Drying Of Thin Films Research Articles

Valorization of agitated thin film dryer (ATFD)-mixed-salt from textile wastewater for its application in leather manufacturing – a sustainable approach

ABSTRACT The textile industry uses sodium chloride and sodium sulphate during the dyeing process to improve the fixation of dyes on fabrics. After wastewater treatment, the reject stream is dried resulting in mixed salts as solid wastes that are not reused. The leather industry also uses a vast quantity of salt for temporary preservation of skins/hides and as swelling-suppressing agent during the pickling (acidification) process. Thus, an attempt was made to utilize the mixed salt obtained from the textile industry to replace sodium chloride in leather processing. It was found that a 40% w/w offer of ATFD salt was able to preserve the skins for 3 months, which was on par with the preservation carried out using a similar quantity of sodium chloride in conventional preservation process. Likewise, for the pickling process, an offer of 10% w/w ATFD salt provided sufficient deswelling action when compared to conventionally used sodium chloride. However, the residual colour of the mixed salts affected the quality of the leather obtained. To overcome this, an electro-oxidation treatment was carried out to obtain decolourized salts. The COD measurements showed that the 1% solution of ATFD-3 salt reduced from 471 ± 25 to 88 ± 16 ppm. A similar trend was also seen in BOD reduction from 80 ± 12 to 18 ± 10 ppm. These results confirmed that the colour removal could be due to the degradation of the organic contaminants present in the ATFD salt. Thus, the treated ATFD salt can be reused for leather processing without affecting leather quality, thus promoting the concept of circular economy.

Numerical study of Two-Phase flow behavior during dryout in a Two-Phase closed thermosyphon under thermal boundary conditions

This paper presents a two-dimensional axisymmetric two-phase closed thermosyphon (TPCT) model filled with R-134a refrigerant using the Volume of Fluid (VOF) method, Lee model, and Continuum Surface Force (CSF) method within Computational Fluid Dynamics (CFD) and simulates the flow characteristics inside the TPCT during the occurrence of dry out. Specifically, it discusses the two-phase flow in the condensation and evaporation sections when dry out occurs. The results indicate that the condensation section exhibits varying forms of vapor–liquid interface waves at different times. Phenomena such as liquid carryover and entrainment become increasingly prominent over time, contributing significantly to refrigerant blockages and dryout in the evaporation section. The mechanism behind dryout in the evaporation section is revealed to be the result of the initially continuous falling film being disrupted by fluctuations in the liquid–vapor interface, leading to the premature drying of thin liquid films in the troughs of these waves.

Innovative vs classical methods for drying heterotrophic Chlorella vulgaris: Impact on protein quality and sensory properties

Drying is a necessary step in the microalgae production chain to reduce microbial load and oxidative degradation of the end product. Depending on the differences in applied temperature and treatment time, the process of drying can have a substantial impact on protein quality and aroma, important characteristics determining the incorporation potential in food products. In this study, we compared the drying of heterotrophic Chorella vulgaris with both innovative (agitated thin film drying (ATFD), pulse combustion drying (PCD) and solar drying (SolD)) and commonly used drying techniques (spray drying (SprD) and freeze drying (FD)). To evaluate the impact on protein quality, we evaluated techno-functional properties, in vitro digestibility (INFOGEST) as well as protein denaturation using differential scanning calorimetry (DSC). A sensory analysis was performed by a trained expert panel, combined with headspace solid-phase microextraction (HS-SPME) - gas chromatography-mass spectrometry (GC–MS) to determine volatile organic compounds (VOCs). ATFD was found to increase techno-functional properties such as gelling, water holding and solubility as well as in vitro protein digestibility. These observations could be related to induced cell disruption and protein denaturation by ATFD. Sensory analysis indicated an increased earthy off-flavor after ATFD. Interestingly, the high-temperature PCD led to an increase in cacao odor while low-temperature FD resulted in lower flavor, odors and VOCs. These results demonstrate that protein quality and sensorial properties of C. vulgaris can be steered through the type of drying, which could help in the selection of application-specific drying methods. Overall, this work could promote the incorporation of microalgal single cell proteins in different innovative food products.

Drying model based on the relative humidity profile of thin-layer tomatoes in an indirect solar dryer

This work defined the development of a model for thin-film drying of tomatoes using an indi-rect solar dryer. Drying experiments were carried out and the drying model was approximated by a simplified model determined by the measurements collected during the experiments, in particular, the measurement of the relative humidity of the tomato during two days of drying coupled with the thermal behaviour of the drying device in free convection. The results show that with good measurements, it is possible to approximate the drying characteristic curve by a linear model with very high statistical performance indicators. The experiments also show that depending on the drying process adopted, the water behaviour of the tomato can change. In addition, the thin-film drying model adopted made it possible to assess the solar drying kinetics of the tomato variety studied. The results obtained finally show that the dryness of the tomato is reached after about 14 hours of drying. The drying temperature reaches an average of 80°C, and the final product water content after the optimal drying time is about 0.40 kg.water/kg.ms on a dry basis. At the end of this study, we concluded that the drying air temperature represents the most important parameter affecting the drying kinetics. The very good agreement between the experimental and numerical results obtained shows that the theoretical model and assumptions used are acceptable, and that our calculation model is reliable.

Agitated thin film drying of non-centrifugal sugars: Impact of processing parameters on the crystallinity and dissolution rates of NCS powder

Agitated thin film drying of non-centrifugal sugars: Impact of processing parameters on the crystallinity and dissolution rates of NCS powder

Acetone release during thin film drying of maltodextrin solutions as model system for spray drying

Acetone release during thin film drying of maltodextrin solutions as model system for spray drying

Refractance Window Drying Of Aonla Pulp To Produce Powder

Aonla fruits are found to be rich in ascorbic acid and have been reported to be useful in curing many diseases. Refractance Window (RW) drying is a novel thin-film drying process, generally used for drying of heat sensitive farm produce for retention of necessary quality attributes. Aonla pulp of 3 mm thickness was dried using RW drying process to obtain powder. RW drying was conducted to study the single layer drying kinetics, and other quality parameters such as colour, thermal properties, sieve analysis, FT-IR and SEM analysis. RW drying of 3 mm thick pulp entered into falling rate drying period after 6 min of constant rate drying. The diffusivity of moisture values for 3 mm thick pulp RW drying was 5.48 x 10-10 to 3.5 x 10-9 m 2 s -1. The dried powder was bright, more yellow and less green as compared to pulp. FT-IR results show that shift of spectrum peaks were more pronounced for 212 μm powders particles than for 500 μm powder particles with respect of pulp. Ascorbic acid presence is characterized by peaks obtained at 1633 cm-1, 1741 cm-1 in IR spectrum of pulp, 1747 cm-1 and 1629 cm-1, 1749 cm-1 in 500 μm and 212 μm powders particles, respectively. SEM analysis for powder particles shows that the RW dried powder particles were of uniform thickness and smooth surfaces.

Solar drying of apple and orange waste: Evaluation of a new thermodynamic approach, and characterization analysis

During the industrial processing of agricultural products, the steps to be followed are more numerous and lead to the appearance of a varied range of waste, a source of pollution in the environment. However, this waste is an important source of energy for ruminants, which greatly benefit from it. This work is an experimental and thermodynamic study of the solar drying of apple and orange waste. In this work, we present a new approach for the thermodynamics study of drying apple and orange waste, as well as the evaluation of this waste as a complement in the feeding of ruminants. This evaluation has led to the study of the properties of four powders obtained by drying apple and orange waste with two methods, namely thin-film drying under the sun, and thin-film drying in the greenhouse solar dryer. Several experiments were carried out on the powders obtained, to study the effect of drying on their physical, physicochemical, microbiological, and microscopic properties. The goal is to know and determine the optimal drying method that provides us with dry, healthy, nutritious, and better quality food waste to be included in ruminant rations. According to the obtained results from this comparative study, it was found that the waste dried inside the greenhouse dryer is of better quality. The thermodynamic parameters derived from the proposed new approach are discussed and compared with literature results. The negative values of Gibbs free energy indicate that solar drying of apple and orange waste is a spontaneous process.

Characteristic drying curve behavior of whey and casein micelle proteins via thin-film drying

Drying characteristics of milk whey protein concentrate (WPC) and micellar caseins (MC) were investigated through a custom-designed mobile thin-film dryer. Several mixtures containing different WPC to MC ratios were tested in drying experiments. Both the constant drying period and falling rate period were identified. It was noticed the initial drying rates at constant drying period were slightly hindered by the presence of protein even at low concentrations. The drying kinetics was investigated by the characteristic drying curve (CDC) method and the drying behavior at the falling rate period was evaluated by a specific parameter n. As the result, while WPC exhibited a uniform master characteristic drying curve through different drying conditions, samples with certain amount of MC showed the more “scattered” curves, which lead to a wide distribution of n. Besides, it was observed that a thin layer of crust formed during the drying process. The analysis of the drying characteristics of MC led to a meaningful correlation with the morphology and structural properties. As the morphology of the crust was determined by the velocity and temperature of the impinging air, it became an inherent limitation for this thin film drying method to investigate materials with such crust formation phenomena.

Low-pressure conductive thin film drying of açaí pulp

Açaí has a high content of anthocyanins and unsaturated fatty acids, and drying parameters can affect the stability of these compounds. This study used a conductive thin-film dryer at a laboratory scale to mimic the (vacuum) drum drying of açaí pulp. The effect of drying chamber pressure on the drying kinetics and powdered product characteristics was investigated. Hot air drying and freeze-drying experiments were performed as references. A pilot-scale conductive dryer, namely a vacuum drum dryer, was used as well to dry açaí pulp. Conductive drying at low pressures led to lower boiling temperatures and shorter drying times but also more vigorous bubble formation. The anthocyanin content and antioxidant activity of contact-dried samples at low pressures were comparable to those of freeze-dried and significantly higher than those of hot air-dried. However, conductive drying caused greater lipid oxidation compared to freeze-drying and hot air drying. Oil loss was observed during vacuum drum drying except for the lowest pressure and the shortest drying time. Therefore, the results suggest that chamber pressure during conductive thin film drying should be carefully selected to obtain high-quality açaí powder.

Concept, design, and measurement methodology of a highly dynamic thin film dryer for experimental in situ drying manipulation.

This paper describes the technical setup and validation of a thin film drying device in which the conditions such as air temperature, relative humidity, and velocity can be controlled in the range of 20-200 °C, 0-1.5ms-1, and vapor mass flows up to 1200gmin-1. For the first time, it is possible to perform in situ manipulation of the drying kinetic in a highly dynamic manner. The setup allows for a precise online determination of drying and rehydration kinetics; the recording of relevant process parameters such as air humidity, air and surface temperature; and the monitoring of optically observable material properties. The concept for rapid real-time changes in drying conditions is explained, and the constructive details are elucidated. Highly precise gravimetry by a proposed measurement methodology and simultaneously avoiding condensation during rapid parameter changes is accomplished. This is achieved by the combination of minimized thermal inertia of the system, air conditioning via carrier gas-free evaporation, and a highly responsive active insulation. The influence on the drying kinetics by temperature, humidity, and air velocity is shown with experiments on aqueous maltose solution, and the experimental precision is validated. The validation showed a high grade of accuracy regarding gravimetric determination with a maximum observed mass difference of 0.21% referring to the dried product. The dynamics of the setup under in situ changes in drying conditions is exemplified by further experiments. In addition, the presented setup for the first time enables the real time manipulation and observation of kinetically coupled processes such as crystallization behavior, morphology formation, or material degradation during drying. Therefore, it has important practical value for the development of efficient and energy-saving drying methods and products with specific, tailor-made properties.

Hot-pressing polyelectrolyte complexes into tunable dense saloplastics

Salt-plasticized polyelectrolyte complexes of sodium polystrenesulfonate (Na-PSS) and polydiallyldimethylammonium chloride (PDADMAC) were found to be fully dense (non-porous) when hot-pressed under optimal conditions. The quality of these saloplastics is determined by the molecular weights of polyelectrolytes, the salt type and concentration, as well as processing conditions like pressure and temperature. Higher molecular weights give more compact precipitates that are easy to process while decreasing the molecular weight led to particulate ones. Both the type and concentration of salt on complex formation and doping are explored and are found to play an equally important role. The effects of individual hot-pressing parameters, namely, pressure and temperature are studied thoroughly, facilitating the formation of uniform free-standing films over a wide range of thicknesses from 8 μm to 1 mm. For the first time, saloplastics were studied as free-standing films that are dense even at the nanometer scale. In their dry states, they were brittle and strong, showing a uniform Young's modulus over a range of relevant thicknesses, while the wet states were rubbery and elastic, showing a decreasing trend with thickness. In the wet state, the inverse trend is due to the quicker drying of thin films. Within a single hot-pressing step, protruding shapes and structures from the surface were efficiently made at different length scales. Moreover, saloplastics were also successfully reinforced with thin woven and nonwoven fibers for enhanced tensile strengths, higher than conventional thermoplastics. Overall, this work demonstrates an easy approach to fabricate dense saloplastics and their unique mechanical properties.

Experimental and numerical investigation of the influence of nozzle design on the industrial convection drying of thin films

Analytical simulation is a powerful tool for the optimization of the convective drying of continuous thin film coatings. Knowledge of the heat transfer coefficient is a prerequisite for applying such simulations. In this work, the heat transfer coefficient distributions in industrial dryers with oblique twin nozzles is investigated. Convergent nozzles show higher heat transfer than divergent nozzles. The results are used as boundary condition for a dryer simulation, which is in good agreement with experimental data. An alternative nozzle design, using a wider outlet area and a lower velocity is also investigated. A more homogeneous local Nusselt number is observed.

Evaluation of sensory and physico-chemical properties of Langra variety mango leather

The sensory and nutritive quality attributes of fruits have observed to be lost when dried to leathers using solar, hot air convection and several other traditional drying processes. Refractance Window (RW) technique is a novel thin-film drying process, generally used for drying of heat sensitive food products for retention of necessary quality attributes. Six samples of mango leathers have been prepared using RW and tray drying process and one sample was procured from the market. Fuzzy logic sensory analysis of seven samples of mango leather was done by a panel of 20 judges. Mango leather sample S4 dried using RW drying process was ranked first among all the mango leather samples with sensory scale as ‘Good’ and the highest similarity value as ‘0.9116’ followed by others. Market sample S5 was rated lesser than RW dried samples and higher than tray dried samples. The order of preferences for analyzed mango leather samples was S4 > S2 > S7 > S5 > S3 > S1 > S6. However, the ranking of sensory attributes of mango leather in-general was taste > mouthfeel > color > aroma.

ANALYSIS OF EVAPORATIVE DRYING OF THIN INK FILMS USING HIGH-VELOCITY HOT-AIR IMPINGING JETS: A COMPREHENSIVE REVIEW

Hot impinging air jets are usually used to increase heat and mass transfer. The dehydration of materials is a procedure of common significance in the chemical processes, forensic science and food industries; in the fabrication of paper, plastics and textiles as well. Effective drying of thin ink films is becoming progressively significant in the quickly development printing, packaging and coating industries. In order to minimize capital and operating cost, variables need to be optimized. For both researchers and commercial dryers, an optimization of the nozzles under striking air jets is offered for ink drying. To supply information to industrial users, a comprehensive literature review was presented to the research. An outline of the previous work of impinging air jets is also given.

An internal model control design method for failure-tolerant control with multiple objectives

The selection of control structure is a critical step in the design of a control system since it can largely affect the achievable control performance. This paper presents a general internal model control (IMC) structure with multiple degrees-of-freedom for the design of control systems with multiple objectives (i.e., reference tracking and load and output disturbance rejection), so that controllers are designed independently of each other. The optimal performance of controllers is shown to remain intact when a controller is taken off-line, for example, due to actuator and/or sensor failures. This feature circumvents the need to redesign the remaining on-line controllers for optimal failure-tolerant control. The proposed control approach is used to derive IMC control structures for multi-loop cascade and coordinated control systems. The performance of the control approach is demonstrated on a simulated thin-film drying process in continuous pharmaceutical manufacturing for several multi-loop control structures and a variety of control-loop component failures.

Intermittent Drying of Mango Slices ( Mangifera indica L. ) “ Amelie ” : A New Model

The present work has focused on the determination of a new model of intermittent thin film drying of mango. During the experiments, the samples spread on three trays, were placed in a through-flow modular electric dryer. The masses of the fresh products studied were 500 and 800g having an initial moisture content of 80%. Drying was carried out using three inlet air temperatures 40; 50 and 60°C for four cycles of 120 minutes and for each intermittency value α = ¼,α= ½ and α = ¾. The experimental values obtained have permitted to draw the profiles of moisture ratio for each temperature. Theses profiles have conducted for a test of twelve different thin film models encountered in the literature. For each given cycle and value of the selected intermittency, the results showed that all the curves were described by the same model. Taking into account the intermittency and the number of cycles, a new thin layer drying model has been developed. The simulation of this new drying model showed a good agreement with the experimental curves obtained under the same drying conditions with R2 = 0.996, independently of the drying air temperature and the value of intermittency α.

Real‐Time Study on Structure Formation and the Intercalation Process of Polymer: Fullerene Bulk Heterojunction Thin Films

Fullerene intercalation between the side chains of conjugated polymers has a detrimental impact on both charge separation and charge transport processes in bulk heterojunction (BHJ) organic photovoltaic cells (OPVs). In situ grazing incidence X‐ray scattering experiments allow to characterize the structure formation, drying kinetics, and intercalation in blends of phenyl‐c61‐butyric acid methyl ester (PC60BM) and poly(2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) named (pBTTT‐C14) from their 1,2‐orthodichlorobenzene (oDCB) solutions with different volume fractions of dodecanoic acid methyl ester (Me12) as a solvent additive. The structure formation process during evaporation of the solvent:additive mixture can be described by five periods, which are correlated to a multistep contraction of the lamellar stacking of the bimolecular crystals. The onset of crystallization is delayed by increasing the additive volume fraction in the coating solution leading to a promoted crystallinity. A conclusive picture of fullerene intercalation and additive‐tuned structural evolution during the drying of thin films of the polymer:fullerene BHJ blends will be presented.

Coating and Drying of Thin Liquid Films: Effect of Rheological Properties of Liquids on Defect Formation

Coating and Drying of Thin Liquid Films: Effect of Rheological Properties of Liquids on Defect Formation

Energy and exergy analyses of solar drying sardine fillets

Fish is a highly perishable food product. It has a very short because it contains up to 78% of water. The aim of this work is to examine the effect of solar drying on the dehydration kinetics of Moroccan sardine fillets. The curves of the experimental kinetics of drying sardine fillets are carried out at four temperatures (50, 60, 70 and 80°C) with two air flow rates of 300 and 150 m3/h. Nine thin-film drying models are adapted to the drying data. The Midilli-Kucuk model allows better adaptation than the other models according to R2, S and χ2. The data shows that the moisture content reduced from 3.98% to 0.08% db (dry basis). In regards to a conducted study of a part concerning the exergy loss, exergy transfer rate from evaporation and exergy efficiency of the drying chamber is carried out.