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

Results of a fluid mechanics measurement program in oscillating flow within a circular duct are presented. The program began with a survey of transition behavior over a range of oscillation frequency and magnitude and continued with a detailed study at a single operating point. Such measurements were made in support of Stirling engine development. Values of three dimensionless parameters, Re(sub max), Re(sub w), and A(sub R), embody the velocity amplitude, frequency of oscillation and mean fluid displacement of the cycle, respectively. Measurements were first made over a range of these parameters which included operating points of all Stirling engines. Next, a case was studied with values of these parameters that are representative of the heat exchanger tubes in the heater section of NASA's Stirling cycle Space Power Research Engine (SPRE). Measurements were taken of the axial and radial components of ensemble-averaged velocity and rms-velocity fluctuation and the dominant Reynolds shear stress, at various radial positions for each of four axial stations. In each run, transition from laminar to turbulent flow, and its reverse, were identified and sufficient data was gathered to propose the transition mechanism. Models of laminar and turbulent boundary layers were used to process the data into wall coordinates and to evaluate skin friction coefficients. Such data aids in validating computational models and is useful in comparing oscillatory flow characteristics to those of fully-developed steady flow. Data were taken with a contoured entry to each end of the test section and with flush square inlets so that the effects of test section inlet geometry on transition and turbulence are documented. Volume 1 contains the text of the report including figures and supporting appendices. Volume 2 contains data reduction program listings and tabulated data (including its graphical presentation).

Fluid mechanics experiments in oscillatory flow. Volume 1: Report

Measurements of mean velocity and turbulence intensity are presented for the mixing region of a film cooling situation in which the coolant is laterally injected. Measurements are performed using triple-sensor anemometry so that all three velocity components are documented. Flow with one row of film cooling holes inclined 35° to the surface, with lateral injection (Φ = 90°), is documented. The freestream turbulence intensity level is 12%, and coolant-to-mainstream velocity ratios are 0.5 and 1.0 (the density ratio is unity). General flow field characteristics ore discussed and compared. Additional comparisons are made with similar measurements in a flow in which the injection is streamwise (Φ = 0°).Copyright © 1998 by ASME

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Flow measurements in film cooling flows with lateral injection

\n For increased specific thrust and efficiency, more effective film-cooling schemes are developed with each successive gas turbine design. Adding secondary film-cooling holes to each primary film-cooling hole represents such improvement without significantly increasing cost. Presented is an experimental investigation on the effects of secondary-to-primary hole diameter ratio on film-cooling performance and flow structure in the coolant-to-passage flow merge zone. Film-cooling effectiveness values and heat transfer coefficients are measured in the vicinity of the hole by the thermochromic liquid crystal (TLC) technique. Measured in-flow temperature fields in the coolant emerging zone identify flow makeup, whether coolant or passage. Furthermore, complementary flow and thermal fields are numerically documented. The Reynolds number based on mainstream velocity and primary hole diameter is 20,300, a representative value. Performance features are compared at three blowing ratios (0.5, 1.0, and 1.5) and two mass flow ratios (3.43% and 5.15%). Secondary holes improve film-cooling effectiveness, especially when blowing rate is high. Secondary holes create an “antikidney vortex structure” that weakens the main kidney vortex pair which helps keep coolant attached to the surface, allowing more effective laterally spreading. However, adding secondary holes increases heat transfer coefficients, especially at high blowing rates. The secondary-to-primary hole diameter ratio is an important parameter. Larger secondary holes can counteract the detrimental effects of having higher blowing ratios, but with increased blowing ratios this improvement subsides. An optimum diameter ratio is sought.

An Experimental Study of Sister Holes Film Cooling With Various Secondary-to-Primary Hole Diameter Ratios

Experimental results from a study of the effects of passing wakes upon laminar-to-turbulent transition in a low-pressure turbine passage are presented. The test section geometry is designed to simulate the effects of unsteady wakes resulting from rotor-stator interaction upon laminar-to-turbulent transition in turbine blade boundary layers and separated flow regions over suction surfaces. Single-wire, thermal anemometry techniques are used to measure time-resolved and phase-averaged, wall-normal profiles of velocity, turbulence intensity and intermittency at multiple streamwise locations over the turbine airfoil suction surface. The Reynolds number based on suction surface length and stage exit velocity is 50,000. This study compares a previously documented base case flow having an approach flow turbulence intensity of 2.5 percent and a wake passing Strouhal number of 0.792 to two additional cases: one having an increased rod spacing case having a wake passing Strouhal number of 0.396, and another having an elevated approach flow turbulence intensity of 10 percent. From these data, the effects of increased rod spacing and elevated FSTI upon transition and separation processes in the near-wall flow are documented. The results show that a decreased wake passing Strouhal number results in an earlier separation with a larger separation bubble, while the elevated FSTI results in earlier separation, but with a shorter, thinner, separation bubble. The data and animations are included in an accompanying CD ROM.

Experimental Investigation of Transition to Turbulence as Affected by Passing Wakes: Effects of High FSTI and Increased Rod Spacing. Animations and Data Files

Conventional heat sink systems with blowers or fans are approaching maximum thermal management capability due to dramatically increased heat dissipation from the chips of high power electronics In order to increase thermal performance of air-cooled heat sink systems, more active or passive cooling components are continually being considered One technique is to agitate of the flow in the heat sinks to replace or aid conventional blowers In the present study, an active heat sink system that is coupled with a piezoelectric translational agitator and micro pin fin arrays on the heat sink surfaces is considered The piezoelectric translational agitator generates high frequency and large displacement motion to a blade It is driven by an oval loop shell that amplifies the small displacement of the piezo stack actuator to the several-millimeter range The blade, made of carbon fiber composite, is easily extended to a multiple-blade system without adding much mass The micro pin fin arrays were created with the LIGA photolithography technique The cooling performance of the heat sink system was demonstrated in single-channel and multiple-channel test facilities The singlechannel test results show that the active heat sink with the agitator operating at a frequency of 686 Hz and peak-to-peak displacement of 14 mm achieved a low thermal resistance of 0053 C/W in a channel with a 79 m/sec flow velocity Different configurations of the translational agitator with multiple blades were fabricated and tested in a 26-channel, full-size heat sink Vibrational characteristics are also provided© 2012 ASME

Terrence W. Simon

Papers

Fluid mechanics experiments in oscillatory flow. Volume 1: Report

Flow measurements in film cooling flows with lateral injection

An Experimental Study of Sister Holes Film Cooling With Various Secondary-to-Primary Hole Diameter Ratios

Experimental Investigation of Transition to Turbulence as Affected by Passing Wakes: Effects of High FSTI and Increased Rod Spacing. Animations and Data Files

An Active Heat Sink System With Piezoelectric Translational Agitators and Micro Pin Fin Arrays