Optimal sizing of a solar–biogas-based cooking system for a cluster of villages

Energy supplies particularly in remote and far-flung rural areas are in pathetic situation. Leave aside other needs, most of the rural communities still use wood as a source of energy for cooking. Burning of wood is not only an inefficient method, but also hazardousness for the person working on the stove. People have been working for cleaner and efficient means of cooking for decades. Solar cooker- and biogas-based cook stoves are two of the successfully implemented technologies in this area. Although solar cooker requires no maintenance, the initial investment is quite high for a cluster of villages. In addition to this, the intermittency involved in solar energy makes this an unreliable source.

In this paper, a cluster of villages of Narendra Nagar block of Tehri Garhwal district of Uttarakhand, India, has been studied in terms of their thermal requirements. The potential of solar energy and biomass energy has been estimated. An integrated solar–biogas system has been proposed to satisfy this cooking demand. To obtain the optimal sizes of solar cooker and biogas generator, MATLAB codes have been developed. It was found that this system is more economical and much reliable than the other two cases.     

Simulation of a Turbulent Impinging Jet into a Layer of Porous Material Using a Two–Energy Equation Model

This article presents numerical results for a turbulent jet impinging against a flat plane covered with a layer of permeable and thermally conducting material. Distinct energy equations are considered for the solid porous material attached to the wall and for the fluid that impinges on it. Parameters such as Reynolds number, porosity, permeability, thickness, and thermal conductivity of the porous layer are varied in order to analyze their effects on the local distribution of Nu. The macroscopic equations for mass, momentum, and energy are obtained based on volume-average concept. The numerical technique employed for discretizing the governing equations was the control volume method with a boundary-fitted nonorthogonal coordinate system. The SIMPLE algorithm was used to handle the pressure-velocity coupling. Results indicate that inclusion of a porous layer eliminates the peak in Nu at the stagnation region. For highly porous and highly permeable material, simulations indicate that the integral heat flux from the wall is enhanced when a thermally conducting porous material is attached to the surface.     

Thermal Emission of a Disc Body of Semitransparent Material

INTRODUCTIONThethermalemissionofseveraJshapesofsemi-transparelltbodieshasbeeninvestigatedinthepastdecades.Forexample,Mcmahonderivedananalyt-icalexPressionforthehemisphericalendssivityofasemitransparentparallelslabl1];Gardonpresentedamethodforevaluatingtheemissivityofaglassslabl21;byimprovingtheGardon'smethod,Isardcalculatedtheendssivitiesofglassspheres,cylindersandtubes,andobtainedanapproximateexpressionwithtwoex-ponentialtermsl3];TuInerandLove,byusingtheMollterCarlomethod,simulatedthe…     

Numerical Simulation of the Flow over a Model of the Cavities on a Butterfly Wing

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Alternative Use of a Compressed Component of a Digestate from Agricultural BGSs （Biogas Stations）

The paper presents the results of a two-year research of properties and the way of use of briquettes and pellets made of separated and partially dehydrated digestate from agricultural BGSs （biogas stations）. Digestate is a by-product of BGS. There are approximately 170 agricultural BGSs operating in the Czech Republic. Unprocessed digestate with the dry mass content around 6% is usually applied to soil as a lighter mineral fertilizer. If digestate is separated and the separated solid component of the digestate is further dehydrated to 14 % moisture, it can be processed by pressing to the form of very solid pellets and briquettes, also with various additives. It was also ascertained that mechanical strength and shape of briquettes does not change due to long-term storage. In this form, the compressed digestate can be used in various ways. One of the ways is its energetic use by direct burning. That is why we have observed its calorific value and combustion heat. Another alternative use of compressed digestate from BGS is its application in targeted treatment of in particular mechanical properties of soil and its water regime. The briquettes and pellets have great water sorption properties--the briquette retains water and as a consequence grows up to four times in size. This specific property was analysed and it was ascertained that the speed of water sorption depends on the composition of the compressed mixture （i.e., the type of material and the size of its particles）, but also on the total weight of the produced briquettes （i.e., their size）. Similar dependency was ascertained for other briquette materials that were analysed.     

Distribution of air–water annular flow in a header of a parallel flow heat exchanger

The air and water flow distribution are experimentally studied for a heat exchanger composed of round headers and 10 flat tubes. The effects of tube protrusion depth as well as header mass flux, and quality are investigated, and the results are compared with previous 30 channel data. The flow at the header inlet is annular. For the downward flow configuration, water flow distribution is significantly affected by tube protrusion depth. For flush-mounted geometry, significant portion of water flows through frontal part of the header. As the protrusion depth increases, more water is forced to rear part of the header. The effect of header mass flux or quality is qualitatively the same as that of the protrusion depth. For the upward flow configuration, however, significant portion of water flows through rear part of the header. The effect of protrusion depth is the same as that of the downward flow. However, the effect of header mass flux or quality is opposite to the downward flow case. Compared with the previous 30 channel configuration, the present 10 channel configuration yields better flow distribution. Possible explanation is provided from flow visualization results.     

Reconstruction of a heat exchanger network under industrial constraints — the case of a crude distillation unit

Heat exchanger network retrofit using a pinch based approach is presented. In this approach, the criterion of minimum sensitivity of heat exchanger to fouling effects is accounted for. The present paper introduces this criterion without explaining its details that are described in the literature. A summary is given of HEN reconstruction in a crude distillation unit processing 4.2 million ton crude oil per year. While the total heat quantity of hot streams is 110 MW, the heat recovery in the existing HEN is 60 MW. Using Pinch Analysis, the target value of heat recovery at ΔT_min=10 K was determined at 91 MW. Measurements were carried out on the existing HEN with the aim to determine the influence of fouling effects on the heat transfer in the exchangers. Taking local constraints including fouling into account, HEN reconstruction was proposed. The heat savings in the reconstructed HEN was estimated at 75 MW.     

Numerical Simulation of a Negative Impulsive Wave

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Flow of Viscous Oil in the Volute of a Centrifugal Pump

IntroductionIn a centrifugal pumP, the imPeller and the volutetogether decide its perfOrmance[']. Thus the volute is animportant element for a centrifugal pumP and theinvestigation into the flow in a volutC has drawn moreattenhons continuously. Bowerman and Acosta (l957)explored the flow in a volute and tWo-dimensionalcentrifugal impeller by using a Fltot probe[']. The resultshave shown that fOr efficien operation, the volute mustbe matched to the imPeller at the design flow rate. Atdesig…     

Eco Insulation Materials： Reduction of Cooling Loads of a House Made of Breeze Block or Laterite in a Dry Tropical Climate

In this paper, we study the influence ofeco materials for roof insulation and fiber-reinforced mortar coatings on cooling loads of a home in dry tropical climate. The walls of the house are made of cinderblock or laterite and the insulating material of a roof panel is made with lime （24%）, cement （6%）, water （50%） of vegetable fibers hibiscus sabdariffa （16%）, tree widespread in Burkina Faso and sugar cane bagasse （4%）. This panel roof insulation and the fiber-reinforced mortar were characterized at the Laboratory of Physics and Chemistry of the environment by the hot plate method. The building is modeled in TRNSYS using climate data from the city of Ouagadougou. The results obtained show that in the warmer months of the year, that is to say in March and April, the relative differences between heat gains the configurations ＂breeze block-coating mortar and roof not insulated＂ and ＂laterite- fiber-reinforced mortar coating and insulated roof＇ vary between 15.6% and 16.8%. The configuration ＂laterite-fiber-reinforced mortar coating and insulated roof allows a reduction of annual heat gains of 15.5% compared to the configuration ＂breeze block-coating mortar and roof not insulated＂.     

Structure and properties of lithium trivanadate—a potential electroactive material for a positive electrode of secondary storage

Quantum-chemistry calculations were carried out to predict not only the structure, but also the energetic and electrical parameters of lithium trivanadates of the formulae Li_1+xV₃O₈ (where x=1, 2 and 3). Altogether 21 entities were considered: four with the formula LiV₃O₈, 14 with the formula Li₂V₃O₈ two with the formula Li₃V₃O₈ and one with the formula Li₄V₃O₈. A lithium–vanadium bronze with the formula Li_1.3V₃O₈ was synthesised and investigated in order to compare experimental and predicted characteristics. The presence of Li_1+xV₃O₈ units in the synthesised material was confirmed by infrared (IR) measurements. The predicted value of the open circuit voltage (OCV) change for the insertion of one lithium atom equal to 0.559 V compares well with the experimental value of 0.52 V for the insertion of the first lithium atom into the synthesised bronze. These results form the basis for predicting the properties and modelling or technologically interesting electroactive materials.     

Comparison of a Reaction Front Model and a Finite Difference Model for the Simulation of Solid Absorption Process

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The temperature response of a metallic rod near a “steam explosion”

This communication presents the results of a series of experiments designed to investigate anomalous thermal responses of metallic bars subjected to rapid local cooling. Heating to 150 °C and subsequent rapid cooling of one end of a copper bar resulted in a temporal increase in the temperature of the other end of the bar of about 4 °C. Similar behavior was observed for other metallic bars, namely steel, aluminum, and brass. We will refer to this effect as “Heating Through Cooling”. The physics of this phenomena appears to be similar to the process called a “steam explosion”.     

Simulation of the behaviour of a set of Cu2SCdS unit photocells

With the help of a general simulation program (the Spice II program from the University of California, Berkeley), adapted to photocell modelling, we studied the behaviour of a large solar photocell consisting of smaller Cu₂SCdS unit solar cells in parallel. In particular we examined a theoretical set of photocells identical with the best cell made in the laboratory, a set of 30 real photocells characterized individually and the effect of introducing low efficiency cells.We indicate the role of each parameter characterizing the photocells in order to improve the behaviour of photovoltaic panels of larger dimensions.     

Online humidification diagnosis of a PEMFC using a static DC–DC converter

This paper deals with the online checking of the humidification of a Proton Exchange Membrane Fuel Cell (PEMFC). Indeed, drying or flooding can decrease the performance of the PEMFC and even lead to its destruction. An online humidification diagnosis can allow a real-time control. A good indicator of the membrane humidification state is its internal resistance. As known, the membrane ionic conductivity increases with the membrane water content. This resistance can be calculated at high frequency by dividing the voltage variation by the current variation. The proposed scheme makes use of measurements of current and voltage ripples coming from the association of a static DC–DC converter and the fuel cell. The experiment thus consists in computing the internal resistance in wet and dry conditions.     

Study of a Novel Rotary Cyclone Gas-Solid Separator

Based on the analytical study of the characteristics of fine particle motion in swirling flow, a new design idea on flow organization and construction aimed at increasing the positive radial flow in the separation chamber of the rotary cyclone separator (PRV type) was proposed. Experimental verification including the test of variation of separation efficiency and pressure loss with the first and secondary flow ratio show that this new type separator has higher and more stable separation efficiency in broad flow ratio range while the pressure loss is far below the conventional rotary cyclone separator and even comparable with that of simple cyclone separator     

Kinetics of Ignition of n—Pentane in a Shock—Tube

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The Effect of Spherical Surface on Noise Suppression of a Supersonic Jet

Experiments were carried out to eliminate the screech tone generated from a supersonic jet. Compressed air was passed through a circular convergent nozzle preceded by a straight tube of same diameter. In order to reduce the jet screech a spherical reflector was used and placed at the nozzle exit. The placement of the spherical reflector at the nozzle exit controlled the location of the image source as well as minimized the sound pressure at the nozzle exit. The weak sound pressure did not excite the unstable disturbance at the exit. Thus the loop of the feedback mechanism could not be accomplished and the jet screech was eliminated. The technique of screech reduction with a flat plate was also examined and compared with the present method. A good and effective performance in canceling the screech component by the new method was found by the investigation. Experimental results indicate that the new system suppresses not only the screech tones but also the broadband noise components and reduces the overal     

Variation of Transition Characteristics in a Wall Jet

The characteristics of a laminar wall jet submitted to different configurations have been experimentally explored in order to obtain a better knowledge of transition modifications. In fact different parameters can accelerate or delay the transition using a smooth or rough surface, heated or not, submitted to vibrations or not. In this study, significant effects can be noticed. It has been possible to measure the beginning of growth rates of disturbance amplitude using a wind tunnel and comparing the results with the linear stability theory.