Impact of Biobased Surfactants on Hygrothermal Behaviour of Gypsum Foams

2022 ◽  
Author(s):  
Nourhan Mortada ◽  
Annabelle Phelipot-Mardele ◽  
Christophe Lanos
Keyword(s):  
Thermal Conductivity ◽  
Mixing Time ◽  
Air Bubbles ◽  
Foaming Agents ◽  
Biobased Surfactant ◽  
Buffer Value ◽  
The Impact ◽  
Direct Foaming Method ◽  
Moisture Buffer Value ◽  
Hygrothermal Behaviour

Reduce the impact of the building sector has become a key point of sustainable development. The production of lightweight materials for the building industry is therefore a must. To produce such materials, foaming is a process commonly used to trap air bubbles and achieve a range of low densities. A sufficient low thermal conductivity and an acceptable ability to regulate humidity variations in order to limit overall energy consumption are the sought properties. In this study, a direct foaming method is applied to formulate gypsum foams using a commercial Plaster and two biobased foaming agents based on proteins. An anionic surfactant (α-olefin sulphonate sodium salt) is used as a reference surfactant. Varying the mixing time, protein content and water content, gypsum foams were produced. The foam volume is measured continuously during the mixing step and the foam homogeneity is controlled. The densities of fresh foams and of the hardened foams are used to identify the links between formulation and foams properties. Gypsum foam specimens with different densities ranging from 300 to 750 kg/m3 are produced. The thermal conductivity and the Moisture Buffer Value measurements are performed. Such properties appear directly linked to the porosity and pore connection of the foams. The obtained results highlight the contribution of biobased surfactant to the performance of gypsum foams.

Analyse of the Evolution of the Hygrothermal Properties of the Hemp-Based Mortar within the Framework of the Total Weathering Protocol

2022 ◽  
Author(s):  
Dmytro Kosiachevskyi ◽  
Kamilia Abahri ◽  
Anne Daubresse ◽  
Evelyne Prat ◽  
Mohend Chaouche
Keyword(s):  
Thermal Conductivity ◽  
Accelerated Aging ◽  
Total Porosity ◽  
Point Of View ◽  
Environmental Benefits ◽  
Microstructural Characteristics ◽  
Building Insulation ◽  
Buffer Value ◽  
Before And After ◽  
Moisture Buffer Value

The use of bio-based composites for building insulation is interesting from the point of view of hygrothermal performances, economic and environmental benefits. Among different organic fibers for these materials, hemp is interesting because of its huge availability in France. Nevertheless, the broad application of the hemp-based insulation mortars is hampered due to the lack of a database on their durability. This paper consists of a better understanding of the evolution of the hemp-based composite and its hygrothermal properties. The main objectives are, first, to study the evolution of the hemp insulation mortar microstructure and properties under the accelerated aging cycles, and second, to characterize and analyze the interconnection between observed changes. Experimentally, the protocol of accelerated aging inspired by standardized one was proposed, the microstructural characteristics and the hygrothermal properties, as the total porosity, the thermal conductivity, and the moisture buffer value (MBV) before and after the aging cycles was identified. The MBV characterization was performed for both hemp mortar and hemp shives. The obtained results reveal the increase of the hemp mortar porosity and the decrease of the hemp mortar's thermal conductivity. Furthermore, the MBV value of hemp mortar changes slightly, unlike that of the bulk hemp, which is explained by the mineral matrix's influence. These results consist of data for a better forecast on the degradation of the hemp mortar.

scholarly journals Numerical simulation of variable thermal conductivity on 3D flow of nanofluid over a stretching sheet

2020 ◽  
Vol 9 (1) ◽  
pp. 233-243 ◽  
Author(s):  
Nainaru Tarakaramu ◽  
P.V. Satya Narayana ◽  
Bhumarapu Venkateswarlu
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Stretching Sheet ◽  
Three Dimensional ◽  
Variable Thermal Conductivity ◽  
Normal Velocity ◽  
Transfer Coefficients ◽  
Similarity Transformations ◽  
Frictional Coefficients ◽  
The Impact

AbstractThe present investigation deals with the steady three-dimensional flow and heat transfer of nanofluids due to stretching sheet in the presence of magnetic field and heat source. Three types of water based nanoparticles namely, copper (Cu), aluminium oxide (Al2O3), and titanium dioxide (TiO2) are considered in this study. The temperature dependent variable thermal conductivity and thermal radiation has been introduced in the energy equation. Using suitable similarity transformations the dimensional non-linear expressions are converted into dimensionless system and are then solved numerically by Runge-Kutta-Fehlberg scheme along with well-known shooting technique. The impact of various flow parameters on axial and transverse velocities, temperature, surface frictional coefficients and rate of heat transfer coefficients are visualized both in qualitative and quantitative manners in the vicinity of stretching sheet. The results reviled that the temperature and velocity of the fluid rise with increasing values of variable thermal conductivity parameter. Also, the temperature and normal velocity of the fluid in case of Cu-water nanoparticles is more than that of Al2O3- water nanofluid. On the other hand, the axial velocity of the fluid in case of Al2O3- water nanofluid is more than that of TiO2nanoparticles. In addition, the current outcomes are matched with the previously published consequences and initiate to be a good contract as a limiting sense.

Characteristics of Flame Bases for V-Gutters Stabilized Premixed Flames

2013 ◽  
Author(s):  
Fan Gong ◽  
Yong Huang
Keyword(s):  
Thermal Conductivity ◽  
Temperature Gradient ◽  
Equivalence Ratio ◽  
Premixed Flames ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Heat Conducting ◽  
Inlet Velocity ◽  
The Impact

The objective of this work is to investigate the flame stabilization mechanism and the impact of the operating conditions on the characteristics of the steady, lean premixed flames. It’s well known that the flame base is very important to the existence of a flame, such as the flame after a V-gutter, which is typically used in ramjet and turbojet or turbofan afterburners and laboratory experiments. We performed two-dimensional simulations of turbulent premixed flames anchored downstream of the heat-conducting V-gutters in a confined passage for kerosene-air combustion. The flame bases are symmetrically located in the shear layers of the recirculation zone immediately after the V-gutter’s trailing edge. The effects of equivalence ratio of inlet mixture, inlet temperature, V-gutter’s thermal conductivity and inlet velocity on the flame base movements are investigated. When the equivalence ratio is raised, the flame base moves upstream slightly and the temperature gradient dT/dx near the flame base increases, so the flame base is strengthened. When the inlet temperature is raised, the flame base moves upstream very slightly, and near the flame base dT/dx increases and dT/dy decreases, so the flame base is strengthened. As the V-gutter’s thermal conductivity increases, the flame base moves downstream, and the temperature gradient dT/dx near the flame base decreases, so the flame base is weakened. When the inlet velocity is raised, the flame base moves upstream, and the convection heat loss with inlet mixture increases, so the flame base is weakened.

scholarly journals Numerical Simulation of Heat Mass Transfer Effects on MHD Flow of Williamson Nanofluid by a Stretching Surface with Thermal Conductivity and Variable Thickness

Coatings ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 684
Author(s):  
Saeed Islam ◽  
Haroon Ur Rasheed ◽  
Kottakkaran Sooppy Nisar ◽  
Nawal A. Alshehri ◽  
Mohammed Zakarya
Keyword(s):  
Thermal Conductivity ◽  
Boundary Layer ◽  
Mass Transfer ◽  
Differential Equations ◽  
Variable Thickness ◽  
Heat Mass Transfer ◽  
Mathematical Formulation ◽  
Stretching Surface ◽  
Nanofluid Flow ◽  
The Impact

The current analysis deals with radiative aspects of magnetohydrodynamic boundary layer flow with heat mass transfer features on electrically conductive Williamson nanofluid by a stretching surface. The impact of variable thickness and thermal conductivity characteristics in view of melting heat flow are examined. The mathematical formulation of Williamson nanofluid flow is based on boundary layer theory pioneered by Prandtl. The boundary layer nanofluid flow idea yields a constitutive flow laws of partial differential equations (PDEs) are made dimensionless and then reduce to ordinary nonlinear differential equations (ODEs) versus transformation technique. A built-in numerical algorithm bvp4c in Mathematica software is employed for nonlinear systems computation. Considerable features of dimensionless parameters are reviewed via graphical description. A comparison with another homotopic approach (HAM) as a limiting case and an excellent agreement perceived.

Minimizing of foaming in digesters by pre-treatment of the surplus-sludge

2000 ◽  
Vol 42 (9) ◽  
pp. 235-241 ◽  
Author(s):  
M. Barjenbruch ◽  
H. Hoffmann ◽  
O. Kopplow ◽  
J. Tränckner
Keyword(s):  
High Pressure ◽  
Activated Sludge ◽  
Treatment Methods ◽  
Foaming Agents ◽  
Instance Reduction ◽  
Filamentous Microorganisms ◽  
Hydrophobic Substances ◽  
Pre Treatment ◽  
Heating Up ◽  
The Impact

Several reasons can lead to the emergence of foam in digesting tanks, for instance overloading or the impact of hydrophobic substances. Furthermore, the foaming is in regular periods going together with the emergence of filamentous microorganisms. Up to now, several strategies to avoid foaming have been tested out (for instance reduction of the sludge load in the activated sludge stage, lowering of the sludge level in the digestion tank, dosage of anti foaming agents), but these have been done relatively unsystematically and with more or less success. For our contribution, laboratory-scale digestion tests were run to analyse mechanical and thermal pre-treatment methods for the destruction of the surplus sludge. Whereas the disintegration by a high pressure homogeniser did only achieve a low reduction of the foam phase, the thermal pre-treatment at 121°C made for an effective subduing of the foam emergence. Both methods allowed for a cutting up of the filaments, but only the heating up effected the reduction of the hydrophobic substances; thus, the foaming is possibly caused by them.

scholarly journals The Impact of Variable Thermal Conductivity of Insulation Materials on the Building Energy Performance in Hot Climate

2019 ◽  
Vol 103 ◽  
pp. 02001 ◽  
Author(s):  
Maatouk Khoukhi ◽  
Ahmed Hassan ◽  
Shaimaa Abdelbaqi
Keyword(s):  
Thermal Conductivity ◽  
Energy Performance ◽  
Variable Thermal Conductivity ◽  
Transfer Model ◽  
Ambient Conditions ◽  
K Value ◽  
Hot Climate ◽  
Building Wall ◽  
Wall Assembly ◽  
The Impact

This paper illustrates the impact of embedding an insulation layer of variable thermal conductivity in a typical building wall on the cooling effect and energy performance. The evaluation was performed by applying a conjugate heat transfer model, which was tested in extremely hot conditions of Al Ain (UAE). The thermal performance of a building incorporating insulation layers of variable thermal conductivity (k-value) was compared to a non-variable thermal conductivity system by quantifying the additional heat transferred due to the k-relationship with time. The results show that, when the k-value is a function of operating temperature, its effects on the temperature profile through the wall assembly during daytime is significant compared with that obtained when a constant k-value for the polystyrene (EPS) insulation is adopted. A similar trend in the evolution of temperatures during the day and across the wall section was observed when EPS material with different moisture content was evaluated. For the polyurethane insulation, the inner surface temperature reached 44 °C when constant k-value was adopted, increasing to 48.5 °C when the k-value was allowed to vary under the same ambient conditions.

Strain Engineering of Thermal Conductivity of Two-Dimensional MoS2 and h-BN

MRS Advances ◽  
2016 ◽  
Vol 1 (32) ◽  
pp. 2297-2302 ◽  
Author(s):  
Xiaonan Wang ◽  
Alireza Tabarraei
Keyword(s):  
Thermal Conductivity ◽  
Tensile Strain ◽  
Phonon Dispersion ◽  
Hexagonal Boron Nitride ◽  
Three Dimensional ◽  
Strain Engineering ◽  
Normal Strain ◽  
Dynamics Modeling ◽  
Molecular Dynamics Modeling ◽  
The Impact

ABSTRACTWe have used reverse nonequlibrium molecular dynamics modeling to study the impact of uniaxial stretching on the thermal conductivity of monolayer molybdenum disulfide (MoS2) and hexagonal boron nitride (h-BN). Our results predict an anomalous response of the thermal conductivity of these materials to normal strain. Thermal conductivity of h-BN increases under a tensile strain whereas thermal conductivity of MoS2 remains fairly constant. These are in striking contrast to the impact of tensile strain on the thermal conductivity of three dimensional materials whose thermal conductivity decreases under tensile strain. We investigate the mechanism responsible for this unexpected behavior by studying the impact of tensile strain on the phonon dispersion curves and group velocities of these materials.

scholarly journals The Thermal Properties of Sea Ice

1963 ◽  
Vol 4 (36) ◽  
pp. 789-807 ◽  
Author(s):  
Peter Schwerdtfecer
Keyword(s):  
Thermal Conductivity ◽  
Sea Ice ◽  
Physical Properties ◽  
Specific Heat ◽  
Energy Content ◽  
Air Bubbles ◽  
Solid Mixture ◽  
Latent Heats ◽  
Complex Substance ◽  
Ice Model

Abstract Compared with freshwater ice, whose physical properties are well known, sea ice is a relatively complex substance whose transition to a completely solid mixture of pure ice and solid salts is completed only at extremely low temperatures rarely encountered in nature. The physical properties of sea ice are thus strongly dependent on salinity, temperature and time. Many of these properties are still not fully understood or accurately known, particularly those important for the understanding of a natural ice cover. The specific heat for example is an important term in the calculation of the heat energy content of a cover. However, Malmgren (1927), whose calculated values of the specific heat of sea ice are in general use, neglected the direct contribution of the brine present in inclusions. Re-examination of the question of specific and latent heats of sea ice has led to distinguishing between the freezing and melting points and enabled significant observations in this range. Similarly, because the thermal conductivity is a necessary parameter in the description of the thermal behaviour of ice. the sea-ice model suggested by Anderson (1958) has been modified and extended in the present work to the case of saline ice containing air bubbles. This enabled the completion of calculations of density and conductivity. In order to illustrate the theoretically calculated values. measurements were made on sea-ice samples to determine the specific heat, density and thermal conductivity.

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