An electronic device, such as a power transistor mounted on a finned heat sink, can be modeled as a spatially isothermal object with internal heat generation and an external convection resistance. (a) Consider such a system of mass M, specific heat c, and surface area As, which is initially in equilibrium with the environment at T. Suddenly, the electronic device is energized such that a constant heat generation (W) occurs. Show that the temperature response of the device is where T T() and T() is the steady-state temperature corresponding to t l ; i Ti T(); Ti initial temperature of device; R thermal resistance ; and C thermal capacitance Mc. (b) An electronic device, which generates 60 W of heat, is mounted on an aluminum heat sink weighing 0.31 kg and reaches a temperature of 100 C in ambient air at 20 C under steady-state conditions. If the device is initially at 20 C, what temperature will it reach 5 min after the power is switched on? 5.
Lecture 14: Thermodynamics Part 2 Objectives Key concepts o Energy, heat, and work all have the same dimension o Energy is a conserved quantity 1st law of thermodynamics o Energy has quality as well as quantity 2nd law of thermodynamics o Objects like rocks or working fluids have several forms of energy Internal energy, gravitational potential energy, kinetic energy o Calculate 5 types mechanical energy (work) o Formulate solution strategy by applying 1st law o Identify simple systems that violate the 1st law o Explain the effect of assumptions on the 1st law First law of thermodynamics Energy can be converted from one form to another, but total ene