Thermal conductivity units/equivalents

Discussiott Note that the temperature difference between the center and the surface of the wire is 21 C. Also, the thermal conductivity units W/m C and W/m K are equivalent. 

Discussion This is the same result obtained earlier. Note that heat conduction through a plane wall with specified surface temperatures can be determined directly and easily without utilizing the thermal resistance concept. However, the thermal resistance concept serves as a valuable tool in more complex heat transfec problems, as you will see in the following examples. Also, the units W/m "f and W/m K for thermal conductivity are equivalent, and thus inter changeable. This is also the case for °C and K for temperature differences. 

K-factor K-factor is a term sometimes used for the thermal insulation value or coefBcient of thermal conductivity. It is numerically equivalent to the thermal conductivity expressed in British units (BTU in.)/(ft h°FA and its inverse (1/K) is known as the R-factor. K-factors and R-factors are commonly used for thermal insulating materials such as plastic foam. 

The rise in temperatme of an IC encapsulated in plastic is primarily determined by the thermal conductivity of the leadframe material, and is generally about twice that of its hermetically packaged equivalent. Until recently, the leadframe material has been exclusively a nickel-iron alloy (Alloy 42), and for a 14 lead dual-in-line package the thermal resistance (i.e., rise in die temperature per unit power dissipated) is about 120°C/W. In order to cope with the increasing power dissipation of ICs, high copper content alloys (OLIN) have been introduced to reduce the thermal resistance by about 50%. 

The thermal conductivity k, which is analogous to electrical conductivity, is a property of the thermal material. It is equivalent to the rate of heat transfer between opposite faces of a unit cube of the material, which are maintained at temperatures differing by 1°. In SI unit, k is expressed asW/mK. 

For the coolant conditions shown in Table II, the cross-sectional coolant channel area required for helium cooling would be about the same as for water and only about twice that required for sodium. By allowing a coolant pressure of 70 atm (about 1000 psia), the helium coolant is superior to pressurized water at 1500 psi and approximately equivalent to sodium in its heat removal capacity per unit coolant area. The capacity for heat removal should not, of course, be confused with the conductivity of the coolant. In this respect, the sodium coolant is superior to the high-pressure gas, although it can be argued that the high conductivity of the sodium coolant is not particularly necessary and indeed creates some problems in thermal stresses. 

Let us denote the Fermi function of probability for a capture center to be occupied by an electron by/ and the probability of the occupancy of a state in the conduction band by. The recombination rate of an electron from the conduction band (in the energy interval dE around the value E) on traps in a unit volume of material is proportional to N(E)dE (concentration of electrons with energies within the interval under consideration) and N, (concentration of vacant traps). Let Csr = be the average probability per unit time for an electron from the interval dE to be captured at an empty center. Here v = [Skt>T/nm Y is thermal velocity of electron and cr is experimentally determined effective cross section of the electron capture at the center. The parameters Op and Vp are defined for holes in an equivalent manner. The rate of recombination at traps is... 

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