Development of new wire mesh packings for improving the performance of zero carryover spray tower

This paper presents the experimental results of chemical dehumidification of air by aqueous CaCl₂ liquid desiccant. A new design of the spray tower for eliminating carryover without increasing the pressure drops has been done. New types of wire mesh packings have also been proposed for improving the performance of the conventional spray tower. Three different configurations of the wire mesh packings have been designed and tested to improve the performance of tower with least cost addition. Experimental results have been presented in terms of ’change in specific humidity’, rate of moisture removal and tower effectiveness. Comparison of the experimental results of towers using these three packings with the conventional spray tower show improvement in the performance of spray tower (∼30%) without mounting air side pressure drop burden. Mass flow rate of liquid desiccant, mass flow rate of air, inlet specific humidity of air, and concentration of desiccant solution are found to have major influence on the performance.     

Experimental investigation of the heat and mass transfer between air and liquid desiccant in a cross-flow regenerator

The regenerator is one of the essential components in a liquid desiccant air-conditioning system, whose efficiency directly influences the system performance. A performance test-bed for a cross-flow regenerator was established in the present analysis. Celdek structured packings were used in the regenerator and LiBr aqueous solution was used as the liquid desiccant. Moisture removal rate and regenerator effectiveness are adopted to describe the mass transfer performance of the regenerator. Effects of air and desiccant inlet parameters on the regenerator performance are experimentally investigated, and performance comparisons between present cross-flow regenerator and other counter-flow configurations available in the literature are also carried out. The comparison results show that the impacts of air and desiccant inlet parameters show similar tendency with those of counter-flow regenerators. A dimensionless mass transfer correlation is proposed, which gives results in good agreement with the experimental findings.     

Microstructures and macroscopic conductivity of randomly packed and uniaxially pressed sphere compacts

The present paper deals with simulation of microstructures and macroscopic conductivity of randomly packed, uniaxially pressed and sintered particles. Random packings of identical spheres are constructed by using a sequential deposition method and their microgeometry after the compaction in sintering is geometrically created by proportional reduction in distances between the sphere centers only in the vertical direction and by mass addition around overlapped necks. Some of microgeometrical characteristics of the created compacts are statistically examined. Using the data on the packings and geometrical models, macroscopic thermal conductivities of the compacts are estimated. It is found that the conductivities are greatly different from those of simple cubic packings, although both the packings have almost the same coordination number, and that anisotropy in the conductivity is induced by the compaction in addition to gravity. The conductivities are expressed as a function of the compaction and sintering degrees for practical purposes.     

SIMULATED EFFECTIVE THERMAL CONDUCTIVITY OF SINTERED,RANDOMLY PACKED SPHERES AND STATISTICAL STRUCTURES OF PACKINGS

Effective thermal conductivity of sintered spherical particles is estimated by a computer simulation. The simulation consists of (i)simulated random packing of equal spheres by a method of "rigid sphere free fall into a virtual box," (ii) finite element method (FEM) estimation of the thermal resistance of a "sintered" pair of spheres, and (iii) simulated heat conduction tests of a "random network," as a model of sintered particles, of thermal resistors with the estimated resistance; these tests yield the effective conductivity of sintered spherical particle aggregates. Statistical structures of the random packings of spheres are examined. The random packings constructed are standard "loose random packings." The cumulative diameter distribution of circles appearing on cross-sections of the packings is in complete agreement with the theoretical prediction for all three orthogonal directions, implying that the packing structures are isotropic. And, despite this result, the zenithal distribution of branch orientations deviates from a uniform one; more spheres are in contact with their neighbors at the zenithal angles of theta approxequal 45 degrees. The effective conductivities obtained are not isotropic but transversely isotropic, which is due to the deviation of branch orientations.     

A note on the effect of a solid deflector on mass efflux distribution through a radial packed bed

Radially packed beds are used in industry for the production of ammonia and styrene. This paper discusses the effect of a solid body deflector on the maldistribution across the bed. The effect of fluid density and packing density is also examined. It is found that convex (or inverted) deflectors and denser packings help in the reduction of maldistribution. A model case is studied and the numerical technique may be applied to a variety of realistic problems.     

可靠性高的S1100柴油机新缸垫

本文介绍一种新材料气缸垫的研制，辅之柴油机关结构的改进，为提高51100柴油机气缸垫可靠性、防止缸套断裂提供了一条较为有效的途径．     

一种多孔介质蒸发冷却中冷器性能的初步研究

文中简介蒸发冷却中冷器的原理和结构,并通过风洞实验检验各种填料的阻力特性和降温特性,选取合适的填料介质试验。结果表明：蒸发冷却式中冷器原理简单,将其替换原有中冷器应用是可行的,可用于柴油机、燃气轮机进口及ICR船用燃气轮机上。     

Determination of the thermal properties of ceramic sponges

The knowledge of thermal properties of technical components or internals in chemical reactors is often a key characteristic for planning and designing chemical engineering processes. As an alternative to packed beds or packings, sponges turned out to be used in new application fields in chemical and process engineering. Therefore an experimental study was performed to investigate the two-phase thermal conductivity of solid ceramic sponges made of alumina, mullite and oxidic-bonded silicon carbide (OBSiC) at moderate temperatures. A two-dimensional model is used for analysing the measured temperature profiles and for calculating the thermal conductivity. It can be observed, that the thermal conductivity increases with decreasing porosity and is nearly constant when the pore size (ppi number) is varied. The thermal conductivity data are modelled by an approach similar to the well known Krischer model. Compared to a packed bed of spherical particles, the values of the thermal conductivity of sponges turn out to be about five times higher.     

Models for metal hydride particle shape,packing, and heat transfer

A multiphysics modeling approach for heat conduction in metal hydride powders is presented, including particle shape distribution, size distribution, granular packing structure, and effective thermal conductivity. A statistical geometric model is presented that replicates features of particle size and shape distributions observed experimentally that result from cyclic hydride decrepitation. The quasi-static dense packing of a sample set of these particles is simulated via energy-based structural optimization methods. These particles jam (i.e., solidify) at a density (solid volume fraction) of 0.671 ± 0.009 – higher than prior experimental estimates. Effective thermal conductivity of the jammed system is simulated and found to follow the behavior predicted by granular effective medium theory. Finally, a theory is presented that links the properties of bi-porous cohesive powders to the present systems based on recent experimental observations of jammed packings of fine powder. This theory produces quantitative experimental agreement with metal hydride powders of various compositions.     

Microfibrous structured catalytic packings for miniature methanol fuel processor: Methanol steam reforming and CO preferential oxidation

The microfibrous structured catalytic packings for miniature fuel processor consisting of a methanol steam reformer and a subsequent CO cleanup train has been investigated experimentally. A highly void and tailorable sinter-locked microfibrous carrier consisting of 3.5 vol% 8 μm diameter Ni-fibers is used to entrap 35 vol% 150-250 μm catalyst particulates for both methanol steam reforming (MSR) and CO preferential oxidation (PROX). We demonstrate a microfibrous entrapped Pd-ZnO/Al₂O₃ catalyst packings for high efficiency hydrogen production by the MSR reaction. The use of microfibrous entrapment technology significantly enhances the catalyst utilization efficiency by a 4-fold improvement of the weight hourly space velocity (WHSV), compared to the single Pd-ZnO/Al₂O₃ particulates as keeping the methanol conversion at >98%. The microfibrous entrapped Pt-Co/Al₂O₃ catalyst packings can drive the CO from 2% down to <50 ppm at 150 °C with O₂/CO ratio of 1 using a gas hourly space velocity (GHSV) of 32,000 h⁻¹. Finally, a prototype fuel processor system integrating MSR reformer and CO PROX train is demonstrated as three reactors in series. Such test rig is capable of producing roughly 1700 standard cubic centimeter per minute (sccm) PEMFC-grade H₂ (equivalent to ∼163 W of electric power) in a longer-term test, in which the MSR reactor is operated at 300 °C using a methanol/water (1/1.1, mole) mixture WHSV of 9 h⁻¹ and CO PROX reactors at 150 °C using an O₂/CO molar ratio of 1.3, respectively. In the test of this prototype system, MSR reactor delivers >97% methanol conversion throughout the entire 1200-h test; the CO cleanup train placed in line after 800-h MSR illustrates the capability to decrease the CO concentration from ∼3.5% to ∼1% at PROX-1 and then to less than 20 ppm at PROX-2 until to the end of test.     

A Versatile Computer Simulation Model for Rotary Regenerative Heat Exchangers

A simulation technique for predicting the thermal performance of rotary regenerative heat exchangers, in particular those used for heating the intake air to power station boilers, has been developed and verified by means of site measurements. Various geometries of both rotating-hood and rotating-matrix types of air heaters can be accommodated in the simulation model, including packings of corrugated steel plates of various specified profiles and any given thicknesses and lengths in the flow direction. Rotational speed, leakage, blockage, and non-uniform inlet flow distribution may be taken into account as input variables. The heat transfer and pressure drop correlations for the various plates considered, which also form part of the input data, were determined experimentally using a single-blow transient test facility, constructed as part of this research program. The effect of erosion of the plates by fly ash particles carried in the outlet flue gas on heat transfer performance is also considered, and experimental results show that erosion has little effect on the thermal performance (up to the point that structural integrity is about to be compromised), but also that the pressure drop is reduced.     

Liquid piston gas compression

A liquid piston concept is proposed to improve the efficiency of gas compression and expansion. Because a liquid can conform to an irregular chamber volume, the surface area to volume ratio in the gas chamber can be maximized using a liquid piston. This creates near-isothermal operation, which minimizes energy lost to heat generation. A liquid piston eliminates gas leakage and replaces sliding seal friction with viscous friction. The liquid can also be used as a medium to carry heat into and out of the compression chamber. A simulation is presented of the heat transfer and frictional forces for a reciprocating piston and a liquid piston. In the application of an air compressor, with a pressure ratio of 9.5:1 and a cycle frequency of 20 Hz, the liquid piston decreased the energy consumption by 19% over the reciprocating piston. The liquid piston and the reciprocating piston exhibited a total efficiency of 83% and 70% respectively. The liquid piston demonstrated significant improvements in the total compression efficiency in comparison to a conventional reciprocating piston. This gain in efficiency was accomplished through increasing the heat transfer during the gas compression by increasing the surface area to volume ratio in the compression chamber.     

液体除湿空调系统的数学模型与性能分析

建立了一种液体除湿空调系统，核心部件为液体吸收式除湿器，蒸发冷却器是重要组成部分，两者的主体均采用蜂窝结构。给出了统一的数学模型，对除湿器和冷却器内复杂的传热传质过程进行描述。数值模拟结果与实验数据基本一致。运用上述模型编制程序，对系统性能进行预测，表明液体除湿空调系统方案可行。     

Prediction of pressure drop in a packed bed dehumidifier operating with liquid desiccant

In this paper a more rigorous model, which is valid for both structured and random packing columns, is used for predicting the irrigated pressure drop in a desiccant–air contact system. Calcium chloride solution is considered as the desiccant. Four different random packing materials and three different structured packing materials are considered in the present study. The effects of random packing shape and the type of structured packing on the hydraulic performance are studied. The model has been validated for a wide range of operating values available in the literature. It is found that the structured packing has the lower pressure drop and higher capacity compared with random packings. Among the random packing materials considered in the present study, Intalox saddles can provide the least irrigated pressure drop and among the structured packing materials the sheet-type Mellapak 250 Y has the lowest pressure drop.     

Numerical study of liquid film cooling in a rocket combustion chamber

A numerical study is reported to investigate the liquid film cooling in a rocket combustion chamber. Mass, momentum and heat transfer characteristics through the interface are considered in detail. A marching procedure is employed for solution of the respective governing equations for the liquid film and gas stream together. The standard turbulence k–ε model is used to simulate the turbulence gas flow and a modified van Driest model is adopted to simulate the turbulent liquid film flow. Radiation of gas stream is also considered and simulated with the flux model. Downstream of the liquid film the gaseous film cooling is numerically studied simultaneously. Results are presented for a mixed gases–water system under different condition. Various effects on the liquid film length are examined in detail. There is a good agreement between the numerical prediction and experimental result on the liquid film length.     

Flow and heat transfer of liquid plug and neighboring vapor slugs in a pulsating heat pipe

A model of fluid flow and heat transfer on liquid slug and neighboring vapor plugs in a pulsating heat pipe (PHP) is proposed. A new energy equation for the liquid slug is built by aid of Lagrange method. The shear stress term related with the fluid flow state is included in the motion equation of the liquid slug. A sensitive heat term is replaced by a phase change term in the energy equation of the vapor plug. Based on our analysis on the displacement variation of the liquid slug with time, it is known that the harmonic force acting on the liquid slug in PHPs is the pressure difference between the vapor plugs. The flow oscillation can be considered as a forced damping vibration of one degree of freedom system. The phase difference of the oscillating flow between with and without the gravity effect can reach 45°. The amplitude and angular frequency of flow oscillation is irrespective with the initial displacement of liquid slug. If the flow pattern remains strictly slug flow in the entire system, the contribution of the sensible heat exchange to the total heat transfer of the PHP is about 80%.     

Investigation of a combined solar–heat pump system for residential heating. Part 1: experimental results

In order to investigate the performance of the combined solar–heat pump system with energy storage in encapsulated phase change material (PCM) packings for residential heating in Trabzon, Turkey, an experimental set‐up was constructed. The experimental results were obtained from November to May during the heating season for two heating systems. These systems are a series of heat pump system, and a parallel heat pump system. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP), seasonal heating performance, the fraction of annual load meet by free energy, storage and collector efficiencies and total energy consumption of the systems during the heating season. Copyright © 1999 John Wiley & Sons, Ltd.     

SPHERE PACKING ALGORITHM FOR HEAT TRANSFER STUDIES

Sintering is an important process for most ceramic systems and optical fibers. Many of the defects, introduced at the sintering stage, are formed because of the thermal processes. As such, there has been significant interest in modeling the underlying thermal processes. However, because of the complexities involved, most of the existing analyses tended to utilize a porous medium assumption whereby the temperature is computed through some average thermal properties that are in turn related to the porosity of the structure. The assumption is that the porosity can describe uniquely the property of the structure. This has never been directly confirmed, as most of the existing packing algorithms cannot achieve sufficient microstructural control. In the present work, an algorithm is introduced to enable a greater degree of control on the microstructure of the packing (mean coordination number and mean contact area). The subsequent thermal analysis confirmed that packings with the same porosity could have different thermal conductivity values.     

Liquid flow in a cubic cavity generated by gas motion along the free surface

Flow and turbulence generation in a cubic cavity filled by the liquid driven by the gas shear stress over a liquid/gas interface are considered. The coupled gas/liquid flow model is formulated to gain basic understanding of gas flow effects on melt convection, heat and mass transfer during crystal growth by the Czochralski and Directional Solidification methods. As in real crystal growth applications, the gas velocity is assumed to be much higher than the liquid velocity. The gas flow is considered to be laminar for both case of laminar and turbulent liquid convection. The flow of liquid is studied to find conditions of liquid turbulent transition at increasing gas shear stress. A novel dimensionless number is proposed and validated to describe the gas shear stress effect on the liquid flow. Engineering applications to control melt flow structure and oxygen transport during silicon crystal growth are discussed.