Enhanced Heat Transfer in a Flat Rectangular Duct With Streamwise-Periodic Disturbances at One Principal Wall

1983 ◽  
Vol 105 (4) ◽  
pp. 851-861 ◽  
Author(s):  
E. M. Sparrow ◽  
W. Q. Tao
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Local Maxima ◽  
Periodic Disturbances ◽  
Pressure Distributions ◽  
Friction Factors

Experiments were performed in a flat rectangular duct to determine the heat transfer and pressure drop response to periodic, rod-type disturbance elements situated adjacent to one principal wall and oriented transverse to the flow direction. In a portion of the experiments, heat transfer occurred only at the rodded wall, while in the remainder, heat was transferred at both principal walls of the duct. Highly detailed axial distributions of the local heat transfer coefficient were obtained. These distributions revealed the rapid establishment of a periodic (i.e., cyclic) fully developed regime as well as recurring local maxima and minima. Cycle-average, fully developed heat transfer coefficients were evaluated and were found to be much larger than those for a smooth-walled duct. Linear pressure distributions were measured between periodically positioned stations in the fully developed region, and the corresponding friction factors were several times greater than the smooth-duct values. The heat transfer and friction data were very well correlated using parameters that take account of the effective surface roughness associated with the disturbance rods.

scholarly journals Analysis of Backward and Forward Effects on a Grooved Co-axial Heat Exchanger by Response Surface Methodology

2019 ◽  
Vol 111 ◽  
pp. 01092
Author(s):  
Şahin GÜNGÖR ◽  
Levent AYDIN ◽  
Umut CEYHAN ◽  
Büşra KAYA ◽  
Ziya Haktan KARADENİZ
Keyword(s):  
Heat Transfer ◽  
Response Surface Methodology ◽  
Response Surface ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heated Wall ◽  
Transfer Coefficients ◽  
Pipe Model ◽  
Energy Equations

In the literature, it is proved that grooved pipe models are thermally more efficient than the smooth pipe model. Different than the previous studies in which the groove dimensions are constant along the pipe, we study the effect of groove radius and the gap between adjacent grooves on the local heat transfer coefficients using computational fluid dynamics software. The grooved section consists of three sub-sections to see the effects of groove dimension in stream-wise flow direction. We vary the radius of circular grooves parametrically in each section to optimize the local groove radius throughout the pipe. We couple the fluid flow (1200<Re<24000) with energy equations, and the grooved sections are set as heated wall at constant temperature of 350 K. The optimal mesh has been selected by performing mesh independence study and finer mesh has been used in heated wall section. The radii of grooves are varied from 2 to 6 mm with an increment of 0.2 mm considering the manufacturability of the pipe, to do so we use the design of experiments (DOE). All DOE tools in ANSYS software are examined and compared with full factorial results. After DOE process, local heat transfer coefficient values of all groove parts are examined by response surface methodology (RSM).

Ice Formation and Heat Transfer With Water Flow Around Isothermally Cooled Cylinders Arranged in a Line

1990 ◽  
Vol 112 (3) ◽  
pp. 707-713 ◽  
Author(s):  
T. Hirata ◽  
H. Matsui
Keyword(s):  
Heat Transfer ◽  
Cold Water ◽  
Flow Direction ◽  
Storage System ◽  
Local Heat Transfer ◽  
Energy Storage System ◽  
Correlation Equation ◽  
Local Heat ◽  
Ice Formation ◽  
Transfer Coefficients

The ice formation phenomenon and heat transfer around isothermally cooled cylinders that are lined up in the direction of flow in a crossflow of cold water were examined experimentally. Under the conditions of low Reynolds numbers and low cooling temperatures, the cylinders became linked by an ice layer. The amount of ice formed around the cylinders was much more than that for a single cylinder. A correlation equation was proposed for the amount of linked ice around the cooled cylinders. It was found that the local heat transfer coefficients on the linked ice surface showed an alternating decrease and increase in the flow direction. The mean value of the local Nusselt number showed the same characteristic as that on a flat plate in a turbulent flow. A dimensionless parameter that represents how efficiently the cylinders can work as a thermal energy storage system was introduced.

Maldistributed Inlet Flow Effects on Turbulent Heat Transfer and Pressure Drop in a Flat Rectangular Duct

1983 ◽  
Vol 105 (3) ◽  
pp. 527-535 ◽  
Author(s):  
E. M. Sparrow ◽  
N. Cur
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Inlet Flow ◽  
Heat Transfer Coefficients ◽  
Flow Maldistribution

The effects of flow maldistribution caused by partial blockage of the inlet of a flat rectangular duct were studied experimentally. Local heat transfer coefficients were measured on the principal walls of the duct for two blockages and for Reynolds numbers spanning the range between 6000 and 30,000. Measurements were also made of the pressure distribution along the duct, and the fluid flow pattern was visualized by the oil-lampblack technique. Large spanwise nonuniformities of the local heat transfer coefficient were induced by the maldistributed flow. These nonuniformities persisted to far downstream locations, especially in the presence of severe inlet flow maldistributions. Spanwise-average heat transfer coefficients, evaluated from the local data, were found to be enhanced in the downstream portion of the duct due to the flow maldistribution. However, at more upstream locations, where the entering flow reattached to the duct wall following its separation at the sharp-edged inlet, the average coefficients were reduced by the presence of the maldistribution.

Turbulent Flow and Heat Transfer in Bends of Circular Cross Section: I—Heat Transfer Experiments

1986 ◽  
Vol 108 (1) ◽  
pp. 40-47 ◽  
Author(s):  
E. M. Sparrow ◽  
G. M. Chrysler
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Section ◽  
Circular Cross Section ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Local Maxima ◽  
Naphthalene Sublimation Technique ◽  
Naphthalene Sublimation

Experiments were performed to determine the local heat transfer characteristics of bends of circular cross section to which fluid was delivered either via a sharp-edged inlet or via a hydrodynamic development tube. The naphthalene sublimation technique, a mass transfer method, was used to facilitate the experiments. Bends subtending turning angles of 30, 60, and 90 deg were investigated, and the Reynolds number was varied between 5000 and 100,000. It was found that the local heat transfer coefficients at the outside of the bend were, for the most part, larger than those at the inside of the bend, but the deviations decreased as the Reynolds number increased. The streamwise distributions of the local transfer coefficient were markedly affected by the inlet condition; those for the sharp-edged inlet exhibited a universal shape, while the shapes of those for the tube-fed inlet depended both on the Reynolds number and on whether the distribution corresponded to the inside or the outside of the bend. In addition, the distributions for the case of the sharp-edged inlet exhibited higher local maxima and approached the fully developed regime more rapidly than did those for the tube-fed inlet. The heat transfer results were supplemented by flow visualization.

Heat Transfer Coefficients in an Orthogonally Rotating Duct With Turbulators

1995 ◽  
Vol 117 (1) ◽  
pp. 69-78 ◽  
Author(s):  
Shou-Shing Hsieh ◽  
Ying-Jong Hong
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Coolant Temperature ◽  
Transfer Coefficients ◽  
Base Surface ◽  
Square Duct ◽  
Number Range ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the influence of rotation on local heat transfer coefficient for the turbulent flow in a short square duct (L/DH = 15) with a pair of opposite rib-roughened walls. The ribs are configured in an in-line arrangement with an attack angle of 90 deg to the main flow. The coolant used was air with the flow direction in the radially outward direction. The Reynolds numbers ranged from 5000 to 25,000; the rib pitch-to-height ratio was 5; and the rib height-to-hydraulic diameter ratio was kept at a value of 0.20. The rotation number range was 0 to 0.5. Local Nusselt number variations along the duct were determined over the trailing and leading surfaces. In addition, local heat transfer measurements on all sides of a typical rib as well as on a typical exposed base surface between two consecutive ribs in a fully developed region were conducted at various rotational speeds. It is shown that the Coriolis acceleration tends to improve the heat transfer due to the presence of strong secondary flow. Centripetal buoyancy is shown to influence the heat transfer response with heat transfer being suppressed on both leading and trailing surfaces as the wall-to-coolant temperature difference is increased with other controlling parameters hold constant. Results are also compared with previous investigations. It was found that the results agree very well with those reported by other works in this field.

Heat Transfer and Skin Friction for Turbulent Boundary-Layer Flow Longitudinal to a Circular Cylinder

1963 ◽  
Vol 30 (1) ◽  
pp. 37-43 ◽  
Author(s):  
E. M. Sparrow ◽  
E. R. G. Eckert ◽  
W. J. Minkowycz
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
Prandtl Numbers ◽  
Layer Flow

An analysis has been carried out for the turbulent velocity and thermal boundary layers which develop along a cylinder whose axis is parallel to the free-stream flow. Local and average friction factors are calculated as functions of the length Reynolds number Rex for various cylinder sizes (characterized, by the radius Reynolds number Rer0). For corresponding flow conditions, the friction factor for a cylinder always exceeds that for the flat plate. Local heat-transfer coefficients corresponding to the case of uniform wall heat flux have been obtained for Prandtl numbers of 0.7 and 5. As with the friction factors, the cylinder heat-transfer coefficients exceed those for the flat plate. This effect of the cylindrical geometry on heat transfer diminishes with increasing Prandtl number.

Investigation of the Effects of Flow Swirl on Heat Transfer Inside a Cylindrical Cavity

1991 ◽  
Vol 113 (2) ◽  
pp. 348-354 ◽  
Author(s):  
A. Salce ◽  
T. W. Simon
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cylindrical Cavity ◽  
Flow Direction ◽  
Axial Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Sensitive ◽  
Transfer Coefficients ◽  
Cavity Bottom

Experiments were conducted to determine local heat transfer coefficients on the inside surfaces of a cylindrical cavity that is cooled by a swirling air flow. Temperature-sensitive liquid crystals were used as temperature sensors. Five blowing (cooling) modes were tested: three with swirl numbers of 0.36, 0.84, and 1.73; a fourth with no swirl (axial flow), and a fifth that was similar to the fourth but had the flow direction reversed. Flow visualization and static pressure measurements were performed to improve understanding of the situation. The smoke-wire technique was successfully used to picture the flow patterns. Plots of local Nusselt number along the cavity surfaces were obtained for the five blowing modes and for three different Reynolds numbers. The swirling cases had similar flow fields with higher heat transfer rates near the cavity top and lower rates near the cavity bottom (the opposite of the nonswirling cases). A tornadolike structure on the cavity bottom was observed in the swirling cases. This structure became stronger and more violent as the degree of swirl and the Reynolds number were increased. The Nusselt number curves for the two nonswirling cases were of similar shape, although the flow direction was reversed.

Local Heat Transfer to Staggered Arrays of Impinging Circular Air Jets

1983 ◽  
Vol 105 (2) ◽  
pp. 354-360 ◽  
Author(s):  
A. I. Behbahani ◽  
R. J. Goldstein
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Air Jets ◽  
Impingement Surface

Measurements are made of the local heat transfer from a flat plate to arrays of impinging circular air jets. Fluid from the spent jets is constrained to flow out of the system in one direction. Two different jet-to-jet spacings, 4 and 8 jet diameters, are employed. The parameters that are varied include jet-orifice-plate to impingement-surface spacing and jet Reynolds number. Local heat transfer coefficients vary periodically both in the flow direction and across the span with high values occurring in stagnation regions. Stagnation regions of individual jets as determined by local heat transfer coefficients move further in the downstream direction as the amount of crossflow due to upstream jet air increases. Local heat transfer coefficients are averaged numerically to obtain spanwise and streamwise-spanwise averaged heat transfer coefficients.

scholarly journals Local Heat Transfer to Staggered Arrays of Impinging Circular Air Jets

1982 ◽  
Author(s):  
A. I. Behbahani ◽  
R. J. Goldstein
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flat Plate ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Air Jets ◽  
Impingement Surface

Measurements are made of the local heat transfer from a flat plate to impinging arrays of staggered circular air jets. Fluid from the spent jets is constrained to flow out in one direction. Two different jet-to-jet spacings, 4 and 8 jet diameters, are employed. The parameters that are varied include jet-orifice-plate to impingement-surface spacing and jet Reynolds number. Local heat transfer coefficients vary periodically both in the flow direction and across the span with high values occurring at stagnation regions. Stagnation regions of individual jets as determined by local heat transfer coefficients move further in the downstream direction as the amount of crossflow due to upstream jet air increases. Local heat transfer coefficients are averaged numerically to obtain spanwise and streamwise-spanwise averaged heat transfer coefficients.

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