Thermophysical Properties of Biporous Heat Pipe Evaporators

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Tadej Semenic ◽  
Ying-Yu Lin ◽  
Ivan Catton
Keyword(s):  
Thermal Conductivity ◽  
Heat Pipe ◽  
Capillary Pressure ◽  
Linear Function ◽  
Copper Powder ◽  
Thermophysical Properties ◽  
Particle Diameter ◽  
Diameter Ratio ◽  
Vapor Permeability ◽  
Neck Size

Thirty biporous slugs with 3 different cluster diameters and 5 different particle diameters (15 combinations with 2 repetitions) and 12 monoporous slugs with 6 different particle diameters were sintered from spherical copper powder, and thermophysical properties were measured. The neck size ratio for all the particles was approximately 0.4. The porosity of monoporous samples was found to be independent of particle diameter and was equal to 0.28, and the porosity of biporous samples was found to be independent of cluster and particle diameters, and was equal to 0.64. The liquid permeability and maximum capillary pressure of small pores were found to be a linear function of the particle diameter. Similarly, vapor permeability was found to be a linear function of the cluster diameter. The thermal conductivity of monoporous samples was measured to be 142±3W∕mK at 42±2°C, and it was independent of particle diameter. The thermal conductivity of biporous samples was found to be a function of cluster to particle diameter ratio.

The Effect of Turbulence on Momentum and Heat Transport in Packed Beds with Low Tube to Particle Diameter Ratio

2018 ◽  
Vol 16 (11) ◽  
Author(s):  
F. I. Molina-Herrera ◽  
C. O. Castillo-Araiza ◽  
H. Jiménez-Islas ◽  
F. López-Isunza
Keyword(s):  
Thermal Conductivity ◽  
Heat Transport ◽  
Mass Flux ◽  
Flow Model ◽  
Particle Diameter ◽  
Packed Bed ◽  
Diameter Ratio ◽  
Packed Beds ◽  
Measured Temperature ◽  
Orthogonal Collocation

Abstract This is a theoretical study about the influence of turbulence on momentum and heat transport in a packed-bed with low tube to particle diameter ratio. The hydrodynamics is given here by the time-averaged Navier-Stokes equations including Darcy and Forchheimer terms, plus a κ-ε two-equation model to describe a 2D pseudo-homogeneous medium. For comparison, an equivalent conventional flow model has also been tested. Both models are coupled to a heat transport equation and they are solved using spatial discretization with orthogonal collocation, while the time derivative is discretized by an implicit Euler scheme. We compared the prediction of radial and axial temperature observations from a packed-bed at particle Reynolds numbers (Rep) of 630, 767, and 1000. The conventional flow model uses effective heat transport parameters: wall heat transfer coefficient (hw) and thermal conductivity (keff), whereas the turbulent flow model includes a turbulent thermal conductivity (kt), estimating hw via least-squares with Levenberg-Marquardt method. Although predictions of axial and radial measured temperature profiles with both models show small differences, the calculated radial profiles of the axial velocity component are very different. We demonstrate that the model that includes turbulence compares well with mass flux measurements at the packed-bed inlet, yielding an error of 0.77 % in mass flux balance at Rep = 630. We suggest that this approach can be used efficiently for the hydrodynamics characterization and design and scale-up of packed beds with low tube to particle diameter ratio in several industrial applications.

Thermophysical Properties of Biporous Sintered Copper

2005 ◽  
Author(s):  
Ying-Yu Lin ◽  
Tadej Semenic ◽  
Ivan Catton
Keyword(s):  
Thermal Conductivity ◽  
Capillary Pressure ◽  
Effective Thermal Conductivity ◽  
Thermophysical Properties ◽  
Silicone Oil ◽  
Pressure Drops ◽  
Sintered Copper ◽  
Measurement Results ◽  
The One ◽  
Working Liquid

Thermophysical properties of bidispersed (biporous)-sintered copper are measured. An apparatus to measure effective thermal conductivity of dry samples is built. It is calibrated using bulk samples with known thermal conductivity. Permeability is measured based on flow resistance though the porous samples. Velocity at different pressure drops is measured and the permeability calculated using Darcy’s law. The experiment is performed using silicone oil as working liquid. The error of the method is less than three percent. Capillary pressure for all samples is measured based on amount of liquid that is held by the porous sample. The Young-Laplace relationship is used to relate capillary pressure to effective pore radius. Porosity of the samples is measured using density method. According to the measurement results, effective thermal conductivity of biporous samples is much lower than for comparable monoporous samples. Permeability and porosity of biporous samples are much higher than the monoporous samples. Capillary pressure of the biporous samples is very close to the one measured for the monoporous samples.

Thermophysical Properties of Monoporous Sintered Copper

2005 ◽  
Author(s):  
Ying-Yu Lin ◽  
Tadej Semenic ◽  
Ivan Catton
Keyword(s):  
Thermal Conductivity ◽  
Capillary Pressure ◽  
Thermophysical Properties ◽  
Flow Resistance ◽  
Pore Radius ◽  
Silicone Oil ◽  
Pressure Drops ◽  
Sintered Copper ◽  
Powder Diameter ◽  
Effective Pore Radius

Thermophysical properties of monodispersed-sintered copper are measured. An apparatus to measure effective thermal conductivity of dry and wet samples is built. It is calibrated using bulk samples with known thermal conductivity. Permeability is measured based on flow resistance though the porous samples. Velocity at different pressure drops is measured and the permeability calculated using Darcy’s law. The experiment is performed using water and silicone oil as working liquids. The error of the measurement is less then five percent. Capillary pressure for all samples is measured based on amount of liquid that is held by the porous sample. The Young-Laplace relationship is used to relate capillary pressure to effective pore radius. Porosity of the samples is calculated by measuring the dimension of samples and weighing the amount of liquid in fully saturated samples. Thermal conductivity and capillary pressure are found to decrease as powder diameter increases; permeability and porosity increases with powder diameter.

scholarly journals Thermophysical Properties of Cement Mortar Containing Waste Glass Powder

Crystals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 488
Author(s):  
Oumaima Nasry ◽  
Abderrahim Samaouali ◽  
Sara Belarouf ◽  
Abdelkrim Moufakkir ◽  
Hanane Sghiouri El Idrissi ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Specific Heat ◽  
Thermophysical Properties ◽  
Glass Powder ◽  
Cement Mortar ◽  
Soda Lime ◽  
Waste Glass ◽  
Soda Lime Glass ◽  
Volumetric Specific Heat ◽  
Waste Glass Powder

This study aims to provide a thermophysical characterization of a new economical and green mortar. This material is characterized by partially replacing the cement with recycled soda lime glass. The cement was partially substituted (10, 20, 30, 40, 50 and 60% in weight) by glass powder with a water/cement ratio of 0.4. The glass powder and four of the seven samples were analyzed using a scanning electron microscope (SEM). The thermophysical properties, such as thermal conductivity and volumetric specific heat, were experimentally measured in both dry and wet (water saturated) states. These properties were determined as a function of the glass powder percentage by using a CT-Meter at different temperatures (20 °C, 30 °C, 40 °C and 50 °C) in a temperature-controlled box. The results show that the thermophysical parameters decreased linearly when 60% glass powder was added to cement mortar: 37% for thermal conductivity, 18% for volumetric specific heat and 22% for thermal diffusivity. The density of the mortar also decreased by about 11% in dry state and 5% in wet state. The use of waste glass powder as a cement replacement affects the thermophysical properties of cement mortar due to its porosity as compared with the control mortar. The results indicate that thermal conductivity and volumetric specific heat increases with temperature increase and/or the substitution rate decrease. Therefore, the addition of waste glass powder can significantly affect the thermophysical properties of ordinary cement mortar.

scholarly journals Influence of Macroscopic Wall Structures on the Fluid Flow and Heat Transfer in Fixed Bed Reactors with Small Tube to Particle Diameter Ratio

Processes ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 689
Author(s):  
Thomas Eppinger ◽  
Nico Jurtz ◽  
Matthias Kraume
Keyword(s):  
Heat Transfer ◽  
Fixed Bed ◽  
Particle Diameter ◽  
Diameter Ratio ◽  
Spherical Particles ◽  
Reactor Wall ◽  
Entry Length ◽  
Fixed Bed Reactors ◽  
Wall Structures ◽  
Small Tube

Fixed bed reactors are widely used in the chemical, nuclear and process industry. Due to the solid particle arrangement and its resulting non-homogeneous radial void fraction distribution, the heat transfer of this reactor type is inhibited, especially for fixed bed reactors with a small tube to particle diameter ratio. This work shows that, based on three-dimensional particle-resolved discrete element method (DEM) computational fluid dynamics (CFD) simulations, it is possible to reduce the maldistribution of mono-dispersed spherical particles near the reactor wall by the use of macroscopic wall structures. As a result, the lateral convection is significantly increased leading to a better radial heat transfer. This is investigated for different macroscopic wall structures, different air flow rates (Reynolds number Re = 16 ...16,000) and a variation of tube to particle diameter ratios (2.8, 4.8, 6.8, 8.8). An increase of the radial velocity of up to 40%, a reduction of the thermal entry length of 66% and an overall heat transfer increase of up to 120% are found.

EXAMINATION OF THERMOPHYSICAL CHARACTERISTICS OF A HEAT-PROTECTIVE MATERIAL BASED ON FIBERGLASS DURING DESTRUCTION

2021 ◽  
pp. 91-97
Author(s):  
D.Ya. Barinov ◽  
◽  
S.Yu. Shorstov ◽  
M.G. Razmahov ◽  
A.I. Gulyaev ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermophysical Properties ◽  
Thermal Effects ◽  
Space Technology ◽  
Muffle Furnace ◽  
Thermophysical Characteristics ◽  
Initial State ◽  
Protective Material ◽  
Temperature Dependences

When designing advanced samples of aviation and rocket and space technology, during the operation of which the temperature on the surface of the material can exceed the temperature of destruction, it is important to have an understanding of the values of thermophysical properties. The work investigates the thermophysical properties of fiberglass in the initial state and after the binder is burned out in a muffle furnace. The temperature dependences of thermal effects, heat capacity, thermal diffusivity and thermal conductivity were determined, density was measured, and thermogravimetric analysis was carried out. Using a stereomicroscope, the microstructure of the lateral cut of the samples was examined and its evolution was determined during the burning of the binder.

Effect of capillary pressure on performance of a heat pipe: Numerical approach with FEM

2012 ◽  
Vol 32 ◽  
pp. 93-99 ◽  
Author(s):  
Nat Thuchayapong ◽  
Akihiro Nakano ◽  
Phrut Sakulchangsatjatai ◽  
Pradit Terdtoon
Keyword(s):  
Heat Pipe ◽  
Capillary Pressure ◽  
Numerical Approach

PROPERTIES OF HEAT FLUX FUNCTIONS AND A LINEAR THEORY OF HEAT FLUX

1995 ◽  
Vol 09 (09) ◽  
pp. 1113-1122 ◽  
Author(s):  
LIQIU WANG
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Temperature Gradient ◽  
Linear Function ◽  
Linear Theory ◽  
Strain Tensor ◽  
Positive Definiteness ◽  
Positive Definite ◽  
Flux Vector ◽  
Heat Flux Vector

The symmetry and positive definiteness of thermal conductivity tensor K are used to derive some properties of heat flux functions ɸi (i=0, 1, 2). All ɸi are shown to be real-valued. Both ɸ0 and ɸ2 are found to be positive definite, and ɸ1 is constrained between −(ɸ0 + ɸ2) and (ɸ0 + ɸ2). By assuming heat flux vector q to be a linear function of temperature gradient ∇θ and velocity strain tensor D, ɸi reduce to three coefficients which are independent of D and ∇θ.

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