Combined free‐and‐forced convection: I. Heat transfer in aiding flow

Abstract

A study of the rate of heat transfer to air at low velocities was performed in a heated stainless tube, 4.42‐in. inside diameter and 102‐in. long. The air flowed upward through the tube, under which conditions the buoyancy forces aided the forced flow. The investigation covered a Reynolds number range from 385 to 4,930, and nominal wall temperatures of 100, 500 and 950°C. For laminar aiding flow, the local Nusselt number could be correlated with (NGr/NRc). For turbulent flow, the local Nusselt number was correlated with the Grashof number independently of the axial position for fully‐developed flow, and agreed with published data for pure free convection.

Mixed convection heat transfer and flow in vertically heated channels

“…Aung and Worku [7,8] have presented the numerical analysis for both asymmetric wall temperature and asymmetric wall heat flux in a vertical channel and found the criteria for the occurrence of flow reversal. It has been found that in a vertical tube the aiding buoyancy force can enhance the heat transfer rate [9,10] while the opposing buoyancy force can reduce the heat transfer rate [ll]. However, Wirtz et.…”

Free and Forced Convective Heat Transfer

“…If we compare equation (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) and (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21), we see that the differences occur Expressions for noncircular tubes are presented in a variety of sources (4-6). In many cases, it is possible to use the relation between equivalent diameter and Deq.…”

“…In many cases, it is possible to use the relation between equivalent diameter and Deq. = 4Rh (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24) Exceptions are discussed in reference 6. One additional point should be made about the foregoing heat transfer equations.…”

“…For this reason a semiempirical approach is used to determine heat transfer coefficients. The relation used for cylinders (and objects as well) is h D kf (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) The f subscript refers to the temperature at which the properties are determined. This temperature (the film temperature) is…”

“…We must now correct to six rows. The correction factor from Table 6 In order to solve for the correct side, we use equation (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). Here the side and n are given in Table 6-2.…”