Towards the design of high efficiency woodstoves

The paper describes the various methods that lead to the development of high efficiency woodstoves. The main design constraints that need to be adhered to are the reduction in fuel consumption, keeping the power output higher than, or the same as, that of the traditional system, and the incorporation of user friendly aspects such as low weight, low floor area, low cost, etc. The parameters that affect the stove performance most are the combustion chamber parameters, the fuel parameters and the self-draught parameters. The effects of these are discussed in detail. Some design considerations, such as matching of the heat transfer coefficients, matching of the heat source and the heat exchanger, maximization of the area of contact between the vessel and the flame, and the choice of chamber diameter are also described. Discouraging the use of clay vessels and encouraging the use of grates in traditional stoves can alone decrease the fuel consumption to about half of the present consumption besides increasing the power output. The results of this study will provide working information for stove designers towards the development of high efficiency woodstoves.     

Performance of a portable mini solar-pond

For the present experiments, such a pond was located at JUST, i.e. at 32°N latitude. Its walls were inclined at 45° to the horizontal. The pond was built of galvanized steel (1.44 mm thick) with a circular surface area and total depth of 1 m² and 500 mm, respectively. The effects of the solar-pond's depth and its water's salinity on the store's temperature distributions were determined experimentally and compared with theoretical predictions. A dimensional analysis was carried out to show the effect of the mini solar-pond's size on its thermal behaviour.     

Performance evaluation of direct methanol fuel cells for portable applications

This study examines the feasibility of powering a range of portable devices with a direct methanol fuel cell (DMFC). The analysis includes a comparison between a Li-ion battery and DMFC to supply the power for a laptop, camcorder and a cell phone. A parametric study of the systems for an operational period of 4 years is performed. Under the assumptions made for both the Li-ion battery and DMFC system, the battery cost is lower than the DMFC during the first year of operation. However, by the end of 4 years of operational time, the DMFC system would cost less. The weight and cost comparisons show that the fuel cell system occupies less space than the battery to store a higher amount of energy. The weight of both systems is almost identical. Finally, the CO₂ emissions can be decreased by a higher exergetic efficiency of the DMFC, which leads to improved sustainability.     

Thermal rating and design of woodstoves: A new approach

The paper is divided into two parts. In the first part, the results of tests on 13 stoves currently being marketed in India, compared with two traditional stoves, are presented. The bulk of the tests (about 140) pertain to variation of efficiency against fuel burning rate. Also, a few tests on the variation of chimney heights (18 tests) and damper position (20 tests) were conducted. The levels of efficiency were quite low on account of improper dimensioning of the stoves. Except for two stoves, all recorded consistently low efficiency figures. In the second part of the paper, the results of tests on combustion chambers of different sizes, ranging from a diameter of 180 mm to 500 mm, are presented in the form of design equations. The optimum length to diameter ratio is about 0.35, and optimum height of the ash chamber is 0.2 times the height of combustion chamber. A new approach to the sizing of combustion chambers is presented.     

Residential bioenergy heating: A study of consumer perceptions of improved woodstoves

Consumers’ choices play a key role for the development of biomass heating in the residential sector. The city of Oslo has granted subsidies to households who change to new, improved low-emission woodstoves. The purpose of this study is to expand the knowledge about users’ experiences and attitudes to residential biomass heating. An adapted model of the Theory of Planned Behavior was used to model households’ inclination to continue using their woodstoves for heating. More than 800 questionnaires were collected from households that recently had invested in an improved woodstove. The respondents were satisfied with the new woodstoves. The respondents also considered themselves competent to use and maintain the stove and few had problems acquiring fuelwood. Further analyses showed that the intention to continue to use the new woodstove depends on economic benefits, heating performance, perceived time and effort to operate the stove, environmental effects of heating as well as perceived subjective norm. The results imply that when marketing a modern technology for bioenergy heating, both public authorities and producers should consider issues related to the users’ perception of subjective norm, such as perceived status of using bioenergy or environmental concerns, when designing campaigns to promote the use of woodstoves.     

Thermochemical transformation of CO2 for CH4 production using metal hydride and carbonates as portable sources

The thermochemical reaction between MgH₂ and Li₂CO₃ is investigated for the first time for the CO₂ transformation into fuels with and without nickel as a catalyst. Successful production of CH₄ with high yields is reached depending on different reaction conditions such as microstructural refining, MgH₂:Li₂CO₃ molar ratio, temperature and time. In absence of a catalyst, a methane yield of 68.2% was achieved by heating the milled MgH₂:Li₂CO₃ mixture at 450 °C for 5 h. The global mechanism involves the reduction of CO₂ from Li₂CO₃ by MgH₂/Mg, producing CH₄ and Li₂O/MgO. For the Ni-catalyzed system, the highest methane yield of >90% was reached at 400 °C after 5 h of thermal treatment. The global process responds to a Sabatier reaction, with a contribution of a direct reduction of CO₂ depending on the starting mol ratio. The results demonstrate that thermochemical activation of the Ni-catalyzed MgH₂:Li₂CO₃ mixture is a powerful process for the generation of CH₄ and CO₂ utilization.     

Performance of high power metal hydride reactors

Metal hydride reactors were built with porous powder metal hydride (PMH) compacts. An improved reactor built with copper coated PMH compacts of LaNi₅ with a 1.27 cm diameter produced a nominal specific cooling power of 1.5 kW/kg hydride. A similar reactor, built with copper coated PMH compacts of Ca_0.4Mm_0.6Ni₅, showed 2.2 kW/kg hydride. Results with copper coated PMH compacts showed improved thermal conductivity. The compacts are structurally strong and prevent migration of fine metal hydride particles. Life-cycle tests were performed on the reactor with LaNi₅ for over 3000 cycles and the cooling power of the reactor gradually decreased by approximately 55%.     

Performance characteristics of mobile heat pump for a large passenger electric vehicle

In this study, the performance of a mobile heat pump for an electric bus, which uses the wasted heat of electric devices for a heating and air source for a cooling, was evaluated. Both cooling and heating performances of the mobile heat pump were tested under various experimental conditions, and then optimized by varying the refrigerant charge and the compressor frequency. The cooling capacity at all compressor frequencies was over 23.0 kW, which is sufficient for the cooling loads of an electric bus. The heating COP decreased but the heating capacity increased with the rise of outdoor temperature and the compressor frequency. The heating COP was 2.4 at an outdoor temperature of 10.0 °C. The observed heating and cooling performance characteristics of the mobile heat pump means it could be used for cabin heating and air conditioning of an electric vehicle with a short driving range.     

大容量高效锅炉受热面壁温测点布置方法

本文结合国内首台1000MW双切圆π型二次再热锅炉受热面壁温运行情况,分析现有壁温测点布置存在的问题,总结得出各受热面壁温测点布置原则及方法,为后续锅炉受热面壁温测点布置提供依据。     

Performance investigation of double-stage metal hydride based heat pump

In this paper, the performance investigation of a Double-Stage Double-Effect Metal Hydride Heat Pump (DSDE-MHHP) working with LaNi_4.1Al_0.52Mn_0.38, LmNi_4.91Sn_0.15 and Ti_0.99Zr_0.01V_0.43Fe_0.09Cr_0.05Mn_1.5 hydride alloys is presented. The effects of half cycle time (θ), hydride mass ratio (M_R), sensible heat exchange factor (?) and operating temperatures, viz. heat source (T_D), heat sink (T_M), and refrigeration (T_C) temperatures on the amount of hydrogen transferred between the paired reactors, coefficient of performance (COP) and specific cooling power (SCP) of the DSDE-MHHP system are investigated. For the present analysis the heat rejection temperature (T_H) is maintained constant at 373 K. Numerically predicted hydride bed temperatures are compared with experimental data and a good agreement is observed between them. It is observed from the numerical results that the COP and SCP of the DSDE-MHHP system increase with heat source and refrigeration temperatures, and decrease with heat sink temperature. For operating temperatures of 578, 373, 298 and 283 K (T_D, T_H, T_M and T_C), the average COP and SCP of the system are found to be 0.81 and 48.1 W/kg of total alloy mass, respectively.     

Performance investigations of a single-stage metal hydride heat pump

This paper discusses the performance investigations of a single-stage metal hydride heat pump (SS-MHHP) working with five different alloy pairs, namely, MmNi_4.6Al_0.4/MmNi_4.6Fe_0.4, LaNi_4.61Mn_0.26Al_0.13/La_0.6Y_0.4Ni_4.8Mn_0.2, LmNi_4.91Sn_0.15/Ti_0.99Zr_0.01V_0.43Fe_0.09Cr_0.05Mn_1.5, LaNi_4.6Al_0.4/MmNi_4.15Fe_0.85 and Zr_0.9Ti_0.1Cr_0.9Fe_1.1/Zr_0.9Ti_0.1Cr_0.6Fe_1.4. The performance of the system is predicted by solving the unsteady, two-dimensional coupled heat and mass transfer processes in metal hydride bed of cylindrical configuration using a fully implicit finite volume method. The influences of operating temperatures such as heat source (T_H), heat sink (T_M) and refrigeration (T_C) temperatures on the coefficient of performance (COP) and specific cooling power (SCP) of the system are presented. The predicted hydride bed temperature profiles are compared with the experimental data reported in the literature and a reasonably good agreement is observed between them. The optimum operating temperature ranges of each pair of alloys are suggested. For the selected operating temperatures, a maximum COP of 0.66 is predicted for Zr_0.9Ti_0.1Cr_0.9Fe_1.1/Zr_0.9Ti_0.1Cr_0.6Fe_1.4 hydride pair, while LmNi_4.91Sn_0.15/Ti_0.99Zr_0.01V_0.43Fe_0.09Cr_0.05Mn_1.5 hydride pair produces the highest SCP of 53.25 W/kg of total mass of the system.     

Performance studies of a large size nontracking solar cooker

A large size nontracking solar cooker has been designed, fabricated and tested. The cooker is based on the hot box principle. The cooker has been tested extensively and its performance has been compared with a solar oven, a hot box solar cooker and a solar cooker (tilted absorber). The stagnation temperatures are in increasing order for the hot box solar cooker, the solar cooker (tilted absorber), the large size nontracking solar cooker and the solar oven. The performance of this solar cooker is comparable with that of a solar oven. The former is not tracked towards sun while the latter is tracked every 30 min. The efficiency of a large size nontracking solar cooker is 24.9%. The energy saved by this new solar cooker has also been calculated and its payback period has been computed by considering interest, maintenance and inflation in fuel prices and maintenance cost. The payback periods are 1.10–3.63 years depending on which fuel it replaces. Relatively short payback periods show that the use of the cooker is economical, and it is easy to operate since no tracking is required.     

便携式增压系统状态检测仪的开发

开发了一种用于柴油机增压系统不解体状态评价和故障诊断的便携式仪器,本文着重介绍了仪器的工作原理、结构及特点.     

Architecture for portable direct liquid fuel cells

Direct fuel cells (DFCs) are receiving increased interest for portable power applications. Cell and stack architecture is a vital technical issue for portable DFCs. The architecture of a DFC not only has to meet particular application requirements such as a compact size and easy handling, but also has to ensure desired performance, reliability and fabrication costs. In this paper, the most recent advances related to portable DFCs and their architecture are reviewed. The current status of system architecture, stack/unit cell architecture, flow-field designs and MEA morphology strategies along with analysis are surveyed. In addition, promising methods of passive fuel delivery are also presented.     

Performance and long-term stability of Ti metal and stainless steels as a metal bipolar plate for a direct methanol fuel cell

In this study, STS 316L (Stainless Steel 316L), STS 430, and Ti metal are investigated as metal bipolar plates for a direct methanol fuel cell (DMFC). The corrosion resistance of these materials is investigated by potentiodynamic and chronoamperometry tests. Their cell performance and long-term stability are then studied under a real fuel cell test. The corrosion resistance of the metal bipolar plates is in the order of Ti > STS 316L > STS 430. However, the results of the real fuel cell test differ from the results of the corrosion resistance. Ti shows the lowest performance due to a sharp performance decrease in ohmic loss regions, while STS 430 shows a lower performance decrease in ohmic loss regions. Although STS 430 has less resistance to corrosion than STS 316L in the simulated environment, STS 430 performs better as a metal bipolar plate for a DMFC than STS 316L, particularly, with regard to cell performance, cell resistance, and durability.     

Performance analysis of a compressor driven metal hydride cooling system

A compressor-driven metal hydride cooling system is analyzed in terms of its energetic and exergetic efficiencies. Applying the first and second laws of thermodynamics, the system COP, contribution of individual irreversibilities and the second law efficiency of the system are obtained. Effects of important design and operating parameters on system performance are presented. Performance comparison is made between systems working with established metal hydrides (MmNi_4.5Al_0.5 and Fe_0.85Mn_0.15Ti) and an assumed metal hydride of high hydrogen storage capacity. Studies reveal that the system performance depends mainly on the temperature drops at the high- and low-temperature reactors and compressor efficiency. It is observed that when the temperature drops are high, there is no significant difference between the well-established hydrides and the assumed hydride. It is observed that in order to compete with commercially available vapour compression refrigeration systems in terms of performance, the metal hydride reactors need to be designed for minimum temperature difference between the external medium and the hydride beds.     

Design of control systems for portable PEM fuel cells

The current evolution in the design of fuel cell systems, together with the considerable development of integrated control techniques in microprocessor systems allows the development of portable fuel cell applications in which optimized control of the fuel cells performance is possible. Control, in the strict sense, implies a thorough knowledge of both the static and dynamic behaviour of the system comprising the stack, manifold and the compressor that enables oxygen supply. The objective of this control, far from being simply to maintain the stack free from oxygen and hydrogen shortages, is to achieve the necessary values of these gases, minimizing compressor consumption, which is the cause of the greatest inefficiency of fuel cells. This objective is essential when fuel cell systems are involved in situations where the net power of the stack is reduced and any unnecessary consumption lowers the total power available to the user. The design of an efficient control system requires the following steps: (1) modeling of the stack, compressor and other pneumatic elements involved in the system. (2) Calculation of the control equations and simulation of the entire system (including control). (3) Emulation of the stack and other pneumatic elements and simulation utilizing the designed control system. (4) Physical realization of the control system and testing within the fuel cell system. The design of a control system for fuel cell systems is introduced to manage PEMFC stacks. The control system will guarantee the correct performance of the stack around its optimal operation point, in which the net power is maximized. This means that both, the air flow and the stack temperature are controlled to a correct value.     

Performance of large solar water heating system: Thermosyphon mode

Two large solar water heating systems (non-pressure type), each having 1000-1. capacity, have been installed at IIT New Delhi and their performances have been studied under the thermosyphon mode between the collectors and the storage tank. A simple transient analysis of the system, incorporating the effect of withdrawal of hot water from the storage tank, has been developed. The effect of stratification in the storage tank has been studied experimentally. It is found that the experimental observations are in good agreement with the theoretical results obtained by the present model.