Multi-objective optimization of a dimpled channel for heat transfer augmentation

Staggered arrays of dimples printed on opposite surfaces of a cooling channel is formulated numerically and optimized with hybrid multi-objective evolutionary algorithm and Pareto optimal front. As Pareto optimal front produces a set of optimal solutions, the trends of objective functions with design variables are predicted by hybrid multi-objective evolutionary algorithm. The problem is defined by three non-dimensional geometric design variables composed of dimpled channel height, dimple print diameter, dimple spacing, and dimple depth, to maximize heat transfer rate compromising with pressure drop. Twenty designs generated by Latin hypercube sampling were evaluated by Reynolds-averaged Navier–Stokes solver and the evaluated objectives were used to construct Pareto optimal front through hybrid multi-objective evolutionary algorithm. The optimum designs were grouped by k-means clustering technique and some of the clustered points were evaluated by flow analysis. With increase in dimple depth, heat transfer rate increases and at the same time pressure drop also increases, while opposite behavior is obtained for the dimple spacing. The heat transfer performance is related to the vertical motion of the flow and the reattachment length in the dimple.     

Optimization of a stepped circular pin-fin array to enhance heat transfer performance

A Stepped circular pin-fin array is formulated numerically and optimized with Kriging metamodeling technique to enhance heat transfer performance. The problem is defined by two non-dimensional geometric design variables composed of height of the channel, height of smaller diameter part of the pin-fins, and smaller diameter of the pin-fins, to maximize heat transfer rate compromising with friction loss. Ten designs generated by Latin hypercube sampling were evaluated by three-dimensional Reynolds-averaged Navier–Stokes solver and the evaluated objectives were used to construct the surrogate model. The predictions of objective function by Kriging model at optimum point show reasonable accuracy in comparison with the values calculated by RANS analysis. Optimum shape of pin-fins strongly depends on the weighting factor which measures importance of the friction loss term in the objective function. The thermal performances are much higher than that of the straight pin-fin at sampling optimum points with different weighting factors.     

Convective heat transfer in a rotating annulus device

Convective heat transfer in a horizontal annulus device rotating around its horizontal axis has been examined. The results show that heat transfer in the annulus depends on the rotational speed. At a certain value of the rotational speed there is only conduction in the annulus. A criterium is given to calculate this rotational speed from the physical properties of the liquids. For the calculation of the heat transfer in the standstill of the annulus two equations are proposed.

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Konvektiver Wärmeübergang in einem rotierenden Ringspalt

Zusammenfassung Der Wärmeübergang bei Konvektion in einem um seine Horizontalachse rotierenden Ringspalt wurde untersucht. Wie die Ergebnisse zeigen, hängt der Wärmeübergang von der Drehzahl ab. Ab einer bestimmten Drehzahl wird Wärme nur noch durch Leitung übertragen. Es wird ein Kriterium angegeben, diese Drehzahl aus den physikalischen Daten der Flüssigkeiten zu berechnen. Zur Berechnung des Wärmeübergangs im Stillstand werden zwei Gleichungen vorgeschlagen.

     

Condensation heat transfer in a rotating horizontal cylinder with a scraper

A dryer used in the drying process of paper production is usually a rotating horizontal cylinder in which steam condenses. This study concerns some experiments and analyses of condensate flow and heat transfer in a dryer with a scraper.

A laminar film model and a solid film model are introduced for the theoretical analyses. In the former the condensate flow is assumed to be laminar. In the latter the condensate film is assumed to adhere to the cylinder wall. In the analysis with the laminar film model, the film thickness diverges at relatively slow rotations. A criterion for the critical condition at which the divergence commences is proposed. From the solid film model, analytical expressions can be derived for the film thickness and the heat transmission coefficient through the condensate film and the cylinder wall.

The experiments are conducted with an acrylic resin cylinder and a stainless steel cylinder. The experimental result on heat transmission agrees with the analytical result for the solid film model if a condensate film about 25 μm thick remains in spite of scraping.     

Unsteady heat and mass transfer in a rotating nanofluid layer

The present paper studies the effect of rotation on the thermal instability in a horizontal layer of a Newtonian nanofluid which incorporates the effect of Brownian motion along with thermophoresis. In order to find the concentration and the thermal Nusselt numbers for unsteady state, a nonlinear analysis, using a minimal representation of the truncated Fourier series of two terms, has been performed. The results obtained are then presented graphically. It is observed that rotation delays the rate of heat and mass transferred, representing a delay in the onset on convection. This shows a stabilizing effect for a rotating system against a nonrotating system.     

Convective heat transfer in a rotating horizontal cylindrical fluid layer

This paper describes the thermal convection and heat transfer in a cylindrical fluid layer rotating around a horizontal axis, with various constant temperatures set at the layer boundaries. The influence of the rotational speed of the cylindrical fluid layer on the convective heat transfer in this layer is studied. The study results are presented as functions of dimensionless parameters that characterize the action of two convective mechanisms: centrifugal and thermal-oscillatory. It is shown that, with low rotational speed, the heat transfer is determined by quasistationary gravitational convection.     

Measurement and calculation of guide vane performance in expanding bends for wind-tunnels

 The design of guide vanes for use in expanding bends was investigated both experimentally and numerically. The primary application in mind is the use of expanding corners in wind-tunnels for the purpose of constructing compact circuits with low losses. To investigate the performance of guide vanes in realistic situations expansion ratios between 1 and 53 were tested in the experiments. These were carried out in an open wind-tunnel specially built for the present purpose. The experimental results demonstrated that suitably designed guide vanes give very low losses and retained flow quality even for quite substantial expansion ratios. For wind-tunnel applications expansion ratios around 1.3 seem appropriate, Optimization of a guide vane design was done using a two-dimensional cascade code, Mises. A new vane optimized for an expansion ratio of 43 gave a two-dimensional total pressure-loss coefficient as low as 0.041 for a chord Reynolds number of 200,000. Received: 7 April 1997/Accepted: 11 August 1997     

Turbulent heat transfer characteristics of water flow in a rotating pipe

Large-Eddy-Simulation of turbulent heat transfer for water flow in rotating pipe is performed, for various rotation ratios (0 ≤ N ≤ 14). The value of the Reynolds number, based on the bulk velocity and pipe diameter, is Re = 5,500. The aim of this study is to examine the effect of the rotating pipe on the turbulent heat transfer for water flow, as well as the reliability of the LES approach for predicting turbulent heat transfer in water flow. Some predictions for the case of non-rotating pipe are compared to the available results of literature for validation. To depict the influence of the rotation ratio on turbulent heat transfer, many statistical quantities are analyzed (distributions of mean temperature, rms of fluctuating temperature, turbulent heat fluxes, higher-order statistics). Some contours of instantaneous temperature fluctuations are examined.     

Multi-objective optimization of discrete film hole arrangement on a high pressure turbine end-wall with conjugate heat transfer simulations

This paper discussed a method of combining a full automatic multi-objective optimization and conjugate heat transfer calculation to obtain optimal cooling layouts on a transonic high pressure guide vane under a realistic turbine working condition. The improvement in cooling design from the optimized models was analyzed in detail, along with a discussion of sensitivities of two objective functions to five design variables. The full automatic method comprises the process of geometry creation, mesh generation, numerical solution and post data analysis. The vane is solid and the end-wall is arranged in a linear cascade. On the end-wall, film holes are all cylindrical and classified in five regions, with region A near the leading edge of the vane, region B near the suction side, regions C and D near the pressure side, and region E for the rest. Five design variables are three pitch-to-hole ratios in regions B, D, E and two compound angles of film holes in regions A and D. Two selected objective functions are area averaged overall cooling effectiveness of the end-wall and aerodynamic losses in a cross-plane at x/C_ax = 1.06 just downstream of the outlet of the cascade. For the optimization process, the multi-objective genetic algorithm based on the Non-dominated Sorted Genetic Algorithm-II was applied. The Latin hypercube sampling method was used to choose 21 experimental design points in the design space, which are also the sources for constructing the surrogate models with the Kriging model. The results demonstrate that the method using full automatic optimization and conjugate heat transfer calculation has achieved an increase of 8.7%–9.5% in area-averaged overall cooling effectiveness and a reduction of about 4.8%–6.1% in aerodynamic losses. The highest increase in cooling effectiveness exists in the region near the pressure side with a mild increase in the middle of the passage. The largest heat flux reduction exists in the regions near the pressure side and the crown of the suction side. The change of compound angle in region A near the leading edge has a negligible influence on overall cooling effectiveness but a high impact on aerodynamic losses. It's advisable to maintain the compound angle and pitch-to-diameter ratio at low values in region D near the pressure side to obtain high cooling performance.     

Optical investigation of the heat transfer from a rotating cylinder in a cross flow

The heat transfer from a rotating cylinder in an air-cross flow was investigated by purely optical measuring techniques. Flow velocities were measured by a two-dimensional LDV both in the vicinity of the cylinder and in the boundary layer. A new optical device based on light-deflection in a temperature field was developed to examine local temperature gradients in the boundary layer of the rotating cylinder. Finally, a Michelson-interferometer was installed to produce real-time pictures of isothermal lines around the heated cylinder. The impact of rotation on flow patterns, boundary layer behaviour and heat transfer could be clearly identified. It appears that the velocity-ratio acts like an independent parameter, in that flow patterns correspond to this dimensionless number. Furthermore, it seems that rotation dominates over cross flow, both fluid-dynamically and thermally above = 2.This work was carried out at the University of the Federal Armed Forces in Munich/Germany.     

Flow and heat transfer in a rotating enclosure with axial throughflow

An analysis is made of the fluid flow and heat transfer processes in a circular cylindrical enclosure rotating about its own axis. A coolant is passed through the enclosure, entering and leaving through centrally located apertures in the end walls. This configuration is intended as a model of rotating enclosures in devices such as gas turbines and air compressors. The Navier-Stokes and energy equations were solved by a finite-difference formulation which can accommodate either steady or transient conditions. Buoyancy forces associated with the rotational body forces were included in some cases. All solutions were performed for laminar flow. For the parameter ranges investigated it was found that rotation inhibited the recirculating motion within the enclosure and thereby decreased the heat transfer relative to that for the stationary enclosure. Buoyancy further reduced the heat transfer owing to the break up of residual circulatory motions in the outer portion of the enclosure. Still stronger buoyancy brought about a slight increase in the heat transfer. The coolant flow was confined to a corridor adjacent to the axis of the enclosure, and there was no mixing between the coolant and the fluid in the enclosure proper.     

Unsteady heat transfer from a rotating disk to fluids with low Prandtl numbers

Summary An analysis is presented concerning unsteady heat transfer from a rotating disk to a low Prandtl number fluid under the condition of a step change in surface temperature with time. Entire time history results for the surface heat flux are given for Prandtl numbers up to 0.04, and these results are obtained by means of a first-order perturbation about the solution for zero Prandtl number. Steady-state heat transfer predicted by this method agrees almost precisely with exact values.     

Law of heat transfer in the region of a gas curtain

The article gives the result of an experimental investigation of heat transfer in the region of a gas curtain behind the permeable part of the surface in a subsonic turbulent boundary layer in the range of blowing intensities j=0.001–0.04.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 160–163, March–April, 1976.The authors thank G. A. Lyubimov for his continuing interest and aid in the work.     

Multi-objective optimization of a plate and frame heat exchanger via genetic algorithm

In the present paper, a plate and frame heat exchanger is considered. Multi-objective optimization using genetic algorithm is developed in order to obtain a set of geometric design parameters, which lead to minimum pressure drop and the maximum overall heat transfer coefficient. Vividly, considered objective functions are conflicting and no single solution can satisfy both objectives simultaneously. Multi-objective optimization procedure yields a set of optimal solutions, called Pareto front, each of which is a trade-off between objectives and can be selected by the user, regarding the application and the project’s limits. The presented work takes care of numerous geometric parameters in the presence of logical constraints. A sensitivity analysis is also carried out to study the effects of different geometric parameters on the considered objective functions. Modeling the system and implementing the multi-objective optimization via genetic algorithm has been performed by MATLAB.     

Flow and heat transfer with prescribed skin friction in a rotating fluid

This paper investigates the rotating flow and heat transfer of a viscous fluid induced by a stretching surface. The nonlinear problem subject to a given skin friction at the boundary is solved. Analytic solution is obtained using homotopy analysis method. The velocity, temperature, and stretching velocity is calculated for different values of the rotation parameter (λ). The obtained results are compared with the well known results of rotating flow induced by a stretching surface by using four sets of boundary conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

锻造操作机机构受力性能的多目标优化设计

考虑到锻造操作机的重载特性,为避免因受力不均造成局部受力过大而危及机械结构的安全性,本文以某DDS锻造操作机为例,进行操作机的机构受力性能优化设计。通过灵敏度分析,以关键的机构受力构件在整个工作空间上的平均受力作为优化目标,基于多目标遗传算法NSGA II对操作机的主运动机构进行尺寸优化设计,以合理分配机构受力。与原设计相比,优化后的操作机具有更为良好的整体受力性能。本文的研究工作有助于操作机的机构设计。     

Direct numerical simulation of turbulent heat transfer in a wall-normal rotating channel flow

Investigations into the characteristics of turbulent heat transfer and coherent flow structures in a plane-channel subjected to wall-normal system rotation are conducted using direct numerical simulation (DNS). In order to investigate the influence of system rotation on the temperature field, a wide range of rotation numbers are tested, with the flow pattern transitioning from being fully turbulent to being quasilaminar, and eventually, fully laminar. In response to the Coriolis force, secondary flows appear as large vortical structures, which interact intensely with the wall shear layers and have a significant impact on the distribution of turbulence kinetic energy (TKE), turbulence scalar energy (TSE), temperature statistics, and turbulent heat fluxes. The characteristic length scales of turbulence structures responsible for the transport of TSE are the largest at the quasilaminar state, which demands a very large computational domain in order to capture the two-dimensional spectra of temperature fluctuations. The effects of the Coriolis force on the turbulent transport processes of the temperature variance and turbulent heat fluxes are thoroughly examined in terms of their respective budget balances.     

Laminar heat transfer in the entrance region of ducts

A finite difference technique is used for the evaluation of the rate of heat transfer in the thermal entrance region of ducts with axial conduction. The velocity profile is fully developed and flow in a tube and between parallel plates is studied. Local and average Nusselt numbers and mixing temperatures are presented as a function of the Péclet number. A criterion is also established which proves useful for predicting the conditions under which axial conduction may be ignored.Nomenclature C transformation constant - c _v specific heat, constant volume - D _h hydraulic diameter - h local convective film coefficient, Eq. (15) - h* local convective film coefficient, Eq. (16) - h _m ^* mean convective film coefficient, Eq. (17) - k thermal conductivity - Nu local Nusselt number, hD _h/k - Nu* local Nusselt number, h*D _h/k - Nu _m ^* mean Nusselt number, hQD _h/k - Pe Péclet number, D _h v _m/ - q rate of heat transfer - r radial coordinate - r _o tube radius - R nondimensional radial coordinate, r/r _o - S transformed axial coordinate, Eq. (10) - T temperature - T _e entrance temperature - T _m mixing temperature, Eq. (18) - T _w wall temperature - v _z axial velocity - v _m mean axial velocity - V nondimensional axial velocity, v _z /v _m - y transverse coordinate in parallel plate flow - y _o half width of parallel plate duct - Y nondimensional transverse coordinate, y/y _o - z axial coordinate - Z nondimensional axial coordinate, z/r _o or z/y _o - Z ⁺ nondimensional axial coordinate divided by Peclet number, Z/Pe - thermal diffusivity - nondimensional temperature, (T–T _w)/(T _e–T _w) - mean nondimensional temperature, - _m nondimensional mixing temperature, Eq. (22) - density - i axial position index - j radial or transverse position index