Design and performance of an internal heat exchange desiccant wheel

A fundamental limitation in the dehumidification performance of adiabatic desiccant wheels occurs due to heating of the air stream to be dried. This results from both the carry-over of heat stored in the wheel and the release of the adsorption heat. Previous authors have identified an isothermal dehumidification process as theoretically superior, though the practicalities of constructing such a wheel have meant that demonstrating the benefit is difficult. Recently experimental data from testing of an internally cooled wheel was published. Here we use this data to calibrate a mathematical heat and mass transfer model of the internally cooled heat exchange desiccant wheel. The model is then used to estimate the performance for selected modifications to the design and materials. The results show that more than a 40% improvement is possible relative to the previously tested cooled wheel. The results have application to the development of desiccant air-conditioners.     

Influence of the atmospheric pressure on the mass transfer rate of desiccant wheels

The performance of a desiccant wheel is evaluated by modelling a representative channel. The hypothesis of negligible resistances to heat and mass transfer in the cross-direction is assumed in the thin porous desiccant wall of the channels and the airflow is treated as a bulk flow. Parametric studies were conducted to investigate the influence of the atmospheric pressure decrease from 101,325 Pa to 60,000 Pa (0-4217 m of altitude) on the mass transfer rate of desiccant wheels considering distinct channel lengths and different inlet airflow rates, a large range of values of the rotation speed, as well as three alternative ways to specify the inlet conditions of the regeneration and of the process airflows. A procedure to derive correlations based on the numerical results is presented for the correction factor of the mass transfer rate when a desiccant wheel is operating at non-standard atmospheric conditions. Four parametric studies were performed, the derived correlations were tested and a good agreement was found between the estimated correction factor and the correction factor calculated after the numerical results.     

Use of compound desiccant to develop high performance desiccant cooling system

The paper is aimed to develop a high performance rotary solid desiccant cooling system using a novel compound desiccant wheel (DW). The unique feature of the desiccant wheel is that it can work well under a lower regeneration temperature and have a higher dehumidification capacity due to the contribution of the new compound desiccant materials. Experimental results indicate that the novel desiccant wheel under practical operation can remove more moisture from the process air by about 20–40% over the desiccant wheel employing regular silica gel. A mathematical model that is used to predict the system performance has been validated with the test results. By integrating the desiccant wheel with evaporative cooling, heat recovery and heating for regeneration sections, a solid desiccant cooling system can be formed. Simulation results show that because of the use of the new compound desiccant, the desiccant cooling system can work under much lower regeneration temperature and have a relative high COP, thus low grade thermal energy resources, such as solar energy, waste heat, etc., can be efficiently utilized to drive such a cooling cycle.     

A numerical approach for predicting the failure locus of fiber reinforced composites under combined transverse compression and axial tension

A computational model based on the finite element method is presented for the estimation of strength of a fiber-reinforced lamina subjected to a combination of the transverse compression and axial tension. A complex damage mechanism including fiber breakage, fiber/matrix debonding and matrix plastic deformation is reproduced in the proposed model by using appropriate constitutive equations. The numerical simulation of mechanical response of the unidirectional lamina under biaxial loading is used to obtained the failure locus. Subsequently, the model is verified against an analytical solution and experimental data. It was found that the numerical calculations agree better with experimental results than analytical predictions.     

Simple box model for dense-gas dispersion in a straight sloping channel

A box model for instantaneous release and subsequent one-dimensional spreading of isothermal dense gases on sloping surfaces is presented. A numerical solution and an approximate analytical solution of the model equations are compared to the experimental data obtained in a sloping heavy-gas channel of the Institute of Fluid Dynamics at ETH-Zürich. The influence of the rear wall of the containment from where the cloud is released is analysed. Different entrainment assumptions, in particular the scaling of the entrainment parameters, are discussed. The numerical values of the entrainment parameters are tuned by computer optimization in order to obtain best agreement of the theoretical results with experimental data.     

Two-fluid model simulation of two-phase flow problems using a conservative finite-volume method

A conservative finite-volume method is employed for simulations of two-phase flows with a two-fluid model using separate conservation equations for each fluid. The mathematical model is based on ensemble- and phase-averaged transport equations and a set of simple constitutive laws for interfacial phenomena. The equation system is solved iteratively and in a segregated manner with the IPSA and PEA algorithms developed by Spalding [7]. The method is verified by comparison with analytical solutions and experimental data for one-dimensional steady and unsteady two-phase flows. A formal solution error estimation procedure based on extrapolation techniques is employed to assess the numerical accuracy of the results.     

Analytical solution for the simultaneous heat and mass transfer problem in air washers

An analytical solution approach for the simultaneous heat and mass transfer problem in air washers operating as evaporative coolers is presented. A one-dimensional model using the coupled mass and energy balance equations in the air washer is presented. Then, starting from a linear approach for the experimental curve of the air saturation, an analytical solution for the model was derived. The solution showed an excellent agreement with the available results found in the literature. The influence of several important parameters for the cooling process such as temperature and ambient air humidity, air flow rate and feeding water temperature, in the air cooling rate was investigated. The efficacy of the process can be greatly increased by reducing the cooling water temperature and the applied air flow rate. The analytical solution can be easily included into the models used for simulating desiccant air-conditioning systems operating in conjunction with air washers.     

除湿溶液除湿性能的对比实验研究

在对液体除湿制冷机理论研究的基础上,建立了液体除湿空调实验台.分别采用氯化钙溶液及不同比例的氯化钙与氯化锂的混合溶液作为除湿溶液,对系统的除湿性能进行了实验研究,对影响除湿量的各主要因素进行了分析,并得到了实验工况下的除湿量的回归方程,为除湿剂的选择提供实验依据.     

Characterization of desiccant wheels with alternative materials at low regeneration temperatures

A number of new desiccant materials have been proposed which have the potential to improve the performance of desiccant wheels being regenerated at low temperature. Desiccant wheels containing two such desiccant materials (zeolite and superadsorbent polymer) were compared with a conventional silica gel desiccant wheel. The superadsorbent polymer desiccant wheel achieved greater dehumidification than the silica gel wheel when dehumidifying high relative humidity air with low temperature (50 °C) regeneration air. The temperature of dehumidified air exiting the polymer wheel was also lower. The zeolite desiccant wheel was generally less effective at dehumidifying air and had a higher pressure drop.     

单转向轮摆振机理与稳定性研究

为研究典型单转向轮系统摆振机理及稳定性,建立杠杆驱动轮椅车转向轮系统非线性动力学微分方程,应用ODE方法进行求解;搭建了参数可调的转向轮摆振实验装置,利用实验手段研究摆振现象,验证了转向轮系统动力学模型的有效性;并对此动力学模型线性化,进行稳定性分析;利用遗传优化算法对转向轮系统进行参数优化设计,针对实验研究的转向轮摆振实验装置进行稳定性分析,采用增加阻尼轴承的方法改善实验中转向轮系统的稳定性.通过研究转向轮系统参数变化对摆振的影响规律,提出防范摆振的方法,获得具有实用价值的结论：通过增加转向轮拖距长度、合理选择质量参数或者增加系统的阻尼都可以减小甚至消除摆振.因此,该研究具有较好的工程实用价值,并对类似转向轮系统稳定性分析有一定的参考价值.     

The Transient Hot-Wire Technique: A Numerical Approach

The measurement of the thermal conductivity of a fluid by means of the transient hot-wire technique so far has made use of an analytical solution of the energy conservation equation for an ideal model, coupled with a set of approximate analytical corrections to account for small departures from the model. For this solution to be valid, constraints were always imposed on the experimental conditions and the construction of the apparatus, resulting in an inability to measure the thermal conductivity of high-thermal diffusivity fluids. In this paper, the set of energy conservation equations describing the transient hot-wire apparatus is solved using the numerical finite-element method. Because no approximate solutions are involved, this provides a much more general treatment of the heat transfer processes taking part in the real experiment, removing all the aforementioned constraints. In the case of the measurement of the thermal conductivity of liquids (fluids with low thermal-diffusivity values), the numerical solution fully agrees with the existing analytical solution. In the case of the measurement of the thermal conductivity of gases, the present solution allows the extension of the application of the transient hot-wire technique to experimental conditions where the value of the thermal diffusivity of the fluid is high.     

Performance investigation of desiccant liquid air membrane energy exchanger: Air and lithium chloride effects

The desiccant liquid air membrane energy exchanger is a promising technology used to recover both latent and sensible heat. In this paper, a numerical investigation is carried out to provide the optimal operating fluids properties as well as to enhance the exchanger performance. The physical problem involves a two dimensional model including the momentum, heat and mass transport equations in both air and desiccant liquid channels. The impact of air and desiccant liquid properties on the heat and mass transfer distributions is determined. Optimal values of inlet air and desiccant liquid properties are established. The thermal and mass fields inside desiccant liquid air membrane energy exchanger are numerically presented. This performance investigation provides a solution to improve the heat and mass transfer rates in the addressed membrane based technology.     

Modeling and validation of full fabric targets under ballistic impact

The impact of three different projectiles (0.357 Magnum, 9-mm FMJ and 0.30 cal FSP) onto Kevlar® was modeled using a commercial finite-element program. The focus of the research was on simulating full-scale body armor targets, which were modeled at the yarn level, by reducing to a minimum the number of solid elements per yarn. A thorough validation of the impact physics was performed at the yarn level, single-layer level, and a full body armor system. A verification was performed by checking the numerical model against analytical predictions for yarn impact. For one-layer and multiple-layer targets validation consisted on matching experimental data of pyramid formation recorded by an ultra-high-speed camera. The full-scale targets were also instrumented with nickel–chromium wires that stretch with the yarn during the penetration event. The wires provided a second validation data set since the numerical model can reproduce the signal recorded by the wires. The third and final validation of the model is provided by a comparison of the ballistic limit predicted by the model and data obtained in tests. This is a check of the failure model used in the numerical simulations. This paper shows that the main features of the impact physics are well reproduced by the finite-element model. Prediction of ballistic limits for the 9-mm FMJ and FSP projectiles were within the scatter of the tests, while for the 0.357 projectile the difference was only 15%.     

Calculation and experimental examination of complex modes of elastoplastic deformation

A model is examined of elastoplsatic deformation based on the concept of plastic compliances, and one of the structural models of elastoplsatic deformation used for describing cyclic processes is studied. The form of equations suitable for both analytical calculations and numerical applications is proposed. The calculated results are compared with the experimental data obtained on tubular specimens.Translated from Problemy Prochnosti, No. 8, pp. 14–17, August, 1990.     

Prediction of incidence effects on oscillating airfoil aerodynamics by a locally analytical method

A complete mathematical model is formulated to analyse the effects of mean flow incidence angle on the unsteady aerodynamics of an oscillating airfoil in an incompressible flow field. A velocity potential formulation is utilized. The steady flow is independent of the unsteady flow field. However, the unsteady flow is coupled to the steady flow field through the boundary conditions on the oscillating airfoil. The numerical solution technique for both the steady and unsteady flow fields is based on a locally analytical method. In this method, analytical solutions are incorporated into the numerical technique, with the discrete algebraic equations which represent the differential flow field equations obtained from analytic solutions in individual local computational grid elements. This flow model and locally analytic numerical solution method are then verified through the excellent correlation obtained with the Theodorsen oscillating flat plate and Sears transverse gust classical solutions. The effects of mean flow incidence on the steady and oscillating airfoil aerodynamics are then investigated.     

An implicit potential method for incompressible flows

In this paper, we consider a novel numerical scheme for solving incompressible flows on collocated grids. The implicit potential method utilizes an implicit potential velocity obtained from a Helmholtz decomposition for the mass conservation and employs a modified form of Bernoulli's law for the coupling of the velocity–pressure corrections. It requires the solution only of the momentum equations, does not involve the solution of additional partial differential equations for the pressure, and is applied on a collocated grid. The accuracy of the method is tested through comparison with analytical, experimental, and numerical data from the literature, and its efficiency and robustness are evaluated by solving several benchmark problems such as flow around a circular cylinder and in curved square and circular ducts.Copyright © 2013 John Wiley & Sons, Ltd.     

Solid desiccant solar air conditioning unit in Tunisia: Numerical study

In this paper, a method for the provision of the human thermal comfort through solar activated solid desiccant cooling technologies is discussed. These technologies were numerically studied under different Tunisian climatic conditions (relatively cold and humid: Bizerte; hot and dry: Remeda; moderate: Djerba). The studied solid desiccant cooling is based on the use of a fixed solid desiccant bed instead of a rotary desiccant wheel. The development of the mathematical equations modeling the functioning of the different components (solid fixed bed, heat exchanger, humidifier, solar collector) is based on heat and mass transfers' balances. Results showed good functioning and applicability of these studied systems for various outdoor conditions of the major Tunisian cities.     

Multi-level residue harmonic balance solution for the nonlinear natural frequency of axially loaded beams with an internal hinge

In this article, an analytical approach, namely, multi-level residue harmonic balance is introduced and developed for the nonlinear free vibration analysis of axially loaded beams with an internal hinge. The main advantage of this method is that only one set of nonlinear algebraic equations is required to be solved for obtaining the zero level solution while the high accuracy of the higher level solutions can be obtained by solving a set of linear equations. The new approximate analytical solution method is developed for solving the governing differential equations. The accuracy and efficiency of the proposed method are verified by a numerical method. In the comparison, the results obtained from the proposed method well agree with those from other methods. The effects of vibration amplitude, axial force, and hinge location on the fundamental frequencies of various beam cases are investigated. The optimum and worst hinge locations are also studied.     

Analytical investigation and numerical simulation of the stress–strain state in mechanically heterogeneous welded joints with a single-V butt weld

This paper aims to investigate the stress–strain state in mechanically heterogeneous welded joints with a single-V butt weld by an analytical model along with a numerical simulation. Analytical expressions for the stress–strain state in both the weld and the main material are proposed. In order to verify the proposed expressions, a numerical simulation of the stress–strain state in a mild welded joint with a single-V butt weld was carried out on the basis of the finite element method and the results were compared with the analytical solution obtained applying the proposed analytical model. EP-787 and JONI 13/45А steels were used for the weld while 15X2MFА steel was used for the main material in the analysed welded joints. A comparison of the analytical solution with the finite element analysis results showed a good agreement. The proposed equations could be used in design practice for calculations of the stress–strain state in welded joints.     

The Generation of a Dense Hot Plasma by Intense Subpicosecond Laser Pulses

A simple model is developed for describing the interaction of intense femtosecond laser pulses with solid-state targets which is based on a set of equations of two-temperature hydrodynamics for electrons and ions of a plasma formed upon ionization of the target matter, equations describing the variation of ion composition of plasma upon ionization and the heat energy expenditure on thermal ionization, and equations defining the energy contribution by laser radiation to the target matter. A self-similar solution is suggested which well describes the heating of plasma electrons during the time of effect of a femtosecond laser pulse in a wide range of its parameters. Lagrangian computer codes developed for this purpose are used to derive, in a one-dimensional approximation, a numerical solution for the set of equations for the parameters corresponding to femtosecond experimental facilities under development in Germany and Russia. Profiles of hydrodynamic quantities (electron and ion temperature, plasma pressure and density, mean ion charge) obtained in the numerical solution at different moments of time may be used for preliminary assessment of the results of future experiments with a view to optimizing their parameters.