H2.

2. A vial that is used for lyophilization has a curved base that makes poor contact with the lyophilizer shelves, leaving a 0.1 mm gap between the bottom of the vial and the shelf. If the mean path of gas molecule is longer than this spacing, heat will be transported between the Vial and the shelf by gas molecules that bounce between the two surfaces. The lyophilizer is operated so that the system temperature is near -25 C. a. At what pressure will the mean free path be the same size as the vial-shelf spacing? b. When the mean free path is smaller than the vial-shelf spacing, the heat transfer coefcient between the vial and shelf is proportional to pressure. Why? If we wish to maintain the product temperature at -25 C, would we need to increase or decrease the shelf temperature as the chamber pressure is decreased