Are there many journals that do not accept TeX/LaTeX? I have been told by our head of department, a veteran academic with a lot of publications behind his name, that I am not allowed to write my masters dissertation with TeX/LaTeX, as many journals do not accept TeX/LaTeX documents, and now I have to use Word. I work in thermoflow research.
I can almost not believe that journals would prefer Word over TeX/LaTeX, or is this in actual fact true?
I would appreciate answers from people actually working in academic publishing.
The answer is that in some fields (La)TeX dominate whereas in other fields (La)TeX is largely unknown. Obviously any field where equations are required is more likely to be using (La)TeX for writing and publishing. However, it is not uncommon that journals, or rather, type-setters of journals, use LaTeX for final production regardless of submitted format. The same applies to book publishers. But, the fact is that the use varies and one needs to check with the journal to which you wish to submit.

The fact that you are not "allowed" to write your thesis with (la)TeX is perhaps because your advisor does not use it. I am an avid LaTeX user and am struggling to convince both colleagues and students in my department to at least try using it so I know how difficult it can be. In the end, I need to use both to be able to communicate with my colleagues and peers. So although I do not see why you should not set the thesis in (La)TeX in the end, you probably need to use word for the manuscript so that your advisor can provide input on files you supply. But, check how many journals actually use LaTeX in your field and strike up a discussion with your fellow students and your advisor. I think it is worthwhile to be fairly fluent in using many tools.

Edit: I will just add that I was convinced by a friend to use TeX (not LaTeX, it was a long time ago) when I wrote my thesis (a monograph at a US university) while almost no-one in the department used TeX; but then my advisor always provided feedback from double-spaced printouts which were platform independent. Those were the days.