# 6.2 Long-time: exercise (example)

Course subject(s) 6. Unsteady conduction and diffusion

If you like steak, you know exactly how you like your steak: rare, well done, or somewhere in between.
Leaving the debate of which one is the best aside, we can look at these types of making a steak from a Transport Phenomena point of view.
Associate the correct terms with the correct steak. You will be asked to consider the heating time period, the heat transfer coefficient and the driving force.

### Exercise 2

To increase the hardness of stainless steel, a process called quenching is performed on the steel. What happens during quenching is that the steel is rapidly cooled down using a fluid.
In this exercise, we will look at how long this quenching process has to be done for a thick steel plate.

### Exercise 3

The Italian artist Gian Lorenze Bernini made the world famous sculpture Apollo and Daphne between the years of 1622 and 1625. The marble statue shows Daphne and Apollo from a scene in Metamorphoses by the Latin writer Ovid. Bernini sculptured Apollo and Daphne at the exact moment that Apollo cornered Daphne and turned her into a laurel three. He did this because she didn’t answer his love for her, a truly tragic story. The statue can nowadays be found in Galleria Borghese in Rome, Italy.

Imagine if such a beautiful sculpture would be exposed to salt water for a long time, and thereby being saturated with salt. Of course, the museum would want to remove this salt from the marble so it will put the statue in a huge water bath that is being stirred. Then, the salt will be transported from within the statue to the water. Since the bath is so huge, you may assume that the salt concentration in the water will stay at 0 kg/m3during the whole process.

To study the process, first an experiment with a cylinder shape column with a diameter of 15 centimetres is done. After 400 days, the average salt concentration has dropped to only 1% of the original salt concentration. You may assume that this is a diffusion controlled process for long time mass transfer.