Performance analysis of solar powered absorption refrigeration system

The present work provides a detailed thermodynamic analysis of a 10 kW solar absorption refrigeration system using ammonia-water mixtures as a working medium. This analysis includes both first law and second law of thermodynamics. The coefficient of performance (COP), exergetic coefficient of performance (ECOP) and the exergy losses (ΔE) through each component of the system at different operating conditions are obtained. The minimum and maximum values of COP and ECOP were found to be at 110 and 200°C generator temperatures respectively. About 40% of the system exergy losses were found to be in the generator. The maximum exergy losses in the absorber occur at generator temperature of 130°C for all evaporator temperatures. A computer simulation model is developed to carry out the calculations and to obtain the results of the present study.     

Thermodynamic modelling of a double-effect LiBr-H2O absorption refrigeration cycle

The goal of this paper is to estimate the conductance of components required to achieve the approach temperatures, and gain insights into a double-effect absorption chiller using LiBr-H₂O solution as the working fluid. An in-house computer program is developed to simulate the cycle. Conductance of all components is evaluated based on the approach temperatures assumed as input parameters. The effect of input data on the cycle performance and the exergetic efficiency are investigated.     

Thermo physical properties of acetone–zinc bromide for using in a low temperature driven absorption refrigeration machine

Thermal physical properties (vapor pressure, density, viscosity, specific heat capacity, specific electrical resistance and specific enthalpy of mixing) of the solution acetone–zinc bromide, which will be used as a working solution in an absorption refrigeration machine, are measured and analyzed. The experimental data were correlated with high accuracy. The required state diagrams (log p, T and h, T) for this solution as well as the log P, h-diagram for the pure acetone are calculated, represented, correlated and discussed. The results indicate that the solution acetone-zinc bromide might be suitable as a working solution to operate an absorption refrigeration machine at low temperature.     

Performance study of unglazed cylindrical solar collector for adsorption refrigeration system

In the present communication, the unglazed cylindrical solar adsorber module is suggested for refrigeration and theoretical models for the heat and mass transfer in the cylindrical adsorber with heat balance equations in the collector components have been developed. It has been found that, both the SCP and COP_solar raises with increasing the evaporation temperature and drop off with the increase of the condensation temperature. The COP_solar increased from 0.15 to 0.52 with the increase of the total solar energy absorbed by the collector while the COP_cycle varied in the range of 0.57–0.73. The efficiency of unglazed solar collector varied from 36 to 44 %. The cost of current unglazed adsorption refrigeration system is compared with the glazed system, and it is 33 to 50 % less than the cost of glazed system.     

Ceramic foam substrates for automotive catalyst applications: fluid mechanic analysis

Several properties of ceramic foams render them promising substrates for various industrial processes. For automotive applications, the foam properties that need to be further studied include the substrate impact on the exhaust gas flow, in terms of pressure drop and flow uniformity. In this paper, pressure drop measurements are performed with different honeycomb and ceramic foam substrates, and pressure drop correlations are discussed. The flow uniformity upstream and downstream of the substrates is evaluated using particle image velocimetry. The results show that ceramic foam substrates induce higher pressure drop, while increasing the uniformity of the flow. In contrast to honeycomb monoliths, the flow uniformity downstream of ceramic foams does not decrease with increasing flow velocity. The higher flow uniformity of ceramic foams is not only caused by their higher pressure drop, but also by flow homogenization that occurs inside the ceramic foam structure, as a result of the momentum exchange perpendicular to the main flow direction.     

Thermodynamic analysis of a thermal storage unit under the influence of nano-particles added to the phase change material and/or the working fluid

The thermal storage unit consists of two concentric cylinders where the working fluid flows through the internal cylinder and the annulus is filled with a phase change material. The system carries out a cyclic operation; each cycle consists of two processes. In the charging process the hot working fluid enters the internal cylinder and transfers heat to the phase change material. In the discharging process the cold working fluid enters the internal cylinder and absorbs heat from the phase change material. The differential equations governing the heat transfer between the two media are solved numerically. The numerical results are compared with the experimental results available in the literature. The performance of an energy storage unit is directly related to the thermal conductivity of nano-particles. The energy consumption of a residential unit whose energy is supplied by a thermal storage system can be reduced by 43?% when using nano-particles.     

Suspension of layered particles: an optimum electrorheological fluid for d.c. applications

 A comparison is made between two types of solid particles used in electrorheological fluids: particles with homogeneous electrical properties versus layered particles with a semi-conducting core surrounded by an outer layer of lower conductivity. Rheological measurements of these suspensions under steady shear and d.c. electric field show that the layered particle system produces the same yield stress but with a substantially reduced electric current. X-ray spectroscopic analysis confirms that these particles have a thin layer of SiO_x on the outer surface which causes the reduction in conductivity. Measurement of the dielectric permittivity followed by analysis using the Maxwell-Wagner model of polarization indicates that the conductivity of the outer layer is about 0.62 times that of the core region. Received: 13 January 1999 Accepted: 26 July 1999     

Linear stability analysis for plane-Poiseuille flow of an elastoviscoplastic fluid with internal microstructure for large Reynolds numbers

We study the linear stability of Plane Poiseuille flow of an elastoviscoplastic fluid using a revised version of the model proposed by Putz and Burghelea (A.M.V. Putz, T.I. Burghelea, Rheol. Acta 48 (2009) 673–689). The evolution of the microstructure upon a gradual increase of the external forcing is governed by a structural variable (the concentration of solid material elements) which decays smoothly from unity to zero as the stresses are gradually increased beyond the yield point. Stability results are in close conformity with the ones of a pseudo-plastic fluid. Destabilizing effects are related to the presence of an intermediate transition zone where elastic solid elements coexist with fluid elements. This region brings an elastic contribution which does modify the stability of the flow.     

Hydrodynamics of viscous fluid through porous slit with linear absorption

The exact solutions for the viscous fluid through a porous slit with linear ab-sorption are obtained. The Stokes equation with non-homogeneous boundary conditions is solved to get the expressions for the velocity components, pressure distribution, wall shear stress, fractional absorption, and leakage flux. The volume flow rate and mean flow rate are found to be useful in obtaining a convenient form of the longitudinal velocity component and pressure difference. The points of the maximum velocity components for a fixed axial distance are identified. The value of the linear absorption parameter is ran-domly chosen, and the rest available data of the rat kidney to the tabulate pressure drop and fractional absorption are incorporated. The effects of the linear absorption, uniform absorption, and flow rate parameters on the flow properties are discussed by graphs. It is found that forward flow occurs only if the volume flux per unit width is greater than the absorption velocity throughout the length of the slit, otherwise back flow may occur. The leakage flux increases with the increase in the linear absorption parameter. Streamlines are drawn to help the analysis of the flow behaviors during the absorption of the fluid flow through the renal tubule and purification of blood through an artificial kidney.     

Exergy analysis of vapor compression refrigeration cycle with two-stage and intercooler

In this study, exergy analyses of vapor compression refrigeration cycle with two-stage and intercooler using refrigerants R507, R407c, R404a were carried out. The necessary thermodynamic values for analyses were calculated by Solkane program. The coefficient of performance, exergetic efficiency and total irreversibility rate of the system in the different operating conditions for these refrigerants were investigated. The coefficient of performance, exergetic efficiency and total irreversibility rate for alternative refrigerants were compared.     

Multicomponent fluid flow analysis using a new set of conservation equations

In this work hydrodynamics of multicomponent ideal gas mixtures have been studied. Starting from the kinetic equations, the Eulerian approach is used to derive a new set of conservation equations for the multicomponent system where each component may have different velocity and kinetic temperature. The equations are based on the Grad's method of moment derived from the kinetic model in a relaxation time approximation (RTA). Based on this model which contains separate equation sets for each component of the system, a computer code has been developed for numerical computation of compressible flows of binary gas mixture in generalized curvilinear boundary conforming coordinates. Since these equations are similar to the Navier-Stokes equations for the single fluid systems, the same numerical methods are applied to these new equations. The Roe's numerical scheme is used to discretize the convective terms of governing fluid flow equations. The prepared algorithm and the computer code are capable of computing and presenting flow fields of each component of the system separately as well as the average flow field of the multicomponent gas system as a whole. Comparison of the present code results with those of a more common algorithm based on the mixture theory in a supersonic converging-diverging nozzle provides the validation of the present formulation. Afterwards, a more involved nozzle cooling problem with a binary ideal gas (helium-xenon) is chosen to compare the present results with those of the ordinary mixture theory. The present model provides the details of the flow fields of each component separately which is not available otherwise. It is also shown that the separate fluids treatment, such as the present study, is crucial when considering time scales on the order of (or shorter than) the intercollisions relaxation times.     

A new exact solution for the flow of a Maxwell fluid past an infinite plate

A new exact solution corresponding to the flow of a Maxwell fluid over a suddenly moved flat plate is determined. This solution is in all accordance with a previous one and for λ→0 it goes to the well-known solution for Navier-Stokes fluids.     

A data-driven machine learning approach for yaw control applications of wind farms

This study proposes a cost-effective machine-learning based model for predicting velocity and turbulence kinetic energy fields in the wake of wind turbines for yaw control applications. The model consists of an auto-encoder convolutional neural network(ACNN) trained to extract the features of turbine wakes using instantaneous data from large-eddy simulation(LES). The proposed framework is demonstrated by applying it to the Sandia National Laboratory Scaled Wind Farm Technology facility consistin...     

有限元边坡稳定分析方法及其应用

本文介绍了一种基于有限元应力分析的边坡稳定评价方法,讨论了边坡稳定安全系数定义的物理意义,介绍了搜索最危险滑动面的广义数学规划命题和模式搜索方法,同时给出了该方法的计算结果与其它方法计算结果的对比算例以及该方法的应用实例。     

Thermodynamic analysis of shark skin texture surfaces for microchannel flow

The studies of shark skin textured surfaces in flow drag reduction provide inspiration to researchers overcoming technical challenges from actual production application. In this paper, three kinds of infinite parallel plate flow models with microstructure inspired by shark skin were established, namely blade model, wedge model and the smooth model, according to cross-sectional shape of microstructure. Simulation was carried out by using FLUENT, which simplified the computation process associated with direct numeric simulations. To get the best performance from simulation results, shear-stress transport k-omega turbulence model was chosen during the simulation. Since drag reduction mechanism is generally discussed from kinetics point of view, which cannot interpret the cause of these losses directly, a drag reduction rate was established based on the second law of thermodynamics. Considering abrasion and fabrication precision in practical applications, three kinds of abraded geometry models were constructed and tested, and the ideal microstructure was found to achieve best performance suited to manufacturing production on the basis of drag reduction rate. It was also believed that bionic shark skin surfaces with mechanical abrasion may draw more attention from industrial designers and gain wide applications with drag-reducing characteristics.     

Acoustic design of porous media with dimensionless numbers: redesign for new applications

In order to facilitate the design of porous materials for new acoustic applications, using the background knowledge of previous engineering applications, Biot’s equations of sound propagation in porous media are fully rewritten with dimensionless numbers. For illustration, a first application is performed in which the dimensionless numbers are used to redesign an air saturated skeleton in order to obtain similar dissipative properties when the new designed skeleton is saturated with kerosene. A second application redesigns the steel skeleton using aluminium as base material conserving the dimensionless numbers and the acoustic properties. Dimensionless equations could also be useful to define equivalent experiments at different scales or equivalent frequencies.     

ON A CLASS OF NEW KKM THEOREM WITH APPLICATIONS

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Nonplanar post-buckling analysis of simply supported pipes conveying fluid with an axially sliding downstream end

In this study, the nonplanar post-buckling behavior of a simply supported fluid-conveying pipe with an axially sliding downstream end is investigated within the framework of a three-dimensional(3 D) theoretical model. The complete nonlinear governing equations are discretized via Galerkin’s method and then numerically solved by the use of a fourth-order Runge-Kutta integration algorithm. Different initial conditions are chosen for calculations to show the nonplanar buckling characteristics of th...