Confusion about writing acronyms in section title
A third option:

Section 1: Effect of VLW
It is seen that Very Long Word (VLW) used in article sections are confusing part.

This is useful if VLW is truly very long, and messes up your titles, and you can trust most people have at least heard of it, and will have a clue of what you are talking about. Placing the full version next to it makes it discoverable.
Note that the operating distinction is &quot;will have a clue&quot;, reading the title should give the reader a quick idea of what it is about.
If the acronym is not well known enough, use the full word, and assume people will skip titles when they read the article in detail.