Consulting Services

Virial, Inc. offers scientific and engineering consulting services in the areas of radiometry, photometry, radiation thermometry (pyrometry), optical instrumentation and radiation heat transfer. Our services include system analysis, computer modeling, performance assessment and optimization 

Our area of expertise

RADIATION CHARACTERISTICS OF THERMAL RADIATION SOURCES

Blackbody cavities

  • Arbitrary surface of revolution with polygonal generatrix (inclined bottom is allowed)

  • Isothermal or non-isoithermal internal surface

  • Diffuse, specular, and mixed reflection from internal walls

  • Arbitrary conditions of observation or detector placement

  • Several aperture diaphragms between cavity and detector

  • Spectral, total, or band-pass (with account of radiometer/pyrometer spectral responsivity)  effective emissivities

  • Effective (radiation, radiance, of distribution) temperatures of cavity 

  • Reference temperature matching

  • Spatial distributions of spectral or total irradiance

  • Angular distributions of spectral or total radiance
Example 1. High-temperature blackbody BB3500 (A) with working temperature up to 3500 K, developed by Vega International, Inc. for primary standard of irradiance in UV-Vis-NIR spectral range, was numerically modeled by means of the Monte Carlo code STEEP3.
Cylindrical lateral walls of BB3500 made of pyrographite, internal cone bottom – of graphite (B). For various temperature distributions along cavity generatrix (C) the normal spectral effective emissivities (D) was calculated. Thereby from requirements to effective emissivity, the requirements to temperature field homogenity were derived.

Surfaces with artificial roughness

  • Linear or concentric grooves

  • Arbitrary groove profile

  • Diffuse, specular, and mixed reflection from groove walls

  • Large- or small scale nonisotermality (along groove or whole surface)

Radiating surfaces with non-imaging concentrators

  • Flat or grooved surface

  • Arbitrary surface of revolution or quadric surface for mirror concentrato

  • Hot or cold mirror
Example 2. Low-temperature blackbody BB100 developed by Vega International, Inc. was numerically modeled by the Monte Carlo method. The flat bottom with concentric V-grooves is covered by Martin Marietta Infrablack. The profiled mirror concentrator is polished and gold-coated.

The use of the Monte Carlo code STEEP3 allows taking into consideration the flats of V-grooved bottom, which reduce the integrated effective emissivity of a blackbody. At the optimization of the shape of concentrator, the radiative heat transfer inside the cavity, formed by 96 surfaces of revolution, was simulated.

THERMAL MODELING OF BLACKBODY RADIATORS
  • Heat transfer due to conduction, convection and radiation
  • Temperature-depending thermophysical properties
  • Calculation of resolving angle factors for radiative heat transfer
  • Calculation of steady-state temperature field

Example 3. Steady-state temperature field within three teeth (ring-shaped area) of low-temperature blackbody BB100 V-grooved bottom (Courtesy of Dr. Alexander I. Zhbanov). The teeth are placed at the distances 0, ½, and 1 of bottom radius. Thermal conductivity and radiation losses through the aperture after multiple reflections were taking into account. The solution was obtained numerically with finite element code ATAKA (See: Zhbanov A.I., Smirnov A.E., Prokhorov V.V., Shevtsov V.N. Calculation of the axisymmetrical temperature fields with account of radiative transfer by the finite element method - International Symposium on Heat and Mass Transfer. Part 9. Computing Experiment in Heat and Mass Transfer Problems. Minsk, 1988, pp. 92-94)

Example 4. Temperature of blackbody BB1000 (its construction is analogous to one of BB100 - see Example 2) is determined by thermal balance of power released in electric heater and thermal losses due to: 
  • radiation through the aperture 
  • thermoconductivity along heat sink 
  • coupled radiative-conductive transfer through 30-40 layers of multi-foil insulation 

For evaluation purpose at the stage of preliminary design the modeling program that solves non-linear boundary problem for ordinary differential equation has been developed. On the screenshot below, you can see the time dependencies for average temperature of cavity radiating bottom and each kind of heat losses.

ABSORPTION CHARACTERISTICS FOR THERMAL DETECTORS OF RADIATION
  • Arbitrary surface of revolution (inclined bottom is allowed)
  • Diffuse, specular, and mixed reflection from internal walls
  • Arbitrary conditions of irradiation
  • Spectral and total (for given source) effective absorptivities
  • Distributions of absorbed fluxes over internal surface

Example 5. Effective absorptivity vs. absorptivity of cavity walls (left-handed graph) and distributions of absorbed radiation flux density along generatrix of 15°-conical detector of radiation (right-handed graph), computed by the Monte Carlo method for various value of cavity wall diffusity (D = 1 corresponds to perfectly diffuse reflection, D = 0 - to perfectly specular)

RADIOMETERS WITH COMPOSITE GLASS FILTERS

OPTIMIZATION OF THICKNESS AND PARTIAL AREAS FOR COMPOSITE GLASS FILTERS 

  • Multilayer and/or mosaic glass filter
  • Arbitrary configuration of incident radiation beam · 
  • Several algorithms of multidimensional optimization with constraints · 
  • L1, L2, and C metrics with several types of weighting function · 
  • Arbitrary goal function, including photopic and scotopic efficiency curves · 
  • Preliminary selection of glasses from embedded database 

Example 6. Relative response of photometer comprising Si photodiode and composite glass filter was fitted to V() curve by optimizing the thicknesses for four glass components. Optimization was performed for L2 metric by the Hooke-Jeeves method using the GlaFiRa program.

INTEGRATING SPHERES

Numerical modeling of multiple reflections in integrating sphere for various applications (measurements of reflectance, transmittance, luminous flux; large-area uniform-radiance sources, attenuators of radiation, etc.)

  • Several circular or rectangular openings (ports) and screens (baffles)
  • Arbitrary angular distribution of luminance (radiance) for internal and external sources
  • Choice of BRDF model from several ones with possibility to fit their parameter to experimental data
  • Calculation of illuminance (irradiance) due to multiple reflection in every point
  • Calculation of luminance (radiance) due to multiple reflection in every point along every direction
  • Calculation of luminous flux (radiation flux) on ports and detectors
  • Calculation of comparison uncertainties for heterogeneous samples (sources)

Example 7. Angular distribution of radiance incident on sample at reflectance measurement with integrating sphere.