Advances of thermal conductivity models of nanoscale silica aerogel insulation material
Introduction
Thermal insulation material is a kind of material that can significantly reduce the heat flux through it. The utilization of the thermal insulation material can save energy on one hand and meet the temperature requirement of equipment/building on the other hand. Thus insulation material is of great importance for many engineering applications, such as energy, building, aeronautics and astronautics and so on. Thermal conductivity is one of the most important parameter that reflect the insulation performance of the thermal insulation material. With the rapid development of high technology(hypersonic vehicle, space shuttle), the requirement for high efficient thermal insulation material become more and more urgent. Traditional thermal insulation material (fiberglass, asbestos, rock wool, etc) become difficult to meet the requirement for these high-tech equipment. Therefore, developing new-type thermal insulation material become a major trend in the development of thermal insulation materials. Among them, aerogel is one of the most promising new-type high efficient thermal insulation material.
Aerogel usually refers to such a kind of lightweight nanoscale solid material that is constituted by the aggregation of nanoscale particles to form a nanostructured solid network. Aerogel has nanoporous structure with 1–20 nm particle diameter and 2–50 nm pore diameter, and its porosity can be up to 90% [1]. The special nanoscale porous network structure (Fig. 1) brings about a lot of excellent properties of aerogel material and makes it applicable to a widely fields in industry such as thermal insulation, energy, building, chemical industry, catalysis, aeronautics and astronautics and so on. Hrubesh [2] had summarized the special properties and the corresponding application of aerogel material, see Table 1.
As a kind of new type nanoporous heat insulation material, aerogel has the advantages of lightweight and highly efficient heat insulation performance, so it has attracted more and more attentions, especially in the rapidly developed aerospace area [3], [4], [5], [6]. In the 1990s, NASA applied aerogel material in two Space exploration programs: Mars Pathfinder and Stardust; this opened the aerogel application in the field of space exploration [3]. In 2003, the Sample Collection for the Investigation of Mars (SCIM) and Satellite Test of the Equivalence Principle (STEP) in NASA's Mars Exploration Rovers both used aerogel material as insulation material, and it was considered to be one of the key factors of the success of the plans [3]. In 2005, NASA prepared to use aerogel material in the thermal protection system of Venus spacecraft [6]. Up to now, NASA has never stopped the efforts in aerogel research. Besides, as the new type insulation material, aerogel also has more and more applications in civilian field and modern industry [7], [8], [9], [10]. Cuce et al. [11] gave a comprehensive review on aerogel and its utilization in buildings. An economic analysis and future potential of aerogel were also considered in their study.
Since the traditional thermal insulation materials can hardly meet the high demand in modern industrial, aerospace and other fields, the development of the nanoporous aerogel insulation material becomes important. Because of its nanostructure, aerogel has some special heat transfer phenomenon which makes heat transfer inside the material much more complex. Therefore, analyzing the heat transfer modes and the internal heat transfer mechanisms, constructing a suitable thermal conductivity model for aerogel material and studying the influence of various influencing factors on the heat transfer performance of material, have significant values in the performance prediction, optimization as well as practical application for the silica aerogel composite insulation material. And this could also provide theoretical foundation for the further development of new heat insulation material with high temperature resistant, lightweight and high efficiency.
Recently, many scholars have studied and discussed the heat transfer models of silica aerogel nanoporous insulation material. The object of this paper is to review the current heat transfer models for the aerogel material and to help the subsequent studies of aerogel material. The structure of this paper is as follows: In Section 2, the nanoscale heat transfer features inside nanoporous aerogel material and the heat transfer features of composite aerogel insulation material will be introduced. In Section 3, the current thermal conductivity models for the three basic heat transfer modes inside aerogel material, which are gaseous heat transfer, solid heat transfer and radiative heat transfer, are discussed, respectively. Afterward, on the basis of models of each heat transfer mode, the total effective thermal conductivity models for the nanoporous aerogel material and its composite insulation material are reviewed. Our previous work on the effective thermal conductivity of aerogel insulation material is then introduced as an illustration of establishing the effective thermal conductivity model of the material. Finally, as a fast developed molecular simulation method, the molecular dynamics (MD) plays an important role in the simulation of aerogel materials and we will make a briefly introduction of MD.
Section snippets
Nanoscale heat transfer inside nanoporous aerogel material
In porous materials, there are three basic modes of heat transfer, which are convection, conduction and radiation heat transfer.
Convection is the macroscopic movement of the fluid, which leads to a relative displacement and mixes the cold part and hot part of the fluid to produce the heat transfer in the fluid. For porous media, it was reported that when the pore diameter is lower than 4 mm, heat transfer by the convection could be neglected [12], [13]. Since the internal pore diameters of
Thermal conductivity models of aerogel material
The existing models of thermal conductivity of aerogel materials will be introduced according to the three basic heat transfer modes which are gaseous heat transfer, solid heat transfer and radiative heat transfer, respectively. Then the total effective thermal conductivity models for the nanoporous aerogel material and its composite insulation material are summarized. Molecular dynamics plays an important role in the simulation of aerogel materials, so it will be briefly introduced in a
Conclusions and prospects
In this paper, we have made a comprehensive review about the existing aerogel-related heat transfer models. The heat transfer models are divided into 5 parts. First, the existing models of thermal conductivity of aerogel materials corresponding to the three basic heat transfer modes (gaseous heat transfer, solid heat transfer and radiative heat transfer) are introduced. Then the effective thermal conductivity models for the nanoporous aerogel material and its composite insulating material are
Acknowledgements
This work was supported by the State Key Program of National Natural Science of China (No. 51436007) and the National Key Basic Research Program of China (973 Program) (No. 2013CB228304).
References (112)
Aerogel applications
J. Non-Cryst. Solids
(1998)Aerogel insulation systems for space launch applications
Cryogenics
(2006)- et al.
Aerogel insulation for building applications: a state-of-the-art review
Energy Build.
(2011) - et al.
Improvements of reinforced silica aerogel nanocomposites thermal properties for architecture applications
Int. J. Biol. Macromol.
(2015) - et al.
Thermal conductivity and characterization of compacted, granular silica aerogel
Energy Build.
(2014) - et al.
Toward aerogel based thermal superinsulation in buildings: a comprehensive review
Renew. Sustain. Energy Rev.
(2014) - et al.
Effective thermal conductivity of the solid backbone of aerogel
Int. J. Heat Mass Transf.
(2013) - et al.
Monolithic silica aerogel insulation doped with TiO2 powder and ceramic fibers
J. Non-Cryst. Solids
(1995) - et al.
Theoretical modeling of carbon content to minimize heat transfer in silica aerogel
J. Non-Cryst. Solids
(1995) - et al.
Relationship between pore size and the gas pressure dependence of the gaseous thermal conductivity
Colloids Surf. A Physicochem. Eng. Asp.
(2007)
Coupling model for heat transfer between solid and gas phases in aerogel and experimental investigation
Int. J. Heat Mass Transf.
High strength SiO2 aerogel insulation
J. Non-Cryst. Solids
Synthesis of nanostructured mullite from xerogel and aerogel obtained by the non-hydrolytic sol-gel method
Nanostruct. Mater.
Radiative heat transfer study on silica aerogel and its composite insulation materials
J. Non-Cryst. Solids
Thermal conductivities study on silica aerogel and its composite insulation materials
Int. J. Heat Mass Transf.
Structural and thermal study of highly porous nanocomposite SiO2-based aerogels
J. Non-Cryst. Solids
Microstructural characterization and properties of ambient-dried SiO2 matrix aerogel doped with opacified TiO2 powder
J. Alloys Compd.
Integration of mineral powders into SiO2 aerogels
J. Non-Cryst. Solids
Theoretical study on thermal conductivities of silica aerogel composite insulating material
Int. J. Heat Mass Transf.
A 3-D numerical heat transfer model for silica aerogels based on the porous secondary nanoparticle aggregate structure
J. Non-Cryst. Solids
Determination of mesopore size of aerogels from thermal conductivity measurements
J. Non-Cryst. Solids
Heat conduction modeling in 3-D ordered structures for prediction of aerogel thermal conductivity
Int. J. Heat Mass Transf.
An analytical model for combined radiative and conductive heat transfer in fiber-loaded silica aerogels
J. Non-Cryst. Solids
Effective structure of aerogels and decomposed contributions of its thermal conductivity
Appl. Therm. Eng.
Effects of non-ideal structures and high temperatures on the insulation properties of aerogel-based composite materials
J. Non-Cryst. Solids
Prediction of the gaseous thermal conductivity in aerogels with non-uniform pore-size distribution
J. Non-Cryst. Solids
Optimization of monolithic silica aerogel insulants
Int. J. Heat Mass Transf.
Modeling of phonon heat transfer in spherical segment of silica aerogel grains
Phys. B Condens. Matter
Multi-length and time scale thermal transport using the lattice Boltzmann method with application to electronics cooling
Int. J. Heat Mass Transf.
A fractal model for predicting the effective thermal conductivity of liquid with suspension of nanoparticles
Int. J. Heat Mass Transf.
Correlation between structure and thermal conductivity of organic aerogels
J. Non-Cryst. Solids
Radiative characteristics of opacifier-loaded silica aerogel composites
J. Non-Cryst. Solids
Theoretical model of radiative transfer in opacified aerogel based on realistic microstructures
Int. J. Heat Mass Transf.
Thermal transport in organic and opacified silica monolithic aerogels
J. Non-Cryst. Solids
Heat transfer in opacified aerogel powders
J. Non-Cryst. Solids
Mechanical structure–property relationship of aerogels
J. Non-Cryst. Solids
Analysis of the effective thermal conductivity of fractal porous media
Appl. Therm. Eng.
An intermingled fractal units model to evaluate pore size distribution influence on thermal conductivity values in porous materials
Appl. Therm. Eng.
Predictions of effective physical properties of complex multiphase materials
Mater. Sci. Eng. R Rep.
Thermal characterization of carbon-opacified silica aerogels
J. Non-Cryst. Solids
Molecular dynamics study of the thermal conductivity of amorphous nanoporous silica
Int. J. Heat Mass Transf.
Aerogels Handbook
Aerogel: space exploration applications
J. Sol–Gel Sci. Technol.
Review of modern spacecraft thermal control technologies
HVAC&R Res.
Aerogel Insulation for the Thermal Protection of Venus Spacecraft, NASA SBIR 2005 Solicitation
Silica aerogel: synthesis and applications
J. Nanomater.
Heat Transfer Mechanism and Thermal Design of Nanoporous Insulating Materials
Thermal properties of organic and inorganic aerogels
J. Mater. Res.
Structure and thermal conductivity of silica aerogels from computer simulations
Heat Transfer
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