Thermal Diffusion Column Research Articles

Development of a CFD-based simulation model and optimization of thermal diffusion column: application on noble gas separation

Abstract In this study, numerical simulations were carried out to investigate the separation of the helium-argon gas mixture by thermal diffusion column. This research determined the significant parameters and their effects on the process performance. Effects of feed flow rate, cut ratio, and hot wire temperature in a 950 mm height column with an inner tube of 9.5 mm radius were examined through the simulation of the thermal diffusion column. For minimizing the number of simulations and obtaining the optimum operating conditions, response surface methodology (RSM) was used. Analysis of separative work unit (SWU) values as a target function for helium-argon separation clearly showed that the maximum amount of SWU in thermal diffusion column was achieved, when hot wire temperature increased as large as technically possible, and the feed rate and cut ratio were equal to 55 Standard Cubic Centimeters per Minute (SCCM) and 0.44, respectively. Finally, the SWU value in optimum conditions was compared with the experimental data. Results illustrated that the experimental data were in good agreement with simulation data with an accuracy of about 90%.

Thermal Diffusion Separation of Petroleum Diamondoids and\t\t\tProtodiamondoids

Diamondoids were separated from protodiamondoids (precursors of diamondoids)\t\t\t\t\tin a saturated fraction (150–350°C) of crude oil by thermal diffusion. It was\t\t\t\t\tfound that in the course of thermal diffusion separation,\t\t\t\t\t\tC10–C13 adamantanes\t\t\t\t\t\t(tricyclo[3,3,1,13,7]decanes) and\t\t\t\t\t\tC14–C16 diamantanes\t\t\t\t\t\t(pentacyclo[7,3,1,14,12,02,7,06,11]tetradecanes)\t\t\t\t\tare separated from the corresponding protoadamantanes and protodiamantanes and\t\t\t\t\tdescend to the lower sections of the thermal diffusion column. In contrast to\t\t\t\t\tadamantanes and diamantanes,\t\t\t\t\t\tC18–C19 triamantanes\t\t\t\t\t\t(heptacyclo[7,7,1,13,15,01,12,02,7,04,13,06,11]octadecanes)\t\t\t\t\tare not separated from prototriamantanes and are concentrated in the lower\t\t\t\t\tsections of the thermal diffusion column. Catalytic isomerization of this\t\t\t\t\tthermal diffusion fraction with aluminum bromide was carried out to further\t\t\t\t\tconfirm that the numerous compounds that have the same characteristic ions as\t\t\t\t\ttriamantanes but elute later are polycyclic (most likely bridged) hydrocarbons,\t\t\t\t\tspecifically prototriamantanes. As a result, all these polycyclic compounds were\t\t\t\t\tisomerized into triamantanes. Similarly, in the course of isomerization of\t\t\t\t\tthermal diffusion fractions containing protoadamantanes and protodiamantanes,\t\t\t\t\tall of these turned into adamantanes and diamantanes, respectively.

Numerical study of n-heptane/benzene separation by thermal diffusion column

Abstract In this article, numerical simulations are performed to investigate the performance of the thermal diffusion column for the separation of n-heptane/benzene mixture. The present work tried to optimize column by analyzing significant parameters such as feed flow rate, temperature and cut. In order to obtain the hydrodynamic and temperature and mass distribution inside thermal diffusion column, computational fluid dynamic (CFD) method is applied to solve the Navier–Stocks equations. Numerical simulations are conducted to study the main parameters in both stationary and time-dependent conditions. By using the separation work unit as a function of cut, the optimal cut for maximum SWU occurs within a limited range of 0.47–0.5 for feed rate between 0.5 and 4 g·min−1. Our findings reveal that the optimum feed rate in the range of optimum cut is about 1 g·min−1. In transient study, results show that the best cut for reaching to steady-state condition is θ = 0.5.

Optimization of nanoparticle focusing by coupling thermophoresis and engineered vortex in a microfluidic channel

Enriching nanoparticles in an aqueous solution is commonly practiced for various applications. Despite recent advances in microfluidic technologies, a general method to concentrate nanoparticles in a microfluidic channel in a label free and continuous flow fashion is not yet available, due to strong Brownian motion on the nanoscale. Recent research of thermophoresis indicates that thermophoretic force can overcome the Brownian force to direct nanoparticle movement. Coupling thermophoresis with natural convection on the microscale has been shown to induce significant enrichment of biomolecules in a thermal diffusion column. However, the column operates in a batch process, and the concentrated samples are inconvenient to retrieve. We have recently designed a microfluidic device that combines a helical fluid motion and simple one-dimensional temperature gradient to achieve effective nanoparticle focusing in a continuous flow. The helical convection is introduced by microgrooves patterned on the channel floor, which directly controls the focusing speed and power. Here, COMSOL simulations are conducted to study how the device geometry and flow rate influence transport and subsequent nanoparticle focusing, with a constant temperature gradient. The results demonstrate a complex dependence of nanoparticle accumulation on the microgroove tilting angle, depth, and spacing, as well as channel width and flow rate. Further dimensional analyses reveal that the ratio between particle velocities induced by thermophoretic and fluid inertial forces governs the particle concentration factor, with a maximum concentration at a ratio of approximately one. This simple relationship provides fundamental insights about nanoparticle transport in coupled flow and thermal fields. The study also offers a useful guideline to the design and operation of nanoparticle concentrators based on combining engineered helical fluid motion subject to phoretic fields.

Recovery of deuterium from H–D gas mixture in thermal diffusion columns connected in series with countercurrent-flow transverse sampling streams

The equations for predicting the degrees of separation of H2, HD and D2 from H–D gas mixture by thermal diffusion in countercurrent-flow concentric-tube Frazier schemes of single and multiple columns, have been derived. The equations for predicting the recovery of deuterium (D) in HD and D2 were then obtained with the use of the atomic weight ratio. The degrees of separation, as well as separation factors, for deuterium recovery in the cryogenic-wall thermal diffusion devices were estimated, with the use of the experimental data obtained by Arita et al., 1998 and with the transport coefficients correlated in the previous work. Considerable improvement in deuterium recovery is achievable if a Frazier scheme with multiple columns is employed, instead of using the single-column device, either with the same column height, or with the same total sum of column heights, especially for the operation under larger volume flow rate and/or higher operating pressure. Further, countercurrent-flow operation is better than concurrent-flow operation in multi-column devices.

The theoretical study of the deuterium enrichment of H-D gas mixture in continuous-type thermal-diffusion columns

The separation equations for enrichment of deuterium in H-D (Hydrogen-Deuterium) gas mixture by continuous-type thermal diffusion columns were developed theoretically. The transport equation modeling treats the enriching and stripping sections separately for each component of H2-HD-D2 system to estimate the concentration between the bottom and top ends of the thermal diffusion column. The empirical expressions of the transport coefficients were determined with the previous experimental data (Arita et al., 1998) correlating in the exponential form in terms of operating pressure. The theoretical predictions of the degree of separation and separation factor for recovery of deuterium from H-D gas mixture are in good agreement with the experimental results.

Improvement in deuterium recovery from water–isotope mixture by thermal diffusion in the device of branch columns

Deuterium recovery from water–isotopes mixture using thermal diffusion can be improved by employing the branch column device, instead of single column devices, with the same total column length. The remixing effect due to convection currents in a thermal diffusion column for heavy water enrichment is thus reduced and separation improvement increases when the flow rate or the total column length increases. The improvement in separation can reach about 50% for the numerical example given.

Measurement of Thermal Conductivity of Gases Using Thermal Diffusion Columns: Air and Helium

This paper describes a method for determining the thermal conductivity of a gas by using a thermal diffusion column and uses it for finding the thermal conductivity of air and helium upto 140 degree centigrade. The study widens the scope for finding the thermal conductivity of a gas at still higher temperatures.

Conjugated mass transfer in an inclined thermal-diffusion column for heavy water enrichment with plate aspect ratio variations

A two-dimensional mathematical model was developed theoretically to predict the degree of separation of heavy water in an inclined flat-plate thermal-diffusion column. An orthogonal expansion technique for solving separation problems of heavy water enrichment under plate aspect ratio and inclination angle variations was carried out analytically. The effects of plate aspect ratio and inclination angle on the degree of separation have been investigated with a consideration of a fixed operating expense. Considerable improvements in device performance are obtained if the thermal-diffusion columns are inclined at the optimal angles as compared to the vertical orientation. Further improvement can be achieved if the flow-rate fractions of top and bottom products are suitably adjusted.

Modified Separation Theory of Heavy Water Enrichment by Thermal Diffusion in the Cocurrent-Flow Frazier Schemes

The separation theory for heavy water enrichment from water-isotope mixture in the cocurrent-flow Frazier scheme of thermal diffusion columns, has been modified with the values of pseudo product form of concentration determined by the method of least squares method, instead of simply taking the concentration in the product form as the feed concentration performed in previous works. The results indicate that serious errors occurred for the estimation of heavy water enrichment in the previous works, especially for employing the Frazier scheme with a larger number of thermal diffusion columns.

The analytical study on heavy water enrichment in concentric circular thermal-diffusion columns with optimal plate spacing for improved performance

A two-dimensional mathematical model was developed theoretically to predict the degree of separation of heavy water in concentric circular thermal-diffusion columns with total fixed expense and with plate spacing variations. An orthogonal expansion technique for solving separation problems of heavy water enrichment to estimate optimal plate spacing for maximum separation has been developed analytically. Considerable improvements in device performance were obtained when the thermal-diffusion column with optimal plate spacing were used. The effects of plate spacing and mass flow rate and on the degree of separation have been investigated with a consideration of the fixed total expense. Further improvement can be achieved if the feed position and flow-rate fractions of top and bottom products are suitably adjusted.

Thermal diffusion in branch columns for improved separation

The remixing effect due to the forced convection currents in a continuous-flow thermal diffusion column can be reduced by employing the device of branch columns, instead of the device of single column, with the same total column lengths. The improvement in separation increases when the flow rate or the total column lengths increases. It is found that the improvement in separation can reach about 50% for the numerical example given.

Heavy water enrichment by thermal diffusion in the flat‐plate frazier scheme with column heights increased at a constant ratio for improved performance

AbstractThis study investigates heavy water enrichment using the Frazier scheme of flat‐plate thermal diffusion columns with the column number adjusted and the column heights varied at a constant ratio with the total sum of column heights fixed. The equations for predicting the best number of columns and the best column‐height ratio for maximum separation are derived. Considerable improvement in performance is obtainable if the column‐height ratio and/or column number in a modified Frazier scheme are properly assigned, instead of using the conventional Frazier scheme of uniform column height with the same total sum of column heights. © 2013 Canadian Society for Chemical Engineering

The optimal number of thermal diffusion columns for deuterium recovery from H–D gas mixture in the countercurrent-flow Frazier scheme with the total sum of column heights fixed

The effect of the column number on deuterium recovery from H–D gas mixture in the countercurrent-flow Frazier scheme of thermal diffusion columns with the total sum of column heights fixed, has been investigated. The equations for predicting the optimal number of columns and the corresponding maximum separation have been derived. Considerable improvement in deuterium recovery is obtainable if the multi-column device with the optimal number of columns is employed, instead of using the single-column device with the same total sum of column heights, especially for the cases of higher volume flow-rate operation and larger total sum of column heights. Furthermore, countercurrent-flow operation is much better than forward-flow operation.

Performance analysis for an inclined thermal diffusion column with side-stream operation for heavy water enrichment

Heavy water enrichment using an inclined Clusius–Dickel thermal diffusion column with side-stream operation has been investigated theoretically. The mathematical model to determine the separation efficiency and the best inclination angle have been developed. Significant improvement in heavy water enrichment can be obtained relative to a classic, vertical without side-stream, design. The study of the effects of design and operating variables points out the design provides greater improvement for lower feed flow rate and higher top and side product ratios.

Effect of the column number on deuterium recovery from H–D gas mixture in the forward-flow Frazier scheme of thermal-diffusion columns with the total sum of column heights fixed

The equations for estimating the optimal column number and the corresponding maximum performance for deuterium recovery from H–D gas mixture by thermal diffusion in the forward-flow Frazier scheme of concentric-tube columns with the total sum of column heights fixed, have been derived. Considerable improvement in deuterium recovery is obtainable if the multi-column device with the optimal number of columns is employed, instead of using the single-column device, with the same total sum of column heights, especially for the case of higher volume flow-rate operation and larger total sum of column heights.

Further study on heavy water enrichment by thermal diffusion in the countercurrent-flow Frazier scheme

The separation theory for heavy water enrichment from water–isotope mixture in the countercurrent-flow Frazier scheme of thermal diffusion columns has been modified by the method of least squares. The results show that if the degree of separation is calculated from the modified separation equation, a serious error will be prevented, especially for employing the Frazier scheme with larger number of thermal diffusion columns.

Deuterium Recovery from H-D Gas Mixture by Thermal Diffusion in the Device of Branch Columns for Improved Performance

The strength of forced convection currents, as well as the remixing effect in a continuous-flow thermal diffusion column for recovery of deuterium from H-D gas mixture, can be reduced by employing the device of branch columns, instead of the device of single column, with the same total column length. The improvement in separation increases when the flow rate or the total column length increases. It is found that the improvement in recovery can reach about 50% for the numerical example given.

Recovery of deuterium from H–D gas mixture by thermal diffusion in the Frazier scheme

The separation equation for predicting the deuterium recovery from H–D gas mixture by thermal diffusion in the cocurrent-flow Frazier schemes has been derived. The degrees of separation, as well as separation factors, for deuterium recovery in the Frazier scheme of cryogenic wall thermal-diffusion columns were estimated, with the use of the experimental data obtained by Arita et al. and the transport coefficients correlated in the previous work. Considerable enhancement in deuterium recovery is achievable if the number of thermal diffusion columns in a Frazier scheme is continuously increased, especially for the operation under higher volume flow rate and/or lower operating pressure.

The optimal column number for the improvement in heavy water removal rate from water-isotopes mixture by thermal diffusion in the countercurrent-flow Frazier scheme with the total sum of column heights fixed

The effect of column number on the enrichment of heavy water from water–isotope mixture in the countercurrent-flow Frazier scheme with total sum of column heights L fixed, has been investigated. The equations, which may be employed to predict the optimal column numbers for maximum performances, have been derived. Considerable improvement in removal rate is obtainable if the scheme is constructed with the optimal column number of thermal diffusion columns, especially for larger flow rate with smaller L, or smaller flow rate with larger L.