Abstract
In the past few decades, significant efforts have been made to improve the theoretical understanding of thermal transport mechanisms in thermal insulation materials and push the thermal conductivity's lower limits. However, most works focused singularly on specific types of materials, and the models used for thermal conductivity predictions are diverse - a model that fits one material might not fit others. Here, we improve and unify the gas and solid thermal conductivity models for porous materials. Through experimental characterization of several different materials as well as literature data for other materials, these models are validated. We have also found that the pressure-dependent gas thermal conductivity of most materials can be well fitted by using one or two pore sizes without using a complex pore size distribution. With the refined models, we decompose the effective thermal conductivity of several thermal insulation materials into gas, solid, and radiation contributions. For cellular (polystyrene and polyurethane) foams, the relative contributions from air, solid, and radiation are 58–75%, 3–11%, 16–38%, respectively. For granular porous materials (polyurethane and silica in this work), the contributions from air, solid, and radiation are 45–66%, 34–46%, and 0–8%, respectively. This work is expected to provide guidance on the design and optimization of the next generation of thermal insulation materials, for example, through the effort of reducing gas conduction and radiation in foams and suppressing gas and solid conduction in aerogels.
Original language | English |
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Article number | 108164 |
Journal | International Journal of Thermal Sciences |
Volume | 187 |
DOIs | |
State | Published - May 2023 |
Funding
This research was supported by the US Department of Energy's ( DOE's ) Office of Energy Efficiency and Renewable Energy (EERE), Building Technologies Office (BTO) under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC, and used resources at the Building Technologies and Research Integration Center, a DOE-EERE User Facility at Oak Ridge National Laboratory. The authors are grateful for the discussion with Alan McGaughey from Carnegie Mellon University. This work is supported by the project “Models to Evaluate and Guide the Development of Low Thermal Conductivity Materials for Building Envelopes” funded by the DOE's BTO and EERE . M.F. acknowledges the financial support from the National Science Foundation (grant CBET-1952210 ). The authors acknowledge the support from NanoPore Incorporated, National Institute of Standards and Technology , and BASF Corporation for providing samples used in this research. The authors also acknowledge the support from Jerry Atchley for preparing the samples and running experiments, Anthony Gehl for developing the DAQ for experimental setup, and Jaswinder Sharma, Kai Li, Qianying Guo, and Kinga Unocic for their help with conducting SEM measurements. The authors thank Olivia Shafer for formatting and technical editing. This paper has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US Government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). This paper has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US Government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).This research was supported by the US Department of Energy's (DOE's) Office of Energy Efficiency and Renewable Energy (EERE), Building Technologies Office (BTO) under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC, and used resources at the Building Technologies and Research Integration Center, a DOE-EERE User Facility at Oak Ridge National Laboratory. The authors are grateful for the discussion with Alan McGaughey from Carnegie Mellon University. This work is supported by the project “Models to Evaluate and Guide the Development of Low Thermal Conductivity Materials for Building Envelopes” funded by the DOE's BTO and EERE. M.F. acknowledges the financial support from the National Science Foundation (grant CBET-1952210). The authors acknowledge the support from NanoPore Incorporated, National Institute of Standards and Technology, and BASF Corporation for providing samples used in this research. The authors also acknowledge the support from Jerry Atchley for preparing the samples and running experiments, Anthony Gehl for developing the DAQ for experimental setup, and Jaswinder Sharma, Kai Li, Qianying Guo, and Kinga Unocic for their help with conducting SEM measurements. The authors thank Olivia Shafer for formatting and technical editing.
Keywords
- Effective medium theory
- Knudsen effect
- Radiative heat transfer
- Thermal conductivity
- Thermal insulation materials