Line Heat Research Articles

Characterization of a Thermal Insulating Material Based on a Wheat Straw and Recycled Paper Cellulose to Be Applied in Buildings by Blowing Method

The thermal envelope is a key component of a building’s energy efficiency. Therefore, considerable efforts have been made to develop thermal insulating materials with a better performance than the existing products. However, in the current climate change scenario, these materials must be sustainable, principally during their production stage. In this context, the use of recycled raw materials and agro-industrial waste can be the basis of a material with a low environmental impact and a good thermal performance. In this study, cellulose and wheat straw were characterized. Then, they were mixed in different proportions and densities and the best thermal behavior was selected. The materials were chemically analyzed by TAPPI 2007, thermogravimetric and infrared spectroscopy, together with the measurement of their thermal conductivity with a thermal property analyzer based on the transient line heat source method. The results show that both raw materials are chemically similar to each other. When mixed, they have a thermal conductivity ranging from 0.031 to 0.036 (W/mK), being comparable with several conventional thermal insulators. On the other hand, to achieve the commercial use of this material, an installation through a blowing process has been proposed and proves to be highly promising, achieving a proper density and efficiency in its application.

Fully analytical solution in time and space domains on temperature in multi-barrier nuclear waste repository

Temperature evolution is one of the crucial factors in safe operation and geometric design of high-level radioactive waste disposal repositories. A three-dimensional two-layer axisymmetric heat transfer model was established to study the temperature evolution of the repository in the case of single canister. Applying a series of mathematical tools such as the finite Fourier sine transform, separation of variables and Duhamel's theorem, a fully analytical solution was obtained, which can visually and quickly represent the temperature evolution in both time and space. The validity of the model and solution was confirmed by comparing it with the existing line heat source solution, semi-analytical solution and finite element simulation results. The canister surface temperature was obtained by superimposing the temperature difference between the internal and external surfaces of buffer layer on the rock wall temperature. A single-panel calculation model was established, and dimensional and parameter analysis were carried out using the obtained fully analytical solution. According to the quantitative analysis using the obtained solution, increasing the canister spacing has a better effect on reducing the peak temperature than increasing the tunnel spacing. The effect of the two ways in reducing the peak temperature weakens with increasing the spacings.

Deformation and Springback Behavior of Sheet Metal With Convex-Shaped Surfaces in Heat-Assisted Incremental Bending Process Based on Minimum Energy Method

Abstract Three-dimensional sheet metal forming is one of the biggest challenges in the shipbuilding industry. The forming quality of the traditionally applied line heating method depends entirely on the skills of the technicians. Moreover, this approach is inefficient and error-prone. This calls for a need to develop new forming technologies that are easy to control and more efficient. In this paper, a novel forming method called heat-assisted incremental bending is presented. The minimum energy loading path of bidirectional curvature sheet along the direction of Gaussian curvature is adapted to deform the sheet metals with a convex shape surface. Besides, the auxiliary heating method and the auxiliary supporting are exclusively included in the forming process to improve the formability and accuracy. In this study, the convex-shaped sheet metal with large curvature is obtained along the two loading trajectories in two principal curvature directions, respectively. Results proved that using the minimum energy loading trajectory and including the auxiliary supports and heating can reduce the forming force to the greatest extent and effectively reduce the number of stamping points, thus improving the sheet metal forming efficiency and forming accuracy.

Mixing and diffusion in protoplanetary disc chemistry

We develop a simple iterative scheme to include vertical turbulent mixing and diffusion in PRODIMO thermo-chemical models for protoplanetary discs. The models are carefully checked for convergence towards the time-independent solution of the reaction-diffusion equations, as, for example, used in exoplanet atmosphere models. A series of five TTauri disc models is presented where we vary the mixing parameter αmix from zero to 10−2 and take into account: (a) the radiative transfer feedback of the opacities of icy grains that are mixed upwards; and (b) the feedback of the changing molecular abundances on the gas temperature structure caused by exothermic reactions, and increased line heating and cooling. We see considerable changes in the molecular and ice concentrations in the disc. The most abundant species (H2, CH4, CO, the neutral atoms in higher layers, and the ices in the midplane) are transported both up and down, and at the locations where these abundant chemicals finally decompose, for example by photo processes, the release of reaction products has important consequences for all the other molecules. This generally creates a more active chemistry, with a richer mixture of ionised, atomic, molecular, and ice species, and new chemical pathways that are not relevant in the unmixed case. We discuss the impact on three spectral observations caused by mixing and find that: (i) icy grains can reach the observable disc surface where they cause ice absorption and emission features at IR to far-IR wavelengths; (ii) mixing increases the concentrations of certain neutral molecules observable by mid-IR spectroscopy, in particular OH, HCN, and C2H2; and (iii) mixing can change the optical appearance of CO in ALMA line images and channel maps, where strong mixing would cause the CO molecules to populate the distant midplane.

Determination of Optimal Line-Heating Conditions for Flatness Control of Wind Tower Blocks Using Strain as Direct Boundary Method.

The wind tower block is welded with the flange to assemble the wind tower. The inherent strain due to local heating and cooling of the weld affects the flatness of the flange. Therefore, line heating is performed to satisfy the design criteria of the flange flatness, but the work variables depend on the operator's empirical judgment. This study proposed a method to determine the optimum linear heating conditions to control the welded flatness of wind tower blocks and flanges. A proposed method uses the inherent strain method, a simple analysis method, and the optimization is performed based on the deformation superposition method. The changes in flange flatness due to welding and single-point heating were calculated. Then, the flatness change due to single-point heating is superimposed with a scale factor, which represents the magnitude of line heating, and is added to the flatness change due to welding. Using the optimization procedure, the line heating conditions used to derive the flatness that satisfies the design criteria were derived and applied to the analytical model for verification.

Model development according to increase in the active resistance of the conductor to ac current at the surface effect

Purpose. When alternating current with higher harmonics passes through the cable, heating is carried out by the root mean square value of all harmonics. Taking into account the different resistance of the cable depending on the frequency due to the effect of the surface effect, it is advisable to calculate the coefficient of increase in the total current resistance, assuming the action of each harmonic as independent. However, there are prerequisites to consider existing calculation models difficult for algorithmic implementation in software packages. Therefore, the purpose of the work is to develop a calculation model to take into account the increase in the active resistance of the conductor to alternating current due to the surface effect for further use in simulation modeling packages such as, for example, MATLAB.
 Methodology. Methods of linear algebra, linear regression, defining the coefficient of determination.
 Findings. Dependencies for determining the resistance value of high-voltage cable lines to high-frequency currents, which take into account the cross-section and harmonic composition of the current, have been obtained. According to the existing and substantiated graphs (dependencies) obtained on the basis of classical expressions from the literature, new simplified calculation dependencies were obtained (for the cross-section of copper cable lines 240 - 1000 mm2) when current harmonics above the fifth at a base frequency of 50 Hz. Such calculated ratios will allow taking into account several harmonic components of the current during line heating in the MATLAB Simulink software environment.
 The obtained values of the coefficient of determination in defining the calculated dependencies are close to 1, which indicates the correctly selected type of equation and the correctly selected coefficient k for different cross-sections of the cable line.
 Originality. The scientific novelty lies in the development of a new dependence, justified by the high value of the multiple correlation coefficient, the correction factor for the increase in the resistance of the cable core from the harmonic number and the empirical coefficient of the regression model, taking into account the cross section of the cable line.
 Practical value. The practical value of the work consists in obtaining dependencies that can be used in analytical and simulation models when determining the amount of heating of cable lines taking into account the current of harmonics above the fifth at a base frequency of 50 Hz. Such an application will allow in many cases to replace the physical experiment with a simulation in the MATLAB Simulink software environment, which will reduce the necessary human and material costs.

Analysis of thermoelectric viscoelastic wave characteristics in the presence of a continuous line heat source with memory dependent derivatives

Analysis of thermoelectric viscoelastic wave characteristics in the presence of a continuous line heat source with memory dependent derivatives

Processing-Scheme Design for Forming Curved Ship Plate and Analysis of Calculation Cases

The forming process of curved ship plate suffers from a low degree of automation, mainly due to the lack of an effective processing-scheme design method. In this paper, based on the proposed concept of the “basic amount of forming plasticity”, which can connect the plastic strain induced by the line heating and the deformation to form the target shape, a database is firstly established to describe the plastic strain provided by the heating coil with specific processing parameters, considering the effect of the plate boundary and adjacent heating lines. Secondly, a finite element method is developed and presented to calculate the plastic strain needed to form the target shape. Finally, a processing-scheme design method for forming the curved ship plate is verified by the case study of three typical types of shape: sail-type plates, saddle-type plates, and curved plates with torsion. The verification result shows the processing-scheme design method can provide helpful guidance for the practical forming process in shipyards.

General solution and Green’s function for fluid-saturated infinite and semi-infinite orthotropic poro-thermoelastic materials

In this study, two-dimensional (2D) steady-state general solution and Green’s function for orthotropic materials under the influence of poro-thermoelasticity (PTE) are investigated. Using the superposition principle and operator theory, the complete general solution of corresponding governing equations is calculated and stated in terms of harmonic functions. Based on these compact general solutions, the 2D Green’s function for a steady line fluid source and line heat source in the interior of an infinite orthotropic PTE plane and on the surface of a semi-infinite orthotropic PTE plane is presented. Consequently, eight newly implemented harmonic functions with undetermined constants are obtained. The equilibrium, boundary, and continuous conditions are used to obtain undetermined constants, and the corresponding coupled field is obtained by inserting these harmonic functions into the general solution. All coupled field’s components are described in terms of elementary functions, which can be used as the benchmarks for various numerical codes and approximate solutions.

Optimization design of process parameters for cold and hot composite roll forming of the AHSS square tube using response surface methodology

Advanced high-strength steel (AHSS) is a highly competitive material for the automobile industry to resolve the challenge of weight reduction and passenger safety. Cold and hot composite roll forming is a newly developed manufacturing technology, which aims to overcome the defects such as microcrack, severe work hardening, thickness reduction, and large corner radius in the traditional cold roll forming process of AHSS. In this paper, the mathematical models that represent the effect of line velocity, heating power, and deformation amount on the yield strength, outer corner radius, and microcrack length in the corner section of cold and hot composite roll-formed AHSS square tube are investigated by the response surface methodology with Box-Behnken design. The analysis of variance shows that the linear velocity has the greatest influence on the three responses, followed by the heating power and deformation amount. Furthermore, the experimental verification is carried out under the optimal combination of process parameters to manufacture the AHSS square tube with the desired performance. Compared to the cold roll-formed AHSS square tube, the product of strength and elongation in the corner section is increased by 53%, the corner thickness is increased by 60%, the outer corner radius is decreased by 94%, and the microcrack defect is not generated. The average magnitude of errors between the predicted and actual values is about 5%, which implies that the optimization design is accurate and reliable.

Dynamic modelling of the steady state and load processing operation of a domestic refrigerator cooled through natural convection

A dynamic model of a domestic refrigerator is developed in this study and is used to analyse both the steady state (cyclic) and warm load cooling (load processing) operation. The compressor is modelled semi-empirically using loss parameters, while the capillary tube is modelled by incorporating both friction and momentum pressure drop. Heat exchangers (condenser and evaporator) are modelled as tubes divided into finite volume cells. The capillary tube-suction line heat exchanger is treated by connecting part of the capillary tube to the suction line via a heat resistor. The cabinet model consists of submodels for walls, air and shelves connected in a network to allow for thermal interaction. All the components are then arranged in a cycle, and cyclic operation is validated at 32 °C using a fixed speed compressor. A sensitivity analysis is then carried out by varying the compressor speed. In the second part of the study, the model is modified to include the effect of placing a warm load of water in the refrigerator and simulating the subsequent processing operation. This is validated using an experiment in which 20 L of water at 27 °C is placed inside the Fresh Food compartment. Results show that the power consumption value is captured well, with the average power consumption deviating less than 10% for all tests. The energy consumption is within ±5% for all tests. For load processing, the deviation in water temperature was a maximum of 1.2 °C for the whole cooling period.

Thermoelastic interactions on temperature-rate-dependent two-temperature thermoelasticity in an infinite medium subjected to a line heat source

Thermoelastic interactions on temperature-rate-dependent two-temperature thermoelasticity in an infinite medium subjected to a line heat source

On the memory-dependent derivative electric-thermoelastic wave characteristics in the presence of a continuous line heat source

In the present work, the definition of memory-dependent derivative (MDD) heat transfer in a solid body was used to investigate the problem of wave characteristics in an unbounded electric-thermoelastic solid due to a continuous line heat source in the presence of a uniform magnetic field. Both Laplace and Hankel's transform strategies are used to acquire the widespread answer in a closed-form. Analytical findings were obtained for the distribution within the medium of various fields such as temperature, displacement, and stresses. For the inversion of the Laplace transformations, a computational approach is used. The distributions of the numerical consequences of the non-dimensional considered bodily variables are represented graphically. Detailed comparative evaluation is represented thru the numerical outcomes to estimate the results of the kernels, time-delay, figure-of-merit, and magnetic number on the behavior of all variables. The effect offers a concept to research main electric-thermoelastic materials as any other type of pertinent materials.

Heat distribution concepts for small solar district heating systems – Techno-economic study for low line heat densities

• Two novel distribution concepts are compared to conventional district heating. • A novel distribution system with central domestic hot-water heating is presented. • Hybrid distribution outperforms a conventional steel pipe system. • A complete low-temperature system outperforms hybrid distribution. • Reduction in line heat density favours a low-temperature GRUDIS system. The high operating temperatures in today’s district heating networks combined with the low energy demand of new buildings lead to high relative network heat losses. New networks featuring lower operating temperatures have reduced relative heat losses while enabling an increase in the use of solar heat. The primary aim of this study was to determine if a particular district heating system can be made more effective with respect to heat losses and useful solar energy, by considering different distribution concepts and load densities. A small solar assisted district heating system with a novel hybrid distribution system has been modelled based on a real case study. This model serves as a basis for two other models where the distribution system and heating network operating temperature is changed. A secondary aim of the study was to determine the economic implications of making these changes, by using costs estimates to calculate the contribution of essential system components to total system cost. Results indicate that a novel distribution concept with lower network temperatures and central domestic hot water preparation is most energy efficient in a sparse network with a heat density of 0.2 MWh/m∙a and a performance ratio of 66%, while a conventional district heating system performs worst and has a performance ratio of less than 58% at the same heat density. In an extremely sparse network with heat density of 0.05 MWh/m∙a, the performance ratio is 41% and 30% for these systems, respectively. A simple economic analysis indicates that the novel distribution concept is also best from an economic point of view, reducing the initial investment cost by 1/3 compared to the conventional concept, which is the most costly. However, more detailed calculations are needed to conclude on this.

Gradient models of moving heat sources for powder bed fusion applications

In this paper, we derive closed form solutions for the quasi-stationary problems of moving heat sources within the gradient theory of heat transfer. This theory can be formally deduced from the two-temperature model and it can be treated as a generalized variant of the Guyer–Krumhansl model with the fourth order governing equation. We show that considered variant of the gradient theory allows to obtain useful singularity-free solutions for the moving point and line heat sources that can be used for the refined analysis of the melt pool shape in the laser powder bed fusion processes. Derived solutions contain single additional length scale parameter that can be related to the mean size of the powder particles . Namely, we show that developed gradient models allow to describe the decrease of the melt pool depth with the increase of the powder’s particles size that was observed previously in the experiments. We also derived the dimensionless relations that can be used for the experimental identification of the model’s length scale parameter for different materials. Semi-analytical solution for the Gaussian laser beam is also derived and studied based on the Green function method within the considered theory.

Horizontal convective flow from a line heat source located at the liquid–gas interface in presence of surface film

Development of the convective flow from a line heat source located at the liquid surface is studied for the case when thermocapillary convection is inhibited by the surface film. Surface film is formed by small amounts of surfactants present in non-deionized (distilled or natural) water. It imposes a no-slip boundary condition for velocity at the surface and determines the fluid dynamics of the surface layer. For the heat source located at the surface, the vertical stratification is stable and the flow is driven by a horizontal pressure gradient, formed by non-uniform heating of the liquid along the surface. Experimental studies include measurements of velocity fields using particle image velocimetry, surface relief measurements using moon-glade background oriented Schlieren and surface temperature measurements using infrared thermography. Also, numerical simulations of the flow development are performed and a new similarity solution for the steady state in a laterally unbounded domain is constructed, which takes into account the pressure gradient. The results are shown to be in good agreement with experimental data. The obtained dependencies of the maximal velocity, boundary layer thickness, local and total Nusselt numbers on the Rayleigh number are consistent with literature data obtained for the non-uniformly heated bottom case, which demonstrates universal properties of horizontal convection.

Numerical simulation of natural convection MHD flow in a wavy L‐shaped cavity with line heat source using hybrid EFGM/FEM

AbstractIn the current paper, the natural convection of power‐law nanofluid within a wavy l‐shaped cavity under the magnetic field has been simulated by a hybrid (EFGM/FEM) technique with parallel implementation. A line heat source with length Lhs and height Hhs is applied on the right vertical wall of the cavity. The cavity is filled with power‐law non‐Newtonian nanofluid. Parallel implementation with hybrid EFGM/FEM is used to solve the governing partial differential equations. Effect of Rayleigh number, Hartmann number, power‐law index, aspect ratio, nanoparticle volume fraction, location, and length of the heat source has been studied on the fluid flow, isotherms, and heat transfer. It is observed that the power‐law index, Hartmann number, and height of heat source have a decreasing effect on heat transfer rate while the Rayleigh number, length of heat source, and volume fraction of nanoparticle increases the heat transfer rate. Heat transfer rate improves by 51% and 73% with increasing the volume fraction of nanoparticles and Rayleigh number while heat transfer rate reduces by 28% with increasing the Hartmann number. The main application of such problems is found in the building corners, lubricating machines, and medical and electronic equipment (thermometer device and PCB). The hybrid method is one of the novel contributions of the author. Parallel implementation of the meshfree method (EFGM) is one of the novel features of this paper.

Determining the Thermal Properties of the Pangasius Using a Dual Needle Heat-Pulse Sensor

In the field of food cooling and freezing computation, the accurate determination of thermo-physical properties such as specific heat, thermal conductivity and density is necessary and specially important to optimize the energy consumption of equipment. These parameters depend on the food composition and temperature usually determined by theoretical or experimental method or the combination of both. Experimental method using differential scanning calorimetry (DSC) is the best approach to yield correct results. However, DSC method requires expensive equipment and it might be not suitable for limited funding in some Vietnamese research centers. Therefore, the line heat source was chosen in this study.This paper introduces a new approach to determine thermal properties of the Vietnamese Pangasius in the temperature range from-40 °C to +40 °C using the line heat source. The results indicated that there is good correllation between the obtained measured data and the results calculated using theoretical models as well as other published experimental results.

Flow and heat transfer analysis of a domestic refrigerator with complex wall conditions

• A comprehensive numerical model with complex wall conditions for domestic refrigerators is developed and validated with experiments. • The flow and temperature distributions inside the compartments are discussed. • The impacts of the anti-condensation tube, VIPs and SLHX on the wall temperature and heat transfer are investigated. • The difference in heat leakage between with and without complex wall conditions reaches 6.2%. The heat transfer and temperature distributions inside the compartments and walls for a domestic refrigerator are vital to food storage and energy consumption. The refrigerator walls consist of many complex structural parts such as anti-condensation tube, vacuum-insulation panels (VIPs) and suction line heat exchanger (SLHX), which are closely related to the heat transfer. To investigate the influence of the complex walls on the heat transfer, this study presents a comprehensive numerical model for the domestic refrigerator with considering the complex wall conditions and an experiment is conducted to validate the accuracy of the model. The flow and temperature distributions inside the compartments are analyzed. The impacts of the anti-condensation tube, VIPs and SLHX on the wall temperature are investigated with and without complex wall conditions. The heat leakage through the walls of the refrigerator into the compartments from the environment is reported. The results show that the complex walls have a large impact on the heat transfer of the refrigerator. The difference in heat transfer between the two conditions with and without complex wall reaches 6.2%. The generic numerical model shows that the complex wall conditions should be considered when the manufacturers calculate the heat load and optimize the wall thickness to design a refrigerator.

Novel Numerical Modeling of Concentric and Lateral Capillary Tube Suction Line Heat Exchangers

Novel Numerical Modeling of Concentric and Lateral Capillary Tube Suction Line Heat Exchangers