On the use of heated needle probes for measuring snow thermal conductivity

Heated needle probes provide the most convenient method to measure snow thermal conductivity. Recent studies have suggested that this method underestimates snow thermal conductivity; however the reasons for this discrepancy have not been elucidated. We show that it originates from the fact that, while the theory behind the method assumes that the measurements reach a logarithmic regime, this regime is not reached within the standard measurement procedure. Using the needle probe without this logarithmic regime leads to thermal conductivity underestimations of tens of percents. Moreover, we show that the poor thermal contact between the probe and the snow due to insertion damages results in a further underestimation. Thus, we encourage the use of fixed needle probes, set up before the snow season and buried under snowfalls, rather than hand-inserted probes. Finally, we propose a method to correct the measurements performed with such fixed needle probes buried in snow. This correction is based on a lookup table, derived specifically for the Hukseflux TP02 needle probe model, frequently used in snow studies. Comparison between corrected measurements and independent estimations of snow thermal conductivity obtained with numerical simulations shows an overall improvement of the needle probe values after application of the correction.

Fractal model of thermal contact conductance of two spherical joint surfaces considering friction coefficient

Purpose The purpose of this study is to propose a fractal model of thermal contact conductance (TCC) of two spherical joint surfaces, considering friction coefficient based on the three-dimensional fractal theory. Design/methodology/approach The effects of friction coefficient, fractal parameters, radius of curvature and contact type on TCC were analyzed using numerical simulation. Findings The results indicate that the TCC decreases with the increase of friction coefficient and fractal roughness and increases with the increase of fractal dimension and radius of curvature; the contact type of two spherical joint surfaces has an important influence on the TCC, and the TCC of external contact is smaller than that of internal contact under the same contact load. Originality/value A fractal model of TCC of two spherical joint surfaces considering friction coefficient is proposed in this paper. Achievements of this work provide some theoretical basis for the research of TCC of bearings and other curved surfaces.

Development, construction and tests of the Mu2e electromagnetic calorimeter mechanical structures

The “muon-to-electron conversion” (Mu2e) experiment at Fermilab will search for the charged lepton flavour violating neutrino-less coherent conversion of a muon into an electron in the field of an aluminum nucleus. The observation of this process would be the unambiguous evidence of the existence of physics beyond the standard model. Mu2e detectors comprise a straw-tracker, an electromagnetic calorimeter and an external veto for cosmic rays. In particular, the calorimeter provides excellent electron identification, a fast calorimetric online trigger, and complementary information to aid pattern recognition and track reconstruction. The detector has been designed as a state-of-the-art crystal calorimeter and employs 1348 pure Cesium Iodide (CsI) crystals readout by UV-extended silicon photosensors and fast front-end and digitization electronics. A design consisting of two identical annular matrices (named “disks”) positioned at the relative distance of 70 cm downstream the aluminum target along the muon beamline satisfies the Mu2e physics requirements. The hostile Mu2e operational conditions, in terms of radiation levels (total expected ionizing dose of 12 krad and a neutron fluence of 5 × 1010 n/cm2 @ 1 MeVeq (Si)/y), magnetic field intensity (1 T) and vacuum level (10−4 Torr) have posed tight constraints on scintillating materials, sensors, electronics and on the design of the detector mechanical structures and material choice. The support structure of each 674 crystal matrix is composed of an aluminum hollow ring and parts made of open-cell vacuum-compatible carbon fiber. The photosensors and front-end electronics for the readout of each crystal are inserted in a machined copper holder and make a unique mechanical unit. The resulting 674 mechanical units are supported by a machined plate of vacuum-compatible plastic material. The plate also integrates the cooling system made of a network of copper lines flowing a low temperature radiation-hard fluid and placed in thermal contact with the copper holders to constitute a low resistance thermal bridge. The data acquisition electronics are hosted in aluminum custom crates positioned on the external lateral surface of the disks. The crates also integrate the electronics cooling system as lines running in parallel to the front-end system. In this paper we report on the calorimeter mechanical structure design, the mechanical and thermal simulations that have determined the design technological choices, and the status of component production, quality assurance tests and plans for assembly at Fermilab.

Influence of boundary conditions on the optimization of a geothermal heat pump studied using a thermodynamic model

This paper is the logical follow-up to a work [1] whose results were presented at the 28th French Thermal Congress which was to be held in Belfort in 2020. The model developed at that time is completed in this proposal to consider the specificity of the geothermal heat pump. This is a machine operating upon a mechanical vapor compression cycle, the limit of which is an inverse Carnot cycle. Its specificity consists of a cold loop at the source with the geothermal exchanger and the evaporator, then a hot loop at the sink with the condenser and a floor heat exchanger in the application considered here. We are particularly concerned with the optimal sizing of these heat exchangers through their effectiveness. The parametric sensitivity of this distribution to various boundary conditions is studied, especially by focusing on different conditions at the source: (1) imposed soil temperature, corresponding to a Dirichlet condition, (2) imposed heat flux (including adiabatic case), corresponding to a Neumann condition, (3) imposed mechanical power consumed by the heat pump, and (4) imposed coefficient of performance COP, to all cases being associated a finite thermal capacity in thermal contact with the geothermal exchanger operating in steady-state conditions.

Spatial distribution prediction of pre-Sinian volcanic and metamorphic rocks in Xinhenan-Sandaoqiao area, Northern Tarim Basin

The main type of oil and gas reservoir in the Xinhenan-Sandaoqiao area is buried hills. The distribution pattern and scale of reservoirs are obviously controlled by pre-Sinian basement strata. However, the lithologic combination and spatial distribution pattern of pre-Sinian basement in this area are still unclear. In this paper, the spatial distribution of pre-Sinian basement volcanic and metamorphic rocks is studied by using the method of multifactor comprehensive analysis. Firstly, the lithology and lithologic combination of igneous and metamorphic rocks are determined according to cores and thin sections. Guided by the seismic reflection characteristics of different lithologic combinations, different lithologic combinations are identified on the profile by combining the seismic reflection characteristics of single well and multiwell. Secondly, using cluster analysis technology, three seismic attributes sensitive to lithology are selected from 10 attributes, crossplots of three seismic attribute values are constructed, and the distribution range of attribute values corresponding to different lithologic combinations is defined for plane lithologic identification. Finally, the plane lithology distribution of the surface layer of pre-Sinian basement is described by combining plane and profile. Six distribution types were identified: deep metamorphic bedrock area in Kuqu depression, dynamic mixed metamorphic rock and intermediate-acidic intrusive rock area, metamorphic bedrock in thrust napple slopes area, thermal contact metamorphic rock area, intermediate-acidic intrusive rock area, dynamic metamorphic rock area and gneiss area in faulted uplift core.

A Rigorous Analysis of Self-Heating Effects in Nanoscale Dielectric Pocket Double-Gate-All-Around (DP-DGAA) MOSFETs

Dielectric Pocket Double-Gate-All-Around (DP-DGAA) MOSFETs are one of the preferred choices for ULSI applications because of significantly low off-current, reduced power dissipation, and high immunity to short channel effect. However, DP-DGAA MOSFETs suffer from self-heating owing to the unavailability of proper heat take-out paths. In this paper, the electrothermal (ET) simulations have been performed with hydrodynamic and thermodynamic transport models to analyze the self-heating effects (SHEs) in DP-DGAA MOSFETs. The electrothermal characteristics against various device parameters such as spacer length, device thickness, thermal contact resistance, and drain voltage have been investigated. The effect of SHE on the drive current has also been evaluated. Further, the impact of thermal contact resistance and ambient temperature variations of the device on SHE and thermal noise have been analyzed using Sentaurus TCAD simulator.

Temperature Profiles During Cryolipolysis

Cryolipolysis is a noninvasive clinical procedure for the local reduction of adipose tissue. Paddles as cold as ~10 °C are placed in good thermal contact the epidermis. The goal is to cool the subcutaneous adipose tissue to ~10 °C, which induces apoptosis and an inflammatory response in the adipocytes. The dermis is, of course, cooler than the adipocytes, but the triglyceride in the adipocytes are thought to crystalize, causing apoptosis. The clinical procedure have been developed empirically. A mathematical model could aid in understanding the mechanisms of response and improving the design of the procedure. Here, the Pennes equation is used to model the temperature of the tissue during cooling. The two parameters identified are the thermal diffusivity of the tissue and a blood perfusion parameter, which also gives the characteristic length. Green's functions are used to solve the Pennes equation, which simplifies to a transient fin equation.

Development of Ti PVD Films to Limit the Carburization of Metal Powders during SPS Process

Spark plasma sintering technique is used for the fabrication of dense materials with a fine-grained microstructure. In this process, a powder is placed into a graphite mold and a uniaxial pressure is applied by two graphite punches. A graphite foil is inserted between the punches and the powder and between the mold and the powder to ensure good electrical, physical and thermal contact. One of the major drawbacks during sintering of metal powders is the carburization of the powder in contact with the graphite foils. In this study, a PVD coating of titanium was applied on the graphite foils in contact with the metal powder (pure iron). The results are promising, as the investigations show that the application of a Ti PVD film of 1.5 and 1.1 µm thickness is effective to completely avoid the carburization of iron powder. Carbon diffuses inside the PVD film during sintering. In parallel, iron diffusion was revealed inside the Ti coating of 1.5 µm thickness. On the other hand, a Ti PVD film of 0.5 µm thickness provides a protection against carbon diffusion just on the sides in contact with the mold, proving that the coating thickness represents an important parameter to consider.