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

In an isothermal compressed air energy storage (CAES) system, it is critical that the high pressure air compressor/expander is both efficient and power dense. The fundamental trade-off between efficiency and power density is due to limitation in heat transfer capacity during the compression/expansion process. In our previous works, optimization of the compression/expansion trajectory has been proposed as a means to mitigate this tradeoff. Analysis and simulations have shown that the use of optimized trajectory can increase power density significantly (2-3 fold) over ad-hoc linear or sinusoidal trajectories without sacrificing efficiency especially for high pressure ratios. This paper presents the first experimental validation of this approach in high pressure (7bar to 200bar) compression. Experiments are performed on an instrumented liquid piston compressor. Correlations for the heat transfer coefficient were obtained empirically from a set of CFD simulations under different conditions. Dynamic programming approach is used to calculate the optimal compression trajectories by minimizing the compression time for a range of desired compression efficiencies. These compression profiles (as function of compression time) are then tracked in a liquid piston air compressor testbed using a combination of feedforward and feedback control strategy. Compared to ad-hoc constant flow rate trajectories, the optimal trajectories double the power density at 80% efficiency or improve the thermal efficiency by 5% over a range of power densities.

Air Compression Performance Improvement via Trajectory Optimization: Experimental Validation

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 simulates the effects of unsteady wakes resulting from rotor-stator interaction 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 streamwise 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 5 X 10 4 . This low Reynolds number would apply to small engines flying at high altitude

Influence of Wake Passing Frequency and Elevated Turbulence Intensity on Transition.

Often, in optical and electronic equipment, heating is concentrated in very small regions, and, because of materials constraints, cooled walls must be as thin as possible. Also, for efficiency, many high-flux cooling designs involve forced-convection boiling heat transfer. Though efficient, a design with boiling heat transfer can be difficult for it must properly account for the complexities of the boiling flux-temperature relationship. Of concern is locating the point of incipience to boiling and the point of maximum nucleate boiling heat flux, Critical Heat Flux (CHF), and describing the complex behaviors in the vicinities of these points. Characteristics of boiling near these points are discussed in terms of boundary layer behavior. Changes in either the heater size or the wall thickness affects the boiling curve, particularly the CHF behavior. Results from experiments which were conducted on small, heated regions are discussed in light of their application to the design of high-power optical and electronic devices. The effects of flow velocity, subcooling, pressure, heating length, dissolved gas content, and flow streamline curvature are addressed.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Flow boiling critical heat flux on small heated regions

In this paper, the topic of laminar to turbulent flow transition, as applied to the design of gas turbines, is discussed. Transition comes about when a flow becomes sufficiently unstable that the orderly vorticity structure of the laminar layer becomes randomly oriented. Vorticity with a streamwise component leads to rapid growth of eddies of a wide range of sizes and eventually to turbulent flow. Under “natural” transition, infinitesimal disturbances of selected frequencies grow. “Bypass transition” is a term coined to describe a similar process, but one driven by strong external disturbances. Transition proceeds so rapidly that the processes associated with “natural” transition seem to be “bypassed.” Because the flow environment in the turbine is disturbed by wakes from upstream airfoils, eddies from combustor flows, jets from film cooling, separation zones on upstream airfoils and steps in the duct walls, transition is of the bypass mode. In this paper, we discuss work that has been done to characterize and model bypass transition, as applied to the turbine environment.

Terrence W. Simon

Papers

Air Compression Performance Improvement via Trajectory Optimization: Experimental Validation

Influence of Wake Passing Frequency and Elevated Turbulence Intensity on Transition.

Flow boiling critical heat flux on small heated regions

Transition to turbulence under low-pressure turbine conditions.

Critical heat flux and subcooled flow boiling with small heated regions on straight and concave-curved walls