Combined forced and natural convection with low-speed air flow over horizontal cylinders

Abstract

This article describes experimental work on the mixed convection régime with flow normal to electrically heated cylinders. The forcing velocities used were in the range 0·0085–3 ft./sec (i.e. 10−2 < Ref < 45) and temperature differences in the range 30°C to 200°C (i.e. 10−3 < Ra < 10) were covered.Correlations are proposed for the forced convection and natural convection conditions. A correlation is also developed for the combined forced and natural convection region by a vectorial addition of the flow parameters, which gives good agreement with the experiments except over a limited range in the contraflow régime.

Boundary Layers of Air Adjacent to Cylinders

“…Although the effect of a turbulence intensity of 0.5 appeared to increase somewhat as tne wind velocity was raised from 20 to 400 cm/sec (for a 2-cm diarieter cylinder), for convenience we will simply reduce the factor 0.74 in equation 4 by 22%. The following relations are important at low wind speeds, large diameters, and large temperature differences between the plant tissue and the ambient air (9,16,23,25). For a temperature difference of 5 C (moderately large) and a wind velocity of 10 cm/sec (low), forced convection exceeds natural convection for diameters up to 100 cm for horizontal cylinders (16,25).…”

Unsteady conjugate heat/mass transfer from a circular cylinder in laminar crossflow at low Reynolds numbers

“…The majority of relations worked-out to calculate Nu are valid for Pr ¼ 0:71 (Pr does not appear practically in these relations) (see, as example, [1,2,5,21]). In anemometry, the unsteady conjugate heat/mass transfer from a circular cylinder in laminar crossflow presents some interest only for the frequency response of the resistance thermometer.…”

“…The articles dedicated to forced convection heat transfer from a circular cylinder (as example, [1,2,21]) give a special attention to the influence of the variable fluid properties on the transfer rate. Nusselt [24] proposed the following idea in order to solve in a very simple manner this problem: the computation of the non-dimensional parameters at an effective temperature of the system, T eff .…”

An anemometry technique for turbulence measurements at low velocities

“…As known generally, the heat transfer characteristics of a fine wire at low velocities are considerably different from those in the pure forced convection (Hatton et al 1970). In high Reynolds-number flows, the V-shaped hot-wire is not subject to any effects of the wire supports, and the directional sensitivities of the hot-wire can be obtained from those which were well established for conventional inclined hot-wires by taking account of the geometry of the V-shaped hot-wire (Hishida and Nagano 1988a).…”