Influence of Surface Temperature on Surface Fouling–Theoretical Approach

Mech. Power Eng. Dept., Faculty of Engineering, Mansoura University, Egypt
Influence of Surface Temperature on Surface Fouling–Theoretical Approach
Mostafa M. Awad
mostawad100@yahoo.com
Abstract:
A theoretical approach for investigation the effect of surface temperature on surface particulate fouling has been developed. This approach is based on the basic fouling processes. As a result of this study, for each working condition, there was a specific surface temperature, defined as critical surface temperature, Below this temperature, i.e. the working temperature is less than the critical one, the fouling rate will increase by increasing surface temperature and it has the maximum value nearest the critical temperature. Above the critical temperature, i.e. the working temperature is greater than critical one, the fouling rate has a negative sign, and it means that some erosion of the heat transfer surface will be occurred. This erosion has maximum value nearest the critical temperature and decreases with temperature. At the critical temperature no fouling will be built up. On the light of these results, all contrary conclusions presented in literatures which concluded that; “the increase in surface temperature may lead to increase, decrease or have no effect on the amount of material depositing at a surface " are right conclusions. This depends on the working temperature is below, equal or above the critical surface temperature. A new formula describing the critical surface temperature with the affecting parameters has been deduced.
Introduction
Fouling of heat transfer surface is defined as the accumulation of unwanted material on the heat transfer surface. This accumulation deteriorates the ability of the surface to transfer heat besides to the increase of the pressure drop through the heat transfer apparatus. Many investigators have studied the fouling phenomenon theoretically and experimentally. Kern and Seaton [1, 2] and Ken [3], made the groundwork of the fouling studies. Recently, Nesta and Bennett [4] introduced a new design of heat exchangers. They concluded that minimize wall temperature and maximize the flow velocity tends to minimize fouling; they also found that the heat exchanger material has a pronounced effect on fouling particularly when biological fouling is a concern. Yang et al., [5] constructed a model for the fouling induction period. They found that the shorter induction periods are dealing with higher surface temperature. Subbarao et al., [6] studied particulate fouling of glass particles under high temperatures. They concluded that the fouling layer formation is strongly dependent on the gas phase temperature and gas phase velocity and once the deposit has formed, increasing gas velocity hasn't any effect on removal of particles from the deposited layer. Mostafa et al., [7], studied experimentally the effect of surface temperature on both the precipitation fouling and particulate fouling. They found that the fouling resistance increases with temperature in the case of precipitation fouling, where it decreases with temperature in the case of particulate fouling. Fouling is influenced by a great number of affecting parameters, on the one hand by physical ones such as; flow velocity, temperature and the chemical nature and surface finish of the wall. On the other hand, the chemical concentration of the different compounds (solute, solvent, impurities) has to be taken into account. The great number of these parameters and their interdependence explain the difficulties encountered when predicting fouling by a theoretical approach. That is the reason why this phenomenon is essentially represented by empirical laws for each particular case. This allows optimal operating conditions and technical solutions to be obtained which avoid, or at least reduce, fouling, for a specific process. According to many previous researchers; the most important ones are the flow velocity and the surface temperature.
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