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NEA-0632 RAPVOID.

RAPVOID, H2O Flow and Steam Flow in Pipe System with Phase Equilibrium

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1. NAME OR DESIGNATION OF PROGRAM:  RAPVOID.
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2. COMPUTERS
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Program name Package id Status Status date
RAPVOID NEA-0632/01 Tested 01-MAY-1980

Machines used:

Package ID Orig. computer Test computer
NEA-0632/01 IBM 3033 IBM 3033
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3. DESCRIPTION OF PROBLEM OR FUNCTION

This code evaluates the flow through a complex system of pipes from a water-steam reservoir.
It evaluates the complete characteristics of the flow allowing for slip and in the case of long pipes assuming equilibrium between phases. It discovers choke points wherever they may occur including  several choke points in series and evaluates the flow parameters both upstream and downstream of the choke point. It also evaluates the depressurisation of the reservoir.
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4. METHOD OF SOLUTION

The basic assumption in RAPVOID is that the emission can be treated as pseudo-steady state with the total discharge rate conserved. Inertial effects can be allowed for by calculating the additional pressure differential required to accelerate the entire pipework contents.

The flow in the pipes allows for friction and if no heat passes through the pipe walls, the flow in the pipework is adiabatic but not isentropic. Allowance can also be made for heat transfer through the walls.

At geometric discontinuities losses are allowed for by putting a frictional multiplier into the pipework to give an additional length of pipe equivalent to the estimated number of velocity heads lost.

First the total pressure is estimated at the outlet, then the discharge rate is derived by finding the static pressure at outlet,  which gives the highest isentropic discharge rate. It is then possible to calculate the static and total pressures increment by increment up the pipework and to compare the total pressure at the entry to the pipework with the total pressure in the discharge vessel. The iteration on the discharge total pressure is then continued until a match is obtained between the inlet total pressure and the total pressure within the vessel.

If there are choke points within the pipework upstream of the final  outlet, the code examines this possibility by comparing the mass flow at each change of section with the choked mass flow for the relevant total pressure and enthalpy. If the choked mass flow is lower, then the code iterates to obtain the converged mass flow at the most upstream critical choke position that it discovers. Having  converged into this solution, it then examines the conditions downstream of this choke point for the derived mass flow.

The method of determining the critical flow for a given total pressure and enthalpy is to discover the static pressure which gives the maximum flow (AEEW M1364).
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5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

A practical difficulty arises in running the code if the pipework is evenly divided into mesh lengths as the static pressure gradient tends to infinity as critical conditions are approached. The practical method of overcoming this difficulty is to discover the incremental length  of pipe responsible for a selected pressure change and progressively deducting these incremental lengths until the other end of the pipe  is reached.
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6. TYPICAL RUNNING TIME:
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7. UNUSUAL FEATURES OF THE PROGRAM:
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8. RELATED AND AUXILIARY PROGRAMS:
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9. STATUS
Package ID Status date Status
NEA-0632/01 01-MAY-1980 Tested at NEADB
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10. REFERENCES

- W.H.L. Porter:
  "RAPVOID - A Computer Code for Deriving the Release of a Two-
  Phase Single-Component Mixture Through a Complex Array of Pipes
  and the Resulting Depressurisation of the Discharge Vessel"
  AEEW M1512.
- W.H.L. Porter:
  A Method for Analysing Critical Flow of Steam-Water Mixtures
  AEEW M1364.
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11. MACHINE REQUIREMENTS:
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12. PROGRAMMING LANGUAGE(S) USED
Package ID Computer language
NEA-0632/01 FORTRAN-IV
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13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:
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14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS:
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15. NAME AND ESTABLISHMENT OF AUTHOR

          W. H. L. Porter
          AEE Winfrith
          Near Dorchester, Dorset
          United Kingdom.
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16. MATERIAL AVAILABLE
NEA-0632/01
File name File description Records
NEA0632_01.001 INFORMATION FILE 6
NEA0632_01.002 SOURCE 2483
NEA0632_01.003 S.P. INPUT 73
NEA0632_01.004 S.P. OUTPUT 1335
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17. CATEGORIES
  • H. Heat Transfer and Fluid Flow

Keywords: flow blockage, flow rate, heat transfer, pipes, steam, two-phase flow, water.