The thermal analysis has a key role in piston water pump design; in fact, the pumps have to endure long time operation and the lubrication system has to accomplish the task of both reducing the friction between moving components and to transfer the heat produced by the frictions in order to avoid overheating. The lubricating and cooling effects depend on a number of parameters of the lubricating system, such as the amount of oil in the crank case and the material and the geometry of the components; selecting the best configuration for all the pump operating conditions is a challenging objective and needs accurate testing. The numerical approach described in the present work can help the designer to decrease the number of tests as well as to increase the understanding of the basic phenomena involved.
The numerical simulation includes the real geometry of the pump crank case and accounts for the actual operating conditions. Thus, the interaction between fluid and air is taken into account as well as the piston and conrod motions. Moving parts are simulated by combining overset and morphing mesh techniques; while the multi-component multi-phase flow is modelled by means of the VOF approach. Particular care is devoted to the physical properties of oil during the warming up phase and proper temperature dependent functions are introduced to describe the viscosity and the specific heat. Energy dissipation due to friction is estimated on the bases of formulations available in literature. The model simulates the heat transfer between moving metal parts and the fluid during the actual operation. Also the heat transfer between fluid and ambient is calculated, accounting for conduction through the metal crank case walls
Reliability and accuracy of the adopted numerical model is addressed and validated using a numerical vs. experimental comparison. The lubrication system configuration and the crank case geometry can be optimized simulating various working conditions and ambient temperatures. In addition, the number of the experimental tests in the conditioned room can be significantly reduced.