Unsteady Heat Transfer Flow Research Articles

Numerical investigation of velocity slip and temperature jump effects on unsteady flow over a stretching permeable surface

In this paper, the boundary layer flow and heat transfer of unsteady flow over a porous accelerating stretching surface in the presence of the velocity slip and temperature jump effects are investigated numerically. A new effective collocation method based on rational Bernstein functions is applied to solve the governing system of nonlinear ordinary differential equations. This method solves the problem on the semi-infinite domain without truncating or transforming it to a finite domain. In addition, the presented method reduces the solution of the problem to the solution of a system of algebraic equations. Graphical and tabular results are presented to investigate the influence of the unsteadiness parameter A , Prandtl number Pr, suction parameter $f_{w}$ , velocity slip parameter $\gamma$ and thermal slip parameter $\phi$ on the velocity and temperature profiles of the fluid. The numerical experiments are reported to show the accuracy and efficiency of the novel proposed computational procedure. Comparisons of present results are made with those obtained by previous works and show excellent agreement.

Heat transfer analysis in the time-dependent slip flow over a lubricated rotating disc

In this paper, we have performed an analysis to study characteristics of heat transfer in unsteady flow past a lubricated rotating disc. A generalized Newtonian fluid obeying power law constitutive equation has been invoked to model the lubricant. A set of dimensionless coordinates is utilized to convert given partial differential equations into non-linear coupled ordinary differential equations. Interfacial conditions have been derived with the help of continuity of shear stress and velocity of the lubricant and core fluid. The obtained boundary value problems are numerically solved with the help of Keller-Box method. Impact of physical parameters in the presence of lubrication on fluid velocity, temperature and pressure is displayed graphically. The skin friction coefficients and local Nusselt number are examined through tables.

非定常熱流動場における壁近傍の速度-熱伝達の光学的同時計測について

非定常熱流動場における壁近傍の速度-熱伝達の光学的同時計測について

Numerical investigation of forced convection heat transfer in unsteady flow past a row of square cylinders

This paper presents the unsteady laminar forced convection heat transfer from a row of five isothermal square cylinders placed in a side-by-side arrangement at a Reynolds number of 150. The numerical simulations are performed using a finite volume code based on the PISO algorithm in a collocated grid system. Special attention is paid to investigate the effect of the spacing between the cylinders on the overall transport processes for the separation ratios (spacing to size ratio) between 0.2 and 10. No significant interaction between the wakes is observed for spacing greater than four times the diameter at this Reynolds number. However, at smaller spacing, the wakes interact in a complicated manner resulting different thermo-hydrodynamic regimes. The vortex structures and isotherm patterns obtained are systematically presented and discussed for different separation ratios. In addition, the mean and instantaneous drag and lift coefficients, mean and local Nusselt number and Strouhal number are determined and discussed for various separation ratios. A new correlation is derived for mean Nusselt number as a function of separation ratio for such flows.

Energy consideration of the nonlinear effects in a Rijke tube

The goal of this work is to characterize the excited states of a thermoacoustic system with mean flow. The properties of excited regimes are determined by the balance between thermoacoustic energy transformation and acoustic losses. In many systems, the sound intensity is not sufficient for nonlinear acoustic losses to be a major factor in defining nonlinear saturation of thermoacoustic instability. It is the nonlinearity of the heat transfer process that is responsible for limit-cycle stabilization of linearly unstable acoustic modes and for the appearance of higher harmonics. In the present study, both a nonlinear theory based on energy consideration and a model for the nonlinear convective heat transfer in unsteady flow are developed. Experimental data are obtained for the excited regimes of operation of an electric Rijke tube. Model results for hysteresis in the transition between stable and excited states and for limit-cycle parameters are compared with test data.

The effects on heat transfer of unsteady flow around two square bars mounted staggered in a plane channel

The unsteady laminar flow and heat transfer characteristics in a plane channel with two square bars mounted staggered to the approaching flow are numerically analyzed. A finite volume method is applied with a fine grid and time resolution. The longitudinal and transverse separation distances between the bars are varied, whereas the bar height to channel height d/H, and the Reynolds number based on channel height Re, are d/H= 1 8 and 800 respectively. Complex flow patterns develop in the channel due the interaction between the two staggered square bars. For the cases with L/d≥2 shedding of vortices with only one frequency are present in the flow, and biased flow with frequency modulation of the vortices shedding for the cases with L/d<2 are found.

Heat transfer in unsteady flow through a porous medium between two infinite parallel plates in relative motion

An approximate solution to the heat transfer in a flow of a viscous incompressible fluid through a porous medium bounded by two infinite parallel plates, the lower one stationary and the upper one oscillating in its own plane, is presented. Expressions for the mean temperature, the amplitude, and phase of the first and second harmonic of the rate of heat transfer and the mean rate of heat transfer are derived. The mean temperature is shown on graphs and the numerical values of the amplitudes and the phase are entered in a table. It is observed that the mean rate of heat transfer decreases with more ease of percolation but increases with increasing the frequency ω.

Nonlinear behavior of acoustic waves in combustion chambers—II

The approximate analysis developed in Part I of this work is applied to several specific problems. One purpose is to illustrate the use of the formalism, and a second is to demonstrate the validity of the method by comparing results with numerical solutions, obtained elsewhere, for the “exact” equations. A simple problem is treated first, the decay of a standing wave in a box containing a mixture of gas and suspended particles; one example of the steepening of an initially sinusoidal wave in pure gas is included. Viscous losses on an inert surface are treated essentially according to classical linear theory; recent experimental results are used as the basis for incorporating approximately the influence of nonlinear heat transfer in unsteady flow. All of the preceding results are combined in calculations of two examples of unstable motions in a solid propellant rocket motor and in a T-burner.