Flow measurement around a non-circular tube

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.The flow behavior around a cam shaped tube in cross flow has been investigated experimentally using flow visualization and pressure distribution measurement. The range of angle of attack and Reynolds number based on an equivalent circular tube are within 0 ≤α ≤ 360 and 2×104< Re eq <3.4×104, respectively. The pressure drag features are clarified in relation to the flow behavior around the tube. It is found that the highest pressure drag coefficient occurs at α = 90° and 270°over the whole range of Reynolds number. Results show that the pressure drag coefficient of the cam shaped tube is lower than that of a circular tube with the same surface area for more of the angles of attack

Numerical prediction of developing flow in gas pipelines

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.In this paper the numerical modeling of the dynamic behavior of compressible gas flow is investigated in pipelines. The numerical simulation is performed by solving the coupled conservation form of the governing equations for twodimensional, laminar, viscous, supersonic flow in developing region under different thermal boundary conditions. The numerical procedure is a finite-volume based finite-element method applied on unstructured grids. The convection terms are discretized by well-defined Roe Method and diffusion terms by a Galerkin finite element formulation. The temporal terms are evaluated based on an explicit fourth order Runge-Kutta scheme. The results indicate that heating the gas flow leads to an increase in pressure loss. In the other words, cooling the gas flow leads to decrease the pressure drop or power consumption of booster pressure station. Furthermore, change in the gas viscosity has considerable effects on the flow quantities such as pressure loss and friction factor

Stress behaviour across human tooth by temperature gradient resulting of laser irradiation

The authors report the simulation of temperature distribution and thermally induced stress in the premolar tooth under ND-YAG pulsed laser beam. The Three-Phase-Lag (TPL) non-Fourier model is proposed to describe the heat conduction in the human tooth with nonhomogeneous inner structures. A premolar tooth comprising enamel, dentin, and pulp with real shapes and thicknesses are considered and a numerical method of finite difference was adopted to solve the time-dependent TPL bio-heat transfer, strain and stress equations. The surface heating scheme is applied for simulation of laser therapy. The aim of this laser therapy is that the temperature of pulp reaches to 47oC. The results are achieved as a function of laser heat flux showed when laser beam is irradiated downward (from the top of the tooth), the temperature and thermally induced stress increase as a function of time. The temperature increment is high on the top layers of tooth that is a result of strong absorption of beams by enamel. The thermal stress and strain in the enamel and dentin layers are more than the pulp layer that is a result of weak thermal expansion of them proportional to the pulp layer

Qualitative analysis of spray characteristics of impinging jets using a gelled non-Newtonian propellant simulant

The utilization of liquid and solid fuels for propulsion and combustion processes with Newtonian characteristics are widely known. However, recent studies are considering the application of shear-thinning non-Newtonian fuels as alternative simulant since they have some advantages compared to the conventional propellants although there are challenges of providing better spray performance during the corresponding process. This paper, therefore, presents the results of the experimental investigations of the “near-field” spray characteristics with utilizing imaging techniques which evaluates the sheet formation and breakup length of four different spray patterns produced by the jet impingement of a gelled non-Newtonian propellant simulant. The qualitative analysis of this study shows that the spray patterns are different compared to those that are shaped by using Newtonian liquid fuels. This could lead to supposition that the non-Newtonian rheology of the gelled propellant simulant postponed the sheet and ligaments breakup, including the mode change of the atomization. In addition, the atomization of the sheet at different flow parameters could occur due to the formation and the sheet wave instability when aerodynamic and hydrodynamic of their origin are closely considered. This was further supported by the occurrence of perforations in the sheet

Stationary rotary force waves on the liquid–air core interface of a swirl atomizer

A one-dimensional wave equation, applicable to the waves on the surface of the air-core of a swirl atomizer is derived analytically, by analogy to the similar one-dimensional wave equation derivation for shallowwater gravity waves. In addition an analogy to the flow of water over a weir is used to produce an analytical derivation of the flow over the lip of the outlet of a swirl atomizer using the principle of maximum flow. The principle of maximum flow is substantiated by reference to continuity of the discharge in the direction of streaming. For shallowwater gravity waves, the phase velocity is the same expression as for the critical velocity over the weir. Similarly, in the present work, the wave phase velocity on the surface of the air-core is shown to be the same expression as for the critical velocity for the flow at the outlet. In addition, this wave phase velocity is shown to be the square root of the product of the radial acceleration and the liquid thickness, as analogous with the wave phase velocity for shallow water gravity waves, which is the square root of the product of the acceleration due to gravity and the water depth. The work revisits the weirs and flumes work of Binnie et al. but using a different methodology. The results corroborate with the work of Binnie. High speed video, Laser Doppler Anemometry and deflected laser beam experimental work has been carried out on an oversize Perspex (Plexiglas) swirl atomizer. Three distinctive types of waves were detected: helical striations, low amplitude random ripples and low frequency stationary waves. It is the latter wave type that is considered further in this article. The experimentally observed waves appear to be stationary upon the axially moving flow. The mathematical analysis allows for the possibility of a negative value for the phase velocity expression. Therefore the critical velocity and the wave phase velocity do indeed lead to stationary waves in the atomizer. A quantitative comparison between the analytically derived wave phase velocity and that measured experimentally, for this stationary pulsating wave, show very good agreement within a few percent

Geometric parameters and response surface methodology on cooling performance of vortex tubes

This research has investigated the effect of certain geometric parameters on cooling performance of three vortex tubes. The influencing parameters include three length/diameter ratios L/D = 10, 25, 40, three nozzle cases and each case with number n = 2, 4, 6 nozzles, three cold orifice/diameter ratios β = 0.389, 0.5, 0.611 and three inlet pressures Pi = 2, 2.5 and 3 bar. The experiments are conducted based on three factors, two-level and central composite face-centred design with full factorial. The results are analysed according to the principle of response surface methodology. The goodness of fit of the regression model is inspected using the analysis of variance and F-ratio test. The values of R2 and R2-adjusted are close to 100% which show a very good correlation between the observed and predicted values. The results show that the effect of number of nozzles on the energy separation depends on the L/D values