Machine Learning Supports Robust Operation of Thermosiphon Reboilers

The analysis of process and equipment operational data in chemical engineering regularly requires a high level of expert knowledge. This work presents a Machine Learning-based approach to evaluate and interpret process data to support robust operation of a thermosiphon reboiler. By applying an outlier detection, potentially interesting and unstable operating conditions can be identified quickly. A multidimensional regression allows to forecast the circulating mass flow. The results obtained fit well into the current state of research and manual evaluation of thermosiphon reboilers.     

节能型立式热虹吸再沸器的模拟

为了提高再沸器的用能效率，特将固体颗粒引入立式热虹吸再沸器的管程形成气－液－固多相流系统，以强化传热，并提出了该节能型立式热虹吸再沸器的数学模型。模拟计算表明，流态化技术的引入能够强化再沸器的传热，减小换热面积或系统的有效能损失。颗粒的密度对传热的影响较大，其增加可使管内传热系数增大；随着固含率的增加，管内传热系数增大；随着粒径的增加，管内传热 数先增加后减小，有一极大值，颗粒密度的增加可使该极值增大并出现得更早。     

基于HTRI的立式热虹吸再沸器设计优化

立式热虹吸再沸器由于其具有较大的传热系数、较小的占地面积以及安装便捷等优点,在化工行业中得到广泛的应用,本文利用HTRI软件对醋酸仲丁酯装置中醋酸精馏塔再沸器进行设计优化,计算合适的再沸器结构参数,找出合适的静压头,以及最优的进口管径。     

T型管管束的沸腾传热性能

Ｔ型管管束的沸腾传热性能刘进荣（内蒙古工业大学化学工程系,呼和浩特０１００６２）沈自求徐维勤（大连理工大学化学工程研究所,大连１１６０１２）关键词水平管管束Ｔ型管沸腾传热强化卧式再沸器１引言水平管管束沸腾传热广泛应用于石油化工、制冷等工业部门,如蒸...     

气泡在热液相介质中上升时的传热与传质

本文对气泡在热液相介质中上升时的传热与传质进行了分析,建立了数学模型,并进行了数值解,其结果可以说明气液相界面蒸发的特征。本文还通过实验对理论模型进行了验证。     

换热管内置螺旋线圈的阻力及传热特性实验研究

将9种不同结构尺寸的螺线线圈分别置入换热管内进行实验研究,分析了其阻力和传热特性。实验结果表明,在相同的Re下,管内插入螺旋线圈后流体压降和传热系数都有较大提高。通过多元线性回归分析,得到了压降增量和传热系数关联式。由传热性能分析,得到了综合评价因子φ=0.77~1.60,为如何选用性能优越的螺旋线圈提供了参考依据。     

Design Parameter Effects on Expansion in Fluidized Beds with Inserts

The effect of some design parameters on the expansion of particles has been studied in a fluidized bed of 300 mm diameter. Four distributors were examined; three perforated plates, each perforated by holes of 0.8 mm in diameter but different hole densities at 6 mm, 9 mm and 12 mm pitch, and a porous plastic distributor 17 mm thick. Particles of different materials in the Archimedes number range from 100 to 10⁵ were fluidized. The inserts were held vertically as arrays. All experimental data for four distributors were correlated within experimental error by the equation: whereU, U_mf, U₀ are the gas velocity, velocity at minimum fluidization and real or apparent terminal velocity, while e is the bed porosity and e_mf is the porosity at the condition of minimum fluidization. P is the hole pitch of perforated plate distributor in millimeters.     

高粘度流质下管壳式折流板开孔换热器换热性能的数值模拟

通过数值模拟计算研究了4块弓形折流板管壳式折流板开孔换热器在高粘度流质下的强化换热性能。模拟结果表明,在高粘度流质中折流板开后换热器压力分布比未开孔前分布均匀些,温度分布同样遵循相似规律,未开孔折流板背根部会产生滞留区,并且滞留区随着速度的增大而增大,折流板开孔后会对流体产生扰动作用,从而改善滞留区,有助于强化传热。     

Numerical investigations of circular tube fitted with helical screw-tape inserts from the viewpoint of field synergy principle

3-D numerical simulations are performed for heat transfer and fluid flow characteristics of the tubes fitted with helical screw-tape inserts. The comparison between the RNG k-epsilon turbulence model and the SST k-omega turbulence model in prediction of swirling flow shows that the latter has better qualitative and quantitative agreements with the experimental results than the former. The simulation results show that the novel helical inserts with right and left twists alternately have better heat transfer performance than that of the helical inserts with uniformly right twists. The simulation results are analyzed from the viewpoint of field synergy principle, it is found that the principle could explain well the mechanism of heat transfer enhancement of the helical twist inserts. The smaller the mean intersection angle between the temperature gradient and velocity vector, the larger the Nusselt number; in addition, the smaller local intersection angle also implies the higher local heat transfer coefficient.     

Thermodynamic optimisation of distillation columns

In this paper a methodology for thermodynamic analysis and distillation column ‘targeting’ is presented, with emphasis on the use of side condensers and side reboilers. Research in the past has been towards the establishment of a heat distribution curve, showing the way in which heat can be added or extracted across the different column sections. One major disadvantage of these profiles is that they refer to reversible columns, and cannot be used effectively to target for modifications in a real column.The main feature of the proposed methodology is the introduction of a minimum driving force, defined in terms of exergy loss distribution of the existing column, to set realisable targets for side reboiling/condensing in real columns, resulting in considerable energy savings. In addition to providing realisable targets, the new approach also provides the design engineer with information about the best location to place a side exchanger, and the required additional column modifications. The methodology can be applied using conventional column models in commercial process simulation programs, but can be significantly simplified by using reboiled and refluxed absorber models in a bespoke program. Simulation results for modified designs set by the new approach, for binary and multicomponent separations, verify the feasibility of the targets. This contrasts with previous approaches, which result in temperature shifts and heat load penalties after placing side reboilers/condensers, thus requiring additional simulation time and experienced judgement.     

换热管内置开边槽扭带的阻力与传热特性研究＊

将21种不同结构参数的铝制扭带分别置入换热管进行冷态和热态实验,研究并分析了换热管内置开三角形边槽扭带的阻力和传热特性。实验结果表明,插入开边槽扭带后管内的流动阻力和传热系数都有较大的提高。通过多元线性回归分析,得到了相应的阻力系数关联式和换热系数关联式。由强化传热性能评价分析,得到评价因子φ=1．05～1．35,证明了所研究的扭带具有强化传热的应用价值。     

Effects of colloidal properties on sensible heat transfer in water-based titania nanofluids

Nanofluids have attracted considerable attention in recent years as effective working fluids in heat transfer applications. Nanofluids are essentially suspensions of nanoparticles in a base fluid and exhibit higher thermal conductivity than conventional heat transfer fluids.     

Enhancement of Turbulent Flow Heat Transfer in a Tube with Modified Twisted Tapes

Numerical simulations were performed to study the fluid flow and heat transfer in a tube with staggered twisted tapes with central holes. In the range of Reynolds numbers between 6000 and 28 000, the modified twisted tapes increased the Nusselt number by 76.2 ～ 149.7 % and the friction factor by 380.2 ～ 443.8 % compared to the smooth tube. Compared to the typical twisted tapes, the modified twisted tapes produced an acceleration flow through the triangle regions leading to the enhancement of heat transfer, and the holes in the modified tapes reduced the severe pressure loss. It was found that the modified twisted tapes decreased the friction factor by 8.0 ～ 16.1 % and enhanced the heat transfer by 34.1 ～ 46.8 % in comparison with the typical tapes. These results indicated that the performance ratio values of the tube with modified twisted tapes were higher than 1.0 in the range of Reynolds numbers studied. The computed performance ratios of the tube with modified twisted tapes were much higher than those of the tube with typical twisted tapes. This means that the integrated performance of the tube with staggered twisted tapes with central holes is superior to that of the tube with typical twisted tapes.     

管外周向低翅片翅形对纵向流传热性能的影响

管外周向低翅片翅形对纵向流传热性能的影响邓先和，王世平，林培森，邓颂九（华南理工大学化工研究所，广州５１０６４１）关键词传热管周向翅片，轴向流，强化传热１前言当流体纵向冲刷管外周向低翅片时，翅形对传热管传热性能的影响很大。以往常用的螺纹翅片管的周向低...     

Experimental Study on the Heat Transfer Enhancement of Oscillating-Flow Heat Pipe by Acoustic Cavitation

Experimental investigations on the heat transfer characteristics of an oscillating-flow heat pipe with acoustic cavitation in comparison with the ordinary oscillating-flow heat pipe are given in this article. The experimental results showed that the heat transfer rate of an oscillating-flow heat pipe with an acoustic cavitation field imposed on the evaporator section was higher than that without a cavitation field by 8–24.5%. It has been proved that acoustic cavitation can enhance the heat transfer performance of an oscillating-flow heat pipe. However, for the case of acoustic cavitation applied on the condenser section, not all ultrasonic fields applied were effective, and the heat transfer rate increased from ?39 to 77%. Further discussion on the experimental results is provided.     

管壳式换热器管束结构优化发展概述

总结了近年来国内外新型管壳式换热器的管束结构发展进展,从管程、壳程两个方面介绍了管壳式换热器管束结构改进及强化传热机理,并且介绍了几种新型结构在实际生产中的成功应用及其强化传热特点。最后为换热器管束结构发展提出建设性意见。     

Experimental study on thermo-hydraulic performances of nanofluids flowing through a corrugated tube filled with copper foam in heat exchange systems

Thermo-hydraulic characteristics of TiO₂-water nanofluids in thin-wall stainless steel test tubes (corrugated tube and circular tube) filled with copper foam (40 PPI) are experimentally investigated and compared with those in test tubes without copper foam. The effects of nanoparticle mass concentration on flow and heat transfer performances are investigated. In addition, the mutual restriction relationships between Reynolds number (Re), Nusselt number (Nu) and resistance coefficient (f) are discussed respectively. Also, the comprehensive coefficient of performance (CCP) between heat transfer and pressure drop is evaluated. The results show that core-enhancement region for heat transfer using experimental tubes filled with copper foam is notably different from that of tubes without copper foam. There is a corresponding Reynolds number (about Re=2400) for the maximum CCP of each condition. And the heat transfer can be enhanced dramatically and sustained at 8000 ≤ Re ≤ 12000.     

Mixed convection in the heated semi-circular lid-driven cavity for nonNewtonian power-law fluids: Effect of presence and shape of the block

The present work delineates the hydrodynamics and thermal characteristics due to mixed convection in the liddriven semi-circular cavity affected by the presence of the adiabatic block at its geometric center for twodimensional, steady-state, laminar and for non-Newtonian power-law fluids. The semi-circular cavity has a diameter of D. The horizontal wall/lid is sliding with a uniform horizontal velocity(u = U) and is subjugated to the ambient thermal condition; while the curved surface is subjugated to a higher isothermal temperature.The convective characteristics inside the system is explored for the broad range of Richardson number(0.1 ≤Ri ≤ 10), Prandtl number(1 ≤ Pr ≤ 100) and non-Newtonian power-law index(0.5 ≤ n ≤ 1.5) at a constant Grashof number of 10~4. Apart from this, the effect of shape(cross-section) of the inserted block, i.e., circular, square and triangular on heat transfer characteristics has also been explored. It is observed that the shear thickening fluids display better cooling characteristics. Besides, the cavity with immersed triangular block shows better heat transfer results than the circular and square blocks. The deviations observed in the flow and heat transfer characteristics in the cavity by inserting an adiabatic block as compared with cavity without block have been ascertained by calculating normalized Nusselt number(Nu~N). The presence of the block was found to have a diminishing effect on the heat transfer due to convection in the cavity. In the end, the results of the study are summarized in the form of a predictive correlation exhibiting the functional dependence of average Nusselt number with Prandtl number, power-law index, and Richardson number.     

The Proper Use of Mass Diffusion Equations in Drying Modeling: Introducing the Drying Intensity Number

This article intends to clearly define the possibilities and limitations offered by a simple diffusion approach of drying. Actually, many works use a simple diffusion equation to model mass transfer during drying, probably because a simple analytical solution of this equation does exist in the case of simple boundary conditions. However, one has to be aware of the limitations of this approach. Using a comprehensive formulation and a relevant computational solution, the most frequent assumptions of the diffusion approach were rigorously tested. It is concluded that analytical solutions must be discarded for several reasons: analytical solutions, either using Dirichlet or third kind boundary conditions, are often misleading and should be avoided; in the drying process, the coupling between heat and mass transfer is mandatory; nonlinearity (variation of diffusivity with moisture content) can hardly be avoided for mass transfer. In order to reach a verdict, a dimensionless number, the Drying Intensity Number (N_DI), is introduced. It allows the level of coupling between heat and mass transfer to be easily assessed. Thanks to this number, a guide is proposed for choosing the right level of modeling, depending on the drying configuration.     

Influence of Operating Conditions on the Freeze-Drying of Frozen Particles in a Fixed Bed and Modeling Data

Experimental runs have been carried out to investigate the influence of shelf temperature and total gas pressure in the chamber on the primary drying sublimation kinetics of a packed bed of frozen spherical particles of a model 16.6% (w/w) sucrose solution. Sublimation kinetics determined, in situ and on line, by weighing continuously the freeze-dried sample, were observed to increase with the total gas pressures and with the shelf temperatures. A physical model, based on the hypothesis that two “sublimation fronts” advancing at the same time from the bottom of the bed, due to the contact heat flux, and from the top of the bed, due to radiation heat flux, was proposed. Fair agreement was found between simulated and experimental data.