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.

scholarly journals Yearly Energy Performance Assessment of Employing Expanded Polystyrene with Variable Temperature and Moisture–Thermal Conductivity Relationship

Materials ◽  
2019 ◽  
Vol 12 (18) ◽  
pp. 3000 ◽  
Author(s):  
Maatouk Khoukhi ◽  
Shaimaa Abdelbaqi ◽  
Ahmed Hassan
Keyword(s):  
Thermal Conductivity ◽  
Moisture Content ◽  
Energy Performance ◽  
Variable Thermal Conductivity ◽  
Expanded Polystyrene ◽  
High Density ◽  
Insulation Material ◽  
Yearly Average ◽  
The Impact ◽  
Demand And Capacity

This paper investigated the impact of the changes of thermal conductivity of an expanded polystyrene insulation layer embedded in a typical residential building on the cooling effect at different temperatures and moisture contents. The simulation was performed using expanded polystyrene (EPS) in the extremely hot conditions of Al-Ain (United Arab Emirates, UAE) at different levels of density, denoted as low density LD (12 kg/m3), high density HD (20 kg/m3), ultra-high density UHD (30 kg/m3), and super-high density SHD (35 kg/m3), and three moisture content levels (10%, 20%, and 30%), compared to dry LD insulation material. The thermal performance of the building incorporating polystyrene with variable thermal conductivity (λ-value) was compared to one with a constant thermal conductivity by assessing the additional cooling demand and capacity due to the λ-relationship with time, using e-quest as a building energy analysis tool. The results showed that, when the λ-value was modeled as a function of operating temperature, its effect on the temperature profile during daytime was significant compared with the use of a constant λ-value. The monthly energy consumption for cooling required by the building was found to be higher in the case of variable thermal conductivity for the LD sample. The yearly average change in space cooling demand and cooling capacity when employing polystyrenes with constant and variable thermal conductivity increased with the increase of the moisture content. Indeed, the highest changes in cooling demand and capacity were 6.5% and 8.8% with 30% moisture content polystyrene.

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.

Research on Heat Transfer Characteristics of Nano-Porous Silica Aerogel Material and its Application on Mars Surface Mission

2014 ◽  
Vol 924 ◽  
pp. 329-335 ◽  
Author(s):  
Cong Hang Li ◽  
Shi Chen Jiang ◽  
Zheng Ping Yao ◽  
Song Sheng ◽  
Xin Jian Jiang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Silica Aerogel ◽  
Thermal Environment ◽  
Porous Silica ◽  
Heat Transfer Model ◽  
Heat Radiation ◽  
Transfer Model ◽  
Ambient Conditions ◽  
Coupled Heat Transfer

Based on the nanoporous network structure features of silica aerogel, the gas-solid coupled heat transfer model of silica aerogel is analyzed, and the calculation formulas of the gas-solid coupled, the gas thermal conductivity and the heat radiation within the aerogel are derived. The thermal conductivity of pure silica aerogel is calculated according to the derived heat transfer model and is also experimentally measured. Moreover, measurements on the thermal conductivities of silica aerogel composites with different densities at ambient conditions are performed. And finally, a novel design of silica aerogel based integrated structure and thermal insulation used for withstanding the harsh thermal environment on the Martin surface is presented.

Effect of Operating Temperatures on Thermal Conductivity of Polystyrene Insulation Material: Impact on Envelope-Induced Cooling Load

2014 ◽  
Vol 564 ◽  
pp. 315-320 ◽  
Author(s):  
Maatouk Khoukhi ◽  
Mahmoud Tahat
Keyword(s):  
Thermal Conductivity ◽  
Thermal Insulation ◽  
Energy Performance ◽  
Building Envelope ◽  
Insulation Material ◽  
Cooling Load ◽  
Thermal Insulation Material ◽  
Insulation Materials ◽  
Energy Performance Of Buildings ◽  
The Impact

The impact of the thermal conductivity (k-value) change of polystyrene insulation material in building envelope due to changes in temperature on the thermal and energy performance of a typical residential building under hot climate is investigated. Indeed, the thermal and energy performance of buildings depends on the thermal characteristics of the building envelope, and particularly on the thermal resistance of the insulation material used. The thermal insulation material which is determined by its thermal conductivity, which describes the ability of heat to flow cross the material in presence of a gradient of temperature, is the main key to assess the performance of the thermal insulation material. When performing the energy analysis or calculating the cooling load for buildings, we use published values of thermal conductivity of insulation materials, which are normally evaluated at 24°C according to the ASTM standards. In reality, thermal insulation in building is exposed to significant and continuous temperature variations, due essentially to the change of outdoor air temperature and solar radiation. Many types of insulation materials are produced and used in Oman, but not enough information is available to evaluate their performance under the prevailing climatic condition. The main objective of this study is to investigate the relationship between the temperature and thermal conductivity of various densities of polystyrene, which is widely used as building insulation material in Oman. Moreover, the impact of thermal conductivity variation with temperature on the envelope-induced cooling load for a simple building model is discussed. This work will serve as a platform to investigate the effect of the operating temperature on thermal conductivity of other building material insulations, and leads to more accurate assessment of the thermal and energy performance of buildings in Oman.

Influence of Initial Stress and Variable Thermal Conductivity on a Fiber-Reinforced Magneto-Thermoelastic Solid with Micro-Temperatures by Multi-Phase-Lags Model

2021 ◽  
pp. 2250007
Author(s):  
Amnah M. Alharbi ◽  
Samia M. Said ◽  
Elsayed M. Abd-Elaziz ◽  
Mohamed I. A. Othman
Keyword(s):  
Magnetic Field ◽  
Thermal Conductivity ◽  
Initial Stress ◽  
Thermodynamic Temperature ◽  
Variable Thermal Conductivity ◽  
Fiber Reinforced ◽  
Phase Lags ◽  
Multi Phase ◽  
The Impact ◽  
Physical Quantities

This paper presents the theory of multi-phase-lags thermoelasticity that was used to study the wave propagation on a fiber-reinforced thermoelastic medium with micro-temperatures. The medium was considered to be homogeneous, isotropic and thermal conductivity as a linear function of thermodynamic temperature. The Fourier transform and Laplace transform are employed to solve the governing equations and obtained the solution of the physical quantities. The graphical illustrations of the impact that initial stress, variable thermal conductivity, magnetic field, and the phase-lags have on the field functions are presented. The variable thermal conductivity, initial stress, and magnetic field have a good impact in all the physical quantities.

Analytical simulation of time dependent electromagneto-hydrodynamic flow of Williamson fluid due to oscillatory curved convectively heated Riga surface with variable thermal conductivity and diffusivity

2021 ◽  
pp. 095440892110623
Author(s):  
M. Naveed ◽  
Z. Abbas ◽  
M. Imran
Keyword(s):  
Thermal Conductivity ◽  
Boundary Layer ◽  
Heat Production ◽  
Magnetic Parameter ◽  
Variable Thermal Conductivity ◽  
Time Dependent ◽  
Williamson Fluid ◽  
Analytical Simulation ◽  
Fluid Parameter ◽  
The Impact

The main objective of the present article is to provide an analytical simulation for time dependent boundary layer flow of non-Newtonian Williamson fluid due to stretchable curved oscillatory Riga surface. Also the characteristics of heat and mass transport are studied under the influence of variable thermal conductivity and diffusivity along with convective heat and mass boundary conditions. Additionally, energy equation is also characterized with the impact of heat production. Curvilinear coordinate scheme is followed to attain the boundary layer expressions for the flow model. The governing nonlinear partial differential equations are solved analytically via homotopy analysis method (HAM). Graphs are plotted to examine comprehensively the consequences of various concerned parameters like modified magnetic parameter and radius of curvature, Williamson fluid parameter, relation of the surface's oscillating frequency to its stretching rate constant, Prandtl number, variable conductivity and heat production parameters, Schmidt number and variable diffusivity parameter on concentration, temperature, pressure and velocity profile. Also the outcomes of afore said variables on surface drag force, rate of temperature and mass transmission (Nusselt and Sherwood numbers) are shown in tabular form. The liquid velocity amplitude is enhanced with modified magnetic parameter and shows opposite behavior for Williamson fluid parameter.

Investigation of Potential Benefits of Using Bricks of High Thermal Capacity and Conductivity in a Rotating Calcining Kiln

2008 ◽  
Author(s):  
Lei Zhao ◽  
Ting Wang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Potential Energy ◽  
Thermal Energy ◽  
Energy Savings ◽  
Thermal Capacity ◽  
K Value ◽  
Hot Gas ◽  
The Impact

Petroleum coke is processed into calcined coke in a rotary kiln, where the temperature profiles of flue gas and coke bed are highly nonuniform due to different flow and combustion mechanisms. Motivated by saving energy costs, the effect of refractory brick’s thermal properties on potential energy savings is investigated. This study focuses on investigating potential energy savings by replacing inner one third of existing bricks with higher thermal capacity (Cp) and/or higher thermal conductivity (k) bricks. This investigation is motivated by postulating that the bricks with higher thermal capacity can store more thermal energy during the period of contacting with the hot gas and release more heat to the cock bed when the bricks rotate to below and in contact with the coke bed. A rotational, transient marching conduction numerical simulation is conducted using the commercial software FLUENT. The impact of brick heat capacity and thermal conductivity on transporting thermal energy to the coke bed is analyzed. The results show: (a) Increasing the heat capacity of brick layer reduces brick temperature which helps increase the heat transfer between the hot gas and brick, in other words it does help brick store more heat from the hot gas, but, heat transfer between brick and coke is reduced, which is opposite to the original postulation. (b) Higher brick thermal conductivity decreases brick temperature thus increases heat transfer between hot gas and the brick layer. The heat transfer from brick to coke bed is also increased, but not significantly. (c) Usually a brick with a higher Cp value also has a higher k-value. Simulation of a brick layer with both four times higher Cp and k values actually show appreciable heat is transported from the brick to the coke bed for one rotation for both lower and higher Cp and k bricks. The difference is not significant.

Radiation and Thermal Decomposition Analysis in a Reactive Slab of Variable Thermal Conductivity.

2018 ◽  
Vol 7 (3.19) ◽  
pp. 27
Author(s):  
RS Lebelo ◽  
KS Moloi ◽  
CC Chitumwa ◽  
SO Adesanya
Keyword(s):  
Thermal Conductivity ◽  
Heat Loss ◽  
Chemical Reaction ◽  
Co2 Emission ◽  
Combustion Process ◽  
Decomposition Analysis ◽  
Variable Thermal Conductivity ◽  
Radiative Heat Loss ◽  
Exothermic Chemical Reaction ◽  
The Impact

In this article, the impact of radiative heat loss in a stockpile of combustible material is investigated. The heat loss is attributed to the exothermic chemical reaction when the carbon containing material of the stockpile reacts automatically with the oxygen trapped within the stockpile. The study is modelled in a rectangular slab of thermal conductivity that varies with the temperature and loses heat to the surrounding environment by radiation. The differential equations governing the problem are solved numerically using the Runge-Kutta-Fehlberg (RKF) method coupled with the Shooting technique. The effect of each embedded kinetic parameter on the temperature, oxygen (O2) depletion and carbon dioxide (CO2) emission, is analyzed and the results are graphically expressed and discussed accordingly. The results show that the kinetic parameters which enhance the exothermic chemical reaction correspondingly increase the temperature and the CO2 emission during the combustion process, and in turn, these parameters also increase the depletion of O2.  

scholarly journals Impact of Temperature-Dependent Heat Source/Sink and Variable Species Diffusivity on Radiative Reiner–Philippoff Fluid

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
T. Sajid ◽  
M. Sagheer ◽  
S. Hussain
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mass Transfer ◽  
Heat Source ◽  
Transfer Rate ◽  
Variable Thermal Conductivity ◽  
Physical Parameters ◽  
Molecular Diffusivity ◽  
Source Sink ◽  
The Impact

The principle aim of the current communication is to scrutinize the impact of distinguished effects like variable thermal conductivity and variable molecular diffusivity on non-Newtonian Reiner–Philippoff fluid moving over a stretchable surface. The process of heat transfer is carried out in the presence of nonlinear thermal radiation, variable thermal conductivity, and heat generation/absorption. Furthermore, the study of mass transfer phenomena is carried out in the existence of variable molecular diffusivity. The PDEs regarding our model are renovated into ODEs by utilizing similarity transformation. Furthermore, the dimensionless model is tackled with the help of the RK4 method in conjunction with the shooting technique. The effects of different physical parameters that emerged during the numerical simulation on mass transfer rate, heat transfer rate, and velocity field are portrayed in the form of tables and graphs. It is noteworthy that an elevation in the heat source/sink parameters causes a reduction in the temperature profile. Moreover, a positive variation in the species diffusivity parameter augments the mass fraction field. A variation in the fluid parameter is found to be significantly affecting the shear thinning and shear thickening behaviour of the fluid. Reliability of the numerical outcomes is judged by comparing the obtained outcomes with the already available literature. The article is unique in its sense that the heat and mass transfer analysis of Reiner–Philippoff fluid under the aforementioned effects has not been investigated yet.

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