An Experimental Study of Turbulent Natural Convection Boundary Layers

Abstract

An experimental investigation on turbulent natural convection boundary layers has been conducted with water on a vertical plate of constant heat flux. Local heat transfer data are presented for laminar, transition, and turbulent natural convection, with the emphasis on the turbulent regime. The data extend to a modified Rayleigh number of 1016 for a threefold range in Prandtl number. The results indicate that natural transition occurs in the range 1012 < Ra* < 1014; i.e., fully developed turbulent flow occurs by Ra* = 104. This latter value can be as low as 2 × 1013 with the use of a trip rod. The physical structure of the turbulent boundary-layer flow was studied using the combined time-streak marker hydrogen bubble method. Temperature data and temperature corrected velocity data obtained by hot-film sensors are presented for Ra* values between 8.7 × 1013 and 7.1 × 1014. For the range of variables investigated, the major conclusions are (a) the local heat transfer coefficient exhibits a slight decrease with length, (b) confirmation that the vortex street layer in the transition region decays into a longitudinal-vortex-type structure, and (c) the outer portion of the thermal and velocity fields can be approximated by power profiles that fit almost all the data available to date.

Numerical correlation for natural convective flows in isothermal heated, inclined and convergent channels, for high Rayleigh numbers

“…This is caused by a mixing between the different fluid layers, or in other words, by the transition from laminar to turbulent regime. These results established a transition near to a critical local Grashof number of 0.9 × 10 12 for Phoenics and 2.5 × 10 12 for Fluent, near to the predicted value proposed in [26] and [27], and fixed in [15].…”

“…Figure 3 shows the profiles of nondimensional temperature obtained with DNS and experimentally [7], and also the profiles given by the 2D A very important research of this study, consists of the way in which the authors treat the problem of transition from laminar to turbulent regime. Based on [26] and [27], they fixed the transition at local Grashof number equal to 10 12 , under Neumann conditions of uniform wall heat fluxes. In this way, the same transition point was reached, for isolated flat plate, and for channel formed by two plates.…”

Design of a Mobile Probe to Predict Convection Heat Transfer on BIPV (Building Integrated Photovoltaic) at UTS (University of Technology Sydney)

“…It means that, for a fixed Ra, Vliet & Liu [10], and Fossa et al [26] have underestimated Nu and have predicted smaller values. While McAdams [7] and Sparrow & Gregg [9] have overestimated Nu and have predicted bigger values for Nu relative to the predicted Nu from the two correlations proposed in this paper.…”

“…Experimental results from the heater-apparatus are used to plot It is noted that, both empirical correlations from the probe and the embedded thermocouple on heater are within the range covered with McAdams [7], Sparrow & Gregg [9], Vliet & Liu [10] and Fossa et al [26]. It means that, for a fixed Ra, Vliet & Liu [10], and Fossa et al [26] have underestimated Nu and have predicted smaller values.…”

“…Vliet and Liu [10] experimentally studied natural convection in water on an UHF vertical surface and developed the local and the average correlations for laminar flow in the form of For local values: Nu = 0.6(Ra) 0.2 for 10 5 < Ra < 10 13 .…”