Shyy Woei Chang

Heat Transfers in Tubes Fitted with Single, Twin, and Triple Twisted Tapes

This experimental study performs heat transfer and pressure drop measurements in three test tubes fitted with single, twin, and triple twisted-tapes with Reynolds number (Re) varying from 1,500 to 14,000. Each element of these continuous twisted-tapes that formulates the single, twin, and triple twisted-tapes has identical width, pitch, and thickness. Heat-transfer augmentations from the plain-tube conditions in three test tubes decrease with the increase of Re, while the descending rate decreases with the increase of twisted-tape in the tube. These twisted-tapes generate the more effective heat transfer enhancements in laminar flow regime than those developed in turbulent flow regime. With 3,000 ≤ Re < 14,000, the local Nusselt numbers in the tubes fitted with single, twin, and triple twisted-tapes were, respectively, 1.5–2.3, 1.98–2.8, and 2.86–3.76 times of the Dittus-Boelter levels. The Fanning friction factors in three test tubes decrease with the increase of Reynolds number. Based on the same pumping power consumption, the tube fitted with single and triple twisted-tapes possess the highest performance factors for laminar and turbulent flows, respectively. Experimental correlations of heat transfer and Fanning friction factor were derived for three tubes fitted with single, twin, and triple twisted-tapes.

Heat transfer in a radially rotating square duct fitted with in-line transverse ribs

Abstract This paper describes an experimental study of heat transfer in a radially rotating square duct with two opposite walls fitted by transverse ribs. The manner in which rotation modifies the forced heat convection is considered for the case where the duct rotates about an axis perpendicular to the ducts axis of symmetry and the flow within is radially outward with particular reference to the design of a gas turbine rotor blade. A selection of experimental results illustrates the individual and interactive effects of Coriolis and centripetal buoyancy forces on heat transfer along the centerline of each rotating rib-roughened surface. A number of experimental-based observations are revealed those confirm the manner for which the Coriolis force and centripetal buoyancy interactively modify the heat transfer even if the rib associating flow phenomena persist when the through flow transverses the ribs. An empirical correlation based on theoretical consideration and experimental data, which is physically consistent, has been developed to permit the evaluation of interactive effects of rib-flows, convective inertial force, Coriolis force and centripetal buoyancy on heat transfer.

Heat Transfer in High-Speed Rotating Trapezoidal Duct With Rib-Roughened Surfaces and Air Bleeds From the Wall on the Apical Side

An experimental study of heat transfer in a radially rotating trapezoidal duct with two opposite walls roughened by 45 deg staggered ribs and bleed from the apical side wall is performed. Centerline heat transfer variations on two rib-roughened surfaces are measured for radially outward flows with and without bleeds at test conditions of Reynolds number (Re), rotation number (Ro), and density ratio (Δρ/ρ) in the ranges of 15,000-30,000, 0-0.8, and 0.04-0.31, respectively. Geometrical configurations and rotation numbers tested have considerably extended the previous experiences that offer practical applications to the trailing edge cooling of a gas turbine rotor blade. A selection of experimental data illustrates the individual and interactive influences of Re, Ro, and buoyancy number (Bu) on local heat transfer with and without bleeds. Local heat transfer results are generated with the influences of bleeds on the apical side examined to establish heat transfer correlations with Re, Ro, and Bu as the controlling flow parameters for design applications. The rotation of present trapezoidal duct with rib-roughened surfaces and air bleeds on the apical side worsens the impairing heat transfer impacts due to bleeds. Within the Ro range of 0.1-0.8, bleeds on the apical side of the rotating channel respectively produce 25-50% and 25-40% of heat transfer reductions from the rotational no-bleed references along the leading and trailing centerlines. Such heat transfer reductions due to the combined bleeds and Ro-Bu impacts need design precautions for turbine rotor blades.

Enhanced heat transfer of shaker-bored piston cooling channel with twisted tape insert

This experimental study investigates the heat transfer augmentation in a reciprocating anti-gravity open thermosyphon using a twisted tape insert with relevance to the “shaker-bored” piston cooling system for marine propulsive diesel engine. A selection of experimental data illustrates the interactive effects of inertial, reciprocating, and buoyancy forces on heat transfer in the anti-gravity open thermosyphon with and without a twisted tape insert for subcooled and superheated conditions. The impacts of gravitational buoyancy on heat transfer in the static plain thermosyphon tube are reversed from impairing to improving heat transfer when the flow condition yields from subcooled to superheated condition. In the static thermosyphon tube fitted with twisted tape insert and in the reciprocating thermosyphon tubes with and without twisted tape insert, the buoyancy interactions enhance heat transfer coefficients. Due to the isolated reciprocating force effect, heat transfer coefficients are initially impaired from the static levels at low pulsating numbers but recovered to be enhanced at high pulsating numbers in the reciprocating plain thermosyphon tube. For the reciprocating thermosyphon tube fitted with a twisted tape insert, the isolated reciprocating force effect consistently improves heat transfer. The impacts of isolated reciprocating force and buoyancy interaction on heat transfer are Reynolds number-dependent. Heat transfer coefficients in the reciprocating thermosyphon tube fitted with the twisted tape insert could be augmented to the range of 1.2–6 times of plain tube levels. A set of empirical heat transfer correlations that considers the synergistic effects of inertial force, reciprocating force, and buoyancy interaction in the reciprocating anti-gravity open thermosyphon tube fitted with a twisted tape insert is developed to assist the design activity of the piston-cooling system.

Detailed heat transfer measurements of impinging jet arrays issued from grooved surfaces

Heat transfer augmentation of impinging jet-array with very small separation distances (S/Dj<1) is attempted by using the grooved orifice plate through which the nozzles with different diameters are fitted. The combined effects of groove and nozzle-size distribution in an array have demonstrated considerable influences on heat transfers via their impacts on inter-jet reactions. With a specified coolant flow rate; the detailed heat transfer distributions over the impinging surfaces of three tested arrays are compared to reveal the optimal selections of separation distance and array configuration. Heat transfer modifications caused by varying jet Reynolds number (Re) and separation distance (S/Dj) over the ranges of 1000⩽Re⩽4000 and 0.1⩽S/Dj⩽8 are examined for each test array. In conformity with the experimentally revealed heat transfer physics, a regression-type analysis is performed to develop the correlations of spatially-averaged Nusselt numbers, which permit the individual and interactive effect of Re and S/Dj to be evaluated.

Heat transfer in a reciprocating duct fitted with transverse ribs

This article describes a detailed experimental investigation of heat transfer in a reciprocating square-sectioned duct fitted with transverse ribs. The parametric conditions involved several nominal Reynolds numbers ranging from 2,700 to 9,000 with five different reciprocating frequencies, namely, 0, 0.415, 0.83, 1.25, and 1.67 Hz. This resulted in a pulsating number, which represented the ratio of reciprocating force to inertial force effect, varying from 0 to 10.5. Inside the reciprocating ribbed duct the typical effects of flow reciprocation on heat transfer were illustrated by examining the periodic spatial-time distributions of Nusselt number. The amplitude of the timewise variable reciprocating Nusselt number was dependent on the axial location and increased with increases of Reynolds number. The time-averaged heat transfer due to flow reciprocation could be accounted for by the pulsating number and, in general, the heat transfer level increased with increases of the pulsating number. At a pulsating...

An experimental study of heat transfer in a simulated turbine blade cooling passage

Abstract This paper describes an experimental investigation of heat transfer inside a simulated cooling channel for a gas turbine rotor blade. The channel is circular in cross-section and rotates about an axis which is orthogonal to its centre line. The study is aimed at the development of an experimental procedure and method of data processing which permits the determination of full axial and circumferential heat transfer data over the tubes inner surface. This is referred to as full field heat transfer data. In this respect a study of the combined effect of Coriolis and centripetal buoyancy forces on the forced convection mechanism inside the tube is the strategic aim. The experimental technique involved the determination of the inside surface temperature and heat flux distribution using a solution of the channel wall heat conduction equation. A series of wall temperature measurements on the leading and trailing edges of the channel, together with a prescribed electrically generated heat flux on the external surface, were used as boundary conditions with which to solve the channel wall heat conduction equation. The resulting internal heat flux distribution over the full inner surface was subsequently used to determine the local variation of heat transfer coefficient. The method was validated using data available in the technical literature and subsequently used to study the individual effects of Coriolis induced secondary flow and centripetal buoyancy using new data generated for the investigation.

Heat Transfer in a Rotating Twin-Pass Trapezoidal-Sectioned Passage Roughened by Skewed Ribs on Two Opposite Walls

An experimental study of heat transfer in a radially rotating twin-pass trapezoidal-sectioned duct with two opposite walls roughened by 45° staggered ribs was performed. Two channel orientations of 0° and 45° from the direction of rotation were tested. At each Reynolds number of 5000, 7500, 10000, 12500, and 15000, local Nusselt numbers along the centerlines of two rib-roughened surfaces with five different heating levels were acquired at rotating numbers of 0, 0.1, 0.3, 0.5, 0.7, and 1. A selection of experimental results illustrates the isolated and interactive influences of convective inertial, Coriolis, and rotating buoyancy forces on local and centerline-averaged heat transfers. The isolated Coriolis force-effect improves heat transfer over two unstable surfaces of the rotating twin-pass channel. The rotating buoyancy effect undermines local heat transfer, but its influence is alleviated when the rotating number increases. At rotating number of 0.7 and 1, the rotating buoyancy force acting with counter-flow manner considerably impairs local heat transfer in the end-region of the first passage with radially outward flow. With the rotating numbers in the range of 0.1 to 1, the heat transfer differences between the two channels with orientations of 0° and 45° are in the range of 5–26%. As a strategic aim of the present study, heat transfer correlations are derived to evaluate the centerline-averaged Nusselt numbers over two rib-roughened surfaces that permit the individual and interactive influences of convective inertia, Coriolis force, and rotating buoyancy to be quantified. As the full-field spatial heat transfer variations in the present rotating channel are not measured, the local heat transfer results generated by the present study are limited to the locations measured.

Heat transfer of reciprocating helical tube fitted with full circumferential ribs

Abstract This paper describes a detailed experimental investigation of heat transfer in a reciprocating helical tube fitted with full circumferential ribs with particular reference to the design of a piston for a marine propulsive diesel engine. The parametric test matrix involves Reynolds, Dean, pulsating and buoyancy numbers, respectively, in the ranges 4500–7000, 1050–1600, 0.135–0.458 and 0.000325–0.00943 with five different reciprocating frequencies tested, namely 0, 0.83, 1.25, 1.67 and 2 Hz. The manner in which the pulsating force and reciprocating buoyancy interactively affect the local heat transfer along the inner and outer edges of the coils is illustrated using a number of experimentally based observations. The experimental data reconfirm the presence of Dean vortices with attendant relative increase in local heat transfer on the outer surface, even with the agitated flow field caused by ribs under a reciprocating environment. The pulsating force and reciprocating buoyancy have a considerable influence on the heat transfer present due to the modified vortex flow structures in the ribbed coils. An empirical correlation, which is physically consistent, was developed that permits the individual and interactive effects of pulsating force and reciprocating buoyancy on heat transfer in the ribbed coils to be evaluated.

Heat Transfer in Radially Rotating Pin-Fin Channel at High Rotation Numbers

Endwall heat transfer measurements for a radially rotating rectangular pin-fin channel with the width-to-height ratio (aspect ratio) of 8 are performed at the parametric conditions of 5000 ≤ Re ≤ 20,000, 0 ≤ Ro ≤ 1.4, and 0.1 ≤ Δρ/ρ ≤ 0.21. Centerline heat transfer levels along the leading and trailing endwalls of the rotating pin-fin channel are, respectively, raised to 1.77-3.72 and 3.06-5.2 times of the Dittus-Boelter values. No previous attempt has examined the heat transfer performances for the pin-fin channel at such high rotation numbers. A selection of experimental data illustrates the individual and interactive Re, Ro, and buoyancy number (Bu) effects on heat transfer. Spanwise heat transfer variations between two adjoining pin rows are detected with the averaged Nusselt numbers (Nu) determined. A set of empirical equations that calculates Nu values over leading and trailing endwalls in the developed flow region is derived to correlate all the heat transfer data generated by this study and permits the evaluation of interactive and individual effects of Re, Ro, and Bu on Nu. With the aid of the Nu correlations derived, the operating conditions with the worst heat transfer scenarios for this rotating pin-fin channel are identified.