Scaling of Thermal Positioning in Microscale and Nanoscale Bridge Structures

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Elham Maghsoudi ◽  
Michael James Martin
Keyword(s):  
Heat Transfer ◽  
Silicon Carbide ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Biot Number ◽  
Cvd Diamond ◽  
Bridge Structures ◽  
The Heat Transfer Coefficient ◽  
Dimensionless Displacement ◽  
The Continuum

Heat transfer in a thermally positioned doubly clamped bridge is simulated to obtain a universal scaling for the behavior of microscale and nanoscale bridge structures over a range of dimensions, materials, ambient heat transfer conditions, and heat loads. The simulations use both free molecular and continuum models to define the heat transfer coefficient, h. Two systems are compared: one doubly clamped beam with a length of 100 μm, a width of 10 μm, and a thickness of 3 μm, and a second beam with a length of 10 μm, a width of 1 μm, and a thickness of 300 nm, in the air at a pressure from 0.01 Pa to 2 MPa. The simulations are performed for three materials: crystalline silicon, silicon carbide, and chemical vapor deposition (CVD) diamond. The numerical results show that the displacement and the response of thermally positioned nanoscale devices are strongly influenced by ambient cooling. The displacement depends on the material properties, the geometry of the beam, and the heat transfer coefficient. These results can be collapsed into a single dimensionless center displacement, δ* = δk/q″αl2, which depends on the Biot number and the system geometry. The center displacement of the system increases significantly as the bridge length increases, while these variations are negligible when the bridge width and thickness change. In the free molecular model, the center displacement varies significantly with the pressure at high Biot numbers, while it does not depend on cooling gas pressure in the continuum case. The significant variation of center displacement starts at Biot number of 0.1, which occurs at gas pressure of 27 kPa in nanoscale. As the Biot number increases, the dimensionless displacement decreases. The continuum-level effects are scaled with the statistical mechanics effects. Comparison of the dimensionless displacement with the thermal vibration in the system shows that CVD diamond systems may have displacements that are at the level of the thermal noise, while silicon carbide systems will have a higher displacement ratios.

Evaluation of Heating Process of Apple, Eggplant, Zucchini and Potato by Means of Their Thermal Properties

2016 ◽  
Author(s):  
Hilario Terres ◽  
Sandra Chavez ◽  
Raymundo Lopez ◽  
Arturo Lizardi ◽  
Araceli Lara
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Thermal Properties ◽  
Transfer Coefficient ◽  
Biot Number ◽  
Heating Process ◽  
Energy Devices ◽  
Heating Device ◽  
The Heat Transfer Coefficient ◽  
Transitory State

In this work, the heating process for apple, eggplant, zucchini and potato by means of evaluation of their thermal properties and the Biot number determined in experimental form is presented. The heating process is carried out using a solar cooker box-type as heating device. The thermal experimental properties determined are conductivity (k), density (D), specific heat (C), diffusivity (Dif) and the Biot number (Bi) for each product evaluated. In the experimentation, temperatures for center and surface in each product and water were measured in controlled conditions. For those measures, a device Compact Fieldpoint and thermocouples placed in the points studied were used. By using correlations with temperature as function, k, D and C were calculated, while by using equations in transitory state for the products modeled as sphere and cylinder was possible to estimate the Biot number after calculation of the heat transfer coefficient for each case. Results indicate the higher value for k, C and Dif correspond to zucchini (0.65 W/m °C, 4084.5 J/kg °C, 1.5 × 10−7 m2), while higher value for D correspond to potato (1197.5 kg/m3). The lowest values for k and C were obtained for potato (0.59 W/m °C, 3658.3 J/kg °C) while lowest values for D and Dif, correspond to zucchini (998.2 kg/m3) and potato (1.45 × 10−7 m2/s) respectively. The maximum and minimum values for Bi corresponded to potato (21.4) and zucchini (0.41) in respective way. The results obtained are very useful in applications for solar energy devices, where estimates for properties are very important to generate new results, for example, numerical simulations. Also, results could be used to evaluate the cooking power in solar cookers when the study object is oriented in that direction.

scholarly journals Thermal-Hydraulic Performance of Graphene Nanoribbon and Silicon Carbide Nanoparticles in the Multi-Louvered Radiator for Cooling Diesel Engine

2020 ◽  
Vol 7 (1) ◽  
pp. F22-F29 ◽  
Author(s):  
E. Nogueira
Keyword(s):  
Heat Transfer ◽  
Silicon Carbide ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Analytical Solution ◽  
Transfer Coefficient ◽  
Mass Flow ◽  
Volume Fraction ◽  
Graphene Nanoribbon ◽  
The Heat Transfer Coefficient

Analytical solution for application and comparison of Graphene Nanoribbon and Silicon Carbide for thermal and hydraulic performance in flat tube Multi-Louvered Finned Radiator is presented. The base fluid is composed of pure water and ethylene glycol at a 50% volume fraction. The results were obtained for Nusselt number, convection heat transfer coefficient and pressure drop, for airflow in the radiator core and nanofluids in flat tubes. The main thermal and hydraulic parameters used are the Reynolds number, the mass flow rate, the Colburn Factor, and Friction Factor. In some situations, under analysis, the volume fraction, for Graphene Nanoribbon and Silicon Carbide, were varied. The value of the heat transfer coefficient obtained for Graphene Nanoribbon, for the volume fraction equal 0.05, is higher than twice the amount received by Silicon Carbide. The flow is laminar, for whatever the fraction value by volume of the Graphene nanoparticles when the mass flow of the nanofluid is relatively low. For turbulent flow and relatively small fractions of nanoparticles, the heat transfer coefficient is significantly high for mass flow rates of Graphene Nanoribbon. The pressure drop, for the same volume fraction of nanoparticles, is slightly higher than the pressure drop associated with Silicon Carbide. These high values for the heat transfer coefficient is a favorable result and of great practical importance, since lower values for the fraction in volume can reduce the costs of the compact heat exchanger (radiator). Keywords: analytical solution, nanofluid, compact exchanger, automotive radiator.

An Inverse Method for Drying at High Mass Transfer Biot Number

2003 ◽  
Author(s):  
Gligor H. Kanevce ◽  
Ljubica P. Kanevce ◽  
George S. Dulikravich ◽  
Marcelo J. Colac¸o
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Heat And Mass Transfer ◽  
Biot Number ◽  
Temperature Sensitivity ◽  
Sensitivity Coefficient ◽  
The Heat Transfer Coefficient

The inverse problem of using temperature measurements to estimate the moisture content and temperature-dependent moisture diffusivity together with the heat and mass transfer coefficients is analyzed in this paper. In the convective drying practice, usually the mass transfer Biot number is very high and the heat transfer Biot number is very small. This leads to a very small temperature sensitivity coefficient with respect to the mass transfer coefficient when compared to the temperature sensitivity coefficient with respect to the heat transfer coefficient. Under these conditions the relative error of the estimated mass transfer coefficient is high. To overcome this problem, in this paper the mass transfer coefficient is related to the heat transfer coefficient through the analogy between the heat and mass transfer processes in the boundary layer. The resulting parameter estimation problem is then solved by using a hybrid constrained optimization algorithm OPTRAN.

Effects of Averaging the Heat Transfer Coefficient on Predicted Material Temperature and Its Gradient

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Chien-Shing Lee ◽  
Tom I-P. Shih ◽  
Kenneth Mark Bryden
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Temperature Gradient ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Biot Number ◽  
Maximum Temperature ◽  
Gradual Transition ◽  
The Heat Transfer Coefficient ◽  
Maximum Temperature Gradient

The heat transfer coefficient (HTC) is often averaged spatially when designing heat exchangers. Since the HTC could vary appreciably about a heat transfer enhancement feature such as a pin fin or a rib, it is of interest to understand the effects of averaging the HTC on design. This computational study examines those effects via a unit problem—a flat plate of thickness H and length L, where L represents the distance between pin-fins or ribs. This flat plate is heated on one side, and cooled on the other. Variable HTC is imposed on the cooled side—a higher HTC (hH) over LH and a lower HTC (hL) over LL = L − LH. For this unit problem, the following parameters were studied: abrupt versus gradual transition between hH and hL, hH/hL, LH/L, and H/L. Results obtained show that if the averaged HTC is used, then the maximum temperature in the plate and the maximum temperature gradient in the plate can be severely underpredicted. The maximum temperature and the maximum temperature gradient can be underpredicted by as much as 36.3% and 542%, respectively, if the Biot number is less than 0.1 and as much as 13.0% and 570% if the Biot number is between 0.25 and 0.4. A reduced-order model was developed to estimate the underpredicted maximum temperature.

Evaporation of lignin-lean black liquor

TAPPI Journal ◽  
2015 ◽  
Vol 14 (7) ◽  
pp. 441-450
Author(s):  
HENRIK WALLMO, ◽  
ULF ANDERSSON ◽  
MATHIAS GOURDON ◽  
MARTIN WIMBY
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Black Liquor ◽  
Salt Content ◽  
Solubility Limit ◽  
Lignin Removal ◽  
Kraft Black Liquor ◽  
Black Liquors ◽  
The Heat Transfer Coefficient

Many of the pulp mill biorefinery concepts recently presented include removal of lignin from black liquor. In this work, the aim was to study how the change in liquor chemistry affected the evaporation of kraft black liquor when lignin was removed using the LignoBoost process. Lignin was removed from a softwood kraft black liquor and four different black liquors were studied: one reference black liquor (with no lignin extracted); two ligninlean black liquors with a lignin removal rate of 5.5% and 21%, respectively; and one liquor with maximum lignin removal of 60%. Evaporation tests were carried out at the research evaporator in Chalmers University of Technology. Studied parameters were liquor viscosity, boiling point rise, heat transfer coefficient, scaling propensity, changes in liquor chemical composition, and tube incrustation. It was found that the solubility limit for incrustation changed towards lower dry solids for the lignin-lean black liquors due to an increased salt content. The scaling obtained on the tubes was easily cleaned with thin liquor at 105°C. It was also shown that the liquor viscosity decreased exponentially with increased lignin outtake and hence, the heat transfer coefficient increased with increased lignin outtake. Long term tests, operated about 6 percentage dry solids units above the solubility limit for incrustation for all liquors, showed that the heat transfer coefficient increased from 650 W/m2K for the reference liquor to 1500 W/m2K for the liquor with highest lignin separation degree, 60%.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

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