Calcium carbonate fouling on double-pipe heat exchanger with different heat exchanging surfaces

Nature-Inspired High Temperature Scale-Resistant Slippery Lubricant-Induced Porous Surfaces (HTS-SLIPS)

Scale formation is a longstanding and unresolved problem in a number of fields, including power production, petroleum exploration, thermal desalination, and construction. Herein, a high-temperature scale-resistant slippery lubricant-induced surface (HTS-SLIPS) is developed by one-step electrodeposition and lubricant infusion. The fractal cauliflower-like morphology with lubricant oil is conducive to forming an ultralow contact angle hysteresis of ≈1°. The 10-d real-world boiling trial indicates that by replacing the uncoated surface with HTS-SLIPS, the reduction in scale mass is greater than 200% because of the low surface free energy (4.3 mJ m^-2 ) and outstanding smoothness (R_a  = 41 ± 8 nm) of HTS-SLIPS. Thanks to the scale retardation, the bubble departure frequency of HTS-SLIPS is eightfold higher than that of uncoated surfaces, signifying superior heat transfer efficiency. In these demonstrations, HTS-SLIPS coated spiral tube exhibits better flowability and lower pressure drop than the uncoated one. In addition, favorable compatibility between HTS-SLIPS and mechanical vibration is experimentally verified to strengthen the descaling of SLIPS synergistically. It is anticipated that the simple and scalable coating fabrication approach will be applicable in numerous industrial high-temperature processes where scale formation is encountered.

Fouling mechanism in airblast atomizers and its suppression for water desalination

A detailed experimental study is presented on fouling behavior of the anti-clogging perforated plate atomizer designed for high salinity applications, and compared with a conventional (plain-jet) airblast atomizer. Low-pressure regions around fast moving air in the outer layer of spray (as in conventional atomizers: plain-jet and prefilming) due to Venturi suction were identified as the root cause of atomizer clogging, as they facilitate salt accumulation on the atomizer surface from spray. Accordingly, severe atomizer fouling, and fluctuations in spray cone angle were observed in the conventional airblast atomizer over 2 h at 100°C air and 50°C saline (44° to 76° at 35,000 ppm, and 44° to 91° at 100,000 ppm). In this regard, the perforated plate atomizer provides a novel liquid-film airblast atomization by maintaining a liquid-annulus film (around the air outlet) as the outer layer of spray. Doing so we achieved nearly complete suppression of fouling, and spray cone angle fluctuations (28° ± 1° at 35,000 ppm, and 30° ± 1° at 100,000 ppm). Later, novel liquid-film atomization was adopted in the conventional airblast atomizer. While, the conventional airblast atomization needed atomizer cleaning/maintenance after 35 min for 175°C air and 65°C saline at 100,000 ppm, the liquid-film atomization showed no sign of fouling over 14 h. Hence, current work establishes a benchmark liquid-film airblast atomization mechanism in the anti-clogging perforated plate atomizer for complete suppression of fouling in airblast atomization. This extends the application of airblast atomizers from high evaporation jet engines to ZLD-HDH desalination systems, spraying, powder metallurgy, pharmaceuticals and hospitals, and spray drying and cooling.

Application of artificial neural network (ANN-MLP) for the prediction of fouling resistance in heat exchanger to MgO-water and CuO-water nanofluids

In this work, an artificial neural network (ANN) model was developed with the aim of predicting fouling resistance for heat exchanger, the network was designed and trained by means of 375 experimental data points that were selected from the literature. These data points contain six inputs, including time, volumetric concentration, heat flux, mass flow rate, inlet temperature, thermal conductivity and fouling resistance as an output. The experimental data are used for training, testing and validation of the ANN using multiple layer perceptron (MLP). The comparison of statistical criteria of different networks shows that the optimal structure for predicting the fouling resistance of the nanofluid is the MLP network with 20 hidden neurons, which has been trained with Levenberg-Marquardt (LM) algorithm. The accuracy of the model was assessed based on three known statistical metrics including mean square error (MSE), mean absolute percentage error (MAPE) and coefficient of determination (R²). The obtained model was found with the performance of {MSE = 6.5377 × 10^-4, MAPE = 2.40% and R² = 0.99756} for the training stage, {MSE = 3.9629 × 10^-4, MAPE = 1.8922% and R² = 0.99835} for the test stage and {MSE = 5.8303 × 10^-4, MAPE = 2.57% and R² = 0.99812} for the validation stage. In order to control the fouling procedure, and after conducting a sensitivity analysis, it found that all input variables have strong effect on the estimation of the fouling resistance.

A Review of Crystallization Fouling in Heat Exchangers

A vast majority of heat exchangers suffer from unwanted deposition of material on the surface, which severely inhibits their performance and thus marks one of the biggest challenges in heat transfer. Despite numerous scientific investigations, prediction and prevention of fouling remain unresolved issues in process engineering and are responsible for large economic losses and environmental damage. This review article focuses specifically on crystallization fouling, providing a comprehensive overview of the state-of-the-art of fouling in heat exchangers. The fundamentals of the topic are discussed, as the term fouling resistance is introduced along with distinct fouling behaviour, observed in laboratory and industrial environments. Insight into subsequent phases of the fouling process is provided, along with the accompanying microscale events. Furthermore, the effects of fluid composition, temperature, flow velocity, surface condition, nucleate boiling and composite fouling are comprehensively discussed. Fouling modelling is systematically reviewed, from the early work of Kern and Seaton to recently used artificial neural networks and computational fluid dynamics. Finally, the most common fouling mitigation approaches are presented, including design considerations and various on-line strategies, as well as off-line cleaning. According to our review, several topics require further study, such as the initial stage of crystal formation, the effects of ageing, the interplay of two or more fouling mechanisms and the underlying phenomena of several mitigation strategies.

Analysis of crystallization fouling in electric water heating

In the present study, the main influencing factors of crystallization fouling in electric water heating were investigated. Dependence on the saturation index and four operating parameters was analyzed, namely: liquid temperature, surface temperature, flow rate and electrical leakage current. A focus of the study was the influence of electrical leakage current on the fouling behavior and the morphology of the deposited crystal layers. The investigation shows that the aforementioned parameters influence the fouling process and crystal size growth in a different way. The experimental results were used to find a correlation between the electrical leakage current and induction time. In addition, a modeling approach is presented which allows an estimation of the fouling mass flux.

Fouling and fouling mitigation of calcium compounds on heat exchangers by novel colloids and surface modifications

Fouling is the accumulation of unwanted materials on surfaces that causes detrimental effects on its function. The accumulated materials can be composed of living organisms (biofouling), nonliving substances (inorganic and/or organic), or a combination of both of them. Mineral fouling occurs when a process uses cooling water supersaturated with mineral salt crystals (i.e. hard water). Precipitation ensues on heat transfer surfaces whenever the inversely soluble dissolved calcium salt ions are exposed to high temperature. Mineral salts, dirt, waxes, biofilms, whey proteins, etc. are common deposits on the heat exchanger surfaces, and they create thermal resistance and increase pressure drop and maintenance costs of plants. Fouling of dissolved salts and its mitigation have been studied in detail by varying process parameters, surface materials, coatings on surfaces, additives, etc. by many researchers. In the present stage, researchers have considered polymeric additives, environmental friendly nanoparticles, natural fibers, and thermal conductive coatings (metallic and polymeric) in the study of mitigation of fouling. A better understanding of the problem and the mechanisms that lead to the accumulation of deposits on surfaces will provide opportunities to reduce or even eliminate the problem in certain situations. The present review study has focused on fouling phenomena, environment of fouling, heat exchanger fouling in design, and mitigation of fouling. The findings could support in developing the improved heat exchanger material surfaces, retain efficiency of the heat exchangers, and prolong their continuous operation.

Determining the thickness of sludge on the heat exchanger tube inside an anaerobic digester

The paper presents a simplified method of determining the thickness of sludge on the walls of the heat exchanger piping in a biogas plant digester. The evaluation of the thickness of a sludge layer is based on the biogas plant operation parameters, including the inlet and outlet temperature of the heat exchanger, mass flow and the geometric characteristics of the heat exchanger and physical parameters of the substrate working inside a fermentation chamber. Measurement of the thickness of the sludge layer on the walls of a heat exchanger is only possible at the time of general cleaning of a digester, which necessitates switching off the biogas plant operation. The paper compares the results of predictions with experimental data of the work of a biogas plant digester located in north-eastern Poland, in Ryboły. The presentation of the obtained numerical results is supplemented by the uncertainty analysis. The significance of undertaking such research lies in its applicational aspects, as during the operation of a biogas plant sludge accumulates on the walls of a digester, which provides additional thermal resistance and reduces the thermal efficiency of the heat exchanger.

Antiscaling Magnetic Slippery Surfaces

Scale formation is a common problem in a wide range of industries such as oil and gas, water desalination, and food processing. Conventional solutions for this problem including mechanical removal and chemical dissolution are inefficient, costly, and sometimes environmentally hazardous. Surface modification approaches have shown promises to address this challenge. However, these approaches suffer from intrinsic existence of solid-liquid interfaces leading to high rate of scale nucleation and high adhesion strength of the formed scale. Here, we report a new surface called magnetic slippery surface in two forms of Newtonian fluid (MAGSS) and gel structure (Gel-MAGSS). These surfaces provide a liquid-liquid interface to elevate the energy barrier for scale nucleation and minimize the adhesion strength of the formed scale on the surface. Performance of these new surfaces in both static and dynamic (under fluid flow) configurations is examined. These surfaces show superior antiscaling properties with an order of magnitude lower scale accretion compared to the solid surfaces and offer longevity and stability under high shear flow conditions. We envision that these surfaces open a new path to address the scale problem in the relevant technologies.