Search Results (6)

Shrimp is one of the most popular and widely consumed seafood products worldwide. It is highly perishable due to its high moisture content. Thus, dehydration is commonly used to extend its shelf life, mostly via air drying, leading to a temperature increase, moisture removal, and matrix shrinkage. In this study, a mathematical model was developed to describe the changes in moisture and temperature distribution in shrimp during hot-air drying. The model considered the heat and mass transfer in an irregular-shaped computational domain and was solved using the finite element method. Convective heat and mass transfer coefficients (57.0–62.9 W/m²∙K and 0.007–0.008 m/s, respectively) and the moisture effective diffusion coefficient (6.5 × 10⁻¹⁰–8.5 × 10⁻¹⁰ m²/s) were determined experimentally and numerically. The shrimp temperature and moisture numerical solution were validated using a cabinet dryer with a forced air circulation at 60 and 70 °C. The model predictions demonstrated close agreement with the experimental data ($R^2\ge$ 0.95 for all conditions) and revealed three distinct drying stages: initial warming up, constant drying rate, and falling drying rate at the end. Initially, the shrimp temperature increased from 25 °C to around 46 °C and 53 °C for the process at 60 °C and 70 °C. Thus, it presented a constant drying rate, around 0.04 kg/kg min at 60 °C and 0.05 kg/kg min at 70 °C. During this stage, the process is controlled by the heat transferred from the surroundings. Subsequently, the internal resistance to mass transfer becomes the dominant factor, leading to a decrease in the drying rate and an increase in temperatures. A numerical analysis indicated that considering the irregular shape of the shrimp provides more realistic moisture and temperature profiles compared to the simplified finite cylinder geometry. Furthermore, a sensitivity analysis was performed using the validated model to assess the impact of the mass and heat transfer parameters and relative humidity inside the cavity on the drying process. The proposed model accurately described the drying, allowing the further evaluation of the quality and safety aspects and optimizing the process. Full article

The dryer is an important part of the paper drying process, and the uniformity of the dryer wall temperature distribution has an important influence on paper production quality and efficiency. In this paper, improving the temperature uniformity of the traditional gas dryer wall is taken as the research goal, and the distribution trend and uniformity of the traditional gas dryer wall temperature are studied and analyzed, and the structural improvement plan is put forward. On the basis of this, in order to further improve the uniformity of the wall temperature of the improved gas dryer, the optimization scheme of applying endothermic coating in the low-temperature area of the inner wall of the dryer is proposed. The numerical simulation and experimental research methods are used to compare and analyze the temperature uniformity of the wall of the improved gas dryer. The results show that the axial uniformity of the wall temperature of the modified gas dryer is significantly improved. Compared with the traditional gas dryer, the temperature difference of the cylinder wall is reduced from 40 °C to 13 °C, the maximum axial temperature difference of the cylinder wall is reduced by 57%, and the temperature uniformity is increased from 66.7% to 89.6%. Compared with the improved gas dryer, after the endothermic coating is applied to the low-temperature area of the inner wall of the dryer, the temperature difference of the cylinder wall is reduced from 13 °C to 7 °C, the maximum axial temperature difference of the cylinder wall is further reduced by 46%, and the temperature uniformity is increased from 89.6% to 94.4%. Full article

The article presents studies on the impact of the significant process parameters of a paper machine with a Yankee cylinder on its production capacity and heat energy consumption for drying the paper web. Parameters such as machine speed, web moisture content before and after pressing, parameters of steam supplied to the cylinder and parameters of hot air flowing from the nozzles of the hood were analyzed. The study’s results were used to optimize production to improve the energy efficiency and performance of the machine. In order to use the possible methods of improving the production capacity and heat energy consumption, the parameters of the production process were measured and the basic indicators characterizing the operation of the machine were calculated in the Yankee cylinder–dryer hood system. The correct functioning of the machine components and the possibility of their modernization were also analyzed. Technological and construction changes introduced based on the research results made it possible to increase the production capacity by 10% and to reduce the consumption of heat energy per 1 ton of produced paper by 16.3%. The article presents a description of changes in the technology of paper production and modernization of the tissue machine made in the years 2013–2022. Full article

In this study, the heat and mass transfers in the fabric drying process of a single-cylinder dryer are numerically examined in detail by using MATLAB codes and illustrating 3D velocity and temperature profiles obtained by a CFD-ACE+ software package. Seven different drying materials including Polyethylene terephthalate (PET), Polyethylene, Polypropylene, Cotton, Wool, Rayon, and Nylon are employed as drying materials. Influences of the drying-material thickness, contacting percentage, cylinder temperature, feeding velocity, and cylinder diameter are examined in detail. For all cases in this study, it is found that the maximum temperature of the drying material in the drying process is strongly dependent on the thermal diffusivity of the drying material. The higher the thermal diffusivity of the drying material, the greater the peak temperature achieved. The peak temperature of the drying material increases with the increase in the contacting percentage. The higher feeding velocity leads to a faster increase in the temperature of the drying material; however, the peak temperature of the slower feeding velocity is higher than that of the faster one. The heat transfer between the central layer of the drying material and to ambient environment is limited by the thermal diffusivity of the drying material. Full article

Tissue paper is of high importance worldwide and, continuously, research is focused on improvements of the softening and durability properties of the paper which depend specifically on the production process. Polyamide-amine-epichlorohydrin (PAE) resins along with release agents are widely used to adhere the paper to the yankee dryer (creping cylinder) in paper manufacture. Nevertheless, these resins are highly cationic and they normally adhere in excess to the paper which negatively affects the creping process and the quality of the paper. For this reason, a low cationic polyamine-epichlorohydrin coating (Polycoat 38^®) was synthesized from a diamine supplied by Disproquin S.A.S. and epichlorohydrin. The analysis of the synthesized polymer was carried out by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹H-NMR). The molecular weight of the polymer was obtained by gel permeation chromatography (GPC), physical-chemical properties such as kinematic viscosity, percentage of solids, density, charge density were measured and compared with a commercial PAE resin (Dispro620^®) Thermal stability of the Polycoat 38^® and glass transition temperature in presence of a release agent (Disprosol 17^®) were also evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. Finally, a peel adhesion test and an absorption durability assessment were carried out together with the evaluation of the creeping efficiency of the paper by caliber and tensile measurements in a tissue (towel paper) production plant, demonstrating a superior performance in the paper creping process as compared to some commercially available products. Full article

Production of aerogels starts with solution chemistry and may end with supercritical carbon dioxide drying, which both require a specialized system. Here we present a complete aerogel production system that was developed and used in our laboratory over the last nine years. Our aim was to develop a supercritical dryer and a protocol, whereby the CO₂ pump can be left out, and the entire flow system is operated by the pressure of the CO₂ cylinder. Drying pressure and temperature are controlled by the combination of the filling and heating temperatures. A continuous-mode solvent exchange system has also been developed, in which the solvent consumption during the process can be reduced to one-third of the batch method. In the new medium temperature 1.5 L volume supercritical dryer, the temperature is set to a constant 80–82 °C, and the pressure can be in the 90–200 bar range, depending on the conditions. We have performed approximately 200 dryings thus far, and prepared a wide range of monolithic aerogels, from pristine silica aerogels to polysaccharides and collagen. In this paper, we have summarized not only the technical details, but also the work experiences, as well as advantages and disadvantages of the systems. Full article