Abstract: Cavitation in a valve leads to trouble and inconvenience for factories。 Valves in a piping system are ruined, leading to costly replacements every several months。 To reduce the cost caused by cavitation in a valve, a cage is utilized to make cavitation occur only in the region adjacent to the cage itself; therefore, only the cage needs to be replaced。 To validate the design of a cage, simulation of the turbulent flow field inside a globe valve and the occurrence of cavitation are necessary for a valve designer。 To reach this purpose, prediction of the cavitation inside the globe valve with and without a cage is undertaken, and a cavitation model is established in this study。 The percentage of vapors in each computational cell is calculated using the proposed cavitation model。 Two various cages, the one-stage perforated cage and the one-stage step cage, are considered。 Vapor resulting from cavitation appears in the vortices existing inside the valve and at the downstream region of the globe valve without a cage。 Nevertheless, vapor does not occur in those regions in the globe valve with those two cages; in other words, cavitation inside the globe valve primarily occurs in the vicinity of the cages。 In the valve body and downstream region, ruin from cavitation is prevented when those two cages are installed in the globe valve。 In addition to the globe valve, the proposed cavitation model can be applied to prediction of cavitation in other control valves。 DOI: 10。1061/(ASCE)EY。1943-7897。0000084。 © 2013 American Society of Civil Engineers。76287

CE Database subject headings: Cavitation;  Numerical  analysis;   Valves。

Author keywords: Cavitation;  Globe  valve;  Cage;  Vortex。

Introduction A control valve plays an important role in a closed pipeline system and is widely used in a variety of industries such as chemical engineering and petrifaction。 Among control valves, a globe valve is commonly used as a flow regulation device under extremely high pressure conditions。 For example, the inlet pressure may be higher than 100 bars and from time to time 200 bars。 For a globe valve, which conveys liquids, cavitation is a serious and destructive prob- lem during its operation because pressure may drop owing to the variation of velocity according to Bernoulli’s equation。 The incep- tion of cavitation occurs when the local pressure in a globe valve drops from the increase of velocity and is below the corresponding saturated vapor pressure of a working liquid at a specific temper- ature。 Vapors begin to form in bubbles in low pressure regions and then burst immediately from pressure recovery as they flow downstream, resulting in vibration and erosion。 Additionally, this not only causes vibration of the valve body but also induces a high noise level。 Because of cavitation, a globe valve is damaged quickly。 It is common to replace damaged globe valves in a pipeline

1Dept。 of Mechanical Engineering, National Taiwan Univ。 of Science and Technology, Taipei 10607, Taiwan (corresponding author)。 E-mail: mjchern@mail。ntust。edu。tw

2Dept。 of Mechanical Engineering, National Taiwan Univ。 of Science and Technology,  Taipei  10607, Taiwan。

3Metal Industries Research and Development Centre, Taipei 106, Taiwan。

4Metal  Industries  Research  and  Development  Centre,  Taipei    106,

Note。 This manuscript was submitted on July 27, 2011; approved on May 16, 2012; published online on May 22, 2012。 Discussion period open until August 1, 2013; separate discussions must be submitted for inpidual papers。 This paper is part of the Journal of Energy Engineering, Vol。 139, No。 1, March 1, 2013。 © ASCE, ISSN   0733-9402/2013/1-25-34/$25。00。

system every few months in petroleum industry。 Replacing globe valves damaged by cavitation in a factory becomes a regular and costly affair; this is an important issue in the design of a globe valve。 Currently, most valve manufacturers try to reduce the damage of cavitation and then raise the value of a globe valve。 One possible approach is to utilize a variety of valve cages for this purpose。