Depressuring Unit Heat Input Window
The information entered on this window allows you the define heat flow between the depressuring vessel and an external source or sink. Positive heat values represent heat flow into the vessel. When vapor is present at the initial conditions, depressuring may proceed without application of heat.
You must select one heat input model from the following choices: User-Defined, API 2000, (or Scaled API 2000), RP 520, (or Scaled RP 520), Isothermal, Blowdown (Rigorous and Semi-rigorous forms are offered), and Fire Relief. The default is User-Defined, which in its default form results in zero heat input to the vessel. Refer to the PRO/II Reference Manual for a detailed discussion of each of these models.
Coefficient Constants in Heat Transfer Equations
Depending on the Heat Input model selected, either 0, 3, 5, or 6 of the coefficients may be input. Defaults for these coefficients are 0.0.
The User-Defined equation allows up to 6 coefficients, while the Blowdown equation allows 5. In these two equations, each coefficient "Ci" is used in a separate term. Omitting or providing zero as the value of a coefficient effectively removes it from the equation (i.e., the contribution of the term is zero). By selectively supplying non-zero values for different combinations of coefficients, these two equations support a wider variety of equation forms. For example, the sixth coefficient in the User-Defined equation allows modelling the so-called NORSOK correlation.
For Blowdown equations, coefficient C3 refers to UA and coefficient C4 refers to the ambient temperature.
Initial Wetted Area
You may not enter a value here for the initial wetted area if the Liquid Height has already been specified on the Depressuring Unit Vessel Data Window. Otherwise, you must enter a value for the initial wetted area of the depressuring vessel for the API 2000, Scaled API 2000, ANSI/API 521, ANSI/API 521 with Scaling, and Fire Relief heat models.
Earlier ANSI/API 521 and ANSI/API 521 with Scaling were named as RP 520 and Scaled RP 520.
Calculate Dynamic Wetted Area
Dynamic Wetted Area is an additional entry in the Heat Input model from PRO/II 9.3. By default, it is OFF and the value entered for the initial wetted area is considered for the calculations. When it is turned ON, the Wetted Area is calculated dynamically for the Liquid Holdup changes. To match the results with pre-PRO/II 9.3 versions, user has to select the Calculate Dynamic Wetted Area check box.
Area Scaling Factor
Optionally, you may enter a value for the area scaling factor for the API 2000, Scaled API 2000, RP 520, Scaled RP 520, and Fire Relief heat models only when the Initial Wetted Area is input. The default value for the area scaling factor is 1.0.
Heat Input Scaling Factor
You may input a dimensionless factor for scaling the vessel heat input for any heating model. The calculated heat input is multiplied by this factor. It has default value of 1.0.
Heat Transfer Area
For the Rigorous Blowdown and Semi-rigorous Blowdown heat input models, you must enter a value for the heat transfer area, unless you have input the vessel geometry. In this case, the heat transfer area will be calculated.
Heat Transfer Coefficient
For the heat transfer coefficient used in the Rigorous Blowdown and Semi-rigorous Blowdown calculations, you must select to use a Calculated coefficient, an Overall coefficient, or Individual phase heat transfer coefficients. You must enter a value for the coefficients if you select an Overall coefficient or Individual phase heat transfer coefficients. If you choose to use the Calculated coefficient, you may input a value for a scaling factor. The default is to use the Calculated coefficient with a default value for the scaling factor of 1.0.
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