Influence of Thermal Properties Accuracy on Transient Conduction Models

2010 ◽  
Author(s):  
Pedro Vargas ◽  
Aura L. Lo´pez de Ramos
Keyword(s):  
Heat Capacity ◽  
Thermal Properties ◽  
Transient State ◽  
Variable Properties ◽  
Volumetric Heat Capacity ◽  
Cooling Process ◽  
Heating And Cooling ◽  
Temperature Variable ◽  
The One ◽  
Typical Temperature

The influence of thermal properties accuracy on the heat transfer mathematical models in transient state for food was studied in this work. To pursue this objective, a model in transient state with temperature variable thermal properties was solved using the method of finite differences and the alternate implicit direction scheme to a food inside a cylindrical container under a sudden heating and cooling process, similar to a method of sterilization and/or pasteurization. The model takes into account a linear dependence of the properties with the temperature. An analysis of the behavior of the main thermal properties of the food based on temperature is presented in this article. The results showed that the prediction of the transient state model is more sensitive to perturbations in the values of volumetric heat capacity than thermal conductivity and diffusivity; however, the volumetric heat capacity varies considerably less with temperature. Models with constant properties yield minor deviations when they are evaluated at typical temperature of the cooling or heating processes. The use of the constant thermal diffusivity model with diffusivity is suggested to be evaluated at temperatures between the average and the final heating or cooling process to ensure deviations less than 5%, between the exact model and the simplified one. This solution is considerably simpler than the one obtained with the variable properties model.

scholarly journals Testing a Gypsum Composite Based on Raw Gypsum with a Direct Admixture of Paraffin and Polymer to Improve Thermal Properties

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3241
Author(s):  
Krzysztof Powała ◽  
Andrzej Obraniak ◽  
Dariusz Heim
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Phase Change ◽  
Large Scale ◽  
Building Materials ◽  
Residential Buildings ◽  
Energy Performance ◽  
Polymer Content ◽  
Volumetric Heat Capacity

The implemented new legal regulations regarding thermal comfort, the energy performance of residential buildings, and proecological requirements require the design of new building materials, the use of which will improve the thermal efficiency of newly built and renovated buildings. Therefore, many companies producing building materials strive to improve the properties of their products by reducing the weight of the materials, increasing their mechanical properties, and improving their insulating properties. Currently, there are solutions in phase-change materials (PCM) production technology, such as microencapsulation, but its application on a large scale is extremely costly. This paper presents a solution to the abovementioned problem through the creation and testing of a composite, i.e., a new mixture of gypsum, paraffin, and polymer, which can be used in the production of plasterboard. The presented solution uses a material (PCM) which improves the thermal properties of the composite by taking advantage of the phase-change phenomenon. The study analyzes the influence of polymer content in the total mass of a composite in relation to its thermal conductivity, volumetric heat capacity, and diffusivity. Based on the results contained in this article, the best solution appears to be a mixture with 0.1% polymer content. It is definitely visible in the tests which use drying, hardening time, and paraffin absorption. It differs slightly from the best result in the thermal conductivity test, while it is comparable in terms of volumetric heat capacity and differs slightly from the best result in the thermal diffusivity test.

scholarly journals Relationship Between Dynamic Thermal Properties, Energy Consumption and Comfort with Different Building Envelopes in a Canadian Building

2020 ◽  
Author(s):  
Alexandre Pépin ◽  
Louis Gosselin ◽  
Jonathan Dallaire
Keyword(s):  
Heat Capacity ◽  
Thermal Properties ◽  
Energy Consumption ◽  
Important Variable ◽  
Office Building ◽  
Quebec City ◽  
Thermal Mass ◽  
Building Envelopes ◽  
Heating And Cooling ◽  
Energy Intensities

An office building located in Quebec City (Canada) with different envelope assemblies has been simulated in order to determine the energy consumption and thermal comfort that they provide. The resistance, thermal mass, and materials (concrete, cross-laminated timbers (CLT), and light-frame) are varied in a series of 164 different scenarios and the energy intensities for heating and cooling determined in each case, along with the discomfort index. Results show that the materiel used to provide thermal mass has a larger impact on comfort and energy consumption than the value of the thermal mass thickness itself. It was also attempted to correlate the performance of the envelope and its thermal mass with three dynamic thermal properties (i.e., dynamic transmittance, areal heat capacity, and decrement factor). Apart from thermal resistance, the internal areal heat capacity appeared to be the most important variable to explain variations of performance of the envelope.

Measurement of the Thermal Properties of Innovative Highly-Insulating Non-Structural Concretes

2019 ◽  
Vol 390 ◽  
pp. 41-52 ◽  
Author(s):  
Milena Kušnerová ◽  
Marta Harničárová ◽  
Jan Valíček ◽  
Zuzana Palková ◽  
Zdenko Tkáč ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Thermal Properties ◽  
Mass Parameter ◽  
Thermal Characteristic ◽  
Cementitious Composites ◽  
Thermal Mass ◽  
Volumetric Heat Capacity ◽  
Materials Selection ◽  
Material Parameters ◽  
Measurement Results

Thermal characteristic of insulation concretes is one of the key components in materials selection especially in civil constructions. In this article, non–tabulated material parameters of some innovative highly-insulating non-structural concretes are presented. The specific volumetric heat capacity, specific heat capacity, parameter of temperature diffusivity and thermal mass parameter of the innovative highly-insulating cementitious composites were determined. The experiments were conducted using a prototype automated calorimetric chamber. The measurement results are compared with those obtained by using a commercial multifunctional instrument (Isomet 2114) and are accompanied by the measurement of other significant thermal parameters of the cementitious composites under investigation. The results indicated that there is potential of using the newly created types of concrete for insulation purposes.

Study on the Thermal Properties of Paraffin/Expansion Perlite Composite Phase Change Mortar

2011 ◽  
Vol 374-377 ◽  
pp. 1274-1277 ◽  
Author(s):  
Qing Wang ◽  
Jing Zhang ◽  
Jing Da ◽  
Hui Zhao ◽  
Kun Ran
Keyword(s):  
Mechanical Properties ◽  
Thermal Properties ◽  
Phase Change ◽  
Phase Change Materials ◽  
Paraffin Wax ◽  
Expanded Perlite ◽  
Cooling Process ◽  
Heating And Cooling ◽  
As Adsorption

Phase change materials were prepared by the paraffin wax as phase change materials and expanded perlite as adsorption carrier in this paper. Phase change mortar was prepared by part of the sand been replaced. The heat ability which adjusts and stores heat in the heating and cooling process with different phase change materials was researched and its mechanical properties were tested and evaluated.

Exact Solution of Heat Conduction in a Two-Domain Parallelepiped With an Orthotropic Layer and Its Application to the Estimation of the Three-Dimensional Thermal Conductivity Tensor and Volumetric Heat Capacity of the Orthotropic Layer

2002 ◽  
Author(s):  
Cuauhtemoc Aviles-Ramos
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Exact Solution ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Hybrid Algorithm ◽  
Three Dimensional ◽  
Volumetric Heat Capacity ◽  
Parameter Estimation Problem ◽  
Orthotropic Layer

The three-dimensional exact solution of heat conduction in a two-layer composite is found applying the method of separation of variables. One layer is orthotropic and the other layer is isotropic. This solution is used to calculate sensitivity coefficients with respect to the thermophysical properties of the orthotropic layer at fourteen thermocouple locations. Numerical experiments are carried out to solve a parameter estimation problem that involves the estimation of the thermal conductivities in the x-, y-, and z-directions, the volumetric heat capacity of the orthotropic layer, the effective thermal conductivity of the isotropic layer, and the heat flux input. The exact solution is used to generate temperature readings at fourteen thermocouple locations. First, the parameter estimation problem is solved using the exact temperatures and a hybrid algorithm to estimate the thermal properties and the heat flux. Second, random noise is added to the exact temperatures and the thermal properties and heat flux are estimated using the same hybrid algorithm. It is found that when using the exact temperatures, the minimized quadratic functional has a value of 2.4×10−16 (°C)2 and the estimated properties agree to the ninth decimal place with the “exact” properties.

scholarly journals The Variation Mechanism of Thermal Properties of Loess with Different Water Contents during Freezing

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Xihao Dong ◽  
Shuai Liu ◽  
Yuanxiang Yu
Keyword(s):  
Heat Transfer ◽  
Phase Transition ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Water Content ◽  
Volumetric Heat Capacity ◽  
Soil Particles ◽  
Water Ice ◽  
Variation Mechanism

The thermal properties of soils are affected by many factors, such as temperature, water content, and structure. Based on the transient plane source method of thermal physics, the thermal properties of loess with different water content during the freezing process were tested. We analyzed the variation mechanism of thermal properties from the perspective of phase change. Based on the Pore/Particle and Crack Analysis System (PCAS) and theory of heat transfer, we then analyzed the microstructure and heat conduction process of loess. And a calculation model of volumetric heat capacity of frozen soil was presented. The results show that, in the major phase transition zone, the variation of the thermal properties of loess with temperature is the most significant. And the thermal diffusivity increases sharply with the significant increase of thermal conductivity and the rapid decrease of volumetric heat capacity. Moisture content not only increases the thermal conductivity and volume heat capacity of loess but also makes the influence of temperature on the thermophysical parameters more significant. The effect of temperature on thermal properties is mainly due to the change of heat transfer media caused by phase transition of water-ice, followed by the change of thermal properties of heat transfer media such as soil particles, water, ice, and air with temperature. Increasing the water content reduces the contact thermal resistance between soil particles because of the increase in the thickness of the water film on the surface of soil particles and the thermal conductivity of the heat transfer medium between particles, thus changing the thermal properties of soils.

Comparison of single and dual probes for measuring soil thermal properties with transient heating

Soil Research ◽  
1994 ◽  
Vol 32 (3) ◽  
pp. 447 ◽  
Author(s):  
KL Bristow ◽  
RD White ◽  
GJ Kluitenberg
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Heat Pulse ◽  
Volumetric Heat Capacity ◽  
Transient Heating ◽  
Single Probe ◽  
Soil Thermal Properties ◽  
Dual Probe

Storage and transfer of heat in soils is governed by the soil thermal properties and these properties are therefore needed in many agricultural and engineering applications. In this paper we discuss solutions of the heat flow equation applicable to single and dual probe transient heating methods, and describe measurements made on air-dry sand to show how these methods can be used to obtain soil thermal properties. Measurements show that the two methods yield similar values of thermal conductivity. When determining thermal conductivity from the single probe data, it is best to use nonlinear curve fitting and to include a correction term in the model to account for the presence of the probe. Measurements of volumetric heat capacity made by using the dual probe heat-pulse method agreed well with independent estimates obtained using the de Vries method of summing the heat capacities of the soil constituents. The advantage of using the dual probe method together with the appropriate heat-pulse theory rather than the single probe is that all three soil thermal properties, the thermal diffusivity, volumetric heat capacity, and thermal conductivity, can be determined from a single heat-pulse measurement. Instantaneous heat-pulse theory can be used with the dual probe method to determine heat capacity from short duration heat-pulse data, but it should not be used to determine the thermal diffusivity and thermal conductivity.

Experimental Determination of Thermal Properties of Highly Viscous Liquids

2014 ◽  
Vol 1041 ◽  
pp. 39-42
Author(s):  
Petra Vojkůvková ◽  
Ondřej Šikula
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Experimental Determination ◽  
Direct Method ◽  
Energy Performance ◽  
Viscous Fluids ◽  
Heating And Cooling ◽  
Set Up

This contribution deals with experimental determination of thermal properties needed for transient heat transfer calculation by conduction in highly viscous fluids; which are the density, thermal conductivity and specific heat capacity. Density was determined by direct method, heat capacity was measured with mixing calorimeter and thermal conductivity was studied with two different measuring equipments. Experimental set up for determination of thermal conductivity was designed and constructed by the author. Results were corrected by numerical simulations in CalA software. All measurement quantities were compared with calculations based on the chemical composition of the substance. The determined thermal properties can be used for calculation of energy performance of heating and cooling of highly viscous fluids.

scholarly journals Transient method measured thermal properties of concrete with microspheres and latex based addition

2018 ◽  
Vol 196 ◽  
pp. 04037
Author(s):  
Roman Jaskulski ◽  
Wojciech Kubissa
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Fly Ash ◽  
Thermal Diffusivity ◽  
Thermal Conductivity Coefficient ◽  
Transient Method ◽  
Volumetric Heat Capacity

The goal of the performed research was to determine the influence of microspheres from fly ash and the latex based addition on the thermal properties of concrete. The tested additions were used in two different proportions each and they were combined with each other. As a reference two series of concrete were used: one without any addition and another with 0.2% of air entraining agent. The thermal properties were measured using transient method with ISOMET 2114 apparatus. No clear trends were observed in case of the results of the measurements of the thermal diffusivity and the volumetric heat capacity. While the results of the thermal conductivity coefficient show that both additions has a potential of lowering the thermal conductivity but they are not so efficient as air entraining agent.

Sign in / Sign up

Export Citation Format

Share Document