Study on adsorption refrigeration cycle utilizing activated carbon fibers. Part 1. Adsorption characteristics

Thermal heat driven adsorption systems using natural refrigerants have been focused on the recent energy utilization trend. However, the drawbacks of these adsorption systems are their poor performance in terms of system cooling capacity and coefficient of performance (COP). The objective of this paper is to improve the performance of thermally powered adsorption cooling system by selecting new adsorbent–refrigerant pair. Adsorption capacity of adsorbent–refrigerant pair depends on the thermophysical properties (pore size, pore volume and pore diameter) of adsorbent and isothermal characteristics of the pair. In this paper, the thermophysical properties of two PAN types of activated carbon fibers (FX-400 and KF-1000) are determined from the nitrogen adsorption isotherms. The standard nitrogen gas adsorption/desorption measurements on various adsorbents at liquid nitrogen of temperature 77.3 K were performed. Surface area of each adsorbent was determined by the Brunauer, Emmett and Teller (BET) plot of nitrogen adsorption data. Pore size distribution was measured by the Horvath and Kawazoe (HK) method. As of the adsorption/desorption isotherms, FX-400 shows very small hysteresis when the value of P/P_o exceeds 0.4, while KF-1000 has no hysteresis in the whole range of P/P_o. The adsorption capacity of FX-400 is about 30% higher than that of KF-1000. The adsorption equilibrium data of activated carbon fiber (ACF)-methanol are presented and correlated with simple equations. The adsorption equilibrium data of ACF (KF-1000)-water also presented in order to facilitate comparison with those of ACFs-methanol pair. The results will contribute significantly in designing the adsorber/desorber heat exchanger for thermally driven adsorption cooling system.     

Study on adsorption refrigeration cycle utilizing activated carbon fibers. Part 2. Cycle performance evaluation

Thermal heat driven adsorption systems have been gained considerable attention on the recent energy utilization trend. However, the drawbacks of these adsorption systems are their poor performance. It is urgently necessary to improve the system performance of the adsorption cycles. There are two major ways for the system performance improvement. One is to develop new adsorbent material well suited to low temperature heat regeneration. The other is to enhance heat and mass transfer in the adsorber/desorber heat exchanger. The objective of the paper is to investigate the system performance of an adsorption cycle. The cycle utilizes activated carbon fiber (ACF)/methanol as adsorbent/refrigerant pair. In this paper, specific cooling effect SCE and COP of the system are numerically evaluated from the adsorption equilibrium theory with different hot, cooling and chilled fluid inlet temperatures. It is confirmed that the influences of hot, cooling and chilled fluid inlet temperatures on the system performance are qualitatively similar to those of silica gel/water pair. Even though, the driving temperature levels of ACF/methanol and silica gel/water are different. There is an optimum condition for COP to reach at maximum for ACF/methanol pair. Particularly, the ACF/methanol system shows better performance with lower chilled fluid inlet temperature between −20 and 20 °C.     

The effect of chemical surfactants on the absorption performance during NH3/H2O bubble absorption process

The objectives of this paper are to visualize the bubble behavior by shadow graphic method, to examine the effect of surfactants on the bubble type absorption, and to find the optimal conditions to design highly effective compact absorber for NH₃/H₂O absorption system. The initial concentrations of NH₃/H₂O solution and the kinds and the concentrations of surfactants are considered as key parameters. By measuring the absorption rate for each condition, two effects of the addition of surfactants, the Marangoni and the barrier effect, are compared with each other. The results show that the addition of surfactant enhances the absorption performance up to 4.81 times. The experimental correlations of the effective absorption ratio for each surfactant, 2-ethyl-1-hexanol, n-octanol, and 2-octanol, are suggested within ±15, ±10, and ±10%, respectively.     

Levels of Vibrio parahaemolyticus and thermostable direct hemolysin gene-positive organisms in retail seafood determined by the most probable number-polymerase chain reaction (MPN-PCR) method

The incidence and levels of Vibrio parahaemolyticus and thermostable direct hemolysin gene (tdh)-positive organisms in retail seafood were determined. The most probable number-polymerase chain reaction (MPN-PCR) method using a PCR procedure targeting the species-specific thermolabile hemolysin gene (tlh) and tdh was used to determine the levels of V. parahaemolyticus and tdh-positive organisms, respectively. In seafood for raw consumption, V. parahaemolyticus was found in four (13.3%) of 30 fish samples, 11 (55.0%) of 20 crustacean samples, and 29 (96.7%) of 30 mollusc samples. Levels of V. parahaemolyticus were below 10(4) MPN/100 g in all fish and crustacean samples tested. However, they were above 10(4) MPN/100 g in 11 (36.7%) of the 30 mollusc samples. In all seafood for raw consumption, the level of tdh-positive organisms was below the limit of detection (< 30 MPN/100 g). In seafood for cooking, V. parahaemolyticus was found in 15 (75.0%) of 20 fish samples, nine (45.0%) of 20 crustacean sample, and 20 (100%) of 20 mollusc samples. Levels of V. parahaemolyticus were above 10(4) MPN/100 g in only three (15.0%) and one (5.0%) of the 20 fish and 20 crustacean samples, respectively. However, they were above 10(4) MPN/100 g in 18 (90.0%) of the 20 mollusc samples. In seven (35.0%) of the 20 mollusc samples, tdh-positive organisms were found and their levels ranged from 3.6x10 to 1.1 x 103 MPN/100 g. From four of seven tdhpositive samples, tdh-positive V. parahaemolyticus was isolated.     

Engineering of Escherichia coli L-serine O-acetyltransferase on the basis of crystal structure: desensitization to feedback inhibition by L-cysteine

L-Serine O-acetyltransferase (SAT) from Escherichia coli catalyzes the first step of L-cysteine synthesis in E.coli and is strictly inhibited by the second step product, L-cysteine. To establish a fermentation process to produce L-cysteine, we embarked on a mutational study of E.coli SAT to desensitize the feedback inhibition by L-cysteine. The crystal structure and the reaction mechanism of SAT from E.coli have shown that the substrate L-serine and the inhibitor L-cysteine bind to the identical region in the SAT protein. To decrease the affinity for only L-cysteine, we first built the structure model of L-serine-binding SAT on the basis of the crystal structure with bound L-cysteine and compared these two structures. The comparison showed that the Calpha of Asp92 underwent a substantial positional change upon the replacement of L-cysteine by L-serine. We then introduced various amino acid substitutions at positions 89-96 around Asp92 by randomized, fragment-directed mutagenesis to change the position of the Asp92. As a result, we successfully obtained mutant SATs which have both extreme insensitivity to an inhibition by L-cysteine (the concentration that inhibits 50% activity; IC(50) = 1,100 micromol/l, the inhibition constant; K(i) = 950.0 micromol/l) and extremely high emzymatic activities.     

Frame shuffling: a novel method for in vitro protein evolution

We describe 'frame shuffling', a novel method for preparing artificial protein libraries. With this method, a Y-family DNA polymerase known to introduce frame shift mutations at high rates is utilized to scramble the reading frames of a parental gene. The resultant progeny produce mutant proteins having segmental sequence changes. Such frame-shuffled mutant proteins exhibit physicochemical properties that differ from those of proteins obtained using conventional mutagenesis.     

Fabrication of dielectric nanocubes in ordered structure by capillary force assisted self-assembly method and their piezoresponse properties

Ordered structures of barium titanate (BT) nanocubes, strontium titanate (ST) nanocubes and BT/ST nanocubes mixture were directly fabricated on Si and Pt-coated Si substrates using a capillary force assisted assembly method. The morphology of self-assembled structures was observed using field emission scanning electron microscopy (FE-SEM) and scanning probe microscopy (SPM). It was revealed that nanocubes were arranged with various degrees of ordering to develop multilayer and monolayer regions at the surface of substrates. The elemental mapping of the structure consisting of the nanocubes mixture was also investigated by transmission electron microscopy (TEM) with an energy dispersive X-ray spectroscopy (EDX). It was revealed that BT and ST nanocubes coexisted homogeneously in the structure and had possibility to be arranged in order to each other. The piezoresponse properties obtained by scanning probe microscopy (SPM) indicated that the hetero-interface between BT and ST nanocubes would introduce anomaly in piezoelectric properties.     

Electromagnon Excitation of the Triangular Lattice Antiferromagnet CuFeO2 in High Magnetic Fields

In this paper, we report results of high field ESR measurements of the triangular lattice antiferromagnet CuFeO₂. From polarization measurements for the ESR signals, we show an appearance of the electromagnon excitation in the field-induced 1/5 plateau phase of this compound.     

Waves in a rotating elastic solid

Wave propagation in a uniformly rotating elastic solid is discussed based on displacement equations in a moving frame. The time-harmonic Green’s dyadic for a point body force is obtained in closed form. It is reconfirmed that two quasi dilatational and shear waves are coupled to each other, and the deformation decomposition into the dilatation and rotation is not possible for the rotating solid. Further, it is also confirmed that the velocity of the Rayleigh surface wave depends not only on the rotational velocity but also on its direction and that the Rayleigh wave vanishes when the rotational velocity approaches the Rayleigh wave velocity of the immovable solid.     

THERMAL STRESS AT AN OFF-ANGLED INTERFACE

Thermal stress at an off-angled interface is considered as a model analysis for “weld line” in an injection-molded FRP. The off-angled interface is a line interface between two bonded anisotropic solids, at which the axis ofanisotropy in each solid is inclined to the interface. Applying the regular technique of integral transforms, we obtain the exact solution for temperature and stress induced by a spontaneous heat source. Especially for the temperature we get a closed-form solution in one term of the exponential function. Extensive numerical computations are carried out for a Nylon 66 compounded with 33 wt% glass fiber and show the stress field near the weld line (off-angled interface). The interfacial shear stress attains its maximum value more quickly than the normal stress. However, the highest normal stress on the interface increases with increasing off-angle, the highest shear stress has a maximum at 43-deg off-angle. The shear stress is 2.8 times greater than that in the isotropic solid and is also 1.34 times greater than that for 90-deg off-angle. This indicates that the lowest strength of the weld line would occur when the off-angle is about 43 deg for our case of Nylon 66.