Dear all,
When you need to design a restriction orifice in a minimum recirculation line for a centrifugal pump, I'm wondering if I'm doing a good approach. There is a lot of information available about minimum flow for centrifugal pumps but I'm missing some information to understand it properly.
During preliminary pump sizing, I calculate my system head losses at the desired flow rate and determine the required differential head. Because a minimum recirculation line will be installed, I have to add a certain unknown minimum flow (I don't know what the minimum flow requirement of the pump is as I'm just in the initial designing fase) to the desired flow to account for the continuous minimum flow through this line. Can I do this by taking 20% of the desired flow and add this to this flow rate? So in my pump datasheet (which I'll send to the pump vendor), I state the total flow rate (desired flow rate + minimum flow rate) and calculated differential head.
Hereafter, the vendor proposes a suitable pump with pump performance curve and specifies the required minimum flow rate. I think this is the moment when I can start designing the restriction orifice to ensure a minimum recirculation flow. I would do this by determining the pump's differential head at minimum flow rate from the pump curve. The pressure drop across the restriction orifice + friction losses in the minimum recirculation line + static head - suction pressure at minimum flow shall be equal to the differential head at minimum flow.
As I know the differential head, I can calculate the orifice's bore diameter. Is this a correct approach?