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 heat-transferring 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.
Highlights
1.1 Fouling and ageingThe 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 typical course of the fouling resistances can be separated into three phases
The aim of this work was to identify ageing by means of monitoring a change in thermal conductivity during the growth phase
Summary
1.1 Fouling and ageingThe 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 [2, 3]. The resulting cost increases are estimated at 0.25–0.3% of the respective gross domestic product, for a total cost of several billion Euro per year each in the industrialised countries [3, 4]. Interest has intensified in deepening the understanding of fouling mechanisms. According to Epstein [5], the various fouling mechanisms can be related to individual steps of the fouling process in a matrix: initiation, transport, deposition, removal and ageing. Ishiyama et al [6] conducted a survey on research priorities and needs and concluded that corrosion and ageing still require considerable research
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