Numerical Investigation of Transitional Characteristics for Natural-Convection Flow in Open-Ended Inclined Channel Heated From Below

This report presents an investigation of the characteristics for transitional natural-convection flow in an open-ended inclined channel heated from below in the air under uniform heat flux intensity and non-Boussinesq condition. The investigated range of modified Rayleigh number and inclination is from 5.93 × 106 to 1.45 × 109 and 30–90 deg to the horizontal, respectively. Fine-resolution implicit large Eddy simulation is performed to solve the compressible governing equations using the modified preconditioned all-speed Roe scheme, hybrid boundary condition, and dual-time-stepping technique. The Nusselt number based on the maximum wall-temperature differs significantly while based on averaged wall-temperature is closer to the previously proposed laminar correlations. Transition is found to be pronounced at a lower angle of inclination (30 deg) for the considered heat flux intensity. The absolute magnitude of the critical length for the start and end of the transition when converted to nondimensional parameters is found to be higher compared to similar data for natural convection flow over a flat plate in water but the ratio of the end to start of the transition is found to be comparable. Single-roll longitudinal vortices periodically placed in spanwise direction exists in the transition region whose wavelength is found to be higher than those reported for channel flow under the isothermal condition and flow over a flat plate in water. Correlations for Nusselt number, critical aspect ratio, and vortex wavelength to the modified Rayleigh number are presented.

Heat Concentration around a Cylindrical Interface Crack in a Composite Tube

Cracks always form at the interface of discrepant materials in composite structures, which influence thermal performances of the structures under transient thermal loadings remarkably. The heat concentration around a cylindrical interface crack in a bilayered composite tube has not been resolved in literature and thus is investigated in this paper based on the singular integral equation method. The time variable in the two-dimensional temperature governing equation, derived from the non-Fourier theory, is eliminated using the Laplace transformation technique and then solved exactly in the Laplacian domain by the employment of a superposition method. The heat concentration degree caused by the interface crack is judged quantitatively with the employment of heat flux intensity factor. After restoring the results in the time domain using a numerical Laplace inversion technique, the effects of thermal resistance of crack, liner material, and crack length on the results are analyzed with a numerical case study. It is found that heat flux intensity factor is material-dependent, and steel is the best liner material among the three potential materials used for sustaining transiently high temperature loadings.

Non-Fourier Heat Conduction of a Functionally Graded Cylinder Containing a Cylindrical Crack

The present work investigates the problem of a cylindrical crack in a functionally graded cylinder under thermal impact by using the non-Fourier heat conduction model. The theoretical derivation is performed by methods of Fourier integral transform, Laplace transform, and Cauchy singular integral equation. The concept of heat flux intensity factor is introduced to investigate the heat concentration degree around the crack tip quantitatively. The temperature field and the heat flux intensity factor in the time domain are obtained by transforming the corresponding quantities from the Laplace domain numerically. The effects of heat conduction model, functionally graded parameter, and thermal resistance of crack on the temperature distribution and heat flux intensity factor are studied. This work is beneficial for the thermal design of functionally graded cylinder containing a cylindrical crack.

Radiant absorption characteristics of corrugated curved tubes

The utilization of modern paraboloidal concentrators for conversion of solar radiation into heat energy requires the development and implementation of compact and efficient heat absorbers. Accurate estimation of geometry influence on absorption characteristics of receiver tubes is an important step in this process. This paper deals with absorption characteristics of heat absorber made of spirally coiled tubes with transverse circular corrugations. Detailed 3-D surface-to-surface Hemicube method was applied to compare radiation performances of corrugated and smooth curved tubes. The numerical results were obtained by varying the tube curvature ratio and incident radiant heat flux intensity. The details of absorption efficiency of corrugated tubes and the effect of curvature on absorption properties for both corrugated and smooth tubes were presented. The results may have significance to further analysis of highly efficient heat absorbers exposed to concentrated radiant heating.

Efficiency of Water Curtains

It is possible to use a water curtain to preclude a house fire spreading. Water curtains are designed pursuant to theoretical calculations. Experiments were prepared and realised with a goal to determine the radiant heat flux intensity reduction of fire passing through a water curtain in VŠB, TU – Ostrava.