Molecular Understanding of Fouling Induction and Removal: Effect of the Interface Temperature on Milk Deposits

Improving Cleaning Efficiency through the Measurement of Food Fouling Adhesive Strength

This study aims to investigate the impacts of factors, including textural properties, surface roughness, and contact angle, on the cleaning performance of food soils and develop a preliminary mathematical model to predict the cleaning score, depending on the soil-surface properties. The force required to remove soil from the surface was determined by a texture analyzer equipped with a newly designed probe. Potato puree and egg yolk soils showed high adhesive forces compared to other deposits. Margarine required the lowest force to detach from the surfaces. A soil-surface characteristic number (SSCN) was constructed from the results of contact angle, roughness, and textural analysis to predict the cleaning score depending on the soil-surface properties. The experimental work presented indicates that a higher SSCN was associated with lower cleaning scores for soil-surface combinations. Furthermore, a predictive model was developed to define the relationship between cleaning scores and SSCN. The applicability of the model was validated by measuring the cleaning performance of caramel and pudding soils on glass, porcelain, and stainless-steel household surfaces by using an automatic method. Therefore, it can be concluded that the SSCN approach can be improved in further studies to predict cleaning scores of soil-surface combinations in the experimental rig or automatic dishwasher.

Understanding Flow Fouling Deposition and Solute Hideout-Return Behavior at the Phase Change Interface

Nuclear energy is a competitive green energy, yet corrosion deposition and boron hideout on pressurized water reactor fuel cladding surfaces could cause localized corrosion and power shift, resulting in huge safety and economic risks. Alleviation of these problems requires the understanding of the corrosion deposition mechanism and related boron behavior. In this study, we explore corrosion product deposition in typical fuel assembly channels under subcooled boiling conditions and propose a boron hideout and return mechanism to explain the reason for the failure of the power reduction inhibiting a power shift. Porous corrosion depositions with the same morphology and thickness as the real depositions in a fuel cycle are obtained in a week via the accelerated deposition method simulating a real subcooled boiling and water chemical environment. Stronger subcooled boiling generates more bubbles, resulting in higher supersaturation of corrosion products at the gas-liquid interface. The corresponding precipitated stable crystals are smaller, and the formed deposition layer is looser and thicker with smaller particles. On the basis of the above characterizations, the effect of subcooled boiling, solute concentration, and water chemistry on the corrosion deposition mechanism is revealed. High-resolution characterization methods indicate that boron hides within the depositions mainly in the form of H3BO3 and Li2B4O7. The boron coolant concentration increases by 307.9 ppm after power reduction, confirming the return behavior of porous hidden boron. Hidden boron return behavior brings potential challenges for estimating critical conditions and plant response operations. The results of this study provide a precise method for understanding the corrosion product deposition and boron hideout-return behavior to further develop mitigation strategies for power shift and localized corrosion security issues.

Recovery of cleaning agents from Clean-In-Place (CIP) wastewater using nanofiltration (NF) and direct contact membrane distillation (DCMD)

Increasing concerns about freshwater sources necessitate the management of wastewater, such as the wastewater generated from Clean-in-Place (CIP) operations. In this investigation, a membrane system composed of nanofiltration (NF) and direct contact membrane distillation (DCMD) was proposed to manage model dairy CIP wastewater that contained NaOH as an alkaline cleaning agent. During the NF step, prefiltration by a 4 kDa membrane or a 4 kDa membrane followed by a 200 Da membrane (4 kDa/200 Da) was used to remove the whey protein and lactose. With these two membranes in series of NF, the protein concentration was reduced by 92.4% and the lactose content was reduced to a non-detectable level when compared to the model CIP wastewater. Before concentrating the permeates from NF steps, three DCMD membranes (FR, Solupor, and ST) with different characteristics were evaluated to manage the NF permeates from 4 kDa or 200 Da NF. An increase in the feed temperature from 40 °C to 60 °C resulted in an increase in the water flux during DCMD operation, except for FR. In addition, it was found that ST generated the highest water flux when compared to the other membranes. Using ST and a feed temperature of 60 °C, the permeates from 4 kDa or 4 kDa/200 Da were continuously concentrated for 7 h with DCMD. During this concentration, there was no significant decline in flux. The cleaning effectiveness of the cleaning agent (NaOH) recovered by NF and DCMD was compared with a fresh cleaning solution using quartz crystal microbalance with dissipation (QCM-D). It was found that the cleaning agents recovered by 4 kDa/200 Da NF presented a statistically identical cleaning rate compared to fresh NaOH. This research highlights the potential of NF and DCMD to regenerate alkaline cleaning agents, while reclaiming water from dairy CIP wastewater.

Monitoring and Characterization of Milk Fouling on Stainless Steel Using a High-Pressure High-Temperature Quartz Crystal Microbalance with Dissipation

Fouling at interfaces deteriorates the efficiency and hygiene of processes within numerous industrial sectors, including the oil and gas, biomedical device, and food industries. In the food industry, the fouling of a complex food matrix to a heated stainless steel surface reduces production efficiency by increasing heating resistance, pumping requirements, and the frequency of cleaning operations. In this work, quartz crystal microbalance with dissipation (QCM-D) was used to study the interface formed by the fouling of milk on a stainless steel surface at different flow rates and protein concentrations at high temperatures (135 °C). Subsequently, the QCM-D response was recorded during the cleaning of the foulant. Two phases of fouling were identified. During phase-1, the fouling rate was dependent on the flow rate, while the fouling rate during phase-2 was dependent on the flow rate and protein concentration. During cleaning, foulants deposited at the higher flow rate swelled more than those deposited at the lower flow rate. The composition of the fouling deposits consisted of both protein and mineral species. Two crystalline phases of calcium phosphate, β-tricalcium phosphate and hydroxyapatite, were identified at both flow rates. Stratification in topography was observed across the surface of the QCM-D sensor with a brittle and cracked structure for deposits formed at 0.2 mL/min and a smooth and close-packed structure for deposits formed at 0.1 mL/min. These stratifications in the composition and topography were correlated to differences in the reaction time and flow dynamics at different flow rates. This high-temperature application of QCM-D to complex food systems illuminates the initial interaction between proteins and minerals and a stainless steel surface, which might otherwise be undetectable in low-temperature applications of QCM-D or at larger bench and industrial scales. The methods and results presented here have implications for optimizing processing scenarios that limit fouling formation while also enhancing removal during cleaning.