Smoke Hang Time
The hang time, or persistency of the smoke effect
produced by all artificial smoke systems is a function of some key
Boiling range and evaporation rate of the
The higher the boiling range and lower the evaporation rate of the
smoke chemical, the greater the smoke persistency.
Viscocity and surface tension
Generally, within chemical groups, the higher the viscosity and
surface tension, the higher the boiling range.
The bigger the particle size, the lower the ratio of surface area
to volume, hence the greater persistency. However, remember, the
bigger the particle size, the faster the settling velocity (ie more
chance of residue being left on surfaces).
Generally, the higher the ambient temperature of the air in which
the smoke is suspended, the faster the smoke will "evaporate".
Many smoke systems (largely those based on the entertainment
industry requirements) produce a dense white smoke effect, but one
that evaporates very quickly. Hence, although the initial burst
is impressive, filling large volumes with smoke becomes problematical,
as one quickly reaches the stage where the smoke produced a few
minutes ago has evaporated, and smoke density no longer increases.
Also, systems which quote a smoke output unqualified by smoke density
or visibility are of no use when trying to make comparisons.
The hang time table below better allows a user to
establish the relative performance of smoke systems, in particular
with regard to large volume or extremely dense smoke concentrations.
Generally, oil based smokes, with their very high
boiling range, will produce a smoke effect that lasts for an exceptionally
long time. This makes our Phantom Oil Based Smoke Generators particularly
suitable for smoke logging exceptionally large volumes, which would
need perhaps 10 or 12 times as many high output water based systems
to achieve the same performance.
For our most persistent water based smoke, we have
selected a water miscible pharmeuctical grade chemical with the
highest boiling range in its class, and used a very high percentage
of this active ingredient in the mix. This gives the “Holy
Grail” in terms of water based smoke of high persistency combined
with the small particle size and hence insignificant settling velocity.
Where quickly dispersing smoke is required (localised
air flow tracing for example) the PS21 or 2.2kW High Output Smoke
Machine with smoke fluid B would be chosen, as the active ingredient
has the lowest boiling range of the commonly used simulants.
Using the Hang Time Index in conjunction with quoted
smoke output figures, (providing those figures are quantified in
terms of smoke density or visibility) allows a simplistic comparison
to be made of smoke systems.
This is particularly relevant with larger volumes
or denser smoke concentrations, where the persistency of the smoke
becomes of greater significance.
|Smoke Hang Time (at 20C)
Oil based smoke system
|3 - 4 hours
PS27 Type A, PS23,
|1.25 - 1.5 hours
PS27 Type B, PS21
|2 - 4 minutes
Portable Smoke Machine - units to deliver quick
dispersing smoke (PS21) or long lasting (PS23). Off-power facility
on basic models. 240/110v. (PS21, PS23 and PS25)
High Output Smoke Generator - continuous high output
2.2kW machine with a choice of fluids available for either quick
dispersing smoke or persistent. 240/110v. (PS27)
Based Smoke Machine - oil-based smoke machines
with continuous high output for large scale applications (see
photo below). The generated smoke can withstand high temperatures.
The units can also be re-programmed to accept water based fluids.
The Oil Based Smoke
Generator in operation