scholarly journals NUMERICAL THERMAL STUDY OF HEAT TRANSFER ENHANCEMENT IN LAMINAR-TURBULENT TRANSITION FLOW THROUGH ABSORBER PIPE OF PARABOLIC SOLAR TROUGH COLLECTOR SYSTEM

2021 ◽  
Vol 17 ◽  
Author(s):  
Marwa M. Ibrahim ◽  
Mohamed Mahran Kasem
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Study ◽  
Transition Flow ◽  
Transfer Enhancement ◽  
Collector System ◽  
Turbulent Transition ◽  
Flow Through ◽  
Laminar Turbulent Transition

CFD Simulations of Flow and Heat Transfer in a Zigzag Channel With Flow Pulsation

2010 ◽  
Author(s):  
Bolaji O. Olayiwola ◽  
Gerhard Schaldach ◽  
Peter Walzel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Steady Flow ◽  
Inclination Angle ◽  
Oscillation Amplitude ◽  
Fluid Mixing ◽  
Transfer Enhancement ◽  
Flow And Heat Transfer ◽  
Flow Through

Heat transfer enhancement by pulsating flow in a zigzag channel has been numerically studied using a commercial CFD software for the ranges of laminar flow 0 < Re < 550. The influence of inclination angle α of the zigzag channel and oscillation parameters is investigated. The amplitude of the pulsatile flow was varied between 0.5 mm and 4 mm. The frequency f ranges between 0.5 Hz and 5.5 Hz. For steady flow, fluid mixing is promoted by self induced fluctuation due to the instability of the flow. The Reynolds number Re for the occurrence of significant eddy decreases with increase of the inclination angle of the channel. Superposition of oscillation additionally promotes further fluid mixing by the propagation of different scales of vortices. In comparison to straight channels, significant heat transfer in the laminar regime is possible using a zigzag channel with inclination angle greater than 15°. Further intensification of the heat transfer is possible with superposition of oscillation on the main flow through the channel. However, the heat transfer enhancement due to imposed oscillation is found to increase with decreasing Reynolds number. The effect of the imposed oscillation yields heat transfer enhancement E of up to 1.41 when compared with steady flow in zigzag channel at Reynolds number Re = 107, frequency f = 2.17 Hz and oscillation amplitude A = 1mm using a zigzag channel with an inclination angle α = 15°. Further heat transfer enhancement E of up to 1.80 at the same flow and oscillation conditions is possible with a zigzag channel having inclination angle α = 45°. The influence of oscillation frequency on the heat transfer enhancement E becomes significant as soon as the Womersley number W > 41.32. The effect of superposition of oscillation is not significant using a zigzag channel with inclination angle α = 60°. When the oscillation amplitude is increased up to 4 mm at Reynolds number Re = 107, frequency f = 2.17 Hz and inclination angle α = 45°, the heat transfer enhancement E of about 3.3 is obtained.

Influence of Crossflow-Induced Swirl and Impingement on Heat Transfer in an Internal Coolant Passage of a Turbine Airfoil

2000 ◽  
Vol 122 (3) ◽  
pp. 587-597 ◽  
Author(s):  
S. V. Ekkad ◽  
G. Pamula ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Feed System ◽  
Nusselt Numbers ◽  
Flow Through ◽  
Transient Liquid Crystal Technique ◽  
Measured Pressure

Detailed heat transfer distributions are presented inside a two-pass coolant channel with crossflow-induced swirl and impingement. The impingement and passage crossflow are generated from one coolant passage to the adjoining coolant passage through a series of straight or angled holes along the dividing wall. The holes provide for the flow turning from one passage to another typically achieved in a conventional design by a 180-deg U-bend. The holes direct the flow laterally from one passage to another and generate different secondary flow patterns in the second pass. These secondary flows produce impingement and swirl and lead to higher heat transfer enhancement. Three different lateral hole configurations are tested for three Reynolds numbers (Re=10,000, 25,000, 50,000). The configurations were varied by angle of delivery and location on the divider wall. A transient liquid crystal technique is used to measure the detailed heat transfer coefficient distributions inside the passages. Results with the new crossflow feed system are compared with the results from the traditional 180-deg turn passage. Results show that the crossflow feed configurations produce significantly higher Nusselt numbers on the second pass walls without affecting the first pass heat transfer levels. The heat transfer enhancement is as high as seven to eight times greater than obtained in the second pass for a channel with a 180-deg turn. The increased measured pressure drop (rise in friction factor) caused by flow through the crossflow holes are compensated by the significant heat transfer enhancement obtained by the new configuration. [S0022-1481(00)03103-0]

Sign in / Sign up

Export Citation Format

Share Document