Numerical Study of Single-Hole and Multi-Holes Orifice Flow Parameters

Importance of accurate fluid flow measurement in industry is crucial especially today with rising energy prices. There is no ideal measuring instrument due to numerous errors occurring during process of physical quantities measurement but also due to specific requirements certain instruments have like fluid type, installation requirements, measuring range etc. Each measuring instrument has its pros and cons represented in accuracy, repeatability, resolution, etc. Conventional single-hole orifice (SHO) flow meter is a very popular differential-pressure-based measuring instrument, but it has certain disadvantages that can be overcame by multi-holes orifice (MHO) flow meter. Having this in mind, the aim of this paper is to help gain more information about MHO flow meters. Both SHO and MHO gas (air) flow meters with same total orifice area and the pipe area ratio beta were numerically studied and compared using computational fluid dynamics (CFD). Simulation results of 16 different orifices with four different beta (0.5, 0.55, 0.6 and 0.7) were analysed through pressure drop and singular pressure loss coefficient. Standard k-epsilon turbulence model was used as a turbulence model. Beside singular pressure loss coefficient, pressure recovery as well as axial velocity for both the SHO and MHO were reported. Results showed lower (better) singular pressure loss coefficient and pressure drop as well as quicker pressure recovery in favour of the MHO flow meters. Also, centreline axial velocity results were lower for MHO compared to corresponding SHO. CFD simulation results were verified by experimental results where air was used as a working fluid. The influence of geometrical and flow parameters on singular pressure loss coefficient was also reported and results showed that MHO hole distribution did not have significant influence on singular pressure loss coefficient.