In this demonstration we're going to analyse a floodlight
The floodlight model consists of a metal case and cover, quartz glass window and rubber seal
There is also a polished reflector and lamp holder
The bulb itself is a gas filled glass tube containing a tungsten filament, molybdenum connectors and ceramic insulators
We begin by running the flow analysis wizard
The first boxes allow us to name the flow project and choose the unit system
We then specify the type of analysis
In this case it is external because we wish to consider the air surrounding the floodlight
We choose heat conduction and radiation, and pick from available radiation models
The HVAC and LED licence versions include extra radiation models, and we will pick the Discrete Ordinates model
The comprehansive FloEFD reference manual helps us to choose the best options
To solve the natural convection, we also need to specify the gravity vector
There are also options for transient studies, rotation, and free surface behaviour
The next step is to specify the fluids
In this case, air is the default fluid and argon will later be assigned to the space inside the lamp bulb
Then we specify the default solid to be aluminium
Because we are calculating radiation, we specify a radiative surface type for all walls
Here, we choose aluminium sheet from the Engineering Database because it has an appropriate emissivity
Ambient conditions such as temperature and atmospheric pressure are specified in the next box
After finishing the wizard, a computational domain is constructed
The computational domain can be resized.
In this case to make the model quicker to solve, and also to reduce the space behind the light which is assumed to be mounted on a wall.
Because the geometry is symmetrical, we can model just half of it, with a symmetry boundary condition applied to the Y,Z plane
The next step is to assign a fluid sub-domain to the volume inside the bulb
This is identified by picking any surface in contact with the fluid region, and we specify argon with a pressure of 2 atmospheres
Note we can input units on the fly and FloEFD converts to the chosen unit system
To save time, I’ve jumped ahead in the setup and populated a number of solid materials, radiative surfaces and analysis goals.
Here, we assign solid material properties to the bulb and window
Numerous materials exist in the pre-defined engineering database
We assign quartz glass with radiation absorption to these parts
Next is the heat load definition. The bulb is a 150W type, which dissipates its heat by convection and radiation processes
The first step is to set the filament temperature to 2900 kelvin
The next thing is to set a surface goal to keep track of the convective heat transfer rate
Goals provide a useful way of controlling the calculation, outputting key results and tracking solution quantities
To make this easier to follow, we can rename the goal
Now comes the clever bit. I’m assigning a radiation source boundary condition to the filament, but the radiation power is going to be worked out by the solver
So instead of assigning a constant power, we can use a formula dependency.
Total dissipation from the bulb is 150W, so we enter 150 divided by 2 because it is a half model, and subtract the convective heat transfer rate which is the goal quantity we just defined
In this way, the proportion of heat radiated from the filament will be adjusted during the computation so that the total convection plus radiation adds up to 75W.
The blackbody temperature is 2900K
Next we add the remaining volume goals, to illustrate the process
These will monitor maximum and average bulb temperature
These goals can also be renamed
Last but not least is to apply relevant mesh settings
For this model to give good results we need a global initial mesh setting of 4..
..and a local mesh refinement of the solid cells associated with the filament, terminal and bulb glass
The model can now be solved
It takes several minutes to mesh, ray trace and solve the flow equations, so we’ll jump forward again to a completed project
There are many post processing tools, here are just a few ways to visualise the results
This is a surface temperature plot, looking at the outer glass surfaces
This is a section plot showing temperature and air velocity vectors
And finally a streamline plot showing flow traces coloured by air temperature