Effect of Periodic Pulsations on Heat Transfer in Simultaneously Developing Laminar Flows: A Numerical Study

2010 ◽  
Author(s):  
Balkrishna Mehta ◽  
Sameer Khandekar
Keyword(s):  
Heat Transfer ◽  
Amplitude Ratio ◽  
Numerical Study ◽  
Transport Coefficients ◽  
Internal Flow ◽  
Laminar Flows ◽  
Operating Conditions ◽  
Parallel Plates ◽  
Species Transport ◽  
Unidirectional Flow

Heat transfer in the channels and ducts are well understood in the steady laminar flows for engineering applications. In contrast, unsteady flows have potential for research as many aspects of such flows are still unclear. Periodic pulsating flow in a channel is a kind of unsteady flow which requires further investigation because (i) many upcoming applications, especially in mini-micro scale engineering domain e.g. enhanced mixing, MEMS applications, bio-fluidic devices and thermal management of electronics etc. (ii) critical review of literature reveals that there is prevailing confusion related to the species transport coefficients. Thus, need for a systematic parametric study, both numerical and experimental, cannot be overemphasized. In this paper, two different configurations of laminar pulsatile internal flow, i.e. Case (i): unidirectional flow with axial superimposed pulsations (flow in circular axisymmetric tube) and, Case (ii) unidirectional flow with superimposed transverse pulsations (parallel plates) have been numerically scrutinized. Effect of frequency (Womersley number, Wo), Prandtl number (Pr), Reynolds number (Re) and amplitude ratio, on the instantaneous and time averaged heat transfer and friction factor (Poiseuille number) is studied. It is found that the change in species transport is either marginal or highly limited and is primarily occurring in the developing length of the channel/ plate. Nusselt number under pulsating conditions in the fully developed flow regime is not very different from its steady counterpart. Enhancement of species transport due to such periodic pulsatile internal flows, over and above the non-pulsatile regular flow conditions, is questionable, and at best, rather limited. Enhancement in heat transfer is seen in Case (ii) under certain operating conditions. This latter configuration is more attractive than the former and further optimization studies are required to improve understanding.

Numerical Simulation of Gas Flow and Heat Transfer in Cross-Wavy Primary Surface Channel for Microtubine Recuperators

2005 ◽  
Author(s):  
H. X. Liang ◽  
Q. W. Wang ◽  
L. Q. Luo ◽  
Z. P. Feng
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Gas Turbine ◽  
Numerical Study ◽  
High Reliability ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Flow And Heat Transfer ◽  
High Heat Transfer ◽  
The Cross

Three-dimensional numerical simulation was conducted to investigate the flow field and heat transfer performance of the Cross-Wavy Primary Surface (CWPS) recuperators for microturbines. Using high-effective compact recuperators to achieve high thermal efficiency is one of the key techniques in the development of microturbine in recent years. Recuperators need to have minimum volume and weight, high reliability and durability. Most important of all, they need to have high thermal-effectiveness and low pressure-losses so that the gas turbine system can achieve high thermal performances. These requirements have attracted some research efforts in designing and implementing low-cost and compact recuperators for gas turbine engines recently. One of the promising techniques to achieve this goal is the so-called primary surface channels with small hydraulic dimensions. In this paper, we conducted a three-dimensional numerical study of flow and heat transfer for the Cross-Wavy Primary Surface (CWPS) channels with two different geometries. In the CWPS configurations the secondary flow is created by means of curved and interrupted surfaces, which may disturb the thermal boundary layers and thus improve the thermal performances of the channels. To facilitate comparison, we chose the identical hydraulic diameters for the above four CWPS channels. Since our experiments on real recuperators showed that the Reynolds number ranges from 150 to 500 under the operating conditions, we implemented all the simulations under laminar flow situations. By analyzing the correlations of Nusselt numbers and friction factors vs. Reynolds numbers of the four CWPS channels, we found that the CWPS channels have superior and comprehensive thermal performance with high compactness, i.e., high heat transfer area to volume ratio, indicating excellent commercialized application in the compact recuperators.

Numerical study of unsteady MHD Couette flow and heat transfer of nanofluids in a rotating system with convective cooling

2016 ◽  
Vol 26 (5) ◽  
pp. 1567-1579 ◽  
Author(s):  
Ahmada Omar Ali ◽  
Oluwole Daniel Makinde ◽  
Yaw Nkansah-Gyekye
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Couette Flow ◽  
Numerical Study ◽  
Integration Scheme ◽  
Parallel Plates ◽  
Content Type ◽  
Flow And Heat Transfer ◽  
Mhd Couette Flow ◽  
Rotating Channel

Purpose – The purpose of this paper is to investigate numerically the unsteady MHD Couette flow and heat transfer of viscous, incompressible and electrically conducting nanofluids between two parallel plates in a rotating channel. Design/methodology/approach – The nanofluid is set in motion by the combined action of moving upper plate, Coriolis force and the constant pressure gradient. The channel rotates in unison about an axis normal to the plates. The nonlinear governing equations for velocity and heat transfer are obtained and solved numerically using semi-discretization, shooting and collocation (bvp4c) techniques together with Runge-Kutta Fehlberg integration scheme. Findings – Results show that both magnetic field and rotation rate demonstrate significant effect on velocity and heat transfer profiles in the system with Cu-water nanofluid demonstrating the highest velocity and heat transfer efficiency. These numerical results are in excellent agreements with the results obtained by other methods. Practical implications – This paper provides a very useful source of information for researchers on the subject of hydromagnetic nanofluid flow in rotating systems. Originality/value – Couette flow of nanofluid in the presence of applied magnetic field in a rotating channel is investigated.

Natural Convection in an Enclosure With Blend of Micro Encapsulated Phase Change Materials

2013 ◽  
Author(s):  
Yasmin Khakpour ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Thermal Expansion ◽  
Natural Convection ◽  
Phase Change ◽  
Latent Heat ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Pure Water ◽  
Operating Conditions ◽  
Effective Density

This numerical study investigates the effect of using a blend of micro-encapsulated phase change materials (MEPCMs) on the heat transfer characteristics of a liquid in a rectangular enclosure driven by natural convection. A comparison has been made between the cases of using single component MEPCM slurry and a blend of two-component MEPCM slurry. The natural convection is generated by the temperature difference between two vertical walls of the enclosure maintained at constant temperatures. Each of the two phase change materials store latent heat at a specific range of temperatures. During phase change of the PCM, the effective density of the slurry varies. This results in thermal expansion and hence a buoyancy driven flow. The effects of MEPCM concentration in the slurry and changes in the operating conditions such as the wall temperatures compared to that of pure water have been studied. The MEPCM latent heat and the increased volumetric thermal expansion coefficient during phase change of the MEPCM play a major role in this heat transfer augmentation.

Numerical Study on Heat Transfer Characteristics From Parallel Plates With Cavities Swept by a Visco-Elastic Fluid

2010 ◽  
Author(s):  
Hiroshi Suzuki ◽  
Shinpei Maeda ◽  
Yoshiyuki Komoda
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Thermal Field ◽  
Numerical Study ◽  
Geometric Parameters ◽  
Two Dimensional ◽  
Parallel Plates ◽  
Heat Transfer Characteristics ◽  
Elastic Fluid ◽  
Heat Transfer Augmentation

Two-dimensional numerical computations have been performed in order to investigate the development characteristics of flow and thermal field in a flow between parallel plates swept by a visco-elastic fluid. In the present study, the effect of the cavity number in the domain and of Reynolds number was focused on when the geometric parameters were set constant. From the results, it is found that the flow penetration into the cavities effectively causes the heat transfer augmentation in the cavities in any cavity region compared with that of water case. It is also found that the development of thermal field in cases of the present visco-elastic fluid is quicker compared with that of water cases. The present heat transfer augmentation technique using Barus effect of a visco-elastic fluid is effective in the range of low Reynolds number.

Numerical Characterization of Flow and Heat Transfer in Pre-Swirl Systems

2017 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Jacopo D’Errico
Keyword(s):  
Heat Transfer ◽  
Gas Turbines ◽  
Numerical Study ◽  
Physical Phenomenon ◽  
Computational Procedure ◽  
Operating Conditions ◽  
Simulation Techniques ◽  
Numerical Characterization ◽  
Unsteady Simulation

This paper deals with a numerical study aimed at the validation of a computational procedure for the aerothermal characterization of pre-swirl systems employed in axial gas turbines. The numerical campaign focused on an experimental facility which models the flow field inside a direct-flow pre-swirl system. Steady and unsteady simulation techniques were adopted in conjunction with both a standard two-equations RANS/URANS modelling and more advanced approaches such as the Scale-Adaptive-Simulation principle, the SBES and LES. The comparisons between CFD and experiments were done in terms of swirl number development, static and total pressure distributions, receiving holes discharge coefficient and heat transfer on the rotor disc surface. Several operating conditions were accounted for, spanning 0.78·106<Reφ<1.21·106 and 0.123<λt<0.376. Overall the steady-state CFD predictions are in good agreement with the experimental evidences even though it is not able to confidently mimic the experimental swirl and pressure behaviour in some regions. Although the use of unsteady sliding mesh and direct turbulence modelling, would in principle increase the insight in the physical phenomenon, from a design perspective the tradeoff between accuracy and computational costs is not always favourable.

scholarly journals Numerical Study of MHD Flow and Heat Transfer Through Porous Medium Between Two Parallel Plates With Hall and Ion Slip Effects

2020 ◽  
Vol 7 ◽  
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Numerical Study ◽  
Mhd Flow ◽  
Parallel Plates ◽  
Electrically Conducting ◽  
Flow And Heat Transfer ◽  
Slip Effects ◽  
Ion Slip ◽  
Temperature And Pressure

This paper studies the effects of Hall and ion slip on two dimensional incompressible flow and heat transfer of an electrically conducting viscous fluid in a porous medium between two parallel plates, generated due to periodic suction and injection at the plates. The flow field, temperature and pressure are assumed to be periodic functions in ti e ω and the plates are kept at different but constant temperatures. A numerical solution for the governing nonlinear ordinary differential equations is obtained using quasilinearization method. The graphs for velocity, temperature distribution and skin friction are presented for different values of the fluid and geometric parameters.

Modeling of a 3-Dimensional Conjugate Heat Transfer on the Channel-Composite-Wall for Electronics Cooling

2006 ◽  
Author(s):  
K. Yazawa ◽  
H. Yoshino ◽  
Y. Nishino ◽  
S. Nakagawa ◽  
M. Ishizuka
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Conjugate Heat Transfer ◽  
Thermal Characteristic ◽  
Internal Heat ◽  
Electronics Cooling ◽  
Internal Flow ◽  
Passive Cooling ◽  
Parallel Plates ◽  
Composite Wall

We report the modeling of a novel approach to passive heat transfer from electronic equipment through an enclosure wall with built-in vertical channels. This passive cooling method is based on the different temperature requirements between the enclosure surface and the internal heat-generating devices. This approach takes advantage of natural convection, known as the chimney effect, resulting from higher temperatures in vertically oriented channels. In addition to channel convection, the skin surface exposed to the environment dissipates the heat passively by both natural convection and radiation. The configuration of the wall and channels, termed a Channel-Composite-Wall (CCW), creates a novel form of passive cooling that we have analyzed and modeled. The inner side of the CCW is assumed to be uniformly heated. The three-dimensional flow regime is observed by means of PIV (particle image velocimetry) experiments and numerical studies. The unique velocity profile inside each channel is observed and can be regarded as similar to the flow in the differently heated parallel plates. The channel flow is modeled by breaking the channel down into two sections plus the exposed skin wall. Based on these observations, the relationship between the internal flow field and external convective flow can be considered to be handled separately. The thermal characteristic is also studied based on the correlations. The thermal conductivity and thickness of the solid partition of channels are found to be significant contributors to performance. The analytic model of the CCW was verified by numerical calculations and experiments. The model reasonably closely expresses the characteristics of this comprehensive conjugate heat transfer. The model can thus be used for the development of passively cooled electronics enclosure.

scholarly journals Rotating Heat Transfer Experiments With Turbine Airfoil Internal Flow Passages

1986 ◽  
Author(s):  
Joel H. Wagner ◽  
Jay C. Kim ◽  
Bruce V. Johnson
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Large Scale ◽  
Flow Direction ◽  
Internal Flow ◽  
Operating Conditions ◽  
Coolant Temperature ◽  
Rossby Number ◽  
Transfer Coefficients ◽  
Bulk Fluid

Internal convective cooling is used to maintain acceptable gas turbine rotor blade temperatures. The heat transfer from the blade coolant passage walls is governed by forced convection, Coriolis forces and buoyance due to wall and coolant temperature differences. Currently little data is available to designers regarding the combined effects of these three parameters. To obtain required data, a rotating heat transfer facility was developed for experiments with large scale models and run at rotation and flow parameters typical of current gas turbine operating conditions. Analysis of the equations of motion showed that the perinent nondimensional parameters were Reynolds number, Rossby number, the difference in wall fluid and bulk fluid density and geometric ratios. The models were instrumented to measure average heat transfer rates on the coolant passage wall elements, and with pressure taps for friction data. An initial set of experiments have been conducted with rough wall geometries, typical of those used in blades. Results from the rotating experiments showed large heat transfer coefficient increases and decreases on the coolant passage leading and trailing surfaces compared to nonrotating heat transfer coefficients. The heat transfer was shown to be a function of inward or outward flow direction and Rossby number for the experiments conducted.

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