Heat exchanger fouling is a common phenomenon during high temperature processing of milk. The temperature of milk raises from 90 degrees C to 150 degrees C during Ultra-High-Temperature (UHT) sterilization process. At such high temperature, the minerals and denatured proteins deposit on the heat exchanger surface, also known as fouling. Fouling acts as resistance to heat transfer, hence the performance of the heat exchanger is reduced. Using hydrodynamics and heat balance concept, a mathematical model was formulated. Simulation was performed with the model to predict the fouling behavior as a function of time and position within the helical triple tube heat exchanger (HTTHE). At an early period of operation, the uniform fouling deposit occurs throughout the length of the heat exchanger due to constant heat exchanger wall temperature. With progress of time, the fouling deposit and also Biot number (i.e., local fouling factor) increases towards the outlet of the heat exchanger since the interface temperature between fouling deposit and milk approaches towards the bulk milk temperature, that increases towards the heat exchanger outlet. The fouling deposit stabilizes after 105 min since no net deposit occurs after that time. (c) 2004 Elsevier Ltd. All rights reserved.