Heat-driven hydride slurry heat pumps

Thermodynamic analysis and experiments are presented for a heat-driven hydride slurry heat pump (HHSHP). The thermodynamic analysis indicates that a HHSHP can achieve cooling coefficient of performance (COPc) values >0.7. A packed bed reactor was designed and fabricated to evaluate the importance of the absorption resistance in the hydrogen-liquid-hydride slurry (HLHS) reactor. It was observed that the packed bed reactor minimizes the absorption resistance effectively. With the use of packed bed reactors the HHSHP may be a practical heat pump system.     

Electroosmotic flow in irregular shape microchannels

The electrokinetic flow through star-point family microchannels is studied. Mathematical solutions using a semi-analytical approach are employed to model the steady, fully developed electroosmotic flow in the closed-end star point family microchannels. The model can be extended to other irregular shape channels. The effects of sharp corners, electrolyte concentration and packed capillary radius, R₀ are analyzed. Comparisons of the flow characteristics and induced pressure gradient inside and outside of the packed capillaries are presented.     

Adjusting Microscale to Atomic-Scale Structural Order in PbS Nanocrystal Superlattice for Enhanced Photodetector Performance

An investigation is presented into the effect of the long-range order on the optoelectronic properties of PbS quantum dot (QD) superlattices, which form mesocrystals, for potential use in photodetector applications. By self-assembly of QD nanocrystals on an Si/SiO_x substrate, a highly ordered and densely packed PbS QD superlattice with a microscale size is obtained. The results demonstrate that annealing treatment induces mesocrystalline superlattices with preferred growth orientation, achieved by dislodging ligands. The improved orientation and electronic coupling of the mesocrystalline superlattices exhibit superior photodetector performance compared to disordered QD structures and closely packed superlattices. This improved performance is attributed to atomic alignment between QDs, leading to enhanced electronic coupling. The findings suggest that these mesocrystalline superlattices have promising potential for the next generation of QD optoelectronic devices.     

Numerical modeling of heat and mass transfer during the drying of granulated polymers in a packed bed

A model is proposed for calculating heat and mass transfer in a packed bed exposed to a drying agent. Results are presented from a numerical realization of the model for the drying of granulated polyamide of type PA-6.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 6, pp. 995–1000, December, 1990.     

Transport Properties and Viscosity of Liquid CdTe Doped with In, Ge, and Sn

Data are presented on the high-temperature electrical conductivity, thermoelectric power (up to 1825 K), and viscosity (up to 1400 K) of undoped and doped (In, Ge, and Sn) CdTe melts. All of the materials were found to retain semiconducting properties upon melting, with a gradual increase in the contribution of metallic bonding, especially pronounced for the CdTe + 2 mol % Sn melt. The results are interpreted in terms of the double-structured melt model, which considers the coexistence of densely packed metallic regions and crystal-like CdTe clusters. The transition to metallic behavior of conductivity is accounted for by a gradual increase in the volume fraction of the densely packed, metallic phase. The doping effects on the conductivity and thermoelectric power of liquid CdTe are interpreted in terms of s–p hybridization.     

Determination of heat-transfer coefficient in a bed of spheres by a quasistationary cyclic method

Relations are presented for the amplitude ratio and the phase shift of the temperature of a gas in the periodic heating of a packed bed of spheres. The heat-transfer coefficient in the bed is determined by a cyclic method.     

Study of mass transfer between a spherical body and a turbulent gas stream

The results are presented of an investigation of mass transfer for a single sphere and for a sphere in a packed bed with different kinds of packing.     

An Experimental Study on Thermal and Electrical Properties of Packed Carbon Nanofibers

In the present study, the thermal and electrical properties of packed carbon nanofibers (P-CNFs) have been investigated. A short-hot-wire (SHW) technique was applied to determine simultaneously the thermal conductivity and thermal diffusivity of P-CNFs. In SHW measurements, a platinum wire coated with an alumina layer served as both the heating source and the thermometric sensor. A curve fitting method by matching the experimental data and numerical simulated values was proposed for determining the thermal conductivity and thermal diffusivity of P-CNFs with different packed densities. The electrical conductivities were measured by a four-terminal method where a special vessel with electrodes with circular plates was used. The results indicated that the electrical conductivity increases linearly with an increase in packed density. The thermal conductivity and thermal diffusivity also increase with an increase in packed density. The relation between the thermal conductivity and the electrical conductivity has been shown to be approximately linear. The SHW technique combined with the curve fitting method would be applicable to many kinds of materials.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

Quick non-graphical method for deducing slip systems in cubic close packed metals in tension or compression

Abstract

A simple method is presented by which the operative slip system in a single crystal of a cubic close packed metal may be deduced by inspection from the indices of the tensile axis. The method has advantages over the commonly used graphical method, since it does not involve use of the stereogram.

MST/1990     

Effect of a predetection open segment in the column on speed and selectivity in capillary electrochromatography

Columns in capillary electrochromatography (CEC) most commonly have the detection window located immediately after the retaining frit of the packed segment. Here, the properties of "duplex" columns having a predetection open segment between the frit and the detector window are examined with particular regard to the effect of the relative lengths of the packed and open segments on the separation of mixtures containing neutral and charged components. This configuration allows the use of columns with short packed segments in contemporary instruments for rapid separations. It is shown that, by varying the length of the packed segment, the balance of chromatographic and electrophoretic forces can be shifted, and the selectivity can be adjusted if the separation involves the interplay of both mechanisms. Expressions are presented for estimating the retention time in a duplex column if the chromatographic and electrophoretic properties of the sample components are known. The results are expected to facilitate CEC method development in selection of the respective column segment lengths for optimum separation.     

Monolithic versus conventional packed bed second stage regenerator evaluation in a Gifford-McMahon cryocooler

This work focuses on evaluation of the performance of a monolithic, versus standard packed bed, second stage regenerator in a Gifford-McMahon cryocooler. The monolithic, or bonded regenerator bed is made by means of a low temperature epoxy bonding technique developed [Adv. Cryog. Eng. 43B (1998) 1597] and optimized [R. Williamson, Individual Project Report, CFS, University of Victoria, 2001] by the Cryofuel Systems Group (CFS). Regenerator properties and results of several detailed load and no-load tests of the conventional packed bed regenerator and its monolithic form, using two different first stage regenerators, are presented. The monolithic regenerator performs as well as the standard one, despite a slightly higher-pressure drop observed. Analysis of this phenomenon is presented.     

Advantages of perfectly ordered 2-D porous pillar arrays over packed bed columns for LC separations: a theoretical analysis

A series of theoretical calculations is presented to quantify the gain in LC separation efficiency that can be expected if the traditionally used packed bed columns were replaced by columns with a perfectly ordered flow-through pore network. It is shown that a perfectly ordered 2-D array of porous cylindrical pillars could yield reduced plate heights as small as h = 0.65 (for k' ' = 0.75) to h = 0.85 (for k' ' = 2) and separation impedances as small as E = 200 (for k' ' = 0.75) to E = 300 (for k' ' = 2) without having to compromise on the porosity (epsilon = 0.4) and the retention capacity of the packed bed of spheres. Fitting the calculated van Deemter plots with Knox's equation especially shows a strong decrease of the A-term contribution, hence confirming that the improved column performance indeed stems from the increased homogeneity of the packing. The presented results, hence, provide a clear quantitative support for Knox's recent argumentation that the use of more uniform beds could greatly enhance the efficiency of pressure-driven LC.     

多孔石墨泡沫材料内流动阻力的扩展Ergun方程

近年来,金属泡沫、石墨泡沫等多孔功能材料因具有低密度、高导热、耐高温和耐腐蚀等特点而被广泛关注和研究。为了简化石墨泡沫内流动阻力的预测计算,根据石墨泡沫材料微孔的空间几何结构,对比颗粒填充床流动模型的Ergun型方程,建立面心立方(Face centered cubic,FCC)泡沫模型,以流速、孔隙率和比表面积分别相等则流动阻力相等为假设,推导了多孔泡沫孔径与颗粒床粒径间的对应关系,提出了适用于多孔泡沫介质内流动阻力预测的扩展Ergun方程。用所得方程进行了验证计算,并与数值模拟结果作了比较分析。     

Mass transfer characteristics of a structured packing for ammonia rectification in ammonia–water absorption refrigeration systems

In ammonia–water absorption refrigeration systems a purification process of the vapours produced in the generator is required. One type of equipment to carry out the purification process is a packed column. However, detailed experimental studies at the normal operating conditions found in ammonia–water absorption refrigeration systems have not been found. An experimental facility has been designed and built to study the ammonia–water rectification in packed columns. Experimental tests have been performed at the normal operating conditions found in the high-pressure stage of a small power ammonia–water absorption refrigeration system. In this paper, the experimental set-up is described and experimental results of the height equivalent to a theoretical plate (HETP) and the volumetric mass transfer coefficient of a rectifying section with the Sulzer BX packing are presented. The HETP values and the experimental mass transfer coefficients are compared with different data and correlations proposed in the literature; it has been found that the differences are appreciable.     

Effect of chitosan‐propolis edible coatings on stability of refrigerated cachama (Piaractus brachypomus) vacuum‐packed fish fillets

The effect of chitosan‐based coatings containing ethanolic extracts of propolis (EEPs) on the quality of chill‐stored, vacuum‐packed fillets of cachama, an emerging aquaculture species of fish native to the Amazon basins, was evaluated. Coatings were prepared by adding propolis to chitosan following two different strategies: (1) incorporation of microencapsulated EEP and (2) direct incorporation of EEP. Fillets were dip‐coated, vacuum‐packed in medium‐oxygen barrier bags, stored at 4°C, and their quality was evaluated during 20 days, by monitoring lipid oxidation indexes, physicochemical parameters, microbiological quality indicators, texture profile, and sensory acceptance. Chitosan‐EEP coatings significantly increased the time stability of physicochemical, microbiological, and sensory quality indicators of the fish meat compared with control treatments (uncoated vacuum‐packed fillets). In particular, the secondary lipid oxidation of the coated muscles was 12% to 15% lower compared with uncoated samples after 12 days; pH and total volatile base nitrogen (TVB‐N) presented a slower increase in the coated samples; and a greater inhibition of coliforms was observed between days 8 and 16. The chitosan‐EEP coatings had a positive effect in both texture stability and sensory acceptance of the products during storage. Moreover, chitosan coatings with encapsulated EEP had better impact on the evaluated sensory quality parameters. The results indicate that the combination of the barrier properties of chitosan with the bioactive properties of propolis compounds against oxidative free radicals and microbiological deterioration allowed for the edible coatings to extend the shelf life of this aquaculture product with respect to conventionally vacuum‐packed fillets.     

Structure of polymer networks as a percolation system

With the use of the assumption that the structure of an amorphous polymer can be presented as a set of frozen locally ordered regions surrounded by a loosely packed matrix, it is shown that a structure comprising a percolation cluster is formed in epoxypolymers, and in this case the glass-transition temperature is associated with the critical percolation probability, and the glass transition itself is considered as a phase transition. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 2, pp. 241–247, March–April, 1998.     

Closely packed hexagonal conical microlens array fabricated by direct laser photopolymerization

We apply femtosecond laser direct writing in photopolymers for manufacturing of conical microlenses and closely packed arrays thereof. We demonstrate the fabrication of high optical quality axicons of 15?μm in radius, having 150°, 160°, and 170° cone angles. Their optical properties and performance are modeled using the finite-difference time-domain method and compared with experimentally measured data. Additionally, optimization of the laser direct writing parameters regarding these types of micro-objects is presented. Possible applications of closely packed arrays of axicon microlenses are discussed, having potential attractivity in the fields of modern microscopy, light-based material processing, particle manipulation in microfluidic, and optofluidic applications.     

新型多孔质膜反应器的实验研究

为了使反应和分离更好地耦合,采用了催化剂分段填充的方法,将反应和分离由连续进行的过程改为分级进行,构造了一种离散型多孔质膜反应器结构(NPMR)．以异丙醇脱氢生成丙酮为反应体系,在150～250℃的温度范围对这种结构进行了实验研究．结果表明,反应转化率比环隙内充满催化剂的传统多孔质膜反应器(CPMR)有了很大提高．在250℃、10g催化剂、进料速率为2．4mmol／min的实验条件下,产物中丙酮的摩尔分数可由78％提高到90％．     

Periodic Large‐Area Metallic Split‐Ring Resonator Metamaterial Fabrication Based on Shadow Nanosphere Lithography

A fast and cheap, large‐area (>1 cm²), high‐coverage fabrication technique for periodic metallic split‐ring resonator metamaterials is presented, which allows control of inner‐ and outer‐ring diameters, gap angles, as well as thickness and periodicity. This method, based on shadow nanosphere lithography, uses tilted‐angle‐rotation thermal evaporation onto Langmuir–Blodgett‐type monolayers of close‐packed polystyrene nanospheres. Excellent agreement of the process parameters with a simplified model is demonstrated. Pronounced, tunable optical metamaterial resonances in the range of 100 THz are consistent with simulations.     

The Mixed Disc Packing Problem: Part II. An Interactive Optimization Procedure

In this paper we present an interactive optimization procedure for a mixed disc packing problem. The procedure is based on the bounds on the area left uncovered by the circular disks when packed on the circular plate (developed in Part I) and is implemented on a computer graphics terminal. The proposed procedure is applied to problems involving two and three types of discs and results are presented.