6. SPILL

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General introduction

 SPILL is a utility program to calculate time-dependent liquid (and vapour) discharge rates from a pressurised vessel assuming a high-momentum jet arises from this release. During discharge the pressure in the reservoir will drop and temperature, mixture composition and discharge rate will all be functions of time.
It is assumed that a liquid jet rather than a liquid pool will form. See below.

SPILL uses the standard HGSYSTEM multi-compound, two-phase aerosol model.

SPILL will create a link file for AEROPLUME. The choice of a representative discharge rate to be used by AEROPLUME is not trivial as AEROPLUME is a steady-state model. See chapter on SPILL in Technical Reference Manual.

Range of applications and limitations

SPILL should be used as a utility to estimate the time-dependence of the discharge mass flow rate directly from an orifice in a pressurised vessel. It is not suitable for cases where there is pipework between the reservoir and the discharge orifice.

For vessel discharges having low momentum (that is, not resulting in a dispersing jet but rather in a pool on the ground), the HGSYSTEM evaporating liquid pool model LPOOL should be used insteda of SPILL. LPOOL is also fully time-dependent, but will link to HEGADAS-T rather than to AEROPLUME.

In the SPILL model it is assumed that all liquid remains within the jet: dropout of large liquid particles is not accounted for. Within the AEROPLUME model a deposition model is now available, see the MMESOPT input block in the AEROPLUME Chapter and Chapter 9 of the HGSYSTEM 3.0 Technical Reference Manual.

The heat transfer modelling assumes an infinitely thin vessel wall. The mixture temperature is assumed to be equal to the vessel wall temperature. These assumptions are not valid anymore for vessels filled with vapour-only mixtures.

Guidance for use

The SPILL model proves to be reasonably robust. For mixtures with many compounds (more than say 3), run times can be quite long.

SPILL INPUT FILE PARAMETERS

A description of all the input parameters that can occur in a SPILL input file will be given.

The SPILL input file has the DOS filename 'casename.SPI' where 'casename' is the user-supplied name of the problem.

In the following, actual keywords are given in capitals and in bold. The descriptions of less important parameters or parameters that need not normally be set by the user, are given in a smaller font.

All parameters, except TITLE, occur in blocks preceded by a specific block keyword. For SPILL these block keywords are: RESERVOIR, GASDATA, PIPE, AMBIENT and TERMINAT.

The TITLE keyword does not occur in a parameter block.
TITLE The title of the current problem to be run with SPILL. At most 50 alphanumeric characters. Optional, no default.

The RESERVOIR block contains the parameters which describe the reservoir fluid thermodynamic state.
TRES Initial temperature of the reservoir fluid (degrees C).
-50 <=TRES <= 1500.
Mandatory.
PRES Initial absolute pressure within the reservoir (atm).
-200 <=PRES<= 500.
Mandatory.
A negative value of PRES serves as a flag to SPILL: the program will calculate the saturation pressure of the specified mixture assuming all compounds are in the liquid-only state and use this as the value for the reservoir pressure. This option is only available when the two-phase (aerosol) thermodynamics model is being used, in other words when the SPECIES keyword is being used in the GASDATA block as discussed below. It is the user's responsibility to judge whether these assumptions in calculating the reservoir pressure are reasonable or not.
When PRES is positive, it must always be greater than AIRPRESS of the AMBIENT block.
VRES Reservoir volume (m3).
0.001 <=VRES <= 10000
Mandatory.
MRES Reservoir mass contents (tonnes, 1 tonne = 1000 kg).
0.1 MRES 10000
Optional.
If MRES is not specified then SPILL will calculate the maximum mass contents of the reservoir based on current values of PRES, TRES and VRES and on mixture composition as given in GASDATA block.
SPILL also checks whether MRES is consistent with other reservoir data. If necessary the mixture composition will be changed by adding dry air to the mixture.
A user-specified value of MRES is only used if the SPECIES keyword is used in the GASDATA input block and if the initial reservoir mixture is denser than dry air. In all other cases, MRES is calculated by the program based on mixture composition and VRES, TRES and PRES.

The GASDATA block contains the initial composition of the reservoir mixture and the relevant thermodynamic data.
WATERPOL Initial mole fraction water (liquid plus vapour) in reservoir mixture (mole water per mole mixture).
0 <= WATERPOL <= 1.0.
Optional, default is 0.0.
CPGAS Initial specific heat at constant pressure of the dry reservoir mixture (J/(mole K)).
5 <= CPGAS <= 300.
Mandatory if SPECIES keyword is not used (vapour-only mixture), no default. If SPECIES keyword is used then CPGAS is needed when a link file to HEGADAS is being made by AEROPLUME. Thus in practice CPGAS must almost always be specified. Using HGSYSTEM module DATAPROP to find CPGAS and other keywords is strongly recommended.
MMGAS Initial molar mass of dry reservoir mixture (kg/kmole).
2 <= MMGAS <= 200.
Same comments as for CPGAS apply. Again, use of DATAPROP to calculate MMGAS is recommended.
HEATGR Natural convection heat transfer group
5 <= HEATGR <= 100.
Optional, no default. Not used by SPILL or AEROPLUME model but written to HEGADAS link file if this is being made after AEROPLUME run.
Use of DATAPROP to calculate HEATGR is strongly recommended.
SPECIES Reservoir mixture compound properties. Using this keyword at least once implies the use of the full two-phase (aerosol) model or a mixture consisting of at least one compound (excluding water). If the SPECIES keyword is not specified, ideal gas thermodynamics is used with gas properties given by CPGAS and MMGAS. Condensation or freezing of water is still taken into account.
The SPECIES keyword plus parameters must be specified for every compound in the mixture, except water. The sum of the molar fractions (see parameter #2 below) must equal 1.0-WATERPOL.

The use of DATAPROP to generate the input parameters when the SPECIES keyword is being used, is strongly recommended.

Currently a maximum of 8 species can be specified (excluding water). Please note that DATAPROP allows for more species to be specified. DATAPROP also splits dry air (if specified) up into nitrogen and oxygen, thus generating two compounds instead of one. Thus the SPILL link file generated by DATAPROP could contain the SPECIES keyword more than 8 times. The user should combine or remove compounds if this occurs.

Within the above-mentioned restrictions, there are no restrictions within SPILL concerning the number of aerosols forming or the number of compounds per aerosol.
Following the SPECIES keyword for a certain compound, a block of 14 parameters (#1 to #14) must be specified:
#1 compound name (maximum of 12 characters).
#2 mole fraction of this compound in the reservoir mixture (-).
0<= #2<= 1.
#3 ;aerosol class (-).
-1<= #3 <= 50.
#4 specific heat of vapour (J/(mole K)).
5<= #4 <=300.
#5 specific heat of liquid (J/(mole K)).
0<= #5 <=103.
#6 heat of vaporisation (J/mole)
0<= #6 <=105
#7 critical temperature (K).
0<= #7 <=104
#8 critical pressure (atm).
0<= #8 <=103
#9 vapour pressure function coefficient B1.
-108<= #9 <=108.
#10 vapour pressure function coefficient B2.
-108 <= #10 <= 108.
#11 vapour pressure function coefficient B3.
-108 <= #11<= 108.
#12 vapour pressure function coefficient B4.
-108 <= #12 <= 108.
#13 molar mass (kg/kmole).
2 <= #13 <= 200.
#14 liquid density (kg/m3).
1<= #14 <= 105.
Note: the saturated vapour pressure of the compound is described by the Wagner function:

Pv (T) = Pc x exp { [ B1 x Q + B2 x Q1.5 + B3 x Q3 + B4 x Q6 ] / Tr }
where T is the vapour temperature, Pc the critical pressure, Tc the critical temperature, Tr = T/Tc and Q = 1 - Tr.

The PIPE block contains the release pipe/orifice exit-plane conditions.
DEXIT Effective orifice diameter of the discharge pipe (m).
0.001 <= DEXIT <= 5.
Mandatory.
CDG Discharge coefficient for vapour only releases (-).
0.0 <= CDG <= 1.0.
Optional, default is 1.0.
SPILL uses discharge coefficients to calculate values for the mass discharge rate, the user might want to change the default values of these coefficients.
CDL Discharge coefficient for liquid or two-phase releases (-).
0.0 <= CDL <= 1.0.
Optional, default is 0.61.
See remark above.

The AMBIENT block contains parameters describing the conditions of the ambient atmosphere.

AIRPRESS Ambient air pressure at release height (atm).
0.7 <= AIRPRESS <= 1.1.
Optional, default is 1.0 atm.
AIRPRESS must be less than PRES of the RESERVOIR block.
TATM Temperature ambient air for heat transfer only (C).
-50 <= TATM <= 50.
Optional, default is 20 C.
Used to calculate radiative and convective heat transfer between reservoir and surrounding air.
QSOLAR Direct solar heat flux to reservoir (W/m2).
0<= QSOLAR <= 3000
Optional, default is 0 W/m2.
Used in reservoir heat balance.
EMISS Radiative emissivity of reservoir surface (-).
0<= EMISS<= 1.0.
Optional, default is 0.8.
Used to calculate radiative heat flux.
AREA Surface area over which heat transfer takes place (m2).
0<= AREA <= 10000.
Optional, default is 0.0: no heat transfer between reservoir and surrounding air.

The TERMINAT block sets reservoir release termination criteria. Normally these are all inactive (by setting them to a negative value) and the SPILL run will only end when the reservoir is exhausted or when the reservoir pressure falls below the ambient pressure. Sometimes, however, it can be useful to stop the run before this occurs. The TERMINAT parameters can be used for this purpose.
TLST Last required elapsed time after release start (s).
-1000 <= TLST <= 2000.
Optional, default is -1.0 (criterion inactive). If set to a negative value, the termination criterion will not be used.
MLST Last required reservoir mass content (tonnes, 1 tonne = 1000 kg).
-1000 <= MLST <= 1000.
Optional, default is -1.0 (criterion inactive). If set to a negative value, the termination criterion will not be used
LLST Last required reservoir total liquid mole fraction (%).
-1000 <= LLST <= 100.
Optional, default is -1.0 (criterion inactive). If set to a negative value, the termination criterion will not be used.
PLST Last required reservoir pressure (Pa).
-1000 <= PLST <= 1000.
Optional, default is -1.0 (criterion inactive). If set to a negative value, the termination criterion will not be used.
RLST last required reservoir mixture density (kg/m3).
-1000 <= RLST <= 1000.
Optional, default is -1.0 (criterion inactive). If set to a negative value, the termination criterion will not be used.

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