Heat Transfer Enhancement for Blocks in a Channel Using a Rotationally Oscillating Plate

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Esam M. Alawadhi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Dissipation Rate ◽  
Thermal Characteristics ◽  
Reynolds Numbers ◽  
Thermal Dissipation ◽  
Transfer Enhancement ◽  
Maximum Angle ◽  
Oscillating Plate

Heat transfer enhancement using a rotationally oscillating plate in a channel containing heated blocks is numerically studied. The blocks simulate electronic chips with a high thermal dissipation rate. The model consists of a channel formed by two plates with heated blocks attached to bottom walls and a plate installed at the centerline of the channel. The rotationally oscillating plate enhances heat transfer from the blocks through the flow accelerating above the blocks. The effect of the frequency and maximum angle of attack of the plate on the Nusselt number is investigated for different Reynolds numbers. Heat transfer enhancement of the blocks with the plate is evaluated by comparing their thermal characteristics to a channel without plate. The results show that the oscillating plate enhances overall heat flow out of the blocks by 21.72% but with significant pressure drop of 300%.

Numerical Investigation of Heat Transfer Enhancement Due to Flow Agitators Between Fins

2021 ◽  
pp. 1-14
Author(s):  
Aditya Patki ◽  
Shankar Krishnan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Visualization ◽  
Heat Transfer Enhancement ◽  
Time Scales ◽  
Reynolds Numbers ◽  
Critical Parameters ◽  
Transfer Enhancement ◽  
Oscillation Cycle

Abstract The paper investigates the heat transfer characteristics of a channel system consisting of mean axial flow and oscillatory cross flow components. A numerical model has been developed to solve the governing equations associated with the flow. The paper identifies advection, diffusion, and oscillation time scales and intensity of squeezing in the channel as critical parameters controlling system behavior. The total Reynolds number parameter is considered in the paper to understand the combined effect of axial and transverse Reynolds numbers on the Nusselt number. Flow visualization techniques are employed to understand the boundary layer changes that occur over an oscillation cycle. Nusselt number is found to increase with a reduction in advection and oscillation time scales. A linear relationship is observed between the Nusselt number and total Reynolds number when the axial and transverse Reynolds numbers are comparable. Non-dimensional pressure drop is primarily defined by only two parameters: axial Reynolds number and squeezing fraction. The flow visualization results indicate significant heat transfer enhancement in a small fraction of the oscillation cycle characterized by flow conditions similar to Couette flow.

An Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Rectangular Channel With V-Shaped Ribs

2006 ◽  
Author(s):  
Michael Maurer ◽  
Jens von Wolfersdorf ◽  
Michael Gritsch
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
High Reynolds Numbers ◽  
High Reynolds

An experimental and numerical study was conducted to determine the thermal performance of V-shaped ribs in a rectangular channel with an aspect ratio of 2:1. Local heat transfer coefficients were measured using the steady state thermochromic liquid crystal technique. Periodic pressure losses were obtained with pressure taps along the smooth channel sidewall. Reynolds numbers from 95,000 to 500,000 were investigated with V-shaped ribs located on one side or on both sides of the test channel. The rib height-to-hydraulic diameter ratios (e/Dh) were 0.0625 and 0.02, and the rib pitch-to-height ratio (P/e) was 10. In addition, all test cases were investigated numerically. The commercial software FLUENT™ was used with a two-layer k-ε turbulence model. Numerically and experimentally obtained data were compared. It was determined that the heat transfer enhancement based on the heat transfer of a smooth wall levels off for Reynolds numbers over 200,000. The introduction of a second ribbed sidewall slightly increased the heat transfer enhancement whereas the pressure penalty was approximately doubled. Diminishing the rib height at high Reynolds numbers had the disadvantage of a slightly decreased heat transfer enhancement, but benefits in a significantly reduced pressure loss. At high Reynolds numbers small-scale ribs in a one-sided ribbed channel were shown to have the best thermal performance.

Study of the boundary layer heat transfer of nanofluids over a stretching sheet: Passive control of nanoparticles at the surface

2015 ◽  
Vol 93 (7) ◽  
pp. 725-733 ◽  
Author(s):  
M. Ghalambaz ◽  
E. Izadpanahi ◽  
A. Noghrehabadi ◽  
A. Chamkha
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Base Fluid ◽  
Stretching Sheet ◽  
Volume Fraction ◽  
Enhancement Ratio ◽  
Transfer Enhancement

The boundary layer heat and mass transfer of nanofluids over an isothermal stretching sheet is analyzed using a drift-flux model. The relative slip velocity between the nanoparticles and the base fluid is taken into account. The nanoparticles’ volume fractions at the surface of the sheet are considered to be adjusted passively. The thermal conductivity and the dynamic viscosity of the nanofluid are considered as functions of the local volume fraction of the nanoparticles. A non-dimensional parameter, heat transfer enhancement ratio, is introduced, which shows the alteration of the thermal convective coefficient of the nanofluid compared to the base fluid. The governing partial differential equations are reduced into a set of nonlinear ordinary differential equations using appropriate similarity transformations and then solved numerically using the fourth-order Runge–Kutta and Newton–Raphson methods along with the shooting technique. The effects of six non-dimensional parameters, namely, the Prandtl number of the base fluid Prbf, Lewis number Le, Brownian motion parameter Nb, thermophoresis parameter Nt, variable thermal conductivity parameter Nc and the variable viscosity parameter Nv, on the velocity, temperature, and concentration profiles as well as the reduced Nusselt number and the enhancement ratio are investigated. Finally, case studies for Al2O3 and Cu nanoparticles dispersed in water are performed. It is found that increases in the ambient values of the nanoparticles volume fraction cause decreases in both the dimensionless shear stress f″(0) and the reduced Nusselt number Nur. Furthermore, an augmentation of the ambient value of the volume fraction of nanoparticles results in an increase the heat transfer enhancement ratio hnf/hbf. Therefore, using nanoparticles produces heat transfer enhancement from the sheet.

HEAT TRANSFER ENHANCEMENT IN A CHANNEL PARTIALLY FILLED WITH A POROUS BLOCK: LATTICE BOLTZMANN METHOD

2013 ◽  
Vol 24 (09) ◽  
pp. 1350060 ◽  
Author(s):  
M. NAZARI ◽  
M. H. KAYHANI ◽  
R. MOHEBBI
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Lattice Boltzmann Method ◽  
Heat Transfer Enhancement ◽  
Lattice Boltzmann ◽  
Block Size ◽  
Blockage Ratio ◽  
Transfer Enhancement ◽  
Porous Block ◽  
Boltzmann Method

The main goal of the present study is to investigate the heat transfer enhancement in a channel partially filled with an anisotropic porous block (Porous Foam) using the lattice Boltzmann method (LBM). Combined pore level simulation of flow and heat transfer is performed for a 2D channel which is partially filled with square obstacles in both ordered and random arrangements by LBM which is not studied completely in the literature. The effect of the Reynolds number, different arrangements of obstacles, blockage ratio and porosity on the velocity and temperature profiles inside the porous region are studied. The local and averaged Nusselt numbers on the channel walls along with the respective confidence interval and comparison between results of regular and random arrangements are presented for the first time. For constant porosity and block size, the maximum value of averaged Nusselt number in the porous block is obtained in the case of random arrangement of obstacles. Also, by decreasing the porosity, the value of averaged Nusselt number is increased. Heat transfer to the working fluids increases significantly by increasing the blockage ratio. Several blockage ratios with different arrangements are checked to obtain a correlation for the Nusselt number.

Heat Transfer Enhancement in a Rectangular (AR = 3:1) Channel With V-Shaped Dimples

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Reduced Pressure

An alternative to ribs for internal heat transfer enhancement of gas turbine airfoils is dimpled depressions. Relative to ribs, dimples incur a reduced pressure drop, which can increase the overall thermal performance of the channel. This experimental investigation measures detailed Nusselt number ratio distributions obtained from an array of V-shaped dimples (δ/D = 0.30). Although the V-shaped dimple array is derived from a traditional hemispherical dimple array, the V-shaped dimples are arranged in an in-line pattern. The resulting spacing of the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. A single wide wall of a rectangular channel (AR = 3:1) is lined with V-shaped dimples. The channel Reynolds number ranges from 10,000–40,000. Detailed Nusselt number ratios are obtained using both a transient liquid crystal technique and a newly developed transient temperature sensitive paint (TSP) technique. Therefore, the TSP technique is not only validated against a baseline geometry (smooth channel), but it is also validated against a more established technique. Measurements indicate that the proposed V-shaped dimple design is a promising alternative to traditional ribs or hemispherical dimples. At lower Reynolds numbers, the V-shaped dimples display heat transfer and friction behavior similar to traditional dimples. However, as the Reynolds number increases to 30,000 and 40,000, secondary flows developed in the V-shaped concavities further enhance the heat transfer from the dimpled surface (similar to angled and V-shaped rib induced secondary flows). This additional enhancement is obtained with only a marginal increase in the pressure drop. Therefore, as the Reynolds number within the channel increases, the thermal performance also increases. While this trend has been confirmed with both the transient TSP and liquid crystal techniques, TSP is shown to have limited capabilities when acquiring highly resolved detailed heat transfer coefficient distributions.

Heat Transfer Enhancement in Electronic Modules Using Various Secondary Air Injection Hole Arrangements

1998 ◽  
Vol 120 (2) ◽  
pp. 342-347 ◽  
Author(s):  
B. A. Jubran ◽  
M. S. Al-Haroun
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Air Injection ◽  
Transfer Enhancement ◽  
Injection Hole ◽  
Secondary Air Injection ◽  
Secondary Air ◽  
Compound Angle

This paper reports an experimental investigation to study the effects of using various designs of secondary air injection hole arrangements on the heat transfer coefficient and the pressure drop characteristics of an array of rectangular modules at different values of free-stream Reynolds numbers in the range 8 × 103 to 2 × 104. The arrangement used is either one staggered row of simple holes or one row of compound injection holes. The pitch distances between the injection holes, as well as the injection angles, were varied in both the streamwise and spanwise directions. Generally, the presence of secondary air through the injection hole arrangement can give up to 54 percent heat transfer enhancement just downstream of the injection holes. The amount of heat transfer enhancement and pressure drop across the electronic modules is very much dependent on the design of the injection holes. The simple angle injection hole arrangement tends to give a better heat transfer enhancement and less pressure drop than the compound angle holes.

Heat Transfer Enhancement Using a Convex-Patterned Surface

2003 ◽  
Vol 125 (2) ◽  
pp. 274-280 ◽  
Author(s):  
H. K. Moon ◽  
T. O’Connell ◽  
R. Sharma
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Smooth Wall ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Patterned Surface ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel

The heat transfer rate from a smooth wall in an internal cooling passage can be significantly enhanced by using a convex patterned surface on the opposite wall of the passage. This design is particularly effective for a design that requires the heat transfer surface to be free of any augmenting features (smooth). Heat transfer coefficients on the smooth wall in a rectangular channel, which had convexities on the opposite wall were experimentally investigated. Friction factors were also measured to assess the thermal performance. Relative clearances δ/d between the convexities and the smooth wall of 0, 0.024, and 0.055 were investigated in a Reynolds number ReHD range from 15,000 to 35,000. The heat transfer coefficients were measured in the thermally developed region using a transient thermochromic liquid crystal technique. The clearance gap between the convexities and the smooth wall adversely affected the heat transfer enhancement NuHD. The friction factors (f ), measured in the aerodynamically developed region, were largest for the cases of no clearance δ/d=0). The average heat transfer enhancement Nu¯HD was also largest for the cases of no clearance δ/d=0, as high as 3.08 times at a Reynolds number of 11,456 in relative to that Nuo of an entirely smooth channel. The normalized Nusselt numbers Nu¯HD/Nuo, as well as the normalized friction factors f/fo, for all three cases, decreased with Reynolds numbers. However, the decay rate of the friction factor ratios f/fo with Reynolds numbers was lower than that of the normalized Nusselt numbers. For all three cases investigated, the thermal performance Nu¯HD/Nuo/f/fo1/3 values were within 5% to each other. The heat transfer enhancement using a convex patterned surface was thermally more effective at a relative low Reynolds numbers (less than 20,000 for δ/d=0) than that of a smooth channel.

Convective Heat Transfer Enhancement in a Circular Tube Using Twisted Tape

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Zhi-Min Lin ◽  
Liang-Bi Wang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Secondary Flow ◽  
Convective Heat ◽  
Tube Wall ◽  
Twisted Tape ◽  
Transfer Enhancement ◽  
Thermal Boundary Conditions

The secondary flow has been used frequently to enhance the convective heat transfer, and at the same flow condition, the intensity of convective heat transfer closely depends on the thermal boundary conditions. Thus far, there is less reported information about the sensitivity of heat transfer enhancement to thermal boundary conditions by using secondary flow. To account for this sensitivity, the laminar convective heat transfer in a circular tube fitted with twisted tape was investigated numerically. The effects of conduction in the tape on the Nusselt number, the relationship between the absolute vorticity flux and the Nusselt number, the sensitivity of heat transfer enhancement to the thermal boundary conditions by using secondary flow, and the effects of secondary flow on the flow boundary layer were discussed. The results reveal that (1) for fully developed laminar heat convective transfer, different tube wall thermal boundaries lead to different effects of conduction in the tape on heat transfer characteristics; (2) the Nusselt number is closely dependent on the absolute vorticity flux; (3) the efficiency of heat transfer enhancement is dependent on both the tube wall thermal boundaries and the intensity of secondary flow, and the ratio of Nusselt number with twisted tape to its counterpart with straight tape decreases with increasing twist ratio while it increases with increasing Reynolds number for both uniform wall temperature (UWT) and uniform heat flux (UHF) conditions; (4) the difference in the ratio between UWT and UHF conditions is also strongly dependent on the conduction in the tape and the intensity of the secondary flow; and (5) the twist ratio ranging from 4.0 to 6.0 does not necessarily change the main flow velocity boundary layer near tube wall, while Reynolds number has effects on the shape of the main flow velocity boundary layer near tube wall only in small regions.

The Application of Convective Cooling Enhancement of Span-Wise Cooling Holes in a Typical First Stage Turbine Blade

1991 ◽  
Author(s):  
D. J. Stankiewicz ◽  
T. R. Kirkham
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Test Rig ◽  
Heated Oil ◽  
Cooling Enhancement ◽  
Mach And Reynolds Numbers

A technique of heat transfer enhancement is investigated whereby the internal span-wise cooling passages of a typical first stage gas turbine blade are modified by the introduction of circumferential ribs. The technique is verified by the use of a test rig incorporating a heated internally ribbed tube operating at the same range of Mach and Reynolds numbers as the turbine blade as well as by a test rig incorporating actual production blades immersed in a heated oil bath.

Heat Transfer Enhancement in Wavy Micro-Channels Through Multiharmonic Surfaces

2018 ◽  
Author(s):  
Justin Moon ◽  
J. Rafael Pacheco ◽  
Arturo Pacheco-Vega
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Numerical Solutions ◽  
Cold Water ◽  
Bottom Surface ◽  
Transfer Enhancement ◽  
Cross Sectional ◽  
Single Wave ◽  
Micro Channels

In this study, three-dimensional numerical simulations are performed to investigate heat transfer enhancement in multi-harmonic micro-scale wavy channels. The focus is on the influence of channel surface-topography, modeled as multi-harmonic sinusoidal waves of square cross-sectional area, on the enhancing mechanisms. A single-wave device of 0.5 mm × 0.5 mm × 20 mm length, is used as baseline, and new designs are built with harmonic-type surfaces. The channel is enclosed by a solid block, with the bottom surface within the sinusoidal region being exposed to a 47 W/cm2 heat flux. The numerical solutions of the governing equations for an incompressible laminar flow and conjugate heat transfer are obtained via finite elements. By using the ratio of the Nusselt number for wavy to straight channels, a parametric analysis — for a set of cold-water flowrates (Re = 50, 100, and 150) — shows that the addition of harmonic surfaces enhances the transfer of energy and that such ratio achieves the highest value with wave harmonic numbers of n = ±2. Use of a performance factor (PF), defined as the ratio of the Nusselt number to the pressure drop, shows that, surprisingly, the proposed wavy multi-harmonic channels are not as efficient as the single-wave geometries. This outcome is thought to be, primarily, due to the uncertainty associated with the definition of the Nusselt number used in this study, and establishes a direction to investigate the development of a more accurate definition.

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