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A 2008 review paper written by Philips researcher Clemens J. M. Lasance notes that: "Although there is an analogy between heat flow by conduction (Fourier's law) and the flow of an electric current (Ohm’s law), the corresponding physical properties of thermal conductivity and electrical conductivity conspire to make the behavior of heat flow ...
The thermal conductivity of a material is a measure of its ability to conduct heat.It is commonly denoted by , , or and is measured in W·m −1 ·K −1.. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity.
Quantity (common name/s) (Common) symbol/s Defining equation SI unit Dimension Temperature gradient: No standard symbol K⋅m −1: ΘL −1: Thermal conduction rate, thermal current, thermal/heat flux, thermal power transfer
For heat flow, the heat equation follows from the physical laws of conduction of heat and conservation of energy (Cannon 1984). By Fourier's law for an isotropic medium, the rate of flow of heat energy per unit area through a surface is proportional to the negative temperature gradient across it: =
The most fundamental formula for Joule heating is the generalized power equation: = where is the power (energy per unit time) converted from electrical energy to thermal energy, is the current travelling through the resistor or other element,
The number of transfer units (NTU) method is used to calculate the rate of heat transfer in heat exchangers (especially parallel flow, counter current, and cross-flow exchangers) when there is insufficient information to calculate the log mean temperature difference (LMTD). Alternatively, this method is useful for determining the expected heat ...
Note that the thermodynamic relations for the internal energy and enthalpy are given by: = + = + We may also obtain an equation for the kinetic energy by taking the dot product of the Navier-Stokes equation with the flow velocity to yield: = + The second term on the righthand side may be expanded to read: = () With the aid of the thermodynamic relation for enthalpy and the last result, we may ...
The above differential equation, when integrated for a homogeneous material of 1-D geometry between two endpoints at constant temperature, gives the heat flow rate as =, where Δ t {\displaystyle \Delta t} is the time interval during which the amount of heat Q {\displaystyle Q} flows through a cross-section of the material,