The impact of crystallization fouling on a microscale heat exchanger

Due to their very high surface-to-volume ratios micro heat exchangers provide possible advantages in heat and mass transfer operations. Besides the potential of process intensification and low investment the process stability of these micro structured devices is a required criterion for industrial applications. Micro structured devices are very sensitive to unwanted deposition such as crystallization of inverse soluble salts on the surface (fouling). In general, fouling results in (i) an increase of the pressure drop, (ii) a decrease of the heat exchanger performance, (iii) a maldistribution of the flow in the micro structures and (iv) a change of the residence time behavior. This paper presents investigations about the impact of crystallization fouling on the heat transfer performance of a micro heat exchanger. Fouling experiments with calcium carbonate (CaCO3) were analyzed regarding thermal and fluid dynamic behavior. The observed fouling developed heterogeneously from a supersaturated solution in micro channels and caused a decrease of the heat transfer performance and a strong increase of the pressure drop. The extracted fouling resistances Rf were in the range of 10−5–10−3 m2 K W−1. In general, the fouling behavior in microscale is comparable to that in macroscale.

► Crystallization fouling of CaCO3 in a micro heat exchanger was investigated.
► Typical fouling curves were detected with small induction periods.
► The fouling resistance is strongly influenced by the flow rate.
► The asymptotic fouling resistances are comparable to macroscale fouling resistances.
► The pressure drop increased very strong – between factors 2 and 60 depending on the process conditions.