scholarly journals Effect of Pressure on Steady State and Heat Transfer Characteristics in Supercritical CO2 Natural Circulation Loop

2015 ◽  
Vol 127 ◽  
pp. 636-644 ◽  
Author(s):  
Archana V. ◽  
A.M. Vaidya ◽  
P.K. Vijayan
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Supercritical Co2 ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Heat Transfer Characteristics ◽  
Effect Of Pressure ◽  
Transfer Characteristics ◽  
Natural Circulation Loop

scholarly journals Numerical study on heat transfer characteristics of nanofluid based natural circulation loop

2018 ◽  
Vol 22 (2) ◽  
pp. 885-897 ◽  
Author(s):  
Ramesh Bejjam ◽  
Kiran Kumar
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Natural Circulation ◽  
Flow Behavior ◽  
Circulation Loop ◽  
Heat Transfer Characteristics ◽  
Step Size ◽  
Particle Volume ◽  
Transfer Characteristics ◽  
Natural Circulation Loop

In this paper the steady-state analysis has been carried out on single phase natural circulation loop with water and water based Al2O3 (Al2O3-water) nanofluid at 1%, 3%, 5%, and 6% particle volume concentrations. For this study, a 3-D geometry of natural circulation loop is developed and simulated by using the software, ANSYS (FLUENT) 14.5. Based on the Stokes number, mixture model is adopted to simulate the nanofluid based natural circulation loop. For the simulations, the imposed thermal boundary conditions are: constant heat input over the range of 200-1000 W with step size of 200 W at the heat source and isothermal wall temperature of 293 K at the heat sink. Adiabatic boundary condition is imposed to the riser and down-comer. The heat transfer characteristics and fluid-flow behavior of the loop fluid in natural circulation loop for different heat inputs and particle concentrations are presented. The result shows that the mass-flow rate of loop fluid in natural circulation loop is enhanced by 26% and effectiveness of the natural circulation loop is improved by 15% with Al2O3-water nanofluid when compared with water. All the simulation results are validated with the open literature in terms of Reynolds number and modified Grashof number. These comparisons confidently say that the present 3-D numerical model could be useful to estimate the performance of natural circulation loop.

Steady-State Behavior of a Two-Phase Natural Circulation Loop With Thermodynamic Nonequilibrium

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Dipankar N. Basu ◽  
Souvik Bhattacharyya ◽  
P. K. Das
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Control Parameters ◽  
Subcooled Boiling ◽  
Two Phase ◽  
State Behavior ◽  
Natural Circulation Loop ◽  
Steady State Behavior

A model to predict the steady-state behavior of a rectangular two-phase natural circulation loop has been proposed. The analysis employs a one-dimensional two-fluid model to identify various system parameters, with particular emphasis on the subcooled boiling region. The onset of two-phase region and point of net vapor generation and associated liquid temperatures and vapor qualities have been estimated using a few widely recognized correlations. Predicted results demonstrate that the consideration of subcooled boiling may have significant effect on system behavior, particularly around the transition regions. The interaction of saturated bubbles and subcooled liquid and associated change in heat transfer and frictional forces has been discussed in detail. Fluid stream has been observed to have different combinations of flow stream conditions at boiler exit and condenser inlet. Five probable combinations have been identified and a generalized working-regime map has been proposed on Nsub−NZu plane. Attempts have been made to identify the influence of various control parameters. A favorable sink condition (higher coolant flow rate or lower coolant entry temperature) has been found to be of particular importance to attain a wider operating range of wall heat flux and better heat transfer characteristics. A design map has been proposed to identify favorable operating condition in terms of control parameters to ensure complete condensation.

Investigation of Steady-State Characteristics of Natural Circulation Loop

2013 ◽  
Author(s):  
Zheng Huang
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Phase Flow ◽  
Two Phase ◽  
Natural Circulation Loop ◽  
Flow Case

Natural circulation is one of the most important mechanisms of passive safety systems in the advanced NPP design. By using RELAP5, steady-state behaviors of a typical natural circulation loop (NCL) were investigated. The Influences of various system parameters, such as pressure, cooling heat transfer area and loop height were studied. The results show that the heat transfer power of the NCL (i.e. the heat transferred from the heater to the tank by NCL) is linear with respect to the temperatures of boundary heat source and sink, excluding the phase transition region. The NCL operation mode (i.e. two-phase flow or one-phase flow) is mainly determined by the loop pressure. It is found that with the decrease of the pressure, the two-phase flow operation range is widened. The heat transfer power of two-phase flow case is always higher, and varies more substantially with pressure, than that of one-phase flow case under the same boundary temperatures. However, flow instability may occur for two-phase flow case. By increasing the area of heat transfer surface between loop cooling section and tank, the temperature difference between the inlet and the outlet of loop heating section as well as the heat transfer power of the NCL will increase. But the influence is insignificant when the tank temperature is relatively high. It is also observed that for both one-phase flow and two-phase flow, the change of loop height has little effect upon the heat transfer power of the NCL under the given boundary condition in this study.

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