Regulator flow capacity calculations
Regulator flow capacity Kv value, is the important parameter, it reflects the fluid through the valve ability, namely regulator capacity. According to the regulator flow capacity Kv value calculation, and can determine the diameter. In order to properly choose regulator must be accurate calculated the rated flow coefficient Kv value. Regulator rated flow coefficient is defined as the under prescribed conditions, namely the valve both ends pressure differential is 105Pa, fluid density is 1g/cm3, the flow number with m3 / h or t/h flow through regulator when rated stroke.
1. general liquid Kv value calculation a. non-block flow in formula： FL—Pressure restore coefficient, see in table 1. FF—Liquid critical pressure ratio coefficient F=0.96-0.28 Pv—under valve inlet temperature, the liquid saturated steam pressure (absolute pressure), look-up table 4 ~ table 10. Pc - material thermodynamics critical pressure, look-up table 2 and table 3. QL - liquid flow m3 / h. ρ - liquid density g/cm3 P1 - the front pressure (absolute pressure) KPa. P2 - after valve pressure (absolute pressure) KPa. B. blocking flow
In formula, each letter and unit is the same with aboved. 2. Low Reynolds number correction (high viscosity Kv value calculation) liquid viscosity is high, because Reynolds number drops, changed the fluid flow state, when in Re < 2,300, fluid in low-speed laminar flow, so according to the original formula calculated Kv value, error is larger, must be corrected. now the calculated formula is： in formula：φ—粘Viscosity correction coefficient, by Re figure obtained. For single seat valves, sleeve valve and angle valve, etc with one flow path valve, Re=70000 for two seat, butterfly valve and other with two parallel flow path valve: Re=49600 In formula, K 'v - do not consider viscosity modified calculated flow capacity. γ— fluid motion viscosity mm2 / s.
Reynolds number Re viscosity correction curve
3. gas Kv value calculation a. general gas when P2>0.5P1, when P2≤0.5P1, in formula：Qg—gas flow m3/h under standard state， Pm— (P1, P2 is absolute pressure )KPa, △P=P1-P2 G—air proportion（air G=1）， t—gas temperature ℃ b. high pressure gas（PN>10MPa） when P2>0.5P1， when P2≤0.5P1, in formula：Z - gas compression coefficient, can check GB2624-81"flow measurement throttle device design installation and usage"
4.steam Kv value calculation a.saturated steam when P2>0.5P1， when P2≤0.5P1, in formula：Gs—steam flow Kg/h P1, P2meaning and unit is the same as aboved K—steam correcting coefficient partial steam K value is as follows： water steam K=19.4 Methane, ethylene steam K=37 Ammonia steam K=25 Propane, propylene steam K=41.5 11K=68.5 K=43.5. freon 11K=68.5 butane isobutane steam K = 43.5 b. overhot steam when P2>0.5P1, when P2≤0.5P1, in formula：△t—steam superheat degree℃ Gs, P1, P2 meaning and unit are the same。5. two-phase flow Kv value calculation: when medium is gas-liquid two phase flow, generally using calculated respectively liquids and gases Kv value, and then adding deriving regulator total value, this kind of method is Kv based on two fluid independent affection to each point view, but in fact with liquid phase and gas phase, the fluid state trend is also different, so calculated Kv value error is larger, actually commonly used is wet steam and contains abundant water. Here is a kind of steam and condensate mixture liquid Kv value calculation method for calculation steps: (1) according to mix medium steam and hemoglutination liquid content, and calculate vaporizing fluid. (2) according to the vaporization rate and inlet pressure P1 from the graph to check correction coefficient Ks. (3) known flow divided by Ks obtained corresponding steam flow as calculate flow. (4) applied steam Kv value calculating formula to calculate Kv value. 6. Caliber choose steps: according to process, determine the regulator diameter, specific steps are: (1) first according to production ability and equipment load calculation maximum flow Qmax and minimum flow Qmin (2) according to the chosen flow characteristic and the system characteristics of selected S value, then according to the pressure distribution and piping loss, to determine minimum pressure differential Pmin and maximum differential pressure Pmax (3) according to the flow capacity calculated formulas, calculate the maximum flow Kvs. (4) according to Kvs product models standard, selecting greater than Kvs and close Kv value. (5) according to the chosen Kv value and flow characteristics, verify the opening, request regulator the opening between 10% and 90%. (6) calculate R, the checking adjustable ratio. (7) after every verification qualified, according to Kv value to determine the regulator size.
