scholarly journals Heat Transfer in Straw-Based Thermal Insulating Materials

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4408
Author(s):  
Dániel Csanády ◽  
Olivér Fenyvesi ◽  
Balázs Nagy
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Bulk Density ◽  
Heat Transfer Process ◽  
Model Parameters ◽  
Stem Density ◽  
Cellulose Content ◽  
Gas Phases ◽  
Thermal Insulating ◽  
Thermal Insulations

An analytic-empirical model was developed to describe the heat transfer process in raw straw bulks based on laboratory experiments for calculating the thermal performance of straw-based walls and thermal insulations. During the tests, two different types of straw were investigated. The first was barley, which we used to compose our model and identify the influencing model parameters, and the second was wheat straw, which was used only for validation. Both straws were tested in their raw, natural bulks without any modification except drying. We tested the thermal conductivity of the materials in a bulk density range between 80 and 180 kg/m3 as well as the stem density, material density, cellulose content, and porosity. The proposed model considers the raw straw stems as natural composites that contain different solids and gas phases that are connected in parallel to each other. We identified and separated the following thermal conductivity factors: solid conduction, gas conduction in stem bulks with conduction factors for pore gas, void gas, and gaps among stems, as well as radiation. These factors are affected by the type of straw and their bulk density. Therefore, we introduced empirical flatness and reverse flatness factors to our model, describing the relationship between heat conduction in stems and voids to bulk density using the geometric parameters of undisturbed and compressed stems. After the validation, our model achieved good agreement with the measured thermal conductivities. As an additional outcome of our research, the optimal bulk densities of two different straw types were found to be similar at 120 kg/m3.

scholarly journals Thermal conductivity and deformation of Taxodium hybrid ‘Zhongshanshan’ during heat transfer process

BioResources ◽  
2020 ◽  
Vol 15 (2) ◽  
pp. 2645-2655
Author(s):  
Yuehua Zhu ◽  
Yaoli Zhang ◽  
Biao Pan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Moisture Content ◽  
Transfer Process ◽  
Dimensional Change ◽  
Testing Temperature ◽  
Scientific Basis ◽  
Heat Transfer Process ◽  
Wood Moisture Content ◽  
Wood Moisture

The thermal conductivity and the deformation of wood from the Taxodium hybrid ‘Zhongshanshan’ were studied in the process of heat transfer. The results showed that the average thermal conductivity of this wood was 0.1257 W/(m·K) under the condition of 12% wood moisture content and 30 °C heat transfer temperature. When the testing temperature exceeded 0 °C, the thermal conductivity increased linearly with both temperature and wood moisture content and was affected by the moisture content of the wood. During the heat transfer process, the deformation of features caused repeated swelling and shrinkage in the longitudinal, radial, and tangential directions. The dimensional change was greatly affected by the wood’s moisture content and was less affected by the temperature. These results are of great meaning for the study of the heat transfer process of Taxodium hybrid ‘Zhongshanshan’ wood. Furthermore, it provides a scientific basis for the heat preservation effect, drying treatment, and pyrolysis treatment of Taxodium hybrid ‘Zhongshanshan’ wood for use as a building material.

scholarly journals Investigation of thermal model effects on geothermal and oil reservoir well testing behavior during water and steam injection

2020 ◽  
Vol 75 ◽  
pp. 58
Author(s):  
Mahdi Abbasi ◽  
Mohammad Ahmadi ◽  
Alireza Kazemi ◽  
Mohammad Sharifi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Fluid Flow ◽  
Steam Injection ◽  
Model Parameters ◽  
Transfer Model ◽  
Diffusivity Coefficient ◽  
Reservoir Model ◽  
Type Curve ◽  
Water Steam

Global warming and reducing fossil fuel resources have increased the interest in using renewable resources such as geothermal energy. In this paper, in the first step, heat transfer equations have been presented for reservoir during water (steam) injection by considering heat loss to adjacent formations. According to radius of thermal front, the reservoir is partitioned into two regions with different fluid physical properties. The heat transfer model is coupled with a fluid flow model which is used to calculate the reservoir pressure or fluid flow rates. Then by calculating outer radius of heated region and using radial composite reservoir model, the fluid flow equations in porous media are solved. Using pressure derivative plot in regions with different thermal conductivity coefficients, a type curve plot is presented. The reservoir and adjacent formation thermal conductivity coefficients can be calculated by matching the observed pressure data on the thermal composite type curve. Additionally, the interference test in composite geothermal reservoir is discussed. In the composite reservoir model, parameters such as diffusivity coefficient, conductivity ratio and the distance to the radial discontinuity are considered. New type curves are provided to introduce the effect of diffusivity/conductivity contrast ratios on temperature behavior. Improving interpretations, and performing fast computations and fast sensitivity analysis are the benefits of the presented solutions.

Numerical Computation of the Effects of Brownian Motion on the Effective Thermal Conductivity of Suspensions

2007 ◽  
Author(s):  
P. E. Phelan ◽  
J. R. Pacheco
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Brownian Motion ◽  
Dimensional Space ◽  
Numerical Technique ◽  
Heat Transfer Process ◽  
Immersed Boundary ◽  
Brownian Dynamic ◽  
Dynamic Simulations ◽  
Bulk Fluid

In this paper, a numerical scheme based on the immersed boundary method is used to study the motion of nano-sized particles subjected to Brownian motion and heat transfer. Our objective is to use this numerical technique as a tool to better understand the effect that Brownian forces have on the overall heat transfer process. The conventional approach to perform Brownian dynamic simulations is based on the use of a random force in the particle motion such that the fluctuation-dissipation theorem is satisfied. Our preliminary computational results suggest an increase in the thermal conductivity of the bulk fluid. Results are presented for several particles in a two-dimensional space.

scholarly journals Modeling heat transfer process in soils

2018 ◽  
Vol 251 ◽  
pp. 02048 ◽  
Author(s):  
Ian Ofrikhter ◽  
Alexander Zaharov ◽  
Andrey Ponomaryov ◽  
Natalia Likhacheva
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Conductivity ◽  
Analytical Calculation ◽  
Accurate Method ◽  
Heat Transfer Process ◽  
Preliminary Evaluation ◽  
Soil Base ◽  
Undisturbed Sample ◽  
Analytical Formulas

In this paper, a new model is presented for calculating the thermal conductivity of soils, and the main provisions for the derivation of analytical formulas are given. The presented model allows taking into account the density, moisture content and temperature of the soil base. The technique presented in the paper makes it possible to dispense with laborious experiments to estimate the thermal conductivity of the soil. The method of analytical calculation is step by step presented in the paper. Two variants of using the method are proposed: 1) Less accurate method, for preliminary evaluation, without the need to take probe and conduct experiments. 2) More accurate method, with at least one experiment with a disturbed or undisturbed sample. The results of comparison of calculated values of thermal conductivity and experimental data are presented.

The Effect of Additional Polyethylene Glycol (PEG) as Coating Fe3O4 for Magnetic Nanofluid Applications

2021 ◽  
Vol 14 ◽  
Author(s):  
Ganesha Antarnusa ◽  
Yus Rama Denny ◽  
Andri Suherman ◽  
Indri Sari Utami ◽  
Asep Saefullah
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Particle Size ◽  
Polyethylene Glycol ◽  
Fe3o4 Nanoparticles ◽  
Chemical Precipitation ◽  
Heat Transfer Process ◽  
Precipitation Method ◽  
Magnetic Nanofluid ◽  
Peg 6000

Background & Objective: Magnetic nanofluid is a special class of nanofluid that exhibits both magnetic and fluid properties. The main purpose of using magnetic nanofluid as a heat transfer medium comes from the possibility of controlling the flow and the heat transfer process through an external magnetic field. This research aims at identifying the effect of adding polyethylene glycol (PEG) to magnetite (Fe3O4) nanoparticles for magnetic nanofluid applications. Method: The nanofluid were prepared by synthesizing Fe3O4 nanoparticles using the chemical precipitation method, and then dispersed in distilled water using a sonicator. Results: The result of XRD is that nanoparticles had inverse spinel structures and the smallest crystallite size is found in the Fe3O4@PEG-6000 samples. FE-SEM and TEM show that the addition of PEG can reduce the Fe3O4 agglomeration and the smallest particle size is found in the Fe3O4@PEG-6000 samples. The result of FT-IR shows that there is a surface modification of Fe3O4 nanoparticles and PEG polymer. The result of VSM shows the coercivity value is small so that the sample is superparamagnetic material. The addition of PEG increases the thermal conductivity of Fe3O4 nanoparticles. Conclusion: The addition of PEG makes particle size smaller, reduce the agglomeration and increases the thermal conductivity, so that it is potential for magnetic nanofluid applications.

Measurement of Thermal Conductivity of Low Bulk Density Thermal Insulations

2002 ◽  
Vol 2002 (0) ◽  
pp. 39-40 ◽  
Author(s):  
Takahiro OHMURA ◽  
Mikinori TSUBOI ◽  
Masatake ONODERA ◽  
Toshio TOMIMURA
Keyword(s):  
Thermal Conductivity ◽  
Bulk Density ◽  
Thermal Insulations

scholarly journals The Influence of Fold Structure on Heat Accumulation in Hot Dry Rocks

2020 ◽  
Author(s):  
Wenxiang Leng ◽  
Ming Hu ◽  
Yingchun Wang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Process ◽  
One Dimensional ◽  
Hot Dry Rock ◽  
Fold Structure ◽  
Rock Anisotropy ◽  
Rock Thermal Conductivity ◽  
Rock Strata ◽  
Thermal Conductivity Of Rock

Abstract Hot dry rock resources as one of the most promising clean energy in the future, with large reserves, renewable and other advantages, since the 1970 s, many countries all over the world have explored and practiced a lot on the exploration and development of hot dry rock resources, however, few studied the heterogeneity of the rock and the underground geologic structures of hot dry rock resources influence domain enrichment regularity of heat transfer mechanism. Therefore, this article considered the thermal conductivity of rock anisotropy, and set up a horizontal stratum and a fold strata 2D geological model, through numerical simulation with the field rock samples indoor triaxial rock thermal conductivity test results, introducing the thermal conductivity of rock anisotropy index A = K vertical bedding/ K parallel bedding and analyze the underground geologic structures’ influence on heat transfer in the rock. The results show that the anisotropy of rock thermal conductivity has no influence on the heat transfer process in underground rock strata when the rock layer is horizontal, which can be regarded as one-dimensional multilayer wall heat transfer. Fold structure will influence the underground heat transfer direction, so it is not simply seen as a one-dimensional multilayer flat wall heat transfer process in numerical simulation. At the inclined interface of rock strata, "heat flow refraction" usually occurs, which further affects the direction of heat transfer. As a result, heat is concentrated in the syncline of the fold structure in the deep and anticline in the middle and deep layers, while the temperature distribution in the shallow layer is almost unaffected by the structure. The research results of this paper are of great significance to the delineation of the target area and the development and utilization of the hot dry rock resources.

scholarly journals Nanofluid-Enhancing Shell and Tube Heat Exchanger Effectiveness with Modified Baffle Architecture

2021 ◽  
Author(s):  
I Made Arsana ◽  
Ruri Agung Wahyuono
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Heat Transfer Process ◽  
Working Fluid ◽  
Architectural Geometry ◽  
Tube Heat Exchanger ◽  
Heat Exchanger Design ◽  
Shell And Tube ◽  
Efficient Heat Transfer

As shell and tube heat exchanger is widely employed in various field of industries, heat exchanger design remains a constant optimization challenge to improve its performance. The heat exchanger design includes not only the architectural geometry of either the shell and tube configuration or the additional baffles but also the working fluid. The baffle design including the baffle angle and the baffle distance has been understood as key parameter controlling the overall heat exchanger effectiveness. In addition, a room of improvement is open by substituting the conventional working fluid with the nanomaterials-enriched nanofluid. The nanomaterials, e.g. Al2O3, SiO2, TiO2, increases the thermal conductivity of the working fluids, and hence, the more efficient heat transfer process can be achieved. This chapter provide an insight on the performance improvement of shell and tube heat exchanger by modifying the baffle design and utilizing nanofluids.

scholarly journals Mathematical Model for Analyzing Heat Transfer Characteristics of Ablative Thermal Insulating Material

2020 ◽  
Vol 2020 ◽  
pp. 1-19
Author(s):  
Junjie Gao ◽  
Haitao Han ◽  
Daiying Deng ◽  
Jijun Yu
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mathematical Model ◽  
Size Distribution ◽  
Distribution Area ◽  
Heat Transfer Characteristics ◽  
Equivalent Thermal Conductivity ◽  
Insulating Material ◽  
Transfer Characteristics ◽  
Thermal Insulating

A mathematical model based on minimal thermal resistance and equal law of specific equivalent thermal conductivity is developed to discuss the heat transfer characteristics of ablative thermal insulating material from the mesoscopic scale. Based on the statistical results of mesoscopic parameters, the microstructure unit cell model was established to analyze the influence rule of mesoscopic parameterization which includes the size, distribution, and positional relation of microsphere and fiber. The results show that the equivalent thermal conductivity decreases with the density, size, distribution area, and distance of microsphere and the space distance and volume fraction of fiber decreasing. Besides, the equivalent thermal conductivity will become larger when more quality of heat transfers along the fiber direction. Exploring the relationship between the macroscopic heat transfer process and the microstructure is meaningful for exploring the heat transfer behavior of thermal insulating material and improvement of the processing technology.

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