Effects of chaotic acclimation applied on performance of microbial fuel cells

Microbial fuel cells (MFCs) are one of the bioreactors that produce electrons by metabolizing substrate from microorganisms, and have the ability to both degrade waste solution and produce electrons. Recently, the activity of microorganisms has limited the power performance of MFCs. Chaos has been used to stimulate activity of microorganisms, but it has not been used previously in MFCs. In this study, three types of acclimations – native acclimation (NA), MFC acclimation (MFCA), and MFC embedded with chaotic electric field acclimation (CMFCA) – are applied to realize their performance and chemical oxygen demand (COD) removal in MFCs, respectively. Results show that the current density and the power density of CMFCA were improved by 1.33 and 1.25 times than MFCA, and the COD removal of CMFCA reached 85% after five days. In addition, the acclimation stage at the condition of CMFCA appeared after 10 days, but was not found for the MFCA system. These observations would provide positive information for improving the performance of MCFs in the future.     

Multi-effects of gravity and geometric flow channel on the performance of continuous microbial fuel cells

Nowadays microbial fuel cells (MFCs) are a rapidly evolving field and studied extensively because of their simultaneous dual functions of decomposing organic waste matter and eco-power generation. Now, facing their low power density, multiple effects including various gravity conditions ranging from 0 G to 2 G and three kinds of geometric flow channel (serpentine channel, serpentine tapered channel and bio-mixer channel) in MFCs were studied because of their ability to significantly impact the performance of MFCs.Numerical simulation technology, with its significant lessening of time needed and saving experimental costs required was used in this study. Results show that a better power performance was found at a condition of 0.125 G and Reynolds number Re = 41.3 regardless of flow channel in MFCs. In addition, the bio-mixer channel of the flow channels in MFCs will have a better performance than the other two channels because of its lower pressure drop and higher power generation. These findings will provide useful information on enhancing the performance of MFCs, especially with the application of low gravity conditions in the future.     

Experimental Study on the Influence of Rotational Speed on the Performance of a Single-screw Expander with a 175 mm Screw Diameter

A single-screw expander has been designed and manufactured independently. Based on this prototype, testing system has been built and performance experiment has been made. In this article, compressed air was used as working fluid and performance test for the prototype was finished at conditions including different rotational speed and different inlet pressure.

From the experimental data, it is shown that when inlet pressure less than 0.8MPa the output power increases with the increase of rotational speed because of not enough expansion; when inlet pressure more than 0.8MPa, the every biggest output power is appeared in the condition of rotational speed 2600 rpm. The test results also show that the total efficiency is influenced by rotational speed obviously, and the highest total efficiency of this machine is 69.64% in the condition of 3000 rpm and 15 bar.     

Efficiency enhancement in solar air heaters by modification of absorber plate-a review

This paper outlines a complete review on modifications made on the absorber plate of solar air heaters in order to improve the turbulence and heat transfer rate, thereby efficiency. Corrugated sheets, fins, extended surfaces, wire mesh, porous medium, etc., are a few of the modifications used. Most of such alterations in the absorber plate resulted with an increase in efficiency but associated with drawback of increased pumping power due to raising friction factor. Pumping power is considered here as a predominant comparison parameters of various solar air heaters with different absorber plate in terms of effective efficiency.     

Designing a supercritical steam cycle to integrate the energy requirements of CO2 amine scrubbing

Absorption by chemical solvents combined with CO₂ long-term storage appears to offer interesting and commercial applicable CO₂ capture technology. However one of the main disadvantages is related to the large quantities of heat required to regenerate the amine solvent that means an important power plant efficiency penalty. Different studies have analyzed alternatives to reduce the heat duty on the reboiler and the thermal integration requirements on existing power cycles. In these studies integration principles have been well set up, but there is a lack of information about how to achieve an integrated design and the thermal balances of the modified cycle flowsheet. This paper proposes and provides details about a set of modifications of a supercritical steam cycle to overcome the energy requirements through energetic integration with the aim of reducing the efficiency and power output penalty associated with CO₂ capture process. Modifications include a new designed low-pressure heater flowsheet to take advantage of the CO₂ compression cooling for postcombustion systems and integration of amine reboiler into a steam cycle. It has been carried out several simulations in order to obtain power plant performance depending on sorbent regeneration requirements.     

Performance Optimization of a Class of Finite Time Heat Engines

The effect of heat resistance and heat leakage on the optimal performance of finite time heat engines is investigated in this paperbased on a generalized heat transfer law q ∞ Δ(Tⁿ). The analytical relation between optimal power output and efficiency for steady-state flow irreversible heat engines is derived. The analysis includes the optimal performance characteristics of several types of heat engines with different loss item and different heat transfer laws. A numerical example is provided for illustrating the power output versus efficiency characteristics. Results shown that the heat transfer law does affect the performance of these heat engines.     

Comparative performance study of different configurations of organic Rankine cycle using low-grade waste heat for power generation

This paper aims at analyzing the feasibility of a waste heat recovery power generation plant based on parametric optimization and performance analysis using different organic Rankine cycle configurations and heat source temperature conditions with working fluid R-12, R-123, R-134a, and R-717. A parametric optimization of turbine inlet temperature(TIT) was performed to obtain the irreversibility rate, system efficiency, availability ratio, turbine work output, system mass flow rate, second-law efficiency, and turbine outlet quality, along the saturated vapor line and also on superheating at an inlet pressure of 2.50 MP in basic as well as regenerative organic Rankine cycle. The calculated results reveal that selection of a basic organic Rankine cycle using R-123 as working fluid gives the maximum system efficiency, turbine work output, second-law efficiency, availability ratio with minimum system irreversibility rate and system mass flow rate up to a TIT of 150°C and appears to be a choice system for generation of power by utilizing the flue gas waste heat of thermal power plants and above 150°C the regenerative superheat organic Rankine cycle configuration using R 123 as working fluid gives the same results.     

Performance analysis of different orc power plant configurations using solar and geothermal heat sources

ABSTRACT

Energy optimization is performed on hybrid solar-geothermal power plant working according to Organic Rankine Cycle and installed in southern Tunisia. The performances of four different configurations of the power plant are studied. Mass and energy balances are established for the different compounds. The effects of the main operating parameters such as the geothermal water temperature, ambient temperature and direct normal irradiation on the power plant performances are analyzed. A code is established using Engineering Equation Solver software (EES) to perform the required calculations. Obtained results show that the hybrid solar-geothermal power plant with a heat recovery system is the most suitable configuration design giving a better overall energy efficiency of 15.77 and13.11% and a maximum net power of 1089 and 1882 kW in winter and summer, respectively. However, in the summer season, using a heat recovery system can valuable only when the water temperature is higher than 66°C. For air-cooled condenser, the suitable condensing pressure is 1 bar in winter and 1.9 bars in summer.     

Three-dimensional numerical modeling and characterization of two-stage and multilayer thermoelectric couples

The two-stage thermoelectric couple (TE couple) and the multilayer TE couple are proposed and their output performance is compared with the conventional TE couple in this paper. Three dimensional (3-D) numerical and finite element models are established for these three types of TE couples which are analyzed in the ANSYS Workbench environment. Simulation results show that the output voltage and the current of the two newly designed TE couples increase in a certain extent than those of the conventional device before the load resistance reaches a critical value, however, the multilayer TE couple has the best performance. Similar conclusions can be drawn from the results of comparisons with the maximum output power and the maximum heat conversion efficiency between different types of TE couples. When thicknesses of the intermediate ceramic substrate and the intermediate copper conductor change, the output performance of the two newly-designed types of TE couples can be improved further. The maximum output power and the maximum heat conversion efficiency of the multilayer TE couple increase by 71.15% and 14.87%, respectively, when compared with those for the conventional device under certain conditions. Therefore, the multilayer TE couple has the potential to be one of the future development directions of TE couple structures.     

Shift to continuous operation of an air-cathode microbial fuel cell long-running in fed-batch mode boosts power generation

Microbial fuel cells (MFCs) which are operated in continuous mode are more suitable for practical applications than fed batch ones. The aim of the present study was to characterize an air-cathode MFC operating in continuous mode and to determine the intrinsic properties for suitable performance and scalability. Air-cathode MFCs were constructed from plexiglass with a total working volume of 220 mL. Zirfon® separator used in this MFC had cross section area of 100 cm². The air cathode MFCs were operated in fed-batch mode and then shifted to the continuous mode. To determine the behavior of anode and cathode in long term operation (274 days), their contribution in MFC performance was evaluated over time. Once the active biofilm was formed, power production and substrate consumption rate were significantly higher. The internal resistance increased with the passage of time. After stabilization of biofilm when the MFC was placed in close circuit by connecting an external resistance, the anode-reference and cathode-reference electrode behavior showed that anode potential is near to the bacterial cell inside potential. The maximum open circuit voltage achieved was 623 mV and the highest power and volumetric power density were 38.03 mW/m² and 1296 mW/m³, respectively.     

Canopy slope effect on the performance of the solar chimney power plant

Solar chimney power plants constitute an impressive construction by its size and its output seems low for its dimensions. Although many works have been carried out on the subject, there is still much scientific and technical improvement to be done. In the present work, we consider the modeling of turbulent flow under the effect of natural convection within a solar chimney power plant (SCPP) by performing numerical simulation using the Saturne Code coupled with Syrthes code. The objective of the study is the analysis of the collector cover slope influence on the performance of the SCPP in two cases. In the first case, the storage system considered is composed solely of the ground under the collector. For the second case, the storage system is made, in addition to the ground, of a 10 cm thick tub filled with water, covering the entire surface of the collector. The concept of minimizing the entropy production is also studied with the objective of optimizing the geometric configuration as well as the effect of the collector cover slope on the efficiency of SCPP. The boundary conditions are defined according to the meteorological data for a typical day available on the site of Adrar, Algeria. The results allow us to focus on the storage system influence on the SCPP performance and the duration of its operation after sunset. This leads to the improvement of the global efficiency of the SCPP. Results show the positive impact of the extra storage media use and the configuration which improves the velocity at the chimney entrance.     

资源循环复杂物质流系统的Petri网建模方法研究

物质流分析是研究循环经济的重要方法,本文面向资源循环的流程制造企业,对不同复杂度的物质流系统进行了建模方法研究。首先对国内外在物质流领域的建模理论研究进行了综述,然后对物质流的特点和循环物质流的建模方法进行了分析,对基于投入产出表格的物质流分析方法、理论层面基于图论的物质流分析方法以及物质流分析软件进行了综述,最后重点探讨了Petri网建模与仿真工具在循环物质流分析中的建模方法,研究了不同类型Petri网在解决不同复杂度的物质流系统问题中的适用性,为物质流建模与仿真提供理论支撑。     

Sorption-enhanced hydrogen production for pre-combustion CO2 capture: Thermodynamic analysis and experimental results

Hydrotalcite-based materials have been identified as suitable materials for high temperature (400 °C) adsorption of CO₂. In pre-combustion decarbonisation processes for natural gas based power cycles, it should be possible to use this material to improve conversions in the water-gas shift (WGS) and steam-reforming (SMR) reaction. The efficiencies for electricity production from natural gas have been calculated for some different system configurations, in which hydrotalcite-based material could be used. The calculated efficiency penalties ranged from 5.5 to 8.6 percentage points. The assumptions made in the system study have been tested on the laboratory scale. Hydrotalcite-based materials are found to be an excellent choice for use in the sorption-enhanced WGS reactor. The requirements for very low residual concentrations of CO₂ at 400 °C and large amounts of catalyst in the sorption-enhanced SMR reactor make its application less likely. Suggestions are made to how the SE-SMR could be improved.     

Off-design performance analysis of a transcritical CO2 Rankine cycle with LNG as cold source

The transcritical CO₂ Rankine cycle with liquefied natural gas (LNG) as cold source is a promising power system to utilize mid- and low-temperature heat source. Most previous works focused on thermodynamic and thermoeconomic analysis or optimization for the system. In this article, an off-design performance analysis for the system is conducted. An off-design mathematical model for the system is established to examine the variation of system performance with the variations of heat source mass flow rate and temperature. A modified sliding pressure regulation control strategy, which regulates turbine inlet pressure to keep the temperature difference between heat source temperature and turbine inlet temperature constant, is applied to control the system when off-design conditions happen. The results show that when the mass flow rate or the temperature of heat source is less or lower than that of design condition, both the net power output of system and the system exergy efficiency decrease, whereas when they are more or higher than the values of design condition, the net power output of system increases but the system exergy efficiency still decreases. In addition, both CO₂ turbine and NG turbine could almost keep the designed efficiency values under the applied control strategy.     

Landmarks’ use in speech map navigation tasks

Tools for assisting human navigation, especially in-vehicle systems, have been extensively investigated. However, few studies have explored the design of speech-based over-the-phone guidance systems. This study examined the effect of landmarks' use and the effect of landmarks’ frames of reference in route instructions on navigation efficiency during map navigation tasks and satisfaction. Twenty-seven participants performed map navigation tasks using a simulated speech navigation system in three experimental conditions: instructions containing no landmarks, instructions containing landmarks located without reference to either the traveler’s body or the surrounding environment, and instructions containing landmarks located with respect to the traveler’s body. Navigation performances on maps were higher and landmarks enable participants to make fewer directional errors and find their routes more efficiently. Satisfaction levels and navigation performances were lower when instructions did not contain any landmarks. Landmarks’ frames of reference shifting turned out to be different between human-human situations previously used and human-computer situations used here.     

Energy and exergy analysis of a combined Brayton/Brayton power cycle with humidification

ABSTRACT

First and second law approaches have been used to analyze the performance of a humidified Brayton/Brayton power cycle. The energy efficiency and exergy destruction rates consistently improved when the combustion temperature was increased. Both performance indicators improved, reached an optimum, and then deteriorated when the topping cycle pressure ratio increased, while their sensitivity to the bottoming cycle pressure ratio depended on the humidification rate used at the bottoming cycle. Upon increasing the mass flowrate of air through the bottoming cycle, the energy efficiency of the power cycle increased linearly, while the irreversibility generation had a non-monotonic variation. In all cases, a higher degree of humidification always resulted in greater first and second law performances.     

Developing CO2 Emission Parameters to Measure the Environmental Impact on Cooling Applications

This study examines parametric approaches to the calculation of refrigerant-based CO₂ emissions in different cooling areas. Both the exergy analyses of refrigerants, used in domestic, commercial, transportation and industrial applications, and the environmental performances regarding exergetic irreversibility are investigated separately. Then, CO₂ emissions caused by systems are examined via two different parameters, I°) Environmental Impact Factor and ??°) Integrated Impact Factor (CIF). The study is based on a vapor compression cooling cycle model, commonly preferred by cooling applications, and the analyses have been made for 1 kW cooling capacity in relation to evaporator temperatures of the systems. In all cooling application, R134A gas stands out among the others in terms of coefficient of performance and exergy efficiency. Moreover, both emission analyses show that it has the lowest emission value. The paper concludes with an evaluation of the reasons for the refrigerant choice, the design and the selection of such a system, and why exergetic and environmental parameters should be preferred.     

Experimental investigation of a 250-kW turbine organic Rankine cycle system for low-grade waste heat recovery

An organic Rankine cycle (ORC) is generally used for converting low-grade heat into electricity. In this study, an extensive literature survey was conducted to identify current research gaps on experimental ORC systems. Specifically, there is limited experimental data and limited details on thermal and expander efficiencies of ORC systems. In order to address these gaps, the objective of this study included developing a turbine ORC with a power output exceeding 50 kW and thermal efficiency exceeding 8% for a heat source temperature < 120°C. The experimental results indicated that the system achieved a net power output of 242.5 kW and a thermal efficiency of 8.3% (the highest value for a turbine ORC system for the heat source temperature below 120°C). Thus, the study addressed the gaps identified in the research area of ORCs.     

Extrinsic modeling and simulation of helio-photovoltaic system: a case of single diode model

Simulation of helio-photovoltaic system is continuously undergoing revolution through diverse parameter modifications which closely mimic the experimental data. In retrospect, the current work has presented a nonlinear modification of equivalent circuit parameters and simulated the same for different semiconductors (crystalline and thin films); furthermore, established a mathematical relation between the coefficients of solar irradiance and module temperature (SIMT); moreover, investigated the influence of SIMT on the model parameters. The simulation upshot reveals that increment in solar irradiance (SI) intensifies the output current whereas an increase in module temperature (MT) diminishes the output voltage; the SIMT coefficients developed validated well with the manufacturers data; the influence of SI was evident on the photon current, diode current, and shunt resistance whereas the effect of MT was pronounced on the diode current, ideality factor, and shunt resistance. Thus, the provision made by this work is essential for advanced design and simulation of helio-photovoltaic systems.     

Numerical and experimental research on multi-stage pump as turbine system

Recently, researches on pump as turbine (PAT) have been one of the hot issues in fluid machineries. Of these hydraulic turbines, multi-stage PATs are widely used in industrial fields. However, most attentions have been paid on performance of the single-stage PATs and the turbines themselves. In this paper, a potential multi-stage PAT system with load pump was investigated numerically and experimentally. The match relations between PAT and load pump were explored by theory, and an analytical method to predict performance of PAT system was proposed in addition. Computational fluid dynamics method (CFD) was adopted to study the performance characteristics of PAT under a constant rotation or certain head. The operational rules of multi-stage PAT system were analyzed in both constant and variable speed that confirmed the prediction of system performance. The results could give guidance to choose a proper load pump and promote efficiency of PAT system.