• International Journal of Fluid Machinery and Systems
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• v.9 no.3
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• pp.229-236
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• 2016

Exergetic analysis was introduced in optimization of a rotating equilateral triangular internal cooling channel with staggered square ribs to maximize the net exergy gain. The objective function was defined as the net exergy gain considering the exergy gain by heat transfer and exergy losses by friction and heat transfer process. The flow field and heat transfer in the channel were analysed using three-dimensional Reynolds-averaged Navier-Stokes equations under the uniform temperature condition. Shear stress transport turbulence model has been selected as a turbulence closure through the turbulence model test. Computational results for the area-averaged Nusselt number were validated compared to the experimental data. Three design variables, i.e., the angle of rib, the rib pitch-to-hydraulic diameter ratio and the rib width-to-hydraulic diameter ratio, were selected for the optimization. The optimization was performed at Reynolds number, 20,000. Twenty-two design points were selected by Latin hypercube sampling, and the values of the objective function were evaluated by the RANS analysis at these points. Through optimization, the objective function value was improved by 22.6% compared to that of the reference geometry. Effects of the Reynolds number, rotation number, and buoyancy parameter on the heat transfer performance of the optimum design were also discussed.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.127-130
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• 2004

In this study, three-dimensional numerical calculations are peformed to simulate the flow and heat transfer in helically coiled tube steam generator employing a commercial CFD (Computational Fluid Dynamics) code. The problem considered herein includes the boiling phase change flow of tube side fluid and the single-phase counter-current flow of shell side hot fluid transferring heat to the tube side flow thru the tube wall. Detailed investigations are performed for both shell-side and tube-side flow fields in terms of density and volume fractions of each phase of fluids as well as for the tube wall heat transfer field in terms of heat transfer coefficients.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.5
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• pp.678-686
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• 1999

The purpose of this work is to Investigate the pressure drop and the heat transfer characteristics in the channel of plate heat exchanger with crossed-discrete ribs. The flow is assumed to be three-dimensional, laminar and periodically fully developed. Computations have been carried out for angles of attack from $0^{\circ}$ to $90^{\circ}$ and ratios of rib height from 0.15 to 0.46 for various values of Reynolds and Prandtl numbers. The heat transfer was improved by inclined ribs generating helical vortices and secondary flows. The results show that the pressure drop has a maximum value at $70^{\circ}$ and the heat transfer has a maximum value at $45^{\circ}$. As the rib height increases, the pressure drop and the heat transfer increase quadratically, and the increasing rate of pressure drop is higher than that of the heat transfer. As Reynolds number increases, the pressure drop increases in proportion to the square of Reynolds number and the heat transfer increases linearly.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.107-110
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• 2002

The present study deals with CFD analysis of 'The vortex generators on plastic plate heat exchanger'. When a vortex generator is placed on the heat transfer surface, the flow gets more complex because it entails complicated three-dimensional flows such as separation, reattachment, and recirculation. CFX-5.4, a commercial code utilizing unstructured mesh, has been used as a computational method for solving RANS(Reynolds-Averaged Wavier-Stokes) equations, and the applied turbulence model is $k-{\varepsilon}$ model. In addition, those computational analyses were implemented under various conditions , with or without the vortex generator between two plates, the number, form and the size of vortex generator, and different attack of angle. From the calculated temperature, velocity and pressure distribution, vorticity, wall heat flux and so on under those conditions, this study shows the effect of vortex on heat transfer.

• The KSFM Journal of Fluid Machinery
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• v.10 no.2 s.41
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• pp.7-15
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• 2007

A numerical procedure for optimizing the shape of three-dimensional channel with V-shaped ribs extruded on both walls has been carried out to enhance the turbulent heat transfer. The response surface based optimization is used as an optimization technique with Reynolds-averaged Wavier-stoked analysis. Shear stress transport (SST) turbulence model is used as a turbulence closure. Computational results for average heat transfer rate show good agreements with experimental data. The objective function is defined as a linear combination of heat transfer and friction loss-related terms with a weighting factor. Three dimensionless variables such as, rib pitch-to-rib height ratio, rib height-to-channel height ratio, and the attack angle of the rib are chosen as design variables. Nineteen training points obtained by D-optimal designs for three design variables construct a reliable response surface. In the sensitivity analysis, it is found that the objective function is most sensitive to the ratio of rib height-to-channel height ratio. And, optimal values of design variables have been obtained in a range of the weighting factor.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.781-788
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• 2003

In the present study, the heat and flow characteristics of a parallel-flow heat exchanger are numerically analyzed by using three-dimensional turbulent modeling. Heat transfer rate and pressure drop are evaluated using the concept of the efficiency index by varying the locations, the shapes and angles of inlet/outlet, and the protrusion height of flat tube. It is found that negative angle of the inlet improves the heat transfer rate and pressure drop. Results show that the locations of the inlet and outlet should be toward the right side and the left side to the reference model, respectively, in order to enhance the heat transfer rate and pressure drop. Increasing the height of the lower header causes pressure drop to decrease and yields the good flow characteristics. The lower protrusion height of flat tube shows the improvement of the heat transfer rate and pressure drop. The heat transfer rate is greatly affected by the parameters of outlet side such as the location and angle of the outlet. However, the pressure drop is influenced by the parameters of inlet side such as the location and angle of inlet and the height of the header.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2552-2557
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• 2007

Shape optimization of an internal cooling passage with staggered dimples on single surface is performed and performances of surrogates are evaluated in this paper. Optimizations are performed so that turbulent heat transfer can be enhanced compromising with pressure loss due to friction. The three-dimensional governing differential equations have been solved to find the overall Nusselt number and friction factor which are related to the objective functions of this problem. Three design variables were selected among the dimensionless geometric variables. Basic surrogate models such as second order polynomial response surface approximation (RSA), Kriging meta-modeling technique, radial basis neural network (RBNN), and derived press based averaged (PBA) surrogate model are constructed. The optimal points are searched from the above constructed surrogates by sequential quadratic programming (SQP). It is shown that use of multiple surrogates can increase the robustness in prediction of better design with minimum computational cost.

• The KSFM Journal of Fluid Machinery
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• v.10 no.4
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• pp.9-14
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• 2007

The purpose of present work is to analyze the convective heat transfer downstream of mixing vane in subchannel of nuclear reactor with three-dimensional Navier-Stokes equations. SST model is selected as a turbulence closure by comparing the performances of two different turbulent closures. Three different shapes of mixing vane are tested. And, thermal-hydraulic performances of these vanes are discussed. The results show that twist of the vane improves the heat transfer performance far downstream of the vane.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.4
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• pp.381-383
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• 1999

First topic of this paper aims to clarify how oxygen and heat transfer in silicon melt under cusp-shaped magnetic fields. We obtained asymmetric temperature distribution by using time dependent and three-dimensional calculation. Second topic is study on molecular dynamics simulation, which was carried out to estimate diffusion constants of oxygen in silicon melt.

• Journal of Welding and Joining
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• v.19 no.5
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• pp.492-498
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• 2001

In the previous study, temperature monitoring of case about shrinkage fit process was performed and heat transfer model was developed in detail by feedback and tuning among monitoring result, process investigation, and analysis result. The gap element in contact between case and core was effectively used in analysis model. In present study, following things are performed to solve deformation of case due to shrinkage fit process on the basis of previous result. Above all, mechanical material properties of case are measured by case specimen for deformation analysis considering weldment of case. Deformation of case before and after shrinkage fit process is measured, too. Three dimensional deformation model is developed by the comparison and inspection between these experimental data and analysis results. Deformation analysis is simulated with the result of heat transfer analysis, in other words, non-coupled analysis is used. Finally the countermeasure for deformation is brought up through those.