scholarly journals Study on The Influence of Negative Temperature Gradient of U-shaped Girder of Rail Transit in Winter

2020 ◽  
Vol 1549 ◽  
pp. 042121
Author(s):  
Xu Dong ◽  
Guofu Sun ◽  
Gangnian Xu
Keyword(s):  
Temperature Gradient ◽  
Negative Temperature ◽  
Rail Transit

scholarly journals Experimental analysis of gradient of negative temperature for polypropylene fiber concrete U-shaped girder

2020 ◽  
Vol 319 ◽  
pp. 06004
Author(s):  
Xu Dong ◽  
Fengkun Cui ◽  
Xiudong Li ◽  
Songji Xu
Keyword(s):  
Temperature Gradient ◽  
Negative Temperature ◽  
Rail Transit ◽  
Vertical Temperature Gradient ◽  
Vertical Temperature ◽  
Gradient Model ◽  
Transverse Temperature ◽  
Bottom Slab ◽  
Gradient Models ◽  
The Web

To study the negative temperature gradient models of a rail transit U-shaped girder during the winter season, a U-shaped rail transit girder was researched in Qingdao. The temperature field of the midspan section was observed for a 48-h period during the winter. The maximum vertical and horizontal temperature difference distributions were obtained, and the negative temperature gradient models for the winter were established. The results show that the vertical temperature gradient models of the web and bottom slab should be considered. The vertical temperature gradient model of the web is a piecewise function composed of exponential and linear functions. The vertical temperature gradient model of the bottom slab is an exponential function. The transverse temperature gradient of the web is obvious, whereas the transverse temperature gradient of the bottom slab is slight.

scholarly journals Metamorphism and thermal properties of fresh snow (study in the Moscow region)

2016 ◽  
Vol 56 (2) ◽  
pp. 199-206 ◽  
Author(s):  
R. A. Chernov
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Temperature Gradient ◽  
Negative Temperature ◽  
Average Temperature ◽  
The North ◽  
Coefficient Of Thermal Conductivity ◽  
European Part Of Russia ◽  
Snow Conditions

As a result of laboratory tests were obtained values of the coefficient thermal conductivity (Keff) of new snow for different types of the solid precipitation: plates, needles, stellars, graupels. Snow samples were collected during a snowfall and placed in the freezer. For all types of sediment thermal conductivity of snow is equal to 0.03–0.04 W/m·°C. Transformation of new snow occurs within 10 days at average temperature −10 °C and the gradient temperature of 50–60 °C/m. Under these conditions, the metamorphism leads to an increase the density of snow, size of grains and rounded snow particles. At the beginning of the experiment, the thermal conductivity of snow is linearly increased in proportion to the density of the snow. However, after 3–5 days Keff stabilized at about 0.08–0.09 W/m·°C, although the density of the snow and size of grains continued to increase. This effect occurs with the appearance of faceted crystals and loosening of snow. In the future, while maintaining a negative temperature coefficient of thermal conductivity remained unchanged. Thus, the temperature gradient metamorphism affect to the thermal conductivity snow, which plays an important role in maintaining the thermal insulation properties of snow cover. The article describes the formula to calculate the thermal conductivity of the snow conditions in the temperature gradient metamorphism. Such conditions are characteristic of the vast expanses of the north and northeast of the European part of Russia. On the basis of long-term observations in Moscow shows the average minimum and maximum values for the density of the snow woods and fields on the basis of which can be calculated for the thermal properties of the snow.

scholarly journals A Study on Plume Dispersion Characteristics of Two Discrete Plume Stacks for Negative Temperature Gradient Conditions

2021 ◽  
Author(s):  
Hrishikesh Sivanandan ◽  
V. Ratna Kishore ◽  
Mukesh Goel ◽  
Abhishek Asthana
Keyword(s):  
Temperature Gradient ◽  
Vertical Direction ◽  
Negative Temperature ◽  
Atmospheric Temperature ◽  
Plume Dispersion ◽  
Dispersion Characteristics ◽  
Flow Solver ◽  
Lower Temperature ◽  
Two Temperature ◽  
Equal Height

AbstractThe dispersion of air pollutants emitted from industries has been studied ever since the dawn of industrialisation. The present work focuses on investigating the effect of negative atmospheric temperature gradient and the plume stack orientation of two individual equal-height stacks on the vertical rise and dispersion of the plume. The study carried out upon three-stack layout configurations namely inline, 45° and non-inline, separated by an inter-stack distance of 12 times the exit chimney diameter (12 D) and 22 times the exit chimney diameter (22 D) in each case over the two temperature gradients of −0.2 K/100 m and −0.5 K/100 m. The turbulence is modelled using realisable k-ε model, a model used in the FLUENT flow solver. In the case of the inline configuration, the upwind plume shields its downwind counterpart, which in turn allows for higher plume rise at a given temperature gradient. The plume oscillates more in the case of inline than 45° and non-inline cases. Also, for a temperature gradient of −0.5 K/100 m, the plumes oscillate violently in the vertical direction, mainly because, with the initial rise of the plume, cold air from higher altitudes moves down and forms a layer of lower temperature closer to the ground. The present study is important to highlight the plume dispersion characteristics under negative temperature gradient conditions.

Stability of Flow Between Arbitrarily Spaced Concentric Cylindrical Surfaces Including the Effect of a Radial Temperature Gradient

1964 ◽  
Vol 31 (4) ◽  
pp. 585-593 ◽  
Author(s):  
J. Walowit ◽  
S. Tsao ◽  
R. C. DiPrima
Keyword(s):  
Temperature Gradient ◽  
Couette Flow ◽  
Simple Formula ◽  
Negative Temperature ◽  
Radial Temperature Gradient ◽  
Radial Temperature ◽  
Simple Set ◽  
Wide Range ◽  
The Stability ◽  
The Galerkin Method

The stability of Couette flow and flow due to an azimuthal pressure gradient between arbitrarily spaced concentric cylindrical surfaces is investigated. The stability problems are solved by using the Galerkin method in conjunction with a simple set of polynomial expansion functions. Results are given for a wide range of spacings. For Couette flow, in the case that the cylinders rotate in the same direction, a simple formula for predicting the critical speed is derived. The effect of a radial temperature gradient on the stability of Couette flow is also considered. It is found that positive and negative temperature gradients are destabilizing and stabilizing, respectively.

scholarly journals Gradient Metamorphism, Zonal Weakening of the Snow-pack and Avalanche Initiation

1977 ◽  
Vol 19 (81) ◽  
pp. 335-342 ◽  
Author(s):  
C. C. Bradley ◽  
R. L. Brown ◽  
T. R. Williams
Keyword(s):  
Temperature Gradient ◽  
National Park ◽  
Local Maximum ◽  
Negative Temperature ◽  
Field Investigation ◽  
Snow Pack ◽  
Fine Grained ◽  
Material Stiffness ◽  
Euhedral Crystal ◽  
Original Strength

AbstractA co-ordinated study involving both a field investigation in Yellowstone National Park and a laboratory investigation was undertaken to evaluate the process of temperature-gradient metamorphism on the mechanical properties of snow. Both parts of the investigation showed that, when subjected to a negative temperature gradient, low-to-medium density snow metamorphoses first into a fine-grained anhedral depth hoar before finally acquiring a fully developed, and stronger, euhedral crystal structure. Measurements indicated that the subhedral snow was the weakest stage in the metamorphic process and that, while strength may drop to as low as 10% of the original strength, the material stiffness decreased by less than 50% Also, it was observed that the location of weakest snow was usually the point of a local maximum density and largest temperature gradient, thus suggesting a relationship between metamorphic state and thermal conductivity.

Formation and propagation of a shock wave in a gas with temperature gradients

2002 ◽  
Vol 473 ◽  
pp. 245-264 ◽  
Author(s):  
V. S. SOUKHOMLINOV ◽  
V. Y. KOLOSOV ◽  
V. A. SHEVEREV ◽  
M. V. ÖTÜGEN
Keyword(s):  
Shock Wave ◽  
Temperature Gradient ◽  
Numerical Solutions ◽  
Weak Shock ◽  
Negative Temperature ◽  
Temperature Gradients ◽  
Initial Disturbance ◽  
Weak Shock Wave ◽  
Axial Distance ◽  
Uniform Medium

A theoretical analysis was carried out to study the formation and propagation of a weak shock wave in a gas with longitudinal temperature gradients. An equation describing the formation and propagation of a weak shock wave through a non-uniform medium in the absence of energy dissipation was derived. An approximate analytical solution to the one-dimensional wave propagation equation is established. With this, the thermal gradient effects on the shock-wave Mach number and speed were investigated and the results were compared to earlier experiments. Numerical solutions for the same problem using Euler’s equations have also been obtained and compared to the analytical results. The analysis shows that the time of shock-wave formation from the initial disturbance, for mild temperature gradients, is independent of the gradient. The shock wave forms at a longer axial distance from the initial disturbance when the temperature gradient is positive whereas the opposite is true for a negative temperature gradient.

scholarly journals Measurement of sickling by controlled temperature increase

Blood ◽  
1978 ◽  
Vol 52 (6) ◽  
pp. 1189-1195 ◽  
Author(s):  
H Chang ◽  
RL Nagel
Keyword(s):  
Temperature Gradient ◽  
Negative Temperature Coefficient ◽  
Gradual Increase ◽  
Negative Temperature ◽  
Red Cell ◽  
Half Time ◽  
Linear Temperature ◽  
Linear Temperature Gradient ◽  
Alternative Approach ◽  
A Cell

Abstract Previous experiments to study the rate of red cell sickling have employed rapid mixing apparatus for SS cells with dithionite and have shown that the half-time of sickling is quite rapid, on the order of seconds. An alternative approach is to slow down the rate by taking advantage of the negative temperature coefficient of the process. We developed a method in which deoxygenation of a cell suspension is carried out at 0 degrees C. A linear temperature gradient to 37 degrees C is applied, and a gradual increase in the percentage of sickled cells is observed. At a heating rate of 1.5 degrees C/min the temperature at which half of the cells became sickled was 19 degrees C for SS cells treated with dithionite, 22 degrees C for SC cells, 28 degrees C for AS cells, 22 degrees C for cyanate-treated SS cells, and 23 degrees C for SS cells in the presence of 0.1 M butylurea. Thus this method promises to be useful for the study of sickling rates and the screening of potential anti-sickling agents.

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