Experimental Studies for Convective Drying of Potato

An experimental facility was built at the Indian Institute of Technology Delhi in order to examine the characteristics of convective drying of a moist object. The test facility consists of an inlet section, a divergent and convergent section, a settling chamber, a test section, and an outlet section. Initial moisture content and time-dependent moisture content of a rectangular shaped moist object (4 cm × 2 cm × 2 cm) are measured by this test facility. The potato slice was selected as a sample moist object. Moisture content was measured at different air temperatures of 40, 50, 60, and 70°C with an air velocity of 2 m/sec. The density of potato slice was determined for various drying temperatures. The volume shrinkage during drying decreased almost linearly with moisture content. The percentage air pores and porosity increased gradually with decreasing moisture content and increasing drying air temperature. Volumes of water, air, and solid content of potato were determined at different drying air temperatures. The results are validated with theoretical data.     

Experimental and Numerical Analysis of Heat Transfer in a Tall Vertical Concentric Annular Thermo-siphon at Constant Heat Flux Condition

The present work deals with the numerical and experimental analyses to study the detailed behavior of the thermally induced flow of water in an open vertical annulus, circulating through a cold leg forming a closed loop thermo-siphon. Spatio-temporal behavior of fluid flow is also studied for variety of heat fluxes. The annuli in the present study have a radius ratio of 1.184 and aspect ratio (length to annular gap) equal to 352. The objective of the present work is to quantify the effect of heating on design parameters such as liquid and wall temperatures, mass flow rate, and heat transfer coefficient. Experiments have also been conducted on a similar system with water at constant heat flux of 1 kW/m², 2.5 kW/m², 5 kW/m², 7.5 kW/m², 10 kW/m², 12.5 kW/m² and 15 kW/m². For numerical purpose, a two-dimentional solver has been developed for direct numerical simulation of the essential thermally induced flow dynamics The numerical solution was thus performed for Rayleigh numbers ranging between, 4.4 × 10³ and 6.61 × 10⁴ which correspond to the given heat flux, respectively.     

A brushless, exciterless, single-phase, sinusoidal wave synchronousmachine having an auxiliary stator winding

Analytical and experimental studies of a brushless, exciterless, single-phase, sinusoidal-wave synchronous machine operating as a generator or a motor, derived from a three-phase machine, are reported. One phase armature winding of the three-phase machine is used as an auxiliary stator winding of the single-phase machine and is used to supply the exciting power for the other two-phase armature windings acting as the load winding of the single-phase machine. A 1.5 kW, 200 V, 60 Hz, four-pole synchronous machine was used the experiments. It is shown that the waveforms of the armature terminal voltage and the load current are nearly sinusoidal. The advantages of the single-phase machine as a portable generator or small-load motor are discussed     

Open and closed metal hydride system for high thermal power applications: Preheating vehicle components

Many vehicle components operate at temperatures above ambient conditions. At cold start, most of the pollutants are produced and lifespan is reduced. Thermochemical energy storage with high power density could prevent these disadvantages. In order to investigate achievable power densities of a thermochemical energy storage at technically relevant boundary conditions, a laboratory scale device using metal hydrides (LaNi_4.85Al_0.15 and C5^®) is designed and preheating operation modes (open and closed) are analyzed. The impact of the ambient temperature (from ?20 to +20 °C), a s well as other influencing factors on the thermal power output such as heat transfer flow rate, regeneration temperature and pressure conditions are investigated. The experiments proved the suitability of the reactor design and material selection for the considered application boundary conditions. For the coupled reaction (closed system), the ambient temperature has the greatest influence on the thermal power with decreasing values for lower temperatures. Here, values between 0.6 kW/kg_MH at ambient temperature of ?20 °C and 1.6 kW/kg_MH at 20 °C, at otherwise same conditions, were reached. If hydrogen can be supplied from a pressure tank (open system), the supply pressure in relation to equilibrium pressure at the considered ambient temperature has to be large enough for high thermal power. At ?20 °C, 1.4 kW/kg_MH at a supply pressure of 1.5 bar and 5.4 kW/kg_MH at a hydrogen pressure of 10 bar were reached.     

Hydrogen purge and reactant feeding strategies in self-humidified PEM fuel cell systems

A 6 kW proton exchange membrane fuel cell system, operating in self-humidified conditions, was characterized in two anode operative modes: dead-end and flow through with exhaust recirculation. The anode sub-system was specifically designed in order to adjust the level of recycled anodic stream. The role of anode purge frequency, anode recirculation level and air stoichiometric ratio was analysed in the power range 1–5 kW. The aim of this study was to define management strategies to assure efficient and reliable cell performance during steady-state, warm-up and load variation phases. The results evidenced the combined effect of hydrogen purge, air flow rate impulse, and recycled anodic stream on individual cell performance recovery when unstable working conditions were detected during system start-up and load variations.     

Fabrication and characterisation of the graphite bi-polar plates used in A 0.25 kW PAFC stack

The graphite bi-polar plates were fabricated using lamination technique with polyether sulfone (PES) films (50 μm) and graphite foils (400 μn) in between the two porous graphite plates (CBC) by keeping in a specially designed and fabricated fixture with stainless steel plates at the top and bottom. The fixture was then kept in an hydraulic hot press, at loads of 10–20 tons, and heat treated at 410 °C for 30 min. Then these graphite plates were sized to 30 cm × 20 cm × 0.64 cm, leaving 0.4 mm thick graphite foil at the centre of the plate, to avoid the intermixing of the hydrogen and oxygen/air. While, the gas permeability (cm²/sec) of the plates was determined, with N₂ gas using differential pressure method, their electrical resistivity (mΩm) was measured using milliohmmeter and passing DC current to the graphite plates, at loads from 1–5 kgs. The values of permeability and electrical resistivity of the plates are found to be lower than 0.01 cm²/sec and 4–14 mΩm respectively. A stack with 6 cells was assembled using the in house developed graphite bi-polar plates, anodes and cathodes with matrix, to generate a DC power of 0.25 kW (3.6 V × 71.0 amps). It was operated for 300 h successfully using H₂ and Air, 1 bar, at 175 °C. In this paper, the detailed fabrication method of graphite bi-polar plates and their characteristics of gas permeability, electrical resistivity and the results of the 0.25 kW PAFC stack operation are presented.     

On Effective Design and Operating Conditions of Desiccant Dehumidification System

The present study investigates the effect of air flowrate on the adsorption systems both numerically and experimentally. Tests are performed with Zeolite 4A adsorbent. The size of test desiccant channel section is 10 cm × 10 cm × 10 cm, and three test sections in series connections are used as the test section during adsorption and desorption. During adsorption, the inlet pressure is kept at 9 bar while it is reduced to 1.16 bar during desorption. The simulation is first validated with the experimental data. The simulation indicates though a higher airflow during adsorption can produce dry air quickly but may not be able to attain a prescribed very low dew point temperature. Yet lower airflow can dehumidify more moisture and attain much lower dew point but requires substantial time. For the required energy to generate the same dry air flow volume in cyclic operation, it was obvious that a lower flowrate like 150 standard liter per minutes (SLPM) is about 4% lower than that of a higher flowrate of 400 SLPM. For effective regeneration during desorption, a non-uniform heating provided at the first section is proved to be much effective than the uniform heating. It is found that the desiccant loading for only heating at the first section outperforms other arrangements, giving 10% lower desiccant loading than the uniform heating.     

Process simulation of hydrogen production by steam reforming of diluted bioethanol solutions: Effect of operating parameters on electrical and thermal cogeneration by using fuel cells

The possibility to exploit diluted bioethanol streams is discussed for hydrogen production by steam reforming. An integrated unit constituted by a steam reformer, a hydrogen purification section with high- and low-temperature water gas shift, a methanator reactor and a fuel cell were simulated to achieve residential size cogeneration of 5 kW electrical power + 5 kW thermal power as target output.Process simulation allowed to investigate the effect of the reformer temperature, of bioethanol concentration and of catalyst loading on the temperature and concentration profiles in the steam reformer. The net power output was also calculated on the basis of 27 different operating conditions.P_electrical output ranging from 3.3 to 6.0 kW were obtained, whereas the total heat output P_{thermal, total} ranged from 3.9 to 7.2 kW. The highest overall energy output corresponded to P_electrical = 4.8 kW, P_{Thermal, FC} = 3.1 kW, P_{heat recovery} = 4.1 kW, for a total 12 kW energy output. This was achieved by feeding a mixture with water/ethanol ratio = 11 (mol/mol), irrespectively of the catalyst mass, and setting the ref split temperature so to have an average temperature of 635 °C in the ESR reactor.     

Performance Analysis of Small Size Compressed Air Energy Storage Systems for Power Augmentation: Air Injection and Air Injection/Expander Schemes

Two small size second-generation compressed air energy storage (CAES) systems have been investigated. Both plants are based on a 4600 kW Mercury recuperated gas turbine (GT) and on an artificial air storage system. In CAES air injection (CAES AI) plant, the stored compressed air is mixed with the air flow exiting the GT compressor and fed after a recuperative heating to the GT combustion chamber. A topping air expander is included in the CAES air injection/expander (CAES AI/E) plant scheme. Preliminary evaluations have been carried out to assess the maximum achievable GT power augmentation taking safety of operations and plant life duration into consideration. Plant performance has been evaluated during the overall operational cycle (charging, storage and discharging phases). CAES AI plant allows a 30% maximum extra power delivery (some 1500 kW) in respect to the nominal design GT power. The introduction of the topping air expander in CAES AI/E plant allows an additional power production of some 300 kW. Both plants have shown storage efficiency improvements by reducing the discharge period duration. Satisfactory values around 70% have been found in the best operating conditions.     

Wind power potential in Oman

Solar energy and wind are likely to play an important role in the future energy generation in Oman. This article assesses wind power cost per kWh of energy produced using four types of wind machines at 27 locations within Oman. These sites cover all regions in Oman. Hourly values of wind speed recorded between 2000 and 2009, in most cases, were used for all 27 locations. Wind duration curves were developed and utilized to calculate the cost per kWh of energy generated from four chosen wind machines. It was found that the cost of energy is low in the south and middle regions of Oman compared with that in the north region. The most promising sites for the economic harnessing of wind power are Thumrait, Qairoon Hairiti, Masirah, and Sur, with an energy cost of less than 0.117 US$/kWh when 2000 kW, 1500 kW, 850 kW, or 250 kW wind turbines are used.     

Hybrid (solar and wind) energy system for Al Hallaniyat Island electrification

Wind–PV–diesel hybrid power generation system technology is a promising energy option since it provides opportunities for developed and developing countries to harness naturally available, inexhaustible and pollution-less resources. The aim of this study is to assess the techno-economic feasibility of utilizing a hybrid wind–PV–diesel power system to meet the load of Al Hallaniyat Island. Hybrid Optimization Model for Electric Renewables software has been employed to carry out the present study. The simulation results indicate that the cost of generating energy (COE) is $0.222 kWh^?1 for a hybrid system composed of a 70 kW PV system, 60 kW wind turbine and batteries together with a 324.8 kW diesel system. Moreover, using the same system but without batteries will increase the COE to $0.225 kWh^?1, the fuel consumption, the excess energy and the total operating hours for the diesel generators. The PV–wind hybrid option is techno-economically viable for rural electrification.     

Discrete ejector control solution design,characterization, and verification in a 5 kW PEMFC system

An ejector primary gas flow control solution based on three solenoid valves is designed, implemented and tested in a 5 kW proton exchange membrane fuel cell (PEMFC) system with ejector-based anode gas recirculation. The robust and cost effective combination of the tested flow control method and a single ejector is shown to achieve adequate anode gas recirculation rate on a wide PEMFC load range.In addition, the effect of anode gas inert content on ejector performance in the 5 kW PEMFC system is studied at varying load and anode pressure levels. Results show that increasing the inert content increases recirculated anode gas mass flow rate but decreases both the molar flow rate and the anode inlet humidity.Finally, the PEMFC power ramp-rate limitations are studied using two fuel supply strategies: 1) advancing fuel supply and venting out extra fuel and 2) not advancing fuel supply but instead using a large anode volume. Results indicate that the power of the present PEMFC system can be ramped from 1 kW to 4.2 kW within few hundred milliseconds using either of these strategies.     

Evaluation of hydrogen production from harvesting wind energy at high altitudes in Iran by three extrapolating Weibull methods

One of the most appropriate ways for energy storage is producing hydrogen from renewable resources. Wind energy is recognized as one of the widely used renewable energy resources. This paper investigates the use of wind energy for producing hydrogen in Iran. To achieve this, the country is divided into five major regions: center, north, south, east and west. The performance of three large-scale commercial wind turbines, ranging from 1500 kW to 3000 kW at hub height of 80 m and four large-scale wind turbine ranging from 2000 kW to 4500 kW at hub height of 120 m are evaluated for producing hydrogen in 150 wind stations in Iran. All wind data were recorded based on 10-min time intervals for more than one year at different wind mast heights. For estimating Weibull parameters, the Standard Deviation Method (SDM), Empirical Method of Lysen (EML) and Power Density Method (PDM) are used. An extrapolation method is used to determine the shape and the scale parameters of the Weibull distribution at the high attitudes of 80 m and 120 m. Then, power law and surface roughness exponents, capacity factor, annual energy production and annual hydrogen production for the wind sites are determined. The results indicate that rated power is not the only determinative parameter and the highest hydrogen production is from the GW-109/2500 wind turbine at the hub height of 80 m and from E112/4500 at the hub height of 120 m. For better assessment, the amount of hydrogen production is depicted in Geographic Information Science (GIS) maps using power production of the seven wind turbine models. Next by analyzing these GIS maps, it is found that there are significant potentials in north, north-west, east and south of Iran for producing hydrogen from wind energy.     

Analysis of resonant coupling coil configurations of EV wireless charging system: a simulation study

Nowadays, internal combustion engine vehicles are considered as one of the major contributors to air pollution. To make transportation more environmentally friendly, plug-in electric vehicles (PEVs) have been proposed. However, with an increase in the number of PEVs, the drawbacks associated with the cost and size, as well as charging cables of batteries have arisen. To address these challenges, a novel technology named wireless charging system has been recently recommended. This technology rapidly evolves and becomes very attractive for charging operations of electric vehicles. Currently, wireless charging systems offer highly efficient power transfer over the distances ranging from several millimeters to several hundred millimeters. This paper is focused on analyzing electromagnetically coupled resonant wireless technique used for the charging of EVs. The resonant wireless charging system for EVs is modeled, simulated, and then examined by changing different key parameters to evaluate how transfer distance, load, and coil’s geometry, precisely number of coin’s turns, coin’s shape, and inter-turn distance, influence the efficiency of the charging process. The simulation results are analyzed and critical dimensions are discussed. It is revealed that a proper choice of the dimensions, inter-turn distance, and transfer distance between the coils can result in a significant improvement in charging efficiency. Furthermore, the influence of the transfer distance, frequency, load, as well as the number of the turns of the coil on the performance of wireless charging system is the main focus of this paper.     

Study on the limestone sulfation behavior under oxy-fuel circulating fluidized bed combustion condition

In order to investigate the behavior of limestone sulfation under oxy-fuel circulating fluidized bed (CFB) combustion condition, experiments were conducted in a 50 kW oxy-fuel CFB system under the O₂/CO₂ and air combustion conditions. A small cage, containing limestone particles, was dipped into the dense zone of the CFB combustor during the experiments. The calcination of limestone, pore structure of the product layer, and calcium conversion were studied. It was found that the increasing of temperature would promote the calcination of limestone and the high concentration of CO₂ would inhibit calcination of limestone. The formation process of the product layer was completely different between the direct and indirect sulfation, while it was almost the same during the indirect sulfation under the oxy-fuel and air combustion. However, both the temperature and gas compositions played important roles in determining the pore structures of the product layer during the limestone indirect sulfation process. Under the O₂/CO₂ combustion condition, the calcium conversion of indirect sulfation was always higher than that of direct sulfation. The highest final calcium conversion after 60 min was found at 900 °C under the O₂/CO₂ combustion condition.     

Nucleate Pool Boiling Heat Transfer on a Micro-Pin-Finned Surface in Short-Term Microgravity

Nucleate boiling heat transfer of air-dissolved FC-72 on a micro-pin-finned surface was experimentally investigated in microgravity by utilizing the drop tower facility in Beijing. The dimensions of the silicon chips were 10 mm × 10 mm × 0.5 mm and on these, two kinds of micro-pin-fins with the dimensions of 30 × 30 × 60 μm³ and 50 × 50 × 120 μm³ (width × thickness × height, named PF30-60 and PF50-120) were fabricated by the dry etching technique. Nucleate pool boiling on a smooth surface was also studied under both Earth gravity and microgravity for comparison. In general, the micro-pin-fins showed better heat transfer performance when compared with a smooth surface, both under Earth gravity and microgravity. In microgravity, this is mainly due to the fact that bubbles generated on micro-pin-finned surface can depart from the heater surface continuously. For micro-pin-fins, the reduced-gravity critical heat flux was about two-thirds of that in the Earth gravity experiment, but almost three times as large as that for the smooth surface, which is larger than that in the terrestrial experiment. Under different gravity levels, PF50-120 shows a little better heat transfer than that of PF30-60, mainly due to larger heat transfer area. Besides, the fin gap of PF30-60 may generate a larger flow resistance for microconvection around the fin side walls, resulting in a lower heat transfer performance.     

Comparison of the explosion characteristics of hydrogen,propane, and methane clouds at the stoichiometric concentrations

Numerical simulations were performed to study explosion characteristics of the unconfined clouds. The examined cloud volume was 4 m × 4 m × 2 m. The build-in obstruction inside the cloud was the 8 × 8 × 4 perpendicular rod array. The obstacle volume blockage ratio was 0.74. Three gases were considered: hydrogen/air at the stoichiometric concentrations, propane/air at the stoichiometric concentrations, and methane/air at the stoichiometric concentrations. The hydrogen/air cloud explosion has higher peak overpressure and the overpressure rises locally at the nearby region of the cloud boundary. The explosion overpressures of both methane/air and propane/air are lower, compared with the hydrogen/air, and decreases with distance. The maximum peak dynamic pressure is reached beyond the original cloud, which is clearly different from the explosion peak overpressure tends. Furthermore, dynamic pressure of a cloud explosion is of the same order as overpressure. The explosion flame region for the hydrogen/air cloud is approximately 1.25 times of the original width of the cloud. The explosion flame regions for propane/air or methane/air clouds are approximately 1.4 times of the original width of the cloud. Unlike the explosion overpressures, the explosion temperatures have little difference between the three mixture examined in this study. The higher energy of explosive mixture generates a high temperature hazard effect, but the higher energy of explosive mixture may not generate a larger overpressure hazard effect in a gas explosion accident.     

The effects of hydrogen fuel usage on the exergetic performance of a turbojet engine

In this study, the hydrogen fuel effect on the exergetic performance of a turbojet engine used in a military trainer aircraft is investigated. For the first step, the performance assessments of the exergetic performance are conducted according to jet fuel usage and the actual test cell data of the engine. For the second step, an exergetic evaluation is parametrically estimated to use the hydrogen fuel in the engine. Finally, the performance results of the engine run by jet fuel are compared with the performance results of the engine run by hydrogen fuel. Regarding the results of this study, by using hydrogen fuel in the engine, the exergy efficiency of the engine decreases from 15.40% to 14.33%, while the waste exergy rate increases from 6196.51 kW to 6669.4 kW. At the same time, the exergy rate of the fuel rises from 7324.87 kW to 7785.25 kW, hence the specific fuel exergy of the hydrogen fuel is higher than that of the jet fuel. The waste exergy flow cost of the engine rises from 16.52 × 10^?3 US$/kW to 17.79 × 10^?3 US$/kW. The environmental effect factor of the engine escalates from 5.49 to 5.98 and the ecological effect factor increases from 6.49 to 6.98. On the other hand, the exergetic sustainability index of the engine reduces from 0.182 to 0.167 when the sustainable efficiency factor of the engine goes down from 1.182 to 1.167. Between the components, for both jet fuel and hydrogen fuel, the CC has the highest values of the fuel exergy waste ratio, the relative waste exergy ratio, the product exergy waste ratio, the fuel ratio indicator, the product ratio indicator, the waste exergy cost flow, the environmental effect factor, the ecological effect factor, and the exergetic improvement potential when the CC has the lowest values of the exergy efficiency, exergetic sustainability index, and sustainable efficiency factor, respectively. The reason for this result is that the combustion process contains high irreversibities. The obtained results indicate that the hydrogen fuel usage in the turbojet engine badly affects the exergetic performance of the engine and its components (especially the combustion chamber) hence the specific exergy of the hydrogen fuel is higher than the jet fuel's. On the other hand, the exhaust emissions emitted to the environment decrease from 0.509 kg/s to 0.0045 kg/s with the hydrogen fuel usage.     

Optimization of stationary nonimaging reflectors for tubular evacuated receivers aligned north-south

Several manufacturers are developing solar collectors with tubular evacuated receivers aligned north-south. Adding low-concentration, wide-acceptance-angle reflectors to such tubes allows greater tube spacings, reducing the number of tubes per area of collector. It also improves collector efficiency, particularly for conditions of high , such as high temperatures or low light levels. This detailed study optimizes the reflector design for maximum daily energy collection and includes the effects of reflection losses, reflector-receiver alignment errors, variation of selective surface absorptance with angle of incidence on the receiver, and losses through the gap between the receiver and the reflector.Three general conclusions have been reached: The use of optimized nonimaging reflectors with tubular evacuated receivers will increase the energy collection efficiency—particularly for high-temperature and harsh environment conditions.Wide-acceptance-angle reflectors are forgiving to receiver-reflector alignment errors. It is neither necessary nor desirable to design reflectors for undersize receivers in order to compensate for misalignments that result from manufacturing tolerances.The daily energy collection of collectors using these reflectors having acceptance half-angles in a range. near 60° is not a sensitive function of the acceptance angle. Manufacturers' final reflector design decisions will probably be based on technical considerations related to fabrication and assembly techniques and possibly on market-related considerations such as collector appearance.     

Thermal Characteristics of a Chip-Scale Two-Phase Microgap Cooler

Two-phase heat transfer and pressure drop results for a chip-scale, uniformly heated, microgap channel, with nominal gap heights of 100, 200, and 500 μm and using HFE-7100 and FC-87 as the working fluids, are reported. Average heat transfer coefficients in the range of 5 to 30 kW/m²-K were observed, for exit qualities up to 60%. Local heat transfer coefficients, obtained through an inverse computational technique, are found to vary strongly with thermodynamic quality and to fall within ±30% of the predictions of the venerable Chen correlation.