The UPV library has its own classification by topic. Once you have located the book in PoliBuscador, click on the title and note down the Cataloguing Code, e.g. B 3-24/507.
Letter B is for the Central Library.
Code 3-24 refers to the shelf where the book is located, in this case Fluid mechanics and hydraulics.
Number 507 is the book’s correlative place on the shelf.