Ambient Load Research Articles

DEVELOPMENT OF 2.8-GHZ SOLAR FLUX RECEIVERS

We report the development of solar flux receivers operating at 2.8 GHz to monitor solar radio activity. Radio waves from the sun are amplified, filtered, and then transmitted to a power meter sensor without frequency down-conversion. To measure solar flux, a calibration scheme is designed with a noise source, an ambient load, and a hot load at <TEX>$100^{\circ}C$</TEX>. The receiver is attached to a 1.8 m parabolic antenna in Icheon, owned by National Radio Research Agency, and observation is being conducted during day time on a daily basis. We compare the solar fluxes measured for last seven months with solar fluxes obtained by DRAO in Penticton, Canada, and by the Hiraiso solar observatory in Japan, and finally establish equations to convert observed flux to the so-called Penticton flux with an accuracy better than 3.2 sfu.

Binary mixed-refrigerants for steady cooling temperatures between 80 K and 150 K with Joule–Thomson cryocoolers

Joule–Thomson (JT) cryocoolers operating with pure gases attain vapor–liquid equilibrium in the evaporator and yield a steady cooling temperature which depends solely on the pressure. Mixed gases often substitute the pure gases as the working fluid in order to allow lower pressure ratios and improved coefficient of performance; however, mixed refrigerants are known for their cooling temperature dependence on the ambient temperature and heat load. It is possible to control the cooling temperature via the compressor operating parameters, heating device at the evaporator, bypass ports for the fluid, and more. The present research aims to achieve a steady cooling temperature with mixed refrigerants in a manner similar to pure refrigerants; meaning, having enough phases to leave a single degree of freedom of the fluid thermodynamic state. Thus, by stabilizing the pressure a stable temperature is attained.The current study focuses on binary mixtures since they can be analytically investigated in a more convenient manner relative to multi-component mixtures. Nitrogen–ethane and nitrogen–propane mixtures are considered based on former research conclusions. The present research includes an analytical method for calculating the cooling temperature, a numerical method for calculating the cooling power of the JT cryocooler in order to evaluate whether the cooling temperature is feasible, and experimental data are presented to verify some of the calculated results.

Miniature horizontal axis wind turbine system for multipurpose application

A MWT (miniature wind turbine) has received great attention recently for powering WISP (Wireless Intelligent Sensor Platform). In this study, two MHAWTs (miniature horizontal axis wind turbines) with and without gear transmission were designed and fabricated. A physics-based model was proposed and the optimal load resistances of the MHAWTs were predicted. The open circuit voltages, output powers and net efficiencies were measured under various ambient winds and load resistances. The experimental results showed the optimal load resistances matched well with the predicted results; the MHAWT without gear obtained higher output power at the wind speed of 2 m/s to 6 m/s, while the geared MHAWT exhibited better performance at the wind speed higher than 6 m/s. In addition, a DCM (discontinuous conduction mode) buck-boost converter was adopted as an interface circuit to maximize the charging power from MHAWTs to rechargeable batteries, exhibiting maximum efficiencies above 85%. The charging power reached about 8 mW and 36 mW at the wind speeds of 4 m/s and 6 m/s respectively, which indicated that the MHAWTs were capable for sufficient energy harvesting for powering low-power electronics continuously.

The Direct Ethanol Fuel Cell Performance

The effect on performance of single direct ethanol cell due to ethanol solution concentrations (5%, 10% and 15% by volume, ambient temperature (and), continuously changing of ambient temperature ( and), load resistance ( and) and air circulation through the cell were investigated experimentally in this research. The results showed that fuel cells have a high performance at high concentration of ethanol solution, high ambient temperature or operated in the wide range of continuously changing of ambient temperature. The performance was measured by the amount of the initial voltage, current and power obtained from fuel cell. But increasing air circulation through the fuel cell does not affect the performance of cell. The voltage and power drop obtained from the fuel cell increase with varying resistance load. But the current decreases with increases resistance load.

An improved computational approach for thermal modeling of power transformers

Summary Proposed IEEE/ANSI differential equation governing top oil temperature rise, and its improvements are widely used in top oil temperature prediction and parameter estimation for power transformer loss of life calculation and diagnostic systems. Approximately, all transformer thermal models employ backward Euler method to achieve related set of equations (or regressors) and use least square error estimator for parameter estimation. In this paper, we applied a new numerical integration methodology to solve the differential equation of thermal model. Related matrix format is calculated based on the numerical integration rectangle rule. Some comparison metrics are introduced to verify and compare the proposed computation methodology with conventional discretized backward Euler equation. The proposed method was tested on simulated top oil temperature using measured ambient temperature and load data in the field. Results showed a significant and meaningful improvement in top oil temperature prediction. Variations of calculated parameters, in the presence of noise, presented the superiority and advantages of the proposed computational methodology. Copyright © 2014 John Wiley & Sons, Ltd.

Comparative Study of Five Maximum Power Point Tracking Techniques for Photovoltaic Systems

Since the output characteristics of photovoltaic (PV) system depends on the ambient temperature, solar radiation and load impedance, its maximum power point (MPP) is not constant. Under each condition PV module has a point at which it can produce its MPP. Therefore, maximum power point tracking (MPPT) methods can be used to uphold the PV panel operating at its MPP. In this survey, five MPPT algorithms are presented and compared under different atmosphere conditions: Perturb and Observe (P&amp;O) Methods, Incremental Conductance (IncCond) Methods, Constant Voltage (CV), Short Circuit Current (SCC) and Open Circuit Voltage (OCV). These algorithms are widely used in PV systems as a result of their easy implementation as well as their low cost. These techniques were analysed and their performance was evaluated by using the Matlab tool Simulink under various types of solar radiation and temperature. The IncCond method was the most efficient, at rapidly changing conditions.

Design and experimental evaluation on an advanced multisource energy harvesting system for wireless sensor nodes.

An effective multisource energy harvesting system is presented as power supply for wireless sensor nodes (WSNs). The advanced system contains not only an expandable power management module including control of the charging and discharging process of the lithium polymer battery but also an energy harvesting system using the maximum power point tracking (MPPT) circuit with analog driving scheme for the collection of both solar and vibration energy sources. Since the MPPT and the power management module are utilized, the system is able to effectively achieve a low power consumption. Furthermore, a super capacitor is integrated in the system so that current fluctuations of the lithium polymer battery during the charging and discharging processes can be properly reduced. In addition, through a simple analog switch circuit with low power consumption, the proposed system can successfully switch the power supply path according to the ambient energy sources and load power automatically. A practical WSNs platform shows that efficiency of the energy harvesting system can reach about 75–85% through the 24-hour environmental test, which confirms that the proposed system can be used as a long-term continuous power supply for WSNs.

Thermodynamic assessment of active cooling/heating methods for lithium-ion batteries of electric vehicles in extreme conditions

The battery cooling/heating with active methods is required for EVs (electric vehicles) in the extreme temperature conditions. This work presents a new active battery cooling/heating method based on PCS (phase change slurry) cycle. Two typical often used active cooling/heating methods so-called the direct cabin air blow and refrigerant circulation are also illustrated in detail. The thermodynamic assessment is conducted on these battery active cooling/heating methods with both of 1st Law and 2nd Law analysis. The variations of extra thermal load to the vehicle air-conditioning system are investigated as changes of ambient temperature, humidity and thermal load for the direct cabin air blow method. The simulation results show that the direct cabin air blow method causes more extra thermal load to the air-conditioning system without considering the cabin ventilation effect. The PCS cycle method performs higher exergy efficiency than that of using refrigerant circulation method.

Fire design of steel columns: Effects of thermal gradients

The behavior and design of steel columns subjected to thermal gradients due to fire loading were evaluated numerically and experimentally. The numerical (FEM) modeling approach was verified using experimental data from large-scale tests. The FEM modeling approach was used to conduct parametric studies to evaluate the effects of different heating configurations on steel column strength, and failure behavior at elevated temperatures. The analyses were conducted by coupling transient heat transfer analysis with implicit dynamic stress analysis. Columns subjected to four sided heating configuration had uniform temperature distributions through the cross-section. The columns were subjected to non-uniform (partial) heating to produce thermal gradients through the cross-section. The analysis results indicated that the column strength and failure behavior depended on the column slenderness, axial loading, and heating configuration. Failure modes included flexural buckling about the weak axis, flexural buckling about the strong axis, and flexural-torsional buckling. The analysis results also indicated that columns subjected to uniform heating had significantly higher heat influx. In most cases, columns subjected to non-uniform heating failed at lower average temperatures than columns subjected to uniform heating. However, the columns subjected to uniform heating reached their failure temperatures faster than the columns subjected to non-uniform heating due to the higher heat influx. The exceptions were very slender columns subjected to axial loads greater than 50% of their ambient load capacity. The results from the parametric studies were used to develop design equations for wide flange steel columns subjected to non-uniform heating resulting in thermal gradients through the cross-section.

Method for Determination of Operating Temperature of Building Photovoltaic Module

There is no national standard and international standard about nominal module operating temperature (NMOT) test methods for Building Integrated Photovoltaic (BIPV) modules. An in-lab testing method for measuring NMOT of BIPV modules is proposed. Based on the real operation condition of solar cell, the effect of ambient temperature, wind speed and optimal load resistor to operating temperature were analyzed. The surface temperature, interior temperature and back temperature of BIPV module were measured and the NMOT was determined.

Thermal-Work Strain During Marine Rifle Squad Operations in Afghanistan

The physiological burden created by heat strain and physical exercise, also called thermal-work strain, was quantified for 10 male Marines (age 21.9 ± 2.3 years, height 180.3 ± 5.2 cm, and weight 85.2 ± 10.8 kg) during three dismounted missions in Helmand Province, Afghanistan. Heart rate (HR) and core body temperature (T core) were recorded every 15 seconds (Equivital EQ-01; Hidalgo, Cambridge, United Kingdom) during periods of light, moderate, and heavy work and used to estimate metabolic rate. Meteorological measures, clothing characteristics, anthropometrics, and estimated metabolic rates were used to predict T core for the same missions during March (spring) and July (summer) conditions. Thermal-work strain was quantified from HR and T core values using the Physiological Strain Index (PSI) developed by Moran et al. July PSI and T core values were predicted and not observed due to lack of access to in-theater warfighters at that time. Our methods quantify and compare the predicted and observed thermal-work strain resulting from environment and worn or carried equipment and illustrate that a small increase in ambient temperature and solar load might result in increased thermal-work strain.

Effects of adjustable and stationary fans with misters on core body temperature and lying behavior of lactating dairy cows in a semiarid climate

Cows readily seek shade to reduce solar heat load during periods of high ambient temperature. Typically, auxiliary cooling systems are oriented to maximize cooling for shaded cows. However, when a shade structure is oriented north-south, stationary fan and mister cooling systems are unable to track shade as the sun’s angle shifts throughout the day, and thus can become ineffective. The FlipFan Dairy Cooling System (Schaefer Ventilation Equipment, Sauk Rapids, MN) employs fans and misters that follow shade and compensate for wind speed by rotating on a horizontal axis. Multiparous, lactating Holstein cows (n=144) on a commercial dairy in Arizona were cooled by a fixed system comprised of stationary fans and misters acting as control or the adjustable FlipFan operated for 16.5 h/d (0830 to 0100 h). Core body temperatures (CBT) of 64 cows (4 pens/treatment; 8 cows/pen; 6d) and lying behavior of 144 cows (4 pens/treatment; 18 cows/pen; 5d) were collected by intravaginal and leg data loggers, respectively. Cows were balanced by milk production, blocked by days in milk, and randomly assigned to pen within block. Pen was the experimental unit. In a second experiment, isothermal maps were developed using a fixed system of thermal data loggers arranged in the shaded areas of the pens at different times of day and were analyzed for differences in the temperature-humidity index (THI) achieved by each cooling treatment. Ambient conditions consisted of a mean temperature of 33.0°C, mean relative humidity of 40.3%, and mean THI of 80.2. Mean 24-h CBT for FlipFan was lower than control (38.9 vs. 39.1±0.04°C). A treatment × time interaction was observed in which CBT of FlipFan was 0.4°C lower than control from 0600 to 0800h and 1500 to 1600h. Cows cooled by FlipFan spent more time lying down compared with those cooled by control (9.5 vs. 8.6 h/d). Cows under FlipFan had more frequent lying bouts than did those under control (12.8 vs. 10.7 bouts/d). Lower CBT and decreased standing time are consistent with the findings of other studies when ambient heat load was reduced. In the second experiment, the FlipFan system achieved a lower THI in the morning and evening (5.9 and 1.7%, respectively), and the THI also tended to be 0.8% lower in the afternoon compared with that of control. Results indicate that FlipFan is more effective than a stationary fan and mister system at decreasing CBT, increasing lying time and bouts, and providing a more desirable microenvironment for cows throughout the day in a semiarid environment.

Non–linear analysis of short term variations in ambient visibility

Ambient visibility is a complex manifestation arising out of interactions among many atmospheric variables, including ambient aerosol load, and region specific geophysical characteristics. To functionally relate visibility impairment in Delhi region during winter months-months marred with poor visibility conditions–a novel experiment was designed to relate visibility with ambient aerosol load (PM2.5), and relevant meteorological variables: dew point temperature (Dp), height of planetary boundary layer (PBL), ambient temperature (T), relative humidity (RH), wind speed (WS) and wind direction (WD). Time series data sets of Visibility(t) and other variables were subjected to non–linear decomposition using Empirical Mode Decomposition Method (EMD), enabling to obtain total cyclic and acyclic–trend components embedded in all data–sets. Extracted total cyclic visibility components were functionally related with the corresponding components associated with PM2.5 load and meteorological variables. Decomposed acyclic–trend component of the visibility, representing time dependent acyclic trend (AT), was separately related with the corresponding AT components of the considered meteorological variables. The decomposed components of the visibility (total cyclic and AT) were subjected to multiple linear regression to establish a functional relationship between them and a set of variables among the considered variables. The analysis suggests that acyclic–trend associated with Visibility(t) can be predicted better as opposed to the Visibility(t)cyclic component.

Temperature moderation in a multistorey building by melting of a phase-change material

Abstract The current numerical study focuses on the feasibility of furnishing thermal comfort in a structure, by using paraffin wax stored on a plate below the ceiling in a multi-storey building. The method is aimed to reduce energy demands at the increasing thermal loads. In summer, in daytime, walls of the building are exposed to the ambient thermal load, and heat transferred inside is absorbed by the melting wax. The study is numerical. It relates to temperature variations outside and inside, coupled with heat conduction and accumulation in walls, with radiation between the surfaces, with natural convection of air inside and melting of the wax at the ceiling. Fins spacing on the storage plate, visualization of the melting process, and its parametric investigation provide an insight into the physical phenomena. Temperature and flow fields were investigated for 3 mm and 12 mm thick layers of wax. At the specified conditions of the present study a 3 mm layer provides thermal comfort for most of the day, while a 6 mm layer may suffice for the entire day. Fluent 6.3 software was used in the computations.

Measurement of airborne concentrations of tire and road wear particles in urban and rural areas of France, Japan, and the United States

In addition to industrial facilities, fuel combustion, forest fires and dust erosion, exhaust and non-exhaust vehicle emissions are an important source of ambient air respirable particulate matter (PM10). Non-exhaust vehicle emissions are formed from wear particles of vehicle components such as brakes, clutches, chassis and tires. Although the non-exhaust particles are relatively minor contributors to the overall ambient air particulate load, reliable exposure estimates are few. In this study, a global sampling program was conducted to quantify tire and road wear particles (TRWP) in the ambient air in order to understand potential human exposures and the overall contribution of these particles to the PM10. The sampling was conducted in Europe, the United States and Japan and the sampling locations were selected to represent a variety of settings including both rural and urban core; and within each residential, commercial and recreational receptors. The air samples were analyzed using validated chemical markers for rubber polymer based on a pyrolysis technique. Results indicated that TRWP concentrations in the PM10 fraction were low with averages ranging from 0.05 to 0.70 μg m−3, representing an average PM10 contribution of 0.84%. The TRWP concentration in air was associated with traffic load and population density, but the trend was not statistically significant. Further, significant differences across days were not observed. This study provides a robust dataset to understand potential human exposures to airborne TRWP.

Analyzing the Impact of Ambient Temperature Indicators on Transformer Life in Different Regions of Chinese Mainland

Regression analysis is applied to quantitatively analyze the impact of different ambient temperature characteristics on the transformer life at different locations of Chinese mainland. 200 typical locations in Chinese mainland are selected for the study. They are specially divided into six regions so that the subsequent analysis can be done in a regional context. For each region, the local historical ambient temperature and load data are provided as inputs variables of the life consumption model in IEEE Std. C57.91-1995 to estimate the transformer life at every location. Five ambient temperature indicators related to the transformer life are involved into the partial least squares regression to describe their impact on the transformer life. According to a contribution measurement criterion of partial least squares regression, three indicators are conclusively found to be the most important factors influencing the transformer life, and an explicit expression is provided to describe the relationship between the indicators and the transformer life for every region. The analysis result is applicable to the area where the temperature characteristics are similar to Chinese mainland, and the expressions obtained can be applied to the other locations that are not included in this paper if these three indicators are known.

Dual-mode power regulator for photovoltaic module emulation

Photovoltaic (PV) module emulators, which can provide reproducible and controllable input power profile for a load device corresponding to different ambient conditions for a PV module, can significantly reduce the level of effort and cost for the development and optimization of the PV module, load devices, as well as interfacing power converters. In this paper, we introduce a dual-mode power regulator for the PV emulation. The dual-mode regulator consists of a voltage regulator and a current regulator, connected by two diodes for power hybridization. The circuit switches between the two regulators in order to accurately emulate the electrical output behavior of a PV module under different ambient conditions (e.g., solar irradiance, temperature) and load demands. The proposed regulator circuit provides accurate emulation results over the full operating range of the PV module by complementary use of the two regulators. We develop a robust control method for producing an accurate I–V curve with compensation of the loss in the circuit components. We validate the behavior of the proposed circuit and control method by Matlab/Simulink simulations and experiments. The experimental results shows that the PV emulation output is greatly improved with the proposed dual-mode regulator.

Preferences for overhead sprinklers by naïve beef steers: Test of two nozzle types

Sprinklers effectively reduce heat load in cattle. In some studies, however, cattle readily use sprinklers, while others find that they either avoid or show no preference for it. These studies differ in many ways including previous experience of the animals and the amount of water delivered. Our objective was to test preferences for the amount of water delivered using animals that had no previous experience with man-made water cooling. We used a sprinkler system with nozzles mounted over the feed bunk that intermittently spray (on for 7 out of every 20min/24h in this experiment) the animals’ backs while they fed. Steers (366±50kg) were housed in groups of four (n=8 groups; four groups tested simultaneously) and provided two unshaded feed bunks in adjacent, connected pens with and without sprinklers in summer. Each group was tested with two nozzle types that delivered different amounts of water (1.3L/min vs. unsprinkled control; 2.6L/min vs. unsprinkled control). To ensure steers were making an informed choice, they were first fed solely from each feed bunk (with and without sprinklers) for 1 day each, for each nozzle type. Preference was then evaluated for 3 days, during which time the animals were fed ad libitum from both feed bunks. Behavior was recorded with 10-min instantaneous focal sampling from 13:00 to 19:00h each day (air temperature was 32.5±4.8°C during this time [mean±SD]). Steers spent more than 70% of their total time, both standing and lying, in the side of the pen that contained sprinklers (P≤0.009) in both nozzle comparisons. Steers spent more time within 1.6m of the sprayed area in the 1.3L/min treatment compared to the unsprinkled control bunk (63% of 6h, P=0.053), and this preference became more marked as ambient heat load increased. In contrast, cattle showed no overall preference for the area around the feed bunk fitted with 2.6L/min nozzles (57% of 6h in sprinkled bunk compared to unsprinkled bunk, P=0.234), and only preferred this area during warmer weather and when the water was actively being sprayed. These results indicate that naïve cattle will readily choose to use overhead sprinklers, particularly in warmer conditions and when lower amounts of water are delivered. Further work is required to determine the amount of water that cattle will discriminate between and how this influences their physiological response to heat load.

Variations in wood burning organic marker concentrations in the atmospheres of four European cities

The particulate emissions from biomass burning are a growing concern due to the recent evidence of their ubiquitous and important contribution to the ambient aerosol load. A possible strategy to apportion the biomass burning share of particulate matter is the use of organic molecular tracers. Anhydrosugars (levoglucosan, mannosan and galactosan), together with two organic acids (dehydroabietic and pimaric acids), were previously reported as organic markers for particulate wood burning emissions. These five compounds were studied in four European cities (Helsinki, Copenhagen, Birmingham and Oporto), at both a Roadside and an Urban Background station, during a summer and a winter campaign in the fine (PM(2.5)) and the coarse (PM(10-2.5)) size-fractions of the ambient aerosol. Levoglucosan concentrations were highest in the city of Oporto. In winter, levoglucosan was more present in the fine fraction but in summer, concentrations were similar in both size fractions. Levoglucosan concentrations in the fine size fraction were higher in winter, but no seasonal differences were observed for the coarse size fraction. The lack of difference between the Roadside and Urban Background levoglucosan concentrations points towards a regional nature of this type of pollution. Wood burning was estimated to contribute to about 3.1% of the winter PM(10) mass in Oporto, and to 3.7% in Copenhagen. Mannosan followed the trends exhibited by levoglucosan. The ratio between the levoglucosan and mannosan concentrations allowed determination of a preference for softwood over hardwood in all four cities. Galactosan, pimaric acid and dehydroabietic acid were found to be minor compounds.

Analysis of the global bending modes of a floating structure using the proper orthogonal decomposition

In this paper a time-domain procedure to identify the vibration modes of floating structures, based on the analysis of both displacements and accelerations, is presented. The implemented time-domain technique is the proper orthogonal decomposition (POD), known also as Karhunen–Loeve decomposition, that provides the functional basis that accounts for more captured energy than any other orthogonal one. The POD has been applied in its straightforward formulation and in a slightly different version as well, named band-pass POD, that exploits preliminary filtering around the resonant peaks of the analyzed signals to enhance the convergence of the proper orthogonal modes (POMs) to the linear normal modes (LNMs) in the case of poor information about the mass distribution. The presented procedure has been employed to analyze the experimental data provided by accelerometers and strain-gages applied to the flexible backbone of an elastically scaled segmented-hull model tested in both irregular sea and regular waves in the towing-tank. Among several aspects of the identification of wet-modes, it is discussed in particular how the excitation mechanism provided by the sea meets the requirements of the ambient load typically exploited in output-only modal analysis. The comparisons between the mode shapes identified with the two different procedures (classical POD on the displacements and band-pass POD on the accelerations) show the effectiveness of the POD and the possibilities and limitations related to the use of each procedure. Some results related to the present application, like energy ordering of the wet-modes and its dependence on the encountered sea pattern, as well as the modal damping variation with ship forward speed, are discussed in the paper, showing the POD capability to provide new insights in the analysis of hydroelastic phenomena.