Simulations of the kettle reboiler shell side thermal-hydraulics with different two-phase flow models

A computational fluid dynamics approach is presented for the simulation and analyses of the kettle reboiler shell side thermal-hydraulics with two different models of two-phase flow – the mixture and two fluid model. The mixture model is based on solving one momentum equation for two-phase mixture flow and a closure law for the calculation of the slip between gas and liquid phase velocities. In the two fluid modeling approach the momentum balance is formed for each phase, while the gas-liquid interaction due to momentum exchange at the interface surface is predicted with an empirical correlation for the interface friction coefficient. In both approaches the two-phase flow is observed as two inter-penetrating continua. The models are solved for the two-dimensional geometry of the kettle reboiler shell side vertical cross section. The computational fluid dynamics numerical method based on the SIMPLE type algorithm is applied. The results of both liquid and vapor velocity fields and void fraction are presented for each modeling approach. The calculated void fraction distributions are compared with available experimental data. The differences in the modeling approaches and obtained results are discussed. The main finding is that the void fraction distribution and two-phase flow field strongly depends on the modeling of the slip between liquid and gas phase velocity in mixture model or on the interface friction model in two fluid model. The better agreement of the numerically predicted void fraction with the experimental data is obtained with the two fluid model and an interfacial friction model developed for the conditions of two-phase flows in large volumes of kettle reboilers or different designs of steam generators

Simulations of the kettle reboiler shell side thermal-hydraulics with different two-phase flow models

A computational fluid dynamics approach is presented for the simulation and analyses of the kettle reboiler shell side thermal-hydraulics with two different models of two-phase flow – the mixture and two fluid model. The mixture model is based on solving one momentum equation for two-phase mixture flow and a closure law for the calculation of the slip between gas and liquid phase velocities. In the two fluid modeling approach the momentum balance is formed for each phase, while the gas-liquid interaction due to momentum exchange at the interface surface is predicted with an empirical correlation for the interface friction coefficient. In both approaches the two-phase flow is observed as two inter-penetrating continua. The models are solved for the two-dimensional geometry of the kettle reboiler shell side vertical cross section. The computational fluid dynamics numerical method based on the SIMPLE type algorithm is applied. The results of both liquid and vapor velocity fields and void fraction are presented for each modeling approach. The calculated void fraction distributions are compared with available experimental data. The differences in the modeling approaches and obtained results are discussed. The main finding is that the void fraction distribution and two-phase flow field strongly depends on the modeling of the slip between liquid and gas phase velocity in mixture model or on the interface friction model in two fluid model. The better agreement of the numerically predicted void fraction with the experimental data is obtained with the two fluid model and an interfacial friction model developed for the conditions of two-phase flows in large volumes of kettle reboilers or different designs of steam generators

Validation of Atmospheric Boundary Layer Turbulence Model By On-Site Measurements

Modeling atmosperic boundary layer with standard linear models does not sufficiently reproduce wind conditions in complex terrain, especially on leeward sides of terrain slopes More complex models. based on Reynolds averaged Navier-Stokes equations and two-equation kappa-epsilon turbulence models for neutral conditions in atmospheric boundary written in general curvilinear non-orthogonal co-ordinate system, have been evaluated In order to quantify the differences and level of accuracy of different turbulence models, investigation has been performed using standard kappa-epsilon model without additional production terms and kappa-epsilon turbulence models with modified set of model coefficients The sets of full conservation equations are numerically solved by computational fluid dynamics technique. Numerical calculations of turbulence models are compared to the reference experimental data of Askervein hill measurement

Numerical simulation of fire spread in terminal 2 of Belgrade airport

This paper concern the results of software fire spread process prototype in terminal 2 of Belgrade airport using computational fluid dynamics. Numerical simulation of fire for the most critical fire scenario has been performed, primarily obtaining the space and time distribution of: velocity, pressure, temperature, and smoke concentration, assuming that HVAC systems have been switched off and all doors on the evacuation ways have been opened, just as the fire started Also, two simulations have been compared of the smoke ventilation and not ventilation for the same scenario. Within the framework of the results presentation, isosurfaces of constant temperature (100 degrees C) and smoke concentration (4000 ppm) are presented, based on the numerical simulation. Progression of these surfaces along the terminal 2 coincides to the experimental and experience evidence, forming the plume zone just above the fireplace, and spreading in the zone of underground ceiling and stairwell openings

Impact of co2 concentration on indoor air quality and correlation with relative humidity and indoor air temperature in school buildings in Serbia

Previous studies have shown that poorly ventilated classrooms can have negative impact on the health of children and school staff. In most cases, schools in Serbia are ventilated naturally. Considering their high occupancy, classroom air quality test determines the level of air pollution, after which it is possible to implement corrective measures. The research presented in this study, was conducted in four schools which are located in different areas and have different architecture designs. Measurements in these schools have been performed during the winter (heating season) and spring (non-heating season) and the following results were presented: indoor air temperature, relative humidity, and carbon dioxide concentration. These results show that the classroom average concentration of carbon dioxide often exceeds the value of 1500 ppm, during its full occupancy, which indicates inadequate ventilation. Measurement campaigns show that carbon dioxide concentration increased significantly from non-heating to heating season in three of the four schools. Analysis of measurements also determined high correlation between relative humidity and carbon dioxide concentration in all schools in winter season. This fact may constitute a solid basis for the fresh air supply strategy

Impact of co2 concentration on indoor air quality and correlation with relative humidity and indoor air temperature in school buildings in Serbia

Previous studies have shown that poorly ventilated classrooms can have negative impact on the health of children and school staff. In most cases, schools in Serbia are ventilated naturally. Considering their high occupancy, classroom air quality test determines the level of air pollution, after which it is possible to implement corrective measures. The research presented in this study, was conducted in four schools which are located in different areas and have different architecture designs. Measurements in these schools have been performed during the winter (heating season) and spring (non-heating season) and the following results were presented: indoor air temperature, relative humidity, and carbon dioxide concentration. These results show that the classroom average concentration of carbon dioxide often exceeds the value of 1500 ppm, during its full occupancy, which indicates inadequate ventilation. Measurement campaigns show that carbon dioxide concentration increased significantly from non-heating to heating season in three of the four schools. Analysis of measurements also determined high correlation between relative humidity and carbon dioxide concentration in all schools in winter season. This fact may constitute a solid basis for the fresh air supply strategy

Impact of Co2 Concentration on Indoor Air Quality and Correlation with Relative Humidity and Indoor Air Temperature in School Buildings in Serbia

Previous studies have shown that poorly ventilated classrooms can have negative impact on the health of children and school staff. In most cases, schools in Serbia are ventilated naturally. Considering their high occupancy, classroom air quality test determines the level of air pollution, after which it is possible to implement corrective measures. The research presented in this study, was conducted in four schools which are located in different areas and have different architecture designs. Measurements in these schools have been performed during the winter (heating season) and spring (non-heating season) and the following results were presented: indoor air temperature, relative humidity, and carbon dioxide concentration. These results show that the classroom average concentration of carbon dioxide often exceeds the value of 1500 ppm, during its full occupancy, which indicates inadequate ventilation. Measurement campaigns show that carbon dioxide concentration increased significantly from non-heating to heating season in three of the four schools. Analysis of measurements also determined high correlation between relative humidity and carbon dioxide concentration in all schools in winter season. This fact may constitute a solid basis for the fresh air supply strategy

A consideration of the use of ICTM SP-12 pressure sensor for ultrasound sensing

A consideration study for the application of the pressure sensor SP-12 developed and produced by ICTM CMT as an ultrasound sensor is given. The interaction of ultrasound with the sensor’s membrane was analytically described, but for the initial examination of its performance, Finite Elements Method simulation was applied. The sensor SP-12 has eigenfrequencies in the range from 200 kHz to the frequencies higher than 2 MHz. The amplitude of the output signal, which is proportional to Von Mises stress, is highest for the lowest frequency, and it exponentially decreases as the eigenfrequencies increase. This makes the sensor suitable for the ultrasound measurements in the range of hundreds of kH

Mathematical model of two-phase flow in horizontal evaporation

Dobošasti razmenjivači toplote sa horizontalnim cevnim snopom često se koriste u energetskim i tehnološkim postrojenjima za proizvodnju pare. U radu je prikazan nelinearni matematički model dvodimenzionog dvofaznog strujanja sa promenom faze. Model je rešavan odgovarajućim numeričkim algoritmom koji se može primeniti na jednačine konzervacije modela dvofaznog strujanja. Rezultati proračuna omogućavaju pouzdano predviđanje strujno-termičkih procesa dvofaznog strujanja i prenosa toplote u horizontalnom isparivaču.The kettle reboilers are widely used for vapor production in the chemical process and power industry. Nonlinear mathematical model of two-dimensional two-phase fluid flow with phase change is presented. The system of equations was solved using numerical algorithm for two phase flow. Numerical results should be used for reliable prediction of fluid and thermal properties in the processes of two phase fluid flow and heat transport in the kettle reboiler