The paper presents
results on heat transfer from a cylinder in pulsating flow. The results are
local heat transfer distributions that match four different flow modes identified
previously by the authors. A new kind of dimensionless number was introduced
for pulsating flows: this is a ratio of flow acceleration during unsteady
movement to the centrifugal acceleration due to streamlines bending over the
cylinder. The experimental data were generalized as a dependency of the average
heat transfer on the new dimensionless criterion. The generalization offered a
correction factor to a traditional relation for heat transfer between a
cylinder and air flow past the cylinder; this correction takes into account the
effect of parameters of forced flow pulsations on the average heat transfer.
The results of numerical computations of a free laminar convection and heat transfer between two parallel isothermal plates in the presence of a single rib on the channel surface are presented. The investigations have been conducted for a channel with the aspect ratio AR = L/w = 10, where L is the channel height, and w is the distance between the plates. An infinitely thin adiabatic rib was located on one of the channel walls in the middle of its height. The relative rib height l/w was varied in the range 0¸0.8. The wall temperature was higher than the ambient temperature, and the Rayleigh number was varied in the range Ra = 102¸105. The main attention has been
paid to the study of the influence of the rib height and the Rayleigh number on
local and integral heat transfer and the Reynolds number in the channel (the
convective thrust). A fundamental difference in the heat transfer over the
channel height has been shown on the ribbed wall and on a smooth surface. The
computational results have been compared with the case of a symmetric distribution
of the ribs on the both walls with the integral height equal to a single rib.
The paper presents the results of experimental study for hydrodynamic processes occurring during combustion of a stoichiometric mixture propane-oxygen in combustion chambers with different configurations and submerged into water. The pulses of force acting upon a thrust wall were measured for different geometries: cylindrical, conic, hemi-spherical, including the case of gas combustion near a flat thrust wall. After a single charge of stoichiometric mixture propane-oxygen is burnt near the thrust wall, the process of cyclic generation of force pulses develops. The first pulse is generated due to pressure growth during gas combustion, and the following pulses are the result of hydrodynamic pulsations of the gaseous cavity. Experiments demonstrated that efficient generation of thrust occurs if all bubble pulsations are used during combustion of a single gas combustion. In the series of experiments, the specific impulse on the thrust wall was in the range 104-105 s (105-106 m/s) with account for positive and negative components of impulse.
Characteristics of
gas-phase ignition of grinded brown coal (brand 2B, Shive-Ovoos deposit in
Mongolia) layer by single and several metal particles heated to a high
temperature (above 1000 K) have been investigated numerically. The developed
mathematical model of the process takes into account the heating and thermal decomposition
of coal at the expense of the heat supplied from local heat sources, release of
volatiles, formation and heating of gas mixture and its ignition. The
conditions of the joint effect of several hot particles on the main
characteristic of the process – ignition delay
time are determined. The relation of the ignition zone position in the vicinity
of local heat sources and the intensity of combustible gas mixture warming has
been elucidated. It has been found that when the distance between neighboring
particles exceeds 1.5 hot particle size, an analysis of characteristics and
regularities of coal ignition by several local heat sources can be carried out within the framework of the model of
“single metal particle / grinded coal / air”. Besides, it has been shown with
the use of this model that the increase in the hot particle height leads, along
with the ignition delay time reduction, to a reduction of the source initial
temperatures required for solid fuel ignition. At an imperfect thermal
contact at the interface hot particle / grinded coal due to the natural porosity
of the solid fuel structure, the intensity of ignition reduces due to a less
significant effect of radiation in the area of pores on the heat transfer
conditions compared to heat transfer by conduction in the near-surface coal
layer without regard to its heterogeneous structure.
Kinetic calculations
of the plasma processing/utilization process of organic waste in air and steam
ambient were carried out. It is shown that, during the time of waste residence
in the plasma reactor, 0.7 and 1.2 s, at the exit from the reactor there
forms a high-calorific fuel gas with a combustion heat of 3540 and
5070 kcal/kg, respectively. In this process, 1 kg of waste yields 1.16 kg of fuel gas at air
gasification of waste and 0.87
kg of pure synthesis gas at steam gasification. The energy efficiency of the waste gasification
process, defined by the ratio between the calorific value of the resultant fuel
gas and the initial calorific value of the waste amounts to 91 % in
air plasma and 98 % in steam plasma. A comparison between the results of
kinetic and thermodynamic calculations has revealed their good agreement.
Thermodynamic analysis of
plasma gasification of various renewable carbon-bearing materials was carried
out using various oxygen-containing oxidants (oxygen, air, water). The
possibility of obtaining calorific synthesis gas suitable for the needs of heat
power engineering was confirmed.
Structure of ceramics obtained by the plasma spray deposition of spherical TiO2
powders has been investigated. An electron microscopy study of the surfaces and cross sections of particles in the initial powder and of the deposited ceramic coatings was performed. X-ray diffraction and Raman scattering data proved that the coatings were mainly structured as rutile. In addition, Raman and X-ray diffraction data have revealed an amorphous phase, an anatase phase, and non-stoichiometric phases Ti8O15, Ti10O19, Ti7O13, etc.
being present in the coatings. The observed suppression of (011) and (111) XRD peaks and an
increased intensity of (110) peak are indicative of a predominant orientation
of grains in the synthesized ceramics. Mechanisms of formation of the complex
coating structure are discussed.
In the present paper, we report on experimental and simulated data on the impact of cellular-porous-material heating on the wave drag of a cylinder with a frontal gas-permeable porous insert streamlined by a supersonic flow (М∞ = 4.85, Re1∞ = 3.3×106
m-1). Weighing data obtained in the supersonic wind tunnel are
compared with data simulated using a discrete model of the cellular-porous
material. An increase of the wave drag with a growth of porous-insert
temperature and its decrease occurring upon decreasing the temperature are
demonstrated.
The
technology of electricity production by a mini-thermal power plant, operating
on combined cycles of Otto and Rankine, is considered. The main aspects of the
investigation methodology are outlined. It is shown that the design and layout
parameters of all the major energy elements of the developed technology allow
implementing it in a block and modular version; and the efficiency of
electricity supply for the proposed technology will be at least 50 %.
