The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
D. S. Pilkhwal - One of the best experts on this subject based on the ideXlab platform.
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Natural Circulation in a rectangular loop with vertical heater below vertical cooler
Kerntechnik, 2018Co-Authors: G. Raveesh, K. Bodkha, D. S. Pilkhwal, P. Anirudhan, P. K. VijayanAbstract:Abstract Many upcoming new generation reactors employ Natural Circulation for heat transfer in normal mode of operation. Natural Circulation systems are simpler and safer than their forced circulat...
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Experimental studies in a single-phase parallel channel Natural Circulation system: preliminary results
Kerntechnik, 2016Co-Authors: K. Bodkha, D. S. Pilkhwal, S. S. Jana, Pallippattu Krishnan VijayanAbstract:Abstract Natural Circulation systems find extensive applications in industrial engineering systems. One of the applications is in nuclear reactor where the decay heat is removed by Natural Circulation of the fluid under off-normal conditions. The upcoming reactor designs make use of Natural Circulation in order to remove the heat from core under normal operating conditions also. These reactors employ multiple vertical fuel channels with provision of on-power refueling/defueling. Natural Circulation systems are relatively simple, safe and reliable when compared to forced Circulation systems. However, Natural Circulation systems are prone to encounter flow instabilities which are highly undesirable for various reasons. Presence of parallel channels under Natural Circulation makes the system more complicated. To examine the behavior of parallel channel system, studies were carried out for single-phase Natural Circulation flow in a multiple vertical channel system. The objective of the present work is to stud...
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steady state flow and static instability of supercritical Natural Circulation loops
Nuclear Engineering and Design, 2012Co-Authors: B T Swapnalee, P. K. Vijayan, Manish Sharma, D. S. PilkhwalAbstract:For thermodynamically supercritical loops, explicit correlation for steady state Natural Circulation flow is not available. While using the subcritical Natural Circulation flow correlation for supercritical data, it was not able to predict the steady state flow accurately near supercritical pressure condition. A generalized correlation has been proposed to estimate the steady state flow in supercritical Natural Circulation loops based on a relationship between dimensionless density and dimensionless enthalpy reported in literature. Experiments have been performed with supercritical CO2 and water to validate this generalized correlation. The steady state flow rate data with supercritical CO2 has been found to be in good agreement with the proposed correlation. The correlation has also been validated using limited number of supercritical water data. Subsequently supercritical Natural Circulation data for different fluids reported in literature has also been compared with the proposed correlation. It is observed that the same generalized correlation is applicable for other fluids also. Sharp change of fluid properties such as density in the critical region gives rise to instability. The instability could be either density wave type or excursive type (Ledinegg or static instability). Several previous researchers have studied density wave type instability in supercritical Natural Circulation loops, whereas excursive instability is not studied in detail. In the present paper, an analysis has been carried out to predict the threshold of excursive instability for both supercritical water and supercritical CO2. Static instability was not found for CO2 whereas it was found for supercritical water. The effect of pressure is observed to stabilize the loop.
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a generalized flow correlation for two phase Natural Circulation loops
Nuclear Engineering and Design, 2006Co-Authors: Manas Ranjan Gartia, P. K. Vijayan, D. S. PilkhwalAbstract:A generalized correlation has been proposed to estimate the steady-state flow in two-phase Natural Circulation loops. The steady-state governing equations for homogeneous equilibrium model, viz. continuity, momentum and energy equations have been solved to obtain the dimensionless flow rate as a function of a modified Grashof number and a geometric number. To establish the validity of this correlation, two-phase Natural Circulation flow rate data from five different loops have been tested with the proposed correlation and found to be in good agreement.
Pallippattu Krishnan Vijayan - One of the best experts on this subject based on the ideXlab platform.
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Scaling philosophy for Natural Circulation systems
Single-Phase Two-Phase and Supercritical Natural Circulation Systems, 2019Co-Authors: Pallippattu Krishnan Vijayan, Arun K. Nayak, Naveen KumarAbstract:Abstract Scaling philosophies used for the simulation of reactor systems are introduced in this chapter. The power-to-volume scaling philosophy and the three-level scaling philosophy are discussed in detail. The importance of local phenomena scaling in the case of Natural Circulation is described in detail. In addition, the boundary flow scaling and its importance in scaling integral system behavior are described. An introduction is also given to scale distortions. The special case of scaling pressure tube-type reactor systems is also briefly described. The scale model design requires testing for its adequacy which is usually carried out using system codes by performing calculations for the model and prototype. Testing for adequacy of integral test facilities for Natural Circulation behavior is illustrated. In the case of stability, instead of system code, a stability analysis code may be used to perform calculations for the model and the prototype. Since length scales are important to simulate the stability phenomenon, the power-to-volume scaling philosophy is expected to reproduce Natural Circulation instability. However, the dimensionless parameter that characterizes the instability is not readily deciphered from the scaling philosophy.
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Review of applications of Natural Circulation systems
Single-Phase Two-Phase and Supercritical Natural Circulation Systems, 2019Co-Authors: Pallippattu Krishnan Vijayan, Arun K. Nayak, Naveen KumarAbstract:Abstract This chapter briefly reviews the different applications of Natural Circulation systems (NCSs) in various industries. Closed-loop NCSs are extensively used in solar water heaters, geothermal, fossil-fueled, and nuclear power plants. In addition, these systems are used in component-cooling applications such as transformers, electronic devices such as computer chips, and gas turbines. Although NCSs are mainly employed as heat transport devices, they can be engineered for noncooling applications such as passive controls, liquid fins, and study of low-velocity corrosion and deterministic chaos. Examples of open-loop Natural Circulation applications include solar chimneys, buoyancy pumps, air lift pumps, and building ventilation. The largest applications of NCSs are possibly in the chemical process industries. However, the highest power operating NCSs can be found in fossil-fueled power plants. The ESBWR (Economic Simplified Boiling Water Reactor) is the highest power (4500 MW) NCS designed so far. Mini loops with heat transport capability of the order of a few tens of Watts also can be found in the electronics industry. Some of the emerging applications of NCSs are in passive cooling of aircraft, vehicles, building ventilation, and solar thermal power plants. Due to the energy-saving potential of Natural Circulation, its application is increasing in various industry sectors. Natural Circulation applications in electronics device cooling, solar thermal power plants, and residential buildings are expected to increase in the near future. In addition, its passive functioning without operator action or signal is important for enhanced safety and reliability of nuclear reactors, increasing their applications in the nuclear field.
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Experimental studies in a single-phase parallel channel Natural Circulation system: preliminary results
Kerntechnik, 2016Co-Authors: K. Bodkha, D. S. Pilkhwal, S. S. Jana, Pallippattu Krishnan VijayanAbstract:Abstract Natural Circulation systems find extensive applications in industrial engineering systems. One of the applications is in nuclear reactor where the decay heat is removed by Natural Circulation of the fluid under off-normal conditions. The upcoming reactor designs make use of Natural Circulation in order to remove the heat from core under normal operating conditions also. These reactors employ multiple vertical fuel channels with provision of on-power refueling/defueling. Natural Circulation systems are relatively simple, safe and reliable when compared to forced Circulation systems. However, Natural Circulation systems are prone to encounter flow instabilities which are highly undesirable for various reasons. Presence of parallel channels under Natural Circulation makes the system more complicated. To examine the behavior of parallel channel system, studies were carried out for single-phase Natural Circulation flow in a multiple vertical channel system. The objective of the present work is to stud...
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flow instabilities in boiling two phase Natural Circulation systems a review
Science and Technology of Nuclear Installations, 2008Co-Authors: Arun K. Nayak, Pallippattu Krishnan VijayanAbstract:Several decades have been spent on the study of flow instabilities in boiling two-phase Natural Circulation systems. It is felt to have a review and summarize the state-of-the-art research carried out in this area, which would be quite useful to the design and safety of current and future light water reactors with Natural Circulation core cooling. With that purpose, a review of flow instabilities in boiling Natural Circulation systems has been carried out. An attempt has been made to classify the instabilities occurring in Natural Circulation systems similar to that in forced convection boiling systems. The mechanism of instabilities occurring in two-phase Natural Circulation systems have been explained based on these classifications. The characteristics of different instabilities as well as the effects of different operating and geometric parameters on them have been reviewed.
G H Su - One of the best experts on this subject based on the ideXlab platform.
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experimental and theoretical study on single phase Natural Circulation flow and heat transfer under rolling motion condition
Applied Thermal Engineering, 2009Co-Authors: G H SuAbstract:Experimental and theoretical studies of single-phase Natural Circulation flow and heat transfer under a rolling motion condition are performed. Experiments with and without rolling motions are conducted so the effects of rolling motion on Natural Circulation flow and heat transfer are obtained. The experimental results show the additional inertia caused by rolling motion easily causes the Natural Circulation flow to fluctuate. The average mass flow rate of Natural Circulation decreases with increases in rolling amplitude and frequency. Rolling motion enhances the heat transfer, and the heat transfer coefficient of Natural Circulation flow increases with the rolling amplitude and frequency. An empirical equation for the heat transfer coefficient under rolling motion is achieved, and a mathematical model is also developed to calculate the Natural Circulation flow under a rolling motion condition. The calculated results agree well with experimental data. Effects of the rolling motion on Natural Circulation flow are analyzed using the model. The increase in the flow resistance coefficient is the main reason why the Natural Circulation capacity decreases under a rolling motion condition.
Jin Ho Song - One of the best experts on this subject based on the ideXlab platform.
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OPTIMAL GEOMETRIC CONFIGURATION FOR A Natural Circulation LOOP
Nuclear Technology, 2020Co-Authors: Jin Ho SongAbstract:An optimal geometrical configuration that results in a maximum loop flow rate at given volume constraints is investigated for a two-phase Natural Circulation loop and a single-phase Natural Circulation loop. A rectangular loop connected with pipes is considered, which consists of a heater, a cooler, a riser, and a downcomer. By varying the aspect ratio of the loop, the number of pipes in the heating and cooling sections, and the distribution of the volumes between the cold side and the hot side, an optimal loop configuration that results in a maximum loop flow rate is determined from an analytical solution using simplifying assumptions. It is shown that the optimal configuration is beneficial in terms of minimizing the temperature rise and the pressure rise at given heat input. To support the argument, a complementary numerical analysis for a two-phase Natural Circulation flow in a rectangular loop is performed. The results are in good agreement with those predicted by the analytical models.
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Performance of a two-phase Natural Circulation in a rectangular loop
Nuclear Engineering and Design, 2012Co-Authors: Jin Ho SongAbstract:Abstract An analytical solution for the loop mass flow rate for a two-phase Natural Circulation in a rectangular loop is derived. The cases with saturated inlet flow and sub-cooled inlet flow are considered. The loop mass flow rate was obtained as a function of geometric parameters of the loop, frictional loss coefficient, pressure, heat input, and inlet sub-cooling. An optimal configuration for the Natural Circulation was suggested in terms of geometric parameters and heat input for a stable inherent safe operation of the two-phase Natural Circulation loop.
P. K. Vijayan - One of the best experts on this subject based on the ideXlab platform.
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Natural Circulation in a rectangular loop with vertical heater below vertical cooler
Kerntechnik, 2018Co-Authors: G. Raveesh, K. Bodkha, D. S. Pilkhwal, P. Anirudhan, P. K. VijayanAbstract:Abstract Many upcoming new generation reactors employ Natural Circulation for heat transfer in normal mode of operation. Natural Circulation systems are simpler and safer than their forced circulat...
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steady state flow and static instability of supercritical Natural Circulation loops
Nuclear Engineering and Design, 2012Co-Authors: B T Swapnalee, P. K. Vijayan, Manish Sharma, D. S. PilkhwalAbstract:For thermodynamically supercritical loops, explicit correlation for steady state Natural Circulation flow is not available. While using the subcritical Natural Circulation flow correlation for supercritical data, it was not able to predict the steady state flow accurately near supercritical pressure condition. A generalized correlation has been proposed to estimate the steady state flow in supercritical Natural Circulation loops based on a relationship between dimensionless density and dimensionless enthalpy reported in literature. Experiments have been performed with supercritical CO2 and water to validate this generalized correlation. The steady state flow rate data with supercritical CO2 has been found to be in good agreement with the proposed correlation. The correlation has also been validated using limited number of supercritical water data. Subsequently supercritical Natural Circulation data for different fluids reported in literature has also been compared with the proposed correlation. It is observed that the same generalized correlation is applicable for other fluids also. Sharp change of fluid properties such as density in the critical region gives rise to instability. The instability could be either density wave type or excursive type (Ledinegg or static instability). Several previous researchers have studied density wave type instability in supercritical Natural Circulation loops, whereas excursive instability is not studied in detail. In the present paper, an analysis has been carried out to predict the threshold of excursive instability for both supercritical water and supercritical CO2. Static instability was not found for CO2 whereas it was found for supercritical water. The effect of pressure is observed to stabilize the loop.
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Natural Circulation studies in a lead bismuth eutectic loop
Progress in Nuclear Energy, 2011Co-Authors: A Borgohain, D. Saha, P. K. Vijayan, B K Jaiswal, N K Maheshwari, R K SinhaAbstract:Lead Bismuth Eutectic (LBE) is increasingly getting more attraction as the coolant for advanced reactor systems. It is also the primary coolant of the Compact High Temperature Reactor (CHTR), being designed at BARC. A loop has been set up for thermal hydraulics, instrument development and material related studies relevant to CHTR. Steady state Natural Circulation experimental studies were carried out for different power levels. Transient studies for start-up of Natural Circulation in the loop, loss of heat sink and step power change have also been carried out. An 1D code named LeBENC has been developed at BARC to simulate the Natural Circulation characteristics in closed loops. The salient features of the code include ability to handle non-uniform diameter components, axial thermal conduction in fluid and heat losses from the piping to the environment. This paper deals with the experimental studies carried out in the loop. Detailed validation of the LeBENC code with the experimental data is also discussed in the paper.
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a generalized flow correlation for two phase Natural Circulation loops
Nuclear Engineering and Design, 2006Co-Authors: Manas Ranjan Gartia, P. K. Vijayan, D. S. PilkhwalAbstract:A generalized correlation has been proposed to estimate the steady-state flow in two-phase Natural Circulation loops. The steady-state governing equations for homogeneous equilibrium model, viz. continuity, momentum and energy equations have been solved to obtain the dimensionless flow rate as a function of a modified Grashof number and a geometric number. To establish the validity of this correlation, two-phase Natural Circulation flow rate data from five different loops have been tested with the proposed correlation and found to be in good agreement.
