# Calculation Methods - Thick Orifice

The calculation method used is based on the correlations and charts found in Pipe Flow - A Practical & Comprehensive Guide - AIChE [24], p 146. The terms used in the equations below are set out illustrated in Figure 1. Figure 1: Thick Orifice Plate. The loss coefficient for a thick orifice is determined from the following set of equations: Equation 1: where the orifice thickness to diameter ratio t/d o ≤ 1.4. Ko = 0.0696 (1 - β5) λ2 + C (λ - β2)2 + (1 - C)[(λ - 1)2 + (1 + β2)2]. Equation 2: where the orifice thickness to diameter ratio t/d o > 1.4. Ko = 0.0696 (1 - β5) λ2 + (λ - 1)2 + (1 - β2)2 + fo(t/do - 1.4). where: λ = 1 + 0.622 (1 - 0.215β2 - 0.785β5). C = [1 - 0.50(t/1.4do)2.5 - 0.50 (t/1.4do)3]4.5. where: β is the orifice diameter "beta" ratio (β = d/D where "d" is the orifice bore diameter and "D" is the internal pipe diameter). As a reference guide, a beta ratio of 0.45 indicates that the orifice bore diameter is 45% of the pipe inside diameter. Guidelines on design beta ratios are available in ISO 5167 & Perry's Chemical Engineering Handbook. Published literature makes reference to keeping the design beta ratio to within the range of 0.15 to 0.68 to develop the best performance from the orifice plate. If a thick orifice plate is solved in FluidFlow and the calculated beta ratio is outside of this range, a warning message is enunciated to prompt the designer into reviewing the design conditions. Beta ratios outside of this range are noted to introduce flow system errors and other potential flow problems. When sizing orifice plates, ensure the right pressure drop range, maximum flow and optimum beta ratio for best performance of the orifice plate. Note, beta ratio and pressure drop for an orifice plate are related and as such, altering one affects the other. λ is the jet contraction coefficient. fo is the friction factor of the cylindrical surface of the orifice.