Laminar flow in the pressure relief system

The effect of laminar flow in the relief system can be to reduce the flow rate compared with that for turbulent flow by an order of magnitude. 4.4 and Annex 2 describe how to determine whether or not flow will be laminar. In the case of laminar flow, this section gives methods for calculating the mass vent capacity per unit area, 

This value of G can then be used together with relief sizing methods given in chapters 6-8 to find the relief size required. 

Laminar flow is known to reduce the capacity of safety valves for single-phase liquid flow and a capacity correction chart is available13,41. The derivation of this chart has recently been reviewed151 and this review gives additional information about the applicability of the correction factor to different sizes of valve. 

High viscosity fluids may behave in a number of different ways  

The characterisation of the viscosity is difficult for non-Newtonian fluids because the viscosity changes as a result of the flow process, which increases the shear rate. This is further complicated for two-phase fluids because the presence of bubbles will also affect the viscosity. The simpler methods to obtain G for high viscosity fluids make the simplifying assumptions that the fluid viscosity is equal to the liquid viscosity and that the fluid is Newtonian. 

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