A Derivation of the Colburn Analogy

This paper presents a derivation of the empirical Colburn analogy and discusses its implications. Key words: heat transfer, Colburn, j factor, turbulence, power law, log-law, wall layer

The generalised Blasius correlation for turbulent flow past flat plates

This paper presents a theoretical derivation of the empirical Blasius power law correlation for the friction factor. The coefficients in this correlation are shown to be dependent on the Reynolds number. Published experimental data is well correlated. Key words: Blasius, friction factor, turbulence, power law, log-law, wall layer

On the Sieder state correction and its equivalent in mass transfer

The physical background behind the success of the Sieder-Tate correction in heat transfer is analysed. The equivalent correction for mass transfer correlations is based on the ratio of diffusivities at the wall and bulk concentrations. This correction is not required if the Prandtl/Schmidt numbers are evaluated at the wall layer conditions and the Reynolds number at the bulk conditions. This technique brings heat and mass transfer coefficients into agreement.

The wall shear rate in non-Newtonian turbulent pipe flow

This paper presents a method for calculating the wall shear rate in pipe turbulent flow. It collapses adequately the data measured in laminar flow and turbulent flow into a single flow curve and gives the basis for the design of turbulent flow viscometers. Key words: non-Newtonian, wall shear rate, turbulent, rheometer

A Similarity Analysis for Heat Transfer in Newtonian and Power Law Fluids Using the Instantaneous Wall Shear Stress

This paper presents a technique that collapses existing experimental data of heat transfer in pipe flow of Newtonian and power law fluids into a single master curve. It also discusses the theoretical basis of heat, mass and momentum analogies and the implications of the present analysis to visualisations of turbulence.

On The Critical Reynolds Number For Transition From Laminar To Turbulent Flow

In this visualisation, the transition from laminar to turbulent flow is characterised by the intermittent ejection of wall fluid into the outer stream. The normalised thickness of the viscous flow layer reaches an asymptotic value but the physical thickness drops exponentially after transition. The critical transition pipe Reynolds number can be obtained simply by equating it with the asymptotic value of the normalised thickness of viscous flow layer. Key words: Transition, critical stability Reynolds number, critical transition Reynolds number, non-Newtonian pipe flow

On the Karman constant

Numerous studies in the past 40 years have established that turbulent flow fields are populated by transient coherent structures that represent patches of fluids moving cohesively for significant distances before they are worn out by momentum exchange with the surrounding fluid. Two particular well-documented structures are the hairpin vortices that move longitudinally above the wall and ejections inclined with respect to the wall that bring the fluid from the transient viscous layers underneath these vortices into the outer region of the boundary layer. It is proposed that the Karman universal constant in the logarithmic law the sine of the angle between the transient ejections and the direction normal to the wall. The edge of the buffer layer is represented by a combination of the Karman constant and the damping function in the wall layer. Computation of this angle from experimental data of velocity distributions in turbulent shear flows matches published traces of fronts of turbulence obtained from the time shifts in the peak of the correlation function of the velocity. Key works: Turbulence, coherent structures, Karman constant, mixing-length, shear layers