These calculations run in your web browser, using embedded Javascripts; which means that you must set your browser to allow Javascripts .
A laminated flat plate may be the wall or window or roof of a building; it may also be a part of a machine or engine that is made of metal but is coated with some material (paint, ceramic, epoxy, tar, etc etc etc) , or has developed a layer of gunk or oil or something that effects heat transfer. It is any flat area that has more than one material layer for whatever reason. For example, many gas turbine parts have a ceramic coating to protect them from the extreme operating temperatures. On one side is a 2000F gaspath, and on the other side is 500F cooling air .... will the part burn up??
For a laminated (or "composite") flat wall , the overall heat transfer coefficient, U, is:
U = 1/ [ ( 1/h1 ) + (t / k)1 + (t / k)2 + (t / k)3 + .... + ( 1/h2 ) ]
where
h1 is the convection coefficient on one surface
h2 is the convection coefficient on the other surface
the (t / k)'s are the (thickness / material conductivities) of each material layer
Be sure you use meters (not mm's or cm's) for the thickness dimensions.
The total thermal resistance of the wall is....
Rtotal = 1 / ( h1 * A ) + t1 / ( k1 * A ) + t2 / ( k2 * A ) + ... + 1 / ( h2 * A )
For nomenclature reference......
The net heat transfer rate, per unit surface area is:
q/A = U * (Thotfluid - Tcoolfluid) => Watts/m2
where
Thotfluid and Tcoolfluid are the fluid temperatures on each side of the wall.
In terms of the total thermal resistance.....
q = (Thotfluid - Tcoolfluid) / Rtotal
You can use either the U method or the Rtotal method , whichever you prefer, recognizing that Rtotal = 1 / (U * A ).
After calculating the total heat transfer rate per unit area (q/A) you calculated the individual layer temperatures by equations like this....
T 1= T(hot) - (q/A) * ( 1/h1) [ this is the solid surface temperature on the hot side.... see image above ]A room, building or any part may see heat transferred in and out of several of its surfaces at the same time. These may all be different. Each surface or wall or window or door or roof, may have different geometry, surface temperature and total thermal resistance. In such cases, you need to calculate q/A for each area individually and then add up the total heat transferred by....
q = (q/A)1 * A1 + (q/A)2 * A2 + ....You should think about the implication of this important statement.... it means that you can break down a very large, complex heat transfer problem into little solvable pieces ** that are all solved using the exact same equations/spreadsheet/program **, solve them individually and then assemble the answers when you're done. This is basically how all large heat transfer problems are solved.
Once you understand and program the laminate flat plate equations for this homework assignment, you basically have the core solution for large-scale building HVAC heat transfer calculations.
To use the from:
To use this calculator on a lamination with less that 4 layers, do something like this to the thicknesses and k's of the non-existent layers ........(shown here is an image example, it is not a calculator)
