# Result Table - Relief Valve and Bursting Disk

The available results that are listed in the table vary depending upon the fluid phase state and upon the visible properties that you have selected. Figure 1 shows a selection of the available results for a liquid phase state. You can choose the rows you wish to display in the results table via the Set Visible Results Dialog. Figure 1: Available results for a Relief Valve. Only descriptions of the relevant results are shown in this section. If you wish to see the definition for other values click here. -- ID -- (aka User Number): All flowsheet elements have a unique number that is assigned by FluidFlow. It is not possible for the user to change this number because it is used as a unique identifier by the scripting module. Node numbering starts from 1, incrementing upwards, and pipe numbering starts from -1, decrementing downwards. Back Pressure Correction Factor (Kb): With a balanced valve, high back pressure will tend to produce a closing force on the unbalanced portion of the valve disc. This force may result in a reduction in lift and an associated reduction in flow capacity. Capacity correction factors, called back pressure correction factors, are provided by manufacturers to compensate for this reduction in flow. Note, that Kb = 1.0 if back pressure conditions do not apply. Calculated Size: This represents the exact orifice area required based on the design flow and set pressure conditions defined on the Input Editor. Certified Resistance Coefficient (Kr): The resistance of the bursting disk is modelled using a certified resistance coefficient "Kr". The flow resistance for bursting disk devices can be obtained from the manufacturer. The flow resistance is expressed in terms of velocity head loss "Kr". ASME Code certified values should be used where available. Combination Correction Factor (Kc): The correction factor "Kc" is applied to account for pressure loss across a bursting disk upstream of a relief valve during overpressure conditions. Typically, Kc = 0.9 when a bursting disk is installed in combination with a relief valve. Nonetheless, this value can be superseded by a certified manufacturer Kc value for the relief device combination. Composition Mass %: This is the fluid mass composition that remains constant throughout the element. FluidFlow determines the composition because an individual component mass balance is carried out at each node. Discharge Coefficient (Kd): For relief system design purposes, the ideal flow calculated is adjusted to establish the design/actual capacity of the relief valve. The discharge coefficient is the ratio of measured relieving capacity to the theoretical relieving capacity, i.e., Actual Flow Capacity/Theoretical (Ideal) Flow Capacity. The actual mass flow rate through the relief valve is diminished from the theoretical value by the existence of a fluid boundary layer. Therefore, a "discharge coefficient" (Kd) is applied to the theoretical value required to obtain the actual flow rate. Flow: This is the flow through the Relief Valve that FluidFlow has calculated. Flow at NTP: This is the volumetric flow referenced to normal conditions (0°C and 101325 Pa). NTP flow is the same as the gas flows through the element. Flow at STP: This is the volumetric flow referenced to standard conditions (15°C and 101325 Pa). STP flow is the same as the gas flows through the element. In Mach Number: This is the ratio of inlet velocity to the velocity of sound at the inlet conditions. It is not possible to reach a Mach number greater than 1 within this element. The velocity of sound is a thermo-physical property and depends on temperature and pressure. In Stagnation Pressure: The stagnation pressure at the relief valve inlet. This is the sum of kinetic and pressure energies (static pressure + velocity pressure). Stagnation pressure is the pressure a flowing fluid would rise to if brought isentropically to rest, converting its kinetic energy to enthalpy. Stagnation pressure is a measure of the usefulness of the gas's energy. In Stag. Temperature: This is the stagnation temperature at the relief valve inlet. The stagnation temperature is the temperature that the fluid would reach if it were brought to rest isentropically, converting its kinetic energy to enthalpy. In Static Pressure: This is the pressure that acts equally in all directions at the point in the fluid and is present irrespective if the fluid is flowing or if the fluid is at rest. The pressure inside any relief valve is not the static pressure, unless there is no flow. Stagnation pressure is the flowing pressure. In Static Temperature: The static temperature at the relief valve inlet. Static temperature is related to stagnation temperature (ignoring work, heat exchange, and potential energy) by the equation: T 1 = T 1 0 - 0.5v 1 2 / C p In Velocity: The velocity at the relief valve inlet. For gases, velocity increases as the fluid moves across the element. This can also occur with a two-phase flow where flashing exists, or for an incompressible fluid where the temperature rises. Velocity can also decrease as fluid flows across an element, for example, the cooling of a liquid. Joule–Thomson Coefficient: The Joule–Thomson effect describes the increase or decrease in the temperature of a gas when allowed to expand. The change in temperature (T) with a decrease of pressure (P) at constant enthalpy (H) is referred to as the Joule–Thomson coefficient (μJT). FluidFlow uses the Peng Robinson EOS to evaluate the Joule–Thomson coefficient which is expressed as: μJT = (∂T/∂P)H The value of μJT is typically expressed in °C/bar and is dependent on the physical properties of the gas, as well as the temperature and pressure of the gas before expansion. Out Mach Number: This is the ratio of outlet velocity to the velocity of sound at the inlet conditions. It is not possible to reach a Mach number greater than 1 within this element. The velocity of sound is a thermo-physical property and depends on temperature and pressure. Out Stagnation Pressure: The stagnation pressure at the relief valve outlet. This is the sum of kinetic and pressure energies (static pressure + velocity pressure). Stagnation pressure is the pressure a flowing fluid would rise to if brought isentropically to rest, converting its kinetic energy to enthalpy. Stagnation pressure is a measure of the usefulness of the gas's energy. Out Stag. Temperature: This is the stagnation temperature at the relief valve outlet. The stagnation temperature is the temperature that the fluid would reach if it were brought to rest isentropically, converting its kinetic energy to enthalpy. Out Static Pressure: This is the pressure that acts equally in all directions at the point in the fluid and is present irrespective if the fluid is flowing or if the fluid is at rest. The pressure inside a relief valve is not the static pressure, unless there is no flow. Stagnation pressure is the flowing pressure. Out Static Temperature: The static temperature at the element outlet. Static temperature is related to stagnation temperature (ignoring work, heat exchange, and potential energy) by the equation: T 2 = T 2 0 - 0.5v 2 2 / C p Out Velocity: The velocity at the relief valve outlet. For gases, velocity increases as the fluid flows across the valve. This can also occur with a two-phase flow where flashing exists, or for an incompressible fluid where the temperature rises. Velocity can also decrease, for example, the cooling of a liquid. Standard Orifice Size: FluidFlow automatically suggests the closest matching standard orifice size based on the calculated conditions noted above. Note, that this is only applicable to the API RP520 pressure loss model as the ISO 4126 methodology doesn't utilize standard orifice sizes. Total Pressure Loss: This is the calculated total pressure loss. Total pressure loss is not always the same as frictional loss, for example, when a temperature or velocity change occurs. In FluidFlow total pressure loss is defined (from the Energy Equation) as: DP = (z 1 r 1 g + p 1 + 0.5r 1 v 1 2) - (z 2 r 2 g + p 2 + 0.5r 2 v 2 2)