# Overall heat transfer coefficient

## Description

Heat transfer describes the exchange of thermal energy, between physical systems depending on the temperature and pressure, by dissipating heat. The heat transfer coefficient or film coefficient, in thermodynamics and in mechanics is the proportionality coefficient between the heat flux and the thermodynamic driving force for the flow of heat.

There is a simple method for determining an overall heat transfer coefficient that is useful to find the heat transfer between simple elements such as walls in buildings or across heat exchanger. (Note that this method only accounts for conduction within materials, it does not take into account heat transfer through methods such as radiation).

## Variables

U | the overall heat transfer coefficient (W/m^{2}*K) |

A | the contact area for each fluid side (m^{2}) |

h_{1} | the individual convection heat transfer coefficient for one of the fluids (W/m^{2}*K) |

A_{1} | the contact area for one of the fluids' side (m^{2}) |

dx_{w} | the wall thickness (m) |

k | the thermal conductivity of the material (W/m*K) |

h_{2} | the individual convection heat transfer coefficient for the other fluid (W/m^{2}*K) |

A_{2} | the contact area for the other fluid side (m^{2}) |