Fluid-particle interaction from lattice Boltzmann simulations for flow through polydisperse random arrays of spheres

Fluid-solid drag force correlations, such as the Ergun relation, are widely used in many areas of chemical engineering. In many practical applications, the solid phase consist of an assembly of spheres which are, more often than not, polydisperse. In this paper we report on a study of the fluid-particle interaction by fully resolved DNS-type simulations (lattice Boltzmann) of flow through polydisperse random arrays of spheres, both for log-normal and Gaussian size distributions. In a recent paper [Van der Hoef, M.A., Beetstra, R., Kuipers, J.A.M., 2005. Lattice Boltzmann simulations of low Reynolds number flow past mono- and bidisperse arrays of spheres: results for the permeability and drag force. J. Fluid Mech. 528, 233] we have shown that a correction factor should be applied to the monodisperse drag force relations, when used for bidisperse systems. On the basis of the data reported in this paper, we conclude that the correction factor also applies to general polydisperse systems.     

CMOS performance enhancement in Hybrid Orientation Technologies

Possible MOSFET performance enhancement by combining the hybrid-orientation technology (HOT) and process-induced local strain engineering is predicted for sub-45-nm CMOS technology nodes via technology CAD (TCAD) simulation. Mobility enhancements are modeled for both the hybrid orientation and process-induced local strain in CMOS technologies and are used in simulation. RF performance is investigated in detail and peak cutoff frequency, f _T of 524 GHz for n-MOSFETs and 239 GHz for p-MOSFETs are predicted from simulation.     

Nanoparticle‐enhanced light trapping in thin‐film silicon solar cells

A systematic investigation of the nanoparticle‐enhanced light trapping in thin‐film silicon solar cells is reported. The nanoparticles are fabricated by annealing a thin Ag film on the cell surface. An optimisation roadmap for the plasmon‐enhanced light‐trapping scheme for self‐assembled Ag metal nanoparticles is presented, including a comparison of rear‐located and front‐located nanoparticles, an optimisation of the precursor Ag film thickness, an investigation on different conditions of the nanoparticle dielectric environment and a combination of nanoparticles with other supplementary back‐surface reflectors. Significant photocurrent enhancements have been achieved because of high scattering and coupling efficiency of the Ag nanoparticles into the silicon device. For the optimum light‐trapping scheme, a short‐circuit current enhancement of 27% due to Ag nanoparticles is achieved, increasing to 44% for a “nanoparticle/magnesium fluoride/diffuse paint” back‐surface reflector structure. This is 6% higher compared with our previously reported plasmonic short‐circuit current enhancement of 38%. Copyright © 2011 John Wiley & Sons, Ltd.     

Assessment of blends of CO2 with butane and isobutane as working fluids for heat pump applications

In the present study, blends R744/R600 and R744/R600a are being proposed as working fluids in heat pumps for medium and high temperature heating applications. COP based performances have been evaluated for zeotropic mixtures of both working fluid pairs for various compositions and compared against that of pure working fluids. Effect of internal heat exchanger on blend based system performance is also presented and finally heat transfer issues in evaporation and condensation are discussed. Results show that due to gliding temperature during evaporation and condensation, the zeotropic blends, instead of pure counterparts, can be employed very effectively in heat pumps for variable temperature or simultaneous cooling and heating applications (e.g., dairy plants) at conventional high side pressure. The blend R744/R600a can be the best alternative refrigerant to R114 for high temperature heating due to superior COP (more than twice) over R600 and R600a and eliminating the requirement of extremely high side pressure of R744 systems.     

Neural-finite difference method (NFDM) in development of improved differential approximation (IDA) and its application for coupled conduction and radiation heat transfer in a square enclosure: An experimental validation

The present numerical and experimental analysis addresses coupled conduction and radiation heat transfer (CCR) in differentially heated vertical isothermal walls and horizontal insulated walls of a square enclosure with absorbing, emitting and isotropic scattering participating gray medium. The P₁ approximation solution is utilized as the input signal to the neuron model. The computational domain is treated by the neural-finite difference method (NFDM) with ray tracing technique of ray emission model (REM) for the development of improved differential approximation (IDA). The output results are validated with the results of DOM. The practical implementation of IDA for wide range of radiative parameters are illustrated and examined. Experiments have been performed in a square enclosure with solid isothermal walls made of aluminum and insulated walls with bakelite, thus forming air filled cavity. Finally, the consistence of isotherm pattern of the numerical work with the interferogram captured by Mach–Zehnder interferometer corroborates the IDA theory and its realistic approach.     

A view of the thermal wave behaviors in thin plates

The objective of this research is to study the temperature variation in thin dielectric materials. The thermal wave model is being used as the classical Fourier law of heat conduction breaks down when a dielectric material of sub-micron geometry is heated rapidly. The first part of the work reviews the temperature distribution due to thermal wave in semi-infinite bodies. The main emphasis of this paper is to accurately determine the temperature profile in a finite plate made up from a dielectric material. The boundary conditions of the first and the second kind are selected for this study. Using the classical Laplace transform technique, analytical solutions are obtained for finite bodies with different boundary conditions the first kind and the second kind. Due to complexity of the problem, a symbolic algebra provided the solution for examining the thermal behavior of dielectric materials during rapid heating.     

Ejector enhanced vapor compression refrigeration and heat pump systems—A review

The present paper provides a literature review on two-phase ejectors and their applications in vapor compression refrigeration and heat pump systems. Geometry, operation and modeling of ejector, and effects of various operating and geometric parameters, and refrigerant varieties on the ejector performances as well as performance characteristics of both subcritical and transcritical vapor compression systems with various cycle configurations are well-summarized. Moreover, system optimal operation and control to get maximum performance by using ejector as an expansion device are also discussed. However, a lot of research work still needs to be done for large-scale applications in industry and for the replacement/modification of conventional refrigeration and heat pump machines. Favorable performance improvement along with several advantages in installation, operation and control with ejector stimulates the commercialization of ejector enhanced refrigeration and heat pump systems and hoping this contribution will be useful for any newcomer in this field of technology.     

An experimental investigation on the application potential of heterogeneous catalyzed Nahar biodiesel and its diesel blends as diesel engine fuels

From the inception of commercialization of biodiesel, feedstock scarcity is a major issue to be pondered upon in developing countries. In this study, an attempt has been made to use an abundantly available underutilized high oil content (67% of Nahar seed kernel) feedstock derived biodiesel in a compression ignition engine. The experimental investigation on diesel engine reveals slightly reduced brake thermal efficiency and excellent exhaust emissions up to 40% blending of Nahar biodiesel with conventional diesel fuel. At full load, compared to diesel fuel, the BTE dropped by 1.64% and 1.83%, whereas the BSFC increased by 5.07% and 6.76% for B30 and B40 blends, respectively. The tested emission parameters such as CO, HC, NOx, and smoke were decreased by 12.66%, 17.99%, 8.31%, and 10.61% for B30 and 4.87%, 12.76%, 7.98%, and 11.78% for B40, respectively, compared to diesel fuel.

Abbreviation: BD: Biodiesel; DF: Diesel fuel