Project and Objectives

The goal is to simulate the operating thermal conditions of a hybrid-architecture earth-moving machine to obtain the correct boundary conditions for sizing a heat exchanger. The heat exchanger, along with other components considered, will be placed in the underhood environment of the machine. Among the other elements are:

• The internal combustion engine, whose operating temperature is known.
• The exhaust gas system, for which the gas flow rate and temperature at the engine outlet are known.
• The battery pack, for which we know the amount of thermal power dissipated by the cells and the flow rate of the cooling fluid passing through it.
• The fan, which will be positioned in front of the radiators and will generate the recirculating airflow within the underhood.

Approach to the analysis

From left to right: detail of the cooling coils of the battery pack, detail of the recirculating fan, detail of the intake and exhaust vents.

By setting the appropriate boundary conditions for the various elements, the simulation results can be observed, for example:

• Flow lines over the entire computational domain
• Directional flow vectors over the entire domain

• Focus on vectors in the underhood environment to identify potential stagnation/turbulence issues
• Density and temperature of exhaust gases

Temperature and flow direction over the entire domain (left) and focus on the underhood environment (right)

Surface solid temperatures of the outer hood (left) and of a battery (right). On the latter, the effect of the internal passage of the cooling fluid can be observed.

Following this general analysis, the focus shifted to one of the three heat exchangers to be designed. The volume around the heat exchangers was isolated, and a detailed analysis was conducted, transferring the flow and temperature boundary conditions from the previous analysis (transferred boundary conditions).

The volume considered in the detailed analysis with the transferred boundary conditions (left) and the internal fluid volume of the heat exchanger in question (right)

Temperatures on the two main planes passing through the heat exchanger.

Thanks to the transfer of boundary conditions, the distribution of air flow velocities and temperatures closely resembles the actual operating conditions, providing confidence that the assumptions made are at least consistent and unlikely to underestimate or overestimate potential problematic phenomena.

The heat exchanger geometry was already known, but the positions of the inlet and outlet ports for the internal fluid were not yet determined. Three different configurations were simulated, and the findings were as follows:

Conclusion

It is clear that configuration no. 3 is the best option, as it minimizes recirculation and stagnation phenomena while providing the best results in terms of heat dissipation. Compared to configuration 1, it ensures an outlet fluid temperature approximately 10°C lower, and 4°C lower than configuration 2.