Drag coefficient and Stanton number behavior in fluid flow across a bundle of wing-shaped tubes (original) (raw)
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Heat Transfer Conditions in Flow Across a Bundle of Cylindrical and Ellipsoidal Tubes
Numerical Heat Transfer, Part A: Applications, 2006
Transient numerical simulations of fluid and heat flow are performed for a number of heat exchanger segments with cylindrical and ellipsoidal form of tubes in a staggered arrangement. Based on the recorded time distributions of velocity and temperature, time-average values of Reynolds number, drag coefficient, and Stanton number are calculated. The drag coefficient and the Stanton number are smaller for the ellipsoidal tubes than for the cylindrical tubes. With an increasing hydraulic diameter, the difference between the two forms of tubes diminishes. To validate the selected numerical approach, the calculated time-average values are compared with experimental data. The time-average values are further used to construct the drag coefficient and the Stanton number as polynomial functions of Reynolds number and hydraulic diameter. The polynomial functions obtained are to be used as input correlations for a heat exchanger integral model.
Comparison of heat transfer conditions in tube bundle cross-flow for different tube shapes
International Journal of Heat and Mass Transfer, 2006
Detailed transient numerical simulations of fluid and heat flow were performed for a number of heat exchanger segments with cylindrical, ellipsoidal and wing-shaped tubes in a staggered arrangement. The purpose of the analysis was to get an insight of local heat transfer and fluid flow conditions in a heat exchanger and to establish widely applicable drag coefficient and Stanton number
International Journal of Heat and Mass Transfer, 2017
Numerical study on confined flow over circular tube isolated from the bundle of circular tubes in a compact and widely spaced heat exchangers, to explore the influence of flow shedding frequency under forced convection heat transfer. The flow and heat transfer characteristics such as pressure, frictional and total drag coefficients, skin friction coefficient, Strouhal number, volume goodness factor, convective heat transfer coefficient, Nusselt number and effectiveness are estimated for different dimensionless transverse pitch ratios and Reynolds numbers. The highly confined flow past a circular tube makes the flow steady, highly attached and postponed the flow separation, flow shedding and also advances the laminar to turbulent transition. The increases in flow attachments and transitions have been confirmed by observing the frictional drag and skin friction coefficients and also through various contours respectively. Three different flow shedding nature has been observed when Reynolds number increases at different blockage ratios. It is confirmed that the heat transfer enhancement in compact and widely spaced heat exchanger at blockage ratios less than or equal to 3 does not depend on flow shedding frequency. Also, at low Reynolds number region, the heat transfer enhancement is due to highly attached flow. But the gradual increase in Reynolds number advances laminar to turbulent transition and responsible in heat dissipation.
The operating conditions of many heat exchangers are in, or close to, the transitional flow regime. However, in this regime, not a lot of design information is available and some design books even recommend to not design heat exchangers to operate in the transitional flow regime. Furthermore, it is known that the type of inlet of heat exchangers influences the transition characteristics. It was therefore the purpose of this study to measure heat transfer and pressure drop characteristics in smooth horizontal tubes using different types of inlets. The types of inlets were hydrodynamically fully developed, square-edged, re-entrant, and bellmouth. Experiments were conducted on a 14.48-mm inner diameter horizontal tube in which the water was cooled. Reynolds numbers ranged between 1000 and 20,000 and Grashof numbers were on the order of 10 5 . It was found that for adiabatic flow the square-edged inlet delayed transition to Reynolds numbers of around 2600, while the bellmouth inlet delayed it to about 7000. However, for diabatic flow, the transition was independent of the type of inlet. Laminar friction factors were much higher than their theoretically predicted values due to the secondary flows increasing the amount of mixing in the tube. Heat transfer measurements showed that transition with water was totally independent of the type of inlet used.
Flow field and heat transfer investigation in tubes of heat exchangers with motionless scrapers
Applied Thermal Engineering, 2011
Flow pattern and thermal-hydraulic characteristics in an innovative tube insert have been experimentally and numerically investigated. The insert device is a concept envisioned for reciprocating scraped surface heat exchangers. It consists of a concentric rod, on which is mounted an array of semicircular plugs fitted to the inner tube wall. In motionless conditions, the insert works as a turbulence promoter, enhancing heat transfer in laminar regime. Fundamental flow features in the symmetry plane of the tube have been assessed with Particle Image Velocimetry technique. A general model of the flow mechanism has been defined, which allows the identification of three regions along a geometrical pitch: recirculation bubbles, flow acceleration and transverse vortex. Results have been complemented with experimental data on pressure drop and heat transfer. The transition onset is clearly identified, and the mechanisms that promote turbulence at low Reynolds numbers are investigated and discussed. CFD simulations for different Reynolds numbers provide a further insight into the relation of the flow structures with wall shear stress, and their role in the local heat transfer augmentation.
2014
The operating conditions of many heat exchangers are in, or close to, the transitional flow regime. However, in this regime, not a lot of design information is available and some design books even recommend to not design heat exchangers to operate in the transitional flow regime. Furthermore, it is known that the type of inlet of heat exchangers influences the transition characteristics. It was therefore the purpose of this study to measure heat transfer and pressure drop characteristics in smooth horizontal tubes using different types of inlets. The types of inlets were hydrodynamically fully developed, square-edged, re-entrant, and bellmouth. Experiments were conducted on a 14.48-mm inner diameter horizontal tube in which the water was cooled. Reynolds numbers ranged between 1000 and 20,000 and Grashof numbers were on the order of 10 5 . It was found that for adiabatic flow the square-edged inlet delayed transition to Reynolds numbers of around 2600, while the bellmouth inlet delayed it to about 7000. However, for diabatic flow, the transition was independent of the type of inlet. Laminar friction factors were much higher than their theoretically predicted values due to the secondary flows increasing the amount of mixing in the tube. Heat transfer measurements showed that transition with water was totally independent of the type of inlet used.
International Journal of Engineering Research and Technology (IJERT), 2013
https://www.ijert.org/cfd-analysis-of-heat-exchanger-over-a-staggered-tube-bank-for-different-angle-arrangement-of-tube-bundles https://www.ijert.org/research/cfd-analysis-of-heat-exchanger-over-a-staggered-tube-bank-for-different-angle-arrangement-of-tube-bundles-IJERTV2IS1445.pdf The modelling and performance prediction of a cross flow over a tube bundle using computational fluid dynamics (CFD) is the emerging development. The present work report, the analysis of pressure drop and heat transfer characteristics over a staggered tube bank heat exchanger with different tube bundle arrangements by using Fluent Software. The model was set up for a different mass flow rate over a tube bank and hence different Reynolds numbers and friction factor were studied. To improve hydraulic and thermal performance of heat exchanger we have simulated for the different angle arrangements i.e. 30°, 45° and 60°. The pressure drop results from the CFD simulation are compared with that obtained from the correlation.
Heat Transfer and Pressure Drop Characteristics of Smooth Tubes in the Transitional Flow Regime.
Design constraints or changes in process conditions often force heat exchanger equipment to operate in or close to the transitional flow regime. The purpose of this keynote paper is to present measured data for the heat transfer and pressure drop characteristics in the transitional flow regime for water flowing inside horizontal tubes. Adiabatic as well as diabatic experiments were conducted on water inside two horizontal smooth tubes with different diameters. The tubes were configured in a tube-in-tube arrangement, with the warm water stream in the inner tube and the chilled water stream in the annulus. Reynolds numbers in the transitional flow regime ranged between 1 000 and 20 000, Prandtl numbers varied between 4 and 6, and Grashof numbers were in the order of 10 5. Four inlet profiles were investigated, namely hydrodynamically fully developed, square-edged, re-entrant and bellmouth. Adiabatic results of friction factor confirmed that transition from laminar to turbulent flow was strongly dependent on the inlet profile, with transition being delayed to Reynolds numbers as high as 7 000. However, diabatic friction factor and Nusselt number results confirmed that transition was independent of the inlet, with transition occurring at a Reynolds number of approximately 2 100. The transition and Nusselt number independence was attributed to the buoyancy-induced secondary flows in the tube, which suppress any disturbances found in the inlet.
Heat Transfer and Fluid Flow Characteristic in banks Flat Tubes, 2009
In this research a study effect of the length ratio (L/Da) and the height ratio (H/Da) for banks flat tube heat exchanger In-Line and staggered arrangement on force convection heat transfer and friction coefficient by (Fluent-CFD) numerical program. The governing equations (mass, momentum and energy) are solving by using Finite Volume (Fluent-CFD) software for considering steady state, two dimensional, at constant heat flux with Reynold’s number (100≤Re≤8000). The results show that increasing (H/Da), (L/Da) lead to decreasing friction coefficient and enhancement of (Nu) is at (H/Da=2) for all (L/Da) values Inline arrangement and at (H/Da =2, L/Da =5) for staggered arrangement.
Numerical investigation of turbulent flow and heat transfer in flat tube
Journal of Thermal Analysis and Calorimetry, 2018
In this study, the heat transfer and friction characteristics of four different rib geometries-45 angled, Vshaped, W-shaped and M-shaped ribs in a two-pass stationary channel have been numerically investigated. The aspect ratio (Height to Width) of the cooling channel was 1:1 (square). The rib pitch-to-rib height ratio (p/e) and the rib-height-to-channel hydraulic diameter ratio (e/D h) were 16 and 0.125 respectively. The Reynolds number was varied from 20,000 to 70,000. For the computations, the Reynolds averaged NaviereStokes (RANS) equations were solved with the commercial software ANSYS Fluent using the realizable version of k-ε (RKE) model. The heat transfer results were benchmarked with experiments on a test rig with similar geometries and flow conditions. Detailed analysis of the flow characteristics in the two-pass channel was carried out so as to understand the interaction of the ribinduced secondary flows and the bend-induced secondary flows and their contribution to heat transfer enhancement. The heat transfer enhancement provided by V-shaped ribs was 7% higher than 45 ribs, 28% higher than W-shaped ribs and 35% higher than M-shaped ribs. However, the pressure penalty for Vshaped ribs was 19% higher than 45 ribs, 24% higher than W-shaped ribs and 28% higher than M-shaped ribs. On comparing the overall thermal hydraulic performance, V-shaped and 45 ribs were observed to perform significantly better than W-shaped and M-shaped ribs.