Maximum Average Energy Research Articles

Experimental development, techno-economic and environmental analysis of a hybrid solar space heating system in a subtropical climate

Conventional modes of space heating are expensive and cause greenhouse gas emissions resulting in global warming. In this paper, an experimental analysis of a hybrid solar space heating system consisting of flat plate collectors (FPC) and evacuated tube collectors (ETC) along with a convective radiator is presented. Techno-economic and environmental analysis of the system is performed under real winter conditions in a subtropical climate. The experimental setup is designed such that flat plate collectors and evacuated tube collectors can also be operated separately for comparative analysis with the hybrid system (HC). The experimental results show that ETC achieved a maximum average energy efficiency of 72 % followed by the hybrid collector (HC) and FPC with energy efficiencies of 61 % and 57 %, respectively. The maximum exergy efficiency for ETC, HC and FPC are 54 %, 42 % and 33 % respectively in the month of December with low ambient temperatures. The corresponding maximum sustainability index achieved by ETC, HC and FPC, is 1.76, 1.52 and 1.39 respectively. In addition, the panel radiator achieved a maximum heat gain of 1484 W with an average room temperature in the range of 16.4–24.3 ℃. The economic analysis shows that the benefit-to-cost ratio for the hybrid varies from 0.82 to 1.6 and the payback period varies from 8.9 to 7.41 years compared to the electric heater for an inflation rate of 6–13 %. About 38 % more life cycle cost is observed for electric heater as compared to HSSHS. Environmental analysis reveals that 99 % and 78 % more greenhouse gas emissions are caused by conventional heaters compared to hybrid systems. Thus, a hybrid arrangement of FPC and ETC can be more beneficial for space heating compared to individual installations of these low-temperature solar collectors.

Optimal Extreme Random Forest Ensemble for Active Distribution Network Forecasting-Aided State Estimation Based on Maximum Average Energy Concentration VMD State Decomposition

As the penetration rate of distributed generators (DG) in active distribution networks (ADNs) gradually increases, it is necessary to accurately estimate the operating state of the ADNs to ensure their safe and stable operation. However, the high randomness and volatility of distributed generator output and active loads have increased the difficulty of state estimation. To solve this problem, a method is proposed for forecasting-aided state estimation (FASE) in ADNs, which integrates the optimal extreme random forest based on the maximum average energy concentration (MAEC) and variable mode decomposition (VMD) of states. Firstly, a parameter optimization model based on MAEC is constructed to decompose the state variables of the ADNs into a set of intrinsic mode components using VMD. Then, strongly correlated weather and date features in ADNs state prediction are selected using the multivariate rapid maximum information coefficient (RapidMIC) based on Schmidt orthogonal decomposition. Finally, by combining the set of intrinsic mode functions of the ADNs state, calendar rules, and weather features, an ensemble FASE method based on the extreme random tree (ERT) ensemble for the ADNs based on cubature particle filtering (CPF) is developed. An optimization model based on mean absolute error and root mean square error is established to obtain the optimal integration strategy and final estimation results. Simulation verification is performed on the IEEE 118-bus standard distribution system. The results show that the proposed method achieves higher accuracy compared to other estimation methods, with root mean square errors of 1.4902 × 10−4 for voltage magnitude and 4.8915 × 10−3 for phase angle.

Orthogonally Polarized Dual-Wavelength Gain-Switched Ho:LuLiF4 Pulse Laser

A compact, orthogonally polarized, gain-switched a-cut Ho:LuLiF4 laser with intra-cavity pumping by a self-Q-switched Tm:YAP laser is demonstrated here for the first time. The π-polarization laser at 2052 nm and σ-polarization laser at 2066 nm were experimentally observed with the maximum output power values of 299 mW and 126 mW, respectively, and the two polarization directions were always kept mutually orthogonal as the pump power increased. The ratio of the output power between the two orthogonal polarization lasers was nearly 1:1 at a pump power of 18.4 W. The minimum pulse width of the Ho:LLF laser was 326 ns, the maximum repetition rate was 24 kHz, and the maximum average energy was 28 μJ.

Experimental Study of Coal Sample Damage in Acidic Water Environments

We investigated the effects of acidic and circumneutral water on coal samples by uniaxial compression, acoustic emission, and a series of physical tests. In acidic water, the coal samples were damaged, and their ultrasonic velocities decreased, as minerals such as kaolinite and calcite underwent dissolution. When the pH was < 7, the uniaxial compressive strength and elastic modulus decreased, while the duration of the residual strength stage tended to increase. The reactions were stronger at higher H+ concentrations and the number of large pores increased; there was a significant increase in the accumulated acoustic emission counts and maximum average energy near the unstable crack growth stage. The post-peak stage of the coal samples was characterized in the different acidic waters and the failure modes were identified by spectrum analysis. Acidic water damaged the weak areas of coal samples by complex physical and chemical reactions, which made direct tensile failure more likely when the coal samples were loaded.

Application of the Combined Teager-Kaiser Envelope for bearing fault diagnosis

Rolling element bearings are among the most important components of rotating machinery, being the interface between the stationary and the rotating parts. Bearing failures might cause accidents and unexpected machine breakdown. Therefore, there is an important need for novel condition monitoring techniques focusing towards early detection and accurate identification of emerging faults. The key aim of this paper is the proposal of the concept of Multiband Demodulation Analysis (MDA), performed using a bank of bandpass Gabor filters combined with the Teager-Kaiser Energy Separation Algorithm (ESA) for condition monitoring of rolling element bearings. The demodulation takes place in multiple frequency bands, following a multiband analysis scheme, in order to isolate the strongest modulation components in each band. Finally, a maximum average energy tracking process over the various frequency bands is used to yield short-time measurements of the multiband signal modulation energy and the demodulated instant amplitude and frequency. The method is applied, tested and evaluated on vibration signals, captured on two test rigs and its performance is compared with a state of the art diagnostic approaches, the Kurtogram and the empirical mode decomposition, achieving promising results.

A comparative study of the performance of a novel helical direct flow U-Tube evacuated tube collector

The direct flow evacuated tube collector (ETC) is a highly efficient solar energy collector. It has the advantage of using forced convection, which increases its efficiency compared to other ETC systems. In the present study, a helical tube ETC is proposed and compared to the traditional U-tube ETC. The helical tube was designed with three, seven, and eleven helical steps over the 1.8 m length of the ETC and was tested at flow rates of 10, 20, and 30 l/h. The helical tube ETC achieved energy and exergy efficiency enhancements over the traditional U-tube ETC of 6.1%, and 3.8%, respectively, at the 10 l/h flow rate using the eleven-step helical tube ETC. However, the maximum average energy and exergy efficiencies of 38.6% and 18%, respectively, were achieved in the seven-step helical tube ETC at the highest flow rate of 30 l/h. The cost analysis revealed that using the three-step helical tube instead of a traditional U-tube will produce hot water with a cost of 0.012 $/kWh at the 10 l/h flow rate, while the maximum cost will reach 0.15 $/kWh for the eleven-step helical tube using the 30 l/h flow rate.

Experimental Investigation of Flood Energy Dissipation by Single and Hybrid Defense System

In this study, a series of laboratory experiments were conducted to investigate the energy loss through the hybrid defense system (HDS) in the order of dike, moat, and emergent vegetation in steady subcritical flow conditions. The results of HDS were compared with a single defense system (SDS) comprising only vegetation (OV). The dimensions of dike were kept constant while two different shapes (trapezoidal and rectangular) of moat were considered. The impacts of vegetation of variable thickness and density were investigated. Two combinations of HDS were investigated including the combination of dike and vegetation (DV) and the combination of dike, moat, and vegetation (DMV). The effect of backwater rise due to the vegetation, hydraulic jump formation and the impact of the arrival time of floodwater on energy dissipation were investigated. It was observed that on the upstream side of obstructions, the backwater depth increased by increasing the Froude number in both the SDS and HDS. The hydraulic jump observed in HDS was classified and the energy dissipation due to it was calculated. Under various conditions investigated in this paper, the maximum average energy dissipation was 32% in SDS and 46% in HDS. The trapezoidal moat performed better than rectangular moat as energy dissipater. The delay time was also greater with trapezoidal moat as compared to that in rectangular one. The maximum delay time was 140 s in the case of HDS. Hence, the hybrid defense system offered maximum resistance to the flow of water, thus causing a significant energy loss. For each case of SDS and HDS, empirical equations were developed by regression analysis to estimate the energy dissipation amounts.

Comparison Between TDMA and Random Multiple-Access Energy-Harvesting Networks Under Security Constraints

We study the maximum average energy transfer rate at a wireless charging energy-harvesting receiver when multiple transmitting nodes communicate their confidential information to a data receiver. We investigate both the time-division multiple-access (TDMA) and the random multiple-access (RMA) schemes and compare their performance. We address the question of which multiple-access scheme can maximize the average energy transfer rate under secrecy constraints. We also investigate the cases of the RMA scheme with equal access probabilities and the TDMA scheme with equal time-slot assignment probabilities.

Cycled pulsing to mitigate thermal damage for multi-electrode irreversible electroporation therapy

Purpose: This study evaluates the effects of various pulsing paradigms, on the irreversible electroporation (IRE) lesion, induced electric current, and temperature changes using a perfused porcine liver model.Materials and methods: A 4-monopolar electrode array delivered IRE therapy varying the pulse length and inter-pulse delay to six porcine mechanically perfused livers. Pulse paradigms included six forms of cycled pulsing schemes and the conventional pulsing scheme. Finite element models provided further insight into the effects of cycled pulsing on the temperature and thermal injury distribution.Results: ‘Single pulse cycle with no interpulse delay’ deposited maximum average energy (2.34 ± 0.35 kJ) and produced the largest ratio of thermally damaged tissue area and IRE ablation area from all other pulse schemes (18.22% 8.11, p < .0001 all pairwise comparisons). These compared favorably to the conventional algorithm (2.09 ± 0.37 kJ, 3.49% 2.20, p < .0001, all comparisons). Though no statistical significance was found between groups, the ‘5 pulse cycle, 0 s delay’ pulse paradigm produced the largest average IRE ablation cross sectional area (11.81 ± 1.97 cm2), while conventional paradigm yielded an average of 8.90 ± 0.91 cm2. Finite element modeling indicated a ‘10 pulse cycle, 10 s delay’ generated the least thermal tissue damage and ‘1 pulse cycle, 0 s delay’ pulse cycle sequence the most (0.47 vs. 3.76 cm2), over a lengthier treatment time (16.5 vs. 6.67 minutes).Conclusions: Subdividing IRE pulses and adding delays throughout the treatment can reduce white tissue coagulation and electric current, while maintaining IRE treatment sizes.

Ultrasound follow up: Is an undetected spontaneous expulsion of stone fragments a sign of extracorporeal shock wave treatment failure in kidney stones?

After extracorporeal lithotripsy (SWL), a spontaneous expulsion of fragments is often reported. The aim of this study is to demonstrate the presence of a stone free status or the presence of clinically insignificant residual fragments (CIRFs, defined as "asymptomatic, noninfectious, ≤ 3 mm fragments") in people with undetected spontaneous expulsion. Between May and September 2017, we performed a total of 87 treatments. The device used was a Storz Medical Modulith® SLK. All the patients were treated in prone position to reduce respiratory movements and underwent sonography before and four to eight weeks after the treatment. An in line ultrasound targeting was possible with all the stones. People lost to follow up or with ureteral stones were excluded. Patients were divided in groups according to gender, previous treatments, stone diameter and position. We enrolled 73 patients. 57 patients had a single stone and 16 multiple stones. A mean number of 3044 shock waves was administered with a maximum average energy of 0.68mj/mmq. At follow up, 41 patients (56.2%) were found stone free or with CIRFs. The association between undetected expulsion and the presence of CIRFs is considered to be not statistically significant (p = 0.89). Among patients with CIRFs, 25/41 didn't report expulsion. Taking in account the groups our population was divided in, according to gender (p = 0.36), previous treatments (p = 0.44), stone diameter (p = 0.28) and stone position (p = 0.35), the association between undetected spontaneous expulsion and presence of CIRFs was never statistically significant. An undetected spontaneous expulsion of stone fragments could not be considered a sign of SWL treatment failure. The association between undetected expulsion and presence of CIRFs is never statistically significant if gender of the patients, previous treatments, stone diameter and stone position are considered.

Combined pre-detection and sleeping for energy-efficient spectrum sensing in cognitive radio networks

In this paper, we propose a cooperative spectrum sensing scheme including a combined pre-detection and sleeping policy. In the scheme, the designed pre-detection sub-phase is applied at the beginning of the detection of the presence of a primary user, where all sensing nodes are involved to improve the detection performance. The sleeping policy is applied for each sensing node respectively at the end of the pre-detection sub-phase and the beginning of the transmission of the local detection results, in order to decrease sensing energy consumption. We formulate the problem of minimizing the maximum average energy consumption per sensing node in Rayleigh fading channels, considering the constraints of the required global detection and false alarm probabilities and the tolerable interference caused to the primary user. Numerical results show that the scheme achieves significant energy saving as compared to a scheme that includes only a sleeping policy and does not consider pre-detection.

Energy and exergy analysis of a PCM-based solar powered winter air conditioning using desiccant wheel during nocturnal

In this paper, heating and humidification of air for space have been carried out by using a phase change material (PCM)-based solar-powered desiccant wheel air conditioning (SPDWAC) in winter. The analysis of the setup has been done at different air flow rates. At low and high air flow rates, system has mean thermal coefficient of performance of 0.121 and 0.172, respectively, and mean exergy efficiency of 0.0787 and 0.0846, respectively. The mean thermal coefficient of performance of the system at high air flow rate (127.23 kg h-1) is 1.42 times the low air flow rate (63.62 kg h-1) and average exergy efficiency of the system at high air flow rate is 1.07 times the low air flow rate. It is observed that with an increase in air flow rate, efficiency of the evacuated tube solar air collector (ETSAC) increases. The average efficiency of the ETSAC at high air flow rate is 15.60%. The maximum average energy efficiency (17.80%) and exergy efficiency (17.08%) of the PCM storage system have been obtained at high air flow rate. The overall performance of the system showed that the use of PCM storage is feasible to run the system in winter during the hours of darkness.

Hierarchical Ni–Co Hydroxide Petals on Mechanically Robust Graphene Petal Foam for High‐Energy Asymmetric Supercapacitors

A hierarchical structure consisting of Ni–Co hydroxide nanopetals (NCHPs) grown on a thin free‐standing graphene petal foam (GPF) has been designed and fabricated by a two‐step process for pseudocapacitive electrode applications. The mechanical behavior of GPFs has been, for the first time to our knowledge, quantitatively measured from in situ scanning electron microscope characterization of the petal foams during in‐plane compression and bending processes. The Young's modulus of a typical GPF is 3.42 GPa, indicating its outstanding mechanical robustness as a nanotemplate. The GPF/NCHP electrodes exhibit volumetric capacitances as high as 765 F cm−3, equivalent to an areal capacitance of 15.3 F cm−2 and high rate capability. To assess practical functionality, two‐terminal asymmetric solid‐state supercapacitors with 3D GPF/NCHPs as positive electrodes are fabricated and shown to exhibit outstanding energy and power densities, with maximum average energy density of ≈10 mWh cm−3 and maximum power density of ≈3 W cm−3, high rate capability (a capacitance retention of ≈60% at 100 mA cm−2), and excellent long‐term cyclic stability (full capacitance retention over 15 000 cycles).

Weather Data Analysis of Solar Panels and a Wind Turbine From an Exergetic Point of View Based on Experimental Values over One Year

In this article the weather data of solar modules and a wind turbine in the Riyadh region, Saudi Arabia were analyzed. In the analysis, experimental values obtained from the system operation over 12 representative days of each month in the period of January to December 2011 were utilized. The wind turbine and the solar panels considered for the assessment are subparts of a hybrid wind–PV system with hydrogen storage, installed at the Sustainable Energy Technology (SET) Center, Mechanical Engineering Department, King Saud University, Riyadh, Saudi Arabia. Various parameters, such as global irradiance, exergy of solar radiation, exergy losses and exergy efficiency of solar modules, and velocity of wind were analyzed and compared at the location. Among the selected days, the maximum average value of the solar irradiance was 631.49 Wm–2 on July 7 and the corresponding average exergy rate value of the solar radiation was 583.82 Wm–2 with a conversion efficiency of 4.38%, while the absolute exergy losses was calculated to be 95.61%. The minimum average value of the irradiance and the exergy of solar radiation were measured and calculated to be 350.45 and 326.56 Wm–2, respectively, with an exergy efficiency of 8.42% on a cloudy day in May 2011. It was calculated through the wind data analysis that the maximum average wind power density available on November 1, 2011 was 807.51 Wm–2, while the maximum average energy available to the wind turbine for the conversion into the useful output of the inverter was 53,855.74 Wh. It was also determined that the minimum value of the power density was 22.24 Wm–2 on January 3, 2011 and the corresponding maximum energy available to the turbine for conversion was 1,483.22 Wh. It is expected that the data analysis will be very helpful for the future solar energy utilization and developing exergy wind maps for the region to make an efficient use of these renewable energy sources.

To AND or To OR: On Energy-Efficient Distributed Spectrum Sensing With Combined Censoring and Sleeping

Distributed spectrum sensing improves the detection reliability of a cognitive radio network but generally comes at the price of a large power consumption. Since cognitive radios are generally low-power sensors with limited batteries, a combined censoring and sleeping scheme is considered as an energy-efficient algorithm for distributed spectrum sensing. Each sensor switches off its sensing module with a specific sleeping rate. When the sensor is on, a censoring policy is employed to send the sensing result to the fusion center. The result is only transmitted, if it is deemed to be informative. Hence, the energy consumption of each sensor, including the sensing and transmission energies, is reduced. The underlying sensing parameters are derived by minimizing the maximum average energy consumption per sensor subject to a lower-bound on the global probability of detection and an upper-bound on the global probability of false alarm. We analyze the problem for the OR and the AND rule and provide a performance analysis for a case study based on the IEEE 802.15.4/ZigBee standard. It is shown that the combined censoring and sleeping scheme achieves a significant energy saving compared to the case where no censoring or sleeping is taken into account.

Wireless Information Transfer with Opportunistic Energy Harvesting

Energy harvesting is a promising solution to prolong the operation of energy-constrained wireless networks. In particular, scavenging energy from ambient radio signals, namely wireless energy harvesting (WEH), has recently drawn significant attention. In this paper, we consider a point-to-point wireless link over the narrowband flat-fading channel subject to time-varying co-channel interference. It is assumed that the receiver has no fixed power supplies and thus needs to replenish energy opportunistically via WEH from the unintended interference and/or the intended signal sent by the transmitter. We further assume a single-antenna receiver that can only decode information or harvest energy at any time due to the practical circuit limitation. Therefore, it is important to investigate when the receiver should switch between the two modes of information decoding (ID) and energy harvesting (EH), based on the instantaneous channel and interference condition. In this paper, we derive the optimal mode switching rule at the receiver to achieve various trade-offs between wireless information transfer and energy harvesting. Specifically, we determine the minimum transmission outage probability for delay-limited information transfer and the maximum ergodic capacity for no-delay-limited information transfer versus the maximum average energy harvested at the receiver, which are characterized by the boundary of so-called outage-energy region and region, respectively. Moreover, for the case when the channel state information (CSI) is known at the transmitter, we investigate the joint optimization of transmit power control, information and energy transfer scheduling, and the receiver's mode switching. The effects of circuit energy consumption at the receiver on the achievable rate-energy trade-offs are also characterized. Our results provide useful guidelines for the efficient design of emerging wireless communication systems powered by opportunistic WEH.

Monte Carlo simulation of the hole transport properties for wurtzite GaN

The simulation of the hole transport properties of wurtzite phase GaN are performed by the full band ensemble Monte Carlo approach. The band structure data of GaN used in the simulation are obtained by the empirical pseudopotential method. The scattering mechanisms included in the simulation are acoustic phonon scattering, optical phonon scattering, polar optical phonon scattering, piezoelectronic scattering, ionized impurity scattering, as well as the intervalley scattering. The dependence of the hole average drift velocity and average energy in three main symmetry directions for wurtzite GaN on the electric field are obtained. At room temperature, the velocity-field relation shows the non-saturated characteristics. The maximum drift velocity is about 6×106 cm s-1, and the maximum average energy is 0.12 eV in the range of the field of this work. These values are much smaller than the corresponding parameters of the electrons in GaN. Furthermore, the dependence of the diffusion mobility on the impurity density is reported.

A statistical model of auroral ion precipitation

The average global characteristics of precipitating auroral ions were determined using the data from the SSJ/4 detectors on the F6 and F7 satellites of the Defense Meteorological Satellite Program (DMSP). For this study the high‐latitude region was divided into spatial elements in magnetic local time (MLT) and corrected geomagnetic latitude (CGL). One such spatial matrix was created for each of seven levels of magnetic activity as defined by Kp. Approximately 26.5 million, individual, 1‐s spectra were used to determine the average ion spectrum over the energy range from 30 eV to 30 keV in each spatial zone and at each level of activity. Where appropriate, the spectra were extrapolated to 100 keV to provide a more complete estimate of the total integral energy flux, number flux, and average energy. The global patterns of the integral energy flux, integral number flux, and average energy derived from the average spectra vary smoothly with latitude, MLT, and activity. For a given Kp value the higher levels of integral energy flux occur in C‐shaped regions symmetric about a meridian running prenoon to premidnight. The maximum integral energy flux is found premidnight; the minimum peak integral energy flux in latitude is found prenoon. Except in the prenoon region, the overall level of integral energy flux increases with Kp with the premidnight maximum increasing by a factor of 6.1 from Kp = 0 to Kp ≥ 6−. The maximum integral number flux is centered at noon and is taken to be the center of the cusp. The maximum value does not vary significantly with activity, although its location moves to lower latitude with increasing Kp. A minimum in the average energy also occurs in the noon meridian, several degrees poleward of the integral number flux maximum. The separation in latitude between the integral flux maximum and the average energy minimum of the cusp increases with Kp. The maximum average energy occurs on the eveningside of the oval near the equatorward boundary of the ion precipitation and shifts toward noon with increasing activity. The average integral number flux for the precipitating auroral ions is 1‐2 orders of magnitude less than that for the precipitating auroral electrons at all latitudes, MLTs, and activities. The integral energy flux of the ions, on the eveningside of the oval, can equal or exceed that for the electrons near the equatorward edge of the auroral region. Integrated globally, the ratio of the ion to electron number flux varies from 0.024 to 0.015 over the range of activity from Kp = 0 to Kp ≥ 6−. The ratio for the integral energy flux ranges from 0.11 to 0.17 with no trend in activity.

Maximum Average Energy Density as the Criterion for Phase Transition in Thin Superconductive Films

For recent experimental results on thin superconductive films, the maximum average energy density as a macroscopic criterion of superconductivity is in better agreement with observed behavior than are any of the earlier criteria—maximum magnetic field, maximum current density, or maximum energy density. The earlier criteria are briefly reviewed, and characteristic formulas and critical curves are applied to an example for comparison with the proposed criterion. To determine the full significance of the proposed criterion, further experimental and theoretical work is needed.