The input parameters and options for the tool are described below. When the input form has been completed, pressing the button will start the calculation and bring up the "Results" page.

Input parameters

• Contaminant emitting surface of a volume

From the list of volumes and their surfaces, created by the View Factor tool, the user select the contaminant emitting surface. In its present version, the number of emitting surfaces is limited to one.

• Outgassing type

Two types of outgassing are considered:

at a constant rate:

This zero-order reaction describes well the outgassing of a material during evaporation or sublimation from a bulk. The mass loss (in g/cm²/s) is related to the vapour pressure through the Langmuir law (for a pure contaminant):



with P_s the vapour pressure in hPa, M the molecular mass in amu and T the temperature in K. All these parameters must be supplied by the user.

at a rate proportional to the available mass:

Outgassing is often described as a first order reaction whereby using the Arrhenius law temperature dependency:



with m the available mass in g/cm², τ₀ the time constant in s, k the temperature dependant constant in 1/K, T the temperature in K and T₀ the reference temperature in K, which are all input parameters.
• Surface properties

For each surface the user has to set the temperature level "low" or "high", the sticking coefficient related to the contaminant specie and the outgassing coefficients 1/τ at reference temperature (=1/τ₀) and -∂ln(τ)/∂T (=k in the outgassing equation above). The user defines the temperature levels "low" and "high" through entering values for T_low and T_high in K. We remark that surfaces that are contaminated are considered to re-emit the contaminant according the same first order law as above.

• Duration of the outgassing

The duration of the outgassing process is set in seconds.

• Integration time step

To solve the set of coupled differential equations a Runge-Kutta of order 4 is implemented, whereby the time step (in s) is an input from the user. The step size should be of the same order of magnitude as the residence time τ in order to obtain accurate results.

More information on outgassing is provided in the background help pages.

Results

The report file spenvis_ctp.html contains a summary of the input parameters and the final mass of the contaminant specie on each surface together with the mass lost in space and the error on the computed mass due to the numerical treatment.

The output file spenvis_cto.txt contains the evolution of the contaminant mass on each surfaces as function of time.

The output file contam_xy.* displays the evolution of the contaminant mass or surface density as function of time for a selected surface.