混合制冷工质核态沸腾的传热研究

Heat transfer coefficients in nucleate pool boiling were measured on a horizontal copper surface for refrigerants, HFC-134a, HFC-32, and HFC-125, their binary and ternary mixtures under saturated conditions at 0.9MPa. Compared to pure components, both binary and ternary mixtures showed lower heat transfer coefficients.This deterioration was more pronounced as heat flux was increased. Experimental data were compared with some empirical and semi-empirical correlations available in literature. For binary mixture, the accuracy of the correlations varied considerably with mixtures and the heat flux. Experimental data for HFC-32/134a/125 were also compared with available correlated equation obtained by Thome. For ternary mixture, the boiling range of binary mixture composed by the pure fluids with the lowest and the medium boiling points, and their concentration difference had important effects on boiling heat transfer coefficients.     

Hydrodynamic characteristics of a butterfly valve — Prediction of pressure loss characteristics

Investigation on fluidmechanic performance on a butterfly valve has been carried out. A practical valve model of a given thickness and a hub is used for the loss coefficient theory. A theoretical loss coefficient has been formulated from a contraction factor obtained by applying the generalized Borda mouthpiece theory.

Cavitation stages (such as cavitation inception, supercavitation inception, cavitation damage inception, choking cavitation) have been theoretically predicted from the valve loss coefficient. The cavitation prediction has been carried out by applying the free streamline theory, where the relation between the loss coefficient and the critical cavitation factor has been formulated. The results of the theoretical prediction equations agree well with the experimental results.     

A Slope Stability Analysis Considering Undrained Strength Anisotropy of Natural Clay Deposits

The effects of sites and plasticity index (I_p) on the inherent strength anisotropy of eleven different clay deposits are quantitatively examined by the unconfined compression test using a small size specimen with a different angle of inclination to the vertical. A new method for a slope stability analysis, taking the effects of the IASIA method (Inherent And Stress Induced Anisotropies) into consideration, is proposed. The applicability of the IASIA method and the optimum embankment design are examined through case histories of embankment failures on soft soils. The undrained strength anisotropy cannot be estimated by parameters such as the I_p value because of the complicated relationship with the factors influencing undrained anisotropic strength. It must be directly measured. The IASIA method was recommended from a study of a failed embankment. The probability of failure (P_f) and consumer's risk (P_c) from half of the unconfined compressive strength (q_u/2) were (2.5~25.5)% and (4.7~42.3)% less than those of the Iwai q_u/2_(IASIA) and Urayasu q_u/2_(IASIA). Therefore, the design results were underestimated by disregarding strength anisotropies. If, P_f and P_c were considered, the C_t values increased. However, the P_c values drastically decreased to 24.8% from 54.3% concerning the 75-mm sampler and n increased, thus avoiding latent risks. These mean that the IASIA method can be used for optimum embankment design based on performance provisions.     

Force spectroscopy on single polymer incorporated into polymer gels

We conducted the extraction experiments of single polymer incorporated into hydrogels with an atomic force microscope (AFM) as a model for investigating nonspecific intermolecular interactions between macromolecules in a semidilute region at the single molecule level. Small amount of poly(ethylene glycol) (PEG) terminated with a thiol group was inserted in poly(acrylamide) gels, and a part of PEG polymer segments on the gel surface was attempted to pull out of the gels with a gold-coated AFM tip. The observed force-distance curves were classified into two kinds of extraction force profiles: a plateau force, which is almost constant irrespective of the tip-surface distance and a nonlinear force, which nonlinearly increases with the extraction length. Characteristic interaction length, L, and force, F, of these extraction force profiles were measured with changing the crosslinker concentration of gels which strongly affects the network structures. As a result, L of these extraction profiles significantly decreased at crosslinker concentrations higher than a standard one at which most gels have been prepared for investigating their physical properties. On the other hand, F showed no obvious difference on the change in crosslinker concentrations both on the plateau and the nonlinear force profiles. The origin of the observed forces was discussed in terms of gel network structures.     

Feasibility study of a feed-forwarding voltage-reactive power control method based on linear programming for a central control facility

Voltage–reactive power control (VVC) on power systems becomes difficult when a load increases or decreases rapidly, especially in the morning and at noon. This is caused mainly by two problems. One is delayed operation and the other is noncooperative operation of facilities. To solve these problems, an advanced method and algorithms for a centralized feed-forwarding control system are presented. They are based on two main steps: forecasting the power system state for several minutes and dispatching reactive power sources optimally based on stepwise linear programming. The proposed method is evaluated and tested for data of a large-scale power system. The results show that the proposed method keeps the voltage constraints well and reduces redundant operation of facilities. © 1998 Scripta Technica, Electr Eng Jpn, 125(1): 18–26, 1998     

Production of nonproteinaceous amino acids using recombinant Escherichia coli cells expressing cysteine synthase and related enzymes with or without the secretion of O-acetyl-L-serine

Beta-(pyrazol-1-yl)-L-alanine (beta-PA), a model nonproteinaceous amino acid, was specifically synthesized by two methods using recombinant Escherichia coli cells that express cysteine synthase, comprising serine acetyltransferase (SAT) and O-acetylserine sulfhydrylase-A (OASS-A) and related enzymes from E. coli. In the first method (method A), recombinant cells that express wild-type SAT, OASS-A, acetate kinase (AK), and phosphotransacetylase (PTA) showed the highest beta-PA production. beta-PA was produced at 140 mM from 200 mM L-serine and 200 mM pyrazole under optimum conditions. Using the cells expressing SATDeltaC20 (truncated SAT), OASS-A, AK, and PTA, beta-PA was produced at a level of only 80 mM, whereas O-acetyl-serine (OAS) was found to be secreted into the broth. Under optimum conditions, OAS accumulated at levels of around 105 mM from 300 mM L-serine. Thus, in the second method (method B), the secreted OAS was used as the substrate for the syntheses of beta-PA and beta-(triazol-1-yl)-L-alanine (beta-TA). The OAS that accumulated in the broth was efficiently converted to beta-PA and beta-TA at levels of around 90 mM from 105 mM OAS using free OASS-A. In both methods A and B, the addition of glucose was essential for the efficient production of beta-PA and OAS, respectively.     

Preparation of a polyelectrolyte complex gel from chitosan and κ-carrageenan and its pH-sensitive swelling

A polyelectrolyte complex gel was prepared by mixing chitosan and k-carrageenan solutions in the presence of NaCl. To study the effect of ambient pH on the swelling behavior, the diameter of the cylindrical gel(4 mm x 8 mm) immersed in aqueous NaOH, KOH, or HCl solution was measured. In the range of pH 10–12, the diameter increased with time, and the gel reached swelling equilibrium within 6 days. In an NaOH solution of pH 10.5, the maximum swelling occurred, and the volume of the gel at equilibrium was 10.2 times as large as the initial one. At pH below 9 and at pH 13, no swelling was observed. Thus, the swelling of the complex gel prepared in this study was sensitive to a rather narrow range of pH. The swelling equilibrium in the presence of NaCl was also investigated at various pH. © 1993 John Wiley & Sons, Inc.     

Daily electric load forecasting using artificial neural network

A multilayered-type neural network is attractive for daily electric load forecasting because the neural network can acquire a nonlinear relationship among the electric load data and their factors (weather, temperature, etc.) automatically. This paper discusses first some essential issues to be considered in neural network applications. One is difficulty of obtaining sufficient effective training data, another is the influence of abnormal learning data, and one more is the inevitable outerpolation. For these issues, the following three methods are developed in order to forecast more accurately: (1) a structure of the neural networks for insufficient training data; (2) detection and diminishing the influence of abnormal data; (3) employment of interpolation network and outerpolation network with additional data for outerpolation. Furthermore, to increase the sensitivity between electric loads and factors, (4) removal of base load is developed. Those methods work effectively to decrease the average absolute errors of peak-load forecasting and 24-hour load forecasting to 1.78 percent and 2.73 percent, respectively.     

Enzymatic synthesis of N-acyl-l-amino acids in a glycerol-water system using acylase I from pig kidney

N-Medium- and long-chain acyl-l-amino acids were enzymatically synthesized from the corresponding l-amino acids and fatty acids using a reverse hydrolysis. Enzymes that are suitable for the synthetic reaction of N-acyl-l-amino acids were screened on the basis of hydrolytic activity toward N-lauroyl-l-glutamic acid as an indicator. Acylase I from pig kidney (EC 3.5.1.14) showed the highest N-acyl-l-amino acid hydrolytic activity among 57 commercially available enzymes tested. Acylase I effectively catalyzed the synthesis of N-lauroyl-l-amino acids except for N-lauroyl-l-proline and N-lauroyl-l-tyrosine in a glycerol-water system. Under the optimized reaction conditions, N-lauroyl-l-arginine and N-lauroyl-l-glutamic acid were obtained in conversions of 82 and 44%, respectively. The equilibrium constants calculated from the conversion obtained were 5.6, 15.4, 18.0, and 39.4 for the syntheses of N-lauroyl-l-glutamic acid, N_α-lauroyl-l-lysine, N-lauroyl-l-glutamine, and N-lauroyl-l-methionine, respectively. N-Acyl-l-arginines with myristic acid and palmitic acid as the fatty acid were also synthesized using acylase I.