LAB 4 - FAN system Lab5_FD

# LAB 4 - FAN system Lab5_FD - Background and Objectives...

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Background and Objectives Semi-conductor usage has gained popularity in recent years, methods of cooling these types of systems have had to be developed and optimized for the application. Semiconductor systems are characterized by high power densities and small temperature allowances for reliability. Because of the high power density produced, it is necessary to draw heat away through heat sinks at a rate sufficiently high to avoid reaching a critical temperature within the chip where semiconductor operation becomes unreliable. Further complicating matters, heat drawn away from the chip must me transported out of the chassis by some forcing mechanism. In a conventional computer chassis, this is done by forcing air through the chassis, thereby drawing cold air into the chassis to replace air that has already been warmed by the heat sink. The type of fluid motion and volume flow rate over the heat sink determines the maximum rate at which heat can be drawn away from the circuit element. It is therefore necessary to find a forced air system which keeps processor temperature within a margin of safety of operating limits while at the same time, use the simplest, most cost-effective geometry for the chassis. The most basic system consists of a single fan which draws air into the chassis, forcing it over the heat sync and out of the chassis. Many chips, however need more cooling than one fan can apply or have a higher head pressure due to bad ventilation and require two fans which can either be configured in series or in parallel. The purpose of this lab is to compare heat transfers for high head pressure (impedance) and low impedance for single, series, and parallel configurations. Since fin geometry is difficult to measure, it is better to use a bulk theory relating chip temperature to ambient temperature. This relationship, referred to as thermal resistivity is defined in Equation 1 below (Handout, 4). / R T Q = ∆ (Equation 1) For simple 1-D conduction, thermal resistance is related to thickness L, thermal conductivity k, and wall surface area A. This relationship is defined in Equation 2 below. / R L kA = (Equation 2) Heat generated by resistance can be used to model a semiconductor system, and its power can be related through Equation 3.

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2 / P V R = (Equation 3) The overall goals of this lab are to: Understand the effects of airflow impedance on air flow rates and system cooling Understand the effects of series and parallel fan configuration Hypothesize the reason for results Understand the thermal resistance method in predicting junction temperatures 2
Computer chassis number 1 of the San Jose State Engineering department was used. Values for temperatures of the resistors (T juction ), case temperature (T case ), chassis air temperature (T amb ) and the board temperature (T baord ) were obtained using this chassis. The experiment was conducted using the following items: (1) Computer chassis number 1 - with variable impedance control

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## This note was uploaded on 09/08/2010 for the course ME 115 at San Jose State University .

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LAB 4 - FAN system Lab5_FD - Background and Objectives...

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