Intensity Of Heat Removal Research Articles

Structural changes in a railway wheel rim during operation

The structural changes in the near-surface layers of a railway wheel rim are studied during operation in rolling stock. The standard operating conditions of rail transport are shown to be characterized by alternating impact loading; regular braking; and, hence, periods of rapid heating of the surface layers in wheels that are replaced by intense heat removal after the end of braking of rolling stock. In this case, the heating of wheels is sufficient for the beginning of phase transformations, which result in softening, embrittlement, and strain aging of the near-surface layer metal.

On continuous casting of steels using pulse-periodic cooling in a mold

The causes of the difficulties that appear during continuous casting of steels with a wide solidification range are analyzed. It is shown that these difficulties can be overcome using a mold design that provides a pulse-periodic change in the intensity of heat removal from the mold tube walls.

Heat transfer in a closed cavity under conditions of forced vibrational convection

Heat transfer in an enclosure under conditions of forced convection induced by a body (activator) vibrating inside the enclosure is studied numerically. A thermal problem is considered for a vibrational Lewis cell modeling the mass transfer near the interface between two fluids, on which a chemical reaction occurs. The heat transfer is studied as a function of the vibrational-flow velocity and the Prandtl number: the vibrational flows ensure not only intense heat removal from the boundary but also homogeneous mixing of the fluid in the cavity. The dependence of the heat transfer on the vibrational-flow velocity (the Reynolds number based on the average-flow velocity) and on the Prandtl number is constructed.

Considerable rise in the stability of combined superconductors doped by intermetallic compounds with an extremely high low-temperature specific heat

The influence of doping intermetallics based on rare-earth elements and ceramics with an extremely high low-temperature specific heat on the stability of combined NbTi superconductors against electromagnetic disturbances is studied experimentally and theoretically. The objects of investigation are standard NbTi conductors (0.85 mm in diameter) in a copper matrix that are soldered to copper wires containing high-specific-heat dopants. CeCu6, HoCu2, CeAl2, and PrB6 intermetallics (at 4.2 K, their specific heat is on average 150 times that of copper) or Cd2O2S ceramics (at 4.2 K, its specific heat is higher than that of copper by 600 times) are introduced into combined superconductor samples in the form of fine powder. The powder is placed into the copper wire either as one thick (0.6 mm in diameter) strand or as 19 thin (0.1 mm in diameter) strands. An undoped reference sample contains a solid conductor. Samples with a transport current placed in an external transverse magnetic field are subjected to longitudinal magnetic disturbances causing pulsed heating of the samples by eddy currents. The disturbance time is varied in a wide range: from 50 μs to 1.2 ms. To compare the critical energy densities of the disturbances in differently shaped samples, a mathematical technique is developed that is based on analytical solution of the equation of electromagnetic diffusion into the sample. It is found that the critical energy density of doped samples is much higher (by several times) than that of the reference sample. Upon direct cooling of the samples by liquid helium in a vertical channel (the most intense heat removal under steady-state conditions), the effect of stability improvement for the doped samples persists. Moreover, it is shown that the high-specific-heat dopants, raising the heat needed to warm the sample, restrict the heat flux into the liquid and thereby increase the energy removed by the coolant during unsteady heat transfer.

Modeling of Energy Transfer during Combustion of Low-Gas Thermal Compositions in Systems with Intensive Heat Removal

Modeling of Energy Transfer during Combustion of Low-Gas Thermal Compositions in Systems with Intensive Heat Removal

Dynamics of Laser-Induced Phase Transitions in Cadmium Telluride

A numerical simulation of the dynamics of phase transitions induced by nanosecond pulsed radiation from a ruby laser in CdTe has been carried out. It is shown that evaporation of Cd atoms results in cooling of the surface; consequently, a nonmonotonic profile of the temperature field is formed, with the maximum temperature being attained in the bulk of the semiconductor at a distance of about 10–30 nm from the surface. At radiation energy densities above the threshold, the molten state formed under the surface extends both to the surface and into the depth of the semiconductor. Crystallization also proceeds in two directions, namely, from the surface into the depth of the samples due to the growth of nucleation centers in the melt, which is highly depleted in Cd atoms under the conditions of intense heat removal, and from the substrate to the surface due to epitaxial growth.

Possibility, Admissibility, and Desirability of Implementing Pulsed Stochastic Regimes in Reactors with Gaseous Nuclear Fuel

Schemes are proposed for reactors with stationary gaseous fuel and the conditions under which new self-excited oscillatory regimes can be obtained in such reactors are determined. For the schemes proposed for block reactors there is no limit on size and power. An example of a reactor with 200-m core is examined. It is indicated that the fuel oscillations accompanying the neutron pulses can be used to convert nuclear energy directly into mechanical energy or electricity. It is shown that the amplitude of the oscillations can be regulated by changing the intensity of heat removal or by changing the friction in individual sections of the reactor in a manner so that the amplitude does not exceed the admissable limits. The results are obtained by studying distributed models of the reactor numerically.

Origination of Reaction Sites in the Front of Gasless Combustion under the Action of Heat Losses

A numerical study of combustion of a gasless mixture in a narrow cylindrical channel showed that conditions of intense heat removal involve waves passing on the reaction‐front surface, which “bring” the influence of heat losses to deep layers of the filler and, reflecting from the axis, lead to formation of reaction sites near the shell.

Heat transfer characteristics in flow around a spherically blunted cone at incidence and gas injection from a blunted surface

New methods of controlling thermal regimes in a high-enthalpy spatial flow around a body are considered. They are related to gas injection from the blunted surface and heat overflow in the material of the shell. The effect of injection is analyzed for different thermal conductivities. It is shown that highly heat-conducting materials can be successfully used to decrease the maximum temperatures at the windward side due to intense heat removal to the region of a porous spherical bluntness.

A Markovian intensities approach for predicting the behaviour of non-isothermal chemical reactors

The Markovian intensities approach proposed by Gutsche and Hartmann (1995) for predicting the dynamic as well as the steady-state behaviour of chemical reactors is expanded to the non-isothermal case. In comparison with the isothermal case three additional activities are required. The first activity is the derivation of a runaway criterion based on the ratio of the overall Markovian intensity of heat generation to the overall intensity of heat removal. The new criterion is more general than formerly developed ones because it comprises all single mass and heat transport processes occuring within the reactor. Secondly, the intensity ratio is utilized to estimate a characteristic temperature approximating the actual temperature rise in the non-isothermal reactor. This temperature rise is taken in the final activity to predict the dynamic and steady-state behaviour under nonisothermal conditions. A number of simulations demonstrate that the new procedure is applicable to complex non-isothermal catalytic reactors.

Numerical investigation of quenching of the state of a material in a wave of SHS during a two-step reaction

The quenching of a SHS sample under conditions of intense heat removal from the outer surface was investigated numerically. A two-step reaction was considered. The reaction proceeds in the reginmes of blending, control, and takeoff. It was established that in the control and takeoff regimes a significant amount of an intermediate phase is fixed during quenching. In the blending regime the relative fraction of the intermediate product in the quenched sample is small. It is shown that the method of quenching with an impacting water jet can be used to investigate phase-and structure-formation processes during SHS.

Effect of secondary heating during hardening on the strength of alloy D16 sheet

Secondary heating during hardening is an increase in temperature of the cooled part of an article due to transfer of heat from a hotter part as a result of termination or a sharp reduction in the intensity of heat removal during cooling. Experiments were performed for hardening of sheet specimens of alloy D16. The original alloy was cold-hardened with a degree of deformation of 60% Results are discussed.

Thermodynamics of high-speed cooling of aluminum granules

A study has been made, by solving a thermal problem, of the temperature fields and heat flows in solidifying aluminum granules and also of their cooling rates and crystallization dynamics as functions of particle size at constant heat removal intensities and at intensities varying with time. Criteria of optimum metal granule solidification have been introduced, with the aid of which suitable thermal conditions of granule solidification have been determined enabling a type of cooling to be chosen ensuring an optimum structure in cast granules. Thermal stresses have been investigated on the assumption of granules being isotropic elastic solids. Their existence has been confirmed by the character of the dislocation structure forming in metal granules under various cooling conditions. The time dependence of the intensity of heat removal resulting in minimum thermal stresses has been established. Practical recommendations are given for the cooling of aluminum granules during their manufacture.