Experimental study of heat transfer of impinging swirling jets and jets with chevrons

The aim of this work is to study the effect of different forms of passive change in the shape of the flow on the intensity of heat transfer in the impact jet. In this work, a cycle of experiments was performed to investigate an axisymmetric jet flowing normally onto a heated surface. The jet was located both in natural conditions and during swirling of the flow (S = 0.4; 0.7; 1.0). It is shown that the intensity of heat transfer on a heated target in the case of a chevrons jet has little effect on the character, but significantly intensifies heat transfer. In the case of a swirling jet, the intensity distribution on the wall changes its character and locally increases at small distances between the nozzle and the heater.

Impact of High Inertia Particles on the Shock Layer and Heat Transfer in a Heterogeneous Supersonic Flow around a Blunt Body

One of the most important and complex effects associated with the presence of particles in the flow is the gas-dynamic interaction of particles with the shock layer. Of particular interest is the intensification of heat transfer by high inertia particles rebounding from the surface or by the products of erosion destruction, which reach the front of the bow shock wave and violate the gas-dynamic structure of the flow. In this case, according to experimental data, the increase in heat fluxes is much greater than it could be predicted based on the combined action of the kinetic energy of particles and a high-speed flow. The problem is related to the destruction of the flow structure. In this paper, the problem is studied with numerical simulation. We show that the key role in the intensification of heat transfer is played by the formation of an impact jet flowing onto the surface. An area of increased pressure and heat flux is formed in the zone of action of the impact jet. This effect is maintained over time by the successive action of particles.

Fabrication and microstructural analysis of 3A21/7075 aluminum alloy cladding material based on impact jet solid–liquid compound casting

To solve thickness problem for high-strength aluminum alloy used as plastic mold materials and eliminate oxide film on the surface of aluminum alloy, a new compound casting, namely impact jet solid–liquid compound casting, was developed to fabricate 3A21/7075 aluminum alloy cladding material. Then, optical microscope (OM), electron-backscattered diffraction (EBSD) technique, and transmission electron microscope (TEM) together with energy-dispersive spectrometer (EDS) were used to analyze microstructure of 3A21/7075 aluminum alloy cladding material. The OM and EBSD results showed that the 3A21/7075 aluminum alloy cladding material was composed of 3A21 cladding layer, fusion zone (FZ), heat-affected zone, and 7075 matrix. The grain morphology on both sides of FZ had great differences. Moreover, the TEM and EDS results showed that the 3A21 cladding layer showed a bulk phase and lots of fine and dispersed granular phases, while the 7075 matrix appeared undetermined strip phases and amounts of fine and dispersed rod-like phases. Moreover, FZ existed a great deal of fine and dispersed granular phases and rod-like phases. The 3A21/7075 aluminum alloy cladding material could effectively solve the problems mentioned above and the in-depth analysis of microstructures of 3A21/7075 aluminum alloy cladding material was of great importance in terms of engineering value and academic significance.

Long-period variability of ocean circulation at different intensity of wind impact

Within the framework of a numerical model of a two-layer ocean with the depth of layers corresponding to average oceanic conditions, the evolution of large-scale circulation under the action of an external vorticity flow of different intensity with constant dissipation parameters is studied. The characteristic time scales of long-period oscillations of current energy at different values of wind impact, jet flow parameters, and the time-average level of total energy in the mode of long-period oscillations at different wind impact intensity are analyzed. The stability of the long-period oscillation regime under various initial conditions of the problem is discussed.

CFD-simulation of impact jet radiator for thermal testing of microprocessors

One of the final stages of microprocessor development is thermal testing. This procedure is performed on a special stand, the main element of which is a switching PCB with mounted microprocessor sockets, chipsets, interfaces, jumpers and other components which provide various modes of microprocessor operation. Changing the case temperature of the microprocessor is carried out typically using a thermoelectric module. The cold surface of the module with controlled temperature is in direct thermal contact with the microprocessor housing designed for cooler installation. On the hot surface of the module, the radiator is mounted which dissipates the total heat flux from the microprocessor and the module. High density PCB layout, the requirement of free access to the jumpers and interfaces, and the presence of numerous sensors restrict the space for radiator mounting and require the use of an extremely compact radiator, especially in air cooling conditions. One of possible solutions for this problem may be to reduce the area of the heat-transfer surfaces of the radiator due to a sharp growth of the heat transfer coefficient without increasing the air flow rate. A sharp growth of heat transfer coefficient of the radiator can be achieved by making several conic or combined conic-cylindrical dead-end cavities with extra finning in the heat-transfer surface. Such cavities should absorb the impact air jets. In this study, CFD simulation of such radiators has been conducted. It is determined that when the air velocity at the nozzle entrances is 50—100 m/s, the investigated designs of impact-jet radiators have a thermal resistance in the range of 0.5—2.2°Ñ/W. This is quite sufficient for the thermal testing of some types of microprocessors with setting a number of operational modes and performing of certain types of test computations. It is shown that the use of combined dead-end cavities with extra finning is the best of the considered solutions and allows for a sharp (up to 44%) intensification of heat transfer in the radiator in comparison with cylindrical dead-end cavities, but at a cost — the loss of air pressure increases up to 20%. As a result of the study, it was found that the impact-jet radiator with dead-end tapering cone shaped cavities and combined cone-cylinder shaped cavities with extra finning, can successfully solve the problem of heat removal from microprocessors during thermal testing. However, it should be noted, that such radiators have a high aerodynamic resistance and require a high pressure air source for operation.

COOLING SYSTEMS FOR BURNERS JET-NICHE TYPE

The results of the study of cooling systems characteristics for jet- niche type burners are presented. The data of a comparative analysis of the efficiency of cooling system with blowing of the inner end surface of the flame stabilizer by a flat impact jet and the system of round impact jets are presented.