Hi Phdbug,
I'm social sciences, and my chapters are averaging about 12,000 words. One is 14,000, one 11,000...mostly around 12,000 though. I have 8 chapters and although I haven't finished them yet, expect intro and conclusion chapters to be shorter. Have done lit. reviews in a few chapters, but it will mainly go in the introduction.
Not a very detailed answer, but I hope that helps!