Linear Thermal Coefficient Research Articles

Optimization of Thermal Insulation Parameters for Vertical Perimeters in Buildings with Single-Layer Walls

This article presents the results of a study on the impact of selected parameters of a building’s ground-floor zone (the junction of the external and foundation walls, the ground floor slab, and the ground itself) on the temperature field within the external envelope. This study aims to analyze the influence and optimize the parameters of vertical perimeter insulation in the ground-floor zone of the building. Mathematical modeling was selected as the research method. This paper analyzes the relationships between the temperature ϑimg on the inner surface of the wall at the analyzed node and the linear thermal transmittance coefficient ψim of the thermal bridge occurring in this location, as influenced by the following parameters: dp—thickness of the insulation layer in the ground floor slab; df—thickness of the vertical perimeter insulation layer in the foundation wall; t—location of the insulation layer in the ground floor slab relative to the “external wall-foundation wall” contact surface; r—location of the vertical perimeter insulation layer in the foundation wall; and λs—thermal conductivity of the single-layer external wall material. The analysis was conducted under the climatic conditions of Białystok, Poland. Using THERM 7.6 software for computational experiments, data were obtained to develop deterministic mathematical models of these relationships. The models enabled the assessment of the degree and nature of the influence of the studied factors on ϑimg and ψim, optimization of selected parameters, and mathematical description of safe operating conditions for external walls in the ground-floor zone of heated buildings. It was found that the parameters dp, df, and r have favorable effects, increasing ϑimg by 2.57%, 2.51%, and 4.17%, respectively, when varying from their minimum to maximum levels. Conversely, the parameters t and λs negatively impact ϑimg, contributing reductions of −12.01% and −4.66%, respectively, with a cumulative effect of −16.67%. Optimal parameter values were determined based on energy efficiency criteria. This information may be useful for researchers, designers, engineers, and decision-makers when making informed decisions during the design phase of heated buildings.

Methods for improving the thermal performance of thermal bridges of lightweight steel-framed buildings.

The existence of a large number of thermal bridges in the Lightweight Steel-Framed (LSF) building leads to its energy loss. The reduction of the heat transfer of thermal bridges is crucial for increasing the thermal performance of the building envelope. In this study, the infrared technology was first used to measure the temperature of LSF buildings, and clear thermal bridge junctions were determined. The THERM software was then used to simulate the thermal bridge of the external wall-beam junction, external and internal corners of the external wall, and cornice. Finally, according to the results obtained by numerical simulation, the thermal bridge was improved for reducing its thermal loss and meeting the design standard of thermal bridge free. The results of the simulation showed that, when the thickness of the rock wool (RW) of the external wall is greater than 75 mm, the linear thermal bridge coefficient (Ψ-value) at the junction of the external wall-beam is less than 0.01 W/(m·K), which meets the design standard of thermal bridge free. When polyurethane (PU) is used instead of RW for the external wall, its external corner meets the design standard of thermal bridge free in the case where the thickness of the PU is greater than 65 mm. The internal corner of the external wall can meet the design standard of thermal bridge free when PU is used instead of RW. The thermal bridge of cornice can meet this standard by adding a PU thermal insulation layer at the indoor sides, having a thickness greater than 20 mm. Studying the thermal bridge of LSF buildings allows to promote the development of the green building technology in China.

Thermal performances of a bioclimatic building in hot and dry tropical climate

This paper is concerned with the thermal comfort of a double-walls seven stories bioclimatic building built with local construction materials. First of all, we use a numerical code to investigate the construction materials thermal inertia effects on the optimization of the building envelop. Second, the outer and inner surface temperatures are determined utilizing the TRNSYS code. A system of trap is then design to evacuate during nighttimes, the stored daily heat. The conditioned air thermal load differences between the double and simple walls are also investigated. Similarly, the linear thermal loss coefficients and the thermal bridge losses are computed utilizing respectively the ‘Heat’ software and the Degree Day method. The results show a difference of 6 to 7 oC between the outer and the inner maxima surface temperatures. The computation of the conditioned air thermal load indicates a net energy gain of the order of 5.8 % in the office spaces and 12.1% in the bedrooms, respectively for the double and simple walls. The double-walls thermal bridge losses amount to 16.46 % of the total building losses and 20.77 % for the 20 cm thick simple wall. The building envelop optimisation process continues with the study of the effects of the addition of a garden roof on the thermal comfort.

Temperature‐dependent electrical conductivity impact on radiative and dissipative peristaltic transport of boron nitride‐ethylene glycol nanofluid through asymmetric channels

AbstractMathematical simulation of biological fluids is of upmost significance due to its numerous medical uses. Interpreting various biological flows necessitates a thorough knowledge of the peristaltic mechanism. This paper presents a computational study for the peristaltic pumping within vertical asymmetric channels filled with BN‐EG nanofluid under the influence of temperature‐dependent electrical conductivity and thermal radiation. Experimental study showed that the nanofluid created by suspending Boron Nitride particles in a combination of Ethylene Glycol exhibited non‐Newtonian characteristics. Further, the Carreau's fluid model provides accurate predictions about the rheological properties of BN‐EG nanofluid. Various configurations of the outer boundaries are considered, namely, square wave, multi‐sinusoidal wave, trapezoidal wave, and triangular wave. A uniform magnetic field together with nanoparticles and mass concentrations, joule heating, first‐order chemical reaction as well as viscous dissipation are considered. Influences of the Dufour and Soret numbers are examined, and the cases of biological scientific assumptions which is known as low Reynolds number and long wavelength are applied. All the computations are obtained numerically using Mathematica symbolical software (ND‐Solve), and the obtained results are presented in terms of the axial velocity u, heat transfer rate Z, concentration profile Ω, temperature profile θ, extra stress tensor , pressure gradient , pressure rise and stream function ψ. The major outcomes revealed that the maximizing in electrical conductivity coefficient, variable viscosity coefficient and magnetic field parameter is better to obtain a higher rate of the heat transfer while the increase in thermo‐diffusion effects as well as linear thermal radiation coefficient causes a reduction in the rate of heat transfer.

Polymer/Graphene Nanocomposites via 3D and 4D Printing—Design and Technical Potential

Graphene is an important nanocarbon nanofiller for polymeric matrices. The polymer–graphene nanocomposites, obtained through facile fabrication methods, possess significant electrical–thermal–mechanical and physical properties for technical purposes. To overcome challenges of polymer–graphene nanocomposite processing and high performance, advanced fabrication strategies have been applied to design the next-generation materials–devices. This revolutionary review basically offers a fundamental sketch of graphene, polymer–graphene nanocomposite and three-dimensional (3D) and four-dimensional (4D) printing techniques. The main focus of the article is to portray the impact of 3D and 4D printing techniques in the field of polymer–graphene nanocomposites. Polymeric matrices, such as polyamide, polycaprolactone, polyethylene, poly(lactic acid), etc. with graphene, have been processed using 3D or 4D printing technologies. The 3D and 4D printing employ various cutting-edge processes and offer engineering opportunities to meet the manufacturing demands of the nanomaterials. The 3D printing methods used for graphene nanocomposites include direct ink writing, selective laser sintering, stereolithography, fused deposition modeling and other approaches. Thermally stable poly(lactic acid)–graphene oxide nanocomposites have been processed using a direct ink printing technique. The 3D-printed poly(methyl methacrylate)–graphene have been printed using stereolithography and additive manufacturing techniques. The printed poly(methyl methacrylate)–graphene nanocomposites revealed enhanced morphological, mechanical and biological properties. The polyethylene–graphene nanocomposites processed by fused diffusion modeling have superior thermal conductivity, strength, modulus and radiation- shielding features. The poly(lactic acid)–graphene nanocomposites have been processed using a number of 3D printing approaches, including fused deposition modeling, stereolithography, etc., resulting in unique honeycomb morphology, high surface temperature, surface resistivity, glass transition temperature and linear thermal coefficient. The 4D printing has been applied on acrylonitrile-butadiene-styrene, poly(lactic acid) and thermosetting matrices with graphene nanofiller. Stereolithography-based 4D-printed polymer–graphene nanomaterials have revealed complex shape-changing nanostructures having high resolution. These materials have high temperature stability and high performance for technical applications. Consequently, the 3D- or 4D-printed polymer–graphene nanocomposites revealed technical applications in high temperature relevance, photovoltaics, sensing, energy storage and other technical fields. In short, this paper has reviewed the background of 3D and 4D printing, graphene-based nanocomposite fabrication using 3D–4D printing, development in printing technologies and applications of 3D–4D printing.

Preparation and characterization of diphenyl silicone rubber/microfiber glass wool composite thermal control films.

Innovative research on the development of thermal control films for spacecraft surfaces is presented. A hydroxy-terminated random copolymer of dimethylsiloxane-diphenylsiloxane (PPDMS) was prepared from hydroxy silicone oil and diphenylsilylene glycol by a condensation reaction, and then liquid diphenyl silicone rubber base material (denoted as PSR) was obtained by adding hydrophobic silica. Microfiber glass wool (MGW) with a fiber diameter of ∼3 μm was added to the liquid PSR base material, which upon solidifying at room temperature, formed a 100 μm thick PSR/MGW composite film. The infrared radiation properties, solar absorption, thermal conductivity, and thermal dimensional stability of the film were evaluated. Moreover, the dispersion of the MGW in the rubber matrix was confirmed by optical microscopy and field-emission scanning electron microscopy. The PSR/MGW films exhibited a glass transition temperature of -106 °C, thermal decomposition temperature exceeding 410 °C, and low α/ε values. The homogeneous distribution of MGW in the PSR thin film resulted in a notable reduction in its linear expansion coefficient, as well as its thermal diffusion coefficient. Consequently, it exhibited a significant capacity for thermal insulation and retention. For the sample with 5 wt% of MGW, the linear expansion coefficient and thermal diffusion coefficient at 200 °C were reduced to 0.53% and 2.703 mm s-2, respectively. Thus, the PSR/MGW composite film has good heat-resistance stability and low-temperature endurance, along with low α/ε values and excellent dimensional stability. Additionally, it facilitates effective thermal insulation and temperature control, and can be an ideal material for thermal control coatings on spacecraft surfaces.

Analytical solution for temperature equation of a fin problem with variable temperature-dependent thermal properties: Application of LSM and DTM-Pade approximant

Temperature variation through a longitudinal fin with linear and nonlinear temperature-dependent thermal conductivities and heat transfer coefficient, subject to radiative heat flux and convective heat transport is explained in the present examination. For the radiative heat flux, the Rosseland approximation is incorporated and convection mode of energy transmission is accounted on the fin's surface. The associated physical problem is developed in such a manner that the steady-state heat transmission problem is governed with the help of dimensionless variables signified by a second order differential equation (ODE). To solve this equation, an analytical approach, DTM-Pade, and the LSM are implemented. Moreover, the consequence of a few non-dimensional factors on the temperature field are depicted graphically. The investigation's main findings illustrate that a significant decline in the thermal field is caused by an increment in the convection and the radiation mechanism. The internal development of heat affects the thermal distribution in the fin.

Development of eco-ceramic wall tiles with bio-CaCO3 from eggshells waste

Waste valorization is of utmost importance due to the scarcity of natural raw materials. In Europe, up to 150 kton/y of eggshells waste are generated and, usually, landfilling is the only option. This work aims to develop eco-ceramic wall tiles using bio-calcium carbonate from eggshells waste as a raw material. Several pastes were prepared by replacing limestone, the natural raw material used nowadays, with eggshell waste (0, 25, 50, 75 and 100 wt%). Through specimens’ characterization, the total substitution by bio-calcium carbonate with the same granulometry leads to an increase, of 19%, in the flexural strength, without affecting the other properties (linear thermal coefficient, weight loss, firing shrinkage, water absorption, density, colour coordinates), and all values are within industrial limits. Therefore, this work proved that limestone can be totally substituted by eggshell waste. The developed eco-ceramic wall tiles consume less natural raw materials and promote a decrease in the landfilled wastes quantity.

Thermo-optical properties of terbium sesquioxide (Tb2O3) ceramics at room temperature.

Thermo-optical properties of several (Tb1-xYx)2O3 ceramic samples were investigated in this Letter. The linear absorption and thermal conductivity coefficients, as well as the power dependence of thermally induced phase and polarization distortions of laser radiation, were measured. In addition, the effective thermo-optical constants Peff and Qeff were estimated. Thermo-optical properties of the studied ceramics were compared with those of the widely used terbium gallium garnet. It was shown that the material under consideration is highly promising for Faraday isolators operating at high average power laser radiation.

Design, Modeling and Fabrication of TPoS MEMS Resonators With Improved Performance at 1 GHz

In this work, the effects of physical dimensions such as length, width and thickness as well as the mode of vibration and the number of anchors on the performance of longitudinal thin film piezoelectric on silicon (TPoS) MEMS resonators have been studied. TPoS resonators, designed for a resonant frequency of around 1 GHz, were fabricated with a 4 mask CMOS compatible process. A 225 μm wide resonator excited in its 23 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> order had an unloaded quality factor of 9453 (in vacuum), which is the highest value reported so far for similar resonators, motional resistance of 107 Ω and linear thermal coefficient of frequency of -28.4 ppm. We have also studied and modeled the different loss mechanisms in these devices. The model matches well with measured results for resonators of different geometries, modes of vibrations and number of anchors. [2020-0397]

Analytical Mathematical Modeling of the Thermal Bridge between Reinforced Concrete Wall and Inter-Floor Slab

The evaluation of thermal bridges in buildings, following the UNI TS 11300-1:2014 standard, must be carried out with finite element analysis or through the use of atlases compliant with the UNI EN ISO 14683:2018. The paper illustrates the development of an analytical tool to determine the internal linear thermal transmission coefficient (ψi) for the thermal bridge between concrete wall and inter-floor slab, neglected in the main existing catalogs or atlases. This type of thermal bridge is relevant in multi-story buildings, and is typical of public housing districts built between the 1960s and 1970s throughout Europe by means of industrialized systems. Considering energy requalification, due to their low energy efficiency, these buildings require adaptation to the standards imposed by law, and this thermal bridge, which has a high percentage incidence on the total heat losses, cannot be overlooked. From the survey of a representative number of such buildings in Italy, three different technological solutions were examined, with dimensional variations in the individual technical elements and the related functional layers. The combination of these variables resulted in 216 different case studies. The analysis of the existing atlases and catalogues has demonstrated their inapplicability for the selected case studies. For each one of these, ψi was calculated, using off-the-shelf software. The correlation of the data made it possible to determine an analytical mathematical modeling process to assess heat losses due to the analyzed thermal bridge. The validity of this mathematical formula was verified by recalculating the typologies investigated, reaching an error evaluated by means of the mean square deviation equal to ±4%.

Transient Response of Longitudinal Fins under Step Changes in Base Temperature and Heat Flux using Lattice Boltzmann Method

The present article reports the transient response of longitudinal fins having linear and non-linear temperature dependent thermal conductivity, convection coefficient and internal heat generation under two cases of base boundary condition, (i) step change in base temperature and (ii) step change in base heat flux. The fin tip is assumed to be adiabatic. Both, linear and non-linear, temperature dependency of thermo-physical properties is addressed in the mathematical formulation and the solution for the above cases is obtained using Lattice Boltzmann method (LBM) implemented in an in-house source code. LBM, being a dynamic method, simulates the macroscopic behavior by using a simple mesoscopic model and offers enormous advantages in terms of simple algorithm to handle even the most typical of boundary conditions that are easy and compact to program even in case of complicated geometries too. Although the transient response of longitudinal fins has been reported earlier, however power law variation of thermo physical properties for the above two base condition has not been reported till date. The present article first establishes the validity of LBM code with existing result and then extends the code for solving the transient response of the longitudinal fin under different sets of application-wise relevant conditions that have not been treated before. Results are reported for several combination of thermal parameter and are depicted in form of graphs.

Disintegration mechanism of second phase particles under electron beams

The paper suggests a disintegration mechanism of silicon particles in aluminum in the heat-impact zone of a low-energy high-current electron beam. This inclusion was modeled with a round plate (radius R and thickness h). Disintegration of silicon inclusion was assumed to be possible due to discrepancy of elasticity modulus and linear expansion thermal coefficient caused by the evolving dynamic instability. In conditions of high-speed cooling a silicon plate is subjected to compression stresses, since linear expansion coefficient of aluminum is above that of silicon. If these forces applied, instability and fracture of a plate are registered. Using methods of elasticity theory it was found out that the value of these stresses is around 1 GPa. The initial stage of this instability was analyzed by methods of Theory of Plates and Shells. In terms of this theory, a critical stress (∼107–109 Pa) was determined close to the clamped ends of a plate and hinged plates. So, it was concluded, that a suggested mechanism of silicon particles disintegration in the heat-impact zone of an electron beam seems to be the most probable one. Relay-Taylor instability on the inclusion and matrix border is thought to be another mechanism of particles disintegration. According to the linear analysis of this instability, a wavelength with the maximal growth speed of disturbances is ∼4 μm, for inclusions ∼1 μm these findings exceed significantly the experimental data.

Evaluation of the thermal performance of composite insulated panels with metallic skin through steady-state numerical analysis – Part 2

Although the constructive detail type approach analysis already offers an extensive image about the influence of thermal bridges that occurs in the composite insulated panels with metallic skin, studies of the subject go further, by integrating the detail obtained results into parts of the building analyses, with the purpose to identify how factors such as occurrence frequency of the thermal bridge, or the percent of the glazed surfaces existent in regular facades influence the thermal behaviour of the building part, along with the numerical value of the linear thermal transfer coefficients obtained in Part 1 of the paper. Also, for the identified constructive detail with the lowest thermal performance, framework solutions were identified and analysed through steady-state FEM analysis in order to offer a working tool for building energy auditors.

Evaluation of the thermal performance of composite insulated panels with metallic skin through steady-state numerical analysis – Part 1

The energy performance of the buildings is a wide spreaded area on which many research is done nowadays. However, because of the relative new large scale interest on it, there still are subjects that have limited research data available. One of this topics is the thermal performance of composite insulated panels with metallic skin, usually a closure solution for industrial halls, production buildings, commercial buildings or even office buildings. Because of the mandatory request of the Energy Performance Certificates (EPCs) in the European countries and in Romania as well, is highlighted that is a lack of informations regarding the thermal behaviour of this type of technical solution and also, synthetic working data for building energy auditors, as linear thermal transmission coefficients values (Ψ-values) for the usually constructive details that compose a regular industrial hall is missing. Therefore, this paper aims to provide an insight about the thermal behaviour of this type of solution, by offering results of Ψ -values for four different dimensions of sandwich panels, which represents appropriate data for a thermal bridges catalogue that may be used directly by the building energy auditors.

Analysis of the Occurrence of Thermal Bridges in Several Variants of Connections of the Wall and the Ground Floor in Construction Technology with the Use of a Hemp-lime Composite.

This article analyses the connection of the two types of floors on the ground (floors on joists and self-supporting floors), with the external wall made of a hemp–lime composite for the occurrence of thermal bridges. Several factors that may affect the heat transfer in the junction were taken into account: the level of the floor on the ground, the wall thickness, the thermal conductivity of the composite, and the location of the timber frame construction. The technology of using hemp and lime is relatively new, and there is a lack of such analyses in the literature. The two-dimensional (2D) heat-transfer in the described construction joints was analyzed based on the finite-element method with the use of the THERM 7.4 software. The results were presented as averaged and linear thermal transmittance coefficients dependent on the above mentioned factors. The possibility of surface condensation was also checked. The differences in the values of the thermal transmittance of the junction between the two variants of ground floors reached around 0.13%–1.67% and the values of linear thermal transmittance factor reached approximately 2.43%–10.13%. The junctions with the highest floor level showed a decrease in the thermal transmittance value by about 3.00%–5.77% and in the linear thermal transmittance, by about 21.98%–53.83%, compared to the junctions with the lowest floor level. Calculations showed that almost all analyzed junctions are free from surface condensation causing mould growth, because the minimum temperature factors f0.25 were higher than 0.78 (except for junctions with the lowered floor levels). The junction with a floor on the timber joists showed better thermal parameters than the junction with a self-supporting floor in each of the analyzed variants. By increasing the level of floor insulation, it is possible to limit the thermal bridges and improve the thermal properties of the junction.

The The Occurrence of Thermal Bridges in Hemp-Lime Construction Junctions

Thermal bridges increase heat losses in buildings and reduce the temperature of the internal envelope surface, causing moisture condensation and mould growth. This is an important issue for building materials based on organic components such as a hemp-lime composite, as they are particularly susceptible to biological degradation.The hemp-lime composite is used as a filling in timber frame construction. The increased cross-section of wooden elements together with the geometry change in the construction joints can form thermal bridges. The paper presents numerical analyses of temperature distribution in the area of construction elements connections, taking into account several variants of junctions: external walls, corners, and window placement in a wall. The thermal parameters of hemp-lime composites used in the analyses were obtained from the authors’ own research.Despite relatively good insulating properties, timber elements have a noticeable influence on the local increase of the heat transfer in hemp-lime composite structures, forming thermal bridges in the partitions themselves and in the construction nodes. However, the linear thermal transmittance coefficients in the presented joints were not very significant (in the range of 0.026 ÷ 0.092 W/(m·K) depending on the type of connection), proving the usefulness of this type of construction in energy-efficient buildings.

Mapping and Characterizing Thermal Dilation of Civil Infrastructures with Multi-Temporal X-Band Synthetic Aperture Radar Interferometry

Temperature variation plays a significant role in the long-term structural behaviour of civil infrastructures, but very few quantitative studies have measured and analysed the infrastructures’ global thermal dilation because of their large sizes and geometric complexities. The modern Differential Synthetic Aperture Radar Interferometry (DInSAR) technique has great potential in applications of their thermal dilation mapping and characterization due to the techniques’ unique capabilities for use in large areas, with high-resolution, and at low-costs for deformation measurements. However, the practical application of DInSAR in thermal dilation estimation is limited by difficulty in the precise separation from the residual topographic phase and the trend deformation phase. Moreover, due to a lack of thermal dilation characteristics analyses in previous studies, the thermal dilation mechanisms are still unclear to users, which restricts the accurate understanding of the thermal dilation evolution process. Given the above challenges, an advanced multi-temporal DInSAR approach is proposed in this study, and the effectiveness of this approach was presented using three cases studies concerning different infrastructure types. In this method, the coherent, incoherent, and semantic information of structures were combined in order to refine the detection of point-like targets (PTs). Interferometric subsets with small temporal baselines and temperature differences were used for high-resolution topography estimation. A pre-analysis was adopted to determine the transmission direction, spatial pattern, and temporal variation of the thermal dilation. Then, both the traditional least squares estimation and our robust coherence-weighted least squares regression analysis were performed between the time series displacements and the corresponding temperatures to quantitatively estimate the thermal dilation model. The results were verified in terms of the estimated linear thermal dilation coefficient, which indicates the greater reliability of our method. Furthermore, the thermal dilation characteristics of different civil infrastructure types were analysed, which facilitates a greater understanding of the thermal dilation evolution process of civil infrastructures.

The GaNMn3-Epoxy composites with tunable coefficient of thermal expansion and good dielectric performance

GaNMn3/Epoxy composites were prepared by using negative thermal expansion GaNMn3 powders as the metallic filler. By increasing the loading level of GaNMn3 powders, the hardness and heat conductivity were improved comparing with that of neat epoxy. When the loading level lies in 42 vol.% - 58 vol.% for GaNMn3-0.7 μm and 26 vol.% - 43 vol.% for GaNMn3-2.3 μm, the composites present low thermal expansion (the absolute value of linear thermal coefficient is less than 10 ppm/K), weak dielectric loss (less than 0.04), and the dielectric constants exceed 25, exhibiting great potential for applications in embedded-capacitor fields.

Electrical conductivity and thermal expansion of La1 – x Sr x Fe1 – y Ga y O3 – δ (x = 0.2–0.5; y = 0–0.4)

Lanthanum–strontium gallate–ferrites are thought of as perspective electrode materials. A series of La1 –xSrxFe1 –yGayO3 – δ (x = 0.2–0.5; y = 0–0.4) compositions is synthesized by self-propagating high-temperature synthesis. The solid solutions’ existence domain is identified. The linear expansion thermal coefficient and the electric conductivity of the materials in the form of ceramics are studied for single-phase samples.