Takao Kashiwagi

Thermodynamic formalism of minimum heat source temperature for driving advanced adsorption cooling device

This letter presents a thermodynamic formulation to calculate the minimum driving heat source temperature of an advanced solid sorption cooling device, and it is validated with experimental data. This formalism has been developed from the rigor of the Boltzmann distribution function and the condensation approximation of adsorptive molecules. An interesting and useful finding has been established from this formalism that it is possible to construct a solid sorption refrigeration device that operates in a cycle transferring heat from a low temperature source to a heat sink with a driving heat source at a temperature close to but above ambient.

Energy-Efficient Low Rank Coal Drying Based on Enhanced Vapor Recompression Technology

Vapor recompression is considered a highly energy-efficient technology to recover the heat involved in a process. Unfortunately, in conventional vapor recompression technology, not all of the heat can be recovered effectively. In this study, an enhanced vapor recompression technology enabling more effective heat recovery is proposed, and its ability to dry low rank coal (LRC) is evaluated. We consider the factors of exergy recovery and heat coupling. In addition to conventional vapor recompression, enhanced vapor recompression technology used to dry LRC can recover effectively the sensible heat of dried solid LRC through water recirculation. Moreover, we show that there is an optimum amount of recirculated water for each initial and target moisture content. A temperature–enthalpy diagram reveals that the proposed enhanced vapor recompression technology shows effective heat coupling for each type of heat, which results in less exergy loss so that a marked reduction in energy consumption can be achieved.

Experimental study on heat transfer from parallel louvered fins by laser holographic interferometry

Abstract The objectives of this paper are to study experimentally the details of the heat transfer process in louver arrays and to propose the geometrical arrangement of louvers that would be most effective in improving the performance of heat exchangers. That goal is approached via the following steps. In the first step, the temperature field around louvers is visualized, employing the simple flat-louver model made of a thin bakelite plate and thin nichrome foil heaters, and at the same time the heat transfer coefficient on the louvers is measured. The isotherms are visualized by means of laser holographic interferometry. The isotherms for various louver arrangements were obtained; the thermal boundary layer and the wake generated by an upstream louver extending toward the downstream louvers were observed. It is found that the heat transfer coefficient on the downstream louver is sensitive to the behavior of those boundary layers and wakes. In the second step, the arrangement of louvers is examined with the purpose of enhancing heat transfer. A displacement of a downstream louver out of the influence of the heated air wake from the preceding upstream louver is proposed on the basis of both the observation of isotherms and the measurement of heat transfer coefficients in staggered louver arrays. The experimental results indicate that the performance of heat exchangers may be improved by rearranging the louvers with a small-magnitude displacement.

Thermodynamic Modeling of Absorption Chiller and Comparison with Experiments

A simple and accurate thermodynamic model is presented for a four-heat-reservoir, absorption chiller. The performance of chillers, as described by 1/COP , is expressed in terms of the dominant external and internal losses that stem from the finite-rate heat transfer and internal entropy generation in the absorber, condenser, generator, and evaporator. It is found that the relative contributions from these losses of absorption chillers govern their behavior over a wide range of cooling capacities. The successful formulation of the thermodynamic model, as presented in this article, implies that all previous endoreversible approaches are inadequate because they cannot portray the real behavior of absorption chillers accurately. At best, these models give only the upper bounds of experimental realities and thus they can be viewed only as subsets of the generic thermodynamic approach described here. To this end, we present evidence from an experimental facility to show that true absorption chiller behavior is ...

Innovative Steam Drying of Empty Fruit Bunch with High Energy Efficiency

Empty fruit bunch (EFB) is one of the solid wastes from crude palm oil mills and has the lowest value for utilization compared to other solid wastes. To achieve an efficient utilization of EFB, drying is considered the first crucial process due to the high moisture content of EFB. In this study, EFB drying based on exergy recovery is proposed to achieve high energy efficiency. A fluidized bed is adopted as the main dryer. The proposed model is evaluated in terms of energy efficiency, especially regarding the influence of target moisture content and fluidization velocity. Up to 92% of the energy involved in the drying process can be recirculated. The total energy consumption for drying decreases as the target moisture content decreases, though there is no significant impact of fluidization velocity to total energy consumption. In addition, the required total length of the heat transfer tubes immersed inside the fluidized bed dryer is calculated because it relates to fluidization performance and economic issues. Lower target moisture content results in a longer heat transfer tube, and higher fluidization velocity leads to a shorter heat transfer tube.

A study of the radiative ignition mechanism of a liquid fuel using high speed holographic interferometry

The mechanism of radiative ignition of 1-decene is investigated experimentally using a high speed two-wavelength holographic interferometry technique. From the time of CO2 laser irradiation up to ignition, motion pictures with a framing speed of 500 frames per second are used to measure the temperature and fuel vapor concentration distributions in the gas phase near the liquid surface. The effects of oxygen concentration on the growth of the fuel vapor plume are reported for three different environments of nitrogen, air and 40% O2/60% N2 and for peak laser fluxes of 260, 520, and 780 W/cm2. Results indicate that the effects of oxygen concentration appear shortly after the appearance of fuel vapor in the gas phase instead of, as previously believed, only very near the final ignition events. An increase in oxygen concentration speeds the growth rate of the vapor plume and brings the location of ignition closer to the fuel surface at the same peak laser fluxes. Two stages of global chemical reactions, the first slow and the second fast, may be able to describe the behavior observed in oxygen containing environments. An increase in peak laser flux does not change the location of ignition but causes an unstable, complex fuel vapor cloud due to buddling and violent vaporization of the liquid.

High concentration non-imaging Fresnel lens design with flat upper surface

Concentration PV systems are emerging recently and primary lenses have been developed for concentrating solar incident. Although the authors already produced 500X dome-shaped Fresnel lens, its production process was complicated because of the shape. The objective of this study is to investigate new design method for non-imaging Fresnel with flat upper surface so that the production can be easier. The design of prisms is formulated by means of non-linear optimization to have maximum acceptance half angle with edge-ray principle. It is shown that designing more than 500X flat Fresnel lens is possible. The study also presents optimal condition of lens size requiring energy payback year to satisfy from the viewpoint of life cycle energy production and consumption.

Novel power generation from microalgae: Application of different gasification technologies

Energy harvesting from microalgae based on integrated gasification and combined cycle is proposed and evaluated. Two gasification technologies, i.e. conventional thermal gasification and supercritical water gasification, are employed to convert microalgae to syngas. Supercritical water gasification has advantages on bypassing drying, however the energy to elevate the water to supercritical condition is relatively high. Each model was built on the concept of enhanced process integration technology consisting of exergy recovery and conventional process integration in order to minimize the total exergy destruction throughout the whole integrated processes. High energy efficiency of each integrated processes could be achieved, 57% for supercritical water gasification and 42% for conventional gasification.

Energy policy & New National Energy Strategy in Japan

Energy is the bedrock of our daily lives and industry. Now is the time that industry, government and academia must join together and examine highly independent, fully environmentally considerate and rational energy systems. In this presentation, recent Japanese policy will be introduced focusing on new national energy strategy. Looking at future technology trends, it is probable that, in the case of electricity generation, nuclear power, followed by coal and natural gas, will provide the bulk of the base load, and these will be complemented by highly independent symbiotic and regional energy systems, that will form clusters with appropriate size. In the year 2030, oil will be restricted to transport and chemical use, in other words, ldquonoble userdquo for which it is difficult to find alternatives. In the transport sector, as fuel cell vehicles start to reach full commercialization, it is possible that advances in the capabilities of fuel cells will see plug-in hybrids and electrical vehicles cornering a larger share of the market. From the viewpoint of effective energy, or ldquoexergyrdquo, an arrival of the ldquohydrogen societyrdquo is surely only a matter of time. In this address, having gained a grasp of these issues, first of all the Japanpsilas energy strategy in terms of energy-saving, new energies and nuclear power will be looked, and then some observations about the restructuring of the energy system will be presented focusing on thermoelectric technology.

Combined hydrogen production and power generation from microalgae

A combined hydrogen production and storage together with power generation from microalgae is proposed based on enhanced process integration technology (EPI). EPI consists of two core technologies: exergy recovery and process integration. Exergy recovery is performed through exergy elevation and heat coupling to minimize the exergy destruction. Furthermore, the unrecoverable energy/heat in a single process in recovered and utilized in other processes through process integration. The proposed integrated system includes a supercritical water gasification, separation, hydrogenation, and combined cycle. Microalga Chlorella vulgaris is used as a sample for modeling and evaluation. The effects of fluidization velocity and gasification pressure to energy efficiency are evaluated. From process modeling and calculation, it is shown that high total energy efficiency (higher than 60%) and electricity generation efficiency (about 40%) of can be achieved.