Shaker-based heat and mass transfer in liquid metal cooled engine valves

The highly transient process of the working combustion engine generates a “shaker-effect” inside the hollow valve stem where liquid sodium carries the heat from the hot valve head to the valve stem. Here it can pass through the valve guide, based on convective heat transfer and thermal conduction. The efficiency of these transport mechanisms is still not clearly understood, since the design of many liquid cooled valves is mostly based on empirical knowledge and can lead under certain conditions to a breakdown of the system. A simulation of the processes during the movement of the valve including detailed insight into the highly transient and complex two-phase flow phenomena as well as the heat transfer has been realized by means of direct numerical simulation (DNS) based on the volume-of-fluid (VOF) method. The influence of several relevant influencing factors such as the geometry, the acceleration and the liquid fill level were studied. It was found that the fill level is one of the most influencing factors regarding the efficiency of the heat transfer whereas the influence of geometrical dimensions and in particular the aspect ratio of the cavity were almost negligible in our setup. By averaging the fluid flow and the temperature field it has been shown that liquid cooled valves are more efficient compared to a solid valve but clustering of the liquid filling can appear which causes a temporal breakdown of the “shaker-effect”. In addition the influence of the spatial resolution is shown and 2D vs. 3D simulation setups are compared. To our knowledge, no similar heat transfer predictions of the presented type are published in the literature.