Mattias Gustavsson - Academia.edu (original) (raw)

Papers by Mattias Gustavsson

Research paper thumbnail of A Residual Thermodynamic Analysis of Turbulence – Part 2: Pipe Flow Computations and Further Development of Theory

International journal of applied thermodynamics, Jun 1, 2022

Single-phase turbulent pipe flows are analysed utilizing a new theory presented in a parallel pap... more Single-phase turbulent pipe flows are analysed utilizing a new theory presented in a parallel paper. Arguably this new theory implies improvements in matching modelling results with experimental observations: To illustrate, unique for these computations is that a 1 st law balance agreement between simulations and corresponding experiments is achieved, while resolving the time-averaged fluid flow velocity (including the various inner turbulent zones) and accounting for the wall surface roughness. Testing this new approach, the computations of 20 cases of turbulent pipe flow arrives at a remarkably high amount of kinetic energy dissipation occurring at near-wall positions, where some 54-83% of the net kinetic energy dissipation occurs within the viscous sublayer-, and 17-39% within the buffer layer. Although turbulence incorporates time-varying phenomena, e.g. swirls, large eddies, and breakup of the latter, it is argued that simulating these would have practically no effect on the net kinetic energy dissipationand the associated wall shear stressfor the present pipe flow cases. Another illustration of the improvements relate to transition computations: While a proposed nominal transition model arrives at fair values of transition Reynolds numbers, some improvements on this transition analysis can be made, e.g. allowing for the modelling of the turbulence onset/offset hysteresis behaviour. For scientists who wish to model time-varying phenomena, e.g. for the study of mixing, boundary layer thickness, or wall-pressure fluctuations, there should be possibilities to implement this new theory in computational flow solvers.

Research paper thumbnail of Novel Approach for Turbulent Flow- and Onset Analysis

IntechOpen eBooks, Feb 13, 2024

It is a well-known fact that the matching of experimental data to turbulence models have hitherto... more It is a well-known fact that the matching of experimental data to turbulence models have hitherto not been successful. An example of this is the inability to theoretically predict the Re number at which turbulence onset (transition) occurs. In this paper, some advantages of adopting a "far-from-equilibrium" irreversible process analysis are demonstrated: To illustrate, one may at a single geometric point near a solid wall, compute conditions for mass conservation, 1st, and 2nd laws of thermodynamicsassuming either Newton's viscosity law-or an alternative far-from-equilibrium fundamental model to be valid. While these conditions generally differ for various flows, it is observed that these conditions numerically match each other at Re D around 2300 for a fully developed pipe flow, or at Re x between 5 Â 10 5 to 3 Â 10 6 in a developing flat-plate boundary layer flow. This suggests that turbulence onset can be correctly predicted using the novel approach. Criteria and recommendations for experimental flow measurements, i.e. testing conditions, within a proposed far-fromequilibrium zone (e.g. viscous sublayer) is discussed as well.

Research paper thumbnail of Thermal conductivity versus depth profiling of inhomogeneous materials using the hot disc technique

Review of Scientific Instruments, Jul 1, 2016

Research paper thumbnail of Measurement of Thermal Transport in Solids with the Hot Disc Method

International Journal of Thermophysics, Nov 30, 2023

Research paper thumbnail of A Residual Thermodynamic Analysis of Turbulence – Part 1: Theory

International Journal of Thermodynamics

A new theoretical groundwork for the analysis of wall-bounded turbulent flows is offered, the app... more A new theoretical groundwork for the analysis of wall-bounded turbulent flows is offered, the application of which is presented in a parallel paper. First, it is proposed that the turbulence phenomenon is connected to the onset of an irreversible process – specifically the action of a slip flow – by which a new fundamental model can be derived. Fluid cells with specific dimensions – of length connected with the local slip length and thickness connected with the distance between two parallel slipping flows – can be hypothetically constructed, in which a specific kinetic energy dissipation can be considered to occur. Second, via a maximum entropy production process a self-organized grouping of cells occurs – which results in the distinct zones viscous sublayer, buffer layer, and the log-law region to be built up. It appears that the underlying web structure may take the form of either representing a perfect web structure without any visible swirls, or a partially defect web structure ...

Research paper thumbnail of Thermal conductivity and diffusivity of wood

Wood Science and Technology, Dec 7, 1999

Transient simultaneous measurements of thermal conductivity and diffusivity of Swedish wood have ... more Transient simultaneous measurements of thermal conductivity and diffusivity of Swedish wood have been performed with the plane source technique on oven-dry hardwood (birch) samples at room temperature and at 100°C. The in¯uences of temperature, density, porosity and anisotropy on thermal conduction were investigated. The measurements were done in longitudinal (parallel to the grain) and transverse (intermediate between radial and tangential) directions. As the temperature increased from 20 to 100°C, the thermal conductivity of each sample increased slightly for both longitudinal and transverse directions. The effect of density and porosity on the thermal conductivity may be related to the presence of other scattering mechanisms such as voids and cell boundaries. It seems that the dominant mechanism of heat transfer across the cell lumina in these types of wood is the heat conduction through the voids. An attempt was made to explain the behaviour of the effective thermal conductivity by adopting a model based on the ratio between heat conduction in parallel and serial layers of gas, liquid, and solid phases.

Research paper thumbnail of Thermal properties of lithium sulphate

Journal of Physics D: Applied Physics, 1997

The thermal conductivity and diffusivity of lithium sulphate have been measured simultaneously, u... more The thermal conductivity and diffusivity of lithium sulphate have been measured simultaneously, using the transient plane source technique over the temperature range 300 - 900 K. The thermal conductivity decreases slowly up to about 640 K, whereupon a distinct rise occurs, indicating the onset of a pre-transitional behaviour, which causes a continuous growth of the conductivity up to the structural phase transition at 851 K, whereupon a very sharp increase occurs. A similar behaviour has been observed for the thermal diffusivity, for which a very sharp dip occurs at the transition point due to the exceptionally large transition enthalpy. The pre-transitional behaviour of heat transport is associated with the librational disorder of the sulphate anions known from Raman scattering studies of both phases (and neutron scattering from the cubic phase), whereas the translational disorder of lithium cations is of hardly any importance. It is thus possible to link the `paddle-wheel' concept of ion migration in the cubic phase to the enhancement of heat transport observed in the `pre-transition' region, as well as to the large difference in heat-transport rates between the monoclinic and cubic phases.

Research paper thumbnail of Specific Heat Measurements of Large-Size Samples with the Hot Disk Thermal Constants Analyser

Proceedings of the Thirty-third International Thermal Conductivity Conference and Proceedings of the Twenty-first International Thermal Expansion Symposium, 2019

Research paper thumbnail of Sub-Millisecond Measurements of Thermal Conductivity and Thermal Diffusivity Using Micrometer-Sized Hot Strips

A new measurement technique based on the transient hot strip technique has recently been develope... more A new measurement technique based on the transient hot strip technique has recently been developed for studying anisotropic thermal transport properties of thin crystalline films. A micrometer-sized hot strip sensor is evaporated on the surface of the crystalline film sample, which has been deposited on a substrate wafer of limited thickness. From a pulsed transient recording, using sub-millisecond square-shaped pulses, a thermal probing depth that is less than the film thickness is assured. In the ongoing work of verifying the technique, we show results from measurements on z-cut crystal quartz and fused silica, using thermal probing depths of only 30 μm, which closely conform to bulk values found in the literature.

Research paper thumbnail of Pulse transient hot strip technique adapted for slab sample geometry to study anisotropic thermal transport properties of μm-thin crystalline films

Review of Scientific Instruments, 2014

A new method based on the adaptation of the Pulse Transient Hot Strip technique to slab sample ge... more A new method based on the adaptation of the Pulse Transient Hot Strip technique to slab sample geometry has been developed for studying thermal conductivity and thermal diffusivity of anisotropic thin film materials (<50 μm) with thermal conductivity in the 0.01-100 W/mK range, deposited on thin substrates (i.e., wafers). Strength of this technique is that it provides a well-controlled thermal probing depth, making it possible to probe a predetermined depth of the sample layer and thereby avoiding the influence from material(s) deeper down in the sample. To verify the technique a series of measurements were conducted on a y-cut single crystal quartz wafer. A Hot Strip sensor (32-μm wide, 3.2-mm long) was deposited along two orthogonal crystallographic (x-and z-) directions and two independent pulse transients were recorded. Thereafter, the data was fitted to our theoretical model, and the anisotropic thermal transport properties were determined. Using a thermal probing depth of only 30 μm, we obtained a thermal conductivity along the perpendicular (parallel) direction to the z-, i.e., optic axis of 6.48 (11.4) W/mK, and a thermal diffusivity of 3.62 (6.52) mm 2 /s. This yields a volumetric specific heat of 1.79 MJ/mK. These values agree well with tabulated data on bulk crystalline quartz supporting the accuracy of the technique, and the obtained standard deviation of less than 2.7% demonstrates the precision of this new measurement technique.

Research paper thumbnail of Anisotropy in thermal transport properties of cast γ-TiAl alloys

Zeitschrift Fur Metallkunde, 2001

The thermal transport properties have been determined for titanium aluminide with nominal composi... more The thermal transport properties have been determined for titanium aluminide with nominal composition Ti-48Al-2W-0.5Si (at.%), cast to cylindrical bars with different γ/(γ + α 2 ) microstructures. The amount of phases and the orientation of the lamellar plates vary from the core to the rim in each of the bars. Differences in the thermal conductivity of the two phases lead to anisotropy in the thermal transport properties, but with cylindrical symmetry in the bars. A newly developed, high-precision technique, the so-called transient plane source (TPS) technique, was used to resolve the anisotropy in a wide temperature range. Typically, the conductivity increases monotonously from about 12-14 W/m.K at room temperature up to about 20-22 W/m.K at 700 °C for the different materials. The anisotropy in both conductivity and diffusivity is about 15 % at all temperatures, but with fundamental differences between the different materials. The anisotropy of the transport properties is explained...

Research paper thumbnail of Thermal conductivity and thermal diffusivity analyses of low-density polyethylene composites reinforced with sisal, glass and intimately mixed sisal/glass fibres

Composites Science and Technology, 2000

The thermal conductivity and thermal diffusivity of sisal-reinforced polyethylene (SRP), glass-re... more The thermal conductivity and thermal diffusivity of sisal-reinforced polyethylene (SRP), glass-reinforced polyethylene (GRP) and sisal/glass hybrid fibre-reinforced polyethylene (GSRP) has been evaluated at cryogenic to high temperature (120–350 K). It has been observed that the variation of thermal conductivity with temperature is almost the same for LDPE and SRP containing perpendicularly oriented sisal fibres. The difference between the values of thermal conductivity shown by LDPE and GRP is greater than that of SRP and LDPE. The enhanced thermal conductivity of glass fibre is due to the presence of Fe2+ ions in the glass fibres. The linear variation in thermal conductivity with fibre loading is explained with the help of a model suggested by Agari. The difference between the thermal conductivity properties in directions parallel and perpendicular to the applied flux is a maximum for SRP owing to the anisotropic nature of sisal fibre. The difference is marginal for GRP on account of its isotropic nature. The position of GSRP is found to be intermediate. It can been observed that the variation of thermal diffusivity with temperature is just opposite to that of thermal conductivity. This may be due to a reduction in the mean free path of phonons. An empirical equation is derived to explain the variation in thermal conductivity and thermal diffusivity with temperature.

Research paper thumbnail of Modified clay as thermal backfill material for buried electrical cables

Thermal science and engineering, 2020

The power efficiency of underground cables is largely affected by the thermal conductivity of the... more The power efficiency of underground cables is largely affected by the thermal conductivity of the surrounding (backfill) materials hosting the cables/tubes. We are investigating the possibility to enhance thermal conduction in Al-modified clay-bentonite to be used as backfill materials. The Transient Plane Source (TPS) technique is used to measure thermal conductivity. The measurements were performed on five dry samples at room temperature. They were done on an isotropic basis using different amounts of Al concentration (0%, 6%, 8%, 13%, and 25%) of the sample weight. The results showed an overall substantial relative increase in the thermal conductivity values from 0.25 W/m-K to 0.68 W/m-K, as the Al-content increased by 25%. The estimated average U-values of these samples were in the range from 0.40 to 1.1 W/m2 K, which are directly proportional to the relative increase in the measured thermal conductivity.

Research paper thumbnail of Modified clay as thermal backfill material for buried electrical cables

Thermal science and engineering, 2020

The power efficiency of underground cables is largely affected by the thermal conductivity of the... more The power efficiency of underground cables is largely affected by the thermal conductivity of the surrounding (backfill) materials hosting the cables/tubes. We are investigating the possibility to enhance thermal conduction in Al-modified clay-bentonite to be used as backfill materials. The Transient Plane Source (TPS) technique is used to measure thermal conductivity. The measurements were performed on five dry samples at room temperature. They were done on an isotropic basis using different amounts of Al concentration (0%, 6%, 8%, 13%, and 25%) of the sample weight. The results showed an overall substantial relative increase in the thermal conductivity values from 0.25 W/m-K to 0.68 W/m-K, as the Al-content increased by 25%. The estimated average U-values of these samples were in the range from 0.40 to 1.1 W/m2 K, which are directly proportional to the relative increase in the measured thermal conductivity.

Research paper thumbnail of Plate Gap Estimation based on Physical Refining Measurements

To estimate the plate gap in refiners, reliable process measurements besides good physical models... more To estimate the plate gap in refiners, reliable process measurements besides good physical models are required. The model used in this study is developed to cover estimations of the thermodynamic work as well as the refining work simultaneously. The model has been applied to a full-scale industrial first stage refiner and various operating conditions have been studied to verify its robustness. According to the model the estimated plate gap as well as the spatial refining work varies significantly, also during time sequences where the motor load is almost the same. The fiber concentration in the refining zone varies with different operating points as well. Moreover, the fluctuations in the fiber concentration are related to the local pressure gradients which are derived from temperature measurements inside the refining zone. These disturbances affect the radial steam velocity and thereby the fiber velocity substantially. This means that the commonly used control concept of keeping co...

Research paper thumbnail of ” Pulse transient Hot Strip technique– a unique method for measuring anisotropic thermal transport properties in stacked nm-thick layers

Context. Dome C in Antarctica is a promising site for photometric observations thanks to the cont... more Context. Dome C in Antarctica is a promising site for photometric observations thanks to the continuous night during the Antarctic winter and favorable weather conditions. Aims. We developed instruments to assess the quality of this site for photometry in the visible and to detect and characterize variable objects through the Antarctic Search for Transiting ExoPlanets (ASTEP) project. Methods. We present the full analysis of four winters of data collected with ASTEP South, a 10 cm refractor pointing continuously toward the celestial south pole. We improved the instrument over the years and developed specific data reduction methods. Results. We achieved nearly continuous observations over the winters. We measure an average sky background of 20 mag arcsec −2 in the 579-642 nm bandpass. We built the lightcurves of 6000 stars and developed a model to infer the photometric quality of Dome C from the lightcurves themselves. The weather is photometric 67.1 ± 4.2 % of the time and veiled 21.8 ± 2.0 % of the time. The remaining time corresponds to poor quality data or winter storms. We analyzed the lightcurves of σ Oct and HD 184465 and find that the amplitude of their main frequency varies by a factor of 3.5 and 6.7 over the four years, respectively. We also identify 34 new variable stars and eight new eclipsing binaries with periods ranging from 0.17 to 81 days. Conclusions. The phase coverage that we achieved with ASTEP South is exceptional for a ground-based instrument and the data quality enables the detection and study of variable objects. These results demonstrate the high quality of Dome C for photometry in the visible and for time series observations in general.

Research paper thumbnail of Thermophysical Properties of Styrene Butadiene Rubber Filled with Pine Tree Particles Measured by the Transient Plane Source Technique

Research paper thumbnail of Numerical simulation of fluid dynamics and cooling-tube erosion in bubbling fluidized beds

Research paper thumbnail of Measurement of thermal properties

Research paper thumbnail of Fluidized Bed Operating Parameters and Eulerian Erosion Models

A numerical two-fluid code, Gemini 2D, was adapted to study gas-solid fluidization in arbitrary 2... more A numerical two-fluid code, Gemini 2D, was adapted to study gas-solid fluidization in arbitrary 2D domains. The code was also used to study fluid dynamic mechanisms of dense particle flow that cause ductile and brittle erosion of solids. Simulations of the in-bed fluid dynamics of a small-scale pressurized fluidized bed were made with and without internals. The inflow and outflow system of a small-scale bed was studied, where the air-feed system - incorporating an air inflow system, plenum chamber and distributor plate - was modelled. It was found that the simulated large-scale fluid dynamics was significantly improved when a model was included for the air feed system of the bed. In particular, at atmospheric operating conditions, it was found that regular pressure fluctuations occurred at a constant frequency, in good agreement with experimental observations for a slugging bed behaviour. These pressure fluctuations correlate well with a strong temporal variation in the total inflow of air. Animated sequences of the slugging bed behaviour resemble that of a piston-like motion of the major part of the bed mass. Previous modelling of the same bed when a constant influx of air through the distributor plate is assumed resulted in large discrepancies between simulated and experimental bed behaviour. It is concluded that it is necessary to include complementary operating parameters to describe the present fluidized bed system, as the standard operating parameters such as fluidization velocity and operating pressure are not sufficient. A simple erosion model was used to study erosion of cooling tubes for a bed containing two tubes. This model, the monolayer kinetic energy dissipation erosion model, was used to study erosion mechanisms when bubbles pass a tube. In accordance with experimental observations, the impact of bubble wakes results in high instantaneous simulated erosion rates. Time-averaged local erosion rates around tubes were also modelled. This simple Eulerian erosion model was further developed to enable erosion modelling of real engineering metals subject to dense flow impacts of hard particles. The irreversible processes in the simulated flow field in the vicinity of a solid eroding surface can be divided into two fundamental components that can be associated with cutting and deformation wear, respectively. Ductile and brittle erosion were simulated for stationary jet streams of particles impacting a tilted plate. The influence of particle diameter, particle concentration, jet velocity and jet diameter was investigated. The literature has a great many reports of erosion models that can be applied in the case of dilute flows and in studies of single particle impacts. However, these models - generally Lagrangian - are here argued to be difficult to implement successfully for dense flows causing erosion. Examples of such cases are sandblasting or erosion caused by a large collection of particles, which is common in bubbling fluidized beds.

Research paper thumbnail of A Residual Thermodynamic Analysis of Turbulence – Part 2: Pipe Flow Computations and Further Development of Theory

International journal of applied thermodynamics, Jun 1, 2022

Single-phase turbulent pipe flows are analysed utilizing a new theory presented in a parallel pap... more Single-phase turbulent pipe flows are analysed utilizing a new theory presented in a parallel paper. Arguably this new theory implies improvements in matching modelling results with experimental observations: To illustrate, unique for these computations is that a 1 st law balance agreement between simulations and corresponding experiments is achieved, while resolving the time-averaged fluid flow velocity (including the various inner turbulent zones) and accounting for the wall surface roughness. Testing this new approach, the computations of 20 cases of turbulent pipe flow arrives at a remarkably high amount of kinetic energy dissipation occurring at near-wall positions, where some 54-83% of the net kinetic energy dissipation occurs within the viscous sublayer-, and 17-39% within the buffer layer. Although turbulence incorporates time-varying phenomena, e.g. swirls, large eddies, and breakup of the latter, it is argued that simulating these would have practically no effect on the net kinetic energy dissipationand the associated wall shear stressfor the present pipe flow cases. Another illustration of the improvements relate to transition computations: While a proposed nominal transition model arrives at fair values of transition Reynolds numbers, some improvements on this transition analysis can be made, e.g. allowing for the modelling of the turbulence onset/offset hysteresis behaviour. For scientists who wish to model time-varying phenomena, e.g. for the study of mixing, boundary layer thickness, or wall-pressure fluctuations, there should be possibilities to implement this new theory in computational flow solvers.

Research paper thumbnail of Novel Approach for Turbulent Flow- and Onset Analysis

IntechOpen eBooks, Feb 13, 2024

It is a well-known fact that the matching of experimental data to turbulence models have hitherto... more It is a well-known fact that the matching of experimental data to turbulence models have hitherto not been successful. An example of this is the inability to theoretically predict the Re number at which turbulence onset (transition) occurs. In this paper, some advantages of adopting a "far-from-equilibrium" irreversible process analysis are demonstrated: To illustrate, one may at a single geometric point near a solid wall, compute conditions for mass conservation, 1st, and 2nd laws of thermodynamicsassuming either Newton's viscosity law-or an alternative far-from-equilibrium fundamental model to be valid. While these conditions generally differ for various flows, it is observed that these conditions numerically match each other at Re D around 2300 for a fully developed pipe flow, or at Re x between 5 Â 10 5 to 3 Â 10 6 in a developing flat-plate boundary layer flow. This suggests that turbulence onset can be correctly predicted using the novel approach. Criteria and recommendations for experimental flow measurements, i.e. testing conditions, within a proposed far-fromequilibrium zone (e.g. viscous sublayer) is discussed as well.

Research paper thumbnail of Thermal conductivity versus depth profiling of inhomogeneous materials using the hot disc technique

Review of Scientific Instruments, Jul 1, 2016

Research paper thumbnail of Measurement of Thermal Transport in Solids with the Hot Disc Method

International Journal of Thermophysics, Nov 30, 2023

Research paper thumbnail of A Residual Thermodynamic Analysis of Turbulence – Part 1: Theory

International Journal of Thermodynamics

A new theoretical groundwork for the analysis of wall-bounded turbulent flows is offered, the app... more A new theoretical groundwork for the analysis of wall-bounded turbulent flows is offered, the application of which is presented in a parallel paper. First, it is proposed that the turbulence phenomenon is connected to the onset of an irreversible process – specifically the action of a slip flow – by which a new fundamental model can be derived. Fluid cells with specific dimensions – of length connected with the local slip length and thickness connected with the distance between two parallel slipping flows – can be hypothetically constructed, in which a specific kinetic energy dissipation can be considered to occur. Second, via a maximum entropy production process a self-organized grouping of cells occurs – which results in the distinct zones viscous sublayer, buffer layer, and the log-law region to be built up. It appears that the underlying web structure may take the form of either representing a perfect web structure without any visible swirls, or a partially defect web structure ...

Research paper thumbnail of Thermal conductivity and diffusivity of wood

Wood Science and Technology, Dec 7, 1999

Transient simultaneous measurements of thermal conductivity and diffusivity of Swedish wood have ... more Transient simultaneous measurements of thermal conductivity and diffusivity of Swedish wood have been performed with the plane source technique on oven-dry hardwood (birch) samples at room temperature and at 100°C. The in¯uences of temperature, density, porosity and anisotropy on thermal conduction were investigated. The measurements were done in longitudinal (parallel to the grain) and transverse (intermediate between radial and tangential) directions. As the temperature increased from 20 to 100°C, the thermal conductivity of each sample increased slightly for both longitudinal and transverse directions. The effect of density and porosity on the thermal conductivity may be related to the presence of other scattering mechanisms such as voids and cell boundaries. It seems that the dominant mechanism of heat transfer across the cell lumina in these types of wood is the heat conduction through the voids. An attempt was made to explain the behaviour of the effective thermal conductivity by adopting a model based on the ratio between heat conduction in parallel and serial layers of gas, liquid, and solid phases.

Research paper thumbnail of Thermal properties of lithium sulphate

Journal of Physics D: Applied Physics, 1997

The thermal conductivity and diffusivity of lithium sulphate have been measured simultaneously, u... more The thermal conductivity and diffusivity of lithium sulphate have been measured simultaneously, using the transient plane source technique over the temperature range 300 - 900 K. The thermal conductivity decreases slowly up to about 640 K, whereupon a distinct rise occurs, indicating the onset of a pre-transitional behaviour, which causes a continuous growth of the conductivity up to the structural phase transition at 851 K, whereupon a very sharp increase occurs. A similar behaviour has been observed for the thermal diffusivity, for which a very sharp dip occurs at the transition point due to the exceptionally large transition enthalpy. The pre-transitional behaviour of heat transport is associated with the librational disorder of the sulphate anions known from Raman scattering studies of both phases (and neutron scattering from the cubic phase), whereas the translational disorder of lithium cations is of hardly any importance. It is thus possible to link the `paddle-wheel' concept of ion migration in the cubic phase to the enhancement of heat transport observed in the `pre-transition' region, as well as to the large difference in heat-transport rates between the monoclinic and cubic phases.

Research paper thumbnail of Specific Heat Measurements of Large-Size Samples with the Hot Disk Thermal Constants Analyser

Proceedings of the Thirty-third International Thermal Conductivity Conference and Proceedings of the Twenty-first International Thermal Expansion Symposium, 2019

Research paper thumbnail of Sub-Millisecond Measurements of Thermal Conductivity and Thermal Diffusivity Using Micrometer-Sized Hot Strips

A new measurement technique based on the transient hot strip technique has recently been develope... more A new measurement technique based on the transient hot strip technique has recently been developed for studying anisotropic thermal transport properties of thin crystalline films. A micrometer-sized hot strip sensor is evaporated on the surface of the crystalline film sample, which has been deposited on a substrate wafer of limited thickness. From a pulsed transient recording, using sub-millisecond square-shaped pulses, a thermal probing depth that is less than the film thickness is assured. In the ongoing work of verifying the technique, we show results from measurements on z-cut crystal quartz and fused silica, using thermal probing depths of only 30 μm, which closely conform to bulk values found in the literature.

Research paper thumbnail of Pulse transient hot strip technique adapted for slab sample geometry to study anisotropic thermal transport properties of μm-thin crystalline films

Review of Scientific Instruments, 2014

A new method based on the adaptation of the Pulse Transient Hot Strip technique to slab sample ge... more A new method based on the adaptation of the Pulse Transient Hot Strip technique to slab sample geometry has been developed for studying thermal conductivity and thermal diffusivity of anisotropic thin film materials (<50 μm) with thermal conductivity in the 0.01-100 W/mK range, deposited on thin substrates (i.e., wafers). Strength of this technique is that it provides a well-controlled thermal probing depth, making it possible to probe a predetermined depth of the sample layer and thereby avoiding the influence from material(s) deeper down in the sample. To verify the technique a series of measurements were conducted on a y-cut single crystal quartz wafer. A Hot Strip sensor (32-μm wide, 3.2-mm long) was deposited along two orthogonal crystallographic (x-and z-) directions and two independent pulse transients were recorded. Thereafter, the data was fitted to our theoretical model, and the anisotropic thermal transport properties were determined. Using a thermal probing depth of only 30 μm, we obtained a thermal conductivity along the perpendicular (parallel) direction to the z-, i.e., optic axis of 6.48 (11.4) W/mK, and a thermal diffusivity of 3.62 (6.52) mm 2 /s. This yields a volumetric specific heat of 1.79 MJ/mK. These values agree well with tabulated data on bulk crystalline quartz supporting the accuracy of the technique, and the obtained standard deviation of less than 2.7% demonstrates the precision of this new measurement technique.

Research paper thumbnail of Anisotropy in thermal transport properties of cast γ-TiAl alloys

Zeitschrift Fur Metallkunde, 2001

The thermal transport properties have been determined for titanium aluminide with nominal composi... more The thermal transport properties have been determined for titanium aluminide with nominal composition Ti-48Al-2W-0.5Si (at.%), cast to cylindrical bars with different γ/(γ + α 2 ) microstructures. The amount of phases and the orientation of the lamellar plates vary from the core to the rim in each of the bars. Differences in the thermal conductivity of the two phases lead to anisotropy in the thermal transport properties, but with cylindrical symmetry in the bars. A newly developed, high-precision technique, the so-called transient plane source (TPS) technique, was used to resolve the anisotropy in a wide temperature range. Typically, the conductivity increases monotonously from about 12-14 W/m.K at room temperature up to about 20-22 W/m.K at 700 °C for the different materials. The anisotropy in both conductivity and diffusivity is about 15 % at all temperatures, but with fundamental differences between the different materials. The anisotropy of the transport properties is explained...

Research paper thumbnail of Thermal conductivity and thermal diffusivity analyses of low-density polyethylene composites reinforced with sisal, glass and intimately mixed sisal/glass fibres

Composites Science and Technology, 2000

The thermal conductivity and thermal diffusivity of sisal-reinforced polyethylene (SRP), glass-re... more The thermal conductivity and thermal diffusivity of sisal-reinforced polyethylene (SRP), glass-reinforced polyethylene (GRP) and sisal/glass hybrid fibre-reinforced polyethylene (GSRP) has been evaluated at cryogenic to high temperature (120–350 K). It has been observed that the variation of thermal conductivity with temperature is almost the same for LDPE and SRP containing perpendicularly oriented sisal fibres. The difference between the values of thermal conductivity shown by LDPE and GRP is greater than that of SRP and LDPE. The enhanced thermal conductivity of glass fibre is due to the presence of Fe2+ ions in the glass fibres. The linear variation in thermal conductivity with fibre loading is explained with the help of a model suggested by Agari. The difference between the thermal conductivity properties in directions parallel and perpendicular to the applied flux is a maximum for SRP owing to the anisotropic nature of sisal fibre. The difference is marginal for GRP on account of its isotropic nature. The position of GSRP is found to be intermediate. It can been observed that the variation of thermal diffusivity with temperature is just opposite to that of thermal conductivity. This may be due to a reduction in the mean free path of phonons. An empirical equation is derived to explain the variation in thermal conductivity and thermal diffusivity with temperature.

Research paper thumbnail of Modified clay as thermal backfill material for buried electrical cables

Thermal science and engineering, 2020

The power efficiency of underground cables is largely affected by the thermal conductivity of the... more The power efficiency of underground cables is largely affected by the thermal conductivity of the surrounding (backfill) materials hosting the cables/tubes. We are investigating the possibility to enhance thermal conduction in Al-modified clay-bentonite to be used as backfill materials. The Transient Plane Source (TPS) technique is used to measure thermal conductivity. The measurements were performed on five dry samples at room temperature. They were done on an isotropic basis using different amounts of Al concentration (0%, 6%, 8%, 13%, and 25%) of the sample weight. The results showed an overall substantial relative increase in the thermal conductivity values from 0.25 W/m-K to 0.68 W/m-K, as the Al-content increased by 25%. The estimated average U-values of these samples were in the range from 0.40 to 1.1 W/m2 K, which are directly proportional to the relative increase in the measured thermal conductivity.

Research paper thumbnail of Modified clay as thermal backfill material for buried electrical cables

Thermal science and engineering, 2020

The power efficiency of underground cables is largely affected by the thermal conductivity of the... more The power efficiency of underground cables is largely affected by the thermal conductivity of the surrounding (backfill) materials hosting the cables/tubes. We are investigating the possibility to enhance thermal conduction in Al-modified clay-bentonite to be used as backfill materials. The Transient Plane Source (TPS) technique is used to measure thermal conductivity. The measurements were performed on five dry samples at room temperature. They were done on an isotropic basis using different amounts of Al concentration (0%, 6%, 8%, 13%, and 25%) of the sample weight. The results showed an overall substantial relative increase in the thermal conductivity values from 0.25 W/m-K to 0.68 W/m-K, as the Al-content increased by 25%. The estimated average U-values of these samples were in the range from 0.40 to 1.1 W/m2 K, which are directly proportional to the relative increase in the measured thermal conductivity.

Research paper thumbnail of Plate Gap Estimation based on Physical Refining Measurements

To estimate the plate gap in refiners, reliable process measurements besides good physical models... more To estimate the plate gap in refiners, reliable process measurements besides good physical models are required. The model used in this study is developed to cover estimations of the thermodynamic work as well as the refining work simultaneously. The model has been applied to a full-scale industrial first stage refiner and various operating conditions have been studied to verify its robustness. According to the model the estimated plate gap as well as the spatial refining work varies significantly, also during time sequences where the motor load is almost the same. The fiber concentration in the refining zone varies with different operating points as well. Moreover, the fluctuations in the fiber concentration are related to the local pressure gradients which are derived from temperature measurements inside the refining zone. These disturbances affect the radial steam velocity and thereby the fiber velocity substantially. This means that the commonly used control concept of keeping co...

Research paper thumbnail of ” Pulse transient Hot Strip technique– a unique method for measuring anisotropic thermal transport properties in stacked nm-thick layers

Context. Dome C in Antarctica is a promising site for photometric observations thanks to the cont... more Context. Dome C in Antarctica is a promising site for photometric observations thanks to the continuous night during the Antarctic winter and favorable weather conditions. Aims. We developed instruments to assess the quality of this site for photometry in the visible and to detect and characterize variable objects through the Antarctic Search for Transiting ExoPlanets (ASTEP) project. Methods. We present the full analysis of four winters of data collected with ASTEP South, a 10 cm refractor pointing continuously toward the celestial south pole. We improved the instrument over the years and developed specific data reduction methods. Results. We achieved nearly continuous observations over the winters. We measure an average sky background of 20 mag arcsec −2 in the 579-642 nm bandpass. We built the lightcurves of 6000 stars and developed a model to infer the photometric quality of Dome C from the lightcurves themselves. The weather is photometric 67.1 ± 4.2 % of the time and veiled 21.8 ± 2.0 % of the time. The remaining time corresponds to poor quality data or winter storms. We analyzed the lightcurves of σ Oct and HD 184465 and find that the amplitude of their main frequency varies by a factor of 3.5 and 6.7 over the four years, respectively. We also identify 34 new variable stars and eight new eclipsing binaries with periods ranging from 0.17 to 81 days. Conclusions. The phase coverage that we achieved with ASTEP South is exceptional for a ground-based instrument and the data quality enables the detection and study of variable objects. These results demonstrate the high quality of Dome C for photometry in the visible and for time series observations in general.

Research paper thumbnail of Thermophysical Properties of Styrene Butadiene Rubber Filled with Pine Tree Particles Measured by the Transient Plane Source Technique

Research paper thumbnail of Numerical simulation of fluid dynamics and cooling-tube erosion in bubbling fluidized beds

Research paper thumbnail of Measurement of thermal properties

Research paper thumbnail of Fluidized Bed Operating Parameters and Eulerian Erosion Models

A numerical two-fluid code, Gemini 2D, was adapted to study gas-solid fluidization in arbitrary 2... more A numerical two-fluid code, Gemini 2D, was adapted to study gas-solid fluidization in arbitrary 2D domains. The code was also used to study fluid dynamic mechanisms of dense particle flow that cause ductile and brittle erosion of solids. Simulations of the in-bed fluid dynamics of a small-scale pressurized fluidized bed were made with and without internals. The inflow and outflow system of a small-scale bed was studied, where the air-feed system - incorporating an air inflow system, plenum chamber and distributor plate - was modelled. It was found that the simulated large-scale fluid dynamics was significantly improved when a model was included for the air feed system of the bed. In particular, at atmospheric operating conditions, it was found that regular pressure fluctuations occurred at a constant frequency, in good agreement with experimental observations for a slugging bed behaviour. These pressure fluctuations correlate well with a strong temporal variation in the total inflow of air. Animated sequences of the slugging bed behaviour resemble that of a piston-like motion of the major part of the bed mass. Previous modelling of the same bed when a constant influx of air through the distributor plate is assumed resulted in large discrepancies between simulated and experimental bed behaviour. It is concluded that it is necessary to include complementary operating parameters to describe the present fluidized bed system, as the standard operating parameters such as fluidization velocity and operating pressure are not sufficient. A simple erosion model was used to study erosion of cooling tubes for a bed containing two tubes. This model, the monolayer kinetic energy dissipation erosion model, was used to study erosion mechanisms when bubbles pass a tube. In accordance with experimental observations, the impact of bubble wakes results in high instantaneous simulated erosion rates. Time-averaged local erosion rates around tubes were also modelled. This simple Eulerian erosion model was further developed to enable erosion modelling of real engineering metals subject to dense flow impacts of hard particles. The irreversible processes in the simulated flow field in the vicinity of a solid eroding surface can be divided into two fundamental components that can be associated with cutting and deformation wear, respectively. Ductile and brittle erosion were simulated for stationary jet streams of particles impacting a tilted plate. The influence of particle diameter, particle concentration, jet velocity and jet diameter was investigated. The literature has a great many reports of erosion models that can be applied in the case of dilute flows and in studies of single particle impacts. However, these models - generally Lagrangian - are here argued to be difficult to implement successfully for dense flows causing erosion. Examples of such cases are sandblasting or erosion caused by a large collection of particles, which is common in bubbling fluidized beds.