Found a 52.1GB file related to google in mac 'private' folder. can I delete this?
It's a cache file with a name associating it to the browser Google Chrome.

Anything under the path /private/var/folders/* can be deleted and will be repopulated/rebuilt after the next boot.

That is: do not delete /private/var/folders/ itself!

But below that, you may trash anything and then reboot. 

Note that a few files will be in use or protected, so you could only delete them via the Trash after a reboot.

In this case: make sure Chrome is closed, then trash only the big file you found and delete the file. Leave the rest as is.