Temperature Variable Properties Research Articles

A robust computational approach to Lees–Dorodnitsyn laminar hypersonic boundary layers with temperature-dependent properties

The Lees–Dorodnitsyn (L–D) boundary layer equations for two-dimensional, non-reactive, laminar, hypersonic, boundary layer flows, and an assumption of an isentropic external flow are examined. They are applied to various geometries for which the Thin Shear Layer assumptions are valid. This study expands on previous work to develop a novel and robust methodology for computing high-temperature hypersonic flows using a uniform and compact computational stencil implemented through a computational tool, the Bulk-property Boundary Layer (BuBL) solver. In particular, we explore the impact of treating high-temperature effects present in hypersonic flows, namely, treating air as a thermally perfect gas with temperature-variable properties. The ability to solve these flows computationally using second-order finite difference methods is evaluated as are various models for viscosity, Prandtl number, and specific heat. The methodology for solving the external flow properties in the transformed L–D computational domain is also discussed. It is shown that the L–D equations evaluated using the “box” computational stencil are an effective means for evaluating laminar hypersonic boundary layer flows. Solutions for displacement and momentum thicknesses, skin friction, and Stanton number variations are obtained as a function of Prandtl number, specific heat model, and Mach number. Verification and validation measures are performed for the code. Excellent agreement is found in comparisons between BuBL and other computational fluid dynamics and experimental results, thus demonstrating the utility of the proposed methodology.

Numerical study on thermal performance of an air-cooled heat exchanger: Effects of hybrid nanofluid, pipe arrangement and cross section

This study is a numerical investigation of a heat exchanger under external flow. Temperature variable properties are used to solve the governing equations. Air is selected as an external fluid and water and MgO-MWCNTs/EG hybrid nanofluid are selected as radiator fluid. In this paper, the efficiency of the horizontal and vertical radiator are studied using experimental data for thermo-physical properties of MgO-MWCNTs/EG Nanofluid. Then, tubes with circular and elliptic sections are investigated for different flows, inlet temperatures and concentrations. The pressure drop and Nusselt number for each simulation are analyzed. Results are presented in terms of temperature distribution, pressure drop, Nusselt number and their sensitivity analysis for different states. The results indicate that radiators with vertical tubes have better efficiency up to 10% than radiators with horizontal tubes. In addition, heat exchangers with circular pipes have 25% lower pressure drop and those with elliptical tubes had 10% higher Nusselt number. The finding shows that an increase in the Nano-fluid concentration improves the Nusselt number and increases the pressure drop.

A fluid–structure interaction approach to investigate the quenching characteristics of a steel tube with temperature dependent properties

Quenching is commonly used for improving material properties of steel tubes because of their numerous applications. However, quenching generates some residual stress and deformation in the material due to rapid temperature fluctuations. The properties of the steel are strong functions of these variable temperatures and therefore, the estimated stress and deformation by constant property or static quenching analysis are not very realistic. This study describes the first extensive study of the quenching process of a steel tube including temperature dependent properties by three liquid quenchants using the dynamic fluid–structure interaction quench model. The cooling characteristics of the three liquid quenchants are compared to each other along with the transient temperature distributions in the steel tube. The time-varying nodal, axial, and radial residual stress and deformation of the tube are studied. It is found that, the effectiveness of quenching does not depend only on a particular quenchant, but also on the temperature-varying properties of the steel and the uniformity of the cooling which ultimately determine the criteria for selecting a suitable quenchant for a specific purpose.

A numerical method of visco-elastic stress analysis

By representing the visco-elastic behaviour of a material by a number of Kelvin models connected in series and by keeping a running total of creep strain for each such model, the difficulty of retaining the stress history in computer solutions is avoided. A completely general method of numerical visco-elastic stress analysis with constant or temperature variable properties is developed. The method is checked against some known solutions. Examples from the fields of propellant technology, concrete and rock behaviour are included.

Friction and Heat Transfer Characteristics in Turbulent Swirl Flow Subjected to Large Transverse Temperature Gradients

Friction and heat transfer characteristics of turbulent air flowing through tubes with twisted strip swirl promoters were studied experimentally and analytically. Data were obtained for pitch-to-diameter ratios as low as 3.15 and for Reynolds numbers up to 100,000. Both heating and cooling tests were run for tube wall to fluid bulk temperature ratios from 0.6 to 1.9 (degR/degR) to evaluate compressibility and buoyancy effects. Both temperature-varying properties and the centrifugal force field imposed on the compressible fluid by the twisted strips cause considerable deviations from the incompressible heat transfer predictions. Experimental results are presented as deviations to the incompressible predictions and can be correlated by f=fo(Tˆw/Tˆb)−0.1(HeatingandCooling)Nu=Nuo(Tˆw/Tˆb)−0.32(1+0.25Gr/Re)(Heating)Nu=1.07Nuo(Tˆw/Tˆb)−0.1(1−0.25Gr/Re)(Cooling) where the subscript “o” refers to the incompressible analytical solution. The analysis presented is more direct and complete than the previous development by Smithberg and Landis [3]2 by also accounting for curvature effects and the significant tape distortions encountered with tightly twisted strips.