Solidification fouling of paraffin wax from hydrocarbons
01 May 1982-Letters in Heat and Mass Transfer (Pergamon)-Vol. 9, Iss: 3, pp 209-219
TL;DR: In this article, the effects of varying shear stress on the deposit in one experiment and thus obviates the need of doing several experiments as in the case of flow through tubes were studied.
Abstract: Solidification fouling of paraffin wax from a solution in kerosene has been studied in a stirred system where a refrigerant was circulated through a surrounding jacket. The system is unique since it permits the study of the effects of varying shear stress on the deposit in one experiment and thus obviates the need of doing several experiments as in the case of flow through tubes. Effects of rotation speed and wall temperature have been studied. The results indicate that the shear stress has a profound influence on the deposit thickness. Based upon the experimental observations, the initial deposition is hypothesized to be diffusion controlled instead of particulate migration controlled.
TL;DR: In this article, two classifications for cleaning problems, one based on soil type and another based on cleaning mechanism, are proposed to aid in the development of solutions that are effective across the industry.
Abstract: Cleaning of process plant is ubiquitous in the food industry but is still poorly understood. Fouling research has benefitted from the use of a simplified classification of mechanisms. Here we review current work in food and personal product cleaning, and propose two classifications for cleaning problems, one based on soil type and one based on cleaning mechanism. The aim of the classification is both to allow results from different cleaning problems to be compared and to aid in the development of solutions that are effective across the industry.
TL;DR: A review of the literature on water-based cleaning is presented in this paper, where the authors highlight the importance of the right combination of flow characteristics at a given temperature and concentration for achieving fast cleaning in all cases.
Abstract: Fouling of food process plant surfaces and the subsequent cleaning needed is a significant industrial problem, and as the cost of water and chemical disposal increases, the problem is becoming more significant. Current literature on water-based cleaning is reviewed here according to the classification of 3 types of cleaning problems. By doing this, it is hoped that new knowledge can be highlighted applicable to improving industrial cleaning. (i) For type 1 deposits (that can be cleaned with water alone)—Cleaning time appears related to Reynolds number and surface shear stress. An increase in Reynolds number seems to decrease cleaning time. Cleaning temperatures greater than 50 °C do not appear beneficial. (ii) For type 2 deposits (biofilms)—Removal behavior of biofilms seems to be dependent on the microbial aging time on the surface. Keeping a material hydrated on a surface enables easier removal of it with water. a. Water rinsing: Temperature and wall shear stress have varied effects on removal. b. Chemical rinsing: Flow and temperature were seen to have the biggest effect at the start of cleaning, but contact time was more important as cleaning progressed at a given sodium hydroxide solution flow and temperature. (iii) For type 3 deposits (that require a cleaning chemical)—For specifically, protein-based systems excessive chemical forms a deposit difficult to remove. Increasing wall shear stress and temperature was most beneficial to cleaning rather than concentration. The action of temperature can reduce the use of a chemical for type 2 and type 3 soils. The findings suggest that the right combination of flow characteristics at a given temperature and concentration is crucial to achieving fast cleaning in all cases. There are a number of cleaning monitoring methods at various stages of commercialization that may be capable of monitoring bulk cleaning and cleaning at the surface. To optimize cleaning will require integration of measurement methods into the cleaning process.
01 Jan 2005
TL;DR: In this article, the authors discuss the problem of fouling and the associated problems of cleaning, with particular reference to milk fluids, as they have been most thoroughly studied Fouling from milk results from protein and mineral deposition, each of which results in different problems for cleaning.
Abstract: Publisher Summary This chapter discusses the problem of fouling, and the associated problems of cleaning, with particular reference to milk fluids, as they have been most thoroughly studied Fouling from milk results from protein and mineral deposition, each of which results in different problems for cleaning Cleaning time is a function of a number of variables; both chemical (such as the cleaning chemical type and concentration, and the temperature) and physical (such as the flow rate, which affects the fluid shear on the surface of the deposit) In milk cleaning, protein deposit is first swollen by action of hydroxide and then removed by shear The cleaning rate increases with increasing temperature and surface shear stress, but there can be an optimal concentration of hydroxide, above which the deposit becomes difficult to remove A number of methods have been tried to increase the cleaning rate, including pulsed flows, enzyme cleaners, and ice pigs Surface modification has been tried by a number of workers
01 Jul 2010
TL;DR: In this paper, the adhesive interactions between a colloidal silica microparticle and stainless steel, glass and ceramic surfaces were measured using atomic force microscopy (AFM) in the presence of a number of solutions and suspensions of ingredients found in commercially available toothpaste.
Abstract: The objective of this research was to investigate adhesion of different fouling deposits with different contact surfaces using atomic force microscopy (AFM). In this thesis, AFM has been employed to measure: (i) The adhesive interactions between a colloidal silica microparticle and stainless steel, PTFE-coated stainless steel, glass and ceramic surfaces, in the presence of a number of solutions and suspensions of ingredients found in commercially available toothpaste. (ii) To compare the measurements from the AFM and micromanipulation to see the differences and similarities. The micromanipulation technique was developed to measure the adhesive strength of different deposits. The method uses a T-shaped probe made of stainless steel chip, dimension 30 x 6 x 1 mm connected to the output aperture of a transducer (Model BG-1000, Kulite Semiconductor, Leonia, NJ. USA) which was itself mounted on a three dimensional micromanipulator (MicroInstruments, Oxon, UK). The two measurement methods are capable of giving quantitative results for the strength of the forces involved in adhesion; fast moving consumer goods (FMCG) deposits, toothpaste and confectionary stimulant deposits have been studied, and their interactions with stainless steel, glass and PTFE surfaces measured. (iii) Further investigation of AFM adhesion measurements, with caramel, whey protein and sweet condensed milk (SCM) deposits after heating at 30oC, 50oC, 70oC, and 90oC. The two selected spherical microparticles used were stainless steel and PTFE, which were attached to the end of an AFM tip. The data shows that, for removal in all cases using micromanipulation, the pulling energy increases with increasing height above the surface and the slope of the lines of pulling energy versus thickness is similar. Stainless steel shows the highest pulling energy with slightly higher energies than glass and PTFE, whilst PTFE show the lowest interaction. For the AFM data, PTFE again gives much lower adhesion forces. This is due to the different molecular interactions between different surfaces and caramel. There is thus partial agreement between the two methods. The micromanipulation method measures a range of parameters – such as the deformation and flow of the deposits, and so it might not be expected that there would be complete agreement. Here stainless steel and glass show very similar behaviour, as opposed to the differences seen using AFM; the different surface roughness of the two materials might also be expected to have an effect. At different temperatures the results from the different contact positions on the deposits; with an approach speed to the deposits for all experiments was 3μm/s, then a 5 second pause on the deposit and then the rate of retract was 0.25μm/s. Significant (more than an order of magnitude) differences are seen between forces for the same and different deposits, and between different surfaces for the same deposits. Lower forces are seen at 90oC in all cases; at the higher temperature, the force between surface and deposit is less. To design systems to resist fouling, these results suggest that measurements at different process temperatures are needed; data at room temperature has overpredicted the interactions. The results suggest that the AFM force curve measurement technique could be used to study a variety of food deposits that have undergone different processing conditions. The method can help in optimising removal of food deposits in terms of food cleaning protocols. AFM could be a valuable technique in measuring surface properties, and in relating behaviour to surfaces. The capability of the AFM to provide better understanding of materials structure, surface characteristics and the interactive forces at the meso- and nanoscale level. The AFM will enhance the understanding of large-scale engineering processes, especially as materials are increasingly being designed down to the submicrometre level.
01 Jan 1978
TL;DR: In this paper, the authors studied the diffusion equation subject to a phase change at one boundary, provided simple boundary conditions of the first, second, or third kind are specified, and provided exact solutions regarding relative motion between the phases, ablating slabs, and growth of a vapor film.
Abstract: Publisher Summary The study of the diffusion equation subject to a phase change at one boundary is in a relatively satisfactory state, provided simple boundary conditions of the first, second, or third kind are specified. Mathematically interpreted, the interesting features of the problem arise from the nonlinearity, exhibited for all but a few particular boundary motions. This chapter illustrates solution of the equation for diffusion of heat, mass, or some other scalar quantity, subject to the existence of a free boundary. The chapter aims to find exact solutions regarding relative motion between the phases, ablating slabs, and growth of a vapor film. Analytic approximation methods and analog and digital computer solutions are discussed in details. Integral equation methods, variation methods, and boundary layer methods along with active and passive analog solutions and application of numerical schemes are appropriate for bringing clarity to heat conduction or diffusion with phase change. In the search of growth of small particles of a condensed phase, the quasi-steady-state theory is applied particularly where a condensed phase exists whose volume changes slowly with time. This is true, for example, in the sublimation of ice or the condensation of water vapor from air on liquid droplets. While focusing on active and passive analog solutions, freezing problems remain symmetric in one, two, and three dimensions, where the liquid is initially at the fusion temperature. The heat capacity of the solidified phase is taken into account. Thermal properties are considered to be temperature independent.
Abstract: Studies of the deposition of wax from wax/kerosene mixtures onto cooled simulated heat transfer tubes has demonstrated that, following an initial deposition taking a relatively short period of time, the heat transfer resistance fluctuates with time. Theoretical estimates of temperature distribution in the experimental flowing wax/kerosene system suggest that the cloud point temperature of the mixture falls within the laminar boundary layer. Since the cloud point is considered the temperature at which particles of wax appear, the conditions within the boundary layer will influence deposition. Increased flowrate and temperature decrease the number of particles able to deposit while the number is increased by greater wax concentration in the bulk solution. Des etudes faites sur la formation d'un depot de cire, provenant de melanges de cire et de kerosene, sur des tubes refroidis de transfert simule de chaleur ont demontre qu'a la suite de la formation d'un depot de cire en un temps relativement court, la resistance au transfert de la chaleur fluctue avec le temps. Des estimations theoriques de la distribution de la temperature dans le systeme experimental d'ecoulement du melange de cire et de kerosene semblent indiquer que la temperature du point-nuage du melange se trouve dans la couche-limite laminaire. Etant donne qu'on considere le point-nuage comme la temperature a laquelle des particules de cire apparaissent, les conditions qui prevalent dans la couche-limite ont une influence sur la formation du depot de cire. L'augmentation du debit de la temperature a pour effet de diminuer le nombre de particules qui peuvent se deposer, tandis que le nombre desdites particules s'accroit lorsque la concentration de la cire dans la solution totale augmente.