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Fouling surface finish evaluation
Applied Thermal Engineering 27 (2007) 1165–1172 www.elsevier.com/locate/apthermeng
Fouling surface finish evaluation David J. Kukulka *, Mohan Devgun State University of New York College at Buffalo, 1300 Elmwood Avenue Buffalo, NY 14222, USA Received 20 December 2005; accepted 2 February 2006
Abstract Fouling of a surface takes place as the result of a series of complex reactions that cause deposits to form on process surfaces. For many conditions, fouling can be reduced but not necessarily eliminated. The materials considered here are: carbon steel, stainless steel, and aluminium with typical finishes. Sample plates were placed vertically in tanks and exposed to untreated lake water for various time periods. Results are presented that compare surface roughness over time, for the materials/surfaces considered. The progressive change in surface appearance with increasing immersion times is also presented. Stainless steel samples showed a relatively small change in surface appearance for most periods of immersion, with a small increase in surface deterioration for increasing immersion times. Brite aluminum, an aluminium alloy with an anodized surface film, performs similar to stainless steels. Cold rolled carbon steel has the largest variation of surface appearance over time. This review includes observations on fouling and process surface materials/finishes. Conclusions and observations regarding the materials that are commonly used in designs when fouling may be a concern are presented here. Photographs of material frontal surfaces and transient surface roughness are given for a variety of surfaces. 2006 Elsevier Ltd. All rights reserved. Keywords: Fouling; Surface finish; Transient; Surface roughness; Surface photographs; Surface observations
1. Introduction Fouling deposits impede the transfer of heat and increase fluid flow resistance sometimes causing interference with a production process or damaging the product. Prevention and control of fouling becomes costly and time consuming. A fouling conditioning film forms immediately upon contact and is a prerequisite for further fouling to occur. It is then followed by an accumulation phase which is characterized by rapid growth. Finally a pseudo-steady state fouling takes place when the accumulation becomes almost constant. This paper will examine how several types of metals, with various finishes, respond when exposed to untreated lake water. *
Corresponding author. Tel.: +1 716 878 4418; fax: +1 716 878 3033. E-mail addresses: kukulkdj@buffalostate.edu (D.J. Kukulka), devgunms@buffalostate.edu (M. Devgun). 1359-4311/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2006.02.041
Fouling is complex, costly, and affects many different industries. Its development is more rapid in flowing systems where adequate nutrients are available. In systems with shear forces, the deposits may grow only to a few micrometers, while in other systems, deposits can reach the thickness of several centimeters Heitz et al. [1]. In most natural flowing systems the average biofilm thickness ranges from 50 to 500 lm (Costerton) [2]. Stronger shear forces will not prevent the deposits from forming, but lead to a thinner and firmer deposits. Fouling formation depends on the environmental conditions and properties of the process surface. The flow, temperature and chemical composition of the liquid all influence the formation of the deposit. A low or stagnant flow allows growth to more easily attach to the surface. Surface texture also impacts the formation of the deposit, with smooth surfaces not allowing the growth to adhere as easily as a textured surface. Although different from
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industry to industry, most deposits are unwelcome and have the potential to cause severe problems. Biofilms or microbial layers accumulate on a surface to the point where it is no longer usable. Fleming [3] states, ‘‘The extent of biofilm growth is the result of the balance between growth and detachment and it is dependant on the nutrient situation, the temperature and the shear forces.’’ In heat transfer systems, efficiency is reduced through the loss of flow through pipes and an increase in heat transfer resistance. The economic impact of the corrosion and fouling in these systems is enormous. Brennenstuhl et al. [4] reported that microbially influenced corrosion (MIC) caused damage of approximately $55 million in stainless steel heat exchangers within 8 years. Costs arise from the loss of energy, cleaning and repair efforts, parts, and monitoring. According to Taborek et al. [5,6] fouling can be divided into six distinctively different mechanisms: crystallization, particulate/sedimentation, chemical reaction and polymerization, coking, biological/organic material growth, and corrosion; with one or more of these fouling mechanisms occurring. Each mechanism requires a prevention and control technique unique to that mechanism. Also associated with these fouling deposits are the ways these deposits affect process characteristics. Two deposits of equal thickness can have different effects on the heat transfer since the resistance to heat transfer is based on deposit composition (which in turn is dependent on environmental nutrients). Turakhia et al. [7] gives a comparison of thermal conductivities and roughness factors for various deposits. Somerscales [8] presents the history of fouling research from its first appearance in literature in 1756 to the International Conference on Fouling of Heat Exchanger Equipment in 1979. He discusses the origin of the fouling factor as a means of accounting for the fouling while designing heat exchangers. Reutlinger [9] conducted a careful study on the effects of boiler fouling, while Orrok [10] presented measurements of the overall heat transfer coefficient. Both studies were a result of tests that were conducted on clean tubes, as well as tubes that had already been in service Care must exercised in looking at these types of studies since the results are dependent on the composition (nutrients available) of the fluids and the surface material/finish. Hardie and Cooper [11,12] published what is probably the first reliable value of the cleanliness factor for an operating condenser. Chlorination of the water supply in condensers and exchangers was referenced by Frost and Rippe [13], who reported on the value of using intermittent chlorination to improve the performance in the heat transfer of a system. Boruff and Stoll [14] discussed continuous chlorination to suppress the growth of microbial deposits. This led to the organization of the International Conference of the Fouling of Heat Exchangers Equipment in which scientists and engineers were brought together to assess the status of fouling research and attempt to identify the unifying concepts. The proceedings of the conference
were published by Somerscales [15]. Riihimaki et al. [16] presents a thermal analysis of heat exchangers in fouling conditions. Research in more recent years has focused on the prevention and monitoring of fouling. Monitoring devices include removable surfaces, measuring drag resistance, pressure drop, fluid friction resistance, and heat transfer. Tuladhar et al. [17] presents the development of a novel proximity gauging technique for soft deposits. Studies, such as the one undertaken in this paper, have been conducted on the use of surface coatings and exotic materials. Boulange-Peterman et al. [18] observed that the average surface roughness of stainless steel does not correlate to cell adhesion, while Frank and Chmielewski [19] indicate that surface defects correlate more closely with retention and removal of deposits. Callewaert et al. [20] discuss the treatment of stainless steel surfaces with polymers to limit fouling. Everaert and Baeyens [21] discuss the effect of heat transfer surface temperature, roughness, and fluid shear on fouling deposits. Zubair and Shah [22] present a discussion of fouling and the development of effective cleaning techniques. Studies by Jones et al. [23] and Holah and Thorne [24], observe that surface defects are closely associated with significant fouling increases and that deposits returned more rapidly after repeated cleanings. Zettler et al. [25] investigated the influence of surface properties, fluid temperature, fluid composition and fluid velocity on fouling deposits. Mott [26] concludes that smooth materials (glass and electropolished 316 stainless steel) had 35% less deposits than a corresponding ‘‘as received’’ 316 stainless steel. Temperature of a system also plays a critical role in the thickness of a biofilm. Systems with lower temperature thresholds typically have thinner deposits than a system with higher temperatures. Mott [26] shows that by raising the temperature from 30 C to 35 C an 80% increase in deposit thickness can be seen. 2. Experimental details Six inch square test plates were placed in tanks at the Great Lakes Research Center (State University of New York College at Buffalo Laboratory on Lake Erie) for varied amounts of time. Once-through water from Lake Erie was used to provide a flow of 6 l/min at 70 F. After the prescribed time, the tank was drained and the samples were allowed to dry. Photographs were taken of the surface and edges of the samples. Surface roughness measurements were taken with an average value presented. 2.1. Materials studied Aluminum: Brite aluminum, 3003-H14 anodized. Carbon steel: SAE/AISI 1020, cold rolled. Stainless steel: Type 304, satin finish. Stainless steel: Type 304, AgIon coated one side only.
D.J. Kukulka, M. Devgun / Applied Thermal Engineering 27 (2007) 1165–1172
All materials are commercially available and have typical finishes except the AgIon coating on one of the stainless steel samples. 2.2. Tank set up Several 20 gallon test tanks were used in the experimental set up with the same flow and temperature conditions. Samples were held in vertical positions as shown in Fig. 1. In each tank the plates were placed in the same position to maintain consistency throughout the experiment. The inlet hose was placed opposite the drain on the bottom of the tank to create a cross flow over the plates.
Fig. 1. Tank with positioned plates.
2.3. Water temperature and composition Temperature of incoming lake water averaged approximately 70.7 F. A graph of the water temperature for a portion of the time is shown in Fig. 2. Inlet water flow into the test tanks was set at 6 l/min. The make-up of the water used at the Great Lakes Center does not vary greatly and Table 1 shows the analysis of typical raw surface water from Lake Erie. 2.4. Sample processing and data collection After each tank reached its experimental time length, the inlet water to that tank was shut off. The drain tube was then removed allowing the tank to drain in a manner that least disturbed the system. Before the plates were removed, they were allowed to completely air dry. Care was given not to jostle or handle the plates in excess prior to collecting data. The first step after drying was to observe and photograph the surface appearance of each plate. Photographs of the plate surfaces were taken at 10 times magnification to capture the characteristics of the deposits on each plate surface. The next step was to obtain surface roughness measurements. Measurements were taken using PocketSurf I, a portable surface roughness gage with a traverse speed of 0.2’’ (5.08 mm) per second and a probe radius of 0.0004’’ (10 lm). Each sample was tested in three locations on the strip. Data was collected so that the PocketSurf probe traversed across the grain of the metal and also with the grain of the metal. A mean of three surface roughness readings was reported. Each sample was cut and mounted in an acrylic mold to aid in photographing the edge of the sample. The mounted samples were then ground and polished using the succes-
Incoming Average Temperature 74.5
Temperature (Fahrenheit)
74 73.5 73 72.5 72 71.5 71 70.5 70 69.5 3/4/2004
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3/9/2004 3/14/2004 3/19/2004 3/24/2004 3/29/2004 4/3/2004 4/8/2004 4/13/2004 4/18/2004
Date
Fig. 2. Lake water temperature graph.
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Table 1 Water composition and characteristics Ions (ppm) Cations Ca Mg Na K Fe Cu Ba Sr Al Mn
36.58 9.43 13.92 2.12 0.10 0.01 0.02 0.14 0.061 0.000
Total Anions OH CO3 HCO3 SO4 Cl NO3 F
3. Results and conclusion CaCO3 (ppm) 91.45 38.84 30.35 2.71 0.27 0.01 0.02 0.16 0.338 0.000 164.15
0.00 0.00 117.07 38.4 22.49 0.00 0.00
Total Total dissolved solids ppm ions = 240.79 Total dissolved solids ppm CaCo3 = 168.68 Total hardness ppm as CaCo3 = 130.29 Total alkalinity ppm as CaCo3 = 96.00 Fouling index = 5 pH of water = 6.80
0.00 0.0 96.00 39.98 31.71 0.00 0.00 167.69
sively finer grit sizes (down to 600 lm) and final polishing with a one micron alumina suspension. Finally, each sample was photographed using an Olympus microscope, Model SZX12, which was mounted with a Hitachi Digital Camera. The edge of each mounted plate was photographed at 40 times magnification for a consistent comparison of the plate edges.
Several materials (brite aluminium, plain carbon steel, and stainless steel) with various surface finishes were tested. These materials were placed in tanks at the Great Lakes Research Center for varied amounts of time, with once though water from Lake Erie being circulated. After the prescribed time, the tank was drained and the samples were dried. As each set of plates was removed from the medium, observations about the conditions of each plate were made. These observations included: visible film, color change, corrosion, deposit characteristics, etc. Tables 2–5 show the surfaces of the plates and supports the conclusions made in Tables 6–8. Tables 6–8 provide extensive observations of surface conditions for the time periods considered. Surface roughness measurements for each of the materials are summarized in Fig. 3. The graph shows the surface roughness measurement versus the time the plate was exposed to lake water. Since three measurements were taken for each plate sample, the data points are averaged surface roughness values for a particular time period. Each material showed an increase in the surface roughness from the original values to those measured at ninety days. Comparing the surface roughness values over the time period shows a gradual increase in the roughness values with increasing immersion time. Measurements taken of the cold rolled carbon steel have a high degree of error associated with measurements after the initial measurement since a large amount of corrosion existed on the steel surface. When taking plain carbon plate measurements, the probe was not able to record the measurements accurately because of the high variation across the traversed area. This accounts for the highly irregular data points in Fig. 3 for carbon steel. After the conditioning film formed, the amount of fouling increased by approximately 200% during the first ninety days.
Table 2 Photographs showing transient surface deposition (frontal view – 10·) for AgIon stainless steel at 70 F
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Table 3 Photographs showing transient surface deposition (frontal view – 10·) satin stainless steel at 70 F
Table 4 Photographs showing transient surface deposition (frontal view – 10·) for brite aluminum at 70 F
Stainless Steel with the AgIon coating consistently had lower surface roughness than the other samples. This was
expected due to the antimicrobial properties of the material coating. It is reasonable to say that this material would
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Table 5 Photographs showing transient surface deposition (frontal view – 10·) for cold rolled carbon steel at 70 F
Table 6 Surface appearance observations of stainless steels for various time periods 7 Days
30 Days
60 Days
90 Days
AgIon stainless steel
Slight collection of film covering random areas
Slightly more film collection than previous observation. Some areas thick, others with film
More consistent film Thicker, spottier collection on surface collection of of the plate. Thicker than film in some areas previous two observations
Stainless steel satin finish
Slight collection of Slight collection of film; film covering random deposits spotty over area of plate
More consistent deposits than the previous observation
120 Days
Collection of film spotty in areas. Not a noticeable change from the previous observation Deposits on plate are more Not a noticeable consistent and slightly more change from the than the 60 day observations previous observation
Table 7 Surface appearance observations of brite aluminum for various time periods 7 Days
14 Days
28 Days
42 Days
Brite aluminum
The surface of the plate is shiny
The plate still appears shiny with a light collection of film
95% of the surface of the plate is covered with a film
100% of the plate is covered with a collection of film. The film is tan
56 Days
70 Days
84 Days
98 Days
112 Days
100% of the surface is covered with a collection of film. The film is thicker in appearance
100% of the surface is covered with a collection of film. No noticeable change than that of the 56 day observation
100% of the surface is covered with a collection of film. The film appears a lighter tan than previous weeks
100% of the surface is covered with a collection of film. No noticeable change from the 84 day observation
100% of the surface is covered with a collection of film. The film is thicker than that of the previous plates
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Table 8 Surface appearance observations of cold rolled carbon steel for various time periods Material
7 Days
14 Days
21 Days
28 Days
Cold rolled carbon steel
The surface is covered with a collection of film. Small deposits of rust in sections
Large spots of rust and corrosion on top corner and along the bottom of the plate
Large spots of rust and corrosion along the top and bottom of the plate. More rust than the 14 day
Large spots of rust covering 85% of the plate. Rust appears thicker and flakes in spots along the bottom
35 Days
42 Days
49 Days
56 Days
63 Days
Large spots of rust covering most of the plate darker rust color in areas. More consistent than previous weeks
Rust spots covering 90% of the plate. Appears thicker with more flakes across the middle and bottom
Consistent layer of sediment and rust throughout the plate. Less flakes than previous weeks
Less rust spots than previous weeks. Thicker, darker areas of rust than previous weeks. Flakes spots where rust is. Thicker layer of sediment in other areas
Most of the plate is covered with rust and corrosion. Very thick rust layers in areas
70 Days
77 Days
84 Days
Rust spots and corrosion throughout most of the plate. Flakes very thick along top and on the edge of the plate
Very thick layer of rust and corrosion throughout plate. More so than previous weeks. Flakes along the bottom. Darker rust in some areas
Very thick layer of rust and corrosion on the plate. Left corner of plate is very thick and dark rust color with big flakes. Corrosion over top layer of rust
Surface Roughness Measurements
Surface Roughness (micro-inches)
250.00
200.00
150.00
100.00
50.00
0.00 0
10
20
30
40
50
60
70
80
90
100
Days in Tank Aluminum Cold-Rolled Carbon Steel Linear (Cold-Rolled Carbon Steel)
Agion Stainless Stainless Steel - Satin Finish Linear (Agion Stainless)
Linear (Stainless Steel - Satin Finish)
Linear (Aluminum)
Fig. 3. Surface roughness vs. time (days) for various surfaces.
reach steady state earlier than a non-coated sample. Fouling amounts increased by 80% in the first 90 days (after the conditioning film formed) for the satin stainless steel, while the AgIon stainless increased by less than 40%. Brite aluminium behaved similar (75 % increase) to the satin stainless steel.
This study showed the thickness of the deposit became more visible the longer the plate was exposed to the lake water and is correlated through the use of the surface roughness measurements. The length time that the plate is exposed to the ambient fluid as well as the fluid temperature have large effects on the amount of fouling that takes
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place and is currently being studied greater detail. This study will include an examination of other materials/surfaces, plate geometries, fluid flow rates and environmental conditions. References [1] E. Heitz, H.C. Flemming, W. Sand (Eds.), Microbial Influenced Corrosion of Materials, Springer-Verlag, Berlin Heidelberg, 1996. [2] J.W. Costerton, J. Boivin, Microbial influenced corrosion, in: M.W. Mittleman, G.G. Geesey (Eds.), Biological Fouling of Industrial Water Systems, A Problem Solving Approach, Water Micro Associates, San Diego, 1987, pp. 56–76. [3] H.C. Flemming, Biofouling in water treatment, in: H.C. Flemming, G.G. Geesey (Eds.), Biofouling and Corrosion in Industrial Water Systems, Springer-Verlag, Berlin Heidelberg, 1991, pp. 29–46. [4] A.M. Brennenstuhl, P.E. Doherty, P.J. King, T.J. Dunstall, The effects of biofouling on the corrosion of nickel heat exchangers alloys at Ontario hydo, in: N.J. Dowling, M.N. Mittleman, D.C. Danco (Eds.), Microbially Influenced Corrosion and Biodeteriation, University of Tennessee, Knoxville, TN 37932-2567, 1992, pp. 4.25–4.31. [5] J. Taborek, T. Aoku, R.B. Ritter, J.W. Paeln, J.G. Knudsen, Fouling the major unresolved problem in heat transfer – Part I, Chem. Eng. Progr. 68 (2) (1972) 59–67. [6] J. Taborek, T. Aoku, R.B. Ritter, J.W. Paeln, J.G. Knudsen, Fouling the major unresolved problem in heat transfer – Part II, Chem. Eng. Progr. 68 (7) (1972) 69–78. [7] M.H. Turakhia, W.G. Characklis, N. Zelver, Fouling of heat exchange surfaces: measurement and diagnosis, Heat Transfer Eng. 5 (1984) 93–101. [8] E.F.C. Somerscales, J.G. Knudsen (Eds.), Fouling of Heat Exchanger Equipment, Hemisphere Publishing Corp., Washington, DC, 1981. [9] E. Reutlinger, Der Einfluss des Kesselsteines suf Wirtschaftlichheit und Betriebsicherheit von Heizvorrichtungen, Z. Ver. Deutscher Ing. 34 (1910) 545–553, 596–601, 638–642, 676–681. [10] G.A. Orrok, The transmission of heat in surface condensation, ASME Trans. 32 (1910) 1139–1214. [11] P.H. Hardie, W.S. Cooper, A test method for determining the quantitative effect of tube fouling in condenser performance, ASME Trans. 53 (RP-53-3) (1933) 37–49. [12] P.H. Hardie, W.F. Cooper, The accuracy of the cleanliness factor measurement for surface condensers, ASME Trans. 58 (FSP-58-5) (1936) 349–353, discussion vol. 59, pp. 141–144.
[13] M. Frost, W.F. Rippe, Experience in chlorinating condenser cooling water, ASME Trans. 53 (FSP-53-10) (1931) 131–138. [14] C.S. Boruff, K.E. Stoll, Intermittent chlorination of condenser water, Ind. Eng. Chem. 24 (1932) 398–400. [15] E.F.C. Somerscales, The fouling of heat transfer surfaces: a historical review, Heat Transfer Eng. 11 (1) (1990) 19–36. [16] M. Riihimaki, E. Muurinen, R. Keiski, Thermal analysis of a plate heat exchanger in fouling conditions – analysis of process information and calculations based on design equations, CHISA 2004 – 16th International Congress of Chemical and Process Engineering CHISA 2004 – 16th International Congress of Chemical and Process Engineering, Prague, 2004, pp. 7947–7948. [17] T. Tuladhar, W. Paterson, N. Macleod, D. Wilson, Development of a novel non-contact proximity gauge for thickness measurement of soft deposits and its application in fouling studies, Can. J. Chem. Eng. 78 (5) (2000) 935–947. [18] L. Boulange-Peterman, J. Rault, M.N. Bellon-Fontaine, Adhesion of streptococcus thermophilus to stainless steel with different surface topography and roughness, Biofouling 11 (3) (1997) 201–216. [19] J. Frank, R. Chmielewski, Influence of surface finish on the cleanability on stainless steel, Food Prot. 68 (8) (2001) 1178–1182. [20] M. Callewart, P. Rouxhet, L. Boulange-Petermann, Modifying stainless steel surfaces with responsive polymers: effect of PS-PAA and PNIPAAM on cell adhesion and oil removal, J. Adhes. Sci. Technol. 19 (9) (2005) 765–781. [21] K. Everaert, J. Baeyens, Fundamentals and control of heat exchanger fouling, CHISA 2004 – 16th International Congress of Chemical and Process Engineering CHISA 2004 – 16th International Congress of Chemical and Process Engineering, Prague, 2004, pp. 4203–4204. [22] S. Zubair, R. Shah, Fouling of plate-and-frame heat exchangers and cleaning strategies, Int. J. Heat Exchangers 5 (1) (2004) 129–156. [23] C.R. Jones, M.R. Adams, P.A. Zhadan, A.H.L. Chamberlain, The role of surface physiochemical properties in determining the distribution of the autochthonous microflora in mineral water bottles, J. Appl. Microb. 86 (1999) 917–927. [24] J.T. Holah, R.H. Thorne, Cleanability in relation to bacterial retention on unused and abraded domestic sink materials, J. Appl. Bacteriol. 69 (1990) 599–608. [25] H.U. Zettler, M. Weiss, Q. Zhao, H. Muller-Steinhagen, Influence of surface properties and characteristics on fouling in plate heat exchangers, Heat Transfer Eng. 26 (2) (2005) 3–17. [26] I.E.C. Mott, Biofouling and studies using simulated cooling water, Ph.D. thesis, University Birmingham, Birmingham, UK, 1991.
Fouling surface finish evaluation David J. Kukulka *, Mohan Devgun State University of New York College at Buffalo, 1300 Elmwood Avenue Buffalo, NY 14222, USA Received 20 December 2005; accepted 2 February 2006
Abstract Fouling of a surface takes place as the result of a series of complex reactions that cause deposits to form on process surfaces. For many conditions, fouling can be reduced but not necessarily eliminated. The materials considered here are: carbon steel, stainless steel, and aluminium with typical finishes. Sample plates were placed vertically in tanks and exposed to untreated lake water for various time periods. Results are presented that compare surface roughness over time, for the materials/surfaces considered. The progressive change in surface appearance with increasing immersion times is also presented. Stainless steel samples showed a relatively small change in surface appearance for most periods of immersion, with a small increase in surface deterioration for increasing immersion times. Brite aluminum, an aluminium alloy with an anodized surface film, performs similar to stainless steels. Cold rolled carbon steel has the largest variation of surface appearance over time. This review includes observations on fouling and process surface materials/finishes. Conclusions and observations regarding the materials that are commonly used in designs when fouling may be a concern are presented here. Photographs of material frontal surfaces and transient surface roughness are given for a variety of surfaces. 2006 Elsevier Ltd. All rights reserved. Keywords: Fouling; Surface finish; Transient; Surface roughness; Surface photographs; Surface observations
1. Introduction Fouling deposits impede the transfer of heat and increase fluid flow resistance sometimes causing interference with a production process or damaging the product. Prevention and control of fouling becomes costly and time consuming. A fouling conditioning film forms immediately upon contact and is a prerequisite for further fouling to occur. It is then followed by an accumulation phase which is characterized by rapid growth. Finally a pseudo-steady state fouling takes place when the accumulation becomes almost constant. This paper will examine how several types of metals, with various finishes, respond when exposed to untreated lake water. *
Corresponding author. Tel.: +1 716 878 4418; fax: +1 716 878 3033. E-mail addresses: kukulkdj@buffalostate.edu (D.J. Kukulka), devgunms@buffalostate.edu (M. Devgun). 1359-4311/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2006.02.041
Fouling is complex, costly, and affects many different industries. Its development is more rapid in flowing systems where adequate nutrients are available. In systems with shear forces, the deposits may grow only to a few micrometers, while in other systems, deposits can reach the thickness of several centimeters Heitz et al. [1]. In most natural flowing systems the average biofilm thickness ranges from 50 to 500 lm (Costerton) [2]. Stronger shear forces will not prevent the deposits from forming, but lead to a thinner and firmer deposits. Fouling formation depends on the environmental conditions and properties of the process surface. The flow, temperature and chemical composition of the liquid all influence the formation of the deposit. A low or stagnant flow allows growth to more easily attach to the surface. Surface texture also impacts the formation of the deposit, with smooth surfaces not allowing the growth to adhere as easily as a textured surface. Although different from
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industry to industry, most deposits are unwelcome and have the potential to cause severe problems. Biofilms or microbial layers accumulate on a surface to the point where it is no longer usable. Fleming [3] states, ‘‘The extent of biofilm growth is the result of the balance between growth and detachment and it is dependant on the nutrient situation, the temperature and the shear forces.’’ In heat transfer systems, efficiency is reduced through the loss of flow through pipes and an increase in heat transfer resistance. The economic impact of the corrosion and fouling in these systems is enormous. Brennenstuhl et al. [4] reported that microbially influenced corrosion (MIC) caused damage of approximately $55 million in stainless steel heat exchangers within 8 years. Costs arise from the loss of energy, cleaning and repair efforts, parts, and monitoring. According to Taborek et al. [5,6] fouling can be divided into six distinctively different mechanisms: crystallization, particulate/sedimentation, chemical reaction and polymerization, coking, biological/organic material growth, and corrosion; with one or more of these fouling mechanisms occurring. Each mechanism requires a prevention and control technique unique to that mechanism. Also associated with these fouling deposits are the ways these deposits affect process characteristics. Two deposits of equal thickness can have different effects on the heat transfer since the resistance to heat transfer is based on deposit composition (which in turn is dependent on environmental nutrients). Turakhia et al. [7] gives a comparison of thermal conductivities and roughness factors for various deposits. Somerscales [8] presents the history of fouling research from its first appearance in literature in 1756 to the International Conference on Fouling of Heat Exchanger Equipment in 1979. He discusses the origin of the fouling factor as a means of accounting for the fouling while designing heat exchangers. Reutlinger [9] conducted a careful study on the effects of boiler fouling, while Orrok [10] presented measurements of the overall heat transfer coefficient. Both studies were a result of tests that were conducted on clean tubes, as well as tubes that had already been in service Care must exercised in looking at these types of studies since the results are dependent on the composition (nutrients available) of the fluids and the surface material/finish. Hardie and Cooper [11,12] published what is probably the first reliable value of the cleanliness factor for an operating condenser. Chlorination of the water supply in condensers and exchangers was referenced by Frost and Rippe [13], who reported on the value of using intermittent chlorination to improve the performance in the heat transfer of a system. Boruff and Stoll [14] discussed continuous chlorination to suppress the growth of microbial deposits. This led to the organization of the International Conference of the Fouling of Heat Exchangers Equipment in which scientists and engineers were brought together to assess the status of fouling research and attempt to identify the unifying concepts. The proceedings of the conference
were published by Somerscales [15]. Riihimaki et al. [16] presents a thermal analysis of heat exchangers in fouling conditions. Research in more recent years has focused on the prevention and monitoring of fouling. Monitoring devices include removable surfaces, measuring drag resistance, pressure drop, fluid friction resistance, and heat transfer. Tuladhar et al. [17] presents the development of a novel proximity gauging technique for soft deposits. Studies, such as the one undertaken in this paper, have been conducted on the use of surface coatings and exotic materials. Boulange-Peterman et al. [18] observed that the average surface roughness of stainless steel does not correlate to cell adhesion, while Frank and Chmielewski [19] indicate that surface defects correlate more closely with retention and removal of deposits. Callewaert et al. [20] discuss the treatment of stainless steel surfaces with polymers to limit fouling. Everaert and Baeyens [21] discuss the effect of heat transfer surface temperature, roughness, and fluid shear on fouling deposits. Zubair and Shah [22] present a discussion of fouling and the development of effective cleaning techniques. Studies by Jones et al. [23] and Holah and Thorne [24], observe that surface defects are closely associated with significant fouling increases and that deposits returned more rapidly after repeated cleanings. Zettler et al. [25] investigated the influence of surface properties, fluid temperature, fluid composition and fluid velocity on fouling deposits. Mott [26] concludes that smooth materials (glass and electropolished 316 stainless steel) had 35% less deposits than a corresponding ‘‘as received’’ 316 stainless steel. Temperature of a system also plays a critical role in the thickness of a biofilm. Systems with lower temperature thresholds typically have thinner deposits than a system with higher temperatures. Mott [26] shows that by raising the temperature from 30 C to 35 C an 80% increase in deposit thickness can be seen. 2. Experimental details Six inch square test plates were placed in tanks at the Great Lakes Research Center (State University of New York College at Buffalo Laboratory on Lake Erie) for varied amounts of time. Once-through water from Lake Erie was used to provide a flow of 6 l/min at 70 F. After the prescribed time, the tank was drained and the samples were allowed to dry. Photographs were taken of the surface and edges of the samples. Surface roughness measurements were taken with an average value presented. 2.1. Materials studied Aluminum: Brite aluminum, 3003-H14 anodized. Carbon steel: SAE/AISI 1020, cold rolled. Stainless steel: Type 304, satin finish. Stainless steel: Type 304, AgIon coated one side only.
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All materials are commercially available and have typical finishes except the AgIon coating on one of the stainless steel samples. 2.2. Tank set up Several 20 gallon test tanks were used in the experimental set up with the same flow and temperature conditions. Samples were held in vertical positions as shown in Fig. 1. In each tank the plates were placed in the same position to maintain consistency throughout the experiment. The inlet hose was placed opposite the drain on the bottom of the tank to create a cross flow over the plates.
Fig. 1. Tank with positioned plates.
2.3. Water temperature and composition Temperature of incoming lake water averaged approximately 70.7 F. A graph of the water temperature for a portion of the time is shown in Fig. 2. Inlet water flow into the test tanks was set at 6 l/min. The make-up of the water used at the Great Lakes Center does not vary greatly and Table 1 shows the analysis of typical raw surface water from Lake Erie. 2.4. Sample processing and data collection After each tank reached its experimental time length, the inlet water to that tank was shut off. The drain tube was then removed allowing the tank to drain in a manner that least disturbed the system. Before the plates were removed, they were allowed to completely air dry. Care was given not to jostle or handle the plates in excess prior to collecting data. The first step after drying was to observe and photograph the surface appearance of each plate. Photographs of the plate surfaces were taken at 10 times magnification to capture the characteristics of the deposits on each plate surface. The next step was to obtain surface roughness measurements. Measurements were taken using PocketSurf I, a portable surface roughness gage with a traverse speed of 0.2’’ (5.08 mm) per second and a probe radius of 0.0004’’ (10 lm). Each sample was tested in three locations on the strip. Data was collected so that the PocketSurf probe traversed across the grain of the metal and also with the grain of the metal. A mean of three surface roughness readings was reported. Each sample was cut and mounted in an acrylic mold to aid in photographing the edge of the sample. The mounted samples were then ground and polished using the succes-
Incoming Average Temperature 74.5
Temperature (Fahrenheit)
74 73.5 73 72.5 72 71.5 71 70.5 70 69.5 3/4/2004
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3/9/2004 3/14/2004 3/19/2004 3/24/2004 3/29/2004 4/3/2004 4/8/2004 4/13/2004 4/18/2004
Date
Fig. 2. Lake water temperature graph.
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Table 1 Water composition and characteristics Ions (ppm) Cations Ca Mg Na K Fe Cu Ba Sr Al Mn
36.58 9.43 13.92 2.12 0.10 0.01 0.02 0.14 0.061 0.000
Total Anions OH CO3 HCO3 SO4 Cl NO3 F
3. Results and conclusion CaCO3 (ppm) 91.45 38.84 30.35 2.71 0.27 0.01 0.02 0.16 0.338 0.000 164.15
0.00 0.00 117.07 38.4 22.49 0.00 0.00
Total Total dissolved solids ppm ions = 240.79 Total dissolved solids ppm CaCo3 = 168.68 Total hardness ppm as CaCo3 = 130.29 Total alkalinity ppm as CaCo3 = 96.00 Fouling index = 5 pH of water = 6.80
0.00 0.0 96.00 39.98 31.71 0.00 0.00 167.69
sively finer grit sizes (down to 600 lm) and final polishing with a one micron alumina suspension. Finally, each sample was photographed using an Olympus microscope, Model SZX12, which was mounted with a Hitachi Digital Camera. The edge of each mounted plate was photographed at 40 times magnification for a consistent comparison of the plate edges.
Several materials (brite aluminium, plain carbon steel, and stainless steel) with various surface finishes were tested. These materials were placed in tanks at the Great Lakes Research Center for varied amounts of time, with once though water from Lake Erie being circulated. After the prescribed time, the tank was drained and the samples were dried. As each set of plates was removed from the medium, observations about the conditions of each plate were made. These observations included: visible film, color change, corrosion, deposit characteristics, etc. Tables 2–5 show the surfaces of the plates and supports the conclusions made in Tables 6–8. Tables 6–8 provide extensive observations of surface conditions for the time periods considered. Surface roughness measurements for each of the materials are summarized in Fig. 3. The graph shows the surface roughness measurement versus the time the plate was exposed to lake water. Since three measurements were taken for each plate sample, the data points are averaged surface roughness values for a particular time period. Each material showed an increase in the surface roughness from the original values to those measured at ninety days. Comparing the surface roughness values over the time period shows a gradual increase in the roughness values with increasing immersion time. Measurements taken of the cold rolled carbon steel have a high degree of error associated with measurements after the initial measurement since a large amount of corrosion existed on the steel surface. When taking plain carbon plate measurements, the probe was not able to record the measurements accurately because of the high variation across the traversed area. This accounts for the highly irregular data points in Fig. 3 for carbon steel. After the conditioning film formed, the amount of fouling increased by approximately 200% during the first ninety days.
Table 2 Photographs showing transient surface deposition (frontal view – 10·) for AgIon stainless steel at 70 F
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Table 3 Photographs showing transient surface deposition (frontal view – 10·) satin stainless steel at 70 F
Table 4 Photographs showing transient surface deposition (frontal view – 10·) for brite aluminum at 70 F
Stainless Steel with the AgIon coating consistently had lower surface roughness than the other samples. This was
expected due to the antimicrobial properties of the material coating. It is reasonable to say that this material would
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Table 5 Photographs showing transient surface deposition (frontal view – 10·) for cold rolled carbon steel at 70 F
Table 6 Surface appearance observations of stainless steels for various time periods 7 Days
30 Days
60 Days
90 Days
AgIon stainless steel
Slight collection of film covering random areas
Slightly more film collection than previous observation. Some areas thick, others with film
More consistent film Thicker, spottier collection on surface collection of of the plate. Thicker than film in some areas previous two observations
Stainless steel satin finish
Slight collection of Slight collection of film; film covering random deposits spotty over area of plate
More consistent deposits than the previous observation
120 Days
Collection of film spotty in areas. Not a noticeable change from the previous observation Deposits on plate are more Not a noticeable consistent and slightly more change from the than the 60 day observations previous observation
Table 7 Surface appearance observations of brite aluminum for various time periods 7 Days
14 Days
28 Days
42 Days
Brite aluminum
The surface of the plate is shiny
The plate still appears shiny with a light collection of film
95% of the surface of the plate is covered with a film
100% of the plate is covered with a collection of film. The film is tan
56 Days
70 Days
84 Days
98 Days
112 Days
100% of the surface is covered with a collection of film. The film is thicker in appearance
100% of the surface is covered with a collection of film. No noticeable change than that of the 56 day observation
100% of the surface is covered with a collection of film. The film appears a lighter tan than previous weeks
100% of the surface is covered with a collection of film. No noticeable change from the 84 day observation
100% of the surface is covered with a collection of film. The film is thicker than that of the previous plates
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Table 8 Surface appearance observations of cold rolled carbon steel for various time periods Material
7 Days
14 Days
21 Days
28 Days
Cold rolled carbon steel
The surface is covered with a collection of film. Small deposits of rust in sections
Large spots of rust and corrosion on top corner and along the bottom of the plate
Large spots of rust and corrosion along the top and bottom of the plate. More rust than the 14 day
Large spots of rust covering 85% of the plate. Rust appears thicker and flakes in spots along the bottom
35 Days
42 Days
49 Days
56 Days
63 Days
Large spots of rust covering most of the plate darker rust color in areas. More consistent than previous weeks
Rust spots covering 90% of the plate. Appears thicker with more flakes across the middle and bottom
Consistent layer of sediment and rust throughout the plate. Less flakes than previous weeks
Less rust spots than previous weeks. Thicker, darker areas of rust than previous weeks. Flakes spots where rust is. Thicker layer of sediment in other areas
Most of the plate is covered with rust and corrosion. Very thick rust layers in areas
70 Days
77 Days
84 Days
Rust spots and corrosion throughout most of the plate. Flakes very thick along top and on the edge of the plate
Very thick layer of rust and corrosion throughout plate. More so than previous weeks. Flakes along the bottom. Darker rust in some areas
Very thick layer of rust and corrosion on the plate. Left corner of plate is very thick and dark rust color with big flakes. Corrosion over top layer of rust
Surface Roughness Measurements
Surface Roughness (micro-inches)
250.00
200.00
150.00
100.00
50.00
0.00 0
10
20
30
40
50
60
70
80
90
100
Days in Tank Aluminum Cold-Rolled Carbon Steel Linear (Cold-Rolled Carbon Steel)
Agion Stainless Stainless Steel - Satin Finish Linear (Agion Stainless)
Linear (Stainless Steel - Satin Finish)
Linear (Aluminum)
Fig. 3. Surface roughness vs. time (days) for various surfaces.
reach steady state earlier than a non-coated sample. Fouling amounts increased by 80% in the first 90 days (after the conditioning film formed) for the satin stainless steel, while the AgIon stainless increased by less than 40%. Brite aluminium behaved similar (75 % increase) to the satin stainless steel.
This study showed the thickness of the deposit became more visible the longer the plate was exposed to the lake water and is correlated through the use of the surface roughness measurements. The length time that the plate is exposed to the ambient fluid as well as the fluid temperature have large effects on the amount of fouling that takes
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place and is currently being studied greater detail. This study will include an examination of other materials/surfaces, plate geometries, fluid flow rates and environmental conditions. References [1] E. Heitz, H.C. Flemming, W. Sand (Eds.), Microbial Influenced Corrosion of Materials, Springer-Verlag, Berlin Heidelberg, 1996. [2] J.W. Costerton, J. Boivin, Microbial influenced corrosion, in: M.W. Mittleman, G.G. Geesey (Eds.), Biological Fouling of Industrial Water Systems, A Problem Solving Approach, Water Micro Associates, San Diego, 1987, pp. 56–76. [3] H.C. Flemming, Biofouling in water treatment, in: H.C. Flemming, G.G. Geesey (Eds.), Biofouling and Corrosion in Industrial Water Systems, Springer-Verlag, Berlin Heidelberg, 1991, pp. 29–46. [4] A.M. Brennenstuhl, P.E. Doherty, P.J. King, T.J. Dunstall, The effects of biofouling on the corrosion of nickel heat exchangers alloys at Ontario hydo, in: N.J. Dowling, M.N. Mittleman, D.C. Danco (Eds.), Microbially Influenced Corrosion and Biodeteriation, University of Tennessee, Knoxville, TN 37932-2567, 1992, pp. 4.25–4.31. [5] J. Taborek, T. Aoku, R.B. Ritter, J.W. Paeln, J.G. Knudsen, Fouling the major unresolved problem in heat transfer – Part I, Chem. Eng. Progr. 68 (2) (1972) 59–67. [6] J. Taborek, T. Aoku, R.B. Ritter, J.W. Paeln, J.G. Knudsen, Fouling the major unresolved problem in heat transfer – Part II, Chem. Eng. Progr. 68 (7) (1972) 69–78. [7] M.H. Turakhia, W.G. Characklis, N. Zelver, Fouling of heat exchange surfaces: measurement and diagnosis, Heat Transfer Eng. 5 (1984) 93–101. [8] E.F.C. Somerscales, J.G. Knudsen (Eds.), Fouling of Heat Exchanger Equipment, Hemisphere Publishing Corp., Washington, DC, 1981. [9] E. Reutlinger, Der Einfluss des Kesselsteines suf Wirtschaftlichheit und Betriebsicherheit von Heizvorrichtungen, Z. Ver. Deutscher Ing. 34 (1910) 545–553, 596–601, 638–642, 676–681. [10] G.A. Orrok, The transmission of heat in surface condensation, ASME Trans. 32 (1910) 1139–1214. [11] P.H. Hardie, W.S. Cooper, A test method for determining the quantitative effect of tube fouling in condenser performance, ASME Trans. 53 (RP-53-3) (1933) 37–49. [12] P.H. Hardie, W.F. Cooper, The accuracy of the cleanliness factor measurement for surface condensers, ASME Trans. 58 (FSP-58-5) (1936) 349–353, discussion vol. 59, pp. 141–144.
[13] M. Frost, W.F. Rippe, Experience in chlorinating condenser cooling water, ASME Trans. 53 (FSP-53-10) (1931) 131–138. [14] C.S. Boruff, K.E. Stoll, Intermittent chlorination of condenser water, Ind. Eng. Chem. 24 (1932) 398–400. [15] E.F.C. Somerscales, The fouling of heat transfer surfaces: a historical review, Heat Transfer Eng. 11 (1) (1990) 19–36. [16] M. Riihimaki, E. Muurinen, R. Keiski, Thermal analysis of a plate heat exchanger in fouling conditions – analysis of process information and calculations based on design equations, CHISA 2004 – 16th International Congress of Chemical and Process Engineering CHISA 2004 – 16th International Congress of Chemical and Process Engineering, Prague, 2004, pp. 7947–7948. [17] T. Tuladhar, W. Paterson, N. Macleod, D. Wilson, Development of a novel non-contact proximity gauge for thickness measurement of soft deposits and its application in fouling studies, Can. J. Chem. Eng. 78 (5) (2000) 935–947. [18] L. Boulange-Peterman, J. Rault, M.N. Bellon-Fontaine, Adhesion of streptococcus thermophilus to stainless steel with different surface topography and roughness, Biofouling 11 (3) (1997) 201–216. [19] J. Frank, R. Chmielewski, Influence of surface finish on the cleanability on stainless steel, Food Prot. 68 (8) (2001) 1178–1182. [20] M. Callewart, P. Rouxhet, L. Boulange-Petermann, Modifying stainless steel surfaces with responsive polymers: effect of PS-PAA and PNIPAAM on cell adhesion and oil removal, J. Adhes. Sci. Technol. 19 (9) (2005) 765–781. [21] K. Everaert, J. Baeyens, Fundamentals and control of heat exchanger fouling, CHISA 2004 – 16th International Congress of Chemical and Process Engineering CHISA 2004 – 16th International Congress of Chemical and Process Engineering, Prague, 2004, pp. 4203–4204. [22] S. Zubair, R. Shah, Fouling of plate-and-frame heat exchangers and cleaning strategies, Int. J. Heat Exchangers 5 (1) (2004) 129–156. [23] C.R. Jones, M.R. Adams, P.A. Zhadan, A.H.L. Chamberlain, The role of surface physiochemical properties in determining the distribution of the autochthonous microflora in mineral water bottles, J. Appl. Microb. 86 (1999) 917–927. [24] J.T. Holah, R.H. Thorne, Cleanability in relation to bacterial retention on unused and abraded domestic sink materials, J. Appl. Bacteriol. 69 (1990) 599–608. [25] H.U. Zettler, M. Weiss, Q. Zhao, H. Muller-Steinhagen, Influence of surface properties and characteristics on fouling in plate heat exchangers, Heat Transfer Eng. 26 (2) (2005) 3–17. [26] I.E.C. Mott, Biofouling and studies using simulated cooling water, Ph.D. thesis, University Birmingham, Birmingham, UK, 1991.