Is there a 'process algebra' to describe ACID transactions on a database?
There is a paper by Van Beek called An Algebraic Approach to Transactional Processes which describes adding transactions to process algebra:

(a :~ 0 . a:~ a + 2) II (a:~ 1 a:~ a X 2) ((a :~ 0 . a:~ a + 2)) II ((a:~ 1 a:~ a X 2))


This paper even delves into isolation levels. 

The author describes how in Communicating Sequential Processes (CSP), if you have a write blocked on a read, you can get into a deadlock scenario. 

The author references another paper J.A. Bergstra, A. Ponse, and J.J. van Warne. Process algebra with backtracking which allows for rollback of a failed CSP operation.  

There is discussion on the nature of transactions in K.P. Eswaran, J .N. Gray, R.A. Lorie, and 1.1. Traiger. On the notions of consistency and  predicate locks in a data base system. Communications of the ACM, 19(11)

The properties of transactions are described in ] J. Gray and A. Reuter. Transaction Processing: Concepts and Techniques.

The acid properties of transactions are described in J. Gray. The transaction concept: Virtues and limitations and in T. Haerder and A. Reuter. Principles of transaction-oriented database recovery