energy equations using an elliptical numerical procedure for 100 ≤ Ra ≤ 107
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