THE ATTENUATION OF SECOND SOUND IN LIQUID HELIUM II ABOVE 1°K.

1954 ◽  
Vol 32 (6) ◽  
pp. 381-392 ◽  
Author(s):  
K. R. Atkins ◽  
K. H. Hart
Keyword(s):  
Thermal Conductivity ◽  
Continuous Wave ◽  
Pulse Length ◽  
Boundary Effects ◽  
Second Sound ◽  
Sound Beam ◽  
Helium Ii ◽  
Viscosity Effects ◽  
Order Of Magnitude ◽  
Good Agreement

The second sound was in the form of a pulsed continuous wave with a pulse length of 1 to 2 msec, and a carrier frequency of 10 or 20 kc./s. The change in amplitude of the pulse was measured as the distance between the transmitter and the receiver was varied. To avoid boundary effects, no propagation tube was used and allowance had to be made for the spreading of the second sound beam. The attenuation was found to increase with increasing second sound amplitude. The attenuation extrapolated to zero amplitude had a finite value which increased rapidly as the temperature was lowered towards 1°K. Its order of magnitude was too large to be explained by viscosity effects, but was in good agreement with a thermal conductivity effect predicted by Khalatnikov.

Brownian-Motion-Based Convective-Conductive Model for the Effective Thermal Conductivity of Nanofluids

2005 ◽  
Vol 128 (6) ◽  
pp. 588-595 ◽  
Author(s):  
Ravi Prasher ◽  
Prajesh Bhattacharya ◽  
Patrick E. Phelan
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Particle Sizes ◽  
Brownian Movement ◽  
Liquid Temperature ◽  
Interfacial Resistance ◽  
Conduction Model ◽  
Order Of Magnitude ◽  
Base Liquid ◽  
Good Agreement

Here we show through an order-of-magnitude analysis that the enhancement in the effective thermal conductivity of nanofluids is due mainly to the localized convection caused by the Brownian movement of the nanoparticles. We also introduce a convective-conductive model which accurately captures the effects of particle size, choice of base liquid, thermal interfacial resistance between the particles and liquid, temperature, etc. This model is a combination of the Maxwell-Garnett (MG) conduction model and the convection caused by the Brownian movement of the nanoparticles, and reduces to the MG model for large particle sizes. The model is in good agreement with data on water, ethylene glycol, and oil-based nanofluids, and shows that the lighter the nanoparticles, the greater the convection effect in the liquid, regardless of the thermal conductivity of the nanoparticles.

Quantum hydrodynamics and the theory of liquid helium

1953 ◽  
Vol 219 (1137) ◽  
pp. 257-270 ◽  
Keyword(s):  
Energy Spectrum ◽  
Liquid Helium ◽  
Fluid Velocity ◽  
Second Sound ◽  
Quantum Hydrodynamics ◽  
Dynamical Equations ◽  
Helium Ii ◽  
Apparent Variation ◽  
Theory Of Fields ◽  
Good Agreement

The Clebsch formula, u = –∇ ϕ – χ ∇ ψ , for the fluid velocity allows the classical hydro-dynamical equations, including vorticity, to be derived from a variational principle, and put into canonical form. The standard quantization procedure of the theory of fields then gives a set of field operators satisfying the commutation relations obtained (starting from different premises) by Landau (1941). The Hamiltonian contains terms corresponding to the excitation of the ‘roton’ states of Landau’s theory, with an energy spectrum (allowing for the atomicity of real liquids by a ‘cut off’ in the Fourier analysis of the field variables) of the form E = ∆ + p 2 /2 μ . The observed variations of specific heat and second-sound velocity in liquid helium II may be interpreted to give values of ∆ in good agreement with the theory, with an apparent variation of μ with p , perhaps attributable to roton-roton and phonon-roton interactions.

Thermal wave propagation in single crystals of bismuth at 4 K

1970 ◽  
Vol 48 (10) ◽  
pp. 1200-1207 ◽  
Author(s):  
C. R. Brown ◽  
P. W. Matthews
Keyword(s):  
Thermal Conductivity ◽  
Wave Propagation ◽  
Single Crystals ◽  
Thermal Wave ◽  
Low Temperatures ◽  
Continuous Wave ◽  
Quantitative Agreement ◽  
Signal Frequency ◽  
Second Sound ◽  
Thermal Signal

We present preliminary results from continuous-wave experiments made on two single crystals of bismuth. The object of the experiments was the examination of the initial deviations from diffusive propagation with increasing thermal signal frequency. The thermal conductivity of bismuth is phonon-dominated at low temperatures and has a peak of the type found in good dielectric crystals. However, the observed initial deviations were not in quantitative agreement with results obtained by applying a simple theory of second sound in dielectric crystals.

Investigating the Nonlinear Optical Response of Pepper Oil under Low Power Irradiation with Continuous Wave Visible Laser Beam

2020 ◽  
pp. 131-138
Keyword(s):  
Refractive Index ◽  
Nonlinear Refractive Index ◽  
Nonlinear Optical ◽  
Continuous Wave ◽  
Diffraction Integral ◽  
Visible Laser ◽  
Limiting Property ◽  
Kirchhoff Diffraction Integral ◽  
Theoretical Results ◽  
Good Agreement

The nonlinear optical properties of pepper oil are studied by diffraction ring patterns and Z-scan techniques with continuous wave beam from solid state laser at 473 nm wavelength. The nonlinear refractive index of the sample is calculated by both techniques. The sample show high nonlinear refractive index. Based on Fresnel-Kirchhoff diffraction integral, the far-field intensity distributions of ring patterns have been calculated. It is found that the experimental results are in good agreement with the theoretical results. Also the optical limiting property of pepper oil is reported. The results obtained in this study prove that the pepper oil has applications in nonlinear optical devices.

scholarly journals Sustainable Panels Made with Industrial and Agricultural Waste: Thermal and Environmental Critical Analysis of the Experimental Results

2021 ◽  
Vol 11 (2) ◽  
pp. 494
Author(s):  
Paola Ricciardi ◽  
Elisa Belloni ◽  
Francesca Merli ◽  
Cinzia Buratti
Keyword(s):  
Thermal Conductivity ◽  
Life Cycle ◽  
Rice Husk ◽  
Agricultural Waste ◽  
Embodied Energy ◽  
Waste Materials ◽  
Impact Reduction ◽  
Combined Solution ◽  
Order Of Magnitude ◽  
Recycled Waste

Recycled waste materials obtained from industrial and agricultural processes are becoming promising thermal and acoustic insulating solutions in building applications; their use can play an important role in the environmental impact reduction. The aim of the present paper is the evaluation of the thermal performance of recycled waste panels consisting of cork scraps, rice husk, coffee chaff, and end-life granulated tires, glued in different weight ratios and pressed. Six panels obtained from the mixing of these waste materials were fabricated and analyzed. In particular, the scope is the selection of the best compromise solutions from the thermal and environmental points of view. To this aim, thermal resistances were measured in laboratory and a Life Cycle Assessment (LCA) analysis was carried out for each panel; a cross-comparative examination was performed in order to optimize their properties and find the best panels solutions to be assembled in the future. Life Cycle Analysis was carried out in terms of primary Embodied Energy and Greenhouse Gas Emissions, considering a ‘‘cradle-to-gate” approach. The obtained thermal conductivities varied in the 0.055 to 0.135 W/mK range, in the same order of magnitude of many traditional systems. The best thermal results were obtained for the panels made of granulated cork, rice husk, and coffee chaff in this order. The rubber granulate showed higher values of the thermal conductivity (about 0.15 W/mK); a very interesting combined solution was the panel composed of cork (60%), rice husk (20%), and coffee chaff (20%), with a thermal conductivity of 0.08 W/mK and a Global Warming Potential of only 2.6 kg CO2eq/m2. Considering the Embodied Energy (CED), the best solution is a panel composed of 56% of cork and 44% of coffee chaff (minimum CED and thermal conductivity).

scholarly journals 41Ca Concentrations in Modern Bone and Their Implications for Dating

Radiocarbon ◽  
1989 ◽  
Vol 31 (03) ◽  
pp. 305-310 ◽  
Author(s):  
Roy Middleton ◽  
David Fink ◽  
Jeffrey Klein ◽  
Pankaj Sharma
Keyword(s):  
Mass Spectrometry ◽  
Accelerator Mass Spectrometry ◽  
Isotope Enrichment ◽  
Terrestrial Rock ◽  
Order Of Magnitude ◽  
Cow Bone ◽  
Good Agreement

We have made the first measurements without pre-enrichment of 41Ca in terrestrial rock and bone samples using accelerator mass spectrometry. Although the results in tufa deposits from Egypt are in good agreement with the saturation value of 8×10-15 predicted by Raisbeck and Yiou (1979), the average 41Ca:40Ca ratio of 2×10-15 (range: 0.6 to 4.2×10-15) that we measure in modern bone is an order of magnitude lower than that obtained previously by Henning, et al (1987) on a cow bone that was measured using AMS following isotope enrichment. The low value and the variability (more than a factor of seven) of the 41Ca:40Ca ratio in modern bone make the possibility of dating bones using 41Ca unlikely.

Mapping Thickness Dependent Thermal Conductivity of GaN

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Elbara Ziade ◽  
Jia Yang ◽  
Gordie Brummer ◽  
Denis Nothern ◽  
Theodore Moustaks ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Pump Beam ◽  
Continuous Wave ◽  
High Electron Mobility Transistors ◽  
Heat Diffusion ◽  
Phase Lag ◽  
High Electron ◽  
Heat Diffusion Equation ◽  
Phase Images ◽  
Gan Film

Frequency domain thermoreflectance (FDTR) is used to create quantitative maps of thermal conductivity and thickness for a thinning gallium nitride (GaN) film on silicon carbide (SiC). GaN was grown by molecular beam epitaxy on a 4H-SiC substrate with a gradient in the film thickness found near the edge of the chip. The sample was then coated with a 5 nm nickel adhesion layer and a 85 nm gold transducer layer for the FDTR measurement. A piezo stage raster scans the sample to create phase images at different frequencies. For each pixel, a periodically modulated continuous-wave laser (the red pump beam) is focused to a Gaussian spot, less than 2 um in diameter, to locally heat the sample, while a second beam (the green probe beam) monitors the surface temperature through a proportional change in the reflectivity of gold. The pump beam is modulated simultaneously at six frequencies and the thermal conductivity and thickness of the GaN film are extracted by minimizing the error between the measured probe phase lag at each frequency and an analytical solution to the heat diffusion equation in a multilayer stack of materials. A scanning electron microscope image verifies the thinning GaN. We mark the imaged area with a red box. A schematic of the GaN sample in our measurement system is shown in the top right corner, along with the two fitting properties highlighted with a red box. We show the six phase images and the two obtained property maps: thickness and thermal conductivity of the GaN. Our results indicate a thickness dependent thermal conductivity of GaN, which has implications of thermal management in GaN-based high electron mobility transistors.

Through-Plane Thermal Conductivity of PEMFC Porous Transport Layers

2010 ◽  
Vol 8 (2) ◽  
Author(s):  
Odne S. Burheim ◽  
Jon G. Pharoah ◽  
Hannah Lampert ◽  
Preben J. S. Vie ◽  
Signe Kjelstrup
Keyword(s):  
Thermal Conductivity ◽  
Contact Resistance ◽  
Thermal Contact Resistance ◽  
Thermal Contact ◽  
Residual Water ◽  
Order Of Magnitude ◽  
Thermal Conductivities

We report the through-plane thermal conductivities of the several widely used carbon porous transport layers (PTLs) and their thermal contact resistance to an aluminum polarization plate. We report these values both for wet and dry samples and at different compaction pressures. We show that depending on the type of PTL and the existence of residual water, the thermal conductivity of the materials varies from 0.15 W K−1 m−1 to 1.6 W K−1 m−1, one order of magnitude. This behavior is the same for the contact resistance varying from 0.8 m2 K W−1 to 11×10−4 m2 K W−1. For dry PTLs, the thermal conductivity decreases with increasing polytetrafluorethylene (PTFE) content and increases with residual water. These effects are explained by the behavior of air, water, and PTFE in between the PTL fibers. It is also found that Toray papers of differing thickness exhibit different thermal conductivities.

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