Unsteady Heat Transfer in Baffled Channels

1996 ◽  
Vol 118 (3) ◽  
pp. 585-591 ◽  
Author(s):  
G. Wang ◽  
K. Stone ◽  
S. P. Vanka
Keyword(s):  
Heat Transfer ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Process Industry ◽  
Unsteady Heat Transfer ◽  
Enhancement Of Heat Transfer ◽  
Compact Heat Exchangers ◽  
Unsteady Fluid Flow ◽  
Unsteady Fluid ◽  
Energy Equations

In this paper, the enhancement of heat transfer due to unsteady flow in channels with in-line and staggered baffles is investigated through the numerical solution of the governing unsteady fluid flow and energy equations with periodicity in the stream wise direction. For the inline configuration, the flow becomes naturally unsteady at a critical Reynolds number (Q/v) around 110. For the staggered case, this value is around 200. Significant increases in heat transfer rate are observed once the flow becomes unsteady. Results for several Reynolds numbers up to 500 are presented. The present results can be valuable to the design and operation of compact heat exchangers used in process industry.

Numerical Investigation of Flow Field and Heat Transfer in Cross-Corrugated Ducts

1999 ◽  
Vol 121 (2) ◽  
pp. 314-321 ◽  
Author(s):  
H. Blomerius ◽  
C. Ho¨lsken ◽  
N. K. Mitra
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Critical Reynolds Number ◽  
Wave Length ◽  
Reynolds Numbers ◽  
Sine Wave ◽  
Transitional Flow ◽  
Navier Stokes ◽  
Flow Oscillations ◽  
Energy Equations

Flow field and heat transfer in sine-wave crossed-corrugated ducts have been investigated by numerical solution of the Navier-Stokes and energy equations in the laminar and transitional flow regime between Re = 170 and 2000. The ratio of the corrugation wave length λ* to amplitude a* has been varied between 7 and 10. The angle of the corrugation of the neighboring plates has been kept fixed at 45 deg. Results show that the critical Reynolds number for self-sustained flow oscillations is about 240. For Reynolds numbers larger than 1000, the Nusselt number and the friction factor are nearly independent of the dimensionless wavelength. Computational results compare well with available experimental results.

Condensation of Steam on Finned Surfaces With Addition of a Surfactant

2005 ◽  
Author(s):  
Andrew T. Morrison ◽  
S. M. You
Keyword(s):  
Heat Transfer ◽  
Surface Energy ◽  
Reynolds Numbers ◽  
Film Condensation ◽  
Vapor Flow ◽  
Flow Conditions ◽  
Two Phase ◽  
Enhancement Of Heat Transfer ◽  
Flat Surfaces ◽  
Extended Surfaces

A fundamental knowledge of the parameters affecting film condensation is essential for the design of two phase heat exchangers. The current study examines the effect of extended surfaces and surface energy modifications and their interaction for condensation of steam in quiescent and vapor flow conditions. The enhancement of heat transfer for vertical, flat surfaces and two finned surfaces were compared for Reynolds numbers ranging from approximately 10 to 50. The addition of a nonionic surfactant, alcohol alkoxylate, to the system was evaluated for the same surfaces and vapor field conditions. Vapor flow of 0.25 m/s enhanced the heat transfer approximately 40%, while 0.5 m/s vapor velocity produced almost 100% increase in heat transfer. The addition of surfactant to the system produced small enhancement in heat transfer except in the case of condensate hold-up between the fins. In this case, the addition of surfactant increase the heat transfer an additional 25%, likely because the vapor flow and change of surface energy were sufficient to largely eliminate the hold-up of condensate between the fins.

Theoretical Analysis of Resonance Tube End Wall Heating: Solution of Unsteady Fluid Dynamic and Energy Equations

2015 ◽  
Author(s):  
Ramlala P. Sinha
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamic ◽  
Stable Solution ◽  
Heat Conducting ◽  
Cross Sectional ◽  
Arbitrary Boundary ◽  
Resonance Tube ◽  
Unsteady Fluid ◽  
Energy Equations ◽  
End Wall

A solution of the highly complex unsteady compressible flow field inside a cylindrical resonance tube has been obtained numerically, assuming one dimensional, viscous, and heat conducting flow, by solving the appropriate fluid dynamic and energy equations. The resonance tube is approximated by a right circular cylinder closed at one end with a piston oscillating at resonant frequency at the other end. An iterative implicit finite difference scheme is employed to obtain the solution. The scheme permits arbitrary boundary conditions at the piston and the end wall and allows assumptions for transport properties. For the example considered herein, the solution predicts a rise of 95°F in the mean end wall temperature, from 60°F to 155°F, in 14.313 milliseconds which is in good agreement with the experimentally observed values. The solution would also be valid for tapered tubes if the variations in the cross-sectional area are small. In successfully predicting the resonance tube results, an innovative simple but stable solution of unsteady fluid dynamic and energy equations is provided here for wide ranging research, development, and industrial applications in solving a variety of complex fluid flow heat transfer problems. The method is directly applicable to pulsed or pulsating flow and wave motion thermal energy transport, fluid-structure interaction heat transfer enhancement, and fluidic pyrotechnic initiation devices.

scholarly journals Heat transfer and flow structure through a backward-and forward-facing step micro-channels equipped with obstacles

2020 ◽  
pp. 219-219 ◽  
Author(s):  
Hassnia Hajji ◽  
Lioua Kolsi ◽  
Faouzi Askri ◽  
Chemseddine Maatki ◽  
Walid Hassen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Considerable Effect ◽  
Sudden Expansion ◽  
The Finite Element Method ◽  
Enhancement Of Heat Transfer ◽  
Low Reynolds Numbers ◽  
Micro Channels ◽  
Vortex Separation ◽  
Flow Through

This study presents two-dimensional simulations of a flow-through a sudden expansion/contraction micro-channel with the existence of obstacles. The bottom wall is maintained at constant flux, while the other walls are adiabatic. Rectangular adiabatic obstacles are mounted before the expansion region on the upper and lower wall of the channel used. The finite element method was used to discretize the equations that govern the physical model. Results indicate the apparition of a separate vortex, situated in the corner after the sudden expansion of the microchannel for low Reynolds numbers. For higher values and expansion ratios, the vortex separation length increases. The obtained results show that the obstacles have a considerable effect on the dynamics of the flow and enhancement of heat transfer.

scholarly journals Numerical Investigation of Heat Transfer Enhancement in a Rectangular Heated Pipe for Turbulent Nanofluid

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Hooman Yarmand ◽  
Samira Gharehkhani ◽  
Salim Newaz Kazi ◽  
Emad Sadeghinezhad ◽  
Mohammad Reza Safaei
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Volume Fraction ◽  
Rectangular Channel ◽  
Thermal Characteristics ◽  
Reynolds Numbers ◽  
Constant Heat Flux ◽  
Energy Equations ◽  
Volume Method ◽  
Good Agreement

Thermal characteristics of turbulent nanofluid flow in a rectangular pipe have been investigated numerically. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The symmetrical rectangular channel is heated at the top and bottom at a constant heat flux while the sides walls are insulated. Four different types of nanoparticles Al2O3, ZnO, CuO, and SiO2at different volume fractions of nanofluids in the range of 1% to 5% are considered in the present investigation. In this paper, effect of different Reynolds numbers in the range of 5000 < Re < 25000 on heat transfer characteristics of nanofluids flowing through the channel is investigated. The numerical results indicate that SiO2-water has the highest Nusselt number compared to other nanofluids while it has the lowest heat transfer coefficient due to low thermal conductivity. The Nusselt number increases with the increase of the Reynolds number and the volume fraction of nanoparticles. The results of simulation show a good agreement with the existing experimental correlations.

EHD Enhanced Convective Boiling of R-134a in Grooved Channels—Application to Subcompact Heat Exchangers

1997 ◽  
Vol 119 (4) ◽  
pp. 805-809 ◽  
Author(s):  
M. Salehi ◽  
M. M. Ohadi ◽  
S. Dessiatoun
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Flow Boiling ◽  
Flow Direction ◽  
Reynolds Numbers ◽  
Convective Boiling ◽  
Field Polarity ◽  
Electrical Field Strength ◽  
Compact Heat Exchangers ◽  
R 134A

Electrohydrodynamically (EHD) enhanced flow boiling of refrigerant R-134a inside grooved channels of approximately 1-mm hydraulic diameter was investigated with the objective of addressing the applicability of the EHD technique in highly compact heat exchangers. Two sets of experiments were performed. The first set included experiments in a channel with a smooth heat transfer wall, whereas in the second set a corrugated (enhanced) surface was used. In each case experiments were conducted as a function of the applied electrical field strength, electric field polarity, flow Reynolds number, inlet test section vapor quality, and flow direction (upward, downward, or horizontal). It is demonstrated that in all cases the EHD effect can substantially increase the heat transfer coefficient particularly at low Reynolds numbers and when applied over the enhanced heat transfer wall.

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