Masatoshi Akahori

A numerical and experimental investigation of the modeling of microwave heating for liquid layers using a rectangular wave guide (effects of natural convection and dielectric properties)

Abstract The heating of a liquid layer by microwave with a rectangular wave guide has been investigated numerically and experimentally. It was performed for two different liquid layers: water layer and NaCl-water solution layer. A complete mathematical model is proposed, which uses comprehensive two-dimensional heat and momentum equations to describe unsteady temperature and fluid flow fields, coupled with a complete solution of the unsteady Maxwells equations in the time domain can be used to investigate many aspects of the heating process. In this work, the effects of electric conductivity (which corresponds to the percentage by weight of NaCl in liquid layer) and microwave power level on the heating process were examined. Based on a model combining the Maxwell and heat transport and fluid flow equations, the results show that the heating kinetic strongly depends on the dielectric properties.

Experimental and numerical study of microwave drying in unsaturated porous material

Abstract The drying of unsaturated porous material due to microwave drying (2.45GHz) has been investigated numerically and experimentally. Most importantly, this work focuses on the influence of moisture content on each mechanism (vapor diffusion and capillary flow) during microwave drying process. Based on a model combining the electric field and heat-mass transport equations show that the variation of initial moisture content and particle size changes the degree of penetration and rate of absorbed energy within the material. The small bead size leads to much higher capillary forces resulting in a faster drying time.

The characteristics of microwave melting of frozen packed beds using a rectangular waveguide

The melting of frozen packed beds by a microwave with a rectangular waveguide has been investigated numerically and experimentally. It was performed for the two different layers, which consist of frozen and unfrozen layers. This paper focuses on the prediction of the temperature field, as well as the microwave energy absorbed, and the melting front within the layered packed beds. Based on the combined model of the Maxwell and heat transport equations, the results show that the direction of melting against the incident microwave strongly depends on the structural layered packed beds because of the difference in the dielectric properties between water and ice.

A NUMERICAL AND EXPERIMENTAL STUDY OF MICROWAVE DRYING USING A RECTANGULAR WAVE GUIDE

The drying of a capillary porous packed bed of glass beads by microwave energy using a rectangular wave-guide was investigated numerically and experimentally. The effects of moisture content, particle size and microwave power level on the drying kinetics were examined. Most importantly, this work focuses on the prediction of the distribution of the electromagnetic field as well as the temperature and moisture distribution within the capillary porous medium. The model, which combines the electromagnetic, temperature, and moisture fields, predicted results which were in good agreement with the experimental data.

A numerical and experimental investigation of the modelling of microwave melting of frozen packed beds using a rectangular wave guide

Abstract The melting of frozen packed beds by microwave with rectangular wave guide has been investigated numerically and experimentally. It was performed for the two different layers, which consists of frozen and unfrozen layers. Based on the model combined the Maxwell and heat transport equations, the results show that the direction of melting against the incident microwave strongly depends on the structure of layered packed beds because the difference in the dielectric properties between water and ice.

Freezing due to direct contact heat transfer including sublimation

From the energy saving viewpoint, the utilization of LNG cold is very important in the refrigeration industry concerning the low temperature region. In this paper, as a basic study of the freezing due to direct contact, including evaporation, solid–liquid direct contact heat transfer associated with sublimation has been investigated using the dry ice in water experimentally and theoretically. Based on a two-layers-model composed of CO2 vapor and the bulk water around the dry ice, the velocity and temperature fields in two layers was calculated numerically and the calculated results for the freezing condition of the bulk water were compared with the experimental results.

The Effect of Surface Structure on Microwave Heating

In microwave heating, interference of transmission wave and reflection wave in a sample has an important meaning. We focus on the high performance of the heating efficiency due to changing the surface structure of the sample. Using the microwave of TE10 mode and frequency of 2.45GHz in rectangular waveguide, we have investigated the effect of the surface structure of the material on the characteristics of microwave heating, and have indicated the guideline for the optimization of microwave heating by controlling reflected and transmitted waves. It was found that the rectangle surface structure was effective for the high performance of the heating efficiency, by considering the relationship between the mode and the surface structure.Copyright

Water Infiltration and Heat Transfer in One Dimensional Unsaturated Packed Beds.

Water and heat transport in unsaturated packed beds due to supplying hot water have been investigated experimentally and theoretically. Using various sizes of glass beads, capillary pressure and permeability in packed beds were measured in unsaturated beds. The distributions in water saturation and temperature were predicted for one dimensional packed bed, based on a model assuming local thermal equilibrium among water, gas and particles at any specific space. The predicted temperature distributions were compared with the experimental results obtained using various glass sizes. In layered packed beds, water saturation becomes discontinuous at the interface of two layers because of the difference of the water characteristics between two beds. Water penetrates faster in coarse-over fine-textured profile compared with in fine-over coarse-textured profile. Similarly, the temperature rises faster in former profile under the same supplied heat quantity.