Collector,collector-reflector systems—an an analytical and practical study

This paper investigates the use of planar reflectors which substantially improve the performance of flat-plate solar collectors. The experimental setup includes a collector panel and collector-reflector system with maximum useful heat gain. A computer simulation of the analytical and experimental recordings was made to study the comparative features of the systems. The performance study is illustrated as a function of solar altitude, azimuth angles, hour angle and the relative sizes and tilt angles of both the collector and reflector. The use of a booster mirror produces an increase of 10–15°C in water temperature. The shading effect due to the presence of the reflector has also been considered in the present analysis.     

Spatial optimization of an underhood cooling module – Towards an innovative control approach

The present paper reports a numerical investigation of spatial optimization of heat-exchanger by acting on its positioning in the vehicle’s cooling module. This analysis also elucidates how to act on the different parameters influencing heat-exchanger performance in order to optimize their functioning. A two-dimensional computation code permits optimizing the performance of the cooling module by positioning different heat exchangers, in both the driving and stop phases of the vehicle. The ultimate aim is to apply new control approaches to real vehicles so as to reduce pump and compressor energy consumption and thus fuel consumption. Compared to a reference “in-series” configuration of the cooling module HXs (in which the different HXs are superposed in the airflow direction), an “in-parallel” configuration (in which the different HX surfaces are in a row with respect to the air flow direction) increases the thermal power of the HXs by 4.4% and decreases the pressure losses by 0.9%.     

Flow-Field of an Axisymmetric Lobed Mixer

The flow-field of a fuel/air mixing system with an axisymmetric lobed mixer was numerically investigated. Large-scale streamwise vortices are formed immediately downstream of the mixer trailing edge, stretched further downstream, and finally broken into fragments where more intense mixing occurs. Both numerical and experimental results indicate that the length required for streamwise vortices breakdown in the confined flow-field of an axisymmetric lobed mixer is much shorter than that in the case of planar lobed mixers subject to parallel freestreams. For the conditions studied, the streamwise vortices start to breakdown at three wavelengths downstream of the mixer trailing edge.     

Toward an Optimum Design of an Amorphous Silicon Photovoltaic/Thermal System:Simulation and Experiments

Amorphous silicon photovoltaic/thermal(a-Si-PV/T) technology is promising due to the low power temperature coefficient,thin-film property,thermal annealing effect of the solar cells,and high conversion efficiency in summer.The design of a-Si-PV/T system is influenced by a number of thermodynamic,structural,and external parameters.Parametric analysis is useful for a good design of the system.A dynamic distributed parameter model is built and verified in this paper.Outdoor tests are carried out.Th...     

Durability study of an intermediate temperature fuel cell based on an oxide–carbonate composite electrolyte

It was reported that ceria–carbonate composites are promising electrolyte materials for intermediate temperature fuel cells. The conductivity stability of composite electrolyte with co-doped ceria and binary carbonate was measured by AC impedance spectroscopy. At 550 °C, the conductivity dropped from 0.26 to 0.21 S cm⁻¹ in air during the measured 135 h. At a constant current density of 1 A cm⁻², the cell performance keeps decreasing at 550 °C, with a maximum power density change from 520 to 300 mW cm⁻². This is due to the increase of both series and electrode polarisation resistances. Obvious morphology change of the electrolyte nearby the cathode/electrolyte interface was observed by SEM. Both XRD and FT-IR investigations indicate that there are some interactions between the doped ceria and carbonates. Thermal analysis indicates that the oxide–carbonate composite is quite stable at 550 °C. The durability of this kind of fuel cell is not good during our experiments. A complete solid oxide-carbonate composite would be better choice for a stable fuel cell performance.     

Three-dimensional thermal stresses Green’s functions for an unbounded parallelepiped under an inner point heat source

The aim of this study is to derive new constructive formulas and analytical expressions for Green’s functions (GFs) to 3D generalized boundary value problem (BVP) for an unbounded parallelepiped under a point heat source. These results were obtained using the developed harmonic integral representation method. On the base of derived constructive formulas it is possible to obtain analytical expressions for thermal stresses GFs to 16 BVPs for unbounded parallelepiped. An example of such kind is presented for a spatial BVP, GFs of which are presented in the form of the sum of elementary functions and double infinite series, containing products between exponential and trigonometric functions. An integration formula for thermal stresses, caused by the thermal data, distributed on the boundary strips at homogeneous locally mixed mechanical boundary conditions was also derived. The main di?culty to obtain these results was calculating an integral of the product between two GFs for Poisson’s equation. This integral taken on the base of the earlier established statement that main thermoelastic displacement Green’s functions (MTDGFs) satisfy the boundary conditions: (a) homogeneous mechanical conditions with respect to points of findings MTDGFs and (b) homogeneous thermal conditions with respect to points of the application of the heat source.     

Study on an Undershot Cross-Flow Water Turbine

This study aims to develop a water turbine suitable for ultra-low heads in open channels, with the end goal being the effective utilization of unutilized hydroelectric energy in agricultural water channels. We performed tests by applying a cross-flow runner to an open channel as an undershot water turbine while attempting to simplify the structure and eliminate the casing. We experimentally investigated the flow fields and performance of water tur- bines in states where the flow rate was constant for the undershot cross-flow water turbine mentioned above. In addition, we compared existing undershot water turbines with our undershot cross-flow water turbine after at- taching a bottom plate to the runner. From the results, we were able to clarify the following. Although the effec- tive head for cross-flow runners with no bottom plate was lower than those found in existing runners equipped with a bottom plate, the power output is greater in the high rotational speed range because of the high turbine ef- ficiency. Also, the runner with no bottom plate differed from rtmners that had a bottom plate in that no water was being wound up by the blades or retained between the blades, and the former received twice the flow due to the flow-through effect. As a result, the turbine efficiency was greater for runners with no bottom plate in the full ro- tational speed range compared with that found in runners that had a bottom plate.     

Hydrolysis of ammonia–borane catalyzed by an iron–nickel alloy on an SBA-15 support

An unsupported iron–nickel (Fe–Ni) alloy and several Fe–Ni alloy deposited on SBA-15 (Santa Barbara Amorphous-15) supports (Fe–Ni/SBA) with various Fe–Ni contents are prepared and used as catalysts in the hydrolysis of ammonia–borane (AB) for hydrogen generation. By maintaining a constant concentration of Fe–Ni in the AB aqueous solutions, we investigate the influence of the SBA-15 support on the Fe–Ni catalytic activity in the AB hydrolysis reaction. The SBA-15 support helps disperse the Fe–Ni alloy particles on its surface, which consequently improves the catalytic activity of the Fe–Ni. However, the presence of SBA-15 particles in the aqueous solution also retards the migration of the AB molecules in solution toward the Fe–Ni catalysts, increasing the induction time of the AB hydrolysis reaction. Therefore, there is an optimal Fe–Ni content in Fe–Ni/SBA for the catalysis of the AB hydrolysis reaction.     

Natural Convection Heat Transfer in an Enclosure Filled with an Ethylene Glycol—Copper Nanofluid Under Magnetic Fields

This article presents the results of a numerical study on natural convection in a square enclosure filled with ethylene glycol–copper nanofluid in the presence of magnetic fields. Two opposite horizontal walls of the enclosure are insulated and the two vertical walls are kept constant at different temperatures. A uniform horizontal magnetic field is externally imposed. The governing equations (mass, momentum, and energy) are formulated and solved numerically with a finite element using COMSOL Multiphysics. The effects of pertinent parameters such as Rayleigh number (10³ ≤ Ra ≤ 10⁷), Hartmann number (0 ≤ Ha ≤ 120), and solid volume fraction (0 ≤ φ ≤ 0.06) on the flow and the heat transfer performance of the enclosure are examined when the Prandtl number is assumed to be Pr = 151.     

Solidification inside a sphere—an experimental study

This paper presents the investigations of the solidification of an n-hexadecane inside a spherical enclosure. The effect of solidification process was investigated for three different constant surface temperature conditions (13 °C, 8 °C and 3 °C) and for three different initial superheats of n-hexadecane (8 °C, 2 °C and 0 °C). It was observed that the solidification phase front propagates uniformly inwards towards the centre of the sphere. The concentricity of the solid–liquid phase front deteriorates as time progresses due to shrinkages causing formation of voids inside the sphere. A lower constant surface temperature results in a larger solidified mass fraction. The effect of the initial liquid superheats of the PCM on the solidification is insignificant.     

Performance Optimization for an Irreversible Quantum Stirling Cooler

The purpose of this paper is to study the optimal performance for an irreversible quantum Stirling cooler with heat leak and other irreversible losses. The relationship between the optimal cooling load and the coefficient of performance (COP) for the quantum Stirling cooler is derived. The maximum cooling load and the corresponding COP, as well as the maximum coefficient of performance and the corresponding cooling load are obtained. The experimental observation for the optimal region is provided.     

Overall Thermodynamic Model of an Ultra Micro Turbine

The overall thermodynamic model of an ultra micro turbine engine has been established and applied in different situations in this tiny engine where heat transfer is dominant. The aerothermal conditions of the flow were calculated and analyzed. A corresponding calculation software (hot button software) was developed. The first results show that the non-adiabatic operation of the turbomachines leads to a strong penalty in performances. The dramatic influence of the compressor and turbine efficiency is confirmed in a non-adiabatic operation. A better knowledge of heat transfer coefficients at low Reynolds numbers in different components of the micro turbine has to be obtained to refine the results of this study.     

Synergistic effects in an AB5–Co material as an anode for a secondary alkaline battery

The AB₅ alloy and Co powders have been mixed at various weight ratios to form AB₅–Co composite electrodes. The discharge properties such as discharge capacity, discharge plateau, and cycling stability are investigated by charge and discharge testing using Arbin battery testing equipment. Synergistic effects in the composite electrodes contribute to significant improvements of the discharge behavior. For instance, the composite AB₅–25%Co electrode shows a high discharge capacity of 395.1 mAh/g, which is significantly higher than that of AB₅ or Co electrode, and good cycling stability. The discharge process is also characterized by electrochemical impedance spectroscopy. Moreover, the electrochemical discharge mechanism is discussed.     

Modeling the performance of an aluminum–air cell

A mathematical model for analysis and prediction of the performance of the aluminum–air cell has been developed. The model takes into account the kinetics of the anode, cathode, and parasitic reactions. Ohmic losses in the electrolyte and mass transfer are also taken into account. The model prediction of cell performance shows good agreement with experimental data. The mathematical model provides detailed information about cell performance for a wide range of operating and design parameters. For better cell performance, our model studies suggest the use of higher electrolyte flow rates, smaller cell gaps, higher conductivities, lower parasitic current densities and operation at moderate current density. From our analysis, we have determined that, in an aluminum air cell, only the activation and ohmic overpotential are important.     

Design of Process Centrifugal Compressor： an Adapted Algorithm

Considering the essential and influential role of centrifugal compressors in a wide range of industries makes most of engineers research and study on design and optimization of centrifugal compressors. Centrifugal compressors are the key to part ofoil, gas and petrochemical industries as well as gas pipeline transports. Since complete 3D design of the compressor consumes a considerable amount of time, most of active companies in the field, are profoundly interested in obtaining a design outline before taking any further steps in designing the entire machine. In this paper, a numerical algorithm, named ACDA （adapted compressor design algorithm） for fast and accurate preliminary design of centrifugal compressor is presented. The design procedure is obtained under real gas behavior, using an appropriate equation of state. Starting from impeller inlet, the procedure is continued on by resulting in numerical calculation for other sections including impeller exit, volute and exit diffuser. Clearly, in any step suitable correction factors are employed in order to conclude in precise numerical results. Finally, the achieved design result is compared with available reference data.     

Study of Spiral Flow Generated through an Annular Slit

The effect of pressurized air inlets in the reservoir upstream of the annular slit on characteristics of the axial and tangential velocity components is investigated numerically, and the mechanism of occurrence of spiral nozzle flow is clarified. In simulations, Unified Platform for Aerospace Computational Simulation (UPACS) is used. The governing equations under consideration are the unsteady compressible Navier - Stokes. A second-order finite volume scheme with MUSCL (Roe scheme) is used to discretize the spatial derivatives, and a second order-central difference scheme for the viscous terms, and a MFGS (Matrix Free Gauss Seidel) is employed for time integration. Spalart-Allmaras model was used as a turbulence model. The results obtained are compared with velocity distributions in the experiment measured by the two-component fiber optic laser Doppler velocimeter system. The existence of discrete pressurized air inlets that leads to the occurrence of asymmetrical characteristics is a very important factor for the formation of spiral flow.     

Solar assisted air conditioning of buildings – an overview

Goal of this contribution is to draw a picture about some general issues for using solar thermal energy for air conditioning of buildings. The following topics are covered:

• –A basic analysis of the thermodynamic limits for the use of heat cooling in combination with solar thermal energy is drawn; thereby fundamental insights about control needs for solar thermal driven cooling are obtained.
• –A short overview about the state-of-the-art of available technologies, such as closed thermal driven cooling cycles (e.g., absorption, adsorption) and open cooling cycles (e.g., desiccant employing either solid or liquid sorbents) is given and needs and perspectives for future developments are described.
• –The state-of-the-art of application of solar assisted air-conditioning in Europe is given and some example installations are presented.
• –An overview about new developments of open and closed heat driven cooling cycles for application in combination with solar thermal collectors is given and some of these new systems are outlined more in detail.

     

Hydrogen energy research and development in India—an overview

India is trying hard to improve the standard of living of its peoples, and therefore increase the energy consumption. Amongst the many options. India is also researching the various aspects of the hydrogen energy system. This paper presents an overview of hydrogen energy research and development work in India, starting with a summary of the energy situation in the country.     

Numerical and Experimental Studies of an Arc-heated Nonequilibrium Nozzle Flow

The arc-heated high-temperature gas is rotationally and vibrationally excited, and partially dissociated and ionized. When such gas flows inside a nozzle, energy transfers from rotational and vibrational energy modes to translational energy mode, and, in addition, recombination reactions occur. These processes are in thermal and chemical nonequilibrium. The present computations treat arc-heated nonequilibrium nozzle flows using a six temperature model (translational, rotational, N2 vibrational, O2 vibrational, NO vibrational and electron temperatures), and nonequilibrium chemical reactions of air. From the calculated flow properties, emission spectra at the nozzle exit were re-constructed by using the code for computing spectra of high temperature air. On the other hand, measurements of N2+(1-) emission spectra were conducted at the nozzle exit in the 20 kW arc-heated wind tunnel. Vibrational and rotational temperatures of N2 were determined using a curve fitting method on N2+(1-) emission spectra, with