Vapor Condensation Heat Transfer in a Thermoplate Heat Exchanger

The heat transfer and pressure drop in a thermoplate heat exchanger operating as a condenser have been investigated experimentally. In order to separate the heat transfer resistances in the condensation process, the single phase forced convection has been studied using distilled water and Marlotherm oil in the thermoplate and correlations developed for the Nusselt number and the friction factor. For the condensation experiments, an apparatus has been constructed comprising two identical condensers composed of the same thermoplate type as employed in the single phase experiments. Isopropanol is used as a test fluid at pressures below atmospheric pressure. The heat transfer resistances in the condensation experiments are separated and expressions for the condensation heat transfer and pressure drop are developed with the aid of the results obtained in the single phase studies.     

CFD Study of Effects of Module Geometry on Forced Convection in a Channel with Non‐Conducting Fins and Flow Pulsation

CFD simulations were carried out to investigate the effects of the module geometry on forced convection in a rectangular channel containing series of regularly spaced non‐conducting baffles with flow oscillation. The simulations were performed at constant wall temperature. Steady‐flow Reynolds numbers Re in the range of 200 and 600 were studied. The results of the CFD simulations show that, for the effect fin spacing to be significant on heat transfer enhancement in finned system with oscillating flow, the oscillating flow velocity must be higher than the mean flow velocity. Superposition of oscillation yields increasing heat transfer performance with increasing fin height. Fin geometry with pyramidal shape yields highest performance in terms of the heat transfer effectiveness.     

双波纹板管式换热器流场的数值模拟

介绍了一种用于气气交换的错流式双波纹板管式换热器,它具有单位体积换热面积大,结构紧凑、稳定性好以及换热系数高等特点.运用Fluent软件.对不同尺寸的双波纹板管式换热器的流场进行了模拟,经过分析对比得到换热效果最佳时双波纹板片的形状.研究结果表明,换热板片上双波纹的波幅、周期和板间距决定了板式换热器的换热效果和压降等.     

Characterization of a Modular,Scalable Millistructured Plate Reactor

Micro‐ and millistructured reactors offer significant advantages compared to conventional reactors, e.g., in terms of heat and mass transfer as well as safety. For the substitution of larger batch reactors by continuously operated millireactors a comprehensive reactor characterization is required. The heat transfer and hydrodynamics of the millistructured plate reactor PR37 are studied. The meandering of the process channel and its periodically changing cross‐sectional area increase the heat transfer significantly and lead to a dependency of the heat transfer coefficient on the Reynolds and Prandtl number that is not found in straight channels at Reynolds numbers below 2300.     

Effect of Operating Parameters on Gas‐Solid Hydrodynamics and Heat Transfer in a Spouted Bed

Through a combined computational fluid dynamics and discrete element method approach, the effect of the operating parameters on the hydrodynamics and heat‐transfer properties of gas‐solid two‐phase flows in a spouted bed are extensively investigated. Considering the high velocity in the fountain region, gas turbulence is resolved by employing the large‐eddy simulation. The rolling friction model is adopted for more precise predictions of solid behavior near the wall. Subsequently, the gas‐solid flow patterns, gas‐solid velocities, and temperature evolution are investigated. Moreover, different operating conditions and geometry configurations are evaluated with respect to heat‐transfer performance. The results provide a fundamental understanding of heat‐transfer mechanisms in spouted beds.     

THE INFLUENCE OF RECYCLE ON MULTI-PASS LAMINAR COUNTERFLOW HEATERS OR COOLERS

A multi-pass laminar counterflow cooler or heater is an open duct divided into four subchannels with uniform wall temperature by inserting three impermeable sheets. Only the temperature of the flow stream varies along the subchannels. Improvements in heat transfer efficiency were investigated analytically with the use of eigenfunction expansions in the power series. The enhancement results in heat-transfer efficiency for two multi-pass devices (flow pattern A and flow pattern B) are represented graphically and compared with those in a single-pass device (without three impermeable sheets inserted) and those in a double-pass device (only one impermeable sheet inserted). Analytical results show that suitable impermeable-sheet position adjustments can effectively enhance heat transfer efficiencies for two multi-pass devices (flow pattern A and flow pattern B) compared with the efficiencies of single and double-pass devices.     

Enhancement Boiling Heat Transfer Study of a Newly Compact In‐line Bundle Evaporator under Reduced Pressure Conditions

For common flooded‐type evaporators, nucleate boiling heat transfer cannot occur on the heated tubes since heat fluxes and wall superheats of heated tubes are generally quite low. However, when the tube spacing is very small, nucleate boiling in restricted spaces can occur easily under low heat flux or low wall superheat conditions. The generation of nucleate boiling can effectively enhance the heat transfer performance of bundle evaporators. This study investigated experimentally the boiling heat transfer enhancement effects of the restricted space in compact in‐line tube bundles with smooth tubes under various reduced pressures. The experimental results show that the compact in‐line tube bundles have a significantly enhanced heat transfer compared to those of the common tube bundles, and there is an optimum tube spacing that provides the greatest heat transfer enhancement effect. The test pressures have a marked influence on the boiling heat transfer enhancement in the compact bundles. The heat transfer enhancement effect decreases with decreasing test pressure. In addition, the heat transfer enhancement effects of the in‐line tube bundles are also compared with those of the staggered bundles. Under reduced pressure, there is no significant difference between the heat transfer enhancement effects for the two types of bundles.     

THE INFLUENCE OF RECYCLE ON MULTI-PASS LAMINAR COUNTERFLOW HEATERS OR COOLERS

A multi-pass laminar counterflow cooler or heater is an open duct divided into four subchannels with uniform wall temperature by inserting three impermeable sheets. Only the temperature of the flow stream varies along the subchannels. Improvements in heat transfer efficiency were investigated analytically with the use of eigenfunction expansions in the power series. The enhancement results in heat-transfer efficiency for two multi-pass devices (flow pattern A and flow pattern B) are represented graphically and compared with those in a single-pass device (without three impermeable sheets inserted) and those in a double-pass device (only one impermeable sheet inserted). Analytical results show that suitable impermeable-sheet position adjustments can effectively enhance heat transfer efficiencies for two multi-pass devices (flow pattern A and flow pattern B) compared with the efficiencies of single and double-pass devices.     

结构参数对螺旋槽管传热与阻力性能影响的研究

利用计算流体动力学方法,研究了不同雷诺数下,几何尺寸对螺旋槽管传热及阻力性能的影响,结果表明,螺旋槽管在凸肋部前后产生了二次涡流,由螺旋形槽道形成的旋流都对边界层形成了扰动,传热性能得到了提高,同时也增加了阻力.在雷诺数相同时,槽越深,换热性能越好.同时流动阻力也有所增大;螺距、槽半径越大,换热效果降低,流动阻力也随之...     

Radiation Matters in Fixed‐Bed CFD Simulations

Fixed‐bed reactors often operate at elevated temperatures, where radiation can be a significant heat‐transfer mechanism. Particle‐resolved CFD models fixed‐bed reactors on a very detailed macroscopic level. In this study, the contribution of radiative heat transfer is investigated in a 500‐mm bed of 7‐hole pellets. At industrially relevant temperatures (250 – 800 °C) and with a steam‐reforming gas‐phase mixture, the S2S and DOM radiation models were applied. Neglecting radiation results in temperatures being up to 6 % lower. In this case, the main driver is surface‐to‐surface (S2S) radiation. Additional modeling recommendations are given.     

Investigation of natural convection heat transfer in a unique scaled‐down dual‐channel facility

Multiphase Reactors Engineering and Applications Laboratory (mReal) has designed and constructed a scaled‐down dual‐channel facility to investigate plenum‐to‐plenum natural circulation heat transfer through two channels for coolant flow that would be encountered during a loss of flow accident in the prismatic modular reactor (PMR). Heat transfer characterization of the current facility has been investigated under different upper plenum and cooled channel outer surface temperatures using sophisticated flush mounted heat transfer sensors. Results show a reduction in the values of local heat‐transfer coefficient and Nusselt number along the heated channel with increasing outer surface temperatures. One significant observation was the heat transfer reversal close to heated channel exit, where the heat flows from gas to the channel wall. This flow reversal is attributed to recirculation at the heated channel exit to the upper plenum. The average heat transfer results, when compared with previous literature, showed a similar qualitative trend. © 2016 American Institute of Chemical Engineers AIChE J, 63: 387–396, 2017     

Heat Conveyance Mechanism and Applications

The application of heat conveyance is presented under the assumption of low velocity and viscosity, and the factors affecting heat transfer are analyzed. Methods for reducing the flow resistance and increasing the efficiency of integrated heat transfer are presented after the characteristics of the vertical flow field are analyzed. The distributing rules of liquid flowing in the tube and heat transfer are obtained by numerical simulation, which shows that a full tube has the highest integrated heat transfer coefficient when the twisted‐tape insert is ca. 500–600 mm. The analyses indicate that the length of the twisted‐tape insert leads to a wide range of performance, i.e., a higher heat transfer coefficient can be obtained or the floating resistance can be lowered according to the actual working conditions. A higher level of integrated heat transfer coefficient is still maintained under such conditions. The above analyses indicate that the application of heat conveyance could guide the design of new enhanced heat transfer structures.     

Heat and Mass Transfer Analogy Studies of Binary Liquid Mixture in Comparison with Eteanol-n-Heptane Evaporating to Air

ABSTRACT

An expenmental and theoretical study of heat and mass transfer analogy and a comparison of that to a binary liquid mixture evaporation is presented. Common organic solvents, ethanol and n-heptane, were used to form an alcohol - hydrocarbon mixture. Studies were carried out in a horizontal rectangular channel having air flow velocities of 0.2 – 0.9 m/s. Heat transfer coefficients were measured with a copper plate resistor and mass transfer coefficients with a square pool. The heat and mass transfer analogy is presented for a system having two evaporating compounds with a fixed value of air flow and verified by measuring and comparing mass transfer coefficients for distilled water with air flow velocities of 0.2 - 0.9 mls. An illustrative example of the use of the theory for industrial ventilation is presented.     

Short-channel structured reactor: Experiments versus previous theoretical design

The study deals with the so-called short-channel structures (very short monoliths) that were introduced by Ko?odziej and ?ojewska [1] on the theoretical basis. The structures are very short so the entrance (mixing) section occupies majority of the channel length. This leads to highly enhanced heat and mass transfer, but the flow resistance is increased as well. The article presents experimental results of flow resistance, heat and mass transfer for short-channel structures of sine and triangular cross-sectional channel shape. The results presented in terms of dimensionless quantities confirmed theoretical consideration presented in [1]. The efficiencies of the structure have been derived that show the structures as more efficient when compared to classic monoliths or packed bed reactors.     

Numerical Simulation of Sterilization Processes for Shear‐Thinning Food in Taylor‐Couette Flow Systems

The performance of the Taylor‐Couette flow apparatus as a heat sterilizer is numerically investigated. The destruction of Clostridium botulinum and thiamine (vitamin B1) was selected as model reaction. When Taylor vortices were formed in the annular space, the heat transfer significantly enhanced as compared to the case without vortex flow. As a result, the equivalent lethality calculated from the temperature field increased, which is regarded as a quantum leap. Conversely, the improvement of heat transfer induced destruction of thiamine. These results suggest that there is a trade‐off relationship between the enhancement of heat transfer and the avoidance of thermal destruction of nutritional components. In conclusion, the Taylor‐Couette flow sterilizer has the potential for process intensification in heat sterilization processes.     

Efficiencies of Sieve Tray Distillation Columns by CFD Simulation

A 3‐D two‐fluid CFD model in the Eulerian‐Eulerian framework was developed to predict the hydrodynamics and heat and mass transfer of sieve trays. Interaction between the two phases occurs via interphase momentum and heat and mass transfer. The tray geometries are based on the large rectangular tray of Dribika and Biddulph and FRI commercial‐scale sieve tray of Yanagi and Sakata. In this work a CFD simulation is developed to give predictions of the fluid flow patterns, hydraulics, and mass transfer efficiency of distillation sieve trays including a downcomer. The main objective has been to find the extent to which CFD can be used as a design and prediction tool for real behavior, concentration and temperature distributions, and efficiencies of industrial trays. Despite the use of simple correlations for closure models, the efficiencies obtained are very close to experimental data. The results show that values of point efficiency vary with position on the tray because of variation of affecting parameters, such as velocities, temperature and concentration gradients, and interfacial area. The simulation results show that CFD can be used as a powerful tool in tray design and analysis, and can be considered as a new approach for efficiency calculations and as a new tool for testing mixing models in both phases. CFD can be used as a “virtual experiment” to simulate tray behavior under operating conditions.     

Turbulent forced convection in a heat exchanger square channel with wavy-ribs vortex generator☆

Turbulent forced convective heat transfer and flow configurations in a square channel with wavy-ribs inserted diagonally are examined numerical y. The influences of the 30° and 45° flow attack angles for wavy-ribs, blockage ratio, RB=b/H=0.05–0.25 with single pitch ratio, RP=P/H=1 are investigated for the Reynolds number based on the hydraulic diameter of the square channel, Re=3000–20000. The use of the wavy-ribs, which inserted diagonal in the square channel, is aimed to help to improve the thermal performance in heat exchange systems. The finite volume method and SIMPLE algorithm are applied to the present numerical simulation. The results are presented on the periodic flow and heat transfer profiles, flow configurations, heat transfer characteristics and the performance evaluations. The mathematical results reveal that the use of wavy-ribs leads to a higher heat transfer rate and friction loss over the smooth channel. The heat transfer enhancements are around 1.97–5.14 and 2.04–5.27 times over the smooth channel for 30° and 45° attack angles, respectively. However, the corre-sponding friction loss values for 30° and 45° are around 4.26–86.55 and 5.03–97.98 times higher than the smooth square channel, respectively. The optimum thermal enhancement factor on both cases is found at RB=0.10 and the lowest Reynolds number, Re=3000, to be about 1.47 and 1.52, respectively, for 30° and 45° wavy-ribs.     

Boiling Heat Transfer Enhancement of Water/Salt Mixtures on Roll‐Worked Enhanced Tubes in Compact Staggered Tube Bundles

An experimental study was performed for the boiling heat transfer enhancement of water/salt mixtures on both plane and roll‐worked enhanced tubes in compact staggered tube‐bundle evaporators under atmospheric and increased pressure conditions. The effects of tube spacing, position of tubes, test pressure and salt‐water concentration on the boiling heat transfer characteristics in restricted spaces of compact tube bundles consisting of plane and roll‐worked tubes were investigated. The experimental results indicate that the single roll‐worked tubes in a bulk liquid have a greater boiling heat transfer promotion than the single plane tubes. For the plane tubes in compact tube bundles, the effect of tube spacing on the boiling heat transfer is very significant. The boiling heat transfer has a maximum enhancement when the optimum tube spacing is selected. For the roll‐worked tubes in compact bundles, the effect of tube spacing on the boiling heat transfer is also significant as the tube spacing is small. The boiling heat transfer still has a maximum value and a compound enhancement effect of the boiling heat transfer from both the optimum tube spacing and the surface treatment is observed for the enhanced tube bundles.