Heat Transfer Enhancement of Viscoelastic Fluid in the Rectangle Microchannel with Constant Heat Fluxes

2011 ◽  
Vol 117-119 ◽  
pp. 574-581
Author(s):  
Guo Fa Zhou ◽  
Ting Peng
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Secondary Flow ◽  
Viscoelastic Fluid ◽  
Radial Flow ◽  
Heat Fluxes ◽  
Transfer Enhancement ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Macro Scale

It has been found that viscoelastic fluid has evident heat transfer enhancement function in macro scale. But in micro scale, viscoelastic fluid’s flow and heat transfer characteristics are still unknown. In this paper, the heat transfer process of viscoelastic fluid in the microchannel is studied by numerical simulation method. The simulation results show that the maximum heat transfer enhancement of viscoelastic fluid is up to 800%, compared with pure viscous fluid. The viscoelastic fluid has such obvious heat transfer enhancement function because of its strong secondary flow. Laminar sub-layer can be damaged by the strong secondary flow, and thus radial flow generates in laminar sub-layer. The radial flow can increase the interference and mixing effect, and enhances fluid’s turbulence and convection which can enhance heat transfer as a result. So the heat transfer enhancement depends on the intensity of secondary flow which is caused by the second normal stress difference, and it will increase with the raise of the flow rate.

Enhancement of Natural Convection Heat Transfer by a Staggered Array of Discrete Vertical Plates

1980 ◽  
Vol 102 (2) ◽  
pp. 215-220 ◽  
Author(s):  
E. M. Sparrow ◽  
C. Prakash
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Enhancement ◽  
Parallel Plate ◽  
Convection Heat Transfer ◽  
Transfer Enhancement ◽  
Enhanced Heat Transfer ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Parameter Ranges

An analysis has been performed to determine whether, in natural convection, a staggered array of discrete vertical plates yields enhanced heat transfer compared with an array of continuous parallel vertical plates having the same surface area. The heat transfer results were obtained by numerically solving the equations of mass, momentum, and energy for the two types of configurations. It was found that the use of discrete plates gives rise to heat transfer enhancement when the parameter (Dh/H)Ra > ∼2 × 103 (Dh = hydraulic diameter of flow passage, H = overall system height). The extent of the enhancement is increased by use of numerous shorter plates, by larger transverse interplate spacing, and by relatively short system heights. For the parameter ranges investigated, the maximum heat transfer enhancement, relative to the parallel plate case, was a factor of two. The general degree of enhancement compares favorably with that which has been obtained in forced convection systems.

scholarly journals Investigation of the novelty of latent functionally thermal fluids as alternative to nanofluids in natural convective flows

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Zoubida Haddad ◽  
Farida Iachachene ◽  
Eiyad Abu-Nada ◽  
Ioan Pop
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Enhancement ◽  
Volume Fraction ◽  
Heat Of Fusion ◽  
Transfer Enhancement ◽  
Maximum Heat ◽  
Thermal Fluids ◽  
Maximum Heat Transfer ◽  
Wide Range

AbstractThis paper presents a detailed comparison between the latent functionally thermal fluids (LFTFs) and nanofluids in terms of heat transfer enhancement. The problem used to carry the comparison is natural convection in a differentially heated cavity where LFTFs and nanofluids are considered the working fluids. The nanofluid mixture consists of Al2O3 nanoparticles and water, whereas the LFTF mixture consists of a suspension of nanoencapsulated phase change material (NEPCMs) in water. The thermophysical properties of the LFTFs are derived from available experimental data in literature. The NEPCMs consist of n-nonadecane as PCM and poly(styrene-co-methacrylic acid) as shell material for the encapsulation. Finite volume method is used to solve the governing equations of the LFTFs and the nanofluid. The computations covered a wide range of Rayleigh number, 104 ≤ Ra ≤ 107, and nanoparticle volume fraction ranging between 0 and 1.69%. It was found that the LFTFs give substantial heat transfer enhancement compared to nanofluids, where the maximum heat transfer enhancement of 13% was observed over nanofluids. Though the thermal conductivity of LFTFs was 15 times smaller than that of the base fluid, a significant enhancement in thermal conductivity was observed. This enhancement was attributed to the high latent heat of fusion of the LFTFs which increased the energy transport within the cavity and accordingly the thermal conductivity of the LFTFs.

An Experimental Investigation of Heat Transfer Enhancement by Pulsating Laminar Flow in a Triangular Grooved Channel

2012 ◽  
Vol 516-517 ◽  
pp. 249-252 ◽  
Author(s):  
Bing Chang Yang ◽  
Dong Xu Jin
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Strouhal Number ◽  
Enhancement Factor ◽  
Pulsating Flow ◽  
Transfer Enhancement ◽  
Maximum Heat ◽  
Pulsation Amplitude ◽  
Maximum Heat Transfer

Heat transfer enhancement by pulsating flow in a triangular grooved channel has been experimentally investigated. Effects of Reynolds number Re, Strouhal number St, pulsation amplitude A on the heat transfer enhancement were studied. The experimental results show that, the pulsating flow can significantly enhance heat transfer compared to the steady flow case, for instance, an enhancement of 115% is achieved at Re=400, A=0.5 and St=0.3. There exists an optimal Strouhal number corresponding to the maximum heat transfer enhancement factor. The heat transfer enhancement factor increases with the increase of Reynolds number and pulsation amplitude.

Heat Transfer Enhancement in Turbulent Ribbed-Pipe Flow

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Pipe Flow ◽  
Joint Probability ◽  
Turbulent Heat Transfer ◽  
Immersed Boundary ◽  
Turbulent Heat ◽  
Transfer Enhancement ◽  
Maximum Heat ◽  
Maximum Heat Transfer

The present study aims at explaining why heat transfer is enhanced in turbulent ribbed-pipe flow, based on our previous large eddy simulation (LES) database (Kang and Yang, 2016, “Characterization of Turbulent Heat Transfer in Ribbed Pipe Flow,” ASME J. Heat Transfer, 138(4), p. 041901) obtained for Re = 24,000, Pr = 0.71, pitch ratio (PR) = 2, 4, 6, 8, 10, and 18, and blockage ratio (BR) = 0.0625. Here, the bulk velocity and the pipe diameter were used as the velocity and length scales, respectively. The ribs were implemented in the cylindrical coordinate system by means of an immersed boundary method. In particular, we focus on the cases of PR ≥ 4 for which heat transfer turns out to be significantly enhanced. Instantaneous flow fields reveal that the vortices shed from the ribs are entrained into the main recirculating region behind the ribs, inducing velocity fluctuations in the vicinity of the pipe wall. In order to identify the turbulence structures responsible for heat transfer enhancement in turbulent ribbed-pipe flow, various correlations among the fluctuations of temperature and velocity components have been computed and analyzed. The cross-correlation coefficient and joint probability density distributions of velocity and temperature fluctuations, obtained for PR = 10, confirm that temperature fluctuation is highly correlated with velocity-component fluctuation, but which component depends upon the axial location of interest between two neighboring ribs. Furthermore, it was found via the octant analysis performed for the same PR that at the axial point of the maximum heat transfer rate, O3 (cold wallward interaction) and O5 (hot outward interaction) events most contribute to turbulent heat flux and most frequently occur.

Compounded Heat Transfer Enhancement in Enclosure Natural Convection by Changing the Cold Wall Shape and the Gas Composition

2006 ◽  
Vol 129 (7) ◽  
pp. 827-834 ◽  
Author(s):  
El Hassan Ridouane ◽  
Antonio Campo
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Enhancement ◽  
Gas Mixtures ◽  
Gas Mixture ◽  
Transfer Enhancement ◽  
Maximum Enhancement ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Triangular Enclosure

This article addresses compound heat transfer enhancement for gaseous natural convection in closed enclosures; that is, the simultaneous use of two passive techniques to obtain heat transfer enhancement, which is greater than that produced by only one technique itself. The compounded heat transfer enhancement comes from two sources: (1) reshaping the bounded space and (2) the adequacy of the gas. The sizing of enclosures is of great interest in the miniaturization of electronic packaging that is severely constrained by space and∕or weight. The gases consist in a subset of binary gas mixtures formed with helium (He) as the primary gas. The secondary gases are nitrogen (N2), oxygen (O2), carbon dioxide (CO2), methane (CH4), and xenon (Xe). The steady-state flow is governed by a system of 2-D coupled mass, momentum, and energy conservation equations, in conjunction with the ideal gas equation of state. The set of partial differential equations is solved using the finite volume method, for a square and a right-angled isosceles triangular enclosure, accounting for the second-order accurate QUICK and SIMPLE schemes. The grid layouts rendered reliable velocities and temperatures for air and the five gas mixtures at high Ra=106, producing errors within 1% were 18,500 and 47,300 elements for the square and triangle enclosures, respectively. In terms of heat transfer enhancement, helium is better than air for the square and the isosceles triangle. It was found that the maximum heat transfer conditions are obtained filling the isosceles triangular enclosure with a He–Xe gas mixture. This gives a good trade-off between maximizing the heat transfer rate while reducing the enclosure space in half; the maximum enhancement of triangle∕square went up from 19% when filled with air into 46% when filled with He–Xe gas mixture at high Ra=106.

An Experiment Investigation of Heat Transfer Enhancement by Pulsating Laminar Flow in Rectangular Grooved Channels

2013 ◽  
Vol 732-733 ◽  
pp. 74-77
Author(s):  
Yan Li ◽  
Dong Xu Jin ◽  
Yan Qin Jing ◽  
Bing Chang Yang
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Heat Transfer Enhancement ◽  
Enhancement Factor ◽  
Groove Depth ◽  
Pulsating Flow ◽  
Pulsation Frequency ◽  
Transfer Enhancement ◽  
Maximum Heat ◽  
Maximum Heat Transfer

In this paper, the heat transfer enhancement by pulsating laminar flow in rectangular grooved channels was experimentally investigated. Effects of Reynolds number Re, pulsation frequency, groove depth and groove length on the heat transfer enhancement were studied. Experimental results show that Nusselt number increases with Re increases both in steady and pulsating flow cases. Pulsating flow can efficiently enhance heat transfer in the grooved channels and the heat transfer enhancement factor increases with the increase of Re. There exists an optimal pulsation frequency, corresponding to the maximum heat transfer enhancement factor, which is almost the same for different Re, groove depth and groove length.

Heat Transfer Enhancement of Air Flowing Across Grooved Channels: Joint Effects of Channel Height and Groove Depth

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
El Hassan Ridouane ◽  
Antonio Campo
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Parallel Plate ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Groove Depth ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Maximum Heat ◽  
Maximum Heat Transfer

A numerical study was conducted to investigate convective heat transfer and laminar fluid flow in the developing region of two-dimensional parallel-plate channels with arrays of transverse hemicircular grooves cut into the plates. Air with uniform velocity and temperature enters the channel whose plates are at a uniform temperature. The finite-volume method is used to perform the computational analysis accounting for the traditional second-order-accurate QUICK and SIMPLE schemes. Steady-state results are presented for parallel-plate channels with and without hemicircular grooves for comparison purposes. The study revolves around four controlling parameters: (1) the height of the channel, (2) the relative groove depth, (3) the number of grooves, and (4) the Reynolds number. A prototypical 120‐cm-long channel contains two series of 3, 6, and 12 transverse grooves with four relative groove depths δ∕D of 0.125, 0.25, 0.375, and 0.5. Three ratios of channel height to groove print diameter H∕D of 0.5, 1, and 2 are employed. Computations are performed for Reynolds numbers based on the hydraulic diameter ranging from 1000 to 2500. It is found that the grooves enhance local heat transfer relative to a flat passage at locations near their downstream edge. The maximum heat transfer enhancement occurs at an optimal depth of the grooves. For purposes of engineering design, generalized correlation equations for the Nusselt number in terms of the pertinent Re, δ∕D, and the number of grooves N were constructed using nonlinear regression theory.

Heat-transfer enhancement due to slender recirculation and chaotic transport between counter-rotating eccentric cylinders

1992 ◽  
Vol 238 ◽  
pp. 119-154 ◽  
Author(s):  
S. Ghosh ◽  
H.-C. Chang ◽  
M. Sen
Keyword(s):  
Heat Transfer ◽  
Mass Transport ◽  
Heat Transfer Enhancement ◽  
Small Amplitude ◽  
Recirculation Region ◽  
Matched Asymptotic Expansion ◽  
Transfer Enhancement ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Chaotic Transport

Using Stokes flow between eccentric, counter-rotating cylinders as a prototype for bounded, nearly parallel lubrication flow, we investigate the effect of a slender recirculation region within the flow field on cross-stream heat or mass transport in the important limit of high Péclet number Pe where the enhancement over pure conduction heat transfer without recirculation is most pronounced. The steady enhancement is estimated with a matched asymptotic expansion to resolve the diffusive boundary layers at the separatrices which bound the recirculation region. The enhancement over pure conduction is shown to vary as ε½ at infinite Pe, where ε½ is the characteristic width of the recirculation region. The enhancement decays from this asymptote as Pe−½. If one perturbs the steady flow by a time-periodic forcing, fast relative to the convective and diffusive times, the separatrices undergo a homoclinic entanglement which allows fluid elements to cross the separatrices. We establish the existence of this homoclinic entanglement and show that the resulting chaotic particle transport further enhances the cross-stream flux. We estimate the penetration of the fluid elements across the separatrices and their effective diffusivity due to this chaotic transport by a Melnikov analysis for small-amplitude forcing. These and the steady results then provide quantitative estimates of the timeaveraged transport enhancement and allow optimization with respect to system parameters. An optimum forcing frequency which induces maximum heat-transfer enhancement is predicted and numerically verified. The predicted optimum frequency remains valid at strong forcing and large Pe where chaotic transport is as important as the recirculation mechanism. Since most heat and mass transport devices operate at high Pe, our analysis suggests that chaotic enhancement can improve their performance and that a small amplitude theory can be used to optimize its application.

Role of Chamfering Angles and Flow Through Slit on Heat Transfer Augmentation Behind a Surface-Mounted Rib

2016 ◽  
Vol 138 (11) ◽  
Author(s):  
Md Shaukat Ali ◽  
Andallib Tariq ◽  
B. K. Gandhi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Coming Out ◽  
Mixing Enhancement ◽  
Reattachment Length ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Maximum Heat ◽  
Maximum Heat Transfer

Detailed heat transfer and flow field investigations behind a surface-mounted slitted trapezoidal rib have been performed using liquid crystal thermography (LCT) and particle image velocimetry (PIV). In the accomplished experiments, the effects of varying the chamfering angle over the trailing edge of a rib with a centrally placed longitudinal continuous slit carrying an open area ratio equivalent to 25% were studied. The chamfering angle has been varied from 0 to 20 deg in a step of 5 deg. Experiments were carried out for four different Reynolds numbers ranging in between 9400 and 61,480, which were based upon the hydraulic diameter of the rectangular duct. The motive behind the present work is to systematically study the effect of change in chamfering angle of a trapezoidal rib with a centrally placed continuous slit over the flow and heat transfer parameters. Emphasis was made to identify the flow parameters responsible for augmentation in surface heat transfer coefficients (HTCs). Results are presented in terms of mean and rms velocity fields, stream traces, Reynolds stress, vorticity, and surface- and spanwise-averaged augmentation Nusselt number distribution. The reattachment length and the average augmentation Nusselt number have been evaluated for all of the different configurations. Entire configurations under selected range of Reynolds number led to the rise in heat transfer enhancement as against the flat surface without the rib. It is observed that slitted ribs cause shorter reattachment length and better heat transfer enhancement in the downstream vicinity of the rib. Further, the recirculation area behind the rib is enlarged to the point of spanning the nearby downstream vicinity of the rib (x/e<4), which signifies the zone of maximum heat transfer enhancement due to the effect of flow coming out of the slit. Salient critical points and foci of secondary recirculation patterns are extracted, which provides clues to the physical process occurring in the flow, which were responsible for the mixing enhancement behind slitted trapezoidal rib geometries.

Numerical Investigation of Secondary Flow Vortex Core Structure in the Two-Pass Rectangular Channel With 45° Ribs

2015 ◽  
Author(s):  
Jiangnan Zhu ◽  
Tieyu Gao ◽  
Jun Li ◽  
Guojun Li ◽  
Jianying Gong
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Secondary Flow ◽  
Gas Turbine ◽  
Vortex Core ◽  
Side Wall ◽  
Main Flow ◽  
Transfer Enhancement ◽  
Cooling Channels ◽  
Flow Vortex

The secondary flow which is generated by the angled rib is one of the key factors of heat transfer enhancement in gas turbine blade cooling channels. However, the current studies are all based on the velocity vector and streamline, which limit the research on the detailed micro-structure of secondary flow. In order to make further targeted optimization on the flow and heat transfer in the cooling channels of gas turbine blade, it is necessary to firstly investigate the generation, interaction, dissipation and the influence on heat transfer of secondary flow with the help of new topological method. This paper reports the numerical study of the secondary flow and the effect of secondary flow on heat transfer enhancement in rectangular two-pass channel with 45° ribs. Based on the vortex core technology, the structure of secondary flow can be clearly shown and studied. The results showed that the main flow secondary flow is thrown to the outer side wall after the corner due to the centrifugal force. Then it is weakened in the second pass and a new main flow secondary flow is generated at the same time near the opposite side wall in the second pass. The Nusselt number distribution has also been compared with the secondary flow vortex core distribution. The results shows that the heat transfer strength is weakened in the second pass due to the interaction between the old main flow secondary flow and the new one. These two secondary flows are in opposite rotation direction, which reduces the disturbance and mass transfer strength in the channel.

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