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Abstract
The scope of this research is to obtain a film coating on stainless-steel surfaces in order to reduce the interaction between the metal surface and the precipitates, so as to mitigate fouling in heat exchangers. Perfuoropolyethers were used to obtain nano-range fluorinated layers in order to make hydrophobic the stainless-steel surfaces. A pilot plant with two identical heat exchangers was built to investigate the ability of the hydrophobic coating of preventing fouling. The heat exchangers, installed in parallel, operated at the same temperature and pressure conditions, namely, laminar flow regime and inlet flow temperatures of 291–293 K for cold streams and 313–333 K for hot streams. We compared the heat transfer performance of the two heat exchangers. After a 5-month operation, the decrease in the heat transferred was 56% for the coated heat exchanger and 62% for the uncoated heat exchanger. Moreover, the increase of heat transfer resistance due to scale on the uncoated heat exchanger, with respect to the coated one, was three times higher.
NOMENCLATURE
| A | = | heat transfer surface area, 2πDL, m2 |
| CA | = | contact angle, θ degrees |
| cp | = | specific heat of fluid, J/kg-K |
| D | = | diameter, m |
| Gz | = | Graetz number, Re Pr D/L, dimensionless |
| h | = | heat transfer coefficient, W/m2-K |
| k | = | liquid thermal conductivity, W/m-K |
| L | = | length, m |
| lb | = | baffle spacing, m |
| Nu | = | Nusselt number, hD/k, dimensionless |
| Pr | = | Prandlt number, cp μb /k, dimensionless |
| q | = | heat quantity, J/h |
| R | = | overall thermal resistance m2K/W |
| ReG | = | Reynolds number defined by Gnielinski, W L/ ϵF D lb μb, dimensionless |
| Rf | = | fouling resistance, m2-K/W |
| Rwall | = | wall resistance, m2-K/W |
| U | = | overall heat transfer coefficient, W/m2-K |
| W | = | total mass flow rate, kg/h |
Greek Symbols
| ϵF | = | shell void fraction, m |
| θ | = | contact angle, degrees |
| μ | = | fluid viscosity, Pa-s |
Subscripts
| b | = | bulk |
| C | = | cold |
| f | = | fouling |
| H | = | hot |
| in | = | inner |
| mlg | = | logarithmic mean |
| out | = | outer |
| w | = | wall |
Additional information
Notes on contributors
Valeria Oldani
Valeria Oldani is a Ph.D. student in industrial chemistry at Università degli Studi di Milano, Italy. She graduated in industrial chemistry in 2012 at the same university. Her current Ph.D. research work concerns the development of coating systems for fouling protection on heat transfer metal surfaces.
Claudia L. Bianchi
Claudia Bianchi is an associate professor and the leader of the Process and Plants Research Group for Industrial Chemistry at the University of Milan. Her scientific interests cover different fields, such as inorganic materials, surfaces science, and industrial chemistry. The kind of research developed in the laboratories has spillover effects in both environmental and energy fields. Many collaborations are active with other research communities working at universities around the world.
Serena Biella
Serena Biella is an assistant professor in the Department of Chemistry, Materials and Chemical Engineering “Giulio Natta” of Politecnico di Milano. Graduated in chemistry (5-year degree in applied physical chemistry) at Università degli Studi di Milano, from the same university she obtained her Ph.D. in industrial chemistry, studying synthesis and characterization of catalysts for industrial applications. Her scientific activities are in two main research lines: fluorinated and perfluorinated compounds with particular attention to the processes of synthesis, and self-assembly of perfluorocarbon/hydrocarbon hybrid materials with interest in the structural study of these novel compounds. She is author and co-author of more than 40 written compositions, including 23 papers on international journal reviewed by ISI.
Carlo Pirola
Carlo Pirola graduated in industrial chemistry in 2000 at Università degli Studi di Milano and took his Ph.D. in industrial chemistry in 2008 at the same university. In 2011 he became an assistant professor in the chemical plants field. His current main research interests concerns are heterogeneous catalysis applied to the production of biofuels (synthetic Fischer–Trospch and biodiesel), photocatalysis, processes of purification of air and water through photocatalysis and sonochemistry, and separation processes (rectification, absorption processes, membrane liquid–liquid extraction). He is the author of 40 papers in international journals, about 70 conferences and interventions in international congress and meeting, one patent, and six contributions to volumes.
Giuseppe Cattaneo
Giuseppe Cattaneo is the founder and has been the managing director of the company S.T. Special Tanks s.r.l. since 1985. The S.T. Company works in pressure vessels design and building for 25 years. More recently the company became one of the first Italian companies, at an international level, in the field of design and production of skid plants, heat exchanger plants, and pressure vessels for oil and gas industries.