# Boiling water function

i want to make a program that realistically boils water with all the variables but know near nothing about the math

i got the energy transfer equation down

but this seems to be giving me some trouble or more specifically the "convective heat transfer coefficient" http://www.engineeringtoolbox.com/convective-heat-transfer-d_430.html

i would assume i would use this http://www.engineeringtoolbox.com/overall-heat-transfer-coefficient-d_434.html but i dont understand how to use the formula

like is it "1 / U (A) = what ever" or "(1 / U A) = what ever" and what are the little down numbers on A and h?

## 1 Answer

In practice, the equation is somewhat simpler than that given in your second link. The overall heat transfer coefficient, or U, is a combination of all of the individual heat transfer coefficients and thermal conduction through a tube wall. When these are combined, you end up with the equation

$${Q} = {U}{A}\Delta{T}$$, where the $\Delta{T}$ term is the log-mean temperature difference (see http://www.engineeringtoolbox.com/arithmetic-logarithmic-mean-temperature-d_436.html).

Other variables:

Q - heat transferred, BTU

U - heat transfer coefficient, BTU/hr-ft^2-degF

A - area through which the heat transfer is taking place

$\Delta{T}$ - log mean temperature difference, deg F

If you are simulating the boiling of water in a heat exchanger, use this equation. A real-world estimate for U of 200 BTU/hr-ft^2-degF should get you in the ball park.