User Guide to HFLUME

11. HFPLUME

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General introduction

The HFPLUME model is the HF-specific version of AEROPLUME which can be used to simulate pressurised jet releases from a reservoir containing a mixture of HF, water, an inert ideal gas and dry air. HFPLUME uses the full chemistry and thermodynamics of a reacting system of HF/water/inert gas mixture. The HGSYSTEM 3.0 Technical Reference Manual contains a chapter which gives details about the HF chemistry model.

HFPLUME is a steady-state program.

HFPLUME calculations start from user-specified reservoir conditions. A reservoir discharge calculation plus a flash calculation will precede the actual atmospheric dispersion calculation.

The HFPLUME program will generate a link file to one of the far-field HGSYSTEM models (PGPLUME or HEGADAS) if possible. This is done completely automatically.

Range of applications and limitations

The HFPLUME model should not be used for very low-speed jets (slower than ambient wind speed), as wake-effects will be important.

HFPLUME should not be used for unpressurised releases, or for any releases where exit velocities are small compared to ambient wind speed or where initial momentum is quickly destroyed by impact with the ground. In those cases the evaporating liquid pool model LPOOL should be used.

Jets touching the ground at high speed and very steep angles should also not be simulated with HFPLUME.

It is very important when interpreting HFPLUME results to realise that all physical quantities (concentration, density, temperature etc) are always average quantities over the plume cross-section. As a general rule of thumb, peak concentrations will be about a factor 1.3-1.4 higher than the cross-sectional mean concentrations as given in the HFPLUME report file.

Guidance for use
See the AEROPLUME chapter for general information.
The HFPLUME model is not as robust as the AEROPLUME model, mainly due to the complicated HF chemistry and thermodynamics involved.
Numerical difficulties can sometimes be overcome by slightly changing the input parameters. It should be realised that the influence of atmospheric parameters (wind speed, stability class) and also of surface roughness, on the near-field dispersion is not very strong for high-momentum jets. Therefore changing these parameters will not have large effects on calculated near-field HFPLUME results, but might solve numerical problems.

HFPLUME INPUT PARAMETERS

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

The HFPLUME input file has the DOS filename 'casename.HPI' 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 HFPLUME these block keywords are: RESERVOIR, GASDATA, PIPE, AMBIENT, DISP, MMESOPT, TERMINAT and MATCH.
Some of these blocks are identical or very similar to the corresponding AEROPLUME input blocks.

The TITLE keyword does not occur in a parameter block.

TITLE

The title of the current problem to be run with HFPLUME.
At most 50 alphanumeric characters.
Optional, no default.

The RESERVOIR block contains the parameters which describe the reservoir fluid thermodynamic state.

TRES	Temperature of the reservoir mixture (DegreesC). -50 <= TRES <= 150. Mandatory.
PRES	Absolute pressure within the reservoir (atm). 0.7 <= PRES <= 20. Mandatory.
	PRES must be greater than AIRPRESS in the AMBIENT block.
HFRES	Mass percentage HF in reservoir (%) 0 <= HFRES <= 100. Mandatory
HCRES	Mass percentage inert ideal gas in reservoir (%) 0 <= HCRES <= 100. Mandatory
H2ORES	Mass percentage water in reservoir (%) 0 <= H2ORES <= 100. Mandatory
	Note: The sum of HFRES HCRES and H2ORES need not be exactly equal to 100%. If the sum is smaller the HFPLUME program will add dry air to the reservoir mixture to get a 100% mixture. Too large values will be changed by the program and messages will be generated accordingly. For numerical reasons the mass percentage dry air in the mixture should preferably be larger than about 1%.

GASDATA block only contains data concerning the inert ideal gas that can be specified in the RESERVOIR block. All other chemical species data is included in the HF chemistry description of HFPLUME.

CPGAS	Specific heat at constant pressure of the inert ideal gas (J/(mole.k) 5 <= CPGAS <= 200. Mandatory.
MMGAS	Molar mass of the inert ideal gas (kg/kmole). 5 <= MMGAS <= 200. Mandatory.

The PIPE block contains the release pipe/orifice exit-plane conditions.

DMDT	Steady mass discharge rate (kg/s). 0.01 <= DMDT <= 1000. mandatory.
DEXIT	Effective orifice diameter of the discharge pipe (m). 0.001 <= DEXIT <= 5. Mandatory.
ZEXIT	Height above ground level of discharge opening (m). 0.0 <= ZEXIT <= 50. Mandatory.
	ZEXIT should be greater than ZR in the DISP block because otherwise model assumptions used in some atmospheric correlations will be violated.
ANGLE	Inclination of release opening with respect to horizontal (Degrees). -180 <= ANGLE <= 180. Optional, default is 0 degrees (downwind horizontal release).
	Therefore for a vertically upward release ANGLE is 90 degrees
DURATION	Duration of pollutant release (s). -10⁶ <= DURATION <= 10⁶ . Optional, default is -1 (steady release).
	If DURATION <= 0, then a steady release is assumed (infinite duration). Please note that this is not always a realistic scenario as the total amount of released pollutant can become very large. HFPLUME does not use DURATION itself as it only simulates steady releases, but for a proper transition to HEGADAS-S or HEGADAS-T the value of DURATION is needed.

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

Z0	Reference height for atmospheric data in this block (m). 0.1 <= Z0 <= 50. Mandatory.
U0	Ambient wind velocity at height Z0 (m/s). 0.5 < U0 <= 20. Mandatory.
	Please note that U0 can be small but never equal to 0.
AIRTEMP	Ambient air temperature at height Z0 (Degrees C) -50 <= AIRTEMP <= 50. Mandatory.
AIRPRESS	Ambient air pressure at release height ZEXIT (atm). 0.7 <= AIRPRESS <= 1.1. Optional, default is 1.0 atm.
	AIRPRESS must be less than PRES in the RESERVOIR block.
RHPERC	Relative air humidity at release height ZEXIT (%). 0.0 <= RHPERC <= 100. Mandatory.

The DISP block contains parameters describing the dispersion characteristics.

ZR	Land surface roughness (m). 10^-5 <= ZR <= 1. Mandatory.
	ZR must be less than ZEXIT of the PIPE block.
PQSTAB	Pasquill/Gifford stability class. PQSTAB = A, B, C, D, E or F (character). Mandatory.

The MMESOPT block contains the 'switches' which indicate the use of the extra options developed by Earth Technology and sponsored by Martin Marietta Energy Systems. An indicator value of 1 means that the corresponding option is used, a value of 0 means that the option is inactive.

ILIFT Indicator for use of plume lift-off description (-).
ILIFT = 0 or 1.
Optional, default is 0.

No additional data needed.
When ILIFT = 0, HFPLUME will stop program execution when lift-off is detected for a plume after touch-down. When ILIFT = 1, a plume is allowed to become air-borne again after touch-down. See Chapter 9 in the HGSYSTEM 3.0 Technical Reference Manual for details.

The TERMINAT block sets plume development termination criteria. Normally these are all inactive (by setting them to a negative value) and the HFPLUME run will only end when a transition can be made to HEGADAS or to PGPLUME. Sometimes, however, it can be useful to stop the run before this transition occurs. The TERMINAT parameters can be used for this purpose.

DLST	Last required plume diameter (m). -1000 <= DLST <= 1000. Optional, default is -1.0 (criterion inactive)
	If set to a negative value, the termination criterion will not be used.
SLST	Last required displacement measured along plume axis (m). -1000 <= SLST <= 1000. Optional, default is -1.0 (criterion inactive)
	If set to a negative value, the termination criterion will not be used
ZLST	Last required plume centroid height (m). -1000 <= ZLST <= 1000. Optional, default is -1.0 (criterion inactive)
	If set to a negative value, the termination criterion will not be used.
XLST	Last required horizontal displacement (m). -1000 <= XLST <= 1000. Optional, default is -1.0 (criterion inactive)
	If set to a negative value, the termination criterion will not be used.
ULST	Last required plume velocity (m/s). -1000 <= ULST <= 500. Optional, default is -1.0 (criterion inactive)
	If set to a negative value, the termination criterion will not be used.
HFLST	Last required HF concentration (mole %). -1000 <= HFLST <= 100. Optional, default is -1.0 (criterion inactive)
	If set to a negative value, the termination criterion will not be used.
HCLST	Last required inert gas concentration (mole %). -1000 <= HCLST <= 100. Optional, default is -1.0 (criterion inactive)
	If set to a negative value, the termination criterion will not be used.

The MATCH block parameters contain the criteria that determine when the transition from HFPLUME to one of the far-field models (HEGADAS and PGPLUME) will occur. Normally the user should not change these parameters. However, if the user wants to influence the transition location, then the MATCH parameters should be modified. This is only recommended for expert users or after seeking expert advice.

RULST	Excess velocity ratio (-). 10^-3 <= RULST <= 1.0. Optional, default is 0.1.
RELST	Entrainment ratio (-). 10^-3 <= RELST <= 1.0. Optional, default is 0.3.
RGLST	Buoyancy effect for advection (-). 10^-3 <= RGLST <= 1.0. Optional, default is 0.3.
RNLST	Buoyancy effect for passive diffusion (-). 10^-3 <= RNLST <= 1.0. Optional, default is 0.1.
RALST	Aspect ratio for passive diffusion (-). 10^-3 <= RALST <= 1.0. Optional, default is 0.2.

ILIFT	Indicator for use of plume lift-off description (-). ILIFT = 0 or 1. Optional, default is 0.
	No additional data needed. When ILIFT = 0, HFPLUME will stop program execution when lift-off is detected for a plume after touch-down. When ILIFT = 1, a plume is allowed to become air-borne again after touch-down. See Chapter 9 in the HGSYSTEM 3.0 Technical Reference Manual for details.