Liquid Immersion Cooling of a Longitudinal Array of Discrete Heat Sources in Protruding Substrates: I—Single-Phase Convection

1992 ◽  
Vol 114 (1) ◽  
pp. 55-62 ◽  
Author(s):  
T. J. Heindel ◽  
F. P. Incropera ◽  
S. Ramadhyani
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Channel Height ◽  
Heat Sources ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Discrete Heat Sources ◽  
Buoyancy Driven Flows

Experiments have been performed using water and FC-77 to investigate heat transfer from an in-line 1 x 10 array of discrete heat sources, flush mounted to protruding substrates located on the bottom wall of a horizontal flow channel. The data encompass flow regimes ranging from mixed convection to laminar and turbulent forced convection. Buoyancy-induced secondary flows enhanced heat transfer at downstream heater locations and provided heat transfer coefficients comparable to upstream values. Upstream heating extended enhancement on the downstream heaters to larger Reynolds numbers. Higher Prandtl number fluids also extended heat transfer enhancement to larger Reynolds numbers, while a reduction in channel height suppressed buoyancy driven flows, thereby reducing enhancement. The protrusions enhanced the transition to turbulent forced convection, causing the critical Reynolds number to decrease with increasing row number. The transition region was characterized by large heater-to-heater variations in the average Nusselt number.

Numerical Investigation on the Effect of Transversal Septa on Forced Convection in Circular Tubes

2009 ◽  
Author(s):  
O. Manca ◽  
S. Nardini ◽  
D. Ricci
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Circular Tubes ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Conventional sources of energy have been depleting at an alarming rate, which makes future sustainable development of energy use very difficult. Thus, heat transfer enhancement technology plays an important role and it has been widely applied to many applications as in refrigeration, automotive, process industry, solar energy heater, etc. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility for increasing heat transfer with gas is to employ extended surfaces. In this paper a numerical investigation is carried out on forced convection in circular tubes with septa heated by constant fluxes and characterized by different shapes. When gas flows in a tube, septa with one or more openings can be used as fins. Furthermore, when the openings are arranged to give a spiral motion around the cylinder axis wall-fluid contact area increases. As a consequence the presence of the septa may significantly augment pressure drops. The fluid is air and properties are function of temperature. Septa of the same material of the tube are introduced and several shapes and arrangements are analyzed as well as different Reynolds numbers, baffle spacings and heat fluxes applied on the external surface. The investigation is accomplished by means of the commercial code Fluent. A k-e turbulence model is used with enhanced wall treatment options. Results are presented in terms of temperature and velocity fields, local and average heat transfer coefficients, friction factors and pressure drops for different values of heat flux, Reynolds numbers and baffle spacings. The aim of this study is to find the shape and arrangement of septa such to give high heat transfer coefficients and low pressure drops.

Streamwise Flow and Heat Transfer Distributions for Jet Array Impingement With Crossflow

1981 ◽  
Author(s):  
L. W. Florschuetz ◽  
C. R. Truman ◽  
D. E. Metzger
Keyword(s):  
Heat Transfer ◽  
Flow Distribution ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Channel Height ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Circular Jets

Two-dimensional arrays of circular jets of air impinging on a heat transfer surface parallel to the jet orifice plate are considered. The air, after inpingement, is constrained to exit in a single direction along the channel formed by the surface and the jet plate. The downstream jets are subjected to a crossflow originating from the upstream jets. Experimental and theoretical results obtained for streamwise distributions of jet and crossflow velocities are presented and compared. Measured Nusselt numbers resolved to one streamwise hole spacing are correlated with individual spanwise row jet Reynolds numbers and crossflow-to-jet velocity ratios. Correlations are presented for both inline and staggered hole patterns including effects of geometric parameters: streamwise hole spacing, spanwise hole spacing, and channel height, normalized by hole diameter. The physical mechanisms influencing heat transfer coefficients as a function of flow distribution and geometric parameters are also discussed.

Streamwise Flow and Heat Transfer Distributions for Jet Array Impingement with Crossflow

1981 ◽  
Vol 103 (2) ◽  
pp. 337-342 ◽  
Author(s):  
L. W. Florschuetz ◽  
C. R. Truman ◽  
D. E. Metzger
Keyword(s):  
Heat Transfer ◽  
Flow Distribution ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Channel Height ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Circular Jets

Two-dimensional arrays of circular jets of air impinging on a heat transfer surface parallel to the jet orifice plate are considered. The air, after impingement, is constrained to exit in a single direction along the channel formed by the surface and the jet plate. The downstream jets are subjected to a crossflow originating from the upstream jets. Experimental and theoretical results obtained for streamwise distributions of jet and crossflow velocities are presented and compared. Measured Nusselt numbers resolved to one streamwise hole spacing are correlated with individual spanwise row jet Reynolds numbers and crossflow-to-jet velocity ratios. Correlations are presented for both inline and staggered hole patterns including effects of geometric parameters: streamwise hole spacing, spanwise hole spacing, and channel height, normalized by hole diameter. The physical mechanisms influencing heat transfer coefficients as a function of flow distribution and geometric parameters are also discussed.

scholarly journals A Combined Numerical and Experimental Study of Heat Transfer in a Roughened Square Channel with45∘Ribs

2005 ◽  
Vol 2005 (1) ◽  
pp. 60-66 ◽  
Author(s):  
M. E. Taslim ◽  
H. Liu
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient

Experimental investigations have shown that the enhancement in heat transfer coefficients for air flow in a channel roughened with low blockage(e/Dh<0.1)angled ribs is on the average higher than that roughened with90∘ribs of the same geometry. Secondary flows generated by the angled ribs are believed to be responsible for these higher heat transfer coefficients. These secondary flows also create a spanwise variation in the heat transfer coefficient on the roughened wall with high levels of the heat transfer coefficient at one end of the rib and low levels at the other end. In an effort to investigate the thermal behavior of the angled ribs at elevated Reynolds numbers, a combined numerical and experimental study was conducted. In the numerical part, a square channel roughened with45∘ribs of four blockage ratios(e/Dh)of0.10,0.15,0.20, and0.25, each for a fixed pitch-to-height ratio(P/e)of10, was modeled. Sharp as well as round-corner ribs (r/e=0and0.25) in a staggered arrangement were studied. The numerical models contained the smooth entry and exit regions to simulate exactly the tested geometries. A pressure-correction-based, multiblock, multigrid, unstructured/adaptive commercial software was used in this investigation. Standard high Reynolds numberk−εturbulence model in conjunction with the generalized wall function for most parts was used for turbulence closure. The applied thermal boundary conditions to the CFD models matched the test boundary conditions. In the experimental part, a selected number of these geometries were built and tested for heat transfer coefficients at elevated Reynolds numbers up to 150 000, using a liquid crystal technique. Comparisons between the test and numerically evaluated results showed reasonable agreements between the two for most cases. Test results showed that (a)45∘angled ribs with high blockage ratios(>0.2)at elevated Reynolds numbers do not exhibit a good thermal performance, that is, beyond this blockage ratio, the heat transfer coefficient decreases with the rib blockage and (b) CFD could be considered as a viable tool for the prediction of heat transfer coefficients in a rib-roughened test section.

Jet Impingement and Forced Convection Cooling Experimental Study in Rotating Turbine Blades

2009 ◽  
Author(s):  
Hsiao-Wei D. Chiang ◽  
Hsin-Lung Li
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Forced Convection ◽  
Turbine Blades ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Impingement Cooling ◽  
Heat Transfer Coefficients ◽  
Convection Cooling

Both jet impingement and forced convection are attractive cooling mechanisms and have been widely used in cooling of gas turbine blades. Convective heat transfer from impinging jets is known to yield high local and area averaged heat transfer coefficients. Impingement jets are of particular interest in the cooling of gas turbine components where advancement relies on the ability to dissipate extremely large heat loads. The current research is concerned with the measurement and comparison of both jet impingement and forced convection heat transfer in the Reynolds number range of 10,000 to 30,000. The present study is aimed at experimentally testing two different setups with forced convection and jet impingement in rotating turbine blades up to 700 rpm. This research also focused on to observe how Coriolis forces and impingement cooling inside the passage in rotating conditions within a cooling passage. Local heat transfer coefficients are obtained for each test section through thermal-couple technique with slip rings. The cross section of the passage is 10 mm × 10 mm without ribs. The surface heating condition has a uniform heat flux enforced. The forced convection cooling effects were studied using serpentine passages with three corner turns under different rotating speeds and different inlet Reynolds numbers. The impingement cooling study uses a straight passage with a single jet hole under different Reynolds numbers of the impingement flow and the cross flow. In summary, the main purpose is to study the rotation effects on both the jet impingement and the serpentine convection cooling types. Our study shows that rotation effects increase the serpentine cooling and, on the other hand, reduce the jet impingement cooling.

Heat Transfer in a Surfactant Drag-Reducing Solution—A Comparison With Predictions for Laminar Flow

2005 ◽  
Vol 128 (6) ◽  
pp. 557-563 ◽  
Author(s):  
Paul L. Sears ◽  
Libing Yang
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Reynolds Numbers ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Drag Reducing Additive ◽  
Good Agreement

Heat transfer coefficients were measured for a solution of surfactant drag-reducing additive in the entrance region of a uniformly heated horizontal cylindrical pipe with Reynolds numbers from 25,000 to 140,000 and temperatures from 30to70°C. In the absence of circumferential buoyancy effects, the measured Nusselt numbers were found to be in good agreement with theoretical results for laminar flow. Buoyancy effects, manifested as substantially higher Nusselt numbers, were seen in experiments carried out at high heat flux.

Heat Transfer and Pressure Drop Correlations for Square Channels With 45 Deg Ribs at High Reynolds Numbers

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Huitao Yang ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Turbine Blade Cooling ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
High Reynolds ◽  
Cooling Passage

Systematic experiments are conducted to measure heat transfer enhancement and pressure loss characteristics on a square channel (simulating a gas turbine blade cooling passage) with two opposite surfaces roughened by 45 deg parallel ribs. Copper plates fitted with a silicone heater and instrumented with thermocouples are used to measure regionally averaged local heat transfer coefficients. Reynolds numbers studied in the channel range from 30,000 to 400,000. The rib height (e) to hydraulic diameter (D) ratio ranges from 0.1 to 0.18. The rib spacing (p) to height ratio (p/e) ranges from 5 to 10. Results show higher heat transfer coefficients at smaller values of p/e and larger values of e/D, though at the cost of higher friction losses. Results also indicate that the thermal performance of the ribbed channel falls with increasing Reynolds numbers. Correlations predicting Nusselt number (Nu) and friction factor (f¯) as a function of p/e, e/D, and Re are developed. Also developed are correlations for R and G (friction and heat transfer roughness functions, respectively) as a function of the roughness Reynolds number (e+), p/e, and e/D.

A Numerical and Experimental Investigation of Turbulent Heat Transport Downstream From an Abrupt Pipe Expansion

1983 ◽  
Vol 105 (4) ◽  
pp. 862-869 ◽  
Author(s):  
R. S. Amano ◽  
M. K. Jensen ◽  
P. Goel
Keyword(s):  
Heat Transfer ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Separated Flow ◽  
Flow Region ◽  
Reynolds Numbers ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Pipe Expansion

An experimental and numerical study is reported on heat transfer in the separated flow region created by an abrupt circular pipe expansion. Heat transfer coefficients were measured along the pipe wall downstream from an expansion for three different expansion ratios of d/D = 0.195, 0.391, and 0.586 for Reynolds numbers ranging from 104 to 1.5 × 105. The results are compared with the numerical solutions obtained with the k ∼ ε turbulence model. In this computation a new finite difference scheme is developed which shows several advantages over the ordinary hybrid scheme. The study also covers the derivation of a new wall function model. Generally good agreement between the measured and the computed results is shown.

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