Numerical Study On Flow And Heat Transfer Characteristics Of Single Phase Flow And Heat Transfer In A Narrow Rectangular Channel Under Rolling Condition

This paper gave the 3D simulation of the natural circulation of single phase under the rolling situation, and the influence of rolling on the characteristics of liquid flow and heat transfer was analyzed.This paper gave the analysis of the full-scale circuit of natural circulation system equipped with a rectangle channel, in which the deionized water was used. The software ANSYS ICEM was used to establish hexahedral cell, and the calculation was based on the Fluent platform. The rolling situation is introduced to the calculation platform to simulate the sea environment by the user defined function(UDF), and at the same time the gravity orientation needs to be altered.The cases of with and without rolling are given analysis respectively. The main content includes the various operation conditions influence on the ability of natural circulation without rolling, and the rolling conditions effect on the circulation capacity, the flow resistance and heat transfer characteristic. The fictional pressure drop is separated from the total pressure drop base on the method of subitem process. The feature of fictional pressure drop and additional pressure drop was given observed under rolling condition, and the secondary flow which has the effect of changing heat transfer coefficient is introduced. The secondary flow was given quantitative analysis through the Absolute vortex flux. The main reason which results the extreme point delay of the mass flow rate and heat transfer coefficient fluctuation was found. The main results were shown below:(1)The periodic fluctuation of many factors were found, such as flow velocity, pressure drop, heat transfer coefficient within the experiment channel, the heated wall temperature and the outlet temperature of the experiment section. The fluctuation tendency becomes obvious as the rolling period shortened and the amplitude larger. It is found that the full-scale simulation is indispensable, otherwise many factors may be neglected.(2)The more intensified rolling motion will aroused backflow in the system, which may bring the heat transfer weakened and the more complex flow and heat transfer variation, so the empirical relationship used before is none suitable any more.(3)The backflow aroused by the violent rolling leads to the subcooled boiling of natural circulation occurred in advance, at the same time, the heat transfer capability is weakened and the secondary flow is intensified. The secondary flow brings the liquid flow and heat transfer coefficient changed, and the magnitude of vortex near the heated surface is delayed.(4)There are two aspects of the rolling effect on the natural circulation magnitude: on the one hand, the circuit incline is happened in rolling, in which the driving pressure head is changed resulting from the altitude variation; on the other hand, the addition inertia aroused by rolling has the effect of changing the characteristic of system liquid flow. The analysis results show that the latter is more important.