Gas-particle heat transfer coefficients in packed beds at low Reynolds numbers

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.

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

Journal of Heat Transfer ◽

10.1115/1.3090818 ◽

2009 ◽

Vol 131 (7) ◽

Cited By ~ 21

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.

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

Journal of Heat Transfer ◽

10.1115/1.3245674 ◽

1983 ◽

Vol 105 (4) ◽

pp. 862-869 ◽

Cited By ~ 15

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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Heat Transfer and Friction in Channels With Very High Blockage 45° Staggered Turbulators

Volume 5: Turbo Expo 2003, Parts A and B ◽

10.1115/gt2003-38611 ◽

2003 ◽

Cited By ~ 14

Author(s):

Jeremy C. Bailey ◽

Ronald S. Bunker

Keyword(s):

Heat Transfer ◽

Reynolds Numbers ◽

Transfer Coefficients ◽

Flow Area ◽

Test Technique ◽

Heat Transfer Coefficients ◽

Smooth Channel ◽

Constant Pitch ◽

Transfer Behavior ◽

Very High

Heat transfer and friction coefficients have been measured within a rectangular passage of aspect ratio 0.4 containing 45-degree staggered turbulators of very high blockage. Using a constant pitch-to-height ratio of 10 for all geometries, turbulator height-to-channel hydraulic diameter ratios from 0.193 to 0.333 were investigated. This range of e/D creates actual channel blockage ratios e/H from 0.275 to 0.475, presenting significant flow area restrictions. A liquid crystal test technique is used to obtain both detailed heat transfer behavior on the surfaces between turbulators, as well as averaged fully developed heat transfer coefficients. Reynolds numbers from 20000 to 100000 were tested. Nusselt number enhancements of up to 3.6 were obtained over that of a smooth channel, with friction coefficient enhancements of as much as 65. In contrast to low-blockage turbulated channels, the 45-degree turbulated Nu is found to be lower than that at 90-degree orientation, given very similar e/D and e/H values.

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