Sheet Temperature Research Articles

Micropolar nanofluid flow with MHD and viscous dissipation effects towards a stretching sheet with multimedia feature

An applied thermal system for heat and mass transfer and energy management problem of hydromagnetic flow with magnetic and viscous dissipation effects micropolar nanofluids towards a stretching sheet has been studied. A system of partial differential equations for micropolar and nanofluid has been analyzed by a combination of the similarity transformation and accurate finite-difference method. Those solutions are used to obtain distributions of the local convective heat transfer coefficient and the stretching sheet temperature. The related importance dimensionless parameters are Prandtl number Pr, magnetic parameter M, material parameter K, Eckert number Ec, Brownian motion number Nb, thermophoresis parameter Nt and the Schmidt number Sc, respectively. The numerical results are indicated that an increasing in the magnetic parameter is given a decreasing in the values of the velocities and Nusselt number, or an increasing in the values of the shear stress, couple stress at the surface, temperature and concentration. The material parameter K has the opposite effect of magnetic field parameter on the values of the velocities, temperature, concentration, shear stress, Nusselt number and Schmidt number. The temperature is decreased as the Prandtl number increasing, or is increased as the Eckert number increasing. The concentration is decreased as Schmidt number increasing. At last, the study has been presented one multimedia video to show its main contain, it will be appeared at Elsevier AudioSlides website.

Forming of Thermoplastic Matrix Composites with Gas Pressure – the Influence of Blank Holder and Sheet Temperature on the Forming Pressure and Drawing Ratio

Abstract New processes for continuous fiber-reinforced thermoplastics (“organo-sheets”) offer new possibilities e. g. for the production of closed hollow bodies. In the Twin-O-Sheet Process the forming is done via gas pressure without separate diaphragms. This brings new demands on the organo-sheets with respect to gas density. In this article the influence of the forming parameters blank holder temperature and sheet temperature on the achievable gas pressure and drawing ratios with twill-weave PA6/GF organo-sheets are investigated. The results show that higher blank holder temperatures lead to higher drawing ratios despite of lower pressures. Compared to the blank holder temperature the influence of the sheet temperature on the drawing ratio is minor.

Implementing Thermomechanical Properties of 22MnB5 Steel during Hot Single-Point Incremental Forming

The strategy in manufacturing hardened parts used in car bodies is to tailor the mechanical properties. This is done by combining together a high-strength region and a high-toughness region to ensure the crash performance required. Other successive secondary operations such as trimming, joining and welding can be improved as a result of the tailoring process. In this work, the mechanical properties of 22MnB5 alloy sheet material produced by single-point incremental forming have been tailored. For this purpose, the sheets were locally heated by induction during the forming process and subsequently cooled. The sheet temperature was controlled by the CNC milling machine feed rate and induction power. As a result, the produced tailored parts consist of three different regions: ductile, transition and hardened regions. The Vickers hardness values were 583 HV1 and 175 HV1 for the hardened and ductile regions, respectively. The proposed application allows forming and quenching at the same time without transfer and to reduce the process time.

Numerical Heat and Mass Transfer of a Micropolar Fluids Flow with Magnetic Effect to Past a Stretching Sheet

A heat and mass transfer and energy management problem of for hydromagnetic flow with magnetic effect micropolar fluids past through a stretching sheet has been studied. Governing equations are included continuity equation, momentum equation, angular momentum equation, energy equation and the concentration equation of a micropolar fluid have been analyzed by a combination of the similarity transformation and a accurate finite-difference method. These solutions are used to obtain distributions of the local convective heat transfer coefficient and the stretching sheet temperature. The ranges of these dimensionless parameters, the Prandtl number Pr, the magnetic parameter M, the material parameter K, the Eckert number Ec and the Schmidt number Sc are from 0.3 to 0.71, 0 to 20, 0 to 2, 0 to 0.8 and 0.5 to 10, respectively. The numerical results indicate that, an increase in the magnetic parameter gives a decrease in the values of the velocities and Nusselt number, or an increase in the values of the shear stress, couple stress at the surface, temperature and concentration. The material parameter has the opposite effect of magnetic field parameter on the values of the velocities, temperature, concentration, shear stress, Nusselt number and Schmidt number. The temperature decreases as the Prandtl number increases, or increases as the Eckert number increases. The concentration decreases as Schmidt number increases.

Assessment of a mattress with phase change materials using a thermal and perception test

Mattresses composed by phase change materials (PCMs) may improve the thermoregulation of the human body. The aim of the study was to analyse the thermoregulatory efficiency of a PCMs and a conventional mattresses via the evaluation of the skin temperature, thermal comfort and thermal perception. Twenty participants lay on a PCMs and a conventional mattress for 20min in each mattress on the same day. Skin temperature of the back of the participants and temperature of the sheet of the mattresses were measured before and immediately after lying on each mattress. Thermal comfort and thermal perception were also reported during the last minute of the lying test. The PCMs mattress resulted in a lower increase in skin temperature (0.3–1.0°C, p=0.002 and ES=1.4) and a greater increase of the sheet temperature (0.2–1.6°C, p=0.02 and ES=0.8). No differences in thermal comfort and thermal perception were observed between mattresses (p>0.05 and ES<0.8). The analysis of the superficial temperature (skin, sheet) was an adequate tool to identify differences in the thermoregulatory efficiency of different mattresses. The use of PCMs in mattresses improved the heat dissipation of the human body during lying in a proportion between 2.7% and 25.6%. However, the thermoregulatory differences were not big enough to alter the thermal comfort and thermal perception of the participants after 20 min of test.

Simulation of the bite condition of AZ31 sheet rolling

Sheet rolling is a simple plastic deformation of which, there are many formulas to describe its bite condition, however, there is no rigorous theoretical analysis and result and the applying ranges of these formulas are limited. Although the bite condition is not an important problem in engineering or academy, it is really a term influenced by many factors and it is difficult, maybe impossible to be expressed by an equation. In this paper, by finite element software, the bite condition or the critical friction factor under different thicknesses of AZ31 sheet, rolling reduction, sheet temperature and roller temperature are calculated and with large result data, the change regulation of the bite condition appears which is shown in a colour brick model. This example shows that, avoiding rigorous theoretical analysis, a complex situation can be numerically illustrated well by finite element software.

Finite Element Simulation of Heat Transfer during Cryogenic Asymmetric Sheet Rolling of Aluminum Alloys

Aluminum and its alloys are widely used as structural materials in aerospace, automotive and other industries due to low density and high specific strength. Efficient way to increase strength and other properties of aluminum alloys is to form an ultra fine grain structure using severe plastic deformation methods. Cryogenic asymmetric sheet rolling under liquid nitrogen temperature is a process of severe plastic deformation that can be used to improve the aluminum alloys structure and properties. Prediction of sheet temperature during plastic deformation is very important. The temperature of sheet is changed due to the conversion of mechanical work of deformation into heat through sliding on contact surfaces. This paper presents the results of the finite element simulation of heat transfer during cryogenic asymmetric sheet rolling of aluminum alloy 6061. The effect of thickness reduction, rolling velocity and friction coefficient on the deformation heating and temperature field of aluminum alloy 6061 was found. The results of investigation could be useful for the development of the optimal treatment process of aluminum alloys by cryogenic severe plastic deformation to obtain the ultra fine grain structure and high strength properties.

Mechanical properties of pristine and nanoporous graphene

We present molecular dynamics simulations of monolayer graphene under uniaxial tensile loading. The Morse, bending angle, torsion and Lennard-Jones potential functions are adopted within the mdFOAM library in the OpenFOAM software, to describe the molecular interactions in graphene. A well-validated graphene model using these set of potentials is not yet available. In this work, we investigate the accuracy of the mechanical properties of graphene when derived using these simpler potentials, compared to the more commonly used complex potentials such as the Tersoff-Brenner and AIREBO potentials. The computational speed up of our approach, which scales O(1.5N), where N is the number of carbon atoms, enabled us to vary a larger number of system parameters, including graphene sheet orientation, size, temperature and concentration of nanopores. The resultant effect on the elastic modulus, fracture stress and fracture strain is investigated. Our simulations show that graphene is anisotropic, and its mechanical properties are dependant on the sheet size. An increase in system temperature results in a significant reduction in the fracture stress and strain. Simulations of nanoporous graphene were created by distributing vacancy defects, both randomly and uniformly, across the lattice. We find that the fracture stress decreases substantially with increasing defect density. The elastic modulus was found to be constant up to around 5% vacancy defects, and decreases for higher defect densities.

Solar wind‐driven variations of electron plasma sheet densities and temperatures beyond geostationary orbit during storm times

AbstractThe empirical models of the plasma sheet electron temperature and density on the nightside at distances between 6 and 11 RE are constructed based on Time History of Events and Macroscale Interactions During Substorms (THEMIS) particle measurements. The data set comprises ∼400 h of observations in the plasma sheet during geomagnetic storm periods. The equatorial distribution of the electron density reveals a strong earthward gradient and a moderate variation with magnetic local time symmetric with respect to the midnight meridian. The electron density dependence on the external driving is parameterized by the solar wind proton density averaged over 4 h and the southward component of interplanetary magnetic field (IMF BS) averaged over 6 h. The interval of the IMF integration is much longer than a typical substorm growth phase, and it rather corresponds to the geomagnetic storm main phase duration. The solar wind proton density is the main controlling parameter, but the IMF BS becomes of almost the same importance in the near‐Earth region. The root‐mean‐square deviation between the observed and predicted plasma sheet density values is 0.23 cm−3, and the correlation coefficient is 0.82. The equatorial distribution of the electron temperature has a maximum in the postmidnight to morning MLT sector, and it is highly asymmetric with respect to the local midnight. The electron temperature model is parameterized by solar wind velocity (averaged over 4 h), IMF BS (averaged over 45 min), and IMF BN (northward component of IMF, averaged over 2 h). The solar wind velocity is a major controlling parameter, and IMF BS and BN are comparable in importance. In contrast to the density model, the electron temperature shows higher correlation with the IMF BS averaged over ∼45 min (substorm growth phase time scale). The effect of BN manifests mostly in the outer part of the modeled region (r &gt; 8RE). The influence of the IMF BS is maximal in the midnight to postmidnight MLT sector. The correlation coefficient between the observed and predicted plasma sheet electron temperature values is 0.76, and the root‐mean‐square deviation is 2.6 keV. Both models reveal better performance in the dawn MLT sector.

Stable temperature coefficient of resistance in TiSiON thin film resistors deposited by magnetron co-sputtering

Thin films of titanium/silicon (Ti:Si) are widely employed in the electronics industry because of their metal-like characteristics. The use of films as thin film resistor (TFR) based on Ti:Si has not yet been reported. In this paper, the TFR characteristics of TiSiON with different compositions and deposited in Argon atmosphere with either 1% Oxygen or 1% Oxygen/3% Nitrogen are studied. The film composition was varied through a co-sputtering approach from titanium and silicon targets and the sheet resistance (Rsh) and temperature coefficient of resistance (TCR) were evaluated. The film composition was evaluated by X-ray photoelectron spectroscopy (XPS); carrier mobility, type and concentration by Hall effect methods and film microstructure by X-Ray diffraction. Nitrogen addition during the deposition reduces oxidized species in the TFR and increases film stability. The addition of nitrogen results in TFR films with partially oxidized titanium and silicon and TFR values closer to zero TCR without impacting film resistance. Films deposited without nitrogen result in more unstable films and larger TCR. A near-zero TCR film was found for a Ti:Si ratio of 1.6, exhibiting a Rsh at 25 °C of 0.7 kOhms with a TCR value of −171 ppm/°C after annealing at 450 °C in forming gas.

Dynamic snap-through buckling of CNT reinforced composite sandwich spherical caps

This paper investigates the nonlinear dynamic buckling response of axisymmetric carbon nanotubes reinforced composite sandwich spherical caps subjected to suddenly applied pressure. To solve this problem, a finite element approach is adopted using an axisymmetric shear flexible shell element, free from spurious constraints causing shear and membrane locking especially for the case of thin shells. The geometric nonlinearity is accounted for in the formulation using von Karman’s strain-displacement relations. Newmark’s integration technique along with the modified Newton-Raphson iteration scheme is employed to solve the nonlinear governing equations. The critical dynamic pressure value is considered as the pressure load beyond which the maximum average displacement response shows instant growth in the time history of the shell structure. The obtained results are validated against the available analytical solutions for the case of isotropic spherical caps. A detailed parametric study is carried out to bring out the effects of shell geometry parameter, volume fraction of the CNT, core-to-face sheet thickness, temperature, boundary conditions and different types of pulse on the dynamic snap-through characteristics of spherical shells.

Development of an outdoor photovoltaic module test platform

A new outdoor photovoltaic (PV) module test platform was introduced to measure I–V characteristic curve of PV module in this study. The proposed test platform was designed centring on the programmable electronic load (E-load) which used the transfer characteristics of metal–oxide–semiconductor field-effect transistor (MOSFET) and controlled PV module output current by controlling the drain current I D of MOSFET indirectly. Ultimately, controlling the PV module work on any operating point of the I–V curve. This test platform can automatically shift operation mode contraposing the I–V curve of PV module. It can continuously measure I–V curves and ambient data in the outdoors including the total irradiance, temperature of PV module back sheet and ambient temperature. The test results show the proposed test platform's accuracy meets the user's requirements, and more details of I–V curve can be obtained than by using traditional measurement mode.

Effect of Press Slide Speed and Stroke on Cup Forming Using a Plain-Woven Carbon Fiber Thermoplastic Composite Sheet

Carbon-fiber-reinforced thermoplastic (CFRTP) is viewed as a prospective material for high-cycle production of CFRP parts. This paper deals with a process whereby a preheated thermoplastic plain-woven carbon fiber fabric sheet is formed into a circular cup by a mechanical servo-press. The effects of press parameters, specifically the bottom dead center and slide speed in the forming of CFRTP cup, on the press load, pressure, internal temperature, shape accuracy, and internal structure have been investigated. A plain-woven carbon-fiber-reinforced PA6 thermoplastic sheet was used. The sheet consisted of four layers of woven 3K carbon and had a thickness of 1 mm. The sheet was heated to 320°C under a halogen heater so that it would be around the recommended temperature for forming 260°C after transfer to the mold. The sheet was pressed into a circular cup shape by a cold mold while the periphery was cramped by a heated holder so as not to cool the sheet before it was pulled into the mold cave. Die clearance was designed considering the thickness increase due to the fiber concentration during the forming. By increasing the slide stroke to the bottom dead center, the applied press load was increased and the internal structure was improved, showing no voids. By increasing the slide speed, the final press load was reduced and shape accuracy was improved through a good pressure distribution on the mold. Measurement of the surface temperature of the sheet during the forming revealed that it remained in the melting region of the resin in the case of fast slide speed, but dropped below the melting temperature in the case of low slide speed. This difference apparently led to spring-in or spring-back after the forming. The experimental results indicate that appropriate balance among press speed, bottom dead center, and sheet temperature is important in the high-cycle forming of CFRTP.

Thermoresponsive poly[tri(ethylene glycol) monoethyl ether methacrylate]-peptide surfaces obtained by radiation grafting-synthesis and characterisation

This report demonstrates the feasibility of radiation grafting for the preparation of polymer layers functionalised with short peptide ligands which promote cell adhesion. Thermoresponsive poly [tri(ethylene glycol) monoethyl ether methacrylate] (PTEGMA) layers were synthesised on a polypropylene substrate by post-irradiation grafting. A cell adhesion moiety, the CF-IKVAVK peptide modified with a methacrylamide function and a fluorescent label were introduced to the surface during the polymerisation process. The amount of CF-IKVAVK was easily controlled by changing its concentration in the reaction mixture. The changes in the surface composition, morphology, philicity and thickness at each step of the polypropylene functionalisation confirmed that the surface modification procedures were successful. The increase in environmental temperature above the cloud point temperature of PTEGMA caused a decrease in surface philicity. The obtained PTEGMA and PTEGMA-peptide surfaces above TCP were tested as scaffolds for fibroblast sheet culture and temperature induced detachment.

An experimental study on dimensional accuracy, surface quality, and hardness of Ti-6Al-4 V titanium alloy sheet in hot incremental forming

In this study, an electrical heater device that employs alternative electrical current was designed and used to perform the sheet incremental forming process at elevated temperatures. The main advantage of the new device over the existing designs is the use of alternate current electricity which makes the process safer for the operator, requires less expensive equipment, and is more available than the direct current electricity. In this device, the electrical current passes through the tool and generates the maximum heat at the sheet-tool interface. The device was mounted on an incremental forming setup, and the temperature was measured during the forming process. The temperature measurements showed that the device was able to effectively raise the sheet temperature. Furthermore, Ti-6Al-4 V sheets were incrementally formed into a few basic important shapes: conical frustum, variable wall angle conical frustum, and pyramidal frustum. The effect of different process parameters on the dimensional accuracy, surface quality, and workhardening of the fabricated workpieces was studied. The results showed that the highest deviation from ideal geometry occurs at the workpiece tip, and it considerably decreases a few millimeters away from the tip. In addition, the roughness of the inner surface where the tool contacts the workpiece is greater than the outer surface. Micro-hardness test results also showed that the hardness increased from flange to vertex of the workpiece where larger plastic deformation and hence more workhardening is expected to occur.

A comprehensive experimental investigation on the influences of the process variables on warm incremental forming of Ti-6Al-4V titanium alloy using a simple technique

The incremental forming has recently acquired a significant importance in various applications, such as automotive, aerospace, and medical industries. The present investigation is concerned with the warm incremental forming of Ti-6Al-4V titanium alloy. With this regard, the groove test was employed as a simple technique to study the effects of different variables, namely, the process temperature, the vertical pitch, and the tool diameter, on the forming limit diagram of the material, the springback, drawing depth, final temperature of the sheet, and the thickness variation of the product. The sheet temperature was the most important parameter affected by the interfacial friction and the other process variables. The experimental findings illustrated that the greater the vertical pitch and/or the tool diameter, the larger the formability and drawing depth of the sheet sample before its fracture. Moreover, decreasing the tool diameter and increasing the vertical pitch and the initial process temperature resulted in more thickness reduction. The actual process temperature simultaneously affected the elastic modulus and the flow stress of the component. However, the flow stress reduction due to the temperature rise overcame the elastic modulus decrease and, finally, the springback was lower at higher process temperatures.

Optimal heating condition of mouthguard sheet in vacuum-pressure formation: part 3 styrene-based thermoplastic elastomer.

The aim of this study was to identify suitable heating conditions of polyolefin-polystyrene co-polymer sheets in vacuum-pressure formation, monitor the sheet temperature during molding, and examine the thickness of the fabricated mouthguard. Mouthguards were fabricated with polyolefin-polystyrene co-polymer sheets (4.0-mm thick) utilizing a vacuum/pressure-forming device, which was subjected to vacuum forming for 10 s and pressure molding for 2 min. Four heating conditions were compared, defined by the amount of sag distance of 5, 10, 15, or 20 mm from the center of the softened sheet below the clamp. The working model was trimmed to a height of 20 mm at the cutting edge of the maxillary central incisor and to a height of 15 mm at the mesiobuccal cusp of the maxillary first molar. The radiation thermometer was used to measure the sheet temperatures of the center of the heated and non-heated surfaces under each condition. The sheet thickness after fabrication was determined for the incisal and the molar portions, and dimensional measurements were obtained using a measuring device. The differences in the sheet thickness produced by the different heating conditions were analyzed by Games-Howell's multiple comparison tests. For condition of 5 mm sagged, the temperature on the non-heated surface did not reach a sufficient softening temperature and the thickness was smallest. Mouthguard thickness was largest in the order of 15 mm sagged condition, followed by 20 mm sagged condition and then by 10 mm sagged condition, but a statistical difference was not observed in the labial and the buccal surface among the three conditions. This study demonstrated that for sufficient softening, it was necessary to heat the sheet to obtain a sag of 10 mm or more, and that the mouthguard thickness decreased as the sag increased.

Effect of sheet temperature on web densification during calendering

We used two different experimental methods to study the effects of sheet temperature at a given moisture content on web densification and sheet smoothness. Commercially prepared paperboard obtained from the WestRock Mahrt mill in Cottonton, AL, USA, was used in this study. Laboratory made handsheets prepared from Mahrt high yield kraft pine pulp were also used for portions of this work. Sheets were sealed in moisture-proof bags, heated to various temperatures, and calendered at multiple nip loads. The resulting changes in sheet density were determined. Additionally, a pilot-scale calender was modified to preheat the non-print side of the sheet before entering the nip. The modified sheet run allowed for an increase in the bulk temperature of the board with minimal changes in the moisture content of the print surface. Increasing the bulk temperature increased board density at a given print surface smoothness. We determined that increasing the board temperature by 14°C resulted in about a 1% increase in board density. The results of this study help explain the commercial results obtained with thermal gradient calendering.

Radiative heat transfer of variable viscosity and thermal conductivity effects on inclined magnetic field with dissipation in a non-Darcy medium

The study of thermal radiative heat transfer of an electrically conducting fluid over a continuously stretching sheet in the presence of a uniform inclined magnetic field with dissipation in a porous medium is investigated for power-law variation in the sheet temperature. The fluid viscosity and thermal conductivity are assumed to vary as a function of temperature. The governing partial differential equations of the model are reduced to a system of coupled non-linear ordinary differential equations by applying similarity variables and then solved numerically using shooting technique with fourth-order Runge–Kutta method. The results for Skin friction and Nusselt numbers are presented and discussed.

Atmospheric summer teleconnections and Greenland Ice Sheet surface mass variations: insights from MERRA-2

The relationship between leading atmospheric teleconnection patterns and Greenland Ice Sheet (GrIS) temperature, precipitation, and surface mass balance (SMB) are investigated for the last 36 summers (1979–2014) based on Modern-Era Retrospective analysis for Research and Applications version 2 reanalyses. The results indicate that the negative phase of both the North Atlantic Oscillation (NAO) and Arctic Oscillation, associated with warm and dry conditions for the GrIS, lead to SMB decreases within 0–1 months. Furthermore, the positive phase of the East Atlantic (EA) pattern often lags the negative NAO, reflecting a dynamical linkage between these modes that acts to further enhance the warm and dry conditions over the GrIS, leading to a favorable environment for enhanced surface mass loss. The development of a strong negative NAO in combination with a strong positive EA in recent years leads to significantly larger GrIS warming compared to when the negative NAO occurs in combination with a negative or weak positive EA (0.69 K versus 0.13 K anomaly). During 2009 and 2011, weakened (as compared to conditions during the severe surface melt cases of 2010 and 2012) local high pressure blocking produced colder northerly flow over the GrIS inhibiting warming despite the occurrence of a strong negative NAO, reflecting an important role for the EA during those years. In particular, the EA acts with the NAO to enhance warming in 2010 and 2012, and weaken high pressure blocking in 2009 and 2011. In general, high pressure blocking primarily impacts the western areas of the GrIS via advective temperature increases, while changes in net surface radiative fluxes account for both western and eastern GrIS temperature changes.