Influence of gap-ratio on flow dynamics and heat transfer for a square cylinder approaching a moving wall in turbulent regime

AbstractDirect numerical simulation (DNS) of an impinging jet flow with a nozzle-to-plate distance of two jet diameters and a Reynolds number of 10 000 is carried out at high spatial resolution using high-order numerical methods. The flow configuration is designed to enable the development of a fully turbulent regime with the appearance of a well-marked secondary maximum in the radial distribution of the mean heat transfer. The velocity and temperature statistics are validated with documented experiments. The DNS database is then analysed focusing on the role of unsteady processes to explain the spatial distribution of the heat transfer coefficient at the wall. A phenomenological scenario is proposed on the basis of instantaneous flow visualisations in order to explain the non-monotonic radial evolution of the Nusselt number in the stagnation region. This scenario is then assessed by analysing the wall temperature and the wall shear stress distributions and also through the use of conditional averaging of velocity and temperature fields. On one hand, the heat transfer is primarily driven by the large-scale toroidal primary and secondary vortices emitted periodically. On the other hand, these vortices are subjected to azimuthal distortions associated with the production of radially elongated structures at small scale. These distortions are responsible for the appearance of very high heat transfer zones organised as cold fluid spots on the heated wall. These cold spots are shaped by the radial structures through a filament propagation of the heat transfer. The analysis of probability density functions shows that these strong events are highly intermittent in time and space while contributing essentially to the secondary peak observed in the radial evolution of the Nusselt number.

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Reduction of fluid forces and heat transfer on a square cylinder in a laminar flow regime using a control plate

International Journal of Heat and Fluid Flow ◽

10.1016/j.ijheatfluidflow.2011.12.008 ◽

2012 ◽

Vol 34 ◽

pp. 15-27 ◽

Cited By ~ 37

Author(s):

S. Malekzadeh ◽

A. Sohankar

Keyword(s):

Heat Transfer ◽

Laminar Flow ◽

Flow Regime ◽

Square Cylinder ◽

Laminar Flow Regime ◽

Fluid Forces ◽

Control Plate

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Adjoint Optimization of Heat Transfer Within a Stirling Engine

10.1115/power2021-65804 ◽

2021 ◽

Author(s):

Anthony A. DiCarlo ◽

Rickey A. Caldwell

Keyword(s):

Heat Transfer ◽

Heat Sink ◽

Convective Flow ◽

Transfer Rate ◽

External Heat ◽

Stirling Engine ◽

Flow Dynamics ◽

Optimization Approach ◽

Cfd Simulations ◽

Hot Air

Abstract This work aims to determine the optimal heat sink fin shape to promote the efficient rise of hot air away from the heat sink. The heat transfer and convective flow dynamics external to a commercial Stirling engine are investigated. In particular, this study employs an adjoint optimization approach based on CFD simulations to determine the sensitivity of the objective function to the shape of the heat sink and influence on the natural convection heat flow away from the external heat sink. This deterministic optimization approach increases the heat transfer rate of the heat sink by nearly 20% in this study when performing a small number of design iterations.

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Experimental Convective Heat Transfer With Nanofluids

ASME 2008 6th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2008-62099 ◽

2008 ◽

Author(s):

S. Kabelac ◽

K. B. Anoop

Keyword(s):

Heat Transfer ◽

Thermal Conductivity ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Convective Heat Transfer ◽

Convective Heat ◽

Turbulent Regime ◽

Heat Transfer Characteristics ◽

Forced Convective Heat Transfer ◽

Transfer Characteristics

Nanofluids are colloidal suspensions with nano-sized particles (<100nm) dispersed in a base fluid. From literature it is seen that these fluids exhibit better heat transfer characteristics. In our present work, thermal conductivity and the forced convective heat transfer coefficient of an alumina-water nanofluid is investigated. Thermal conductivity is measured by a steady state method using a Guarded Hot Plate apparatus customized for liquids. Forced convective heat transfer characteristics are evaluated with help of a test loop under constant heat flux condition. Controlled experiments under turbulent flow regime are carried out using two particle concentrations (0.5vol% and 1vol %). Experimental results show that, thermal conductivity of nanofluids increases with concentration, but the heat transfer coefficient in the turbulent regime does not exhibit any remarkable increase above measurement uncertainty.

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