Half-cycle Time Research Articles

Zn-anode stability in additive added perchlorate electrolyte for aqueous Zn-MnO2 battery

Extensive research has been conducted on aqueous Zn-MnO2 batteries in the most common ZnSO4 electrolyte. However, the present study focuses on Zn anode stability and subsequent pairing with the commonly utilized MnO2 cathode in a low-concentration aqueous Zn (ClO4)2 electrolyte containing an organic additive, triethyl phosphate (TEP). The structural stability of Zn anodes in optimized additive-added and additive-free electrolytes is analyzed by assembling series of Zn∥Zn symmetry cells under various electrochemical conditions with varying depth of discharges between 20 and 60 %. As such, additive added electrolyte stabilizes the Zn anode over 250 h under high areal capacity/low areal current density of 38.3 mAh cm−2/11.3 mA cm−2 with 60 % depth of discharge at long half-cycle time of 29.5 h. The Zn-MnO2 paired cells in the Zn (ClO4)2 electrolyte with and without additives registered reversible capacities of 262 and 247 mAh g−1, respectively, at 0.05 A g−1. These electrochemical features are completely different from those of the common ZnSO4 electrolyte, whose electrochemical mechanism is still a subject of debate.

Correlation of interfacial and dielectric characteristics in atomic layer deposited Al2O3/TiO2 nanolaminates grown with different precursor purge times

Considering the potential applications of Al2O3/TiO2 nanolaminates (ATA NLs) in storage capacitors, device-grade ATA NLs are fabricated using an ALD system, wherein the effect of precursor purging time on interfacial, and dielectric properties is thoroughly investigated. With an increase in half-cycle purging time from 2 to 4 s, the observed improvement in interface quality and sublayer density of these NLs is ascribed to the efficient removal of reaction by-products and impurities. Moreover, with an increase in purge time from 2 to 4 s, the increase in dielectric constant and concurrent decrease in dielectric loss from ∼132 to 154 and from ∼0.29 to 0.2, respectively, are primarily assigned to the improvement in sublayer conductivity contrast assisted Maxwell–Wagner interfacial polarization across Al2O3/TiO2 interfaces. The NL based devices fabricated at 4 s purging time, exhibited a capacitance density of ∼18.94 fF/μm2, low equivalent oxide thickness of ∼1.82 nm, and reduced leakage current density of ∼3.04 × 10−5 A/cm2 at 2 V applied bias, which demonstrates its suitability as high-k materials for energy storage applications. Furthermore, this study not only gives an insight of the purging time induced growth chemistry of ATA NLs but also explores the possibility of improving its dielectric performance essential for multifaceted applications.

Experimental studies on a closed cycle compressor operated metal hydride based cooling system with large hydrogen inventory

The current manuscript reports the experimental results of a closed loop metal hydride (MH) based compressor driven cooling system (CDCS) employing large-scale reactors. Two identical tube bundle reactors (TBR) with 19 MH tubes were designed, constructed and packed with 26.5 kg La0.8Ce0.2Ni5 alloy each for the experiments. The TBR modules were coupled with a custom-built compressor to provide cooling effect in quasi-continuous mode of operation. The compressor was tested to operate smoothly up to a hydrogen flow rate of 0.5 g. s−1 in the temperature range of 10–35 °C, yielding pressure ratio up to 12.8. Test runs were performed by altering refrigeration temperature (10–20 °C), sink temperature (30–35 °C), and half-cycle time (120–600 s). The maximum cooling power attained at 20 °C refrigeration temperature and 30 °C sink temperature was 1.44 kW, generating 537.3 kJ cooling within 600 s. The corresponding mean coefficient of performance (COP) and specific cooling power (SCP) were 0.95 and 36.4 W.kg−1 for 480 s half-cycle time. To avoid overheating of the compressor base, the half-cycle time was restricted to maximum of 600 s.

Performance evaluation of a two-stage air-cooled silica gel + water adsorption cooling system: Effect of key operational parameters

The primary objective of this work is to extract some design criteria of the upper-stage adsorber bed in a two-stage two-bed adsorption cooling system. The second objective is to experimentally investigate the effects of air-cooled heat sink, and hot water source temperatures on the chiller performance. These studies are important as the adsorber bed design together with the input operational parameters determines the chiller performance. It was observed that the performance indicators, namely, cooling capacity (CC) and coefficient of performance (COP) exhibit opposite trends with the reduction in the temperature of the sink where heat of adsorption is rejected. The performance parameters are evaluated for heat source temperatures in the range of 75–85 °C against different half-cycle times. The CC and COP are found to vary between 148 - 324 W and 0.09–0.11 respectively depending on the heat source temperature and half cycle time. The novelty of the present work is in providing experimental evidence on influence of heat source temperatures on two-stage adsorption chillers when air cooling is adopted for all heat rejections to the ambient. Another key finding is that the upper stage performance is critical because of smaller volume and lower heat transfer area available in it compounded by higher uptake differences across which it operates.

Three-dimensional numerical analysis of fin-tube desiccant-coated heat exchanger for air dehumidification in tropics

High-performance desiccant-coated heat exchangers (DCHEs) can be employed in air-conditioning systems to improve energy efficiency. While there are significant developments in experimental studies, theoretical approaches for analyzing the DCHE are impeded by the complex and coupled heat and mass transport mechanisms. Therefore, a 3D mathematical model has been developed in this work to study the dehumidification performance of a DCHE. Unlike other works reported in the literature, the developed model is able to simulate the complex coupling between heat and mass transfers in the entire volume of the heat exchanger. The model is calibrated and validated with experimental data, and a maximum discrepancy of ±8 % is recorded. A time-dependent study on the performance of the DCHE is carried out to understand the distribution of temperature, reaction rates, and water uptake in the heat exchanger. Effects of key influencing operational factors are investigated and discussed. It is indicated that the DCHE enters a stable performance state regardless of its initial adsorption state. The regeneration time should be equal to the dehumidification time to optimize the performance. A higher thermal COP is achieved under lower cooling/regeneration temperature, lower air flowrate, and shorter half-cycle time, while higher inlet air humidity ratio. Higher coated desiccant mass also provides a higher thermal COP, but this enhancement levels off once the coating grows. For DCHEs with less coating, reducing cycle time is recommended over increasing the coating amount.

Water-rich conditions during titania atomic layer deposition in the 100 °C-300 °C temperature window produce films with TiIV oxidation state but large H and O content variations

Titania films prepared by atomic layer deposition attract great attention due to the widespread application of the oxide as a photocatalytic material, or more recently, as a promising charge storage material for lithium or proton batteries. We implement here advanced tools (Ion Beam Analysis and X-ray Photoelectron Spectroscopy, aided by Ellipsometry and X-ray Diffraction) to characterize films grown in the 100 °C-300 °C temperature window, using tetrakis(dimethylamino)titanium (TMDAT) as the metal precursor and water vapor as the oxidant. We examine the outcomes of the ALD process as a function of the deposition temperature, applying equal oxidant and precursor half-cycle time lengths, which contrasts with common deposition processes where the water half-cycle is considerably shorter than that of the metal precursor. Under the present ALD scheme, n-type conductive films are obtained where the oxidation state of titanium is overwhelmingly TiIV at all temperatures, while the hydrogen content (O/Ti ratio) varies considerably, from ∼ 15 at% (∼1.8) at 100 °C to ∼ 3 at% (∼2) at 300 °C. The ideality of the ALD process is discussed through the identification of nitrogen-containing molecules detected at the oxide surfaces. By extending the structural and compositional range of ALD titania films, new opportunities of application are expected to appear.

Experimental Performance Analysis of Adsorption Modules with Sintered Aluminium Fiber Heat Exchangers and SAPO-34-Water Working Pair for Gas-Driven Heat Pumps: Influence of Evaporator Size, Temperatures, and Half Cycle Times

A major challenge for gas-driven adsorption heat pumps is the production of compact, efficient, and cost-effective adsorption modules. We present the experimental data of a design based on sintered aluminum fiber heat exchangers, a technology currently under development. The adsorption module presented here is the result of the downsizing of a larger module. The downsized module has an adsorption heat exchanger that is 60% of the size of the larger-scale component, and an evaporator-condenser that is only 30% of the size of the larger-scale component. It is designed to fit the heating requirements of a wall-hung heat pump for a single-family home. For the first time, a comprehensive experimental study of the influence of half-cycle time, evaporator and adsorption temperature, and driving temperature on the efficiency and power of the module is presented. At temperature conditions relevant for the application of a gas-driven adsorption heat pump, i.e., evaporator temperature < 10 °C and adsorption temperature > 30 °C, we found that the downsizing has its price in terms of a higher thermal capacity of the components in relation to the adsorbent mass (9.6 kJ/(kg∙K) for ‘Size S’) vs. 5.6 kJ/(kg∙K) for ‘Size L’). We carried out an evaluation of heat and mass transfer resistances to compare the ‘Size L’ module directly with the ‘Size S’ module. Both modules have nearly the same volume-scaled heat and mass transfer resistances of 0.012 dm3 K/W (adsorption heat exchanger during adsorption) and 0.005 dm3 K/W (evaporator–condenser during evaporation), and consequently a very similar volumetric power density. This evaluation proves the applicability and the consistency of the concept of heat and mass transfer resistances, and the scalability of this adsorption module technology.

Aluminium fumarate metal-organic framework coating for adsorption cooling application: Experimental study

• Mechanical properties of aluminium fumarate coating were experimentally tested. • Effect of coating thickness was investigated through a COMSOL model. • Operating conditions were investigated through an experimental parametric study. • Performance of aluminium fumarate coated and packed systems were compared. • Aluminium fumarate coated system outperformed packed one in cooling applications. This study discusses integrating aluminium fumarate metal-organic framework (MOF) as a coated layer instead of conventional packing to improve the adsorption system performance. The mechanical strength of the MOF coating layer was tested showing enhanced heat transfer properties and high durability. An experimental parametric study was conducted where parameters such as half-cycle time, evaporator water inlet, adsorption bed water inlet, condenser water inlet and desorption bed inlet temperatures were investigated and the coated heat exchanger performance was compared to conventional packing. Results showed that the aluminium fumarate coated heat exchanger had an optimum half-cycle of 500 s which is shorter than the packed one which was 900 s. Also, at a cycle time of 1000 s, the aluminium fumarate coated heat exchanger produced 600 W kg 1 which is three folds of what was produced from the packed one. The significant enhancement in the specific cooling power highlights the potential of integrating aluminium fumarate as a coated layer instead of packing.

Dynamic simulation of high-purity twin-bed N2-PSA plants

At present, nitrogen production from air by pressure swing adsorption (PSA) is simulated almost exclusively at low product purity levels (< 99% N2). However, with increasing global demand for highly purified gases provided by energy-efficient separation processes the requirement for either extensive experimental research in the high-purity range or predictive computer simulations arises. This paper presents a mathematical model of a twin-bed PSA plant equipped with a carbon molecular sieve (Shirasagi MSC CT-350) for the generation of high-purity nitrogen (99.9–99.999% N2). The model is implemented in the process simulator Aspen Adsorption™. The influence of operating conditions as well as the cycle organisation on the process performance is validated, especially the influence of pressure, temperature, half-cycle time, purge flow rate, and cutting time. The precision of the performance prediction by numerical simulations is critically discussed. Based on the new insights efficiency improvement strategies with a focus on reduced energy consumption are introduced and discussed by means of radar charts.

Parametric investigation of the desalination performance in multichannel membrane capacitive deionization (MC-MCDI)

Recently, multichannel membrane capacitive deionization (MC-MCDI) has garnered significant attention due to its remarkable desalination performance over traditional CDI systems. However, for implementation in practical desalination applications, significant advances in the desalination performance of MC-MCDI are still needed, especially in enhancing the engineering design as well as understanding and optimizing the operating conditions. In this study, we propose an innovative approach to enhance the desalination performance of MC-MCDI by optimizing the operational conditions, such as the half-cycle time (HCT) for the charging step, operational cell voltage, salinity of the electrolyte, and feed flow rate. An optimized HCT (3 min) and the reverse-voltage mode (1.2 V and −1.2 V for charging and discharging) led to an increase in cumulative salt adsorption capacity (cSAC) of 49 mg/g, which was calculated based on the total amount of removed ions over 30 min of charging time. Furthermore, a significant cSAC of 160 mg/g was achieved with a highly saline electrolyte in the side channel (500 mM NaCl), while the change in the feed flow rate could maximize the ion removal rate of 0.035 mg/g/s. With these optimized operational conditions, MC-MCDI is highly stable over 100 cycles with an average charge efficiency of 96%. These results provide valuable insight into how desalination performance can be drastically enhanced through judicious engineering of the system, and selection of operational conditions. Finally, these results suggest that MC-MCDI has a high potential to become a remarkably effective cell design for industrial and environmental applications. Also, we emphasize the generality of our electrochemical configuration, which can be adapted also with novel electrode materials that can further enhance the overall system performance.

Uninterrupted power supply to BESS based microgrid system using adaptive reclosing approach

As more than 80% of faults on overhead lines are temporary (transient) in nature which is caused due to lightning strikes, momentary bird or tree limb contact, wind bringing conductors in contact, etc. These type of faults gets cleared by itself in a short duration. But the use of a conventional reclosing scheme results in an outage time which is much larger than the actual fault duration. This is due to the use of fixed dead times in conventional reclosing schemes. This unnecessary outage results in increased consumption of stored energy of energy storage system causing considerable losses. This paper proposes an empirical mode decomposition based adaptive reclosing technique which can sense the exact instant of fault clearance and modify the prefixed dead time to an adaptive value. Within half cycle time period after fault clearance reclosing command can be issued for the breaker. The performance of the proposed algorithm is verified in a modified IEEE 13 bus distribution network model considering a battery energy storage system and hybrid distributed generators. The simulation and modelling of the various fault cases in the microgrid structure are done using EMTDC/PSCAD software.

Protection scheme for hybrid transmission system using fuzzy inference system and microcontroller

This paper presents a fuzzy inference system and microcontroller-based protection scheme for a combined underground (UG) cable and overhead (OH) transmission line system. The scheme detects, classifies, and locates the fault occurring either in an UG cable or OH transmission line network. Furthermore, the scheme identifies the faulty section. An existing Indian power network i.e., real power system network of C.G. state, consisting of 132 kV, 50 Hz power transmission network connecting Doma substation 220/132 kV to the 132/33 kV Gas Insulated Substation Rawanbhata through combined transmission network is considered. This real power transmission network is simulated by using MATLAB/Simulink software. In this paper, the hardware implementation is also carried out using an open-source hardware, Arduino, which consists of an Atmel 8-bit AVR microcontroller. Both the simulation and hardware results validate that the proposed scheme is accurately detecting, classifying, and locating the fault in less than a half cycle time. Moreover, the percentage error in determining the location of a fault is less than 0.7%.

Simulation on annual performance of solar adsorption heat pump system using composite natural mesoporous material in different metrological conditions

Abstract This paper presents research on the annual cooling performance of the solar adsorption heat pump (AHP), which applies a composite natural mesoporous material that is referred to as Wakkanai Siliceous Shale (WSS) as an adsorbent. One way to efficiently employ thermal energy is to reduce the sensible heat loss that occurs when changing the ad/desorption mode by extending the cycle time. The average temperature of the regeneration water for the half cycle time of 14 min was approximately 8.7 °C higher than that for the half cycle time of 8 min. In this case, the system with WSS + LiCl 20 wt% showed an increase in AHP cooling performance of approximately 15%. The higher adsorption capacity of the WSS composite enabled operation of the system with a longer cycle time. In terms of the annual operation of the AHP, although the achievable AHP cooling energy in Dubai was higher than that in Hawaii, much higher cost savings can be obtained in Hawaii than in Dubai because of the high electricity cost in Hawaii. The estimated payback periods in Hawaii and Dubai are 6.6 years and 15.6 years, respectively.

Performance optimization of a solar adsorption chiller by dynamically adjusting the half-cycle time

The half-cycle time effect on the performance of a solar single-stage dual-bed adsorption chiller, in Athens, Greece, in July, is investigated. The adsorption chiller coupled with the solar system is simulated, in real time, during the day for a) constant and b) adjusted half-cycle times and the system performance is monitored. In the former case, the half-cycle time is fixed, while in the latter one is dynamically adjusted according to the varying solar radiation intensity. Using a wide range of constant half-cycle times it is found that the maximum daily cooling capacity is obtained at some constant half-cycle time, which is larger than the optimum one of a single adsorption cycle. Similarly, using a wide range of adjusted half-cycle times, the one, providing the maximum cooling capacity is defined. The analysis is performed in a systematic manner through a proposed algebraic expression. It is found that the dynamically optimized adjusted half-cycle time operation mode provides about 12% higher daily and monthly cooling capacities than the corresponding maximum constant ones. This significant increase has been also confirmed for various incident solar radiation intensities.

A novel cycle for adsorption desalination system with two stages-ejector for higher water production and efficiency

In this paper, a novel hybridization between adsorption desalination cycle and two ejectors is proposed to increase the freshwater productivity by several folds. Silica gel/water is used as a working pair for this integration. The proposed hybrid system, donated as AD2EJ, has two sorption beds, two evaporators, two condensers, and two ejectors. Performance of the hybrid cycle is evaluated numerically in terms of specific daily freshwater production (SDWP) and Coefficient of Performance (COP). Mathematical models of the adsorption desalination cycle and ejectors are validated. The numerical results reveal that the optimal half-cycle time is about 400 s, at which the SDWP of the AD2EJ system is calculated as 23.0 m3 per ton of silica gel at a COP of 1.64 using a regeneration temperature of 85 °C. This amount of freshwater is 3 times higher than that of the basic adsorption desalination system (ADS). Further enhancement is achieved by linking the condenser and evaporator of the AD2EJ cycle via an internal heat recovery circuit. The SDWP of this system (AD2EJ-HR) is found to be 79.4 m3/ton at a COP of 2.22 at a regeneration temperature of 95 °C and 400 s half-cycle time.

Experimental investigation of temperature swing adsorption system for air dehumidification

Produce of continuous-dehumidified air free from traces of water vapour is essential in many industrial applications. Temperature swing adsorption (TSA) system and heatless based pressure swing adsorption (PSA) system are generally used to produce ultra-low dew point temperature dehumidified air. In this work, an internally heated TSA system is developed and investigated for its suitability for producing dehumidified air using molecular sieve desiccant. The system is evaluated by conducting experiments in three phases, such as screening, optimization, and validation, to identify the significant parameters using statistically designed experiments. The results indicated that the most critical parameters affecting the quality of the dehumidified air are desorption temperature and space velocity. The other parameters, half-cycle time, bed length and adsorption temperature are found to have meager effects on the system performance. A regression equation is also obtained for predicting the moisture content of the product air in terms of the significant parameters of TSA system. This equation also forms a basis for designing a TSA system to a large scale and provides the tool needed to optimize the drying sub-system within the framework of the drying system. The results show that the feed air can be dehumidified to a level ranging from −20 °C to −70 °C dew point temperature and is most suitable for variety of industrial applications. The performance indicators of TSA system is also compared with PSA system to establish a qualitative guideline for the selection of an appropriate method for air dehumidification purposes. TSA system can be effectively and economically employed to produce the dehumidified air with the operating pressure varying above 3 bar.

Integrating Feedback Control and Run-to-Run Control in Multi-Wafer Thermal Atomic Layer Deposition of Thin Films

There is currently a lack of understanding of the deposition profile in a batch atomic layer deposition (ALD) process. Also, no on-line control scheme has been proposed to resolve the prevalent disturbances. Motivated by this, we develop a computational fluid dynamics (CFD) model and an integrated online run-to-run and feedback control scheme. Specifically, we analyze a furnace reactor for a SiO2 thin-film ALD with BTBAS and ozone as precursors. Initially, a high-fidelity 2D axisymmetric multiscale CFD model is developed using ANSYS Fluent for the gas-phase characterization and the surface thin-film deposition, based on a kinetic Monte-Carlo (kMC) model database. To deal with the disturbance during reactor operation, a proportional integral (PI) control scheme is adopted, which manipulates the inlet precursor concentration to drive the precursor partial pressure to the set-point, ensuring the complete substrate coverage. Additionally, the CFD model is utilized to investigate a wide range of operating conditions, and a regression model is developed to describe the relationship between the half-cycle time and the feed flow rate. A run-to-run (R2R) control scheme using an exponentially weighted moving average (EWMA) strategy is developed to regulate the half-cycle time for the furnace ALD process between batches.

Experimental testing of aluminium fumarate MOF for adsorption desalination

Many researchers consider adsorption systems as a solution for global problems such as global warming and water scarcity. The experimental and numerical data available in literature are basically focusing on using conventional adsorbent materials such as silica gel and zeolites. Recently, metal-organic framework (MOF) materials have been proposed to substitute these conventional adsorbents. Nevertheless, the potential of MOFs has been only numerically investigated without any experimental data from a real system. To fill this research gap, this work presents for the first time the experimental testing of a MOF material, aluminium fumarate, and how it can enhance the performance of adsorption desalination systems. A parametric study to investigate the effect of different parameters such as chilled water, adsorption cooling water, condensation cooling water, desorption heating water temperatures and half cycle time on the performance of the adsorption system has been conducted. The suitability of the aluminium fumarate system for adsorption desalination was also assessed through analysing the quality of water produced from the system. Finally, the performance of the aluminium fumarate was also compared to conventional adsorbents such as silica gel. The superior performance of aluminium fumarate highlights the potential of the material in adsorption desalination application.

Multiscale computational fluid dynamics modeling of thermal atomic layer deposition with application to chamber design

This work develops a first-principles-based three-dimensional, multiscale computational fluid dynamics (CFD) model, together with reactor geometry optimizations, of SiO2 thin-film thermal atomic layer deposition (ALD) using bis(tertiary-butylamino)silane (BTBAS) and ozone as precursors. Specifically, an accurate macroscopic CFD model of the ALD reactor chamber gas-phase development is integrated with a detailed microscopic kinetic Monte Carlo (kMC) model that was developed in Ding et al. (2019), accounting for the microscopic lattice structure, atomic interactions and detailed surface chemical reactions. The multiscale information exchange and the transient simulation of the microscopic distributed kMC algorithms and the macroscopic CFD model are achieved through a parallel processing message passing interface (MPI) structure. Additionally, density functional theory (DFT)-based calculations are adopted to compute the key thermodynamic and kinetic parameters for the microscopic thin-film growth process. Recognizing the transient non-uniformity and the possibility to reduce the current ALD cycle time, the optimal configuration of reactor geometry is designed and evaluated including a showerhead panel adjustment and geometry modifications on reactor inlet and upstream. It is demonstrated that with suitable reactor chamber design the required BTBAS ALD half-cycle time can be reduced by 39.6%.

Experimental investigation of an adsorption air-conditioner using silica gel-water working pair

Compared to adsorption chiller, adsorption air-conditioner can get significant benefit of less cost and complexity when it directly provides chilled air for air-conditioning. Hence, adsorption air-conditioner is suitable for residential solar cooling application. A 3 kW adsorption air-conditioner using silica gel-water working pair is designed and manufactured and its performance is fully tested under different conditions. The experimental results show that cooling power and COP can reach 3.98 kW and 0.632, respectively, without obvious periodic fluctuation of chilled air outlet temperature and relative humidity. Smaller hot water flow rate can help to reduce unmatching between heating and cooling operation of adsorption bed. Optimal half cycle time of this adsorption air-conditioner is found to be 750 s. COP of adsorption air-conditioner is generally larger than that of adsorption chiller which provides chilled water because of higher evaporation temperature. Besides, cooling water outlet temperature can reach 39.9 °C which can meet the requirement of domestic hot water use. So that adsorption air-conditioner can be used for cooling and heating cogeneration in a residential solar cooling application and achieve good performance.