Closed-loop oscillating heat-pipe with check valves (CLOHP/CVs) air-preheater for reducing relative humidity in drying systems

A CLOHP/CV air-preheater has been used for recovering the waste heat from the drying cycle. The CLOHP/CV heat-exchanger consisted of copper tubes 3.58 m long and internal diameter 0.002 m. The evaporator and condenser sections were 0.19 m long, the adiabatic sections 0.08 m long, the hot air velocity was 0.5, 0.75 or 1.0 m/s with the hot air temperature 50, 60 or 70 °C, and the relative humidity was 100%. The working fluid was R134a with a filling ratio of 50%. The hot-air temperature increased from 50 to 70 °C; the heat-transfer rate increased slightly. The velocity increase from 0.5 0.75, to 1.0 m/s led to the heat-transfer rate slightly decreasing. The velocity increase from 0.5 to 1 m/s led to a slight decrease in effectiveness. As the hot-air temperature increases from 50 to 70 °C, the effectiveness slightly increased; and the relative humidity was reduced to the range 54–72% from 89% to 100%. The CLOHP/CV air-preheater can reduce the relative humidity and achieve energy thrift.     

Experimental study of the performance of a circular tube solar collector with closed-loop oscillating heat-pipe with check valve (CLOHP/CV)

This paper describes the performance of a circular glass tube solar collector with a set of closed-loop oscillating heat-pipes with check valves (CLOHP/CV). The assembly was divided into three sections, i.e. circular glass tube, adiabatic gap and condenser water tank. A circular 10-set glass tube solar collector of 0.058 m diameter and 1.50 m length was housed on a collecting plate. The inside circular glass tube consisted of a CLOHP/CV and collecting plate. The adiabatic gap was 0.05 m. The condenser water tank was made from a 0.03 × 0.05 m² zinc sheet. The CLOHP/CV consisted of the collecting plate cover with inner diameter of 0.003 m and 26.40 m total length per set, and it contained two check valves with evaporator 1.50 m long, adiabatic gap 0.05 m and condenser 0.30 m long. R-134a was used as the working fluid with filling ratio of 50%. The CLOHP/CV arrangement was aligned at an inclination angle of 18 degrees from the horizontal plane, with 6 turns per set. A 0.001 m thick aluminum sheet was used to make a collecting plate with 0.10 × 1.50 m² test area. Efficiency evaluations were conducted during daylight hours over a 2-month period and included extensive monitoring and recording of temperatures with type-K thermocouples placed at key locations throughout the system. The results confirmed the anticipated fluctuation in collector efficiency dependent on the time of day, solar energy irradiation, ambient temperature and circular tube surface mean temperature. An efficiency of approximately 76% was achieved, which correlates with the efficiency of the more expensive heat-pipe system. The CLOHP/CV system offers the additional benefits of corrosion-free operation and absence of freezing during winter months.     

Heat-transfer characteristics of a closed-loop oscillating heat-pipe with check valves

The heat-transfer characteristics of this system i.e. a CLOHP/CV, depend on the ratio of check valves (R_cv), aspect ratio (L_e/d_i) and the dimensionless parameters of the heat transfer. The CLOHP/CV used employed a copper tube with inner diameters of 1.77 and 2.03 mm. The evaporator, adiabatic and condenser lengths were equal to 50, 100 and 150 mm. The selected working fluids were water (H₂O), ethanol (C₂H₅OH) and R123 (CHCl₂CF₃) with a filling ratio of 50% of total volume. The number of turns was 40. The R_cv values were 20, 8, 5 and 4. The evaporator was heated by hot water, while the condenser section was cooled by distilled water. The inclination of the CLOHP/CV used in the experiments was 90° to the horizontal, with a controlled working-temperature of 50 °C. When the system reached the steady state, the temperature and the flow rate of the cooling water were measured in order to calculate the heat-transfer rate of the CLOHP/CV. The experimental results showed that the heat-flux increases with an increase of R_cv and decreases with an increased aspect ratio. A correlation for predicting the heat-transfer rate for the heat-pipe in the vertical position has been established.     

Closed-ended oscillating heat-pipe (CEOHP) air-preheater for energy thrift in a dryer

The CEOHP air-preheater consisted of two main parts, i.e. the rectangular house casing and the CEOHP. The house casing was designed to be suitable for the CEOHP. The inside house casing divided the CEOHP into three parts, i.e. the evaporator, the adiabatic section and condenser section. The CEOHP air-preheater design employed copper tubes: thirty-two sets of capillary tubes with an inner diameter of 0.002 m, an evaporator and a condenser length of 0.19 m, and each of which has eight meandering turns. The evaporator section was heated by hot-gas, while the condenser section was cooled by fresh air. In the experiment, the hot-gas temperature was 60, 70 or 80 °C with the hot-gas velocity of 3.3 m/s. The fresh-air temperature was 30 °C. Water and R123 was used as the working fluid with a filling ratio of 50%. It was found that, as the hot-gas temperature increases from 60 to 80 °C, the thermal effectiveness slightly increases. If the working fluid changes from water to R123, the thermal effectiveness slightly increases. The designed CEOHP air-preheater achieves energy thrift.     

Proton conducting CS/P(AA-AMPS) membrane with reduced methanol permeability for DMFCs

A novel polyelectrolyte complex (PEC) membrane for direct methanol fuel cells (DMFCs) was prepared by blending a cationic polyelectrolyte, chitosan (CS), with an anionic polyelectrolyte, acrylic acid-2-acrylamido-2-methylpropane sulfonic acid copolymer (P(AA-AMPS)). The presence of –NH₃⁺ species detected by X-ray photoelectron spectroscopy (XPS) revealed that an ionic cross-linked interpenetrating polymer network (IPN) was formed between the two polyelectrolyte polymers. Methanol permeability and proton conductivity were measured and compared with the Nafion^®117 membrane. The dual function of P(AA-AMPS) as both an ionic crosslinker and a proton conductor led to not only a notable reduction in methanol permeability but also an increase in proton conductivity. The CS/P(AA-AMPS) membrane with a P(AA-AMPS) content of 41 wt.% exhibited a methanol permeability (P) of 2.41 × 10⁻⁷ cm² s⁻¹ which was fifteen times lower than that of the Nafion^®117 membrane, whereas its proton conductivity (σ) was comparatively high (3.59 × 10⁻² S cm⁻¹). In terms of the overall selectivity index (β = σ/P), the PEC membrane showed a remarkably higher selectivity than the Nafion^®117 membrane, and, furthermore, the overall selectivity index increased with the increase of P(AA-AMPS) content. The mechanism of proton transfer was tentatively discussed based on the activation energy of conductivity.     

Development of a new moisture transfer (Bi-Re) correlation for food drying applications

In this paper, newly developed Biot-Reynolds (Bi-Re) correlation to determine the moisture transfer parameters is presented. Development of the new correlation is based on the experimental data taken from various sources in the literature. Moisture diffusivity and moisture transfer coefficient are calculated using the previously developed model. The moisture distribution profiles are then obtained for regular objects such as slab, cylinder and sphere. The results obtained from the present study are compared with the experimental data and a correlation available in the literature. It is found that they are in good agreement. Hence, it is believed that the developed correlation is of great significance for design and practicing engineers working in the drying industries.     

Water desalination with concentrating photovoltaic/thermal (CPVT) systems

A coupled system is proposed, comprised of a concentrating photovoltaic/thermal collector field and a multi-effect evaporation desalination plant. The combined system produces solar electricity and simultaneously exploits the waste heat of the photovoltaic cells to desalinate water. A detailed simulation was performed to compute the annual production of electricity and water. The cost of desalinated water was estimated and compared to that of alternative conventional and solar desalination plants. Several economic scenarios were analyzed. The results indicate that the proposed coupled plant can have a significant advantage relative to other solar desalination approaches. In some cases, CPVT desalination is even more cost-effective than conventional desalination.     

Debarking and drying of downy birch (Betula pubescens) and Scots pine (Pinus sylvestris) fuelwood in conjunction with multi-tree harvesting

Fuelwood moisture content is an important parameter for small and medium-sized heating plants. Optimal storage location and good fuelwood storage maintenance promotes drying efficiency and ensures good fuelwood quality. The effective drying period is limited to spring and summer. It is known that partial debarking of wood will enhance drying and improve fuelwood quality.The aim of the study was to test strip debarking as a mean to speed up the drying rate and to lower moisture and bark contents. The prerequisite was that debarking had to be integrated into the processing phase of a single grip harvester. The changes made in the harvester head had to be simple, easily installed and inexpensive.The mechanical objective was solved by drilling holes into the delimbing knives and placing bolts through the knives. In this manner the bolt head would strip bark off the stems when fed through the delimbing knives. The qualitative goal was to see if debarking improved drying rate and if harvesting season and species played a role.The data was collected on non-frozen and frozen pine wood in spring 2005 and in winter 2006, and on non-frozen birch in spring 2007. The debarking results of the non-frozen pine were 3-6% of the total surface area for the normal harvester head and 7-9% for the modified harvester head. The results for frozen pine were correspondingly 1% and 2-2.5%. The debarking results of non-frozen birch were 5-6% and 5-8%. Both studies of pine show that the bolts in delimbing knives doubled the amount of bark removed. There was no significant difference in birch.The delimbed Scots pine fuelwood storages reached 30% moisture content on fresh weight basis during the first drying season at landing. This result was obtained independently of the rate of debarking or the harvesting season. Seasoning over the second summer lowered the moisture content of pine fuelwood by another 5% units to 25%. Birch reached 20% during the first season.     

Numerical simulation of reactive flow in liquid composite molding using flux-corrected transport (FCT) based finite element/control volume (FE/CV) method

The mold-filling simulation of liquid composite molding (LCM) is of great importance in optimizing this cost-effective polymer-composites manufacturing process. The flow in LCM is a convection-dominated reactive, non-isothermal flow involving a moving boundary, so the Galerkin finite element method (FEM) has to be adapted with stabilization techniques to solve such problems. The streamline-upwind Petrov–Galerkin (SUPG) method is one of the most popular stabilized methods. However, the use of SUPG still leads to localized numerical wiggles in the vicinity of sharp solution gradients, which is often encountered in the 3D mold-filling simulation of LCM for thick parts. In this study, we propose to use the flux-corrected transport (FCT) based FEM to solve a set of highly convective transport equations. The numerical examples presented in this paper demonstrate the excellent performance of FCT based FEM in suppressing spurious oscillations in the regions of steep solution-gradients as opposed to the numerical instability of SUPG in such regions. For the first time, the FCT based FEM combined with the control-volume method is employed to simulate the non-isothermal mold-filling process in LCM. We have developed a simulation code PORE-FLOW© based on the scheme proposed in the study. Numerical studies have proven the stability of the FCT based FEM while modeling the mold-filling process of LCM.     

Use of adsorbent beds for energy storage in drying of heating systems

Energy storage is an important feature of many solar energy systems. Because of the small temperature potentials available from flat plate collectors, large masses and volumes are involved when energy is stored by raising or lowering the temperature of a tank of fluid or bed of gravel. This paper proposes energy storage in the form of heat of adsorption in beds of adsorbent material. This is most readily achieved by nominating water as the adsorbate so that water vapour is transferred to or from the absorbent from the humid air flowing through the bed. The large heat of adsorption means that the adsorption of a small mass of water liberates a large amount of energy which mostly is transferred to the air stream. It is shown that adsorbing materials can occupy a much smaller volume than non-adsorbing materials for the same quantity of energy stored, and that thermal insulation can be dispensed with. Provided that the container is impervious to water vapour, energy can be stored indefinitely.     

Hybrid photovoltaic/thermal (PV/T) solar systems simulation with Simulink/Matlab

The purpose of this work consists in thermodynamic modeling of hybrid photovoltaic–thermal (PV/T) solar systems, pursuing a modular strategy approach provided by Simulink/Matlab.PV/T solar systems are a recently emerging solar technology that allows for the simultaneous conversion of solar energy into both electricity and heat. This type of technology present some interesting advantages over the conventional “side-by-side” thermal and PV solar systems, such as higher combined electrical/thermal energy outputs per unit area, and a more uniform and aesthetical pleasant roof area. Despite the fact that early research on PV/T systems can be traced back to the seventies, only recently it has gained a renewed impetus. In this work, parametric studies and annual transient simulations of PV/T systems are undertaken in Simulink/Matlab. The obtained results show an average annual solar fraction of 67%, and a global overall efficiency of 24% (i.e. 15% thermal and 9% electrical), for a typical four-person single-familiar residency in Lisbon, with p-Si cells, and a collector area of 6 m². A sensitivity analysis performed on the PV/T collector suggests that the most important variable that should be addressed to improve thermal performance is the photovoltaic (PV) module emittance. Based on those results, some additional improvements are proposed, such as the use of vacuum, or a noble gas at low-pressure, to allow for the removal of PV cells encapsulation without air oxidation and degradation, and thus reducing the PV module emittance. Preliminary results show that this option allows for an 8% increase on optical thermal efficiency, and a substantial reduction of thermal losses, suggesting the possibility of working at higher fluid temperatures. The higher working temperatures negative effect in electrical efficiency was negligible, due to compensation by improved optical properties. The simulation results are compared with experimental data obtained from other authors and perform reasonably well.The Simulink modeling platform has been mainly used worldwide on simulation of control systems, digital signal processing and electric circuits, but there are very few examples of application to solar energy systems modeling. This work uses the modular environment of Simulink/Matlab to model individual PV/T system components, and to assemble the entire installation layout. The results show that the modular approach strategy provided by Matlab/Simulink environment is applicable to solar systems modeling, providing good code scalability, faster developing time, and simpler integration with external computational tools, when compared with traditional imperative-oriented programming languages.     

Extended-power pinch analysis (EPoPA) for integration of renewable energy systems with battery/hydrogen storages

An extended-power pinch analysis (EPoPA) is proposed as a means of extending the power pinch analysis (PoPA) for optimal design of renewable energy systems with battery and hydrogen storage (RES-BH). The EPoPA concept is based on the storage of wasted electricity that cannot be stored by the battery bank designed by PoPA. This energy is stored in the form of hydrogen and is discharged in the form of electricity when the external electricity source is needed. EPoPA graphical and numerical tools are introduced to determine the minimum required external electricity source, wasted electricity sources, and appropriate hydrogen storage system capacity of the RES-BH system during first and normal operation years. Furthermore, the integration of the RES-BH system with a diesel generator as a high reliable system is investigated in view point of economic. The optimal sizes of diesel generator and hydrogen storage system components, such as electrolyzer, fuel cell and hydrogen tank are obtained with the minimization of the total annual cost (TAC) of the system. The implementation results of the EPoPA tools on three possible case studies indicate that EPoPA, unlike other process integration methodologies such as PoPA, is able to optimally design RES-BH systems.     

Performance calculations for closed-loop air-to-water solar hybrid heating systems with and without a rock bed in the solar air heater

A transient analysis has been carried out on a hybrid solar water heater which comprises a rock bed air heater with optimum design parameters in conjunction with an air-to-water transverse fin shell-and-tube heat exchanger (mixed air and unmixed water type) in which cold water from the storage tank receives heat from the hot air coming out of the air heater which flows in the shell at right angles to the water flowing in the tubes. The system's performance has been evaluated for typical winter weather conditions in Delhi for different combinations of flow rates of air and water for different volumes of the water storage tank. No hot water is assumed to be withdrawn from the tank to serve the load. A comparative analysis of the system's performance with and without a rock bed in the air heater reveals about 11°C higher temperature of storage tank in the former at 50 kg/h m² air flow rate. With both the air heater types, although the system performance was observed to increase with the rates of air and water flow, no significant improvement in system performance was achieved at .     

A new real-time digital simulator of the turbine-alternator-gridsystem (STAR) for control apparatus closed-loop tests

A new generation of real-time digital simulator of the turbine-alternator-grid system (STAR) has been developed by ENEL-R and D-CRA in order to meet the demands of design review, commissioning test, preliminary assessment and final fine-tuning of excitation systems and voltage regulators, as well as of turbine actuators and speed governors. In particular, the electromechanical behavior of the overall turbine-alternator system, with respect to the electrical interconnected grid, may be theoretically studied, by using dynamic simulation models perfected with suitable details. The control systems performances can also be easily checked and fine-tuned, in presence of small and large perturbations, both in normal and in emergency operating conditions. The simulator STAR, which has been successfully used also for the specialists training, can be effectively considered as a real turbine-alternator system. In fact its inputs may be directly connected to the interfaces of the excitation system and turbine governor; moreover, the simulator provides in output the process variables with the suitable format requested by the different control apparatuses. The paper describes the main design topics of the STAR simulator, as mainly regards its hardware and software architecture and the model framework of the turbine (steam, hydro or gas), alternator (with static and rotating exciter) and grid interconnection. The structure of the excitation control system and turbine speed governor, as well as the parameters configuration, run-time simulation, and data visualization procedures are shortly described. Finally, the STAR performances are shown through significant transient responses     

Hierarchical design of Ni(OH)2/MnMoO4 composite on reduced graphene oxide/Ni foam for high-performances battery-supercapacitors hybrid device

Design and synthesis advanced battery-type electrode materials with outstanding electrical conductivity and remarkable theoretical specific capacity are crucial to enhance the comprehensive performances for battery-supercapacitors (SCs). Herein, Ni(OH)₂/MnMoO₄ composite on reduced graphene oxide/Ni foam (rGO/NF) was successfully fabricated through the hydrothermal method and potentiostatic electrodeposition (Ni(OH)₂/MnMoO₄/rGO/NF). The unique honeycomb structure and the efficient synergistic effects among MnMoO₄ and Ni(OH)₂ of the as-prepared battery type electrode, as well as outstanding electronic conductivity of the reduced graphene oxide, were beneficial to the enhanced electrochemically active sites and increased specific capacity. Ni(OH)₂/MnMoO₄/rGO/NF composite employed for SCs yielded the maximum specific capacity of 1329.1 C g⁻¹ and a superb cycle property of 86.8% during 5000 cycles. Furthermore, the battery-supercapacitor hybrid (BSH) device with the Ni(OH)₂/MnMoO₄/rGO/NF and active carbon (AC) as-prepared samples showed the energy density of 61.4 W h kg⁻¹ at the power density of 428.4 W kg⁻¹. The capacity retention of the as-fabricated hybrid device reached 96.4% over 7000 cycles. Those consequences tested that the Ni(OH)₂/MnMoO₄/rGO/NF composite should be the promising category of battery-type electrodes materials of the next generation energy storage devices for the high-performances SCs.     

Novel (Ir,Sn,Nb)O2 anode electrocatalysts with reduced noble metal content for PEM based water electrolysis

A solid solution of IrO₂, SnO₂ and NbO₂, denoted as (Ir,Sn,Nb)O₂, of compositions (Ir_1−2xSn_xNb_x)O₂ with x = 0, 0.125, 0.20, 0.25, 0.30, 0.35, 0.40, 0.425 and 0.50 has been synthesized by thermal decomposition of a homogeneous mixture of IrCl₄, SnCl₂·2H₂O and NbCl₅ ethanol solution coated on pretreated Ti foil. The (Ir,Sn,Nb)O₂ thin film of different compositions coated on Ti foil has been studied as a promising oxygen reduction anode electrocatalyst for PEM based water electrolysis. It has been identified that (Ir,Sn,Nb)O₂ of composition up to x = 0.30 [(Ir_0.40Sn_0.30Nb_0.30)O₂] shows similar electrochemical activity compared to pure IrO₂ (x = 0) resulting in ∼60 mol.% reduction in noble metal content. On the other hand, (Ir,Sn,Nb)O₂ of composition x = 0.20 [(Ir_0.20Sn_0.40Nb_0.40)O₂] shows only 20% lower activity compared to pure IrO₂ though the noble metal oxide, IrO₂ loading is reduced by 80 mol.%. The accelerated life test of the anode electrocatalyst for 48 h followed by elemental analysis of the electrolyte shows that (Ir,Sn,Nb)O₂ improves the stability of the electrode in comparison to pure IrO₂ electrocatalyst in oxygen reduction processes. The excellent electrochemical activity as well as long term structural stability of (Ir,Sn,Nb)O₂ during water electrolysis has been discussed using first-principles calculations of the total energies, electronic structures, and cohesive energies of the model systems.     

Rapid (practical) methodology for creation of fuel cell systems models with scalable complexity

In order to study various aspects of fuel cell systems, like a fuel cell propulsion system for transportation, several challenges arise: in actual real-world operation, as opposed to benchmark tests, the system is subject to a variety of non-stationary and environmental nuisance factors that are hard to monitor and control; investigating the system's behavior at the limits of its ranges while avoiding any adverse effects; due to sensor capabilities and costs, not every relevant variable can be monitored with sufficiently high temporal resolution.For these reasons, simulation tools are playing a crucial role in the analysis of these system aspects. The first step is therefore to create a mathematical representation of the system (a model) which can then be embedded into a simulation environment. To this end, a methodology is needed for the rapid creation of the mathematical representation of a system which is capable of overcoming the hurdles of dynamic and transient variables.Usually, knowledge-based modeling a system this complex takes several years to accomplish and still does not take nuisance factors into account. In contrast, the approach presented here can be finished within a fraction of that time. We propose to employ black-box adaptive modeling; the key issue in here, selecting an appropriate set of input features, can be solved by either applying iterative wrapper methods, or by making use of the automatic relevance detection technique that has been developed earlier within the framework of Bayesian neural networks. These procedures allow to easily scale the complexity of models in order to accommodate different constraints in terms of modeling effort, sensor availability and cost, and required model accuracy. Our approach can as well be used for the development of diagnostic models for on- and off-board diagnostics.     

Improved methods for the determination of drying conditions and fraction insoluble solids (FIS) in biomass pretreatment slurry

Accurate and precise chemical characterization of biomass feedstocks and process intermediates is a requirement for successful technical and economic evaluation of biofuel conversion technologies. The uncertainty in primary measurements of the fraction insoluble solid (FIS) content of dilute acid pretreated corn stover slurry is the major contributor to uncertainty in yield calculations for enzymatic hydrolysis of cellulose to glucose. This uncertainty is propagated through process models and impacts modeled fuel costs. The challenge in measuring FIS is obtaining an accurate measurement of insoluble matter in the pretreated materials, while appropriately accounting for all biomass derived components. Three methods were tested to improve this measurement. One used physical separation of liquid and solid phases, and two utilized direct determination of dry matter content in two fractions. We offer a comparison of drying methods. Our results show utilizing a microwave dryer to directly determine dry matter content is the optimal method for determining FIS, based on the low time requirements and the method optimization done using model slurries.     

Optical properties and stability of water-based nanofluids mixed with reduced graphene oxide decorated with silver and energy performance investigation in hybrid photovoltaic/thermal solar systems

The present work investigates the effect of the nanoparticles concentration on the optical and stability performance of a water-based nanofluid in solar photovoltaic/thermal (PV/T) systems experimentally and numerically. A novel nanofluid is formulated with the inclusion of the reduced graphene oxide decorated with silver (rGO-Ag) nanoparticles in water. Five different concentrations of nanoparticles in the range from 0.0005 to 0.05 wt% is suspended in water to prepare the samples. Optical properties are measured using UV-Vis. The UV-Vis absorption analysis reveals that all samples show consistent optical absorption coefficient (α) at higher value (more than 3 cm⁻¹) in the range of 1.5 to 4 eV. The application of optical filtration (OF) using water/rGO-Ag nanofluid in hybrid PV/T system presented more solar energy absorption through the OF. The hybrid system shows better performance at concentrations less than 0.0235 wt% compared to the PV system without integration with optical filtration. The hybrid solar PV/T system with OF using water/rGO-Ag nanofluid is able to produce thermal energy with efficiencies between 24% and 30%.     

我国热电冷三联产存在问题分析

热、电、冷三联产实现了能源的梯级利用,不但可以达到节约能源的目的,而且可以减少温室气体的排放,实现环保效益。该技术在国内外得到了广泛的发展和应用。从技术、节能、经济性等角度剖析了阻碍我国热、电、冷发展的主要问题,并提出了相应的解决措施。