July 1-6, 2007
Fouling characteristics are dictated largely by the properties of the thermal and hydrodynamic boundary layers. As a result, fouling mitigation strategies must take into account the conditions in this region. hiTRAN® wire matrix tube inserts are a useful tool in altering the conditions near the tube wall, especially in the laminar and transition flow regions. This review paper considers Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) measurements, which were employed in order to show the hydrodynamic differences between plain tubes and those containing inserts. Measurements indicate that the wall shear rate in tubes containing hiTRAN® inserts operating in the laminar flow regime is similar to that for plain bore tubes operating in the turbulent flow regime. Moreover, the increased tube side heat transfer coefficient which results from the reduction of the thermal boundary layer allows operation with smaller EMTDs. This enables the designer to reduce the tube wall temperature to a level below the fouling threshold temperature, e.g. to combat crude oil fouling. The results from the laser analyses into the hydrodynamic boundary layer are backed up by recent research data investigating the effect of hiTRAN® inserts on sedimentation and particulate fouling. The thickness of the fouling layer was measured by applying a combination of photographic and laser measurement techniques. The results are compared to plain tube data and are reported as a function of both flow rate and hiTRAN® insert packing density. The impact of altering the hydrodynamic and thermal conditions near to the wall is subsequently demonstrated for different fouling mechanisms. Studies of the impact of hiTRAN® inserts on biological and chemical reaction fouling in crude oil processing are also reviewed. A better understanding of the threshold shear rates and wall temperatures for different fouling mechanisms is required for any study into the impact of fouling. Combining this knowledge with the principles outlined in this paper clearly emphasises the benefit of using hiTRAN® wire matrix inserts as a powerful tool to mitigate fouling.
J.M. Ritchie, P. Droegemueller, and M.J.H. Simmons, "HITRAN® WIRE MATRIX INSERTS IN FOULING APPLICATIONS" in "Heat Exchanger Fouling and Cleaning VII", Hans Müller-Steinhagen, Institute of Technical Thermodynamics, German Aerospace Centre (DLR) and Institute for Thermodynamics and Thermal Engineering, University of Stuttgart, Germany; M. Reza Malayeri, University of Stuttgart, Germany; A. Paul Watkinson, The University of British Columbia, Canada Eds, ECI Symposium Series, (2007). http://dc.engconfintl.org/heatexchanger2007/52