Numerical Heat Transfer Investigation in a Solar Receiver Heat Exchanger Channel with Punched Elliptical-Winglet Vortex Generators

Laminar flow and heat transfer characteristics in a rectangular channel, containing built-in vortex generators of both the slender delta-wing and winglet-pair type, have been analyzed by means of solution of the full Navier–Stokes and energy equations. Each wing or winglet pair induces the creation of streamwise longitudinal vortices behind it. The spiraling flow of these vortices serves to entrain fluid from their outside into their core. These vortices also disrupt the growth of the thermal boundary layer and serve ultimately to bring about the enhancement of heat transfer between the fluid and the channel walls. The geometric configurations considered in the study are representative of single elements of either a compact gas-liquid fin-tube crossflow heat exchanger or a plate-fin crossflow heat exchanger. Physically, these vortex generators can be mounted on the flat surfaces of the above-mentioned heat exchangers by punching or embossing the flat surfaces. They can also act as spacers for the plate fins. Because of the favorable pressure gradient in the channel, the longitudinal vortices are stable and their influence persists over an area many times the area of the slender vortex generators. From a heat transfer point of view, the delta-wing generator is found to be more effective than the winglet-pair. However, most convective heat transfer processes encounter two types of loss, namely, losses due to fluid friction and those due to heat transfer across finite temperature gradient. Because these two phenomena are manifestations of irreversibility, an evaluation of the augmentation techniques is also made from a thermodynamic viewpoint. Conclusions that are drawn thus include discussion about the influence of vortex generators (wings/winglets) on irreversibility.

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Numerical heat transfer studies of the fatty acids for different heat exchanger materials on the performance of a latent heat storage system

Renewable Energy ◽

10.1016/j.renene.2005.01.014 ◽

2005 ◽

Vol 30 (14) ◽

pp. 2179-2187 ◽

Cited By ~ 58

Author(s):

Atul Sharma ◽

Lee Dong Won ◽

D Buddhi ◽

Jun Un Park

Keyword(s):

Heat Transfer ◽

Fatty Acids ◽

Heat Exchanger ◽

Latent Heat ◽

Heat Storage ◽

Storage System ◽

Latent Heat Storage ◽

Numerical Heat Transfer

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An Exergy-Based Metric for Evaluating Solar Thermal Absorber Technologies for Gas Heating

ASME/JSME 2011 8th Thermal Engineering Joint Conference ◽

10.1115/ajtec2011-44354 ◽

2011 ◽

Author(s):

Maritza Ruiz ◽

Van P. Carey

Keyword(s):

Heat Transfer ◽

Heat Exchanger ◽

Loss Factor ◽

Performance Metrics ◽

Solar Thermal ◽

Pumping Power ◽

Central Receiver ◽

Gas Heating ◽

Goodness Factor ◽

Solar Receiver

The energy conversion effectiveness of the central receiver absorber in concentrating solar thermal power systems is dictated primarily by heat losses, material temperature limits, and pumping power losses. To deliver concentrated solar energy to a gas for process heat applications or gas cycle power generation, there are a wide variety of compact heat exchanger finned surfaces that could be used to enhance the convective transfer of absorbed solar energy to the gas stream flowing through the absorber. In such circumstances, a key design objective for the absorber is to maximize the heat transfer thermodynamic performance while minimizing the pumping power necessary to drive the gas flow through the fin matrix. This paper explores the use of different performance metrics to quantify the combined heat transfer, thermodynamic and pressure loss effectiveness of enhanced fins surfaces used in solar thermal absorbers for gas heating. Previously defined heat exchanger performance metrics, such as the “goodness factor”, are considered, and we develop and explore the use of a new metric, the “loss factor”, for determining the preferred enhanced fin matrix surfaces for concentrated solar absorbers. The loss factor, defined as the normalized exergy loss in the receiver, can be used for nondimensional analysis of the desirable qualities in an optimized solar receiver design. In comparison to previous goodness factor methods, the loss factor metric has the advantage that it quantifies the trade-off between trying to maximize the solar exergy transferred to the gas (high heat transfer rate and delivery at high temperature) and minimizing the pumping exergy loss. In this study, the loss factor is used to compare current solar receiver designs, and designs that use a variety of available plate-finned compact heat transfer surfaces with known Colburn factor (j) and friction factor (f) characteristics. These examples demonstrate how the loss factor metric can be used to design and optimize novel solar central receiver systems, and they indicate fin matrix surfaces that are particularly attractive for this type of application.

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Parametric Study of Vortex Generator Effects in an Additive Manufactured Minichannel Heat Exchanger

ASME 2019 17th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2019-4236 ◽

2019 ◽

Author(s):

Hamidreza Rastan ◽

Tim Ameel ◽

Björn Palm

Keyword(s):

Heat Transfer ◽

Thermal Properties ◽

Additive Manufacturing ◽

Heat Exchanger ◽

Angle Of Attack ◽

Three Dimensional ◽

High Energy ◽

Vortex Generators ◽

Design Parameters ◽

Minichannel Heat Exchanger

Abstract Heat exchangers with mini- and micro-channel components are capable of high energy exchange due to their incumbent large surface area to volume ratio. Concurrently, recent advances in additive manufacturing simplify the creation of metallic minichannels that incorporate turbulators for heat transfer enhancement. As part of the development of a minichannel heat exchanger with turbulators, this study analyzes the three-dimensional conjugate heat transfer and laminar flow in a minichannel heat exchanger equipped with rectangular winglet vortex generators (VGs) through numerical simulation. The minichannels have a hydraulic diameter of 2.86 mm and are assumed to be made from aluminum alloy AlSi10Mg. This material is one of the popular alloys in the additive manufacturing industry (three-dimensional (3D) printing) because of its light weight and beneficial mechanical and thermal properties. The working fluid is distilled water with temperature-dependent thermal properties. The minichannel is heated by a constant heat flux of 5 W cm−2 and the Reynolds number is varied from 230 to 950. The simulations are performed using the COMSOL® platform, which solves the governing mass, momentum, and energy equations based on the finite element method. The effect of the VG design parameters, which include VG angle of attack, height, length, thickness, longitudinal pitch, and distance from the sidewalls, is investigated. It is found that the generation of three-dimensional vortices caused by the presence of the vortex generators can notably boost the convective heat transfer, at the cost of increased pressure drop, potentially reducing the heat exchanger size for a given heat duty. A sensitivity analysis indicates that the angle of attack, VG height, VG length, and longitudinal pitch have the most significant effects on the heat transfer and flow friction characteristics. In contrast, the VG thickness and distance from the sidewalls only had minor influences on the heat exchanger performance over the studied range of design parameters.

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