Application107 Condensation on Windshield

Femtet ver.2023 allows the diffusion analysis with weight of materials taken into account.
The temperature distribution in the area near the windshield is calculated in the fluid-thermal analysis and the distribution of the amount of water vapor in the area is calculated in the diffusion analysis.
The [User-Defined Field] dialog box on the result tab allows the calculation of relative humidity from those distributions, yielding the calculation result. The relative humidity of more than 100% can possibly cause condensation.

Analysis Model
The analysis object is a car.
The ambient temperature is 0℃. Inside the car, the initial temperature is 5℃ and the initial relative humidity is 50%. The airflow from the defroster has a temperature of 30℃ and a relative humidity of 30%.
The timestep is 5 sec and the total calculation time is 120 sec.

The area near the windshield initially has a relative humidity of more than 100%, resulting in condensation.
After the airflow from the defroster increases the temperature in the area near the windshield and sends dry air therein, it is observed that the relative humidity goes under 100% and the condensation is eliminated.