Structure and rate of growth of whey protein deposit from in situ electrical conductivity during fouling in a plate heat exchanger

Abstract

The influences of calcium concentrations ( 70 – 88 mg / l ) , Reynolds number (2000–5000) and temperature ( 60 – 96 ∘ C ) upon the deposit structure and the rate of growth deposition have been investigated in a plate heat exchanger. This was done from in situ measurements of the deposit electrical conductivity via implementation of stainless steel electrodes in channels combined with assessments of deposit thickness. Calcium ions affect structures of deposits and increase the rate of deposit growth upon heated surfaces. This was attributed to the formation of weaker size aggregates at higher calcium concentrations and a higher number of calcium bindings, which reinforce adhesion forces between protein aggregates. Structures and appearances of deposits also were affected by flow rates whatever the calcium concentrations. Deposit growth rate was enhanced by increasing flow rate below a critical Reynolds number comprised between 3200 and 5000. On the contrary, above the critical Reynolds number, a limitation of the deposit and/or an escape of the deposit from the fouled layer into the core fluid occurred, caused by the predominance of particle breakage on the deposit formation. Fouling tended to be reduced at higher flow rate. It was noteworthy that rates of growth decrease during fouling experiments which may be explained by an increase in local shear stresses leading to particle breakage.