Thermal conductivity peculiarities of an engine cooling system containing multigraphene nanoparticles coolant

Introduction. In order to lower the temperatures of forced advanced diesel engines parts and thus increase their reliability an increase in the intensity of thermal conductivity in their cooling cavities is required. For this purpose heat carriers with an increased coefficient of thermal conductivity were created, which were stable two-phase suspensions based on an aqueous solution of ethylene glycol and solid multigraphene nanoparticles with a high coefficient of thermal conductivity.

The purpose of the study was to numerically and experimentally determine the effect of the increased heat conductivity coefficient of two-phase heat carriers “base fluid – solid nanoparticles of multigraphene” on the heat transfer under operating conditions typical of the engine cooling system operation. These conditions were simulated on an experimental setup with CFD-computer modelling. The increased coefficients of thermal conductivity from the heated wall to the base fluid and to the two-phase coolant were compared under the same test conditions. The increased coefficients of thermal conductivity from the heated wall to the base fluid and to the two-phase coolant were compared under the same test conditions. Methodology and research methods. The temperatures of the liquid and the metal wall of the test section were measured on the experimental setup operating in a stationary heat transfer mode. At the same time, the parameters that occured in the engine cooling systems such as: the heated wall washer circuit, design features of the cooling cavity, artificial turbulization of the fluid flow, etc., – were unchanged. When determining three-dimensional fields of coolant velocities along the length of the tested section, as well as fluid and wall temperatures in at any point of the computational model, a numerical estimate of the heat transfer coefficient for coolants was carried out by computer simulation and by computational fluid dynamics (CFD).

Results. The effect on the heat transfer of the increased coefficient of thermal conductivity of multigraph particles heat carriers has been established. The presence of multigraphene nanoparticles in a suspension having a thermal conductivity coefficient of 0.85 W/m·K led to an increase in heat transfer intensity by 30% compared with the base liquid. The obtained experimental results were processed in similarity numbers, which made it possible to obtain the criterion equation for heat transfer under forced convection and turbulent flow of suspensions “liquid – solid particles”.

Scientific novelty is due to the receipt of new data on heat transfer from a heated wall to two-phase heat carriers “base fluid – solid nanoparticles of multigraphene”, as well as the receipt of a new criterion equation for calculating the heat transfer intensity in the cooling systems of internal combustion engines when using such two-phase heat carriers with an increased thermal conductivity.

The practical significance of the results of the work is to increase the reliability and ensure the operability of promising forced engines by reducing the high temperatures of the parts that surrounded and limited the combustion chamber. Heat transfer intensification in the cooling system will reduce the volume of coolant in the circuit and improve the overall dimensions and heat and power characteristics of the heat exchangers of the system.

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