Development of an Interferometric Method for Measurement of Thermal Conductivity of a Transparent Medium

2006 ◽  
Author(s):  
Choondal B. Sobhan ◽  
Renju Kurian
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Measurement Techniques ◽  
Transparent Medium ◽  
Fringe Shift ◽  
Interferometric Method ◽  
Number Distribution ◽  
Nusselt Number Distribution

Interferometric methods are non-intrusive optical measurement techniques, which find extensive use in flow and heat transfer visualization. The present work originates from the idea that by a suitable experimental system and data analysis method, the interferometric technique can be used to estimate its thermal conductivity. A method is developed to obtain the thermal conductivity of a transparent medium using the optical technique of differential interferometry. The basis is of this method is the measurement of the local interference fringe shift values along an isothermal flat plate surrounded by the medium to visualize the heat transfer field. The local Nusselt number distribution along the plate is estimated from fringe shift and compared with theoretical local Nusselt number distribution along an isothermal plate, and this comparison is used to estimate the thermal conductivity of the medium.

Modeling of mixed convection in an enclosure using multiple regression, artificial neural network, and adaptive neuro-fuzzy interface system models

2020 ◽  
Vol 234 (15) ◽  
pp. 3078-3093
Author(s):  
Ece Aylı
Keyword(s):  
Neural Network ◽  
Heat Transfer ◽  
Artificial Neural Network ◽  
Nusselt Number ◽  
Forced Convection ◽  
Number Distribution ◽  
Neuro Fuzzy ◽  
Interface System ◽  
Nusselt Number Distribution ◽  
Artificial Neural

In this study, the heat transfer characteristics of laminar combined forced convection through a horizontal duct are obtained with the help of the numerical methods. The effect of the geometrical parameters of the cavity and Reynolds number on the heat transfer is investigated. New heat transfer correlation for hydrodynamically fully developed, laminar combined forced convection through a horizontal duct is proposed with an average error of 6.98% and R2 of 0.8625. The obtained correlation results are compared with the artificial neural network and adaptive neuro-fuzzy interface system models. Due to the obtained results, good agreement is identified between the numerical results and predicted adaptive neuro-fuzzy interface system results. In conclusion, it is seen that adaptive neuro-fuzzy interface system can predict the Nusselt number distribution with a higher accuracy than the developed correlation and the artificial neural network model. The developed adaptive neuro-fuzzy interface system model predicts the Nusselt number with 1.07% mean average percentage error and 0.9983 R2 value. The effect of the different training algorithms and their ability to predict Nusselt number distribution are examined. According to the results, the Bayesian regulation algorithm gives the best approach with a 2.235% error. According to the examination that is performed in this study, the adaptive neuro-fuzzy interface system is a powerful, robust tool that can be used with confidence for predicting the thermal performance.

Investigations on Nusselt Number Enhancement in Ribbed Rectangular Turbine Blade Cooling Channels of Different Aspect Ratios and Rotation Numbers

2013 ◽  
Author(s):  
Behnam Nouri ◽  
Knut Lehmann ◽  
Arnold Kühhorn
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Turbine Blade ◽  
High Heat ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Aspect Ratios ◽  
Number Distribution ◽  
Nusselt Number Distribution

In the drive for higher cycle efficiencies in gas turbine engines, turbine blades are seeing an increasingly high heat load. This in turn demands improvements in the internal cooling system and a better understanding of both the level and distribution of the internal heat-transfer. A typical approach to enhance the internal cooling of the turbine blade is by casting angled ‘low blockage’ ribs on the walls of the cooling channels. The objective of the present paper is to determine the detailed Nusselt number distribution in rectangular internal channels with ribs. This knowledge can be used to guide the overall design e.g. to achieve high levels of heat-transfer where required. The effects of rotation as well as the interaction effects of the position and direction of ribs on opposite walls of the cooling channel have been investigated. Numerical calculations have been carried out using the commercial CFD code Fluent to investigate the local Nusselt number enhancement factor in rectangular ducts of different aspect ratios (0.5, 1 and 2) which have 45° or 90° angled ribs located on two opposite walls. This has been studied for different Rotation number Ro (0–0.45) and with a Reynolds number >30000. The first series of studies has been carried out with the same experimental setup as by Han [1]. The geometry was slightly changed to avoid the effect of high heat transfer at the entry. This study identifies important vortical structures, which are dependent on the direction and the position of the ribs. This has a profound effect on the distribution of heat-transfer within the passage. It is shown that the two smooth walls of the duct have different average Nusselt number ratio Nu/NuFD enhancement depending on the rib angle. In addition, based on numerical investigations, simple correlations have been developed for the rotational influence of the internal Nusselt number distribution. A major finding is that the effect of rotation is dominant for low aspect ratio channels and the local enhancement due to the rib position and angle is more dominant for high aspect ratio channels.

Unsteady Heat Transfer Analysis of an Impinging Jet

2002 ◽  
Vol 124 (6) ◽  
pp. 1039-1048 ◽  
Author(s):  
Yongmann M. Chung ◽  
Kai H. Luo
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Impinging Jet ◽  
Reynolds Numbers ◽  
Heat Transfer Analysis ◽  
Unsteady Heat Transfer ◽  
Number Distribution ◽  
Nusselt Number Distribution

Unsteady heat transfer caused by a confined impinging jet is studied using direct numerical simulation (DNS). The time-dependent compressible Navier-Stokes equations are solved using high-order numerical schemes together with high-fidelity numerical boundary conditions. A sixth-order compact finite difference scheme is employed for spatial discretization while a third-order explicit Runge-Kutta method is adopted for temporal integration. Extensive spatial and temporal resolution tests have been performed to ensure accurate numerical solutions. The simulations cover several Reynolds numbers and two nozzle-to-plate distances. The instantaneous flow fields and heat transfer distributions are found to be highly unsteady and oscillatory in nature, even at relatively low Reynolds numbers. The fluctuation of the stagnation or impingement Nusselt number, for example, can be as high as 20 percent of the time-mean value. The correlation between the vortex structures and the unsteady heat transfer is carefully examined. It is shown that the fluctuations in the stagnation heat transfer are mainly caused by impingement of the primary vortices originating from the jet nozzle exit. The quasi-periodic nature of the generation of the primary vortices due to the Kelvin-Helmholtz instability is behind the nearly periodic fluctuation in impingement heat transfer, although more chaotic and non-linear fluctuations are observed with increasing Reynolds numbers. The Nusselt number distribution away from the impingement point, on the other hand, is influenced by the secondary vortices which arise due to the interaction between the primary vortices and the wall jets. The unsteady vortex separation from the wall in the higher Reynolds number cases leads to a local minimum and a secondary maximum in the Nusselt number distribution. These are due to the changes in the thermal layer thickness accompanying the unsteady flow structures.

Comparison Between Thermal Conductivity Models on Heat Transfer in Power-Law Non-Newtonian Fluids

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Botong Li ◽  
Liancun Zheng ◽  
Xinxin Zhang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Nusselt Number ◽  
Power Law ◽  
Local Nusselt Number ◽  
Control Volume ◽  
Newtonian Fluids ◽  
Uniform Wall Temperature ◽  
Dependent Model ◽  
Conductivity Models

This paper endeavors to complete a numerical research on forced convection steady heat transfer in power-law non-Newtonian fluids in a circle duct. Incompressible, laminar fluids are to be studied with a uniform wall temperature. A hydrodynamic entrance length is neglected which allows establishing a fully developed flow. The energy equation is solved by using a LU decomposition coupled with control volume technique based on finite difference method. Four thermal conductivity models are adopted in this paper, that is, constant thermal conductivity model, linear thermal conductivity varying with temperature, thermal conductivity varying as a function of velocity gradient, and thermal conductivity varying as a function of temperature gradient. The results are compared with each other and the physical characteristics for values of parameters are also discussed in details. It is shown that the heat transfer behaviors are strongly depending on the power-law index in all models. Comparisons of temperature and local Nusselt number between models are made. It reveals the increasing values of thermal conductivity parameter result in increasing the local Nusselt number when the thermal conductivity is a linear one. Furthermore, there is obvious difference in the local Nusselt number between the constant model and the power-law velocity-dependent model, but Nusselt number varies little from the constant model to the power-law temperature-dependent model.

Effect of Combustor-Turbine Platform Misalignment on the Aerodynamics and Heat Transfer of an Axisymmetric Converging Vane Endwall at Transonic Conditions

2017 ◽  
Author(s):  
David E. Mayo ◽  
Allan Arisi ◽  
Wing F. Ng ◽  
Zhigang Li ◽  
Jun Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Secondary Flow ◽  
Guide Vane ◽  
Separated Flow ◽  
Heat Transfer Augmentation ◽  
Number Distribution ◽  
Nozzle Guide Vane ◽  
Nusselt Number Distribution ◽  
Nozzle Guide

This paper presents a detailed study on the effect of misalignment between the combustor exit and the nozzle guide vane endwall. The Nusselt number distribution and augmentation on an axisymmetric converging endwall as well as stage pressure losses were studied using experimental techniques and computational analysis. The analyzed endwall configurations are representative of the design intent and average off-design endwall configurations of a land-based high-pressure turbine nozzle guide vane. The studies were carried out at isentropic exit Mach number of 0.85, with an exit Reynolds number of 1.5 × 106 based on the true chord, and an inlet turbulence intensity of 16%. The experiment was conducted in a blowdown transonic linear cascade wind tunnel and an infrared camera was used to measure the surface temperature and subsequently the endwall heat transfer coefficient and Nusselt number distribution. Numerical computation analysis using ANSYS Fluent v.16 was used to provide further insight into the near-endwall flow field the predictions compared favorably to experimental data. The findings show that at the two configurations there exist uniquely different endwall secondary flow systems throughout the NGV stage. The interaction of separated flow at the combustor-turbine interface with the vane potential field results in additional secondary flow that is vastly different from that associated with classical endwall flows. This increased secondary flow in the misaligned configuration was marked by a 25% increase in NGV stage losses. The presence of separated flow and additional secondary flows also resulted in flow reattachment inside the vane passage which augmented heat transfer. The region upstream of the vane gage/throat showed heat transfer augmentation of up to 60%, while the endwall region downstream of the throat did not show any considerable heat transfer augmentation.

scholarly journals Unsteady Analysis of Blade and Tip Heat Transfer as Influenced by the Upstream Momentum and Thermal Wakes

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Ali A. Ameri ◽  
David L. Rigby ◽  
Erlendur Steinthorsson ◽  
James Heidmann ◽  
John C. Fabian
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rotor Blade ◽  
Tip Clearance ◽  
Unsteady Heat Transfer ◽  
Adiabatic Wall ◽  
Number Distribution ◽  
Nusselt Number Distribution ◽  
Time Average ◽  
Inlet Conditions

The effect of the upstream wake on the time averaged rotor blade heat transfer was numerically investigated. The geometry and flow conditions of the first stage turbine blade of GE’s E3 engine with a tip clearance equal to 2% of the span were utilized. The upstream wake had both a total pressure and temperature deficit. The rotor inlet conditions were determined from a steady analysis of the cooled upstream vane. Comparisons between the time average of the unsteady rotor blade heat transfer and the steady analysis, which used the average inlet conditions of unsteady cases, are made to illuminate the differences between the steady and unsteady calculations. To help in the understanding of the differences between steady and unsteady results on one hand and to evaluate the effect of the total temperature wake on the other, separate calculations were performed to obtain the rotor heat transfer and adiabatic wall temperatures. It was found that the Nusselt number distribution for the time average of unsteady heat transfer is invariant if normalized by the difference in the adiabatic and wall temperatures. It appeared though that near the endwalls the Nusselt number distribution did depend on the thermal wake strength. Differences between steady and time averaged unsteady heat transfer results of up to 20% were seen on the blade surface. Differences were less on the blade tip surface.

Effect of Nanofluid on Heat Transfer Enhancement for Mixed Convection Flow Over a Corrugated Surface

2020 ◽  
Vol 45 (4) ◽  
pp. 373-383
Author(s):  
Nepal Chandra Roy ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Local Nusselt Number ◽  
Richardson Number ◽  
Thermal Boundary Layer ◽  
Volume Fraction ◽  
Convection Flow ◽  
Mixed Convection Flow

AbstractA mathematical model for mixed convection flow of a nanofluid along a vertical wavy surface has been studied. Numerical results reveal the effects of the volume fraction of nanoparticles, the axial distribution, the Richardson number, and the amplitude/wavelength ratio on the heat transfer of Al2O3-water nanofluid. By increasing the volume fraction of nanoparticles, the local Nusselt number and the thermal boundary layer increases significantly. In case of \mathrm{Ri}=1.0, the inclusion of 2 % and 5 % nanoparticles in the pure fluid augments the local Nusselt number, measured at the axial position 6.0, by 6.6 % and 16.3 % for a flat plate and by 5.9 % and 14.5 %, and 5.4 % and 13.3 % for the wavy surfaces with an amplitude/wavelength ratio of 0.1 and 0.2, respectively. However, when the Richardson number is increased, the local Nusselt number is found to increase but the thermal boundary layer decreases. For small values of the amplitude/wavelength ratio, the two harmonics pattern of the energy field cannot be detected by the local Nusselt number curve, however the isotherms clearly demonstrate this characteristic. The pressure leads to the first harmonic, and the buoyancy, diffusion, and inertia forces produce the second harmonic.

Study of the boundary layer heat transfer of nanofluids over a stretching sheet: Passive control of nanoparticles at the surface

2015 ◽  
Vol 93 (7) ◽  
pp. 725-733 ◽  
Author(s):  
M. Ghalambaz ◽  
E. Izadpanahi ◽  
A. Noghrehabadi ◽  
A. Chamkha
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Base Fluid ◽  
Stretching Sheet ◽  
Volume Fraction ◽  
Enhancement Ratio ◽  
Transfer Enhancement

The boundary layer heat and mass transfer of nanofluids over an isothermal stretching sheet is analyzed using a drift-flux model. The relative slip velocity between the nanoparticles and the base fluid is taken into account. The nanoparticles’ volume fractions at the surface of the sheet are considered to be adjusted passively. The thermal conductivity and the dynamic viscosity of the nanofluid are considered as functions of the local volume fraction of the nanoparticles. A non-dimensional parameter, heat transfer enhancement ratio, is introduced, which shows the alteration of the thermal convective coefficient of the nanofluid compared to the base fluid. The governing partial differential equations are reduced into a set of nonlinear ordinary differential equations using appropriate similarity transformations and then solved numerically using the fourth-order Runge–Kutta and Newton–Raphson methods along with the shooting technique. The effects of six non-dimensional parameters, namely, the Prandtl number of the base fluid Prbf, Lewis number Le, Brownian motion parameter Nb, thermophoresis parameter Nt, variable thermal conductivity parameter Nc and the variable viscosity parameter Nv, on the velocity, temperature, and concentration profiles as well as the reduced Nusselt number and the enhancement ratio are investigated. Finally, case studies for Al2O3 and Cu nanoparticles dispersed in water are performed. It is found that increases in the ambient values of the nanoparticles volume fraction cause decreases in both the dimensionless shear stress f″(0) and the reduced Nusselt number Nur. Furthermore, an augmentation of the ambient value of the volume fraction of nanoparticles results in an increase the heat transfer enhancement ratio hnf/hbf. Therefore, using nanoparticles produces heat transfer enhancement from the sheet.

scholarly journals Analysis of transient mixed convection in a horizontal channel partially heated from below

2021 ◽  
Vol 4 (8(112)) ◽  
pp. 16-22
Author(s):  
Mahmoud A. Mashkour
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Source ◽  
Local Nusselt Number ◽  
Richardson Number ◽  
Stokes Equations ◽  
Heat Convection ◽  
Horizontal Channel ◽  
Outlet Temperature

The heat convection phenomenon has been investigated numerically (mathematically) for a channel located horizontally and partially heated at a uniform heat flux with forced and free heat convection. The investigated horizontal channel with a fluid inlet and the enclosure was exposed to the heat source from the bottom while the channel upper side was kept with a constant temperature equal to fluid outlet temperature. Transient, laminar, incompressible and mixed convective flow is assumed within the channel. Therefore, the flow field is estimated using Navier Stokes equations, which involves the Boussinesq approximation. While the temperature field is calculated using the standard energy model, where, Re, Pr, Ri are Reynolds number, Prandtl number, and Richardson number, respectively. Reynolds number (Re) was changed during the test from 1 to 50 (1, 10, 25, and 50) for each case study, Richardson (Ri) number was changed during the test from 1 to 25 (1, 5, 10, 15, 20, and, 25). The average Nusselt number (Nuav) increases exponentially with the Reynold number for each Richardson number and the local Nusselt number (NuI) rises in the heating point. Then gradually stabilized until reaching the endpoint of the channel while the local Nusselt number increases with a decrease in the Reynolds number over there. In addition, the streamlines and isotherms patterns in case of the very low value of the Reynolds number indicate very low convective heat transfer with all values of Richardson number. Furthermore, near the heat source, the fluid flow rate rise increases the convection heat transfer that clarified the Nusselt number behavior with Reynolds number indicating that maximum Nu No. are 6, 12, 27 and 31 for Re No. 1, 10, 25 and 50, respectively

Hall Effects on Unsteady Magnetohydrodynamic Flow of a Nanofluid Past an Oscillatory Vertical Rotating Flat Plate Embedded in Porous Media

2021 ◽  
Vol 10 (2) ◽  
pp. 259-269
Author(s):  
M. Veera Krishna ◽  
N. Ameer Ahamad ◽  
Ali J. Chamkha
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Nusselt Number ◽  
Friction Coefficient ◽  
Local Nusselt Number ◽  
Hall Current ◽  
Skin Friction Coefficient ◽  
Engineering Industry ◽  
Hall Effects ◽  
The Impact

In the current investigative paper, the impact of Hall current on an unsteady magnetohydrodynamic liberated convection revolving flow of a nanofluid restricted with a uniform absorbent medium over an oscillatory moving vertical smooth plate with convective as well as diffusive frontier conditions has been reviewed. The non-dimensionalized governing differential equations by the appropriate frontier conditions are resolved by the perturbations technique. The impacts of the physical constants on the flow as well as the heat transfer features are displayed graphically and analyzed for Cu as well as Al2O3 nanoparticles. For the engineering industry, the skin friction coefficient, local Nusselt number, along with the Sherwood’s number are examined numerically in detail.

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