Condensation of R407C in a horizontal microfin tube

This paper describes experimental results that show the effects of mass velocity and condensation temperature difference on the local heat transfer characteristics during condensation of R407C in a horizontal microfin tube. The experiments were performed at the saturation temperature of 40 °C, the refrigerant mass velocity of 50, 100, 200 and 300 kg m⁻² s⁻¹, and the condensation temperature difference of 1.5, 2.5 and 4.5 K. A superficial heat transfer coefficient for the vapor phase was obtained by subtracting the heat transfer resistance of condensate film estimated by using a previously developed theoretical model of film condensation of pure vapor from the overall heat transfer resistance. On the basis of the analogy between heat and mass transfer, an empirical equation for the superficial vapor phase heat transfer coefficient was developed. The heat transfer coefficient predicted by the combination of the previously developed theoretical model of film condensation of pure vapor and the empirical equation of the superficial vapor phase heat transfer coefficient agreed with the measured values with the r.m.s. error of 9.2%.     

In-line type micropulse lidar with an annular beam: experiment

An in-line type compact micropulse lidar (MPL) with an annular beam was developed for low-altitude cloud measurement. An optical circulator and a couple of axicon prisms for an annular beam were installed on the lidar optics. The advantage of using the in-line MPL is its ability to obtain a near-range measurement with a narrow field of view of 0.1 mrad and to obtain a depolarization measurement of the orthogonally polarized echoes caused by ice crystals of a low-altitude cloud. The total insertion loss of the lidar optics was 3 dB. Detectors such as avalance photodiode detectors can be operated in an analog mode near the breakdown voltage because of the high isolation of the optical circulator. The ideal lidar echo variation from the nearest distance was verified by measuring the mountain echoes at various distances. The depolarization measurement of a low-altitude ice cloud was also demonstrated.     

Syntheses of functional condensation polymers. II. A polyamide having epoxy groups and its ring-opening derivatives

Polyamides having epoxy groups and their ring-opening derivatives were prepared and characterized, and some of their properties were investigated. Reaction conditions for the low-temperature polycondensation of cis-2,3-epoxysuccinyl chloride (ESC) with aromatic diamines and the interfacial copolycondensation of ESC and adipyl chloride (AC) with aromatic diamines were established to obtain a high molecular weight polyamide having epoxy groups. In addition, the ring-opening reactions of the epoxy groups in the polyamides were carried out with various amines in order to obtain polyamides having hydrophilic pendent groups such as amino and hydroxyl. It was found that the polyamides prepared by ring-opening reaction of the epoxy group with ethylenediamine (EDA) or ethanolamine (EA) had a higher affinity for moisture than those with hexamethylenediamine (HMD) or n-butylamine (n-BA), which might be ascribed to the distance of hydrophilic groups from the polyamide chain. Those polyamides having hydrophilic pendent groups decomposed upon heating at less than 200°C.     

Intense white photoluminescence in ZnO thin film formed by anodization

Intense white photoluminescence (PL) at room temperature has been observed in ZnO thin films formed by anodization at 26? C. The PL depends on the preparation conditions of the films. The PL is attributed to radiative recombination between localized electrons and holes in gap states which are formed by native defects in the films. We suggest that the anodized ZnO films might be useful for optoelectronic devices, since the low temperature anodization process used is inexpensive and fast.     

The stability of zinc oxide transparent electrodes fabricated by R.F. magnetron sputtering

The stability of the electrical, optical and mechanical properties of sputtered zinc oxide (ZnO) thin films with resistivities from 10^?2 to 10^?4 ωcm were investigated. No significant changes in these properties are observed for ZnO films exposed to air at room temperature for 10 months. A change in the electrical resistance of the ZnO films with temperature up to 400 °C is observed in various ambients such as vacuum, inert gases and air. After heat treatment in these ambients at 400 °C, the resistivity of the films increased by one to ten orders of magnitude. The increased resistivity can be returned to the resistivity of the virgin state, within one order of magnitude, by heat treatment in a hydrogen ambient at temperatures near 400 °C. For practical use of ZnO films at high temperatures, the increase in the resistivity might become a disadvantage for ZnO transparent electrodes fabricated by r.f. magnetron sputtering.     

Determination of sequence length distribution in SBR by ozonolysis-g.p.c. method

Sequence distribution of styrene-butadiene copolymer (SBR) was investigated by ozonolysis-g.p.c. All the double bonds of butadiene units in SBR were cleaved by ozonolysis in methylene chloride at ?30°C, followed by reduction degradation to alcohol with lithium aluminium hydride. The g.p.c. of the ozonolysis products observed with a u.v.-detector showed the peaks corresponding to styrene sequences and styrene-1,2 sequences. Hot- and cold-emulsion SBR samples contained short sequences consisting of 1 to 4 styrene units and 1,2 styrene units respectively. The average sequence length of cold-emulsion SBR was slightly longer than that of hot-emulsion SBR. A partial block SBR prepared by solution polymerization contained short styrene sequences of 1 to 5 units and long sequences having a broad distribution of $\text{M}{}_{\mathrm{w}}\text{M}{}_{\mathrm{n}}\text{= 1.6}$ with the maximum around 35 units. The styrene sequences containing the 1,2 unit was scarcely observed in this sample.     

Morphology and breaking of latex particle deposits at a cylindrical collector in a microfluidic chamber

We report an analysis for the morphology and breaking behavior of deposits of spherical latex particles (1 and 3.6 μm in diameter) at a cylindrical collector in a microfluidic channel fabricated by soft-lithography. In-situ observation of particle deposition over a large range of flow rate conditions evidence the relationship between deposit morphology and mode of particle transport toward the collector. For low Pe?clet number (Pe), particle deposits are nearly uniform all over the collector surface except at the rear where particles do not attach. Upon increase of Pe, deposits gradually adopt a columnar morphology at the collector stagnation point. These results are qualitatively consistent with previously reported Monte Carlo simulations of deposits formation in stagnation point flow systems. However, these simulations fail to quantitatively predict the observed deposition at the rear of the collector for sufficiently high flow rate. Additional deposit breaking experiments together with numerical evaluations of particle flux around the collector suggest that such "anomalous" deposition at large Pe is significantly governed by concomitant detachment of deposited particles at the stagnation point and the presence of recirculation flow at the collector rear. Finally, kinetics of deposition are discussed in connection with particle size-dependence of deposit breaking features.     

Ordered mesoporous carbon films prepared from 1,5-dihydroxynaphthalene/triblock copolymer composites

Ordered mesoporous carbon (D-COU-1) films were synthesized by an organic-organic self assembly method using 1,5-dihydroxynaphthalene as carbon source. Channel-like pores with a well-ordered hexagonal structure were observed by TEM observations. The thermal stability of the D-COU-1 film was compared with the COU-1 film prepared using resorcinol (R-COU-1). The XRD results indicate that the structure of D-COU-1 film was less shrinkable under carbonization compared to that of the R-COU-1 film.     

Pressure drop characteristics of flow in a symmetric channel with periodically expanded grooves

Pressure drop characteristics of flow in a periodically grooved channel are investigated experimentally. It is well known that a self-sustained oscillatory flow occurs from a steady-state flow at a certain critical Reynolds number in such grooved channels. The oscillatory flow enhances fluid mixing and leads to an increase in pressure drop. We measure the pressure drop with a pressure transducer. It is found that the pressure drop increases near the critical Reynolds numbers where the two- and three-dimensional oscillatory flows occur. In addition, the three-dimensional flow is confirmed by flow visualization.