Natural convective heat transfer from a vertical isothermal surface to a non-Newtonian Sutterby fluid

This paper deals with the laminar natural convection of a non-Newtonian fluid along a vertical isothermal surface. The boundary-layer equations for a Sutterby fluid are solved numerically, and several characteristics of the non-similarity solution are represented graphically. An approximate expression of local Nusselt number Nu_x is proposed as Nu_x = 0·.50(Gr_0xPr₀)^0·.25(1+m), where m= 0−04 Pr₀^0.23 A^{3·7 Pr₀−0.34} Z₀^0·63A0.66Gr_0x and Pr₀ are Grashof number and Prandtl number based on zero viscosity respectively, and A and Z₀ are non-Newtonian parameters.Local heat-transfer coefficients are obtained by experiments with aqueous solutions of polyethyleneoxide (PEO) and carboxymethylcellulose (CMC). The experimental results are in excellent agreement with the theoretical ones.     

Discharge characteristics of latent heat storage columns packed with cross-linked plastic particles

This investigation deals with experimental and numerical analyses carried out to investigate the discharge characteristics of latent heat storage columns, using cross-linked cylindrical plastic particles as a phase-change type of heat storage material and ethylene glycol as a heat transfer medium. In the experiment, the transient response of the outlet temperature of the heat transfer medium was measured under conditions of varying the initial temperature in the column, the inlet temperature of the heat transfer medium, the mass flow rate of the heat transfer medium, and the mass of the heat storage material packed in the column. In the numerical analysis, the transient temperature distributions in the column was calculated by using an empirical formula for estimating the heat transfer coefficient for a fixed bed, which was recommended in the authors' previous paper. The experimental results were found to be in fair agreement with the numerical results. © 1998 Scripta Technica. Heat Trans Jpn Res, 26(3): 193–206, 1997     

Numerical investigation of static and dynamic characteristics of aerostatic thrust bearings with small feed holes

Recently, laser beam machining and micro drills have made it easier to manufacture small feed holes of less than 0.1 mm diameter. Accordingly, aerostatic bearings with these small feed holes have become commercially available for improving bearing performance. In this work, an aerostatic annular thrust bearing with small feed holes of less than 0.05 mm diameter was treated and the static and the dynamic characteristics of this type of bearing were investigated numerically. In numerical calculations, computational fluid dynamics (CFD) was used to determine discharge coefficients for a small feed hole and the finite difference method (FDM) was used to obtain the bearing characteristics. In addition, the characteristics of this type of bearing were compared with those of aerostatic thrust bearings with typical compound restrictors to show clearly the features of this type of bearing.     

Preparation and fuel cell performance of catalyst layers using sulfonated polyimide ionomers

Sulfonated polyimide (SPI-8) ionomers were used as binders in the catalyst layers, and their fuel cell performance was evaluated. SPI-8 ionomers functioned well in the anode with only minor overpotential even at low humidity (50% relative humidity (RH)). In contrast, the cathode performance was significantly dependent on the content and molecular weight of the ionomers and humidity of the supplied gases. Higher molecular weight of the ionomer caused larger potential drop at high current density at 80 and 100% RH since oxygen supply and/or water discharge became insufficient due to higher water uptake (swelling) of the ionomer. Similar results were obtained at higher ionomer content, because of the increase of thickness in the catalyst layer. The mass transport was improved with decreasing humidity, however, proton conductivity became lower. While the maximum values of j(@0.70?V) for all membrane electrode assemblies (MEAs) were ca. 0.35 A/cm(2), each electrode could have the different appropriate operating conditions. The results suggest that the parameters such as oxygen supply, proton conductivity, and water uptake and discharge need to be carefully optimized in the catalyst layers for achieving reasonable cathode performance with hydrocarbon ionomers.     

Synthetic zinc tetrapyrroles complexing with pyridine as a single axial ligand

Zinc chlorins were prepared from chlorophyll-a. Visible spectra in benzene showed that synthetic zinc chlorins complexed with pyridine as an axial ligand to form the monopyridine adducts. The equilibrium constants for the complexation were dependent upon the chlorin structure: substitution of electron-withdrawing groups at the peripheral position enhanced the coordinated ability of the central zinc. 1H NMR spectra in benzene-d6 also indicated that single pyridine coordinated to the central zinc. Comparison of the equilibrium constant in a zinc chlorin with those of the corresponding zinc bacteriochlorin (7,8-dihydrochlorin) and porphyrin (17,18-dedihydrochlorin) led to an increase in the saturation and flexibility of the tetrapyrrole pi-plane ligands making the central zinc more axial-ligated. All the zinc tetrapyrroles in benzene complexed with pyridine to form 5-coordinated (1:1) complexes, not 6-coordinated bisadducts. The observed equilibrium constants were consistent with the energy changes of the complexation calculated from molecular modeling.     

An enhanced method for measuring cardiac output using Doppler color flow echocardiography

An enhanced method for determining cardiac output using Doppler color flow imaging techniques to measure mitral orifice diameter was developed and validated in an experimental model and in clinical patients. In an in vitro circuit model, color jet width correlated well with actual orifice dimension from 12 to 24 mm (r = 0.99). In the clinical application, mitral valve area was calculated as a X b X pi/4 where a and b represent the width of the color flow stream in the mitral orifice just distal to the annulus in apical long-axis (short-diameter) and 4-chamber (90 degrees rotated, long-diameter) views, respectively. Cardiac output was then computed as the product of mitral valve area and time-velocity integral of transmitral flow from the same site. Cardiac output was also measured by thermodilution and conventional echocardiographic methods using diameters and time-velocity integrals from the left ventricular outflow tract. In 30 patients with nonvalvular heart disease, cardiac output measured by thermodilution ranged from 3.40 to 8.40 L/min. Cardiac output was determined in 28 of 30 patients (93%) by the Doppler color flow imaging technique; it ranged from 3.00 to 8.36 L/min and correlated well with thermodilution: y = 0.90x + 0.63, r = 0.91. Cardiac output was determined in 24 of 30 patients by the conventional left ventricular outflow method (80%). The cardiac output measured by the conventional method correlated less closely with thermodilution (r = 0.84), although there was no statistical difference in correlation coefficiencies between the 2 methods. These results indicate that the Doppler color flow imaging technique can be used to enhance the determination of cardiac output by echocardiography, particularly when the conventional method has resulted in technically inadequate recordings.     

Comparison of automatic boundary detection and manual tracing technique in echocardiographic determination of left atrial volume

Previous reports have indicated that echocardiography with automatic boundary detection (ABD) is useful for the noninvasive estimation of left ventricular volume. However, few data exist regarding the measurement of left atrial (LA) volume, which also provides pivotal information in the clinical setting. Therefore, the feasibility of LA volume measurement by ABD in comparison with the manual tracing using modified Simpson's method (SM) was evaluated. Fifty-nine patients with coronary artery-disease with sinus rhythm were examined. Using ABD, a region of interest was set around the LA border and mitral annulus from an apical four-chamber view. The maximal and minimal LA volume (Vmax and Vmin) were measured from the volume waveform. Using the SM, the maximal and minimal LA volume were measured by the manual tracing on frozen frames at the apical four-chamber view. The ABD displayed a curve of LA volume change that consisted of passive emptying, diastasis, and active emptying phases during the left ventricular diastolic period. Under these conditions, the Vmax and Vmin were 43.7 +/- 11.2 ml and 21.1 +/- 7.6 ml, respectively, yielding the volume change of 22.6 +/- 6.0 ml. By the SM, Vmax and Vmin were 43.1 +/- 9.9 ml (r = 0.94, p < 0.0001, y(ABD) = 0.91x (SM) + 3.6) and 22.0 +/- 9.0 ml (r = 0.91, p < 0.0001, y = 0.94x + 0.7), respectively, and the volume change was 22.8 +/- 6.1 ml (r = 0.82, p < 0.0001, y = 0.84x + 3.8). These results indicate that the ABD from the apical four-chamber approach could provide an accurate estimation of LA volume change, suggesting the potential value of this method in assessing LA function, although some technical difficulties need to be further overcome.     

Characterization of substrate off-angle effects for high-quality homoepitaxial CVD diamond films

We have studied the substrate off-angle effects for the crystalline quality of the homoepitaxial diamond films mainly by using steady-state cathodoluminescence (CL) and time-resolved photoluminescence (PL) measurements. By means of the microwave plasma chemical vapor deposition method under high-power microwave power with high methane concentrations, the homoepitaxial diamond films were grown on the high-pressure/high-temperature-synthesized (HPHT) Ib (001) substrates inclined along either <110> or <100> direction by different off-angles ranging from 2° to 5°. In spite of high growth rates, we have succeeded in improving crystalline quality by employing the HPHT substrates with considerably large off-angles. Both steady-state CL and time-resolved PL measurements clearly indicate that larger off-angles lead to better crystalline quality of the homoepitaxial film, suggesting that further improvements in crystalline quality can be expected when using substrates having even larger off-angles.