scholarly journals Effective Thermal Conductivity of a Wet Porous Medium—Presence of Hysteresis When Modeling the Spatial Water Distribution for the Pendular Regime

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Édouard Canot ◽  
Renaud Delannay ◽  
Salwa Mansour ◽  
Mohamad Muhieddine ◽  
Ramiro March
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Water Distribution ◽  
Thermal Flux ◽  
Liquid Volume ◽  
Liquid Meniscus ◽  
Dry Air ◽  
Different Shapes ◽  
Spherical Grains ◽  
Water Meniscus

This paper deals with the heat transfer between two spherical grains separated by a small gap; dry air is located around the grains and a liquid water meniscus is supposed to be present between them. This problem can be seen as a microscale cell of an assembly of solid grains, for which we are looking for the effective thermal conductivity. For a fixed contact angle and according to the volume of the liquid meniscus, two different shapes are possible for the meniscus, giving a “contacting” state (when the liquid makes a true bridge between the two spheres) and a “noncontacting” one (when the liquid is split in two different drops, separated by a thin air layer); the transition between these two states occurs at different times when increasing or decreasing the liquid volume, thus leading to a hysteresis behavior when computing the thermal flux across the domain.

Measurement of Effective Thermal Conductivity of CNT-Nanofluids by Transient Short-Wire Method

2009 ◽  
Author(s):  
Masamichi Kohno ◽  
Koichi Kimura ◽  
Shogo Moroe ◽  
Yasuyuki Takata ◽  
Peter L. Woodfield ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Effective Thermal Conductivity ◽  
Volume Fraction ◽  
Hot Wire ◽  
Wire Method ◽  
Different Shapes ◽  
Transient Short Hot Wire ◽  
Al2o3 Particles ◽  
Particle Shapes

Thermal conductivity and thermal diffusivity of CNT-nanofluids and Al2O3-nanofulids were measured by the transient short-hot-wire method. The uncertainty of their measurements is estimated to be within 1% for the thermal conductivity and 5% for the thermal diffusivity. Three different shapes of Al2O3 particles were prepared for Al2O3–water nanofluids. For the thermal conductivity of Al2O3-water nanofluids, there are differences in the enhancement of thermal conductivity for differences in particle shapes. Hardly any enhancement of thermal conductivity was observed for SWCNT-water nanofluids because the volume fraction of SWCNT was extremely low. However, we consider by increasing the volume fraction of SWCNTs, it will be possible to enhance the thermal conductivity.

ESTIMATION OF THERMAL CONDUCTIVITY OF POROUS MATERIAL WITH FEM AND FRACTAL GEOMETRY

2009 ◽  
Vol 20 (04) ◽  
pp. 513-526 ◽  
Author(s):  
SHOUJU LI ◽  
YUEFANG WANG ◽  
YINGXI LIU ◽  
WEI SUN
Keyword(s):  
Thermal Conductivity ◽  
Fractal Dimension ◽  
Porous Material ◽  
Effective Thermal Conductivity ◽  
Pore Space ◽  
Thermal Flux ◽  
Solid Matrix ◽  
The Finite Element Method ◽  
Heat Transform ◽  
The Relationship

The relationship between thermal conductivity of porous material and fractal dimension is numerically simulated by using the finite element method. The solid matrix and pore space are generated randomly according to material porosity. Material parameters and element properties are changed by using ANSYS parameter design language. The effective thermal conductivity is derived according to thermal flux through some sections computed by FEM and Fourier heat transform law. The investigation shows that the effective thermal conductivity decreases with increasing porosity. The effective thermal conductivity will decrease exponentially with increasing fractal dimension of porosity space and increase exponentially with increasing fractal dimension of solid matrix.

Role of Thermal-Interaction Between Aggregated Particles in Thermal Conductivity Enhancement of Nanofluids

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Jae Sik Jin ◽  
Joon Sik Lee
Keyword(s):  
Thermal Conductivity ◽  
Thermal Analysis ◽  
Heat Conduction ◽  
Effective Thermal Conductivity ◽  
Volume Fraction ◽  
Thermal Flux ◽  
Linear Chain ◽  
Field Variation ◽  
Thermal Interaction

This study investigates the role of thermal-interaction (TI) between aggregated particles (APs) on the enhanced thermal conductivity of nanofluids. With the assumption of configurations of linear chain-like aggregates in the direction transverse to the thermal flux, two-dimensional heat conduction is considered for estimation of the effective thermal conductivity of regular arrays, which is separated into three components, namely, no thermal-interaction (NTI) effect, longitudinal thermal-interaction (LTI) effect, and transverse thermal-interaction (TTI) effect. We have obtained a solution to the 1D confine case of APs, and a thermal analysis is carried out for different confine systems to investigate their relatively quantitative assessments of thermal contribution to the enhanced effective thermal conductivity using the first-order approximation. We show that these effects are represented as a function of ϕ (where ϕ is the volume fraction of APs) for engineering purposes. It is also found that TI contribution to the enhanced thermal conduction reaches up to around 87.5% when APs contact with each other and that TTI has an important role in the range 0.3785 ≤ ϕ ≤ 0.7031 due to the confine effect of field-variation caused by transversely bidirectional thermal-interactions. When ϕ > 0.7031, LTI effect again plays key role in heat conduction in nanofluid systems owing to closed packing of APs. Consequently, to achieve energy-efficient heat transfer nanofluids that are required in many industrial applications, both APs' distribution configuration and APs' volume fraction have to be considered in the thermal analysis of nanofluids.

A Capillary-Wick Heat Pipe Fabricated on a Plastic Board (Fundamental Experiments on Heat Transport Characteristics)

2015 ◽  
Author(s):  
Yasushi Koito ◽  
Hiroyuki Maehara ◽  
Daisuke Shimada ◽  
Toshio Tomimura
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Phase Change ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Working Fluid ◽  
Experimental Investigations ◽  
Liquid Volume ◽  
Experimental Conditions ◽  
Phase Change Heat Transfer

A capillary-wick heat pipe having the dimensions of 5.0 mm × 5.0 mm × 100 mm (length) is fabricated on a surface of a plastic board, and the experimental investigations are conducted on the operational characteristics of the heat pipe. Plastics are easy to manufacturing, lightweight, low cost, flexible, and besides, the present study aims at the phase-change heat transfer inside the plastic board. A sintered copper powder and water are used as the wick structure and the working fluid of the heat pipe, respectively. In experiments, an evaporator section of the heat pipe is heated by a heater while a condenser section is water-cooled by a heat sink. A heat input and a liquid volume inside the heat pipe are changed, and the temperature distribution of the heat pipe is measured by thermocouples. Moreover, a one-dimensional thermal circuit model is made to evaluate the effective thermal conductivity of the heat pipe. From the experimental results, the continuous phase-change heat transfer inside the plastic board and its effectiveness are confirmed. It is also revealed that the effective thermal conductivity of the heat pipe is 854 W/(m·K) in maximum under the present experimental conditions.

Sign in / Sign up

Export Citation Format

Share Document