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1.0 Introduction
Welcome to GnuRad; GnuRad is a Radiation heat transfer Computer aided modeler.
It allows a user to model a variety of radiation heat transfer problems
without having to write a computer program. GnuRad can model something simple
as energy radiating from a plane surface, or something complex where the model
is a series of connected enclosures containing a participating medium. The
types of models that GnuRad can run is quite extensive, currently limited to
only orthogonal plane gray surfaces with a medium having isotropic scattering.
Some examples of what GnuRad can model are:
- The radiant energy which is absorbed by a furnace wall
- Radiant energy distribution of a room with windows and a fireplace
- The radiation exchange factor of one surface to another
- The temperature distribution in a participating medium based on radiant
energy
GnuRad is a computer program which simulates the radiation heat transfer in an
enclosure or series of connected enclosures. The basic enclosure is 'box'
shaped (regular parallelepiped) having arbitrary dimensions and containing a
medium. Depending on the requirements of the model, boxes can be joined
together, walls can be removed, and the medium can be participating or
non-participating. A wall or medium temperature/emitting flux can be initially
specified in the input or GnuRad can solve for an unknown temperature. Wall
and medium properties are specified in the input file. Wall properties are:
temperature or emitting flux, emissivity, diffuse reflectivity, specular
reflectivity, and number of grid elements which form the wall. Medium
properties are: temperature, extinction coefficient, single scattering albedo,
type of scattering, and the number of 'brick' elements which form the medium.
GnuRad provides five different types of output files which presents the
results in a tabulated format and a text-graphic format. The other output
files are used as inputs to spreadsheets and plotting programs.
GnuRad is a direct physical model where radiant energy is sent and tracked to
and from all participating sources. More precisely, a photon bundle containing
a specific amount of energy is sent from a wall or the medium, and it is
tracked until it is absorbed by a wall or the medium. This process is repeated
until all surfaces and medium have sent their required number of bundles.
Direction and location for sending the bundles is determined by applying the
Monte Carlo technique. Details of the Monte Carlo technique can be found in
several of the books listed in the Reference section of this document.
GnuRad is written in C++ using object oriented programming practices. The
source code and user manual of GnuRad are free to be copied or modified as
long as any changes or enhancements continue to be free. GnuRad is protected
by the GNU public license. This philosophy will allow GnuRad to continue to
grow in options and features. The latest version of GnuRad can be found at this site
It is recommended that the first five sections of this manual be read before
attempting to use GnuRad. Sections two through four give details on how to
construct a model, create an input file, and run a model. Finally, section
five contains nine different sample input files that have descriptive
comments.
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