Longitudinal Heat Research Articles

An apparatus for measurements of thermal conductivity and thermal expansion based on GM cryocooler

The thermophysical properties of matters are extremely important for engineering and materials science. This paper describes a multifunctional apparatus based on GM cryocooler for measurement of thermal conductivity and thermal expansion via steady-state longitudinal heat flow method and strain gauge technique respectively. The apparatus consists of a removable sample test rod on which bulk samples can easily be mounted and placed in the measurement device. Besides, the sample holder is easy to be replaced so that it suits various needs. All measurements are efficiently and accurately carried out at different temperatures by following a set of stability criteria the setup of the apparatus has been calibrated with sample stainless steel and copper, which gives an error within 6% around the published results in the literatures.

“Cooling by Heating”—Demonstrating the Significance of the Longitudinal Specific Heat

When a bulk piece of material is heated at its surface, does its center become hotter or cooler? A Danish group predict theoretically, and confirm experimentally that, when heated at its surface, a supercooled viscoelastic glucose ball actually cools down at its center.

Thermal transport in graphene nanoribbons supported on SiO2

We present a theoretical model for thermal transport in graphene nanoribbons (GNRs) on SiO${}_{2}$ based on solving the phonon Boltzmann transport equation. Thermal transport in supported GNRs is characterized by a complex interplay between line edge roughness (LER) and internal scattering, as captured through an effective LER scattering rate that depends not only on the surface roughness features, but also on the strength of internal scattering mechanisms (substrate, isotope, and umklapp phonon scattering). Substrate scattering is the dominant internal mechanism, with a mean free path (mfp) of approximately 67 nm. In narrow supported GNRs ($Wl130$ nm, i.e., roughly twice the mfp due to substrate scattering), phonon transport is limited by LER and spatially anisotropic. For intermediate widths ($130\phantom{\rule{0.16em}{0ex}}\mathrm{nm}lWl1$ $\ensuremath{\mu}$m) a competition between LER and substrate scattering governs transport, while thermal transport in wide GNRs ($Wg1\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}$m) is dominated by substrate scattering and spatially isotropic. Thermal transport in supported GNRs can be tailored by controlling the ribbon width and edge roughness. We conclude that narrow ribbons act as longitudinal heat conduits while wide ribbons act as good omnidirectional heat spreaders.

Numerical model for microchannel condensers and gas coolers: Part I – Model description and validation

The present work presents a model (Fin1Dx3) for air-to-refrigerant microchannel condensers and gas coolers, with any refrigerant circuitry. The model applies a segment-by-segment discretization to the heat exchanger, adding in each segment a novel bi-dimensional discretization to the fluids flow, fin and tube wall. Fin1Dx3 introduces a new approach to model the air-side heat transfer by using a composed function for the fin wall temperature, which allows to take into account more fundamentally the heat conduction between tubes. The proposed model accounts for: 2D longitudinal heat conduction in the tube wall, the heat conduction between tubes along the fin, and the unmixed air influence on performance. The paper presents the heat exchanger discretization, the governing equations, the numerical scheme employed to discretize equations and the solving methodology. The model has been validated against experimental data for both a condenser and a gas cooler, resulting in predicted capacity errors within ±5%.

Comparison of Air-Gap Thermal Models for MV Power Cables Inside Unfilled Conduit

This paper studies the effects of natural convection on longitudinal heat transfer and on the air-gap thermal resistance of cables inside conduit installations. Oversimplification of the physical placement of cables inside unfilled conduits is the main shortcoming in currently available thermal models. The study closely investigates the share of each heat-transfer mechanism and the effect of the natural placement of trefoil cables inside the conduit. Measurements from various installation setups are investigated for their impact on heat transfer. The installation-dependent convection correlations adopted in this study have broader applications for the dynamic thermal rating of underground cables inside conduit, troughs, and tunnels. Laboratory measurements are compared with numerical solutions from the IEC 60287 standards, Electra 143 methods, and FEA simulations.

The Effect of Plastic Deformation on Low Temperature Mechanical and Magnetic Properties of Austenite 316LN Tube for ITER TF Conductor

While the manufacturing of superconducting CICC (cable in conduit conductor) and winding conductors into winding packs for ITER TF magnets, cold work is unavoidably applied on the jacketing tube. This article investigates the effect of plastic deformation on low temperature mechanical and magnetic properties of austenite 316LN stainless steel tube for ITER TF conductor. To simulate the manufacturing process of TF magnet, tubes were compacted, extended to 2.5% in longitudinal direction and heat treated. After each step, specimens were sectioned using wire cutting EDM, and tensile tests at 4 K, magnetic susceptibility measurements, and hardness tests have been carried out on those specimens. Remarkable reductions of elongation at failure have been observed as the amount of cold work is increased through compaction and extension. Further, correlations among results of tensile tests, magnetic susceptibility measurements and hardness tests are presented.

Development of New Insulation Panels Based on Textile Recycled Fibers

One of the main environmental problems for clothing sub-sector is the production of remnant waste derived from cutting processes of natural or synthetic fibers. This work is focused on the preparation and characterization of new materials made of waste derived from textile industry (polyester and polyurethane) by thermoforming. The final application is the manufacturing of heat insulation panels that could be used in the building sector in order to improve environmental protection and energy efficiency. FTIR characterization was carried out in order to assess the composition of waste used. Thermal transitions of waste material and degradation temperature were studied by Differential Scanning Calorimetry and Thermogravimetric Analysis, respectively. Wastes were ground by a cutting mill with 4-mm sieve. Thermal insulation panels of 200 × 200 × 5 mm (long × with × depth) of different densities were manufactured in a thermoforming hot plate at 190 °C and constant pressure during 15 min. Thermal insulation properties were evaluated by guarded comparative longitudinal heat flow technique. Thermal conductivity of panels was obtained in a range between 0.053 and 0.041 W/mK, depending on the density. The obtained values were similar to other commercial insulation materials.

Theoretical prediction of longitudinal heat conduction effect in cross-corrugated heat exchanger

In the elementary heat exchanger design theory, the longitudinal heat conduction through the heat transfer plate separating hot and cold fluid streams is neglected, and only the transverse heat conduction is taken into account for the conjugate heat transfer problem. In the cross-corrugated heat exchanger, the corrugated primary surface naturally leads to the highly non-uniform convective heat transfer coefficient distribution on opposite sides of the plate. In such a case, the longitudinal heat conduction may play a significant role in the thermal coupling between high heat transfer regions located on opposite sides of the plate. In the present study CFD is used to perform a quantitative assessment of the thermal performance of a cross-corrugated heat exchanger including the longitudinal heat conduction effect for various design options such as different plate thickness and corrugation geometry for a typical operating condition. The longitudinal heat conduction effect is then predicted by the theoretical method using the ‘network-of-resistance’ in the wide range of the heat exchanger design space.

Mold transient heat transfer behavior based on measurement and inverse analysis of slab continuous casting

In this present paper, a two-dimensional (2D) transient finite-difference model was developed. By solving appropriate inverse problem from the measured temperatures by thermocouples buried at various locations in the mold wall, the unknown heat flux between the strand and mold was identified. The temperature calculated in present model agreed well with actual plant data, and the results gave obvious non-uniform characteristics of heat flux and shell thickness, which could better reflect the real casting conditions of strand. The influence of casting speed on average heat flux and shell thickness at the mold outlet was calculated as follows: increase of casting speed caused increase of average heat flux and decrease of solidified shell thickness at the mold outlet. Furthermore, the relationship between average longitudinal heat flux and shell thickness of mold outlet was discussed, and it resulted in that the heat transfer from the strand to the mold remarkably determined the thickness and non-uniformity of the solidified shell.

Communication: Identical temperature dependence of the time scales of several linear-response functions of two glass-forming liquids

The frequency-dependent dielectric constant, shear and adiabatic bulk moduli, longitudinal thermal expansion coefficient, and longitudinal specific heat have been measured for two van der Waals glass-forming liquids, tetramethyl-tetraphenyl-trisiloxane (DC704) and 5-polyphenyl-4-ether. Within the experimental uncertainties the loss-peak frequencies of the measured response functions have identical temperature dependence over a range of temperatures, for which the Maxwell relaxation time varies more than nine orders of magnitude. The time scales are ordered from fastest to slowest as follows: Shear modulus, adiabatic bulk modulus, dielectric constant, longitudinal thermal expansion coefficient, and longitudinal specific heat. The ordering is discussed in light of the recent conjecture that van der Waals liquids are strongly correlating, i.e., approximate single-parameter liquids.

H111 準定常一方向熱流比較法による熱伝導率測定法の研究(OS-2: 機器冷却における熱物性)

In order to establish measurement method of effective thermal conductivity of specimens such as isotropic electrically conductive adhesives for use electronic equipment, steady state comparative-longitudinal heat flow method using cartridge type specimens have been developed. This method needs long time to get some temperature dependent thermal conductivities by waiting several times to get some steady state conditions. We have studied an improved method nnamed quasi-steady state comparative longitudinal heat flow method in which temperature dependency of the thermal conductivity can be obtained by only one time heating. We demonstrated the possibility to obtain the temperature dependency of the thermal conductivity of the specimen by numerical simulation using two-dimensional transient heat conduction model. The error of the thermal conductivity obtained by this quasi-steady method using quasi-steady condition was less than 2%.

Within‐session sensitization and between‐session habituation: A robust physiological response to repetitive painful heat stimulation

Habituation and sensitization are important behavioural responses to repeated exposure of painful stimuli. Whereas within-session response dynamics to nociceptive stimuli is well characterized, little is known about long-term behaviour due to repetitive nociceptive stimulation. We used a standardized longitudinal heat pain paradigm in 66 healthy participants, 21 patients with chronic low back pain and 22 patients with depression who received daily sessions of 60 suprathreshold heat stimuli (48 °C each) for eight consecutive days. All three groups showed the same response: Repeated painful stimulation over several days resulted in substantially decreased pain ratings to identical painful stimuli. The decreased perception of pain over time was associated with a very robust increase in pain ratings in each single pain session, i.e., all participants sensitized within sessions and habituated between sessions. This uniform pattern was equally present in all examined groups. Chronic pain and depression do not seem to interfere with short-term sensitization and long-term habituation in this model of repetitive phasic heat pain.

오프셋 스트립 휜을 가지는 리큐퍼레이터의 내부 형상 최적화

In the present study, a recuperator is suggested to improve the thermal efficiency of a micro gas turbine. Primary design parameters of the recuperator are determined from the ideal cycle analysis. The counter flow plate-fin heat exchanger with offset strip fins is chosen as the type of the recuperator. In order to satisfy the design constraints which are the minimum effectiveness and the maximum pressure drop, the optimization for the internal structure of the recuperator is performed with varying the fin spacing and the fin height of offset strip fins. Also the effects of the thermal conductivity of fins and separation plates and the longitudinal heat conduction on the thermal performance of the recuperator are investigated.

Numerical Simulation and Experiment Research on Temperature Field of Steel Slab in Walking Beam Furnace

This paper presents a study of the temperature fields of steel slab in a walking beam furnace. To simulate the temperature distribution in the slab of heating-up process in heating furnace, a two-dimensional mathematical model was developed. The heat transfer in the furnace was very complex, so the model was developed on the assumptions that the temperature of each section of the furnace was unchangeable, the slab moved in the furnace in even velocity, the heat transfer between the slab and the walking beam was out of consideration, the longitudinal heat conduction of the slab and the effect of the scale on the heat conduction were neglected. The equations were calculated by the finite difference method. A black box experiment research was carried out to measure the temperature history of the slab as it passed through the furnace. The comparison of the calculated results with the measured results showed that the model worked well for simulating the temperature distribution of the slab in walking beam furnace. With this developed model, the optimizing of hot rolling and heating processes of steel slab can be investigated in the future.

Electric, thermoelectric, and thermal conductivities of graphene with short-range unitary and charged impurities

Motivated by the experimental measurement of electrical and hall conductivity, thermopower and Nernst effect, we calculate the longitudinal and transverse electrical and heat transport in graphene in the presence of unitary scatterers as well as charged impurities. The temperature and carrier density dependence in this system display a number of anomalous features that arise due to the relativistic nature of the low energy fermionic degrees of freedom. We derive the properties in detail including the effect of unitary and charged impurities self-consistently, and present tables giving the analytic expressions for all the transport properties in the limit of small and large temperature compared to the chemical potential and the scattering rates. We compare our results with the available experimental data. While the qualitative variations with temperature and density of carriers or chemical potential of all transport properties can be reproduced, we find that a given set of parameters of the impurities fits the Hall conductivity, Thermopower and the Nernst effect quantitatively but cannot fit the conductivity quantitatively. On the other hand a single set of parameters for scattering from Coulomb impurities fits conductivity, hall resistance and thermopower but not Nernst.

Modeling the system of electrogasdynamic final-control elements

A system of electrogasdynamic final-control elements (plasma actuators) intended for increasing the stability of the boundary layer on a swept wing is considered. The actuators operate on the basis of dielectric barrier discharge. The physical model of the discharge in the air is formulated in the diffusion-drift approximation with account for three charged ionized-gas components, namely, electrons, positive nitrogen and oxygen ions, and negative oxygen ions. The boundary conditions on the dielectric surface are formulated with account for finite desorption and recombination rates of the charged particles. The numerical modeling for an actuator system of particular geometry shows a slight influence of the negative ions on the bulk force generated by each actuator. The main actuator parameters, such as the total longitudinal force and heat release, are shown to considerably depend on the dielectric permeabilities of insulation layers separating the external and internal electrodes. The expressions are derived that make it possible to estimate the gas velocity induced by the bulk force action of the dielectric barrier discharge on the gas flow.

Impact of classical assumptions in modelling a microchannel gas cooler

Most of the current air-to-refrigerant heat exchanger models use the classic ɛ-NTU approach, or some of its assumptions. These models do not account for longitudinal heat conduction in the tube and the fin, and the heat conduction between different tubes. This paper presents a more fundamental numerical approach to heat exchanger modelling which takes into account the 2D longitudinal heat conduction in any element, does not apply the fin theory, and captures a more detailed representation of air properties. Using the fundamental numerical approach, the paper assesses the impact of the traditional heat exchanger model assumptions when modelling a microchannel gas cooler working with CO 2. The study revealed significant differences in capacity predictions depending on the ɛ-NTU relationship adopted. Large errors in capacity prediction of individual tubes occurred due to the adiabatic-fin-tip assumption when the neighbouring tubes were of different temperature.

Modeling of Non-Uniform Thermoelement Devices Subject to Lateral Heat Convection

In this paper, we draw attention to the importance of the lateral convection heat transfer effect on the operation of thermoelements with variable cross-sectional area. The significance of lateral heat convection arises from a new application, in which thermoelements form the walls of a MEMS-based convergent-divergent micronozzle in order to pump heat from the divergent part of the micronozzle to the convergent part to enhance overall performance. To assess the effect of thermoelement, we develop a quasi-one-dimensional model for thermoelements, in which, the physical phenomena of Peltier effect, Joule heating, Seebeck effect, longitudinal heat conduction, and lateral heat convection are considered. The general energy equation of the thermoelement with variable material properties is formulated with heat convection modeled as a lateral heat source. We used the model to study thermoelements with rectangular cross section and uniform thickness, but variable width. The width of the element is maximum at the location forming the micronozzle throat. Several geometries have been investigated; a piece-wise linear, parabolic and piece-wise sine wave. Two parameters which play important role in the thermal performance of thermoelement are identified. These are the thermal resistance ratio; ratio of longitudinal conduction resistance to lateral convection resistance, and heating ratio; ratio of Joule heating to Fourier conducted heat. The effects of varying these two parameters as well as thermoelement geometry have been investigated thoroughly and the results are presented in the form of charts to assist the design and material selection of the thermoelement.

Analytical Investigation of the Effect of Viscous Dissipation on Couette Flow in a Channel Partially Filled with a Porous Medium

An analytical study of viscous dissipation effect on the fully developed forced convection Couette flow through a parallel plate channel partially filled with porous medium is presented. A uniform heat flux is imposed at the moving plate while the fixed plate is insulated. In the fluid-only region the flow field is governed by Navier–Stokes equation while the Brinkman-extended Darcy law relationship is considered in the fully saturated porous medium. The interface conditions are formulated with an empirical constant β due to the stress jump boundary condition. Fluid properties are assumed to be constant and the longitudinal heat conduction is neglected. A closed-form solution for the velocity and temperature distributions and also the Nusselt number in the channel are obtained and the viscous dissipation effect on these profiles is briefly investigated.

Molecular Dynamics Simulation on Longitudinal Optical Phonon Mode Decay and Heat Transport in a Silicon Nano-Structure Covered with Oxide Films

A series of molecular dynamics (MD) simulations have been conducted to investigate the heat transport in terms of the phonon dynamics in nanoscale silicon (Si). This work is motivated by a concern over the stagnation of heat at the drain region of nanoscopic transistors, owing to this, a large amount of optical phonons with a low group velocity are emitted from hot electrons, which are ballistically transferred through channel region. The point of this work is the explicit inclusion of the SiO2 film in the MD simulation of the Si lattice. The calculation results show that longitudinal optical (LO) phonons decay faster as Si lattice thickness decreases and turn into acoustic phonons. In contrast, thermal diffusion rate decreases with Si lattice thickness. Both the decay rate of LO phonons and thermal diffusion rate are not governed by oxide thickness. These results imply that the phonon scattering at the SiO2/Si interface is enhanced by thinning the Si layer. In nanoscopic devices, a thin Si layer is effective in diminishing the optical phonons with a low group velocity, but it hinders the subsequent heat transport.