Study on Shrinkage Deformation of Food in Microwave-Vacuum Drying

Selected Papers from the 19th International Drying Symposium (IDS 2014), Part 2Drying shrinkage is an important problem in the food industry. Focusing on microwave vacuum drying, we study the mechanism of deformation due to shrinkage of the food structure. A relationship between the strain and the water content is introduced for a finite element analysis. The temperature and water distributions are obtained by a finite difference method with the use of a variable permeability and diffusion coefficient depending on the water content. Comparisons with experimental data on radishes, carrots, and tofu indicate that the present model can express the deformation as well as the water content inside the materials

Possibility of cryopreservation of medaka eggs using liquid meniscus

The First Pacific Rim Thermal Engineering Conference (PRTEC2016), Marchi 13-17, 2016, Waikoloa Beach Marriott Resort & Spa Hawaii's Big Island, USAThe cryopreservation of fish eggs is an important subject in the field of fishery and preservation of biological species. Thus far, there has been no success in the preservation of fish eggs because of the large size of the eggs and the thick external shell. This paper discusses the effectiveness of using the liquid meniscus formed around the egg for protecting its morphology. Freezing and thawing experiments of medaka eggs were performed under different freezing conditions, and the hatching rate of the egg was examined. Before freezing, the eggs were dehydrated at room temperature in order to reduce the effect of volume expansion caused by freezing. It was confirmed that 100% of the eggs dehydrated by 15% or less were successfully hatched. In the freezing process, a medaka egg was placed on a hydrophobic cooling plate and a thin liquid meniscus was formed around the hydrophilic egg surface. An aqueous solution of trehalose was used as the liquid meniscus as well as a cryoprotectant to prevent damage caused by freezing. Cryopreservation of the egg was not successfully performed for all processes, including intracellular freezing; however, 80% of the eggs were alive even after freezing of the external meniscus. Therefore, it is confirmed that the liquid meniscus is effective for the cryopreservation of the external shell. The liquid meniscus can reduce the physical stress due to extracellular ice growth. Moreover, since the liquid meniscus system has a low heat capacity, the thermal process is easy to control compared to the conventional method. We concluded that the present method can be used for the cryopreservation of fish eggs

Scale effect of slip boundary condition at solid–liquid interface

Rapid advances in microelectromechanical systems have stimulated the development of compact devices, which require effective cooling technologies (e.g., microchannel cooling). However, the inconsistencies between experimental and classical theoretical predictions for the liquid flow in microchannel remain unclarified. Given the larger surface/volume ratio of microchannel, the surface effects increase as channel scale decreases. Here we show the scale effect of the boundary condition at the solid–liquid interface on single-phase convective heat transfer characteristics in microchannels. We demonstrate that the deviation from classical theory with a reduction in hydraulic diameters is due to the breakdown of the continuum solid–liquid boundary condition. The forced convective heat transfer characteristics of single-phase laminar flow in a parallel-plate microchannel are investigated. Using the theoretical Poiseuille and Nusselt numbers derived under the slip boundary condition at the solid–liquid interface, we estimate the slip length and thermal slip length at the interface

Molecular dynamics study on condensation/evaporation coefficients of chain molecules at liquid-vapor interface

The structure and thermodynamic properties of the liquid–vapor interface are of fundamental interest for numerous technological implications. For simple molecules, e.g., argon and water, the molecular condensation/evaporation behavior depends strongly on their translational motion and the system temperature. Existing molecular dynamics (MD) results are consistent with the theoretical predictions based on the assumption that the liquid and vapor states in the vicinity of the liquid–vapor interface are isotropic. Additionally, similar molecular condensation/evaporation characteristics have been found for long-chain molecules, e.g., dodecane. It is unclear, however, whether the isotropic assumption is valid and whether the molecular orientation or the chain length of the molecules affects the condensation/evaporation behavior at the liquid–vapor interface. In this study, MD simulations were performedto study the molecular condensation/evaporation behavior of the straight-chain alkanes, i.e., butane,octane, and dodecane, at the liquid–vapor interface, and the effects of the molecular orientationand chain length were investigated in equilibrium systems. The results showed that the condensation/evaporation behavior of chain molecules primarily depends on the molecular translational energyand the surface temperature and is independent of the molecular chain length. Furthermore, the orientation at the liquid–vapor interface was disordered when the surface temperature was sufficientlyhigher than the triple point and had no significant effect on the molecular condensation/evaporation behavior. The validity of the isotropic assumption was confirmed, and we conclude that the condensation/evaporation coefficients can be predicted by the liquid-to-vapor translational length ratio, even for chain molecules

Nonequilibrium molecular dynamics study on energy accommodation coefficient on condensing liquid surface—Molecular boundary conditions for heat and mass transfer

Nonequilibrium molecular dynamics (NEMD) studies have been conducted to determine molecular boundary conditions at vapor–liquid interfaces for the kinetic theory of condensation and evaporation. In previous studies, a microscopic formulation of the condensation coefficient was defined as the condensation probability of vapor molecules based on equilibrium molecular dynamics simulations and transition state theory. The condensation coefficient was presented as a function of the translation energy of incoming molecules and surface temperature. Based on this, the velocity distributions of evaporating and reflecting molecules were theoretically expressed under equilibrium conditions. In a practical nonequilibrium situation, the energy transfer by the reflecting molecules is important along with the condensation/evaporation probability. However, it is unclear whether the results obtained under equilibrium conditions can be applied under nonequilibrium conditions. This study, therefore, defines the energy accommodation coefficient of reflecting molecules by comparing the energy transfer due to reflection with that under equilibrium conditions. NEMD simulations are conducted using two surfaces facing each other, an evaporating surface and a condensing surface, for argon molecules under different nonequilibrium conditions. The results show that the velocity distribution of reflecting molecules deviates from those under equilibrium conditions, and the energy accommodation coefficient decreases as nonequilibrium conditions increase. Additionally, an inverted temperature profile is observed. Reflecting molecules play an important role in the sensible heat transfer on the condensing surface, and they are not accommodated on the condensing surface. Thus, they raise the temperature in the vicinity of the condensing surface under nonequilibrium conditions

Thermal performance of flat micro heat pipe with converging microchannels

Optimizing the groove size of flat micro heat pipes is crucial for improving their thermal performance. In this study, we developed a grooved converging microchannel array for use in a flat micro heat pipe to enhance the capillary force. A simplified theoretical analysis was used to optimize the groove size for given operating conditions of converging microchannels and straight microchannels. The evaporation section of the grooved microchannel was hydrophilic and had a smaller hydraulic diameter than the hydrophobic condensation section. The smaller diameter of the evaporation section enabled the condensed working fluid to be effectively drawn back to the same section. Experiments were performed to measure the thermal performance of the micro heat pipes under the analyzed operating conditions. Compared to a heat pipe with a straight microchannel, and a heat pipe with an unoptimized converging microchannel, the micro heat pipe with the optimized converging microchannel was confirmed to yield a higher thermal performance. Capillary-driven flow experiments at room temperature and atmospheric pressure were also used to investigate the capillary forces of the different microchannels. The optimized converging microchannel was once again observed to generate the largest capillary force

Effects of Nano/Microstructures on Performance of Si-based Microfuel Cells

We investigated the effects of the contact surface structure of porous Si-based membrane electrode assemblies (MEAs) on the performance of microfuel cells, because the contact area of the triple-phase boundary among the MEA components plays an important role in the performance of polymer electrolyte fuel cells (PEFCs). An n-type silicon substrate was first wet-etched with KOH and subsequently anodically etched to fabricate a porous Si substrate. The cross section of the mechanically polished Si wafer showed pores with high aspect ratios. Electrolyte solutions were filled into the pores to prepare a porous Si membrane (PSM), and the MEA was fabricated by hot-pressing the PSM between two conventional catalyst-coated carbon-paper electrodes. The porous Si-based MEA worked well and showed a power density higher than that of the Nafion®-212-based membrane. Further, we examined the effects of the nano/microstructures at the triple-phase boundary and found that the more densely arranged nano/microstructures reduced the magnitudes of the activation overvoltage and ohmic overvoltage, thereby improving the cell performance.International Symposium on Innovative Materials for Processes in Energy Systems 2013 (IMPRES2013), September 4-6, 2013 in Fukuoka, Japan

Ambient temperature drying of therapeutic protein solution with use of microwave

[EN] High quality drying of therapeutic protein-solution is important in medical and pharmaceutical processing. Freeze-drying is mostly used, but it takes a long drying-time and causes damages of protein structures. In order to improve the drying quality, we propose a microwave vacuum drying performed at ambient temperatures under low-pressure conditions. We are focusing on the Parma-Zyme method for the evaporative drying of protein solutions such as egg white or lysozyme with vitrification. Circular dichroism (CD) spectroscopy is used to detect protein conformation changes due to the drying, and it is found that the ambient temperature drying can preserve the protein conformation.CD analysis and chemical works were supported by Prof. Shigeori Takenaka, Department of Applied Chemistry, Kyushu Institute of Technology. This study was financially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research, Project No. 17K18843.Tsuruta, T.; Ogawa, T.; Abe, R.; Tanigawa, H. (2018). Ambient temperature drying of therapeutic protein solution with use of microwave. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 651-658. https://doi.org/10.4995/IDS2018.2018.7537OCS65165

Effects of Nano/Microstructures on Performance of Si-based Microfuel Cells

We investigated the effects of the contact surface structure of porous Si-based membrane electrode assemblies (MEAs) on the performance of microfuel cells, because the contact area of the triple-phase boundary among the MEA components plays an important role in the performance of polymer electrolyte fuel cells (PEFCs). An n-type silicon substrate was first wet-etched with KOH and subsequently anodically etched to fabricate a porous Si substrate. The cross section of the mechanically polished Si wafer showed pores with high aspect ratios. Electrolyte solutions were filled into the pores to prepare a porous Si membrane (PSM), and the MEA was fabricated by hot-pressing the PSM between two conventional catalyst-coated carbon-paper electrodes. The porous Si-based MEA worked well and showed a power density higher than that of the Nafion®-212-based membrane. Further, we examined the effects of the nano/microstructures at the triple-phase boundary and found that the more densely arranged nano/microstructures reduced the magnitudes of the activation overvoltage and ohmic overvoltage, thereby improving the cell performance

Improvement of Freezing Quality of Food by Pre-dehydration with Microwave-Vacuum Drying

Partial dehydration by microwave vacuum drying has been applied to tuna, oyster and mackerel prior to freezing in order to reduce quality damages due to freezing and thawing. Samples were dehydrated at pressure of 4kPa and temperature lower than 25°C. Two cooling conditions were tested in the experiment by using the freezing chamber of temperatures -20°C and -80°C. The experimental results showed that decreasing the water content in tuna could lower the freezing point temperature and made the freezing time shorter. It was also found that removing some water was effective to reduce the size of ice crystal and the drip loss in mackerel. After thawing, the pre-dehydrated mackerel showed better microstructure than that frozen without pre-treatment. Furthermore, the sensory tests have been done by a group of panelist for the evaluation on aroma, flavor, and general acceptability of mackerels