Numerical study of heat transport in thermally isolated flow-rate microsensors

1992 ◽  
Vol 70 (10-11) ◽  
pp. 904-907
Author(s):  
N. Swart ◽  
A. Nathan
Keyword(s):  
Heat Transfer ◽  
Heat Flow ◽  
Boundary Conditions ◽  
Heat Transport ◽  
Flow Rate ◽  
Energy Equation ◽  
Numerical Study ◽  
Control Volume ◽  
Circuit Simulator ◽  
Temperature Distributions

The temperature distributions in thermally isolated cantilever based flow-rate microsensors have been numerically calculated for different gas temperatures and gas velocities. In particular, we investigate the efficiency of heat transfer to the flowing gas and corresponding directions of heat flow in the system. The above analysis is based on a solution to the energy equation under appropriate boundary conditions. The equation was discretized using a control volume procedure, based on which an equivalent circuit was devised and subsequently simulated using a circuit simulator such as SPICE.

A Complete Solution for Thermal-Elastohydrodynamic Lubrication of Line Contacts Using Circular Non-Newtonian Fluid Model

1992 ◽  
Vol 114 (3) ◽  
pp. 540-551 ◽  
Author(s):  
Hsing-Sen S. Hsiao ◽  
Bernard J. Hamrock
Keyword(s):  
Boundary Conditions ◽  
Newtonian Fluid ◽  
Energy Equation ◽  
Control Volume ◽  
Fluid Model ◽  
Complete Solution ◽  
Circular Model ◽  
Line Contacts ◽  
Stress Boundary Conditions ◽  
Stress Boundary

A complete solution is obtained for elastohydrodynamically lubricated conjunctions in line contacts considering the effects of temperature and the non-Newtonian characteristics of lubricants with limiting shear strength. The complete fast approach is used to solve the thermal Reynolds equation by using the complete circular non-Newtonian fluid model and considering both velocity and stress boundary conditions. The reason and the occasion to incorporate stress boundary conditions for the circular model are discussed. A conservative form of the energy equation is developed by using the finite control volume approach. Analytical solutions for solid surface temperatures that consider two-dimensional heat flow within the solids are used. A straightforward finite difference method, successive over-relaxation by lines, is employed to solve the energy equation. Results of thermal effects on film shape, pressure profile, streamlines, and friction coefficient are presented.

Effect of Periodic Imposed Heat Flux on Three-Dimensional Natural Convection in a Partially Heated Cubical Enclosure

2016 ◽  
Vol 831 ◽  
pp. 83-91
Author(s):  
Lahoucine Belarche ◽  
Btissam Abourida
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Control Volume ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Maximum Temperature ◽  
Cubical Enclosure ◽  
Simplec Algorithm ◽  
Volume Method

The three-dimensional numerical study of natural convection in a cubical enclosure, discretely heated, was carried out in this study. Two heating square sections, similar to the integrated electronic components, are placed on the vertical wall of the enclosure. The imposed heating fluxes vary sinusoidally with time, in phase and in opposition of phase. The temperature of the opposite vertical wall is maintained at a cold uniform temperature and the other walls are adiabatic. The governing equations are solved using Control volume method by SIMPLEC algorithm. The sections dimension ε = D / H and the Rayleigh number Ra were fixed respectively at 0,35 and 106. The average heat transfer and the maximum temperature on the active portions will be examined for a given set of the governing parameters, namely the amplitude of the variable temperatures a and their period τp. The obtained results show significant changes in terms of heat transfer, by proper choice of the heating mode and the governing parameters.

scholarly journals A numerical study of free convective heat transfer within domed skylight cavities

2021 ◽  
Author(s):  
AmirAbbas Sartipi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Control Volume ◽  
Energy Performance ◽  
Vortex Cell ◽  
Design Elements ◽  
Gap Ratio

Domed skylights are important architectural design elements to deliver daylight and solar heat into buildings and connect buildings' occupants to outdoors. To increase the energy efficiency of skylighted buildings, domed skylights employ a number of glazing layers forming enclosed spaces. The latter are subject to complex buoyancy-induced convection heat transfer. Currently, existing fenestration design computer tools and building energy simulation programs do not, however, cover such skylights to quantify their energy performance when installed in buildings. his work presents a numerical study on natural laminar convection within concentric and vertically eccentric domed cavities. The edges of domed cavities are assumed adiabatic and the temperature of the interior and exterior surfaces are uniform and constant. The concentric and vertically eccentric domed cavities were studied when heated from inside and heated from outside, respectively. A commercial CFD package employing the control volume approach is used to solve the laminar convective heat transfer within the cavity. The obtained results showed steady flow for small Grashof numbers. For moderate and large Grashof numbers, depending on the gap ratio and the cases of heating from inside or outside, the flow may be steady or transient periodic with a single vortex-cell or multi vortex-cells. The Nusselt number for the case of heated from inside is greater than the case of heated from outside. The numerical results show that the changes in the gap ratio have smaller effect on Nusselt number in high profile domed skylights than lower profile domed skylights.

scholarly journals Mixed insulating and conducting thermal boundary conditions in Rayleigh–Bénard convection

2017 ◽  
Vol 835 ◽  
pp. 491-511 ◽  
Author(s):  
Dennis Bakhuis ◽  
Rodolfo Ostilla-Mónico ◽  
Erwin P. van der Poel ◽  
Roberto Verzicco ◽  
Detlef Lohse
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Heat Transport ◽  
Bottom Plate ◽  
Bulk Temperature ◽  
Stripe Pattern ◽  
Bénard Convection ◽  
Benard Convection ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

A series of direct numerical simulations of Rayleigh–Bénard convection, the flow in a fluid layer heated from below and cooled from above, were conducted to investigate the effect of mixed insulating and conducting boundary conditions on convective flows. Rayleigh numbers between $Ra=10^{7}$ and $Ra=10^{9}$ were considered, for Prandtl numbers $\mathit{Pr}=1$ and $\mathit{Pr}=10$. The bottom plate was divided into patterns of conducting and insulating stripes. The size ratio between these stripes was fixed to unity and the total number of stripes was varied. Global quantities, such as the heat transport and average bulk temperature, and local quantities, such as the temperature just below the insulating boundary wall, were investigated. For the case with the top boundary divided into two halves, one conducting and one insulating, the heat transfer was found to be approximately two-thirds of that for the fully conducting case. Increasing the pattern frequency increased the heat transfer, which asymptotically approached the fully conducting case, even if only half of the surface is conducting. Fourier analysis of the temperature field revealed that the imprinted pattern of the plates is diffused in the thermal boundary layers, and cannot be detected in the bulk. With conducting–insulating patterns on both plates, the trends previously described were similar; however, the half-and-half division led to a heat transfer of about a half of that for the fully conducting case instead of two-thirds. The effect of the ratio of conducting and insulating areas was also analysed, and it was found that, even for systems with a top plate with only 25 % conducting surface, heat transport of 60 % of the fully conducting case can be seen. Changing the one-dimensional stripe pattern to a two-dimensional chequerboard tessellation does not result in a significantly different response of the system.

Heat Flux to Fluids Within a Rock Fracture in a Geothermal System

2010 ◽  
Author(s):  
Dustin Crandall ◽  
Goodarz Ahmadi ◽  
Grant Bromhal
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Numerical Study ◽  
Rock Fracture ◽  
Working Fluid ◽  
Geothermal System ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Ct Scanner

Fractures in rocks enable the motion of fluids through the large, hot geologic formations of geothermal reservoirs. The heat transfer from the surrounding rock mass to the fluid flowing through a fracture depends on the geometry of the fracture, the fluid/solid properties, and the flow rate through the fracture. A numerical study was conducted to evaluate the changes in heat transfer to the fluid flowing through a rock fracture with changes in the flow rate. The aperture distribution of the rock fracture, originally created within Berea sandstone and imaged using a CT-scanner, is well described by a Gaussian distribution and has a mean aperture of approximately 0.6 mm. Water was used as the working fluid, enabling an evaluation of the efficiency of heat flux to the fluid along the flow path of a hot dry geothermal system. As the flow through the fracture was increased to a Reynolds number greater than 2300 the effect of channeling through large aperture regions within the fracture were observed to become increasingly important. For the fastest flows modeled the heat flux to the working fluids was reduced due to a shorter residence time of the fluid in the fracture. Understanding what conditions can maximize the amount of energy obtained from fractures within a hot dry geologic field can improve the operation and long-term viability of enhanced geothermal systems.

Laminar Mixed Convection in the Entrance Region of a Helical Pipe

1999 ◽  
Author(s):  
B. Zheng ◽  
C. X. Lin ◽  
M. A. Ebadian
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Control Volume ◽  
Three Dimensional ◽  
Entrance Region ◽  
Temperature Fields ◽  
Uniform Structure ◽  
Buoyancy Effect ◽  
Laminar Mixed Convection ◽  
Helical Pipe

Abstract A fully elliptic numerical study is performed to investigate the buoyancy-affected, three-dimensional laminar flow and heat transfer in the entrance region of a helical pipe at a constant wall temperature. The Control Volume Method with second-order accuracy is used to numerically solve the three-dimensional fully elliptic governing equations for the problem. The O-type non-uniform structure grid system is adopted to discretize the computation domain (two complete turns of a helical pipe) in this study. The Bossinesq approximation is applied to deal with the buoyancy effect caused directly by density difference. The developments of flow and temperature fields, profiles and characteristics at different Gr/Re2 are given and discussed. The computed results reveal that the entrance region of heat transfer is increased rapidly when buoyancy force is considered. In the meantime, the buoyancy effect on the average Nusselt number and friction factor is greater at the entrance region of the helical pipe, but it gradually becomes weaker further downstream.

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