What is typically expected of a conference session chair?

Perhaps things are different in electrical engineering, but in math, the chair:

• introduces the speaker, sometimes just saying their name and the title of their talk, sometimes a lengthier introduction ("[speaker] is professor at XYZ University and works on blablabla");
• says "thank you" out loud and starts clapping at the end;
• asks if there are questions or comments from the audience;
• [optional] if the questions are taking too much time, the chair will say something like "we can discuss this more during the break" and go onto the next step;
• once the questions are over, says "let's thank [speaker] again" and starts clapping;
• announces the time of the next talk ("in 10 minutes", "after the break at 10:30"...). Rinse and repeat.

Sometimes the chair will go as far as warning the speaker if the time limit approaches or has passed. An extra task that sometimes pops up is when the organizers want to make an announcement before/after the talk; then the chair will say "[organizer] has an important announcement, please listen". This is pretty much it.

A handy trick is to get the schedule with speakers' names and talks' titles ahead of time. Then you can practice pronouncing speakers' names, and there's no awkward silence while you say "The second speaker this afternoon is [speaker], who will talk about... uh... squints to read the title on the board [title]".

It's also more or less expected for the chair to prepare at least one question about the talk, even a very simple one. This way, if no other member of the audience has any question, then the chair can say "I actually have a question, [insert question]" after the pause that occurs after "any questions?", saving the speaker a bit of embarrassment.

• As a chair, it is a good idea to find and meet your presenters before your session, especially if you don't know them. Few things are more embarrassing than introducing a speaker you don't know, then asking "Uhm, is professor X actually in the room?", only to see X stand up in the first row right in front of you.

• You should make sure that the presentations are available and easily found on the presentation computer, e.g., on the desktop.

Both of these are really joint responsibilities of speakers and the chair.

• Make sure that there is paper on the flipchart and that the whiteboard is clean, and perhaps wipe it down between presentations. It's also considerate for the next session if you take charge to leave the room in a presentable state, with a clean whiteboard or flipchart etc.

• If you notice that a speaker is new at the conference (maybe a first time presenting grad student), it's nice to make a little small talk with her or him and make them feel welcome. Works wonders to reduce the jitters.

• Sometimes a speaker will have handouts. You should take charge that these are distributed, so the speaker can concentrate on the talk.

• Similarly, sometimes you should hand out feedback forms, or remind everyone to vote on their conference app, or other things, depending on the conference.

Overall, the theme is: make the session easy on the presenters, and enjoyable for everyone.

Disclaimer: As usual, there can be different traditions depending on the field. I'll answer on the basis of my experience in a relatively small field, that of metrology, which is between physics and engineering.

The session chair is usually chosen among experienced researchers for the following reasons:

• At least out of courtesy, they are expected to ask questions when nobody else has one, and this usually requires deep knowledge and a sufficiently broad view of the session topic.
• At the beginning or a the end of the session, they are expected to outline the direction of the research about the session topic, taking into account the presented results.
• They can better introduce most of the speakers if they already know them.