CFD Analysis of Convective Heat Transfer in a Vertical Square Sub-Channel for Laminar Flow Regime

Abstract

The development of new practices in nuclear research reactor safety aspects and optimization of recent nuclear reactors needs knowledge on forced convective heat transfer within sub-channels formed between several nuclear fuel rods or heat exchanger tubes, not only in the fully developed regime but also in the developing regime or laminar flow regime. The main objective of this research was to find a new correlation equation for calculating the convective heat transfer coefficient in the vertical square sub-channels. Recently, a simulation study was conducted to find a new heat transfer correlation equation for calculating the convective heat transfer coefficient within a vertical square sub-channel in the developing regime or laminar flow regime for Reynolds number range 400 ≤ Re ≤ 1700. Simulations were carried out using a computational fluid dynamics (CFD) code and modeling already defined in the software. The novelty of the research lies in the analysis of the entrance effect for the sub-channel by proposing a new empirical correlation that can then be inserted into the STAT computer code. The surface temperature distribution around the tangential direction of the active cylinders shows that the implementation of active and dummy cylinders in the current study can simulate sub-channels that exist in a real nuclear reactor core. The current study shows that the flow simulated in this study is in its developing condition (entrance region). A new forced convective heat transfer correlation for the developing region in the form of Nu = 2.094(Gz)0.329 for the Graetz number range 161 ≤ Gz ≤ 2429 was obtained from the current study.

CFD Analysis of Natural Convection on the Outer Surface of the Containment of APWR Model

“…Basically, the equations consist of continuity equation, momentum equation and energy equations [29,30]. These equations can be expressed as following [23]:…”

“…The empirical equation for the correlation of natural convection heat transfer, in the form of a Nusselt number (Nuq) as a function of the modified Rayleigh number (Raq) is given in Eq. ( 5), with x is position measured from the upstream end of the vertical cylinder, while a, b, and c are constants that would be empirically determined from the simulation data [23,[31][32][33].…”

“…To obtain the effectiveness of the use of baffles, as a comparison, it is necessary to analyze the natural convection heat transfer on the outer surface of a containment vessel that is not equipped with a baffle. One method that can be used in this analysis is computational fluid dynamics [16][17][18][19][20][21][22][23][24][25][26]. Heat, mass, and momentum balance equations are solved with the help of numerical analysis [18,23].…”

“…One method that can be used in this analysis is computational fluid dynamics [16][17][18][19][20][21][22][23][24][25][26]. Heat, mass, and momentum balance equations are solved with the help of numerical analysis [18,23]. CFD is a powerful technique for study of the complex flow and compared to the experiment, results from CFD can be often obtained in a shorter time and at a lower cost [19,22].…”

Numerical Simulation and Validation of Laminar Flow Through a Pipe Using CFD

“…For a nuclear research reactor, many researchers have conducted theoretical and experimental studies, on laminar flow in channels and sub-channels of reactor cores with the objective of find new correlations for calculating the convective heat transfer coefficient in the developing regime or laminar flow regime for Reynolds number range 400 ≤ Re ≤ 1700 [1,2]. Most heat exchangers operate in the regime of turbulent flow to reach a high heat transfer coefficient; however, there are still many heat exchangers that operate in the laminar-turbulent transition regime [3].…”