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

Heat transfer-a review of 1985 literature

This paper describes an experimental investigation of the use of Gurney flaps to control laminar separation on turbine blades in a linear cascade. Measurements were made at Reynolds numbers (based upon inlet velocity and axial chord) of 28 × 103 , 65 × 103 and 167 × 103 . The freestream turbulence intensity for all three cases was 0.8%. Laminar separation was present on the suction surface of the Langston blade shape for the two lower Reynolds numbers. In an effort to control the laminar separation, Gurney flaps were added to the pressure surface close to the trailing edge. The measurements indicate that the flaps turn and accelerate the flow in the blade passage toward the suction surface of the neighboring blade thereby eliminating the separation bubble. Five different sizes of Gurney flaps, ranging from 0.6% to 2.7% of axial chord, were tested. The laser thermal tuft technique was used to determine the influence of the Gurney flaps on the location and size of the separation bubble. Additionally, measurements of wall static pressure, profile loss, and blade-exit flow angle were made. The blade pressure distribution indicates that the lift generated by the blade is increased. As was expected, the Gurney flap also produced a larger wake. In practice, Gurney flaps might possibly be implemented in a semi-passive manner. They could be deployed for low Reynolds number operation and then retracted at high Reynolds numbers when separation is not present. This work is important because it describes a successful means for eliminating the separation bubble while characterizing both the potential performance improvement and the penalties associated with this semi-passive flow control technique.Copyright © 2002 by ASME

Using Gurney Flaps to Control Laminar Separation on Linear Cascade Blades

Wind turbine output energy varies over time with local wind speed and is typically inconsistent with grid power demand. Without energy storage, the resulting difference between rated (peak) power and average power output leads to over-sizing of electrical generator and transmission lines. This conventional arrangement can be avoided if wind turbines can be coupled with energy storage to eliminate the output variations and instead produce their average power on a continuous basis. This would allow a smaller, lower-cost, constant-speed generator and a reduced capacity transmission system sized only for average power output. To accomplish this goal, this study discusses a concept for a storage system for a 5 MW off-shore wind turbine, which integrates a spray-based compressed air energy storage with a 35 MPa accumulator. The compressor employs a liquid piston for air sealing and employs water spray to augment heat transfer for high-efficiency. The overall compression is proposed in three stages with pressure ratios of 10:1, 7:1, and 5:1, all operated at 1 Hz to maintain moderate liquid surface acceleration. Based on a simple and fundamental description of the system, compression efficiency was found to be strongly dependent on droplet surface area, which can be achieved through either high mass loading or small drop sizes. The simulations also show that direct injection spray can increase overall three-stage compression efficiency to as high as 89%, substantially better than the 27% associated with a conventional adiabatic compression at the same pressure ratio. In addition, this study introduces a key performance parameter, termed the Levelization Factor, which can be used to quantify the impact of storage on wind energy systems. However, experiments and simulations based on 3-D geometries with design details are needed to determine the potential of this concept.

Spray-cooling concept for wind-based compressed air energy storage

This work supports new gas turbine designs for improved performance by evaluating the use of endwall contouring in a cascade that is representative of a first stage stator passage. Contouring accelerates the flow, reducing the thickness of the endwall inlet boundary layer to the turbine stage and reducing the strength of secondary flows within the passage. Reduction in secondary flows leads to less mixing in the endwall region. This allows improved cooling of the endwall and airfoil surfaces with injected and leakage flows. The present paper documents component misalignment and leakage flow effects on the aerodynamic losses within a passage having one contoured and one straight endwall. Steps on the endwall and leakage flows through the endwall can lead to thicker endwall boundary layers, stronger secondary flows and possibly additional vortex structures in the passage. The paper compares losses with steps of various geometries and leakage of various flow rates to assess their importance on aerodynamic losses in this contoured passage. In particular, features associated with the combustor-to-turbine transition piece and the slashface gap, a gap between two vane segments on the vane platform, are addressed. An n-factorial study is used to quantify the importance of such effects on aerodynamic losses.Copyright © 2005 by ASME

Flow Measurements in a First Stage Nozzle Cascade Having Endwall Contouring, Leakage, and Assembly Features

Thermal and flow field measurements taken within a cascade passage are presented. The cascade has two passages between three airfoils and two endwalls, one flat and one contoured. Measurements were done on and near the contoured endwall. The main objective is to document the effectiveness of cooling the contoured endwall with bleed flow that emerges through two rows of staggered, discrete holes on the contoured endwall, upstream of the airfoils. Similar studies have been performed in our lab with bleed flow emerging from slots upstream of the same contoured endwall. Both those and the present studies are with high free stream turbulence intensity, TI ∼ 9%, of the approach flow. This is characteristic of the approach flow to first stage vanes in most operating engines. In the experiments, the bleed flow is heated slightly above the main stream flow and downstream temperature fields are documented. Three bleed flow rates are tested. It is shown that at a lower flow rate (1.5% of the core flow) the cascade endwall cross-flow carries coolant towards the suction side. However, as the coolant rate is increased, the coolant attains sufficient momentum that no suction-side coolant migration is seen. Velocity measurements taken with triple-sensor, hot-wire anemometry document migration of the bleed flow by way of showing regions of stronger shear, and help describe mixing of the passage flow with the bleed flow. At higher coolant flow rates, strong blockage and mixing effects become evident.Copyright © 2000 by ASME

Terrence W. Simon

Papers

Heat transfer-a review of 1985 literature

Using Gurney Flaps to Control Laminar Separation on Linear Cascade Blades

Spray-cooling concept for wind-based compressed air energy storage

Flow Measurements in a First Stage Nozzle Cascade Having Endwall Contouring, Leakage, and Assembly Features

Measurements in a turbine cascade over a contoured endwall: Discrete hole injection of bleed flow