Investigation of the Behavior of a Photovoltaic Cell under Concentration as a Function of the Temperature of the Base and a Variable External Magnetic Field in 3D Approximation

The photovoltaic (PV) cell performances are connected to the base photogenerated carriers charge. Some studies showed that the quantity of the photogenerated carriers charge increases with the increase of the solar illumination. This situation explains the choice of concentration PV cell (C = 50 suns) in this study. However, the strong photogeneration of the carriers charge causes a high heat production by thermalization, collision and carriers charge braking due to the electric field induced by concentration gradient. This heat brings the heating of the PV cell base. That imposes the taking into account of the temperature influence in the concentrator PV cell operation. Moreover, with the proliferation of the magnetic field sources in the life space, it is important to consider its effect on the PV cell performances. Thus, when magnetic field and base temperature increase simultaneously, we observe a deterioration of the photovoltage, the electric power, the space charge region capacity, the fill factor and the conversion efficiency. However the photocurrent increases when the base temperature increases and the magnetic field strength decreases. It appears an inversion phenomenon in the evolution of the electrical parameters as a function of magnetic field for the values of magnetic field B> 4×10-4 T.

Investigating the Impact of Base Heating and External Electric Field on PV Cell Performance under Intense Illumination

The characterization of the performances of a PV cell is linked to intrinsic factors of this cell. It is therefore important for us to identify the favorable or unfavorable conditions that affect the performance of PV cells. It is from this perspective that it seems judicious to us to study the simultaneous influence of the heating of the base and an external electric field on the performance of a PV cell under intense illumination of 50 suns. Two phenomena contribute to the heating of the base of a PV cell which is heating due to the transfer by conduction of solar radiation energy received by the surface of the PV cell and the heat generated inside the PV cell by various phenomena linked to the movement of photogenerated charged carriers. In this study, we take into account the heating linked to the movement of the charged carriers in the base. After a mathematical modeling of the PV cell considered, some hypotheses are formulated and the expressions of the electrical parameters are established as a function of the electric field and base temperature. Subsequently, we use numerical simulation to highlight the behavior of theses parameters as a function of temperature and of the intensity of the electric field. The results show that for any given temperature, the orientation of the electric field as considered in our work improves the performance of the PV cell while high temperatures degrade these performances. Furthermore, the analysis of the curves shows that the harmful effect of temperature on the performance of a PV cell is more accentuated at large values of electric field.

Microstructure and microhardness of directionally solidified and heat-treated Nb-Ti-Si based ultrahigh temperature alloy

Directionally solidified （DS） specimens of Nb-Ti-Si based ultrahigh temperature alloy were heat-treated at （1 500 ℃, 50 h） and （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, respectively. The results show that the microstructures become uniform, the long and big primary （Nb,X）sSi3 （X represents Ti and Hf elements） plates in the DS specimens are broken into small ones, and the eutectic cells lose their lamellar morphology and their interfaces become blurry after heat-treatment. Meanwhile, the （Nb,X）sSi3 slices in the eutectic cells of the DS specimens coarsen obviously after heat-treatment. Homogenizing and aging treatments could effectively eliminate elemental microsegregation, and the segregation ratios of all elements in niobium solid solution （Nbss） in different regions tend to 1. After heat-treatment, the microhardness of retained eutectic cells increases evidently, and the maximum value reaches HV1 404.57 for the specimen directionally solidified with a withdrawing rate of 100 μm/s and then heat-treated at （1 500 ℃, 50 h） ＋ （1 100 ℃, 50 h）, which is 72.8 % higher than that under DS condition.

Effect of high temperature treatments on microstructure of Nb-Ti-Cr-Si based ultrahigh temperature alloy

To investigate the effects of homogenizing and aging treatments on the microstructure of an Nb-Ti-Cr-Si based ultrahigh temperature alloy,coupons were homogenized at 1 200-1 500 °C for 24 h,and then aged at 1 000 °C for 24 h.The results show that the heat-treated alloy is composed of Nb solid solution（Nbss）,（Nb,X）5Si3 and Cr2Nb phases.With the increase of heat-treatment temperature,previous Nbss dendrites transformed into equiaxed grains,and petal-like Nbss/（Nb,X）5Si3 eutectic colonies gradually changed into small（Nb,X）5Si3 particles distributed in Nbss matrix.A drastic change occurred in the morphology of the Laves phase after homogenizing treatment.Previously coarse Cr2Nb blocks dissolved during homogenizing at temperature above 1 300 °C,and then much finer and crowded Cr2Nb flakes precipitated in the Nbss matrix in cooling.Aging treatment at 1 000 °C for 24 h led to further precipitation of fine particles of Laves phase in Nbss matrix and made the difference in concentrations of Ti,Hf and Al in Nbss,（Nb,X）5Si3 and Cr2Nb phases reduced.

Simultaneous measurement of axial strain and temperature based on twisted fiber structure

In this Letter, an alternative solution is proposed and demonstrated for simultaneous measurement of axial strain and temperature. This sensor consists of two twisted points on a commercial single mode fiber introduced by flame-heated and rotation treatment. The fabrication process modifies the geometrical configuration and refractive index of the fiber. Different cladding modes are excited at the first twisted point, and part of them are coupled back to the fiber core at the second twisted point. Experimental results show distinct sensitivities of 34.9 pm/με with 49.23 pm/℃ and -36.19 pm/με with 62.99 pm/℃ for the two selected destructive interference wavelengths.

Flow Field and Temperature Field in GaN-MOCVD Reactor Based on Computational Fluid Dynamics Modeling

Metal organic chenlical vapor deposition （AIOCVD） growth systems arc one of the. main types of equipment used for growing single crystal materials, such as GaN. To obtain fihn epitaxial materials with uniform performanee, the flow field and ternperature field in a GaN-MOCVD reactor are investigated by modeling and simulating. To make the simulation results more consistent with the actual situation, the gases in the reactor are considered to be compressible, making it possible to investigate the distributions of gas density and pressure in the reactor. The computational fluid dynamics method is used to stud,v the effects of inlet gas flow velocity, pressure in the reactor, rotational speed of graphite susceptor, and gases used in the growth, which has great guiding~ significance for the growth of GaN fihn materials.

Review on the latest developments in modified vanadium-titanium-based SCR catalysts

Vanadium-titanium-based catalysts are the most widely used industrial materials for NO_x removal from coal-fired power plants. Owing to their relatively poor low-temperature deNO_x activity, low thermal stability, insufficient Hg^0 oxidation activity, SO_2 oxidation, ammonia slip, and other disadvantages,modifications to traditional vanadium-titanium-based selective catalytic reduction（SCR）catalysts have been attempted by many researchers to promote their relevant performance. This article reviewed the research progress of modified vanadium-titanium-based SCR catalysts from seven aspects, namely,（1） improving low-temperature deNO_x efficiency,（2） enhancing thermal stability,（3） improving Hg^0 oxidation efficiency,（4） oxidizing slip ammonia,（5） reducing SO_2 oxidation,（6） increasing alkali resistance, and（7） others. Their catalytic performance and the influence mechanisms have been discussed in detail. These catalysts were also divided into different categories according to their modified components such as noble metals（e.g., silver, ruthenium）, transition metals（e.g., manganese, iron, copper, zirconium, etc.）, rare earth metals（e.g., cerium, praseodymium）,and other metal chlorides（e.g., calcium chloride, copper chloride） and non-metals（fluorine,sulfur, silicon, nitrogen, etc.）. The advantages and disadvantages of these catalysts were summarized.Based on previous studies and the author＇s point of view, doping the appropriate modified components is beneficial to further improve the overall performance of vanadium-titanium-based SCR catalysts. This has enormous development potential and is a promising way to realize the control of multiple pollutants on the basis of the existing flue gas treatment system.

High sensitivity D-shaped hole fiber temperature sensor based on surface plasmon resonance with liquid filling

A high sensitivity D-shaped hole double-cladding fiber temperature sensor based on surface plasmon resonance(SPR)is designed and investigated by a full-vector finite element method.Within the D-shaped hole doublecladding fiber,the hollow D-section is coated with gold film and then injected in a high thermo-optic coefficient liquid to realize the high temperature sensitivity for the fiber SPR temperature sensor.The numerical simulation results show that the peaking loss of the D-shaped hole double-cladding fiber SPR is hugely influenced by the distance between the D-shaped hole and fiber core and by the thickness of the gold film,but the temperature sensitivity is almost insensitive to the above parameters.When the thermo-optic coefficient is -2.8×10^(-4)∕℃,the thickness of the gold film is 47 nm,and the distance between the D-shaped hole and fiber core is 5μm,the temperature sensitivity of the D-shaped hole fiber SPR sensor can reach to -3.635 nm∕℃.

Humidity and temperature sensor based on GOQDs-PVA coated tapered no-core fiber combined with FBG

A simple structure optical fiber sensor for relative humidity(RH) and temperature measurement is proposed and verified in this paper, which is based on graphene oxide quantum dots and polyvinyl alcohol(GOQDs-PVA) composite coated tapered no-core fiber(NCF) combined with a fiber Bragg grating(FBG). FBG is insensitive to humidity and sensitive to temperature, which is used to compensate temperature of the sensor. Experimental results show this sensor has humidity sensitivity of 143.27 pm/%RH ranging from 30%RH to 80%RH and the temperature sensitivity of 9.21 pm/℃. The proposed sensor has advantages of simple structure, good repeatability, and good stability, which is expected to be used in both RH and temperature measurement in biological and chemical fields.

Temperature characteristics research of SOI pressure sensor based on asymmetric base region transistor

Based on the asymmetric base region transistor, a pressure sensor with temperature compensation circuit is proposed in this paper. The pressure sensitive structure of the proposed sensor is constructed by a C-type silicon cup and a Wheatstone bridge with four piezoresistors（R_1, R_2, R_3 and R_4/locating on the edge of a square silicon membrane. The chip was designed and fabricated on a silicon on insulator（SOI） wafer by micro electromechanical system（MEMS） technology and bipolar transistor process. When the supply voltage is 5.0 V, the corresponding temperature coefficient of the sensitivity（TCS） for the sensor before and after temperature compensation are -1862 and -1067 ppm/℃, respectively. Through varying the ratio of the base region resistances r_1 and r_2, the TCS for the sensor with the compensation circuit is -127 ppm/℃. It is possible to use this compensation circuit to improve the temperature characteristics of the pressure sensor.

Ultralow-noise single-photon detection based on precise temperature controlled photomultiplier with enhanced electromagnetic shielding

We demonstrate an ultralow-noise single-photon detection system based on a sensitive photomultiplier tube（PMT） with precise temperature control, which can capture fast single photons with intervals around 10 ns.By improvement of the electromagnetic shielding and introduction of the self-differencing method, the dark counts（DCs） are cut down to ~1%. We further develop an ultra-stable PMT cooling subsystem and observe that the DC goes down by a factor of 3.9 each time the temperature drops 10°C. At -20°C it is reduced 400 times with respect to the room temperature（25°C）, that is, it becomes only 2 counts per second, which is on par with the superconducting nanowire detectors. Meanwhile, despite a 50% loss, the detection efficiency is still 13%. Our detector is available for ultra-precise single-photon detection in environments with strong electromagnetic disturbances.

Evaluating multiple parameters dependency of base temperature for heating degree-days in building energy prediction

To improve the prediction accuracy of heating demand, an appropriate base temperature should be estimated before using the heating degree-days (HDD) approach. This study collected the measured data for gas consumption at half-hourly resolution and the building physical characteristics from 89 educational buildings over four years. To determine the base temperature, in addition to the ambient temperature, more detailed independent variables, i.e. solar insolation, relative humidity, wind speed, and one-day ahead residual temperature, were incorporated into a three-parameter change-point multi-variable regression (3PH-MVR) for heating. The mean base temperature using the 3PH-MVR approach was about 0.4℃ lower than the results from the 3PH method only. The relationships between base temperature and annual HDD (based on 15.5℃), building location, and mean daily solar insolation were evaluated. It is found that the annual HDD and the daily insolation had clear impacts on base temperature, while there was a plausible relationship between base temperature and building location. Compared with traditional approach, the proposed 3PH-MVR method considers multiple weather parameters and determines a more robust base temperature, thus improving the prediction accuracy of HDD with higher average R2 value at 0.86 than that of univariate regression (0.82).

Synthesis and characterization of hybrid graphene nanocoolant for heat transfer dissipation in microchannel heat sinks

An attempt is made to examine the effect of hybrid nanocoolant in microchannel heat sink for computer cooling.Two-hybrid coolants with graphene as one of the prime components are synthesized and images of the particles are shown using scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Heat transfer properties like thermal conductivity of the hybrid fluid,specific heat,density,and viscosity are evaluated experimentally and theoretically.The heat transfer characteristics are also studied in heat sink channels of micro level in the processors of personal computers.The parameters like internal heat transfer coefficient,thermal resistances and base temperature representing the processor temperature are examined for the applied heater power of 325 W.The coolant dilution was varied in the range of 0.05 vol%,0.075 vol%and 0.1 vol%and the base temperature is noted.The recorded lowest base temperature is 310.01 K for the concentration of 0.1 vol%graphene-iron oxide(GFO)system for 0.5 mm fin spacing for the graphene-iron oxide hybrid coolant and for graphene oxide–iron oxide(GOFO)hybrid coolant it is 311.24 K for the same operating conditions.

MEMS gyro temperature compensation identification algorithm based on thin plate spline interpolation method

MEMS gyroscopes are widely used in the underwater vehicles owing to their excellent performance and affordable costs.However,the temperature sensitivity of the sensor seriously affects measurement accuracy.Therefore,it is significantly to accurately identify the temperature compensation model in this paper,the calibration parameters were first extracted by using the fast calibration algorithm based on the Persistent Excitation Signal Criterion,and then,MEMS gyro temperature compensation model was established by utilizing the thin plate spline interpolation method,and the corresponding identification results were compared with the results from the polynomial fitting method.The effectiveness of the proposed algorithm has been validated through the comparative experiment.

Temperature Insensitive Open Loop Attenuation Control of a Liquid Crystal Based VOA

A patent pending open-loop liquid crystal based variable optical attenuator is introduced. The temperature dependent performance is compensated through electric monitoring and adjustment utilizing liquid crystal's opto-electronic properties.

Introducing Degree Days to Building Thermal Climatic Zoning in China

Building thermal climatic zoning is a key issue in building energy efficiency.Heating degree days(HDD) and cooling degree days(CDD) are often employed as indexes to represent the heating and cooling energy demand in climatic zoning.However,only using degree days may oversimplify the climatic zoning in regions with complex climatic conditions.In the present study,the application of degree days to current building thermal climatic zoning in China was assessed based on performance simulations.To investigate the key indexes for thermal climatic zoning,the climate characteristics of typical cities were analyzed and the relationships between the climate indexes and heating/cooling demand were obtained.The results reveal that the annual cumulative heating load had a linear correlation with HDD 18 only in regions with small differences in altitude.Therefore,HDD is unsuitable for representing the heating demand in regions with large differences in altitude.A comprehensive index(winter climatic severity index) should be employed instead of HDD,or complementary indexes(daily global solar radiation or altitude) could be used to further divide climate zones.In the current official climatic zoning,the base temperature of 26℃ for CDD is excessively high.The appropriate base temperature range is 18℃ to 22℃.This study provides a reference for selecting indexes to improve thermal climatic zoning in regions with similar climates.

An optimized solar-air degree-day method to evaluate energy demand for poultry buildings in different climate zones

The degree-day method is widely used to determine energy consumption but cannot be directly applied to poultry buildings without improvements in its accuracy.This study was designed to optimize the degreeday calculation and proposes a solar-air degree-day method,which can be used to calculate the cooling and heating degree-days and the annual cooling and heating loads under different climate conditions for poultry buildings.In this paper,the solar-air degree-day method was proposed,which considers the effects of solar radiation with different wall orientations and surface colors.Five Chinese cities,Harbin,Beijing,Chongqing,Kunming and Guangzhou,were selected to represent different climate zones to determine the solar-air degreedays.The heating and cooling energy requirements for different climates were compared by DeST(Designer’s Simulation Toolkit)simulation and the solar-air degreeday method.Approaches to decrease energy consumption were developed.The results showed that the maximum relative error was less than 10%,and the new method was not significantly different from the DeST simulation(P>0.05).The accuracy of calculating energy requirements was improved by the solar-air degree-day method in the different climate zones.Orientation and surface color effects on energy consumption need to be considered,and external walls of different orientations should have different surface colors.