Software limitations

The program has the following limitations in its scope of application:

• the pipeline is considered to be completely filled with fluid;

• when calculating liquid flow, liquids are considered as “Newtonian” (obeying Newton’s viscous friction law);

• calculations can be performed only for pipelines with a diameter of at least 2 mm;

• analysis of multiphase flow is performed only for pipelines that don’t have recycle loops;

• analysis of multiphase flow is performed only for pipelines with no pumps and control valves;

• dynamic losses at tees are not taken into account in multiphase flow and gas flow calculations (as a result, losses on tees for multiphase gas-liquid flow at high Mach numbers may be calculated inaccurately - in case of problems with convergence of calculations at high Mach numbers, it is recommended to turn off the calculation of losses on tees). Also, in some cases of calculating two-phase flow in pipelines with short branches, the resistance of which is determined by losses on tees, and in which the direction of flow can change, the calculation taking into account losses on tees may not converge. In this case, it is also recommended to disable the calculation of losses on tees;

• minor resistance coefficient (valves, fittings, etc.) and friction coefficient are calculated for subsonic flow velocity (Mach number must be no greater than 0.7-0.8). Analysis accuracy is not guaranteed when the Mach number is higher;

• branched pipelines calculation (and flow capacity calculation for unbranched flow) can’t be performed if chocked flow occur in pipeline;

• phase transitions calculation at 'reverse' analysis of two-phase flow with mass transfer between phases in unbranched pipelines is currently implemented in the "beta testing" mode and may have a number of shortcomings

• transient flow analysis is performed only for liquid flow;

• at the transient flow analysis the pipeline is considered to be completely filled with fluid. Thus, it’s not possible to model the filling of an empty pipeline;

• the calculation of the water hammer is performed using the equations of isothermal flow (however, the change in the thermophysical properties of the product due to unequal temperatures at different points in the pipeline for the initial steady flow is taken into account). Since the characteristic time for heat exchange processes is, as a rule, significantly longer than the time it takes for the waterhammer shock-wave to pass, this limitation is not significant for calculating the initial phase of the water hammer process (the first few passes of the waterhammer wave), which is usually of greatest interest for pressure rise calculation. However, for long-term processes (on the order of minutes) with significant differences in the temperature and thermophysical properties of the fluid in different sections of the pipeline, this limitation may be significant;

• local losses in tees are not considered in waterhammer calculation. In some cases (for very short pipelines or branches) this may affect the calculation results. For now, in this case, it is recommended to disable the consideration of tees and in the preliminary calculation of the steady flow;

• when calculating the waterhammer there is no possibility to model incomplete opening, closing or changing the degree of closing of the valves, as well as the opening of the valves with given Kv value;

• the automatic closing of check valves is not taken into account at the steady state flow analysis (when flow goes in the opposite direction). This can lead to errors in the calculation of waterhammer for piping systems in which there are check valves closed at the initial moment of time (the opening/closing of the check valves at waterhammer analysis is considered correctly);

• the analysis of density, viscosity, volume, thermal conductivity, surface tension coefficient and bubble point pressure is performed for fluid present in the software database (including the one of Simulis Thermodynamics); otherwise, it must be entered in the input;

• D'Arcy-Weisbach friction coefficient analysis is performed when the ratio of pipe wall roughness to its diameter is no greater than 0.07;

• when using the “Properties” library, the fluid must have no more than 30 components;

• diameters selection for pipelines with flow regulators (control valves) cannot be performed;

• diameters selection is not performed for pipelines with two-phase gas-liquid flow with mass exchange between phases, three-phase flow and liquids containing a solid phase (thus, diameters selection is performed only for one phase flow and “frozen” 2phase flow in pipelines);

• control valves cannot be placed as the first or last branch element and right before or after tees;

• there is a possibility of divergence in calculations of pipelines with two and three fluids at high fluid velocities;

• slurry flow calculation gives good accuracy only for solids with diameters up to 45 mm, density from 1140 to 3650 kg/m3 and solid content up to 45% by volume;

• the calculation of fluid containing very fine particles (see the minimum particle diameter here) may not give sufficient accuracy, since the particles of such diameters practically don't settle in the liquid, which is currently not taken into account in the program methods;

• for slurry flow the fraction of the solid phase is not calculated when mixing flows with different solid contents – the solid fraction must be set manually for each branch of the pipeline;

• slurry flow analysis can be performed only if flowrates are specified for each branch of the pipeline (the flow distribution calculation for slurry flow is not implemented in the current version of program) and only for pipelines with no loops;

• Climatology database is currently available only in the Russian version of the software.