Effect of Temperature Dependent Fluid Properties on Heat Transfer in Turbulent Mixed Convection

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Francesco Zonta ◽  
Alfredo Soldati
Keyword(s):  
Heat Transfer ◽  
Thermal Expansion ◽  
Mixed Convection ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Large Scale ◽  
Effect Of Temperature ◽  
Complex Flow ◽  
Fluid Properties ◽  
Rayleigh Benard

The effect of the uniform fluid properties approximation (Oberbeck-Boussinesq (OB)) in turbulent mixed convection is investigated via direct numerical simulation (DNS) of water flows with viscosity (μ) and thermal expansion coefficient (β) both independently and simultaneously varying with temperature (non-Oberbeck-Boussinesq conditions (NOB)). Mixed convection is analyzed for the prototypical case of Poiseuille-Rayleigh-Bénard (PRB) turbulent channel flow. In PRB flows, the combination of buoyancy driven (Rayleigh-Bénard) with pressure driven (Poiseuille) effects produce a complex flow structure, which depends on the relative intensity of the flow parameters (i.e., the Grashof number, Gr, and the shear Reynolds number, Reτ). In liquids, however, temperature variations induce local changes of fluid properties which influence the macroscopic flow field. We present results for different absolute values of the shear Richardson numbers (Riτ=|Gr/Reτ2|) under constant temperature boundary conditions. As Riτ is increased buoyant thermal plumes are generated, which induce large scale thermal convection that increases momentum and heat transport efficiency. Analysis of friction factor (Cf) and Nusselt number (Nu) for NOB conditions shows that the effect of viscosity is negligible, whereas the effect of thermal expansion coefficient is significant. Statistics of mixing show that (i) mixing increases for increasing Riτ (and decreases for increasing Reτ) and (ii) the effect of thermal expansion coefficient on mixing increases for increasing Riτ (and decreases for increasing Reτ). A simplified phenomenological model to predict heat transfer rates in PRB flows has also been developed.

Heat Transfer Characteristics of Nitrogen in Supercritical Region Using Redlich-Kwong Equation of State

2019 ◽  
Vol 17 (10) ◽  
Author(s):  
Hussain Basha ◽  
G. Janardhana Reddy ◽  
N. S. Venkata Narayanan
Keyword(s):  
Heat Transfer ◽  
Thermal Expansion ◽  
Equation Of State ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Physical Parameters ◽  
Heat Transfer Characteristics ◽  
Reduced Pressure ◽  
Supercritical Region ◽  
Transfer Characteristics

Abstract The present paper studies through numerical methods, the thermodynamic heat transfer characteristics of free convection flow of supercritical nitrogen over a vertical cylinder. In the present analysis, the values of volumetric thermal expansion coefficient ($\beta$) are evaluated based on Redlich-Kwong equation of state (RK-EOS) and Van der Waals equation of state (VW-EOS). The calculated analytical thermal expansion coefficient values using RK-EOS are very close to NIST data values in comparison with VW-EOS. A set of coupled nonlinear partial differential equations (PDEs) governing the supercritical fluid (SCF) flow are derived, converted into non-dimensional form with the help of suitable dimensionless quantities and solved using Crank-Nicolson implicit finite difference method. The simulations are carried out for nitrogen in the supercritical region. The obtained numerical data is expressed in terms of graphs and tables for various values of physical parameters. The increasing value of reduced temperature decreases the average Nusselt number and skin-friction coefficient, whereas amplifying value of reduced pressure enhance the heat transfer rate and wall shear stress in the SCF region. Present results are compared with the previous results and the two are found to be in good agreement, i. e. the numerically generated results found to be in agreement with existing results.

Development of Porous Material with High Young’s Modulus and Low Thermal Expansion Coefficient in SiC-Vitrified Bonding Material-LiAlSiO4 System

2009 ◽  
Vol 620-622 ◽  
pp. 715-718 ◽  
Author(s):  
Tatsuya Ono ◽  
Koji Matsumaru ◽  
Isaías Juárez-Ramírez ◽  
Leticia M. Torres-Martínez ◽  
Kozo Ishizaki
Keyword(s):  
Thermal Expansion ◽  
Porous Material ◽  
Porous Materials ◽  
Young’S Modulus ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Large Scale ◽  
Young's Modulus ◽  
Negative Thermal Expansion ◽  
Low Thermal Expansion

Machines for manufacturing large scale flat displays are enlarging as the size of glasses increases. This work develops porous materials with a low thermal expansion coefficient and a high Young’s modulus. SiC and LiAlSiO4 were used for a positive and a negative thermal expansion materials, respectively. Compositions of powders for porous materials were determined to obtain a desirable Young’s modulus and thermal expansion coefficient by using SiC-VBM-LiAlSiO4 phase diagram at 20 % of porosity. The empirical values of Young’s modulus and a thermal expansion coefficient are close to the theoretical values by using the diagram. Fabricated porous material had high enough Young’s modulus of 87 GPa, and low enough thermal expansion coefficient of 2 x 10-6 K-1 at temperatures ranging from -17 °C to 190 °C with 22 % of porosity.

Thermoelastic Properties of a Novel Fuzzy Fiber-Reinforced Composite

2013 ◽  
Vol 80 (6) ◽  
Author(s):  
S. I. Kundalwal ◽  
M. C. Ray
Keyword(s):  
Thermal Expansion ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Volume Fraction ◽  
Effect Of Temperature ◽  
Fiber Reinforced ◽  
Thermoelastic Properties ◽  
Fiber Reinforced Composite ◽  
Reinforced Composite ◽  
Generalized Method Of Cells

The effective thermoelastic properties of a fuzzy fiber-reinforced composite (FFRC) have been estimated by employing the generalized method of cells approach and the Mori–Tanaka method. The novel constructional feature of this fuzzy fiber-reinforced composite is that the uniformly aligned carbon nanotubes (CNTs) are radially grown on the circumferential surface of the horizontal carbon fibers. Effective thermoelastic properties of the fuzzy fiber-reinforced composite estimated by the generalized method of cells approach have been compared with those predicted by the Mori–Tanaka method. The present work concludes that the axial thermal expansion coefficient of the fuzzy fiber-reinforced composite slightly increases for the lower values of the carbon fiber volume fraction, whereas the transverse thermal expansion coefficient of the fuzzy fiber-reinforced composite significantly decreases over those of the composite without CNTs. Also, the results demonstrate that the effect of temperature variation on the effective thermal expansion coefficients of the fuzzy fiber-reinforced composite is negligible.

scholarly journals Enhanced heat transport in thermal convection with suspensions of rod-like expandable particles

2021 ◽  
Vol 928 ◽  
Author(s):  
Shi-Yuan Hu ◽  
Kai-Zhe Wang ◽  
Lai-Bing Jia ◽  
Jin-Qiang Zhong ◽  
Jun Zhang
Keyword(s):  
Thermal Expansion ◽  
Heat Transport ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Thermal Convection ◽  
Temperature Fields ◽  
Glycerol Solution ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard ◽  
Large Rayleigh Number

Thermal convection of fluid is a more efficient way than diffusion to carry heat from hot sources to cold places. Here, we experimentally study the Rayleigh–Bénard convection of aqueous glycerol solution in a cubic cell with suspensions of rod-like particles made of polydimethylsiloxane. The particles are inertial due to their large thermal expansion coefficient and finite sizes. The thermal expansion coefficient of the particles is three times larger than that of the background fluid. This contrast makes the suspended particles lighter than the local fluid in hot regions and heavier in cold regions. The heat transport is enhanced at relatively large Rayleigh number ( $\textit {Ra}$ ) but reduced at small $\textit {Ra}$ . We demonstrate that the increase of Nusselt number arises from the particle–boundary layer interactions: the particles act as ‘active’ mixers of the flow and temperature fields across the boundary layers.

scholarly journals Statistical properties of thermally expandable particles in soft-turbulence Rayleigh-Bénard convection

2019 ◽  
Vol 42 (9) ◽  
Author(s):  
Kim M. J. Alards ◽  
Rudie P. J. Kunnen ◽  
Herman J. H. Clercx ◽  
Federico Toschi
Keyword(s):  
Thermal Expansion ◽  
Thermal Expansion Coefficient ◽  
Residence Time ◽  
Expansion Coefficient ◽  
Response Times ◽  
Thermal Response ◽  
Benard Convection ◽  
1D Model ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

Abstract. The dynamics of inertial particles in Rayleigh-Bénard convection, where both particles and fluid exhibit thermal expansion, is studied using direct numerical simulations (DNS) in the soft-turbulence regime. We consider the effect of particles with a thermal expansion coefficient larger than that of the fluid, causing particles to become lighter than the fluid near the hot bottom plate and heavier than the fluid near the cold top plate. Because of the opposite directions of the net Archimedes’ force on particles and fluid, particles deposited at the plate now experience a relative force towards the bulk. The characteristic time for this motion towards the bulk to happen, quantified as the time particles spend inside the thermal boundary layers (BLs) at the plates, is shown to depend on the thermal response time, $ \tau_{T}$τT, and the thermal expansion coefficient of particles relative to that of the fluid, $ K = \alpha_{p}/\alpha_{f}$K=αp/αf. In particular, the residence time is constant for small thermal response times, $ \tau_{T} \lesssim 1$τT≲1, and increasing with $ \tau_{T}$τT for larger thermal response times, $ \tau_{T} \gtrsim 1$τT≳1. Also, the thermal BL residence time is increasing with decreasing K. A one-dimensional (1D) model is developed, where particles experience thermal inertia and their motion is purely dependent on the buoyancy force. Although the values do not match one-to-one, this highly simplified 1D model does predict a regime of a constant thermal BL residence time for smaller thermal response times and a regime of increasing residence time with $ \tau_{T}$τT for larger response times, thus explaining the trends in the DNS data well. Graphical abstract

Turbulence and internal waves in stably-stratified channel flow with temperature-dependent fluid properties

2012 ◽  
Vol 697 ◽  
pp. 175-203 ◽  
Author(s):  
Francesco Zonta ◽  
Miguel Onorato ◽  
Alfredo Soldati
Keyword(s):  
Reynolds Number ◽  
Thermal Expansion ◽  
Thermal Expansion Coefficient ◽  
Channel Flow ◽  
Expansion Coefficient ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Fluid Properties ◽  
Effects Of Temperature ◽  
Dependent Viscosity

AbstractDirect numerical simulation (DNS) is used to study the behaviour of stably-stratified turbulent channel flow with temperature-dependent fluid properties: specifically, viscosity ($\ensuremath{\mu} $) and thermal expansion coefficient ($\ensuremath{\beta} $). The governing equations are solved using a pseudo-spectral method for the case of turbulent water flow in a channel. A systematic campaign of simulations is performed in the shear Richardson number parameter space (${\mathit{Ri}}_{\tau } = \mathit{Gr}/ {\mathit{Re}}_{\tau } $, where $\mathit{Gr}$ is the Grashof number and ${\mathit{Re}}_{\tau } $ the shear Reynolds number), imposing constant-temperature boundary conditions. Variations of ${\mathit{Ri}}_{\tau } $ are obtained by changing ${\mathit{Re}}_{\tau } $ and keeping $\mathit{Gr}$ constant. Independently of the value of ${\mathit{Ri}}_{\tau } $, all cases exhibit an initial transition from turbulent to laminar flow. A return transition to turbulence is observed only if ${\mathit{Ri}}_{\tau } $ is below a threshold value (which depends also on the flow Reynolds number). After the transient evolution of the flow, a statistically-stationary condition occurs, in which active turbulence and internal gravity waves (IGW) coexist. In this condition, the transport efficiency of momentum and heat is reduced considerably compared to the condition of non-stratified turbulence. The crucial role of temperature-dependent viscosity and thermal expansion coefficient is directly demonstrated. The most striking feature produced by the temperature dependence of viscosity is flow relaminarization in the cold side of the channel (where viscosity is higher). The opposite behaviour, with flow relaminarization occurring in the hot side of the channel, is observed when a temperature-dependent thermal expansion coefficient is considered. We observe qualitative and quantitative modifications of structure and wall-normal position of internal waves compared to previous results obtained for uniform or quasi-uniform fluid properties. From the trend we observe in the investigated low-Reynolds-number range, we can hypothesize that, whereas the effects of temperature-dependent viscosity may be masked at higher Reynolds number, the effects of temperature-dependent thermal expansion coefficient will persist.

scholarly journals Out-of-Plane Thermal Expansion Coefficient and Biaxial Young’s Modulus of Sputtered ITO Thin Films

Coatings ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 153
Author(s):  
Chuen-Lin Tien ◽  
Tsai-Wei Lin
Keyword(s):  
Thin Films ◽  
Thermal Expansion ◽  
Thermal Stress ◽  
Young’S Modulus ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Young's Modulus ◽  
Heating Temperature ◽  
Glass Substrates ◽  
Ito Thin Films

This paper proposes a measuring apparatus and method for simultaneous determination of the thermal expansion coefficient and biaxial Young’s modulus of indium tin oxide (ITO) thin films. ITO thin films simultaneously coated on N-BK7 and S-TIM35 glass substrates were prepared by direct current (DC) magnetron sputtering deposition. The thermo-mechanical parameters of ITO thin films were investigated experimentally. Thermal stress in sputtered ITO films was evaluated by an improved Twyman–Green interferometer associated with wavelet transform at different temperatures. When the heating temperature increased from 30 °C to 100 °C, the tensile thermal stress of ITO thin films increased. The increase in substrate temperature led to the decrease of total residual stress deposited on two glass substrates. A linear relationship between the thermal stress and substrate heating temperature was found. The thermal expansion coefficient and biaxial Young’s modulus of the films were measured by the double substrate method. The results show that the out of plane thermal expansion coefficient and biaxial Young’s modulus of the ITO film were 5.81 × 10−6 °C−1 and 475 GPa.

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