The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Heat Transfer Through Porous Multiphase Systems: Measurement, Modelling and Application in Printing of Coated Papers

Philip Gerstner

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Chemistry and Materials Sciences for public examination and debate in Auditorium AS1 at the Aalto University School of Science and Technology (Espoo, Finland) on the 22nd of October 2010 at 12 noon.

Overview in PDF format (ISBN 978-952-60-3377-8)   [5494 KB]
Dissertation is also available in print (ISBN 978-952-60-3376-1)

Abstract

This work examines the thermal transfer through porous media by means of measurement of the effective thermal conductivity and modelling of the structural parameters. While most of the work is of a general nature, the porous media in focus are pigment plus latex binder systems as used for paper coatings. As such, the application field of thermal effects in printing is discussed.

At first the use of a dynamic measurement method for the thermal conductivity of porous coating pigment binder systems in the form of tablets is evaluated. In addition, a Lumped Parameter Model is developed to analyse the measured thermal conductivities in terms of the material volume fractions and their structural configuration. The model therefore uses two independent structural parameters instead of porosity alone as the governing parameter. This enables a discussion following modelling approaches adopting parameter modelling and structural modelling. A combination of both is used to discuss the solid-solid connectivity of pigment binder systems. It is shown by the model parameter of pigment connectivity that a disruption of the pigment packing already at low concentrations of binder occurs related to surface and colloid chemistry factors which cause the binder to accumulate first at pigment nodal points. The analysis of different pigment binder systems shows that, due to the presence of two interacting solid phases, the effective thermal conductivity cannot be modelled by using porosity and pore structure alone, but also requires the additional parameter of dual solid phase connectivity. It is proposed, therefore, that a combination of pore structure analysis and thermal conductivity measurement can be used to identify and parameterise subtleties in interactive particulate systems.

For the application of toner fusing in electrophotography it is shown that a thermally insulating coating layer leads to a concentration of the fusing energy on the surface, thus aiding the fusing/adhesion development of the toner while shielding the base paper from undesired heating. In the heatset web-offset drying process, an insulating precoating in combination with liquid barrier properties can lead to a similar shielding of the base paper and thus helps to maintain an even moisture profile effectively reducing the waving/fluting tendency.

This thesis consists of an overview and of the following 9 publications:

  1. P. Gerstner, J. Paltakari and P.A.C Gane. A method for the measurement of thermal contact diffusivity of paper coating structures: Nord. Pulp Paper Res. J. 23(4):354-362, 2008.
  2. P. Gerstner, J. Paltakari and P.A.C Gane. A lumped parameter model for thermal conductivity of paper coatings: Transp. Porous Med. 78(1):1-9, 2009.
  3. P. Gerstner, J. Paltakari and P.A.C Gane. Measurement and modelling of heat transfer in paper coating structures: J. Mater. Sci. 44(2):483-491, 2009.
  4. P. Gerstner, C.J. Ridgway, J. Paltakari and P.A.C Gane. A structural analysis of the thermal conductivity of paper coatings: application of particle deposition simulation to a lumped parameter model. Proceedings of the 14th Oxford Fundamental Research Symposium, Oxford, UK, 2009, pp. 1255-1292.
  5. P. Gerstner and P.A.C. Gane. The effect of latex binder on thermal conductivity of paper coatings. Proceedings of the 7th International Paper Coating and Chemistry Symposium, Hamilton, Canada, 2009, pp. 33-42.
  6. P. Gerstner, S. Veikkolainen and P.A.C. Gane. Effective thermal conductivity of liquid saturated coatings and their liquid vaporisation behaviour. Proceedings of the TAPPI 11th Advanced Coating Fundamentals Symposium, München, Germany, Tappi Press, Atlanta, 2010.
  7. P. Gerstner and P.A.C. Gane. Considerations for thermally engineered coated printing papers: focus on electrophotography: J. Pulp Paper Sci. 35(3-4):108-117, 2009.
  8. P. Gerstner and P.A.C. Gane. Fusing of electrophotographic toner on thermally engineered coated paper: Nord. Pulp Paper Res. J. 25(1):100-106, 2010.
  9. P. Gerstner, T. Grönblom and P.A.C. Gane. Quality and efficiency enhancement in heatset web-offset drying by adopting thermally designed paper coatings. Proceedings of the 37th IARIGAI Research Conference of Advances in Printing and Media Technology, Montréal, Canada, 2010.

Errata of publications 1, 3 and 5

Keywords: thermal conductivity, porous media, modelling, energy efficiency, electrophotography, heatset web-offset

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Last update 2011-05-26