Cp Curves Research Articles

Investigation of Power Coefficient Behaviors of the Parabolic Wind Rotor Due to its Variable Geometry Parameters

In this work, the effect of changing the diameter of the rotor (2R), the height of the rotor (H), the number of blades (N) and the length of the blade section (C) on the power factor (Cp) were studied. The results were presented in the form of power factor (Cp) curves as a function of tip speed ratio (l 0 ). The aerodynamic mathematical model Multi Streamtube was implemented by a computer program that was designed using Microsoft Visual Basic. A total of 57 configurations were utilized for the investigation of the effects of the various rotor design parameters on the Cp of the rotor. The results indicated that increasing rotor height to diameter ratio (H/R) leads to a decrease in Cp over low tip speed ratio range for all values of solidity,s, (NC/R) investigated. However, higher values of (H/R) result in a raise in Cp over high tip speed ratio range for values of (NC/R) less than 0.2 approximately. Thus, it seems that higher (H/R) values constitute an advantage for fast rotating rotors (low (NC/R) and high tip speed ratio).

Influence of interaction between the diffuser and rotor on energy harvesting performance of a micro-diffuser-augmented hydrokinetic turbine

A way to quantified diffuser-rotor interaction is presented for a micro-diffuser-augmented hydrokinetic turbine (MDAHT) base on the actuator disc theory (Jamieson, 2011). The large eddy simulation/Reynolds-averaged Navier–Stokes model (DES) for computational fluid dynamics were employed to simulate for bare turbine, bare diffuser and diffuser-augmented turbine, respectively. The axial induction factor of bare diffuser was obtained via the average speed of the turbine center plane, and that of both bare turbine and diffuser-augmented turbine were obtained based on the computational CP and CT. The result shows that the interaction between the diffuser and rotor are corresponding to equivalent axial induction factor ai and ai + ad, which is tightly relative to diffuser shape parameters and the operational parameters. Bigger angle of attack and camber of diffusers contributes to higher positive ai and higher negative ai + ad, and more energy harvesting performance on MDAHT is acquired. Besides, angle of attack and camber of diffuser also affected the variation of the CP and CT curve. The maximum TSR point was shifted to higher TSR position with the increase of angle of attack and camber of diffuser, and the angle of attack has a larger influence on the energy harvesting performance for MDAHT comparing with the camber of diffuser. Moreover, the influences of the tip clearances and diffuser contraction ratios on energy harvesting performance versus TSRs were also investigated.

Residual entropy in the zero-temperature limit of toluene glass

The specific heat Cp of toluene, doped with 2 mol% ethanol to avoid rapid crystallization, has been measured in both glass and crystal states, and with special accuracy at low temperatures in the range 1.8−20 K using the thermal relaxation method. By making use of the complementary Cp curves measured in the reference crystal state, we have been able to obtain the entropy curve of the glass and eventually the residual entropy of toluene glass in the zero-temperature limit, that is found to be 5.1 J/(K⋅mol). This value is clearly lower than others pre-viously reported in the literature, which lack the knowledge of the particular specific-heat behavior of glasses at low temperatures and hence overestimated the glass residual entropy at zero temperature. In addition, we have studied in detail such low-temperature “glassy anomalies” in the case of toluene, extending and improving pre- vious measurements. The surprising depletion previously reported of tunneling two-level systems in toluene glass has been confirmed, though this fact coexists with the presence of a broad peak typical of glasses (the so-called boson peak) in Cp/T3 at 4.5 K. For the toluene crystal, the expected cubic Debye behavior has been found at lower temperatures.The specific heat Cp of toluene, doped with 2 mol% ethanol to avoid rapid crystallization, has been measured in both glass and crystal states, and with special accuracy at low temperatures in the range 1.8−20 K using the thermal relaxation method. By making use of the complementary Cp curves measured in the reference crystal state, we have been able to obtain the entropy curve of the glass and eventually the residual entropy of toluene glass in the zero-temperature limit, that is found to be 5.1 J/(K⋅mol). This value is clearly lower than others pre-viously reported in the literature, which lack the knowledge of the particular specific-heat behavior of glasses at low temperatures and hence overestimated the glass residual entropy at zero temperature. In addition, we have studied in detail such low-temperature “glassy anomalies” in the case of toluene, extending and improving pre- vious measurements. The surprising depletion previously reported of tunneling two-level systems in toluene glass has been confi...

Heat Capacity of Pb10 –xLax(GeO4)2 +x(VO4)4 –x (x = 0, 1, 2, 3) Apatites in the Range 320–1000 K

Pb10 – xPrx(GeO4)2 + x(VO4)4 – x (x = 0, 1, 2, 3) apatites have been prepared by solid-state reactions via sequential firing of appropriate oxide mixtures (PbO, Pr2O3, GeO2, and V2O5) in air in the temperature range 773–1073 K. Their unit-cell parameters have been determined as functions of temperature by high-temperature X-ray diffraction measurements, and the linear and volume expansion coefficients of Pb7Pr3(GeO4)5(VO4) have been calculated. The heat capacity of the synthesized Pb10 – xPrx(GeO4)2 + x(VO4)4 – x (x = 0, 1, 2, 3) compounds with the apatite structure has been determined by differential scanning calorimetry in the temperature range 350–1050 K. The cp(T) curves of the samples with x = 1, 2, and 3 have been shown to have extrema (in particular, peaks at 701, 917, and 1018 K for the x = 3 sample) due to phase transitions. The experimental Cp(T) heat capacity data have been used to evaluate the thermodynamic functions of the synthesized apatites.

Effect of hydroxyurea (HU) on gelatinization mechanism of type I collagen suspensions

Mutant hemoglobins thermodynamic phase transitions (HbS, HbC, etc.) have been the causes of serious hemoglobinopathies that have been affecting mankind since the dawn of human race. HbS polymerization is the best known of these transitions and the original cause of sickle cell anemia. Hydroxyurea (HU, NH2CONHOH) is widely used as the main drug administered for the treatment of Sickle Cell Anemia (SCA). Several hypotheses have been raised on the effects of HU on SCA. The most widespread and accepted one points to the production of fetal hemoglobin by the bone marrow, hindering the polymerization of deoxygen-ated HbS. Moreover, recent studies have reported that the short term in vivo effects of the HU have not been elucidated. By ordinary techniques of Materials Science (scanning electron microscopy, viscoelasticity, vis-cosity measurements, DSC and weight loss) we assessed the anti-nucleating, depolymerizing, and anti-gelling direct effects of HU on suspensions and type I bovine collagen gels. Scanning electron microscopy (SEM) revealed that the addition of HU results in the disappearance of the percolating three-dimensional network typical of collagen gels. Vane Rheometry tests pointed to a reduction in the yield stress (σ0) by add-ing HU into collagen gels with a concentration of 2.2 % w/v. In the liquid phase (sol), suspensions increased viscosity over time but decreased with the addition of HU, highlighting the depolymerizing effect of this substance. The weight loss of the sols is also affect by the addition of HU probably related to the lowering of the interactions between collagen/water as HU is added. The DSC essays indicated changes in the Cp curves as HU is added to the gel, decreasing the structural relaxations commonly observed in those gels. As a result, HU showed an effect on the phase transition of the studied gel, strengthening the hypothesis of anti-nucleating and anti-gelling action thereof on physical, reversible gels, and possibly on physical, reversible gels of mutant hemoglobin (HbS). Keywords: hydroxyurea, gelation, collagen, polymerization, sickle cell anemia.

Equivalence of enthalpic nature of the glasses produced by crystal-damage and melt-quenching

Glasses can be generated by two basic strategies of melt quenching and crystal damage. However, questions regarding the similarity and difference of the glasses, in particular, their relation needs to be clarified. Here, a direct comparison of the enthalpic behaviors of the glass transition is presented in molecular glasses produced by melt quenching and ball milling. The absence of an overshoot in the upscan glass-transition heat capacity Cp curves of the milled glasses of distinct energy levels is commonly observed. The overshoot can be retrieved by either aging at temperatures below the glass transition in the milled glasses, or by heating-cooling-heating cycles around the glass transition. Heating the milled glasses can basically arrive at the same supercooled liquids as the melt-quenched glass. A strong dependence of the glass-transition Cp overshoot intensity on the fictive temperature Tf and the non-exponential parameter β is suggested in the milled glasses.

The corrosion inhibitor behavior of iron in saline solution by the action of magnesium carboxyphosphonate

Abstract Herein, we report the synthesis, structural characterization and corrosion assay of a metal phosphonate – Mg(GLY)(H2O)2 obtained from a tridentate ligand N,N-bis-phosphonomethylglycine (GLY) and a magnesium salt (MgSO4·7H2O). The phosphonate was obtained by hydrothermal method at 80°C and also under ultrasounds conditions at 60°C. The FTIR, X-ray powder diffraction, elemental analysis and thermogravimetric analysis were performed in order to fully characterize the synthesized compounds and polarization experiments (CP) and electrochemical spectroscopy (EIS) to investigate the corrosion inhibition properties. The FTIR confirm the formation of magnesium phosphonate, and the X-ray diffraction showed the formation of a semi-crystalline compound. The elemental analysis confirmed the number of water molecules per formula unit of Mg(HO3PCH2)2N(H)CH2COO·2H2O. The presence of nitrogen atom and phosphonate groups in the metal phosphonate structure anticipated that the presence of the small quantity of Mg(GLY)(H2O)2 in saline solution will provide a positive effect on iron surface and act as a corrosion inhibitor. From the CP curves recorded in an aerated nitric saline solution, corrosion parameters (corrosion potential –Ecorr, corrosion density current – Jcorr, polarization resistance – Rp and corrosion rate – Rcorr) were extracted from Tafel plots. The decrease in Jcorr is associated with a shift in Ecorr to more negative values. These results suggest that metal phosphonate behaves as a mixed-type inhibitor, by reducing both the cathodic and anodic reactions. The optimum inhibitor concentration determined was 2 mM. At this concentration the corrosion rate decreases by 23% fold comparatively with iron in nitric acid solution without metal phosphonate. The EIS data in agreement with the polarization measurement resulted from polarization data.

Synthesis and High-Temperature Heat Capacity of Dy2Ge2O7 and Ho2Ge2O7

The Dy2Ge2O7 and Ho2Ge2O7 pyrogermanates have been prepared by solid-state reactions in several sequential firing steps in the temperature range 1237–1473 K using stoichiometric mixtures of Dy2O3 (or Ho2O3) and GeO2. The heat capacity of the synthesized germanates has been determined as a function of temperature by differential scanning calorimetry in the range 350–1000 K. The experimentally determined C p (T) curves of the dysprosium and holmium germanates have no anomalies and are well represented by the Maier–Kelley equation. The experimental C p (T) data have been used to evaluate the thermodynamic functions of the Dy2Ge2O7 and Ho2Ge2O7 pyrogermanates: enthalpy increment H°(T)–H°(350 K), entropy change S°(T)–S°(350 K), and reduced Gibbs energy Ф°(T).

Physical ageing response of polystyrene subjected to the large deformation: The increase in fictive temperature

Film stretch was incorporated in the enthalpy relaxation experiment in order to examine physical ageing response of polystyrene subjected to large deformation. It was stretched in the midst of ageing step, where ageing temperature was located slightly higher than the onset of the glass transition shoulder to minimise the stretching effect on the enthalpy decay, and then heat capacity, cp(T), versus temperature curve was acquired by DSC (differential scanning calorimetry) as functions of the ageing time and stretch ratio. Pre-hold and post-hold stretches are both carried out, those are stretching-and-ageing and ageing-and-stretching, respectively. As a result, the stretching effect appeared as the shift of glass transition shoulder in cp(T) curve; its onset temperature increased with the increase in the stretch ratio. A remarkable discrepancy for the shift of glass transition shoulder was observed between the samples of pre-hold and post-hold stretches. The experimental cp(T) was reproduced by the modelling data calculated on the basis of Tool-Narayanaswamy-Moynihan framework to derive the data of fictive temperature (Tf). It was revealed that Tf isothermally increases with stretching. The amount of Tf increase depends on both the ageing time and stretch ratio. The discrepancy of the shift amount appeared between pre-hold and post-hold stretches was interpreted in terms of the increase in Tf.

Numerical and experimental investigation of an insulation layer with phase change materials (PCMs)

Phase change materials (PCMs) are used in novel thermal insulating materials in order to exploit their high apparent thermal capacity, which is particularly interesting for buildings with moderate thermal inertia because PCMs have a high potential for CO2 reduction in lightweight buildings and their energy consumption as well as for increasing the thermal comfort of the inhabitants. In addition, one of the most promising applications of PCMs is embedding them directly in the insulation layers of a lightweight wall. In fact, due to their apparent thermal capacity, light insulators with embedded PCM particles have good performances in smoothing and shaving of thermal peak loads. Furthermore, in some climatic conditions, they can act as thermal storages by reducing thermal loads in buildings. Many sectors of evidence in the literature indicate that it is necessary to use a hysteresis model with two different curves of specific heat versus melting and solidification to assess the transient thermal performance of PCMs embedded precisely in an insulation layer.The main aim of this research is to develop a detailed dynamic model in order to calculate the effects of PCMs in insulation layers of lightweight walls. In this paper, the results of some actions, used to improve the effectiveness of the models, are investigated. In particular they are the adoption of two distinct cp curves, which improves the accuracy of dynamic simulations and, hence, allows the development of the model using a smaller number of points and a larger time step.Several experimental tests validate the numerical model. Furthermore, this paper presents the way in which the position of the PCM insulation layer, in a typical wallboard, affects the temperature and heat flux, inside each layer, in transient conditions. The results show that, in the case evaluated, the maximum reduction of heat consumption, of about 15%, was obtained when PCMs are located in positions three and four, which are approximately in the middle of the wall. In addition, this specific kind of insulation layer generates a delay of the maximum heat flux that is of about two hours.

Analysis of TNM model calculation for enthalpy relaxation based on the fictive temperature model and the configurational entropy model

Enthalpy relaxation experiments were conducted for polystyrene samples at different annealing temperatures below glass transition temperature (Tg) using a differential scanning calorimeter. The framework of Tool-Narayanaswamy-Moynihan approach was applied to reproduce experimental traces with two models of the structural relaxation times; those are the generalized Arrhenius type characterized by fictive temperature (Tf model) and the configurational entropic type (Sc model). The calculation data of the heat capacity (cp) obtained from the two models were analysed on the basis of the parameter – geometry relationship, in which three factors were given to the geometry of the Tg shoulder and overshoot appeared in cp curve. It was found that both the horizontal shift and the broadening of Tg shoulder occur interdependently in the cp curve calculation of Sc model, while they are almost independent in the calculation of Tf model. In addition, the analysis revealed the process of producing cp overshoot in Tg shoulder, which is expected to be instructive in the optimized cp calculation.

Development and experimental verification of counter-rotating dual rotor/dual generator wind turbine: Generating, yawing and furling

This paper deals with the control techniques for counter-rotating dual rotor/dual generator(CRDRDG) wind turbine and its experimental verifications of the performance in the field. The authors have already proposed the dynamic model and some control techniques in the previous researches, which exploit some features of the CRDRDG structures, and verified the controllers by numerical simulations and lab-scale experiments. In this paper, we present experimental results obtained using a full scale (15[kW]) CRDRDG in the field. To perform the field experiments, an integrated control algorithm is proposed. The experimental results show that the integrated control algorithm effectively maximizes the output power of the CRDRDG wind turbine while operating in the region below rated power, and limits the output power while operating in the region above rated power. Furthermore, the experimental data reveals an additional advantage of the counter-rotating dual rotor system. The data shows that the system can lower the tip speed ratio at which Cp curve attains its maximum, almost by half in comparison to the conventional three bladed single rotor system, possibly reducing the noise caused by rotor blades.

High-temperature heat capacity of the oxide compounds in the Bi2O3–V2O5 system

The compounds BiVO4, Bi4V2O11, and Bi12V2O23 have been prepared by solid-state synthesis using stoichiometric mixtures of Bi2O3 and V2O5. The effect of temperature on the heat capacity of the synthesized bismuth vanadates has been studied by differential scanning calorimetry in the range 350–950 K. The C p (T) curves have extrema at 531.7 K for BiVO4 and at 725.2 and 852.8 K for Bi4V2O11, which are due to polymorphic transformations of these compounds.

Heat Capacity of Confined Polystyrene in Close-Packed Particles

The heat capacity (Cp) of confined polystyrene in particles is investigated in the case of close-packed structure using differential scanning calorimetry (DSC). This confined geometry allows the highest possible free surface area (3/R) in a dense macroscopic sample. We show that Cp of polystyrene increases above that of bulk below bulk glass transition (Tg) T > Tg – 30 °C. Such deviation depends mainly on the fraction of free surface area, which is interpreted by the existence of zone of higher degrees of freedom on the free surface and comfort the previous results of the depression of a volumetric glass transition Tgvol and the higher surface mobility by the photobleaching technique. On the other hand, the main discontinuity of Cp coincides with the bulk glass transition zone Tg, which comforts the finding of the existence of a core with a bulk behavior. The Cp curves exhibit both behaviors observed in confined system: (i) a growth of Cp in the glassy regime which is in agreement with the negative shift ...

Influence of fluctuating wind conditions on vertical axis wind turbine using a three dimensional CFD model

In practical situations, it is important to analyze the performance of VAWT considering the fluctuations of free stream wind. In the present paper, 3D unsteady numerical analysis is employed to investigate the effect of fluctuating wind conditions on the performance of a 1.1kW commercially viable VAWT. VAWT is 3 straight bladed, Darrieus type having NACA 0015 airfoil profile. Turbulence is modeled using Transition SST K-ω model. Free stream velocity U∞ is varied in sinusoidal manner with respect to flow time for Umean=10m/s. In this study, the effect of variation of fluctuation amplitude Uamp, fluctuation frequency fc and tip speed ratio λon the performance of VAWT is investigated. The vortex structures are studied for Uamp =10% and 50%. From the results, it is observed that the uniform and fluctuating wind CP curves do not trace each other. Cycle averaged CP increases with Uamp. A maximum CP of 0.33 is obtained corresponding to Uamp =50%. Cycle averaged CP increases to a maximum value and then decreases with λmean. Maximum CP of 0.31 is obtained corresponding to λmean=2. Cycle averaged CP increases to a maximum value and then marginally decreases with fc. Maximum CP of 0.31 is obtained corresponding to fc =1Hz. Hence the overall performance under fluctuating wind conditions improved when VAWT is operated at higher Uamp,λmean≥2 and fc close to 1Hz.

Specific heat critical behavior in Bi1-xSbx solid solutions

Studies of the specific heat Cp room temperature concentration dependences for the Bi1-xSbx (x = 0–0.12) solid solutions have shown that in the Cp(x) curves, three peaks of Cp are observed near x = 0.015, x = 0.037, and x = 0.07. These peaks are attributed to critical phenomena accompanying second-order concentration phase transitions (PT) from dilute to concentrated solid solutions, to a gapless state, and a semimetal–semiconductor transition, respectively. The numerical values for the critical exponents of the specific heat α for the Cp peaks near x = 0.015 and x = 0.037 have been determined within the framework of fluctuation theory for second-order phase transitions and percolation theory. It was shown that the α values (α = 0.11 ± 0.005) are the same within the margin of error for both peaks and correspond to the values theoretically calculated within the framework of scale-invariant theory for three–dimensional (3D) models and determined experimentally for different physical systems undergoing second-order phase transitions.

Crystallization of a highly viscous multicomponent silicate glass: Rigidity percolation and evidence of structural heterogeneity

A magnesium bearing multicomponent silicate glass was annealed at the temperature slightly above glass transition temperature (Tg) for various periods of time. The crystalline phase of fluorophlogopite with the chemical formula of NaMg3AlSi3O10F2 is precipitated in the floppy regions, which leads to the formation of a core-shell structure. Considering that there exists only four- or six-fold coordinated Mg2+ in the studied glass, the fraction of four-fold coordinated Mg2+ is determined by comparing the maximum size of the crystallite and the floppy region according to the percolation theory. In addition, a striking phenomenon of endotherm above glass transition in heat capacity (Cp) curve is observed for the first time when prolonging the annealing time, which is ascribed to the amorphous heterogeneous structure surrounding the crystallites.

Turbulence influence on optimum tip speed ratio for a 200 kW vertical axis wind turbine

The influence of turbulence intensity (TI) on the tip speed ratio for maximum power coefficient, here called λCp_max, is studied for a 200 kW VAWT H-rotor using logged data from a 14 month period with the H-rotor operating in wind speeds up to 9 m/s. The TI - λCp_max relation is examined by dividing 10 min mean values in different turbulence intensity ranges and producing multiple CP(λ) curves. A clear positive relation between TI and λCp_max is shown and is further strengthened as possible secondary effects are examined and deemed non-essential. The established relation makes it possible to tune the control strategy to enhance the total efficiency of the turbine.

Novel plant development for a high performance 3 kW integrated wind and solar system

This research describes a novel system of four Savonius wind rotors, aligned in parallel. A solar panel system, generating power by solar energy, was positioned in front of the parallel system to guide the airflow impinging on the rotors. This array was installed in rural areas to generate electric power. The effect of the solar panel deflector arrangements, used to guide the air stream, was investigated. This type of plant development has not previously been examined. We employed a computational fluid dynamics software, Fluent, to analyze the flow fields and system performance prior to experimentation, then compared these simulations to our experimental data. The parameters studied include wind velocity, wind direction (with/without solar panel deflector), and the rotational speed of the rotors to identify the relationship between the tip-speed ratio (TSR) and power coefficient (Cp). For the numerical simulation results at TSR 0.8, the maximum Cp value of the parallel system without a solar panel deflector was 0.289, whereas at the optimal spacing between the parallel systems with a deflector (50 cm), the Cp was 0.389. This represents a difference factor of 1.35 between the two Cp values. The velocity vector distribution showed that the deflector could guide the airflow to impinge on the rotors from below, gaining extra wind power. The experimental results show that the wind velocity and rotational speed of the wind rotors exhibit large fluctuations in open fields. To combat this, experiments were repeated in both day and night conditions, in different seasons, to gather a range of Cp and TSR values. The average measured wind speed was 6.99 ± 1.52 m/s. Four Savonius wind rotors in a parallel system can generate 8.25 kW h of energy per day, with an optimal power generation efficiency of 20.7%. Our 3-kW hybrid wind and solar system, which used optimal simulation conditions to determine its experimental design, can generate 14.55 kW h of power per day, with a corresponding optimal power generation efficiency of 21.7%. Our measured Cp curve shows that a deflector can improve the system performance by up to 10.1%.

Thermodynamic Properties of Zincate-Manganites of LaM2 IIZnMnO6 (МII = Mg, Ca, Sr, Ba) Composition

Temperature dependences of the heat capacity of new zincate-manganites of LaM2IIZnMnO6 (MII = Mg, Ca, Sr, Ba) composition are studied via experimental calorimetry in the interval of 298.15–673 K. It is found that all compounds have λ-shape effects on the curve of dependence Cp° ~ ƒ(T) with respect to phase transitions of the second kind. Equations for the temperature dependence of the heat capacity are derived with allowance for phase transition temperatures, and thermodynamic functions H°(T) − H°(298.15), S°(T) and Φxx(T) are calculated on the basis of experimental data on Cp°(T) and the calculated S°(298.15) value.