Unsteady Conjugate Heat Transfer Analysis of an Air Immersed Solid Particle With Application to an Innovative Heat Exchanger

2011 ◽  
Author(s):  
Leonardo Nettis ◽  
Fabio De Bellis ◽  
Luciano A. Catalano ◽  
Roberto Verzicco
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Solid Particle ◽  
Conjugate Heat Transfer ◽  
Gas Flow ◽  
High Efficiency ◽  
Large Diameter ◽  
Solid Particles ◽  
Heat Transfer Analysis ◽  
1D Model

The improvement of both heat recovery Joule-Brayton cycles and closed cycle (externally fired) gas turbine plants is strongly limited by the availability of high efficiency heat exchangers. In such a scenario, a non conventional heat exchanger was recently proposed; this device employs falling solid particles to perform heat transfer between two separate gas flows and was designed with a 1D model neglecting conduction within the particles. Although experimental reliability of this assumption was already obtained, there is no proof available of the quantitative effect introduced by the above mentioned simplification. In this work, Direct Numerical Simulation (DNS) of a solid particle immersed in a gas flow has been performed in order to further validate the hypothesis of negligible conduction and to enhance the design of the proposed heat exchanger. Unsteady Conjugate Heat Transfer (CHT) has been used to predict the final temperature of the solid sphere for Reynolds numbers ranging from 30 to nearly 300, the computational grid being generated with the Immersed Boundary (IB) technique. A validation of the study is presented, together with grid independence and boundary independence assessment. The results fully confirmed the worthiness of the initial assumption, with a 1.4% maximum error for high Reynolds conditions (large diameter particles) with respect to the 1D model. Additionally, the code has been employed to explore the influence both of several particles disposed in a row and of the distance between successive particles.

Unsteady Conjugate Heat Transfer Analysis of an Immersed Particle Innovative Heat Exchanger

2012 ◽  
Vol 4 (1) ◽  
Author(s):  
Leonardo Nettis ◽  
Fabio De Bellis ◽  
Luciano A. Catalano ◽  
Roberto Verzicco
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Conjugate Heat Transfer ◽  
Gas Flow ◽  
High Efficiency ◽  
Large Diameter ◽  
Solid Particles ◽  
Heat Transfer Analysis ◽  
Final Temperature ◽  
1D Model

The improvement of both heat recovery Joule-Brayton cycles and closed cycle (externally fired) gas turbine plants is strongly limited by the availability of high efficiency heat exchangers. In such a scenario, a nonconventional heat exchanger was recently proposed; this device employs falling solid particles to perform heat transfer between two separate gas flows and was designed with a 1D model neglecting conduction within the particles. Although the experimental reliability of this assumption was already obtained for one particle size, there is no proof available of the quantitative effect introduced by the above mentioned simplification and, more importantly, no indication of when this assumption becomes unacceptable. In this work, direct numerical simulation (DNS) of a solid particle immersed in a gas flow has been performed in order to further validate the hypothesis of negligible conduction and to enhance the design of the proposed heat exchanger. Unsteady conjugate heat transfer has been used to predict the final temperature of the solid sphere for Reynolds numbers ranging from 30 to nearly 300, the computational grid being generated with the immersed boundary (IB) technique. A validation of the study is presented, together with grid independence and boundary independence assessment. The results fully confirmed the worthiness of the initial assumption, with a 1.4% maximum error for high Reynolds conditions (large diameter particles) with respect to the 1D model. Additionally, the code has been employed to explore the influence of the wake in the case of aligned particles, namely, the worst possible situation in terms of efficiency of the heat transfer mechanism. Finally, the discrepancy between the results obtained with an axisymmetric domain and a 3D domain, in terms of final temperature of the particle, have been investigated for the highest Reynolds number, when the flow is supposed to lose its axial symmetry.

scholarly journals Numerical Simulation of Secondary Flow in Gas Turbine Disc Cavities, Including Conjugate Heat Transfer

1996 ◽  
Author(s):  
Y.-H. Ho ◽  
M. M. Athavale ◽  
J. M. Forry ◽  
R. C. Hendricks ◽  
B. M. Steinetz
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Conjugate Heat Transfer ◽  
Gas Flow ◽  
Numerical Study ◽  
Labyrinth Seal ◽  
Temperature Fields ◽  
Heat Transfer Analysis ◽  
Flow Rates ◽  
Turbine Disc

A numerical study of the flow and heat transfer in secondary flow elements of the entire inner portion of the turbine section of the Allison T-56/501D engine is presented. The flow simulation included the interstage cavities, rim seals and associated main path flows, while the energy equation also included the solid parts of the turbine disc, rotor supports, and stator supports. Solutions of the energy equations in these problems usually face the difficulty in specifications of wall thermal boundary conditions. By solving the entire turbine section this difficulty is thus removed, and realistic thermal conditions are realized on all internal walls. The simulation was performed using SCISEAL, an advanced 2D/3D CFD code for predictions of fluid flows and forces in turbomachinery seals and secondary flow elements. The mass flow rates and gas temperatures at various seal locations were compared with the design data from Allison. Computed gas flow rates and temperatures in the rim and labyrinth seal show a fair 10 good comparison with the design calculations. The conjugate heat transfer analysis indicates temperature gradients in the stationary intercavity walls, as well as the rotating turbine discs. The thermal strains in the stationary wall may lead to altered interstage labyrinth seal clearances and affect the disc cavity flows. The temperature, fields in the turbine discs also may lead to distortions that can alter the rim seal clearances. Such details of the flow and temperature fields are important in designs of the turbine sections to account for possible thermal distortions and their effects on the performance. The simulation shows that the present day CFD codes can provide the means to understand the complex flow field and thereby aid the design process.

scholarly journals A Conjugate Heat Transfer Analysis of a Triangular Finned Annulus Based on DG-FEM

2018 ◽  
Vol 2018 ◽  
pp. 1-18
Author(s):  
Muhammad Ishaq ◽  
Khalid Saifullah Syed ◽  
Zafar Iqbal ◽  
Ahmad Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Conjugate Heat Transfer ◽  
Strong Influence ◽  
Heat Transfer Analysis ◽  
Conductivity Ratio ◽  
Geometric Configurations ◽  
Specific Configuration ◽  
Double Pipe ◽  
Pipe Heat

A DG-FEM based numerical investigation has been performed to explore the influence of the various geometric configurations on the thermal performance of the conjugate heat transfer analysis in the triangular finned double pipe heat exchanger. The computed results dictate that Nusselt number in general rises with values of the conductivity ratio of solid and fluid, for the specific configuration parameters considered here. However, the performance of these parameters shows strong influence on the conductivity ratio. Consequently, these parameters must be selected in consideration of the thermal resistance, for better design of heat exchanger.

Flow Prediction and Conjugate Heat-Transfer Analysis of a Counter Flow Heat-Exchanger with Protruded Fin

2020 ◽  
Vol 12 (3) ◽  
Author(s):  
Manikandan Mohan ◽  
K.C. Udaiyakumar
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Conjugate Heat Transfer ◽  
Flow Analysis ◽  
Heat Transfer Analysis ◽  
Counter Flow ◽  
Tube Heat Exchanger ◽  
Flow Heat ◽  
Optimized Model ◽  
Cfd Method

Voluminous cram has been carried out in this project which is intended to improve the conjugate heat-transfer performance of a heat-exchanger. In this study, CFD method is effectively used to predict the effect of Protruded Fins in heat exchanger, which protrudes inside the tube in addition to the shell side. CFD analysis on Protruded Finned Heat Exchanger (PFHE) is carried out with three different fin configurations like rectangular, triangular and parabolic fins. The baseline model of counter flow shell-tube heat-exchanger is considered with standard dimensions and analyzed initially without fins. Later the numbers of fins are increased to optimize the fin position and counts. The shape of the fins is then modified to find an optimized model with a higher heat-transfer coefficient. Hence, the present conjugate heat-transfer and flow analysis focus on optimizing the number of fins for a heat-exchanger with counter flow along with the shape optimization of fins. The computational values are measured with the net heat exchange between the cold and hot-fluids in terms of temperature difference. Also, the area averaged surface heat transfer co-efficient (h) of the heat exchanger with different fin configurations are plotted and compared.

scholarly journals A Hybrid Numerical Methodology Based on CFD and Porous Medium for Thermal Performance Evaluation of Gas to Gas Micro Heat Exchanger

Micromachines ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 218 ◽  
Author(s):  
Danish Rehman ◽  
Jojomon Joseph ◽  
Gian Luca Morini ◽  
Michel Delanaye ◽  
Juergen Brandner
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Heat Exchanger ◽  
Conjugate Heat Transfer ◽  
Numerical Study ◽  
Computational Cost ◽  
Heat Transfer Analysis ◽  
Working Fluid ◽  
Micro Heat Exchanger ◽  
Parallel Microchannels

In micro heat exchangers, due to the presence of distributing and collecting manifolds as well as hundreds of parallel microchannels, a complete conjugate heat transfer analysis requires a large amount of computational power. Therefore in this study, a novel methodology is developed to model the microchannels as a porous medium where a compressible gas is used as a working fluid. With the help of such a reduced model, a detailed flow analysis through individual microchannels can be avoided by studying the device as a whole at a considerably less computational cost. A micro heat exchanger with 133 parallel microchannels (average hydraulic diameter of 200 μ m) in both cocurrent and counterflow configurations is investigated in the current study. Hot and cold streams are separated by a stainless-steel partition foil having a thickness of 100 μ m. Microchannels have a rectangular cross section of 200 μ m × 200 μ m with a wall thickness of 100 μ m in between. As a first step, a numerical study for conjugate heat transfer analysis of microchannels only, without distributing and collecting manifolds is performed. Mass flow inside hot and cold fluid domains is increased such that inlet Reynolds number for both domains remains within the laminar regime. Inertial and viscous coefficients extracted from this study are then utilized to model pressure and temperature trends within the porous medium model. To cater for the density dependence of inertial and viscous coefficients due to the compressible nature of gas flow in microchannels, a modified formulation of Darcy–Forschheimer law is adopted. A complete model of a double layer micro heat exchanger with collecting and distributing manifolds where microchannels are modeled as the porous medium is finally developed and used to estimate the overall heat exchanger effectiveness of the investigated micro heat exchanger. A comparison of computational results using proposed hybrid methodology with previously published experimental results of the same micro heat exchanger showed that adopted methodology can predict the heat exchanger effectiveness within the experimental uncertainty for both cocurrent and counterflow configurations.

scholarly journals Fully Coupled Large Eddy Simulation of Conjugate Heat Transfer in a Ribbed Channel with a 0.1 Blockage Ratio

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2096
Author(s):  
Joon Ahn ◽  
Jeong Chul Song ◽  
Joon Sik Lee
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Conjugate Heat Transfer ◽  
Heat Transfer Analysis ◽  
Scale Model ◽  
Computational Domain ◽  
Blockage Ratio ◽  
Ribbed Channel ◽  
Large Eddy ◽  
Cooling Passage

Large eddy simulations are performed to analyze the conjugate heat transfer of turbulent flow in a ribbed channel with a heat-conducting solid wall. An immersed boundary method (IBM) is used to determine the effect of heat transfer in the solid region on that in the fluid region in a unitary computational domain. To satisfy the continuity of the heat flux at the solid–fluid interface, effective conductivity is introduced. By applying the IBM, it is possible to fully couple the convection on the fluid side and the conduction inside the solid and use a dynamic subgrid scale model in a Cartesian grid. The blockage ratio (e/H) is set at 0.1, which is typical for gas turbine blades. Through conjugate heat transfer analysis, it is confirmed that the heat transfer peak in front of the rib occurs because of the impinging of the reattached flow and not the influence of the thermal boundary condition. When the rib turbulator acts as a fin, its efficiency and effectiveness are predicted to be 98.9% and 8.32, respectively. When considering conjugate heat transfer, the total heat transfer rate is reduced by 3% compared with that of the isothermal wall. The typical Biot number at the internal cooling passage of a gas turbine is <0.1, and the use of the rib height as the characteristic length better represents the heat transfer of the rib.

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