CONVECTIVE FIN HEAT LOSS EXPERIMENT Objectives A To investigate the heat transfer characteristics of a fin B To gain a basic understanding of how menu driven data acquisition software can be used to collect experimental test data with a PC Data Acquisition System Equipment 1 Pentium Computer 2 Teknikit Fin Assembly with heater and fan 3 Agilent Benchlink Software 4 Data Acquisition Switch Unit HP 34970A Test Procedure 1 Turn on the computer and the HP data acquisition unit 2 Login to windows NT by typing in user name student and password engineering in lower case 3 Click the Benchlink Data Logger Icon to start the data acquisition program 4 After the welcome menu pops up choose the option Load and existing setup from instrument upload and click OK Find the setup labeled nicesetupfortemps Click OK again when the upload menu pops up The software will then upload all of the information needed for the data acquisition unit to communicate with the computer 5 Note only channel 101 107 are active in this experiment TC101 ambient taped to base of test stand TC102 TC nearest heater and TC 107 TC nearest fin end 6 Start the data collection by clicking Scan from the top menu bar and then Start Scan and then click OK Click Start to start scanning 7 Record steady state ambient readings directly from the screen dump given in the small window on the lower right hand side area of the careen by clicking on the window displaying the numerical values of the TC readings and to make its border blue Then press ALT PRNT SCRN and dump the bitmap into a Microsoft Word file for your records FREE CONVECTION DATA GENERATION 8 Turn on the heater power 9 Data collection will start when the data acquisition begins scanning all the channels at the interval you have set Start scanning by clicking Scan from the top menu bar and then Start Scan Click on Settings to change scan time to 1 sec And then click OK Click Start to start scanning As the fin becomes heated the temperature traces will gradually become off scale You can adjust the reference temperature time div and units div per channel during scanning to optimize your display Use the Benchlink output as a visual aid to declare steady state 10 After steady state is reached you can stop scanning by selecting Scan and then Stop Scan A Scan Stopped dialog box will pop up When prompted enter the data file name and press OK This file now contains your data set for the free convection part of the experiment You can use the data browser under view function to rewind the data to the time segment that you are interested and note the beginning and end of the time frame 11 Repeat Step 7 above to read off steady state temperatures from the data logger for the free convection data generation 12 DO NOT TURN OFF THE HEATER POWER you will need to have it on for the next phase of the test FORCED CONVECTION DATA GENERATION 13 Place the Fan Duct Apparatus on top of the Fin Unit Turn on the fan Resume data collection by selecting Scan and then Start Scan to start scanning Adjust units div and Reference as fin is cooled for optimal display Once steady state is reached stop scanning by selecting scan and then stop scan Make sure you save the file under a separate name this time This file now contains your data set for the forced convection part of the experiment 14 Repeat Step 7 above to read off steady state temperatures from the data logger for the forced convection data generation 15 Exit program and turn off all equipment Analysis and Charts 1 Measure the dimensions of the fin including the distances between each of the thermocouples Make a neat sketch of this information for later use in step 6 below 2 From the steady state date obtain the fin temperatures from the scan immediately before the fan was turned on These are the steady state free convection temperatures The steady state forced convection temperatures are obtained from the very last scan 3 Compute the theoretical free convection Nusselt number using the heat transfer handbook correlation cf Ch 9 of Incropera DeWitt Heat Transfer Nu free theory h free theory L k 0 825 0 387 Ra1L 6 2 1 0 492 Pr 9 16 8 27 where the Rayleigh number is given by RaL GrL Pr g Ts T L3 4 Compute the theoretical forced convection Nusselt number using the heat transfer handbook correlation cf Ch 7 of Incropera DeWitt Heat Transfer Nu forced theory h forced theory L k 0 664 Re1 2 Pr1 3 where the Reynolds number based upon the flow rate m of the fan is given by Re VL mL A The fan is a Papst computer fan Refer to their website for typical flow rates 5 What is the combined theoretical Nusselt number when free and forced convection are present Incropera DeWitt 4th Ed Eqn 9 64 pg 515 n n n Nucombined theory Nu free theory Nu forced theory What is the theoretical combined free and forced exponent n 6 Free convection Heat Transfer Analysis a Divide the fin into i segments with each TC in the middle of each segment The two end segments will only be half the size of the others Calculate the local free convection heat transfer coefficient at each segment using the following expression for free convection from a vertical plate in air at ambient conditions hi 1 45 T T y 0 25 W m 2 K where hi local heat transfer coefficient at segment i W m2 K T average temperature of fin of segment i C or K ambient temperature C or K T ambient temperature C or K y vertical height of fin m b Next compute the area weighted average experimental free heat transfer coefficient given as follows h free experimental hi Ai Ai where Ai surface area of segment i There are three cases for which fin heat transfer can be analytically modeled CASE 1 The fin is very long Tend T For this case the temperature profile can be calculated as T T x e mx b Tbase T where m h free experimental P kAc and the parameters which have not yet been defined are x lateral distance from fin base m Tx fin temperature at distance x from the base oC or K h free experimental average free experimental heat transfer coefficient W m2 K P perimeter around the fin cross section m k thermal conductivity of the fin material W m K The fin is made of aluminum with a thermal conductivity of 138 W m K Ac cross sectional area of the fin m2 CASE 2 The fin is of finite length and loses heat by convection from its end also b cosh m L x cosh mL h sinh m L x mk h sinh mL mk where m is as defined for Case 1 and L length of fin from base meters CASE 3 The fin …