Numerical studies of the advective flow of heptadecane in a horizontal layer with a longitudinal temperature gradient at the lower boundary

Numerical studies of the convective flow of heptadecane in a horizontal layer with a suddenly applied longitudinal temperature gradient at the lower high-thermal conductivity boundary have been carried out by the finite element method. A system of nonstationary dimensionless equations of free convection containing stream function, velocity vortex, and temperature as variables was solved. The calculations were carried out with a free upper boundary with and without taking into account the influence of the thermocapillary effect.

The dynamics of the formation of a plasma channel after the ignition of a discharge in cesium-mercury-xenon pulsed lamps

The paper deals with the spectral characteristics of the radiation of a pulsed discharge into a cesium – mercury – xenon mixture during the formation of a plasma channel from the moment of ignition until reaching the nominal operating mode of the flash lamp. It is shown that as the electric power of the discharge increases, the spectral emission lines of mercury vapors change their intensity, and the cesium lines self-reversal. It is revealed that the intensity of spectral lines in different regions of the plasma channel differs due to the presence of longitudinal temperature gradients.

Continuous assessment of longitudinal temperature force on ballasted track using rail vibration frequency

In this study, the possibility of using the rail vibration frequency to assess the longitudinal temperature force on the rail of ballasted track was investigated experimentally. An empirical formula was subsequently derived to link the frequency index to multiple factors, including the longitudinal temperature force, under-rail stiffness, and fastener spacing. Further tests were conducted to analyse the applicability and accuracy of the frequency index in continuous longitudinal force measurements under different line conditions (i.e. in the non-expansion zone and expansion zone). A technique for using the frequency index to assess the longitudinal temperature force was finally developed. The main results are as follows. (1) The first-order pinned–pinned modal frequency and peak frequency of the mid-span response are very close, and they both change linearly with the longitudinal temperature force on the rail. The rate of change in the vertical direction is larger than that in the horizontal direction. (2) Even if influenced by multiple factors, the peak frequency of the rail mid-span response is suitable for continuous longitudinal temperature force assessment under appropriate measures, and longitudinal temperature force detection could be realized with proper preparation. (3) Using the mid-span response frequency to detect the temperature force of rail located in the expansion zone causes deviation of the results, and under-rail materials whose stiffnesses are insensitive to temperature help reduce this deviation.

Model tests of fire smoke control effects in highway tunnels

In this work, a typical tunnel 150 m in length is selected and modelled at a scale of 1:15 to assess its effects on smoke control. A total of 32 model tests on smoke flow pattern and longitudinal temperature distribution have been carried out based on the Froude similarity criterion. The results show that smoke control is affected by three factors, namely, the longitudinal airflow velocity, number of opened smoke-exhaust dampers, and fire power, out of which the longitudinal airflow velocity has the greatest effect on smoke control.

A Closed-Form Solution for the Analysis of Antifreeze Disease Fortification Length in a Permafrost Tunnel

Frost damage in permafrost tunnels is very common, and this can have a negative influence on traffic. The most serious frost damage typically occurs at a certain length from the tunnel opening. Thus the antifreeze measures of the lining structure in this area need to be strengthened. In this study, the antifreeze disease fortification length for permafrost tunnels is determined from heat transfer and mathematical physics equations by the theoretical analysis method. The temperature distribution characteristics of the lining along the tunnel axis under the influence of the tunnel depth, the tunnel radius, the wind velocity at the tunnel opening, and the thermal conductivity of the insulation layer are analysed. The results show that the longitudinal temperature characteristics in the tunnel axis are influenced by many factors. The proposed antifreeze disease length of the permafrost tunnel was found to be approximately 31 times of the tunnel diameter, which agrees with the results of the numerical simulation. It verifies the rationality of the theoretical calculation. This value, 31 times of the tunnel diameter, can be used as a reference for the design of the tunnel antifreeze disease fortification length.