Review on thermal energy storage with phase change: materials, heat transfer analysis and applications

The boundary layer equations for plane, incompressible, and steady flow are 

$$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Boundary Layer Theory

An introduction to heat transfer

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Numerical Heat Transfer And Fluid Flow

This paper explores the recent research developments in high-heat-flux thermal management. Cooling schemes such as pool boiling, detachable heat sinks, channel flow boiling, microchannel and mini-channel heat sinks, jet-impingement, and sprays, are discussed and compared relative to heat dissipation potential, reliability, and packaging concerns. It is demonstrated that, while different cooling options can be tailored to the specific needs of individual applications, system considerations always play a paramount role in determining the most suitable cooling scheme. It is also shown that extensive fundamental electronic cooling knowledge has been amassed over the past two decades. Yet there is now a growing need for hardware innovations rather than perturbations to those fundamental studies. An example of these innovations is the cooling of military avionics, where research findings from the electronic cooling literature have made possible the development of a new generation of cooling hardware which promise order of magnitude increases in heat dissipation compared to today's cutting edge avionics cooling schemes.

Assessment of high-heat-flux thermal management schemes

Shell side flow condensation of R410A on horizontal tubes at low mass fluxes

The governing equations for liquid and two-phase heat transfer are used to derive fluid figures-of-merit (FOMs) for liquid-forced and natural convection, boiling incipience, and critical heat flux in both pool and flow boiling modes. These FOMs are given to help evaluate and compare the thermal performance of several candidate immersion cooling fluids. In addition, the governing equations are used to determine the sensitivities of thermal performance to fluid property values. >

Fluid selection and property effects in single- and two-phase immersion cooling (of electronic components)

Plate-fin heat sinks have been a successful technology in electronics cooling. Thermal performance of such heat sinks, however, has been driven to improve due to increasing heat generation in modern electronics devices. This paper proposes to introduce short pin fins on surfaces of plate-fin heat sinks to address such challenges. A microfabrication approach based on photolithography and electroplating technologies is devised to fabricate short copper pin fins on copper plates. The photolithography implements desired patterns of pin fins, and the electroplating enables pin fins to directly grow out of the base plate. A series of pin-fin coupons were fabricated using the devised method. A heat transfer test was designed to evaluate heat transfer augmentation by the pin fins. Fabricated coupons were tested in a rectangular channel and their thermal conductance and channel pressure drop were measured. A Design of Experiments (DoE) procedure via the Taguchi method was employed to find the influence of four factors: pin-fin height, diameter, spacing, and cross sectional shape, on the combination of thermal conductance and channel pressure drop for the coupons of different pin-fin parameters. Compared with similar plain coupons, pin-fin coupons of the best design parameters increase the thermal conductance by 78.3 % with only 7.8% increase of channel pressure drop. The devised micro-pin-fin fabrication has been proved as an effective approach to augmenting heat transfer of air-cooled plate-fin heat sinks.

Microfabrication of short pin fins on heat sink surfaces to augment heat transfer performance

Surface roughness is known to have significant effect on turbulent flow depending on the magnitude of the roughness. Also, a pipe is considered hydrodynamically smooth (for a given surface roughness) below certain value of Re. As the flow becomes laminar, there is little known about the surface roughness effect, particularly for small channel diameters (micro-channels). Data available to date from the literature, on micro-channels, indicate that the friction-Re relationship deviates from the known Moody Chart, for laminar flow. These differences are attributed, sometimes, to the surface roughness. Micro-channels are currently under consideration as a candidate for Stirling Engine Regenerators. In this paper, the effect of surface roughness on the flow and heat transfer characteristics has been studied using the CFD-ACE commercial software. A CFD model is created with small tooth like structures on the inner walls of a pipe with equal height and spacing between them. CFD analysis is done for different roughness values and the variation of heat transfer and fluid characteristics with the increase in roughness is studied. The study is done on a pipe with a hydraulic diameter of 0.62 mm by considering it first as smooth and then with average roughness values of 1.0 and 2.2 microns. The results were compared with the analytical solution (for smooth pipes) and experimental results available from the literature.

CFD Modeling of Surface Roughness in Laminar Flow

This paper presents experimental results from a study of the effects of periodically passing wakes upon laminar-to-turbulent transition and separation in a low-pressure turbine passage. The test section geometry is designed to simulate unsteady wakes in turbine engines for studying their effects on boundary layers and separated flow regions over the suction surface by using a single suction surface and a single pressure surface to simulate a single turbine blade passage. Single-wire, thermal anemometry techniques are used to measure time-resolved and phaseaveraged, wall-normal profiles of velocity, turbulence intensity and intermittency at multiple streamwise locations over the turbine airfoil suction surface. These data are compared to steady-state wake-free data collected in the same geometry to identify the effects of wakes upon laminar-to-turbulent transition. Results are presented for flows with a Reynolds number based on suction surface length and stage exit velocity of 50,000 and an approach flow turbulence intensity of 2.5%. While both existing design and experimental data are primarily concerned with higher Reynolds number flows (Re > 100,000), recent advances in gas turbine engines, and the accompanying increase in laminar and transitional flow effects, have made low-Re research increasingly important. From the presented data, the effects of passing wakes on transition and separation in the boundary layer, due to both increased turbulence levels and varying streamwise pressure gradients are presented. The results show how the wakes affect transition. The wakes affect the flow by virtue of their difference in turbulence levels and scales from those of the free-stream and by virtue of their ensemble-averaged velocity deficits, relative to the free-stream velocity, and the concomitant changes in angle of attack and temporal pressure gradients. The relationships between the velocity oscillations in the freestream and the unsteady velocity profile shapes in the near-wall flow are described. In this discussion is support for the theory that bypass transition is a response of the near-wall viscous layer to pressure fluctuations imposed upon it from the free-stream flow. Recent transition models are based on that premise. The data also show a significant lag between when the wake is present over the surface and when transition begins.

Terrence W. Simon

Papers

Shell side flow condensation of R410A on horizontal tubes at low mass fluxes

Fluid selection and property effects in single- and two-phase immersion cooling (of electronic components)

Microfabrication of short pin fins on heat sink surfaces to augment heat transfer performance

CFD Modeling of Surface Roughness in Laminar Flow

Experimental Investigation of Transition to Turbulence as Affected by Passing Wakes. Supplement