Abstract: A tortuous labyrinth passage consists of a series of right angle turns in a disk of high pressure control valve. In this paper, numerical simulations are made for the velocity and pressure distributions in this passage. It is shown that the “series passage” can induce a pressure dropping more effectively. The main function of the “series passage” is to induce a pressure dropping while the “parallel passage” is mainly to regulate the flow-rate. As a cross sectional area process, a series of reduction and expansion, the pressure will also see dropping and partial recovery, which is called the multistage pressure drop. By this way, the velocity can be controlled in a reasonable level anywhere in this tortuous labyrinth passage. With the fluid pressure dropping in a downwards serrated way, the pressure is higher than the local saturate vapor pressure, therefore, no cavitation is induced by the phase transition.68698

Key words: tortuous labyrinth passage, right angle turns, multistage pressure drop, pressure recover

Introduction

The high pressure pump recirculation is one of the most difficult issues and severe duty control valve installations are demanded by the power industry. There are two significant features in this respect. First, the flow must be controlled during a very high pressu- re drop and second, when not in the controlling flow mode, a tight leak proof shut off is required. Failure to achieve either of these functions will quickly result  in

a plant shutdown or the loss of the valuable energy over an extended period[1].

The recirculation valve must perform two impo- rtant functions[2]. Firstly, it must control the fluid during the large pressure letdown  while it is open    at

* Project supported by the National Natural Science Foun- dation of China (Grant Nos. 51176127, 51106099), the Shanghai Science and Technology Commission (Grant No. 13DZ2260900).

Biography: Hai-min WANG (1971-), Male, Ph. D., Associtate Professor

all plug positions and secondly, it must ensure that there is no leakage when the valve is closed. This paper will focus on the control of the large pressure

drop[3]. The kernel throttling component is a stack for- med by welding a number of disks together, and each disk consists of a few tortuous paths just as shown in Fig.1[4].

Fig.1 The disks with 4 tortuous paths on both sides

Figure 1 shows three significant features of the disk channel. (1) Right angle turns. To yield a great pressure drop and to consume the energy of the  fluid, a series right angle turns make up the passage. (2) Expanding passage size. The flow area is   continually

increasing as the fluid pressure decreases. (3) Large number of stages. When the fluid flows through a right angle turn, the pressure will drop at once and then we will see a expanding size, the pressure will recover partly, thus the fluid will experience a number of sta- ges before it flows into the pressure equalizing ring.

As the pressure drop in the passage is mainly caused by the loss of the local resistance. The structu- re of the passage and the boundary conditions are both the key factors that determine the pressure drop   resu-

lts[5]. Many types of orifices or orifice tubes were used to yield a high pressure drop. For example, as the flow

zoning in the different subassemblies of the reactor core is formed by installing permanent pressure dro- pping devices in the foot of the subassembly,   Pandey

et al.[6] developed orifices having a honey-comb type geometry to meet the requirements of a fuel zone for the flow zoning. Senocak and shyy[7] studied the pre- ssure loss characteristics of the square-edged orifice and the perforated plates. Wu et al.[8] modeled hydrau- lic control systems that contain flow modulation valves, and the results are highly influenced by the   accuracy of the equation describing the flow through an orifice.