Thermal ageing of proteinaceous fouling layers during the growth phase
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ORIGINAL
Thermal ageing of proteinaceous fouling layers during the growth phase Lukas Schnöing 1
&
Wolfgang Augustin 1 & Stephan Scholl 1
Received: 10 March 2020 / Accepted: 8 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Fouling in heat exchangers can complicate the characterisation and interpretation of thermal effects because of ageing phenomena that occur within the deposited fouling layer. The prevailing process temperatures between the liquid bulk and heattransferring surfaces create a large thermal conductivity distribution according to the position of the layer within the deposit. During the growth phase, an interaction occurs between the fouling layer formation and ageing. Therefore, deposition and ageing should always be considered in combination to obtain a better understanding of fouling. This paper discusses an experimental method for determining temperature-dependent ageing, expressed as a change in thermal conductivity with time and along the cross section of the fouling layer. An experimental setup is presented that includes a newly developed flow channel and an experimental implementation of an ageing model. In the first experiments, proteinaceous fouling layers were generated from whey protein concentrate (WPC) with and without simulated milk ultrafiltrate (SMUF), applied for different durations to create different fouling layer thicknesses. The thermal conductivity increased more rapidly near the heat-transferring surface than for the entire fouling layer. These findings can be related to the temperatures within the sublayers. List of symbols A area of the fouling layer (m2) cp heat capacity (J kg−1 K−1) k rate constant (s−1) ˙m mass flow (kg s−1) NOFL number of fouling layers (−) q heat flux (W m−2) Rf thermal fouling resistance, (m2 K W−1) SMUF simulated milk Ultrafiltrate (−) t time (min) T temperature (°C) U overall heat transfer coefficient (W m−2 K−1) V volume of fouling layer, (m3) WPC whey protein concentrate (−) x thickness (m) y youth variable (−) Greek symbols ε water content (−) λ thermal conductivity (W m−1 K−1) * Wolfgang Augustin [email protected] 1
Institute for Chemical and Thermal Process Engineering, Technische Universität Braunschweig, Langer Kamp 7, 38106 Braunschweig, Germany
Subscript b channel f fluid growth i in I,II,... out th w 0
bulk flow channel fouling fluid growth phase discrete values, stepwise parameter inlet flow number of sublayers, starting from the wall outlet flow thermal wall clean surface
1 Introduction 1.1 Fouling and ageing The unwanted formation of deposits on heat-transferring surfaces, or so-called fouling, is a significant problem in terms of process engineering and economics in almost all areas of the food processing industry [1]. The negative effects of fouling include higher investments due to oversizing of apparatus, increased energy costs, reduced product quality, increased cleaning frequency, accelerated corrosion and safety aspects
Heat Mass Transfer
[2, 3]. The resulting cost incre
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