Sagar Gulawani - Academia.edu (original) (raw)
Papers by Sagar Gulawani
Industrial & Engineering Chemistry Research, 2007
ABSTRACT Gas−liquid jet reactors are widely used in commercial applications such as condensing je... more ABSTRACT Gas−liquid jet reactors are widely used in commercial applications such as condensing jets for direct contact feedwater heaters and steam jet pumps, because of their efficient heat- and mass-transfer characteristics. These are also used for the blowdown of primary nuclear boiler systems into a water bath, without releasing fissionable materials into the atmosphere. Reacting jets are of major interest in metal processing and thermal energy sources that involve submerged injection of an oxidizer into a liquid metal bath. The design of gas−liquid jet reactors is strongly dependent on the plume dimensions and the flow pattern in the liquid phase. In the present review paper, a critical analysis of the published literature on the fluid dynamics and heat transfer for gas−liquid jet reactors has been performed. The analysis has been extended for the empirical, semiempirical, and analytical attempts for the correlations of experimental observations. The published works on the computational fluid dynamics (CFD) simulations have also been critically analyzed. A comprehensive discussion has been presented and an attempt has been made to arrive at a coherent theme that clearly describes the present status of the published literature. Furthermore, recommendations have been made that are expected to be useful for the design engineers as well as researchers, to improve the reliability in the design of this important class of reactors.
Chemical Engineering Science, 2007
Gas-liquid jet reactors are widely used in chemical industries in various applications such as fe... more Gas-liquid jet reactors are widely used in chemical industries in various applications such as feed-water heaters, metal processing, and thermal energy sources, etc. In all these applications, the principal requirement for the design is a prior knowledge of jet shape and dimensions, which primarily depend upon the nozzle type, size, submergence and its orientation. In the present study, CFD simulations of non-reacting (steam-water) and reacting (SF 6 -Li) jets have been carried out to understand the variation in plume dimensions of gas-liquid jet reactors. For condensation jet and reaction jet, the criteria have been developed to identify the plume boundary based on the hold-up profile of steam/SF 6 gas and the evaporated fuel. The effect of nozzle diameter and its orientation, nozzle gas velocity and bath temperature on the plume dimensions have been studied for both the types of jets. It was observed that the extent of increase in the plume length is always higher in the case of reaction jet as compared to the condensation jet for all the cases. The analyses also proved that, the availability of reactant is much better with the horizontal orientation which leads to stable plume length. The CFD model has been extended for the prediction of the flow pattern and its effect on the rate of condensation/reaction and plume dimensions for both the jet systems. ᭧
Industrial & Engineering Chemistry Research, 2009
High frequency experimental measurements by hot film anemometry (HFA) of liquid velocities and te... more High frequency experimental measurements by hot film anemometry (HFA) of liquid velocities and temperature in the region of vapor-liquid (VL) and solid-liquid (SL) interfaces for two important reactor types, namely, condensation jet and jet loop reactors, have been studied for their heat transfer characteristics. An algorithm for flow structure identification has been devised from velocity data based on (i) zero crossings and (ii) continuous wavelet transform. The wavelet transform algorithm is especially found to be useful in accurately estimating both the age and size distributions of eddies near interfaces in a multiscale framework. Using these distributions, it is shown that the calculated values of heat transfer coefficients (HTC) at the SL and VL interfaces show remarkable correspondence with the HTC values obtained experimentally from instantaneous temperature measurements. For this purpose, a modified capacitance model has been proposed that takes into account the information about both the age and size distributions. The results obtained by the present methodology show the improvement possible for calculating the HTC at interfaces when compared with the earlier surface renewal models. It may therefore be used to study the interaction between flow dynamics and heat transfer behavior in chemical process equipment.
Chemical Engineering Science, 2006
In direct contact condensation (DCC) phenomenon, whenever steam (vapor) is injected with very hig... more In direct contact condensation (DCC) phenomenon, whenever steam (vapor) is injected with very high velocity in sub-cooled water, the momentum and the energy of the steam is transferred to the surrounding liquid, leading to generation of flow pattern, turbulent in nature. The ...
Chemical Engineering Science, 2009
In direct contact condensation (DCC) phenomenon, whenever steam (vapor) is injected with very hig... more In direct contact condensation (DCC) phenomenon, whenever steam (vapor) is injected with very high velocity in sub-cooled water, the momentum and the energy of the steam is transferred to the surrounding liquid, leading to generation of flow pattern, turbulent in nature. The ...
Chemical Engineering Science, 2008
Submerged gas jets into a liquid bath are widely used in metal processing and thermal processes. ... more Submerged gas jets into a liquid bath are widely used in metal processing and thermal processes. These systems are classified as (a) condensation jet and (b) reaction jet systems. This paper presents the CFD simulation of both the types of jets. The CFD model considers phase change, gas-liquid and gas-gas reactions and the accompanied rates of mass transfer. Mass transfer coefficient was estimated using small eddy model where the value of mass transfer coefficient is calculated based on the local values of turbulent kinetic energy (k) and the dissipation rate ( ). A good agreement with the available experimental data of plume length validates the CFD model. The CFD simulations have also been compared with the available experimental data on velocity and temperature profiles which shows excellent agreement. A comparison between the condensation and the reaction jets has been presented in terms of plume dimensions, flow and temperature patterns. The relative predictions of the present model and the rational correlations have been presented for the estimation of plume length for both the types of jet systems. ᭧
Industrial & Engineering Chemistry Research, 2007
ABSTRACT Gas−liquid jet reactors are widely used in commercial applications such as condensing je... more ABSTRACT Gas−liquid jet reactors are widely used in commercial applications such as condensing jets for direct contact feedwater heaters and steam jet pumps, because of their efficient heat- and mass-transfer characteristics. These are also used for the blowdown of primary nuclear boiler systems into a water bath, without releasing fissionable materials into the atmosphere. Reacting jets are of major interest in metal processing and thermal energy sources that involve submerged injection of an oxidizer into a liquid metal bath. The design of gas−liquid jet reactors is strongly dependent on the plume dimensions and the flow pattern in the liquid phase. In the present review paper, a critical analysis of the published literature on the fluid dynamics and heat transfer for gas−liquid jet reactors has been performed. The analysis has been extended for the empirical, semiempirical, and analytical attempts for the correlations of experimental observations. The published works on the computational fluid dynamics (CFD) simulations have also been critically analyzed. A comprehensive discussion has been presented and an attempt has been made to arrive at a coherent theme that clearly describes the present status of the published literature. Furthermore, recommendations have been made that are expected to be useful for the design engineers as well as researchers, to improve the reliability in the design of this important class of reactors.
Chemical Engineering Science, 2007
Gas-liquid jet reactors are widely used in chemical industries in various applications such as fe... more Gas-liquid jet reactors are widely used in chemical industries in various applications such as feed-water heaters, metal processing, and thermal energy sources, etc. In all these applications, the principal requirement for the design is a prior knowledge of jet shape and dimensions, which primarily depend upon the nozzle type, size, submergence and its orientation. In the present study, CFD simulations of non-reacting (steam-water) and reacting (SF 6 -Li) jets have been carried out to understand the variation in plume dimensions of gas-liquid jet reactors. For condensation jet and reaction jet, the criteria have been developed to identify the plume boundary based on the hold-up profile of steam/SF 6 gas and the evaporated fuel. The effect of nozzle diameter and its orientation, nozzle gas velocity and bath temperature on the plume dimensions have been studied for both the types of jets. It was observed that the extent of increase in the plume length is always higher in the case of reaction jet as compared to the condensation jet for all the cases. The analyses also proved that, the availability of reactant is much better with the horizontal orientation which leads to stable plume length. The CFD model has been extended for the prediction of the flow pattern and its effect on the rate of condensation/reaction and plume dimensions for both the jet systems. ᭧
Industrial & Engineering Chemistry Research, 2009
High frequency experimental measurements by hot film anemometry (HFA) of liquid velocities and te... more High frequency experimental measurements by hot film anemometry (HFA) of liquid velocities and temperature in the region of vapor-liquid (VL) and solid-liquid (SL) interfaces for two important reactor types, namely, condensation jet and jet loop reactors, have been studied for their heat transfer characteristics. An algorithm for flow structure identification has been devised from velocity data based on (i) zero crossings and (ii) continuous wavelet transform. The wavelet transform algorithm is especially found to be useful in accurately estimating both the age and size distributions of eddies near interfaces in a multiscale framework. Using these distributions, it is shown that the calculated values of heat transfer coefficients (HTC) at the SL and VL interfaces show remarkable correspondence with the HTC values obtained experimentally from instantaneous temperature measurements. For this purpose, a modified capacitance model has been proposed that takes into account the information about both the age and size distributions. The results obtained by the present methodology show the improvement possible for calculating the HTC at interfaces when compared with the earlier surface renewal models. It may therefore be used to study the interaction between flow dynamics and heat transfer behavior in chemical process equipment.
Chemical Engineering Science, 2006
In direct contact condensation (DCC) phenomenon, whenever steam (vapor) is injected with very hig... more In direct contact condensation (DCC) phenomenon, whenever steam (vapor) is injected with very high velocity in sub-cooled water, the momentum and the energy of the steam is transferred to the surrounding liquid, leading to generation of flow pattern, turbulent in nature. The ...
Chemical Engineering Science, 2009
In direct contact condensation (DCC) phenomenon, whenever steam (vapor) is injected with very hig... more In direct contact condensation (DCC) phenomenon, whenever steam (vapor) is injected with very high velocity in sub-cooled water, the momentum and the energy of the steam is transferred to the surrounding liquid, leading to generation of flow pattern, turbulent in nature. The ...
Chemical Engineering Science, 2008
Submerged gas jets into a liquid bath are widely used in metal processing and thermal processes. ... more Submerged gas jets into a liquid bath are widely used in metal processing and thermal processes. These systems are classified as (a) condensation jet and (b) reaction jet systems. This paper presents the CFD simulation of both the types of jets. The CFD model considers phase change, gas-liquid and gas-gas reactions and the accompanied rates of mass transfer. Mass transfer coefficient was estimated using small eddy model where the value of mass transfer coefficient is calculated based on the local values of turbulent kinetic energy (k) and the dissipation rate ( ). A good agreement with the available experimental data of plume length validates the CFD model. The CFD simulations have also been compared with the available experimental data on velocity and temperature profiles which shows excellent agreement. A comparison between the condensation and the reaction jets has been presented in terms of plume dimensions, flow and temperature patterns. The relative predictions of the present model and the rational correlations have been presented for the estimation of plume length for both the types of jet systems. ᭧