Tomohiro Nomura

DRYING OF SLICED RAW POTATOES IN SUPERHEATED STEAM AND HOT AIR

Drying experiments were conducted on raw potato slices, using atmospheric pressure superheated steam and hot air as drying media at 170 and 240°C. Mass changes of the material were continuously measured, the conditions of cross section near the surfaces were observed with an electron microscope, also color changes of their surface were measured during drying. The respective drying methods and temperature conditions were compared and it was found that, in the case of superheated steam drying, moisture content temporarily increases due to steam condensation in the initial stage of drying, therewith, as well as starch gelatinization rapidly develops. Meanwhile, in case of hot air drying, starch gelatinization occurs more slowly than with superheated steam drying and that non-gelatinized starch granules remain on the surface when drying was completed. Furthermore, surface color measurements showed that samples dried by superheated steam were more reddish than ones dried by hot air and the surfaces were more glossy, because no starch granules remain on the surface in case of superheated steam drying.

SIMULATION OF SUPERHEATED STEAM DRYING CONSIDERING INITIAL STEAM CONDENSATION

A heat and mass transfer model was proposed for the superheated steam drying, focusing on phenomena which occur during the initial stage of drying, i.e., condensation of superheated steam on material surfaces and subsequent shift from condensation to evaporation leading to the beginning of the actual drying (Reverse Process Model). Next, drying equations considering the reverse process were formulated for a shrinking/swelling infinite flat plate to calculate moisture content and temperature distributions in a material, changes in mass of a material with time, and a characteristic drying curve. Then, the influence of the initial thickness of a material and the heat transfer coefficient were investigated. In addition, calculation results were compared with experimental ones with regard to the change in mass of material with time and the characteristic drying curve, and good conformance was obtained for the initial stage of drying.

NOVEL WATER FACILITIES FOR CREATION OF COMFORTABLE URBAN MICROMETEOROLOGY

The cooling effects of artificial water facilities – fountains, waterfalls and urban canals – have not received much attention. To improve the meso-space thermal environment in an urban area, especially that during the midsummer, we propose using novel artificial water facilities to alter the temperature and humidity, so as to improve pedestrian comfort. To study this, we have carried out field measurements and wind tunnel tests, and we report the results in this paper. At first we made measurements of wind velocity, temperature and humidity around such artificial water facilities in Tennoji Park in Osaka city (a typical Japanese large city). The results showed reduced temperatures on the leeward side, and demonstrated the usefulness of water facilities in improving the thermal environment. Also, we constructed an insulated 1/400 scale wind tunnel model of the situation and measured, by means of X-type hot wire anemometer, the air currents on the wind tunnel surfaces in urban, suburban and rural terrains. We also measured, using fine-gauge T-type thermocouples, the air temperature distribution in front of and behind the model of the water facility. The results confirmed the qualitative ranges of the cooling effect provided by the actual water facilities. In particular, the cooling effect produced by a 1.0 mm diameter nozzle fountain was found to extend a distance downstream equal to ten times the height of spout.

The relationship between HCl and mercury speciation in flue gas from municipal solid waste incinerators

The relationship between mercury speciation and HCl concentration was investigated by measuring mercury in the flue gas of MSW incinerators. The proportion of HgCl2 (HgCl2/total Hg) increased with increasing HCl concentration. The HgCl2 proportion distribution showed different characteristics below and above the HCl concentration borderline of about 1000ppm. This distribution characteristic could be explained by the thermodynamic equilibrium analysis based on the two reactions in which Hg0 reacts with HCl and O2 to generate HgCl2 and HgO. The change in mercury speciation upon passing through a dust collector was also investigated. The part of Hg0 changed into HgCl2 when the mercury contained in the flue gas passed through a fabric filter.

Behavior of Inversion Point Temperature and New Applications Of Superheated Vapor Drying

This report summarizes new fields of applications of both superheated vapor drying and highly humid and high temperature air drying. And then it describes fundamental research in developing a controlled superheated vapor dryer.

Effect of Moisture Content on the Expansion Volume of Popped Amaranth Seeds by Hot Air and Superheated Steam Using a Fluidized Bed System

The effect of the initial moisture content (X0) of amaranth seeds on expansion volume after popping was examined in hot air and superheated steam (SHS), using a fluidized bed system (FBS). The moisturized seeds were prepared under various vapor pressures due to various saturated salt solutions. In hot air, the maximum expansion volume was shown by seeds having X0 of 0.16 at 260 °C for 15 sec, reaching 8.7-fold of the pre-popped seeds. Heating by SHS decreased the volume slightly. Thus, popping of amaranth seeds is influenced not only by the moisture content of the seeds, but also by moisture in the heat media.

Popping of Amaranth Seeds in Hot Air and Superheated Steam

Abstract: Amaranth seeds can be popped by evaporation of contained moisture during heating. The relationships among the expansion ratio by popping and the type of heating media, gas temperature, initial moisture content of the seeds and heating time were clarified based on empirical study. And using a simple calculation model, the popping mechanism and effect of initial condensation of superheated steam were investigated. According to the results, the maximum volume of the seeds after popping was 8.7 times greater than that of raw seeds at optimal conditions. Compared with the case of hot air, the expansion ratio by superheated steam was slightly lower.

A reverse process of superheated steam drying from condensation to evaporation

To clarify the mechanism of heat and mass transfer in the early stages of superheated steam drying which accompanies condensation and evaporation, an experiment in which a water surface was used as the dried material was conducted under atmospheric pressure. Temperature profiles in both the gas phase and the liquid phase near the water surface and the liquid level were measured precisely. From the results, heat transfer rates at the water surface and the amount of steam condensed into water were determined; in addition, the relationship between these two was investigated both experimentally and theoretically. Furthermore, a characteristic curve of drying accompanying condensation and evaporation in the early stages of superheated steam drying was derived semiempirically. In this drying characteristic curve, there is a point at which neither condensation nor evaporation occurs. This is defined as the “reverse point.” Introduction of this reverse point and the time ratio for condensation and evaporation during the early stages of superheated steam drying are clarified.

THERMAL PERFORMANCE AND EVALUATION OF SIPERHEATED STEM DRYING SYSTEM USING SOLAR-ASSISTED ABSORPTION HEAT TRANSFORMER

ABSTRACT This paper summarizes the main results of our study carried out under the priority-area research “Energy Conversion and Utilization with High Efficiency” supported by the grant-in-aid of scientific research from the Ministry of Education, Science and Culture of Japan. In the research we focused on applications of solar energy utilization for industrial drying systems. In this paper a new concept of a closed drying system with superheated steam provided from a temperature boosting type heat pump (absorption type heat transformer) was proposed. The heat transformer is driven directly by heat from a solar collector. The performance for different three drying periods and a number of factors affecting it were predicted by a computer simulation. Furthermore the heat and mass transfer characteristics of water evaporation into superheated steam stream by radiative and convective heating were indicated experimentally. It was concluded that the system would be useful for industries where high temperature (...

Development of a Light Weight Pulse‐Tube Cryocooler

Examinations were done of a small‐size Stirling‐type pulse‐tube cryocoolers developed for cooling high‐temperature superconductor devices and semiconductor sensors. To satisfy the requirements for use in such devices, the Stirling‐type pulse‐tube cryocooler WE‐SP2000, the conventional model, needed further improvement. The motor loss of the compressor was analyzed and the compressor efficiency of this model was improved to more than 70% against the 55% of the conventional model. Improvement of cooling efficiency through optimization of the pulse‐tube form was also examined. Moreover, improvement of the U type pulse‐tube cryocooler was examined, and nearly the same performance as an In‐line type expander was achieved. As a result, an improvement in the cooling capacity by about 45% was attained in this model, for cooling capacity of 6.8W at 77K with compressor input power of 200W. A cooling capacity of 2W at 70K needed to cool high‐temperature superconducting devices, the compressor input power was 70W. A ...