Thermogravitational Convective Flow and Energy Transport in an Electronic Cabinet with a Heat-Generating Element and Solid/Porous Finned Heat Sink

Heat transfer enhancement poses a significant challenge for engineers in various practical fields, including energy-efficient buildings, energy systems, and aviation technologies. The present research deals with the energy transport strengthening using the viscous fluid and solid/porous fins. Numerical simulation of natural convective energy transport of viscous fluid in a cooling cavity with a heat-generating element placed in a finned heat sink was performed. The heat-generating element is characterized by constant volumetric heat generation. The Darcy–Brinkman approach was employed for mathematical description of transport processes within the porous fins. The governing equations formulated using the non-primitive variables were solved by the finite difference method of the second-order accuracy. The influence of the fins material, number, and height on the flow structure and heat transfer was also studied. It was found that the mentioned parameters can be considered as control characteristics for heat transfer and fluid flow for the cooling system.

Пути совершенствования системы охлаждения двигателей легковых автомобилей

Пуск автомобильного двигателя сопровождается интенсивным выбросом токсичных газов, особенно углеводородов и моноксидов углерода. Чем ниже температура окружающего воздуха, тем больше при прогреве холодного двигателя выбрасывается в атмосферу этих газов. Для сокращения времени прогрева двигателя после пуска рекомендуется на все автомобили устанавливать предпусковые подогреватели и аккумуляторы тепла. Для более эффективного прогрева двигателя в поддон необходимо установить теплообменник для подогрева масла. Турбокомпрессор должен иметь полость охлаждения корпуса подшипников, насос охлаждающей жидкости двигателя должен быть с электроприводом и с регулируемой частотой вращения. При предпусковом прогреве двигателя подогревателем этот насос при неработающем двигателе будет прокачивать горячую жидкость из теплообменника подогревателя через полость охлаждения двигателя, теплообменник масла в поддоне, полость охлаждения в корпусе подшипников турбокомпрессора. Горячие газы из камеры сгорания подогревателя необходимо использовать для подогрева нейтрализатора отработавших газов. Аккумулятор тепла целесообразно использовать в случае работы автомобиля с периодическими остановками, например, в режиме такси или при перевозке грузов. В этом случае перед пуском двигателя насос за несколько секунд перекачает горячую жидкость из аккумулятора в перечисленные выше полости и сократит время прогрева двигателя после пуска. Эти мероприятия позволят существенно сократить выбросы в атмосферу токсичных газов и повысить надёжность двигателей.Starting of an automobile engine is accompanied by an intense release of toxic gases especially hydrocarbons and carbon monoxides. The lower the environment temperature the more these gases are emitted when the cold engine warms up. To reduce the engine warm-up time after starting it is recommended to install preproduction heater and heat accumulators on all vehicles. For more efficient warming up of the engine it is necessary to install a heat exchanger in the oil pan to heat the oil. The turbocharger must have a cooling cavity for the bearing block, the engine coolant pump must have an electric driver and with an adjustable speed. When the engine is preheated by the heater, this pump when the engine is off will pump hot liquid from the heater heat exchanger through the engine cooling cavity, the oil heat exchanger in the pan and the cooling cavity in the turbocharger bearing block. Hot gases from the combustion chamber of the heater must be used to heat the exhaust gases catalyst. It is advisable to use the heat accumulator in case of operation of the vehicle with periodic stoppings for example in taxi mode or during transport of goods. In this case before starting the engine in a few seconds the pump pumps hot liquid from the accumulator into the cavities listed above and reduces the time of warming up the engine after starting. These measures will significantly reduce the emission of toxic gases into the atmosphere and increase the reliability of engines.

Thermal load analysis and control of four-stroke high speed diesel engine

Aiming at the thermal load problem of the four-stroke high-speed diesel engine piston, a piston thermal fluid-solid coupling model based on the combustion thermal boundary and the two-phase flow oscillation cooling thermal boundary is established. The model considers the problem that the piston can?t fill the cooling cavity due to the reciprocating motion. The effects of different engine speeds and the injection speed on the filling rate are studied. The variation curves of the filling rate of the oil in the cooling cavity are simulated, and the transient heat transfer coefficient and temperature of each crank angle are obtained. The average value is then analyzed by heat flow-solid coupling, and the influence of the filling rate of the piston cavity on the temperature field of the piston is obtained. Through the comparison of the experimental results of the hardness plug measurement method, the calculation of the model is accurate and can be well used for the simulation of the piston temperature field and the evaluation of the thermal load at the critical position. Based on this model, the regularity analysis of the influencing factors of the piston thermal load is carried out. The influencing factors include the filling rate of the cavity, the air-fuel ratio, the injection timing, etc., and finally the engine operating range that meets the heat load requirements is obtained.

REDUCING TEMPERATURE OF CYLINDER LINER DUE TO APPLICATION OF HEAT CARRIER WITH HIGH-CONDUCTIVE MULTIGRAPHENE NANOPARTICLES

The paper considers one of the promising ways to influence the heat transfer in the cooling system of a cylinder-piston group, which is to improve physical properties of coolants. It has been stated that the development of nanotechnology has recently made it possible to significantly increase the thermal conductivity coefficient of base coolant - an aqueous solution of ethylene glycol due to its modification by high-conductive solid multigraphene nanoparticles. The resulting stable two-phase suspensions based on the base coolant and particles of the solid phase are called nanofluids. To evaluate the increase in heat transfer at the “wall-coolant” boundary and the decrease of temperature of this wall when applying nanofluid in the engine cooling system as compared to the base fluid, an experimental setup was developed for simulating the flow of coolant in the annular channel of the cooling cavity of the cylinder liner and the conditions determining the heat transfer in its cooling cavity. As a result of conducting a series of experiments under similar test conditions, a significant increase in the heat transfer coefficient was found at the boundary of the “liner wall-liquid” due to the use of nanofluids with highly heat-conducting multigraphene nanoparticles compared to the base fluid. This led to a decrease in the temperature of the cylinder liner. Reducing the temperature of the heat-loaded engine parts allows to increase the reliability of the promising and forced diesel engines, to increase the degree of boosting at the average effective pressure while maintaining the permissible temperature level of the parts of the cylinder-piston group. Intensification of heat transfer at the “wall-liquid” interface contributes to an increase in the thermal efficiency of various heat exchangers as part of an internal combustion engine associated with the main circuit of the cooling system.

Heat Transfer and Friction Studies in a Tilted and Rib-Roughened Trailing-Edge Cooling Cavity With and Without the Trailing-Edge Cooling Holes

Local and average heat transfer coefficients and friction factors were measured in a test section simulating the trailing edge cooling cavity of a turbine airfoil. The test rig with a trapezoidal cross sectional area was rib-roughened on two opposite sides of the trapezoid (airfoil pressure and suction sides) with tapered ribs to conform to the cooling cavity shape and had a 22-degree tilt in the flow direction upstream of the ribs that affected the heat transfer coefficients on the two rib-roughened surfaces. The radial cooling flow traveled from the airfoil root to the tip while exiting through 22 cooling holes along the airfoil trailing edge. Two rib geometries, with and without the presence of the trailing-edge cooling holes, were examined. The numerical model contained the entire trailing-edge channel, ribs and trailing-edge cooling holes to simulate exactly the tested geometry. A pressure-correction based, multi-block, multi-grid, unstructured/adaptive commercial software was used in this investigation. Realizable k–ε turbulence model in conjunction with enhanced wall treatment approach for the near wall regions, was used for turbulence closure. The applied thermal boundary conditions to the CFD models matched the test boundary conditions. Comparisons are made between the experimental and numerical results.

Heat Transfer and Friction Studies in a Tilted and Rib-Roughened Trailing-Edge Cooling Cavity with and without the Trailing-Edge Cooling Holes

Local and average heat transfer coefficients and friction factors were measured in a test section simulating the trailing-edge cooling cavity of a turbine airfoil. The test rig with a trapezoidal cross-sectional area was rib-roughened on two opposite sides of the trapezoid (airfoil pressure and suction sides) with tapered ribs to conform to the cooling cavity shape and had a 22-degree tilt in the flow direction upstream of the ribs that affected the heat transfer coefficients on the two rib-roughened surfaces. The radial cooling flow traveled from the airfoil root to the tip while exiting through 22 cooling holes along the airfoil trailing-edge. Two rib geometries, with and without the presence of the trailing-edge cooling holes, were examined. The numerical model contained the entire trailing-edge channel, ribs, and trailing-edge cooling holes to simulate exactly the tested geometry. A pressure-correction based, multiblock, multigrid, unstructured/adaptive commercial software was used in this investigation. Realizablek-εturbulence model in conjunction with enhanced wall treatment approach for the near wall regions was used for turbulence closure. The applied thermal boundary conditions to the CFD models matched the test boundary conditions. Comparisons are made between the experimental and numerical results.