Entropy production characteristics through n-heptane evaporation in low Reynolds number incoming air flow

The main component of vehicle internal combustion engine and aircraft engine fuel is n-heptane. Combustion of liquid fuel belongs to diffusive combustion. The combustion process is composed of atomization, evaporation and diffusive combustion, and the evaporation process is vitally important, which critically determines the combustion speed of fuel droplet. Hence it is essential to optimize this process. In this paper, the evaporation of n-heptane droplet was evaluated from the perspective of second law of thermodynamics. A two-dimensional quasi-steady state model of the evaporation process was proposed, and the entropy production of the process was solved by integration of the volumetric entropy production rate in the whole domain. The viscous, conductive, mass transfer entropy production was investigated and compared, with the help of viscous and conductive entropy production rate equations reported in literatures and mass transfer entropy production rate equation derived in this paper, after numerical simulation of the evaporation process with Fluent software. Also, the relative total entropy production was defined. Conductive entropy production was the main part of the total entropy production of n-heptane evaporation in the low-Re air flow. With increasing Re and temperature of airflow, relative total entropy production decreased. In other words, the evaporation process produced less entropy relatively and it became easier, which from a thermodynamics perspective was optimal.