Mass Exchange Devices Research Articles

Artificial gravity in heat and mass exchange apparatus for the life support system of manned space missions

Different water recovery systems for deep space flight are analyzed; the existing systems and their shortcomings are briefly shown. The construction of a centrifugal mass transfer apparatus is presented, it could work in weightlessness conditions. The experimental data for the centrifugal apparatus in the mode of separation of the gas and liquid mixture are presented. The pressure was about 8 meters of water column for proposed construction. The formula for calculating the pressure for a scoop pump is given, which takes into account the rotation frequency, volume flow rate, the geometric dimensions and location of the scoop. Principle schemes for using a new centrifugal mass exchange device for water recovery systems and for capturing atmospheric moisture condensate are proposed. The features of the proposed schemes are analyzed and their potential advantages are determined. The main tasks for future experimental studies of the heat and mass transfer centrifugal apparatus are defined.

Study of the experimental performance of dew point evaporative cooling arrangement for modified fluid flow passages

The satisfactory performance of indirect evaporative cooling techniques (IEC) is governed significantly by the structural and design arrangement of heat and mass exchange devices. The experimental performance of the dew point evaporative cooler has been investigated in the present work with the geometrically modified flow passages for air and water. Conventionally, these passages are formed by either flat or corrugated plates. The trapezoidal corrugated plate has been used to form these passages for air and water. The laboratory trials were conducted for the different combinations of intake air temperature, specific humidity, and air velocity. The performance in terms of dew point and wet bulb efficiency is presented based on laboratory trials. The experimental results achieved dew point and wet bulb efficiencies ranging between 52% and 82% and 74% and 126%, respectively. The geometrically modified flow passages increase the heat exchange area for the same volume of a similar heat exchange device and achieve an increased thermal performance of the proposed cooler.

Numerical Simulation of Heat Transfer in Plate Modules of Heat and Mass Exchange Device

Numerical Simulation of Heat Transfer in Plate Modules of Heat and Mass Exchange Device

State of development of the heavy coolant quality support and control system for NF BREST-OD-300

Liquid lead has been chosen as the coolant for nuclear power plants with inherent safety in Russian Federation. Its physical and chemical properties offer distinct advantages over other types of coolants in FR with inherent safety, but this coolant also possesses certain technological challenges in the course of reactor operation. Heavy liquid metal technology management system for BREST-OD-300 reactor consists of a number of high-end technological devices designed to operate and maintain crucial parameters of lead coolant for decades. Development of these devices required innovative and creative approach as well as strong verification procedures. This presentation will give recent updates on the development of oxygen sensors, mass-exchange devices, hydrogen purification system, coolant filter, hydrogen sensors, which combined present Coolant quality control and management system.

Analytical and numerical schemes for thermodynamically balanced humidification-dehumidification desalination systems

Thermodynamic balancing is a promising method to enhance the performance of heat and mass exchange devices. It is successfully tested for humidification-dehumidification (HDH) desalination systems using an implicit procedure based on tabulated thermodynamic properties (i.e., temperature and enthalpy) of saturated air. This numerical procedure is not robust and is cumbersome to implement thermodynamic balancing and to model hybrid, multi-stage, and complicated systems. This paper provides a robust, explicit, and innovative models that facilitate the utilization of a thermodynamic balancing concept. The present models are used to get a deep understanding of the performance of the closed-air open-water (CAOW) water-heated HDH system with and without extractions. The relation between temperature and specific enthalpy of saturated air on HDH modeling is simplified. Based on that, zero and infinity extraction systems are modeled analytically and pseudo-analytically. To handle more than one extraction, a simple numerical model is presented. The analytical and numerical results are compared with the reported results in the literature. The performance results show that the proposed methods are reliable and accurate.

Automatic parameter adjustment system for packing materials and control of flow modes in mass exchange columns

Abstract The paper provides a new automatic adjustment system for flow modes in packing columns. The system allows automatic adjustment of the operating modes of packing mass exchange devices for rectification, extraction, absorption and gas and liquid catalytic reactions. The authors have described in detail the scheme of the developed system and the modes of automatic adjustment of the main operating parameters. The authors have also described the main features and advantages of using metal shavings, that is wastes of metalworking machines, as packing materials that meet all the requirements of running mass exchange processes and are amenable to automatic regulation.

Hydrodynamic Modes of Heat and Mass Exchange Devices with a Movable Nozzle

Hydrodynamic Modes of Heat and Mass Exchange Devices with a Movable Nozzle

Determination of the efficiency of the plate-type mass transfer apparatus used in petrochemical production

The development of effective separation schemes for oil refining products is an urgent task for modern industry. Clean and super pure materials are the main requirement of modern productions. The implementation of modern technological processes in the petrochemical and oil refining industry requires highly efficient devices, to which high demands are placed on ergonomics, economy, manufacturability and reliability. The effectiveness of the mass-exchange apparatus depends on the conditions of the technological process, the physical properties of the contact phases, taking into account the nature and amount of mechanical impurities circulating in this system. Therefore, the evaluation of the efficiency of mass-exchange devices with different types of contact devices, in order to identify their optimal technological and design parameters, is quite a difficult practical task. The application of a mathematical complex for the evaluation of the efficiency of mass exchanging apparatuses makes it possible to select the optimal operating modes and the design of a column disk apparatus necessary for efficient separation of the mixture. Dependences of the mass transfer coefficients in the gas phase and the efficiency of the Murphy sieve plate are presented, depending on the gradient at different gas velocities in a columnar apparatus for a sieve tray. An increase in the gas velocity reduces the effect of the uneven distribution of the liquid and gas (vapor) on the mass transfer coefficient in the gas phase, and at a gas velocity of 1 m/s and higher, there is no. A 40% reduction in the mass transfer coefficient in the gas phase is observed at a speed of 0.2 m/s, and at 1 m/s - by 1%. Increasing the gradient increases this effect. The decrease in the efficiency of the plate-type mass transfer apparatus by 5–35% used in petrochemical production is due to the gradient of the liquid level, as well as the type of contact device and the gas velocity

FRACTIONATION PROCESS SIMULATION SOFTWARE COMPLEX MULTICOMPONENT MIXTURES

Examines different numerical methods and problems of calculation of the rectification columns. The solution of problems in the transition from simple to complex columns, the presence of water in the system of rectification, taking into account the heat balance calculation. Discuss various algorithms of calculations and designed application package for span and design calculation of complexes of columns, to determine the quantity and quality of products, the heat load on the equipment, water vapour consumption thermophysical characteristics of streams and hydrodynamic loads on elements of columns. A pack of five programmes and databases implemented on Turbo Pascal language and updated on the use of languages-Python and c++. Settlement analysis of industrial fractions equipment allows to develop recommendations for improving the efficiency of mass transfer devices, increasing the depth of selection target components and fractions, improving the quality of the products division, as well as lower energy costs. Developed software package implements functions that allow various functions for calculating industrial equipment and on-line to create input file and generate a table of results that enable the development of recommendations to reduce the cost, increase the depth of selection, quality and energy efficiency mass exchange devices.

Calculation of stable operation of vortex spray countercurrent mass exchange device (VSCMED) depending on hydrodynamic characteristics of gas-drop flow

The paper gives the method of selecting stable operation modes of the vortex spray countercurrent mass exchange device (VSCMED), which includes calculating the flow of drops taking into account flow uniformity and mutual influence. In order to make the calculation, a number of assumptions, which allow to calculate the device for specific conditions, was introduced. When developing techniques, the impact of forces on the motion of the drop was taken into account. As a result of theoretical and practical studies, the flow rate of gas and droplets, the ratio of centrifugal forces and the forces of aerodynamic drag were determined, thus having ensured the optimum mode of stable operation of VSCMED. The results obtained allow to design new models of VSCMED-type devices when developing new productions for the chemical and petrochemical industries.

Experimental study of mass exchange characteristics of vortex spray mass exchange devices

During the study, the theoretical bases of the experimental determination of mass exchange characteristics of VSCMED were investigated, stand for this was designed and manufactured. Graphical dependencies, illustrating the change in the target substance concentration under different hydrodynamic regimes were obtained. The study is aimed at optimizing the geometric dimensions of the vortex mass exchange chambers. The conditions for fine-dispersed spraying of liquid in VSCMED that has a positive effect on increasing the mass exchange surface were considered. Based on the data obtained, we recommend maintaining the speed in the entrance slits of at least 24 m/s while gas velocity in the spray zone will be more than 60 m/s. These conditions allow to obtain the mass transfer coefficient more than 0.00085 mol/m3c and minimal geometrical dimensions of the device.As a result, recommendations for designing devices that allow to develop an engineering calculation methodology of the mass exchange characteristics of the absorption process and geometrical dimensions of VSCMED were obtained.

Effectiveness–mass transfer units (ε–MTU) model of an ideal pressure retarded osmosis membrane mass exchanger

Many membrane-based systems, such as reverse osmosis (RO), forward osmosis (FO) and pressure retarded osmosis (PRO), are being used in desalination, water treatment, and energy production. These systems work on the basis of mass transfer through a semi-permeable membrane which allows for the permeation of water while rejecting salts and other substances. The membrane-based devices are essentially mass exchangers which are analogous to heat exchangers. The driving potentials in these mass exchangers are the concentration and pressure differences, whereas in heat exchangers the driving potential is the temperature difference. Closed form solutions of the permeation rate through an ideal PRO mass exchanger are obtained for parallel and counter flow configurations. The recovery ratio (RR) is obtained as a function of dimensionless parameters such as the number of mass transfer units (MTU), mass flow rate ratio (MR), and osmotic pressure ratio (SR). The resulting mathematical expressions form an effectiveness–MTU model for osmotic mass exchangers. These expressions are analogous to those for heat exchangers and can be used as an initial design for PRO membrane based mass exchange devices.

Impact of extraction on a humidification–dehumidification desalination system

Humidification–dehumidification desalination systems obtain higher water output per unit energy input when the entropy generation of the system is minimized. Past studies have shown that entropy production is lowered when the system's humidifier and dehumidifier have nearly equal rates of enthalpy flow for both air and water streams. In this study, we examine the effect of extracting water or air from one component and injecting into the other, with the aim of bringing the enthalpy rates into balance. We consider the effect of extraction or injection on standalone heat and mass exchange devices. Similar to cases without extraction, it is found that entropy generation is reduced when a component's modified heat capacity rate ratio is brought closer to unity. We then consider the entire system with one or more extractions at various mass flow rates. The results show that it is possible to significantly improve the cycle performance, but that performance can be degraded in some cases. The effect of injection or extraction was greatest for components with high effectiveness and low terminal temperature difference. While multiple extractions resulted in higher performance gains, the impact of a single extraction was greatest with subsequent extractions yielding diminishing returns.

Thermal design of the humidification dehumidification desalination system: An experimental investigation

Humidification dehumidification (HDH) is a promising technology for small-scale seawater desalination and has widespread application in drinking and industrial water treatment systems. This paper demonstrates the significance of a novel parameter known as the ‘modified heat capacity rate ratio’ (HCR) in the thermal design of HDH systems and in simultaneous heat and mass exchange (HME) devices. HCR is of particular importance in developing a fundamental understanding of the concept of thermodynamic balancing. A pilot-scale HDH unit (with a peak production capacity of 700l/day) has been constructed and detailed experiments have been performed on this unit. Based on these experiments, the recently developed theories behind the design of HDH systems with or without mass extraction and injection are validated. Furthermore, important concepts with regard to design and optimization of HME devices have been studied in the present experiments.

ENERGY EFFECTIVENESS OF SIMULTANEOUS HEAT AND MASS EXCHANGE DEVICES

Simultaneous heat and mass exchange devices such as cooling towers, humidifiers and dehumidifiers are widely used in the power generation, desalination, air conditioning, and refrigeration industries. For design and rating of these components it is useful to define their performance by an effectiveness. In this paper, several different effectiveness definitions that have been used in literature are critically reviewed and an energy based effectiveness which can be applied to all types of heat and mass exchangers is defined. The validity and the limitations of the various effectiveness definitions are demonstrated by way of several examples including direct and indirect contact, parallel and counterflow heat and mass exchangers. The limiting case of a simple heat exchanger is also discussed. The importance of thermal balancing in minimizing entropy production and its implications for optimization and design of these devices is dealt with in detail. The application of the energy effectiveness to heat-exchanger-like -NTU correlations is also examined using a detailed numerical model.

Entropy generation minimization of combined heat and mass transfer devices

This paper details a simple procedure by which the entropy generation in simultaneous heat and mass exchange devices can be minimized. Effectiveness for these devices is defined and a new parameter, ‘modified heat capacity rate ratio’ is introduced. It is found that the entropy generation of a combined heat and mass exchange device is minimized (at constant value of effectiveness) when the modified heat capacity rate ratio is equal to one irrespective of the value of other independent parameters. Several typical examples of the cooling towers have been studied to illustrate this concept. A practical application of the concept is also illustrated using a humidification–dehumidification desalination system.

Use of Streamwise Periodic Boundary Conditions for Problems in Heat and Mass Transfer

Fully developed periodic boundary conditions have frequently been employed to effect performance calculations for heat and mass exchange devices. In this paper a method is proposed, which is based on the use of primitive variables combined with the prescription of slip values. Either pressure difference or mass flow rate may be equivalently prescribed. Both constant wall temperature (Dirichlet) and constant heat flux (Neumann) conditions may be considered, as well as the intermediate linear (Robin) boundary condition. The example of an offset-fin plate-fin heat exchanger is used to illustrate the application of the procedure. The mathematical basis by which the method may be extended to the consideration of mass transfer problems with arbitrary boundary conditions, and associated continuity, momentum, and species sources and sinks is discussed.

Multiple-Pass Flow Mass Transfer in a Parallel-Plate Channel by Inserting Permeable Barriers for Improved Device Performance

A multi-pass laminar counterflow mass exchange device is an open conduit divided into four subchannels with uniform wall concentration, by inserting three permeable barriers. Only the composition of the flow stream varies along the channels. The Sherwood numbers as well as the improvement of mass transfer efficiency have been investigated analytically by using an Eigenfunction power series expansion.The device performance results in multi-pass operations are represented graphically and compared with those in a single-pass device (without permeable barriers inserted). Analytical results show that there exists a best permeable-barrier position when both the mass transfer improvement and the increment of power consumption are considered and thus can effectively enhance the mass transfer efficiency compared with that of single-pass operations.

Gas mixtures separation by an absorbing pervaporation method

This article discusses the results of research on absorption and pervaporation processes in combination. The processes realize in the volume of one mass-exchange device. The separating characteristics of the hybrid process were compared with the gas separation membrane process. It is shown why the separation factor absorbing pervaporation essentially increases. The influence of different factors on a separation factor has been studied. The mathematical model well describes the gas mass transfer through the absorbent—membrane system.

Improvement in Performance of Double-Flow Laminar Countercurrent Mass Exchangers.

A laminar counterflow mass exchange device is an open duct divided into two subchannels of uniform wall concentration by inserting a permeable barrier, in which only the composition of the flow stream varies along the channels. Efficiency improvement in mass transfer has been investigated analytically by using an eigenfunction expansion in power series.The results of enhancement in mass-transfer efficiency are represented graphically and compared with those in a single-flow device (without a permeable barrier inserted). Analytical results show that suitable adjustment of the permeable-barrier position can effectively enhance the mass transfer efficiency compared with the efficiency in single-flow operations.