Enhanced microbial inactivation by carbon dioxide through mechanical effects

A non-dairy probiotic beverage based on oat bran extract was produced through fermentation of beverage using a probiotic strain Bifidobacterium lactis. Physicochemical characteristics, viability of probiotic bacteria, and sensory specification were investigated during three weeks of refrigerated storage with various concentration of oat bran extract and carbon dioxide in grape flavor beverage. It was observed that the acidity of the beverage samples significantly increased by increasing the percentage of oat bran extract and carbon dioxide, while the Brix decreased during storage and reached the lowest value after 21 days. The viability of the bacteria was significantly enhanced by increasing the amount of carbon dioxide and oat bran extract concentration until the 14th day after fermentation. The viability extremely decreased with increasing the storage time to 21 days. Oat bran is a rich source of nutrients including carbohydrates, protein, minerals, vitamins and soluble β-glucan. The use of oat bran as a profitable substrate to produce a non-dairy grape flavor probiotic beverage was examined. Due to high viability of the Bifidobacterium lactis after two weeks of storage at 4 °C, the formulation was characterized with 15% (w/v) oat bran extract and 1% carbon dioxide. The highest sensory score was obtained by 15% (w/v) oat bran extract and 0.5% carbon dioxide sample. Therefore, incorporation of the oat bran in formulated grape flavor probiotic could enhance the nutritional value of the beverage.

Effect of diameter on two-phase pressure drop in narrow tubes

Pressure, temperature and density drops along supercritical fluid chromatography columns in different thermal environments. III. Mixtures of carbon dioxide and methanol as the mobile phase

Hydrodynamic cavitation is being increasingly pursued for the development of an intensified and compact wastewater-treatment process. Experimental data on the degradation of water contaminated with three commonly used solvents (acetone; ethyl acetate, EA; and isopropyl alcohol, IPA) using vortex-based cavitation devices are presented. The influence of operating flow or pressure drop across cavitation devices (150 to 300 kPa), operating temperatures (20 to 45 °C), concentrations of pollutant (1000 to 50 000 ppm), and scales of the cavitation reactor (with a scaling-up factor of 4, maintaining the geometric similarity) has been reported. A new reaction-engineering model based on the number of passes through the cavitation device was developed to interpret degradation behavior. The model provides a convenient way to estimate the per-pass degradation factor from batch experiments and allows its extension to continuous processes and to more-sophisticated models for estimating the generation of hydroxyl radicals. The model showed excellent agreement with experimental data. The per-pass degradation factor exhibited a maxima with respect to pressure drop (200–250 kPa) across cavitation devices. Aeration was found to improve degradation performance up to 1 vvm ([L/min]gas/Lliquid]). The initial concentrations of acetone (1000 to 50 000 ppm) and IPA (1000 to 22 000 ppm) were found to have a negligible effect on degradation performance. The per-pass degradation factor for EA was 1.5 and 4 times that of acetone and IPA, respectively. The effect of two scales (nominal capacities of the small- and large-scale devices used were 0.3 and 1.2 m3/h, respectively) was investigated for the first time, and it was found that the per-pass degradation factor decreased with scale. The presented model and experimental data provide new insights into the application of hydrodynamic cavitation for wastewater treatment and provide a basis for further work on the scaling-up of hydrodynamic cavitation devices. The results will be useful to researchers as well as practicing engineers interested in harnessing hydrodynamic cavitation for water treatment.

This study explores the role of sodium chloride (NaCl) in enhancing the efficiency of microbial inactivation using microwave energy with two distinct methods: temperature-controlled treatment and predefined cycle. The primary objective is to maintain a stable temperature within the biological samples during treatment. Detailed descriptions of the treatment system’s design and the function of each element are provided. Simulations are conducted to illustrate the heating behavior of liquids with and without NaCl, revealing significant differences in temperature profiles between the two media. The experimental design and the objective behind each iteration are discussed. The experimental design includes three different power levels to assess their impact on disinfection rates, with durations determined based on extensive preliminary experiments to identify the most effective combinations for microorganism elimination. The experiments aim to compare the efficiency of the temperature-controlled method and the predefined cycle in maintaining desired temperature ranges and enhancing microbial inactivation. A key aspect of the study is the significance of exposure time in temperature-controlled runs. It is observed that exposure time critically influences the inactivation performance, necessitating the design of predefined cycles to achieve more consistent and efficient microbial inactivation. Additionally, in this investigation, the system effectively disinfects three types of microorganisms: bacteria, viruses, and yeasts. The study also examines treatments across three different media to understand the influence of NaCl presence on microbial inactivation efficiency. These insights emphasize the critical importance of optimizing exposure time and incorporating NaCl in microwave-based disinfection processes to achieve more effective microbial inactivation.

High hydrostatic pressure (HHP) is used for microbial inactivation in foods. Addition of carbon dioxide (CO2) to HHP can improve microbial and enzyme inactivation. This study investigated microbial effects of combined HHP and CO2 on Escherichia coli, Bacillus subtilis, and Saccharomyces cerevisiae, and evaluated sensory attributes of treated feijoa fruit puree (pH 3.2). Microorganisms in their growth media and feijoa puree were treated with HHP alone (HHP), or saturated with CO2 at 1 atm (HHPcarb), or 0.4%w/w of CO2 was injected into the package (HHPcarb+CO2). Microbial samples were processed at 200 to 400 MPa, 25 °C, 2 to 6 min. Feijoa samples were processed at 600 MPa, 20 °C, 5 min, then served with and without added sucrose (10%w/w). Treated samples were analyzed for microbial viability and sensory evaluation. Addition of CO2 enhanced microbial inactivation of HHP from 1.7-log to 4.3-log reduction in E. coli at 400 MPa, 4 min, and reduction of >6.5 logs in B. subtilis (vegetative cells) starting at 200 MPa, 2 min. For yeast, HHPcarb+CO2 increased the inactivation of HHP from 4.7-log to 6.2-log reduction at 250 MPa, 4 min. The synergistic effect of CO2 with HHP increased with increasing time and pressure. HHPcarb+CO2 treatment did not alter the appearance and color, while affecting the texture and flavor of unsweetened feijoa samples. There were no differences in sensory attributes and preferences between HHPcarb+CO2 and fresh sweetened products. Addition of CO2 in HHP treatment can reduce process pressure and time, and better preserve product quality. A higher microbial inactivation of Escherichia coli, Bacillus subtilis and Saccharomyces cerevisiae by combining dense phase carbon dioxide and high hydrostatic pressure was observed. For sweetened products there were no significant differences in sensory attributes and preferences between samples treated by the combined method and the fresh samples. In conclusion, addition of CO2 in HHP treatment of juices could reduce process severity and improve product quality.

Tracker thermal control system (TTCS) is an active-pumped two-phase carbon dioxide cooling loop, which is developed for the Alpha Magnetic Spectrometer tracker front-end electronics. The maintenance-free centrifugal pump is a critical component in the design mainly due to the limited pressure head with small mass flows. Therefore a correct pressure drop is required to predict the pressure drop for dynamic modeling. As the normal operational temperature of the carbon dioxide in the TTCS is from − 15°C to +15°C, which is very close to its critical point, 33°C, and many two-phase pressure drop correlations may not fit well here. In this paper, we attempt to correlate the pressure drops between the calculations and the experiment of the two-phase CO2 loop. The comparison will focus on one evaporator. Here, the Lockhart/Martinelli correlation is recorrelated with different definition C value for CO2 according to the test results. Comparison shows that, the new correlation can fit the test results well.

Air-transmitted pathogens may lead to severe epidemics (e.g., COVID-19) showing huge threats to public health. Inactivation of the pathogenic microbes in the air is an essential process, whereas the feasibility of existing air disinfection technologies has encountered obstacles including only achieving physical separation but no inactivation, obvious pressure drops, and energy intensiveness. Here we report a rapid disinfection method for inactivating air-transmitted bacteria and viruses using the nanowire-enhanced localized electric field to damage the outer structures of microbes.[1] This air disinfection system is driven by a triboelectric nanogenerator that converts mechanical vibration to electricity effectively and achieves self-powered. Assisted by a rational design for the accelerated charging and trapping of microbes, this self-powered air disinfection system promotes the microbial transport and achieves high performance: >99.99% microbial inactivation within 0.025s in a fast airflow (2 m/s) while only causing low pressure drops (<24 Pa). This rapid, self-powered air disinfection method may fill the urgent need for the air-transmitted microbial inactivation to protect public health.References Liu, X. Xie, W. Zhao, N. Liu, P. A. Maraccini, L. M. Sassoubre, A. B. Boehm, Y. Cui, Nano Letters 13, 4288-4293 (2013)

Air-transmitted pathogens may cause severe epidemics showing huge threats to public health. Microbial inactivation in the air is essential, whereas the feasibility of existing air disinfection technologies meets challenges including only achieving physical separation but no inactivation, obvious pressure drops, and energy intensiveness. Here we report a rapid disinfection method toward air-transmitted bacteria and viruses using the nanowire-enhanced localized electric field to damage the outer structures of microbes. This air disinfection system is driven by a triboelectric nanogenerator that converts mechanical vibration to electricity effectively and achieves self-powered. Assisted by a rational design for the accelerated charging and trapping of microbes, this air disinfection system promotes microbial transport and achieves high performance: >99.99% microbial inactivation within 0.025 s in a fast airflow (2 m/s) while only causing low pressure drops (<24 Pa). This rapid, self-powered air disinfection method may fill the urgent need for air-transmitted microbial inactivation to protect public health.

Pressure, temperature and density drops along supercritical fluid chromatography columns. I. Experimental results for neat carbon dioxide and columns packed with 3- and 5-micron particles

Pool boiling of nano-fluids on horizontal narrow tubes

Use of the isopycnic plots in designing operations of supercritical fluid chromatography: IV. Pressure and density drops along columns

Carbon Dioxide (CO2) is being investigated as an alternative refrigerant for vapor compression systems. In addition to its environmental benefits, Carbon Dioxide offers certain attractive thermal characteristics such as small surface tension, small liquid viscosity and large refrigerant capacity. Furthermore, combination with microchannels provides CO2 heat exchangers that have low weight, high compaction and high heat transfer coefficient. But certain oil (e.g., lubricate oil for compressor) will be carried into the vapor compression system, which usually has negative effect on heat transfer and pressure drop. The objective of the present paper is to study the effect of oil addition on heat transfer coefficient and pressure drop in supercritical gas cooling process in microchannels. Experiments addressed effect of three different types of oil (two immiscible and one miscible) at various oil concentrations ranging from 0% (no oil) to 5% by weight. As expected, oil addition has significant negative effect on heat transfer coefficients. At higher oil concentrations the heat transfer coefficients are substantially lower and the pressure drops are higher. As far the type of oil is concerned, the immiscible oil demonstrated more negative influence on the heat transfer and pressure drops than the miscible oil.

Axial flow cyclone separator with guide blade has been widely used, due to its low resistance, huge gas processing and small volume. Although its structure is simple, three-dimension strong rotating turbulent flow forms which involves many complex interactions such as dual-phase separation, adsorption and electrostatic interference. This paper is focused on studying the resistance performance of the axial flow cyclone separator. Numerical simulation methods are carried out to acquire the internal flow field characteristics under different operating pressure and temperature conditions. The result shows that the pressure drop decreases under the same operating pressure, as the operating temperature increases. When the operating temperature is the same, the higher operating pressure enhances the value of the pressure drop. Velocity distribution, pressure contours and turbulent viscosity contours have been presented, to analyze the characteristics of the internal airflow, so as to help optimize the design. Experiments are intended to verify the results of numerical simulation and explore the internal flow field of the cyclone separator further. The cyclone separator has 8 rotary blades which are split into 8 parts, namely one blade is 45° in the tangential direction. 0° and 22.5° are chosen in the experiment. The dimensionless pressure distribution is shown. A comparison of the CFD results and the experimental results is made to prove that the numerical simulation methods are correct and accurate. The curve of the numerical simulation results is very close to that of the experimental results with the similar trend. It is concluded that the methods can predict the internal flow field characteristics of the axial flow cyclone separator.

A numerical study was conducted to analyze the heat and mass transfer in a micro heat pipe, with the thin-film theory applied to the phase change at the liquid-vapor interface. The model described the liquid and vapor distributions, phase change rate, wall temperature, pressure drop, and heat transfer rate in a micro heat pipe under normal operation. The reference cross-sectional geometry of the micro heat pipe was triangular, but the model could be applied to various geometries by utilizing a hydraulic diameter. In previous studies, to predict the thermal performance of a micro heat pipe, the phase change interface has usually been modeled using the Young-Laplace capillary equation, and the phase-change ratio has been estimated using terms such as vapor pressure, liquid pressure, and capillary pressure. In this study, a thermal numerical model for a micro heat pipe was developed using an augmented Young-Laplace equation. Consequently, terms that have been commonly excluded in previous studies, including the disjoining pressure, were included. The validity of the model was verified using the experimental results for the wall temperature of the micro heat pipe, wherein the relative error bound was less than 1 °C and 6 °C for the operating and condenser temperatures, respectively. The influence of the disjoining pressure on the heat transfer was analyzed and discussed for various operating temperatures and tilt angles.