Mechanical & Manufacturing Eng (Scholarly Publications)Mechanical & Manufacturing Eng (Scholarly Publications)http://hdl.handle.net/2262/2082017-01-18T04:01:11Z2017-01-18T04:01:11ZForced convection in the wakes of sliding bubblesMURRAY, DARINAPERSOONS, TIMhttp://hdl.handle.net/2262/787762017-01-18T03:01:13Z2016-01-01T00:00:00ZForced convection in the wakes of sliding bubbles
MURRAY, DARINA; PERSOONS, TIM
Both vapour and gas bubbles are known to significantly increase heat transfer rates between a heated surface and the surrounding fluid, even with no phase change. However, the complex wake structures means that the surface cooling is not fully understood. The current study uses high speed infra-red thermography to measure the surface temperature and convective heat flux enhancement associated with an air bubble sliding under an inclined surface, with a particular focus on the wake. Enhancement levels of 6 times natural convection levels are observed, along with cooling patterns consistent with a possible hairpin vortex structure interacting with the thermal boundary layer. Local regions of suppressed convective heat transfer highlight the complexity of the bubble wake in two-phase applications.
2016-01-01T00:00:00ZNumerical optimization of unsteady natural convection heat transfer from a pair of horizontal cylindersMURRAY, DARINAPERSOONS, TIMhttp://hdl.handle.net/2262/787752017-01-18T03:02:02Z2016-01-01T00:00:00ZNumerical optimization of unsteady natural convection heat transfer from a pair of horizontal cylinders
MURRAY, DARINA; PERSOONS, TIM
This paper presents the results of a numerical study of unsteady natural convection
heat transfer from a pair of isothermally heated horizontal cylinders in water. In conjunction
with the developed numerical model, a genetic algorithm is designed to search for the optimal
spacing between the two cylinders that maximizes their overall heat transfer. When the
cylinders are vertically aligned, the heat transfer effectiveness of the upper cylinder is affected
by buoyancy-induced fluid flow induced by the lower cylinder. The established and validated
CFD model is used to analyse spectral data of local Nusselt number and velocity. The
optimization procedure identifies the optimal spacing for Rayleigh numbers ranging from 1e+6
to 1e+7.
2016-01-01T00:00:00ZEffect of oscillation frequency on wall shear stress and pressure drop in a rectangular channel for heat transfer applicationsPERSOONS, TIMhttp://hdl.handle.net/2262/787742017-01-18T03:01:40Z2016-01-01T00:00:00ZEffect of oscillation frequency on wall shear stress and pressure drop in a rectangular channel for heat transfer applications
PERSOONS, TIM
The exploitation of flow unsteadiness in microchannels is a potentially useful technique for enhancing cooling of future photonics systems. Pulsation is thought to alter the thickness of the hydrodynamic and thermal boundary layers, and hence affect the overall thermal resistance of the heat sink. While the mechanical and thermal problems are inextricably linked, it is useful to decouple the parameters to better understand the mechanisms underlying any heat transfer enhancement. The current work characterises the behaviour of the wall shear stress and pressure gradient with frequency, using experimental particle image velocimetry (PIV) measurements and the analytical solution for oscillatory flow in a two-dimensional rectangular channel. Both wall shear stress and pressure gradient are augmented with frequency compared to steady flow, though the pressure gradient increases more significantly as a result of growing inertial losses. The three distinct regimes of unsteadiness are shown to display unique relationships between the parameters pertinent to heat transfer and should therefore be considered independently with respect to thermal enhancement capability. To this end, the regime boundaries are estimated at Womersley number Wo = 1.6 and 28.4 in a rectangular channel, based on the contribution of viscous and inertial losses
2016-01-01T00:00:00ZSupersonic Spray Advanced Modelling SSAMLUPOI, ROCCOhttp://hdl.handle.net/2262/778882016-11-29T03:01:04Z2016-01-01T00:00:00ZSupersonic Spray Advanced Modelling SSAM
LUPOI, ROCCO
PUBLISHED; Queen s University Belfast
2016-01-01T00:00:00Z