Progress 04/15/14 to 04/14/18
Outputs
Target Audience:Government scientists and faculty, staff and graduate students interested in interfacial sciences; Members of industry looking for deeper understanding of oil, water, solids, and vapor interfacial transport at elevated temperatures. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Over this reporting period, the PI's worked with one doctoral student and one post-doctoral researcher. In addition to coursework, the doctoral student took an active role in continued set-up of the laboratory, installation and calibration of instrumentation, statistical design of (her) experiments, and preliminary data analysis. The post-doctoral researcher was involved in these activities independently and in collaboration with the PI. Training and professional development were in the form of basic academic professionall development (establishing a laboratory and design of experiments) to presentation skills and interview techniques. How have the results been disseminated to communities of interest?Two papers werewere published in theJournal of Food Engineering. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
The aim of this portion of the research study was to understand the effect of oil quality, oil temperature, pore diameter and surface wettability on bubble dynamics using a simplified model system consisting of a single pore assembly submerged in oil. Based on the results from this parametric study, hypotheses were developed to qualitatively describe the impact of bubble dynamics on heat transfer rates as applicable to the frying process. Experiments were conducted for fresh and used oil at room temperature and 170 C for different orifice sizes and two surface materials. Increase in temperature led to decrease in bubble volume and bubble formation time. The bubble frequency increased with increase in temperature. Increase in oil temperature causes a linear decrease in oil density and surface tension, and an exponential decrease in viscosity. The changes in fluid properties were characterized in terms of change in Bo and Oh numbers for each orifice diameter studied. For all orifice diameters, Bo increased and Oh decreased with increase in temperature. Hence the smaller formation time and bubble volume observed in the present study agrees with literature findings for aqueous-based studies. Lower bubble volume and formation time can be attributed to decrease in fluid density, viscosity, and surface tension with increase in temperature. Increase in temperature also increases the wettability of oil, hence oil rewets the surface faster, resulting in a decreased lag time. The decrease in lag time could also be attributed to exponential decrease in viscosity which increases the oil's ability to flow back into the void left as the bubble departs. Improved wettability as temperature increased was also observed in the dynamic angle data, where the rate of change of contact angle was higher during the formation stage, and the rewetting was faster during the lag time between bubbles at 170C. Thus, the decrease in volume and increase in frequency with increasing temperature found in the literature agrees with the current findings. Experiments were conducted for fresh and used oil on steel and Teflon surfaces at room temperature and 170C with different orifice diameters. The bubbling results for steel and Teflon were analyzed for 0.75mm and 1mm orifices. The surface and the capillary were made of the same material for both steel and Teflon. Teflon has a lower wettability (equilibrium angle, θ=60Åã) with oil compared to steel (θ=12o). Bubbles formed on the Teflon surface had a higher volume and a lower frequency than the steel surface. Lower frequency of bubbling on a Teflon surface was accompanied with higher lag time between two bubbles on the Teflon surface caused by low wettability. The low wettability prevented oil from rewetting the void created due to bubble pinch-off during the time between consecutive bubbles. However, the bubbles on Teflon experienced a lower formation time compared to steel surface. The bubble forming on the steel surface experienced a significant slow rate of growth during the nucleation stage. Capillary force acting on the steel surface was higher due to high wettability of steel. However, on the Teflon surface, the bubble expanded almost immediately and was acted upon by the partial buoyancy force. This was also observedwhere the angle on a Teflon surface almost immediately decreased to θ < 90 degrees angle. Still images captured from bubble formation on the two orifices showed that the bubble did not completely occupy the orifice perimeter when forming on the steel surface, whereas for Teflon, the bubble occupied the entire orifice perimeter/base, and expanded slightly beyond the orifice rim. It is hypothesized that for nonwetting surface, the liquid sticks to itself and pulls liquid from inside the pore since the liquid does not have affinity to the non-wetting pore walls. Hence, the bubble base is pinned to the orifice rim and the bubble shape is controlled by surface tension forces. For the wetting surface, the liquid adheres to the pore walls, hence during bubble formation, the bubble base is smaller than the orifice rim and the shape of the bubble is controlled by the adhesion forces between liquid and the capillary wall. Thus, smaller bubbles are formed on a steel surface. The oil adhered to the wall also causes a significant drag force on the bubble due to capillarity, leading to an increase in bubble formation time. Thus, the difference in wettability of the surface and the pore walls results in bubbles of different shapes which governs formation and lag time between bubbles emerging from the two surfaces and therein the bubble frequency and volume. The current study gives a basic understanding of the factors governing bubble formation and thus heat transfer during immersion frying stage. During frying, bubbles emerge from multiple orifices and there can be lateral coalescence during the formation stage. The surface pore size distribution in food can lead to formation of bubbles of different sizes which travel at different speeds in the oil and thus increase turbulence in oil further. Degradation of oil during frying may result in enhanced heat transfer rate due to formation of a higher number of small bubbles. Heat transfer during frying is controlled by temperature of oil and oil degradation, as well as food properties such as surface wettability and pore size distribution. The results from this study can be used to understand the changes in heat transfer coefficients in frying as the oil and food properties are changed. In the final phase of this research a parametric study was conducted to understand the effect of orifice diameter, and liquid and surface properties on meniscus formation between subsequent bubbles for a submerged orifice. Parameters studied were liquid viscosity and surface tension, and wettability of the capillary surface. Pressure in the orifice chamber and high-speed video of the meniscus motion were recorded. Meniscus behavior was characterized using the Weber number (We): single bubbles (We < 1), or jetting (We > 1). Bond number (Bo) characterized meniscus motion: capillary driven (Bo < 1), meniscus oscillations (Bo ~1), or gravity weeping (Bo ? 1). Viscosity increase up to 60 times that of water, was not shown to influence meniscus dynamics. Surface tension and wettability were the primary parameters controlling the depth of meniscus entry and position of pinch-off. Meniscus dynamics in oil was similar in behavior to solutions of water with sodium n-dodecyl sulfate. In processes such as frying, oil absorption during immersion stage occurs as a result of meniscus entry into the capillary. Thus, understanding of properties affecting meniscus dynamics can help understand mechanisms that control oil absorption during this stage. This study concluded that for each fluid examined, the capillary diameter and fluid properties can be used to predict whether bubble formation and meniscus dynamics are capillarity or gravity driven and can be estimated based on the Bond number. The study also found that fluid viscosity does not have an impact on bubble formation and meniscus dynamics from a submerged orifice. The fluid surface tension and contact angle between liquid and solid were thus the primary factors controlling the meniscus behavior when comparing capillaries of the same size. The forces of curvature at the time of necking can be used as a predictive parameter to estimate the depth of penetration of liquid inside narrow capillaries, as well as the position of meniscus oscillations in wide capillaries. During processes such as frying, meniscus dynamics during bubble formation can significantly affect the amount of oil absorbed by food. Since surface tension and contact angle are the primary factors affecting meniscus dynamics, development of GRAS oleophobic coatings can be a potential mechanism for reduction of oil absorption during frying.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
Sahasrabudhe, S.N., J.A. Staton, B.E. Farkas 2020. Parametric study on liquid and surface properties affecting meniscus dynamics during bubble formation in capillaries - Applications to frying. Journal of Food Engineering. Vol. 285, Art. 110082
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Sahasrabudhe, S.N., Chaudhari, S.S., Farkas, B.E. 2019. Experimental measurement of factors affecting dynamics of bubble growth from a submerged orifice: Applications to the frying process. Journal of Food Engineering, Vol. 251, pp. 36-44.
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Progress 04/15/17 to 04/14/18
Outputs
Target Audience:Government scientists and faculty, staff and graduate students interested in interfacial sciences; Members of industry looking for deeper understanding of oil, water, solids, and vapor interfacial transport at elevated temperatures. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Over this reporting period, the PI's worked with one doctoral student and one post-doctoral researcher. In addition tocoursework, the doctoral student took an active role in continued set-up of the laboratory, installation and calibration ofinstrumentation, statistical design of (her) experiments, and preliminary data analysis. The post-doctoral researcher wasinvolved in these activities independently and in collaboration with the PI. Training and professional development were in theform of basic academic professional development (establishing a laboratory and design of experiments) to presentation skillsand interview techniques. How have the results been disseminated to communities of interest?Results were published: International Journal of Food Properties and LWT - Food Science and Technology What do you plan to do during the next reporting period to accomplish the goals?Further work on and completion of Obectives 2 and 3: 2.) Measure surface and interfacial energy over an elevated temperature range in oil-air and oil-steam systems containing a variety of oil-soluble surfactants. Both equilibrium and short-time dynamic tensions will be studied; 3.) Quantify the effect of surfactant type and temperature on tension at oil-water and air-water interfaces from ambient temperature to 100°C. Both equilibrium and short-time dynamic tensions will be studied. This will finish the research for this proposal.
Impacts
What was accomplished under these goals?
Density, surface tension and viscosity of five food oils were experimentallymeasured using the Archimedean method, Pendant drop method, andBrookfield viscometer respectively. Measurements were performed from23 ± 1°C to the oils' smoke point at intervals of every 20°C. Density and surfacetension decreased linearly with increasing temperature, whereas the viscositydecreased exponentially. Density was modeled using the modified Rackettequation, surface tension using the Eötvös equation, and viscosity by themodified Andrade equation. The oil type influenced the density and viscosityof oil, but did not affect surface tension. Based on the results, temperature had a significant effect on all three physical properties of oilmeasured. Oil type was shown to have a significant effect on viscosity and density, but did notinfluence surface-tension. Surface tension and density decreased linearly with increasing temperature,whereas the decrease in viscosity followed a power law model. The trends for all thethree physical properties were similar to those reported in literature, and thus results could becorroborated. Mathematical models built to predict the change in surface tension (the Eötvösequation and modified Rackett-Eötvös equations), density (the modified Rackett equation), andviscosity (the modified Andrade equation) seemed to agree well with the experimental data.The error percentage for mathematical models increased with increasing temperature, howeverthe model and experimental values followed the same trend at the range of temperaturesstudied. The mathematical models developed can thus be used to predict the change inphysical properties of oil at high temperatures; specially for controlling process parametersduring frying, spray drying, dairy processing or atomization during biodiesel production.Understanding of transport rate of oil at high temperatures (up to 200°C) when differenttypes oils are used can be used for varied applications such as a better/more accurateprediction of the oil absorption rates during frying, and understanding of drying rate duringspray drying. In the second portion of this ongoing research, the effect of frying oil degradation on surface tension and wettability was further studied. Frying oil degrades via exposure to heat, oxygen and water resulting in the formation of volatile and non-volatile products, which act as surface active substances and change heat and mass transfer rates. Effects of oil degradation during frying were quantified by measuring viscosity, surface tension, and static and dynamic contact angles of fresh oil (Total polar materials, TPM 3-4%) and used oils (TPM 10-20%). Oil viscosity decreased exponentially with increasing temperature (40-200 °C). Used oil viscosity was higher than fresh oil at room temperature; no significant difference was recorded above 60 °C. Pendant drop technique was used to measure air-oil (24-200 °C) and steam-oil (100-200 °C) surface tension of all oil samples. Surface tension decreased linearly as temperature increased. There was no effect of surrounding medium (air or steam) or oil quality on surface tension. Surface tension was time independent for both oils, as observed with a 5 h measurement using rising-bubble technique. Static contact angles of all used oils were lower than fresh oil, indicating increased wettability of used oil, which can affect amount of oil absorbed during frying and post-fry cooling. Hysteresis of used oil (13°-15°) was lower than fresh oil (18°), which can impact drainage during post-fry cooling. Higher TPM values of used oils compared to fresh oil were indicative of the presence of amphiphilic compounds in used oils. Based on the effect of oil physical properties on heat flux during frying, viscosity and surface tension work against one another as oil is degraded. While oil degradation does not affect viscosity at frying temperatures, increased viscosity was observed at room temperature which may affect drainage during post-fry cooling. Improved wettability and decreased hysteresis may impact heat and mass transfer during frying, the motion of oil into food and the rate of drainage during post-fry cooling; these need to be studied further.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Sahasrabudhe, S.N., Rodriguez-Martinez, V., OMeara, M., Farkas, B.E. 2017. Density, viscosity, and surface tension of five vegetable oils at elevated temperatures: Measurement and modeling. International Journal of Food Properties, Vol. 20, pp. 1965-1981.
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Sahasrabudhe, S.N., J.A. Staton, B.E. Farkas 2019. Effect of frying oil degradation on surface tension and wettability. LWT - Food Science and Technology, Vol. 99, pp. 519524.
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Progress 04/15/16 to 04/14/17
Outputs
Target Audience:The target audiences for this reporting period are food scientists and food engineers working in high temperatureinterfacial science and phase change heat transfer in a university setting. Fundamental information on these subjects may be used for greater understanding of boiling, condenstaion, emulsification and frying pprocesses. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Over this reporting period, the PI's worked with one doctoral student and one post-doctoral researcher. In addition to coursework, the doctoral student took an active role in continued set-up of the laboratory, installation and calibration of instrumentation, statistical design of (her) experiments, and preliminary data analysis. The post-doctoral researcher was involved in these activities independently and in collaboration with the PI. Training and professional development were in the form of basic academic professional development (establishing a laboratory and design of experiments) to presentation skills and interview techniques. How have the results been disseminated to communities of interest?Results were published in the journal Food Biophysics. What do you plan to do during the next reporting period to accomplish the goals?Objective 3:Quantify the effect of surfactant type and temperature on tension at oil-water and air-water interfaces from ambient temperature to 100°C. Both equilibrium and short-time dynamic tensions will be studied.
Impacts
What was accomplished under these goals?
Objective 2.) Measure surface and interfacial energy over an elevated temperature range in oil-air and oil-steam systems containing a variety of oil-soluble surfactants. Both equilibrium and short-time dynamic tensions were studied:Equilibrium and time-dependent surface tension properties at the lipid-vapor interface were investigated, due to their importance in many food applications. Common cooking oils and triglycerides, with or without added oil soluble amphiphiles, were studied as a function of time and temperature. Surface tension was found to decrease linearly as temperature was increased, and this linear dependence was analyzed to yield thermodynamic information on the surface excess energy and entropy. The different types of cooking oils were nearly indistinguishable with regard to their surface entropy and energy, but an effect of acyl chain length was observed from data for different purified triglyceride oils. These results were consistent with separate results on pure fatty acids of different chain lengths and degree of unsaturation. Lipid amphiphiles, natively present or deliberately added at low concentration to oil, did not cause a change in either dynamic or equilibrium surface tension of corn or olive oil. We conclude that such amphiphilic molecules, despite their presence within the food oil, lack significant surface activity at their native concentration when presented with the surface between oil and air. A decrease in tension in corn oil was seen when mixed in solution with the short-chain caprylic acid (octanoate), but the decrease was notable (>4%) only when this short-chain fatty acid was added at high concentration (≥ 1 M). Added sorbitan monooleate (Span 80) or dioctyl sulfosuccinate sodium salt (AOT) surfactants, on the other hand, decreased equilibrium surface tension by up to 12% and 18%, respectively, at low concentrations (<0.125 M).
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Tong Xu, Veronica Rodriguez-Martinez, Shreya N. Sahasrabudhe, Brian E. Farkas and Stephanie R. Dungan. 2017. Effects of Temperature, Time and Composition on Food Oil Surface Tension. Food Biophysics, 12(1), 88-96
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Progress 04/15/15 to 04/14/16
Outputs
Target Audience:The target audience for the 2015-2016 reporting period was the scientific community involved in droplet and bubble formationand phase-chage heat transfer with a focus on interfacial science at high temperatures. Some data and information generated may be of interest to the food industry but the bulk of this will come in following years. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Over this reporting period, the PI's worked with one doctoral student and one post-doctoral researcher. In addition to coursework, the doctoral student took an active role in continued set-up of the laboratory, installation and calibration of instrumentation, statistical design of (her) experiments, and preliminary data analysis. The post-doctoral researcher was involved in these activities independently and in collaboration with the PI. Training and professional development were in the form of basic academic professionall development (establishing a laboratory and design of experiments) to presentation skills and interview techniques. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?Over the next reporting period we will be focused on objective two as well as reporting (publishing) finished results from objective one. Objective two is to measure surface and interfacial energy over an elevated temperature range in oil-air and oil-steam systems containing a variety of oil-soluble surfactants. Both equilibrium and short-time dynamic tensions will be studied.
Impacts
What was accomplished under these goals?
Objective 1.)Measure surface and interfacial energies for oil-air and oil-steam surfactant-free systems over an elevated temperature range Immersion frying is a widely used technique to process food by heating in oil at 160-200C. During frying, there is simultaneous heat and mass transfer causing the food to absorb oil, as it loses moisture in the form of steam. The rate of heat transfer, moisture loss and oil uptake are all affected, in part, by physical properties of oil such as density, viscosity and interfacial tension. The objective of this first phase of researchwas to determine and mathematically model these properties at high temperatures, to develop a better understanding of factors controlling oil absorption rates. Density, surface tension and viscosity of canola, soybean, corn, peanut and olive oil were experimentally measured. Viscosity was measured using a Brookfield viscometer connected to a Thermosel. Density was measured by Archimedean method using a solid object of known volume and mass, suspended in the test liquid. Surface tension was measured by pendant drop method using a Kruss goniometer, equipped with an elevated temperature syringe and environmental chamber. Measurements were made from room temperature to the smoke point of each oil, at intervals of 20C. Density was modelled using modified Rackett equation which predicts density using the fatty acid composition of each oil. Surface tension was modelled by Eötvös equation; and viscosity using the Modified Andrade equation. Density and surface tension decreased linearly with increasing temperature (r2 = 0.99), whereas the viscosity decreased exponentially (r2 = 0.94). Eötvös constant of 6.2 showed a good fit for all oils studied, which suggests it can be used for other pure vegetable oils. Overall when compared with their corresponding experimental values, predicted density values had < 2.0% error, while predicted surface tension values had < 10.1% error, and predicted viscosity values had < 12% error. The error was within the equipment's accuracy range. The mathematical models presented in this work can be used as a tool to predict the behavior of oils at high temperatures. This will help to gain a better understanding of oil absorption, as the properties affecting heat and mass transfer rates during frying can be predicted more accurately, at the frying temperature itself.
Publications
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Progress 04/15/14 to 04/14/15
Outputs
Target Audience:The primary activity during this time period was seting up my laboratory after moving to Purdue University. The target audience was thus limited to the PI and post-doc. Changes/Problems:Nothing to report specific to this research. Only the delay in starting up due to the PI's move from one university to another to become Department Head. What opportunities for training and professional development has the project provided?My post-doctoral scientist is very interested in becoming a faculty member one day. I used this opportunity to teach her about setting up a new program and research laboratory. Specific areas include sourcing and evaluation of equipment, evaluation of student applications, benefits and drawbacks of doctoral, masters, and undergraduate researchers, and handling paperwork associated with budgets and personnel. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?For the 2015-2016 period we will bring on a doctoral student and begin work on Goal 1. of the research: "Measure surface and interfacial energies for oil-air and oil-steam surfactant-free systems over an elevated temperature range."
Impacts
What was accomplished under these goals?
During this time period we worked to set up the research laboratory and validate the methods used to address the above stated goals. Very little time was spent on the specific project goals.
Publications
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