八、Calculation of valve pipeline pressure drop
一、The maximum allowable loading (discharging) rate calculation
The calculation of the maximum loading (of discharging) rate shall according to the regulations of the 46CFR39.30.1-d of the USCG.
Thereinto, Q1 is loading rate;
V is maximum loading rate (3m/s);
d1 is inner diameter of the loading pipe.
The flow rate (ventilating capacity) of the CF-ISO high-velocity relief valve is the flow rate of the pressure point, not the flow rate of the liquid cargo steam and the air mixture. Therefore, the volume rate of the flow about the liquid cargo steam and air mixture is as follows.
Thereinto, Qv-a is the volume rate of the flow of the steam;
Q1 is the loading rate of the liquid cargo tank;
VGR is the generating rate of the steam.
Thereinto, Pv，115 is the saturation steam pressure under 115;
The calculation of the maximum loading rate of the liquid cargo tank is as follows:
Thereinto, Pv-a，115 is the density of the steam of the tank and the air mixture under 115;
Pa，115 is the weight of the air in the tank under 115;
Pa，o is the weight of the air under 0℃ and 1013KPa.
二、pressure drop calculation
According to the regulations of 46CFR3P.30.1-d of the USCG, the maximum backpressure of the relief valve pipeline shall be kept below the supportive pressure of the liquid cargo tank while it's loading. Pressure drop of the steam recovery system cannot over the 80％ of the set pressure of the relief valve.
The Darcy's formula is popular for calculating pressure drop.
Thereinto, △P is the pressure drop;
ρ is density of the liquid, P=Pv-a,115;
L is the length of the pipe;
V is the average velocity of flow;
D is the inner diameter of the pipeline;
f is Darcy's frictional coefficient;
g is gravitational acceleration.
三、The Ship Design & Research Institutes and ship-owner can entrust the manufacturer with the calculation of the pressure drop of pipeline, setting of the operating pressure and flow rate according to the capacity of the tank, loading rate and cargoes. It is necessary to provide the above datum completely and fill the following form.
|
