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# Heat Transfer Laboratory ME 412

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This 12 page Class Notes was uploaded by Princess Rolfson on Saturday September 19, 2015. The Class Notes belongs to ME 412 at Michigan State University taught by Staff in Fall. Since its upload, it has received 39 views. For similar materials see /class/207541/me-412-michigan-state-university in Mechanical Engineering at Michigan State University.

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Date Created: 09/19/15

Fall 2010 Design of a Radiation Transmissivity Experiment OBJECHVES 1 To review the basic principles of radiation heat transfer 2 To reexamine the basic tenets of the Scientific Method as related to research design 3 To design an experiment and develop an experimental procedure BACKGROUND The Spartan Thermal Engineering Company has been hired by the Tartar automobile company to perform thermal system modeling for a climate control system In thermal environmental engineering for automobiles it is found that the largest factor in the heating and cooling loads is the result of solar radiation coming into the passenger compartment Thus knowledge of the transmissivity of the windows is of critical importance for the thermal design As an engineer for the Spartan Thermal Engineering Company it is your job to design an experiment to measure the transmissivity of various materials As is the case with any design project it is a good idea to reacquaint oneself with the important physics involved So go to your desk blow the dust off an old heat transfer text and begin to read the chapters dealing with radiation heat transfer Sections of the standard ME 410 textbook lncropera and DeWitt Introduction to Heat Transfer 5th edition of particular interest are 12112301233125127128 There are many circumstances where we are concerned with radiation passing through a medium such as sunlight passing through a window In these cases only some fraction of the radiation will pass through the medium while some fraction is absorbed by the medium and some fraction is reflected We define the fraction of radiation transmitted through the medium as the transmissivity T We may mathematically definet as the ratio of radiation heat flow leaving the medium to the radiation heat flow entering the medium or kit 1 qden Having refreshed the basic concepts of radiation heat transfer you wonder how you can implement these ideas into a useful experiment One of the best references to guide the development of an experiment is the ASTM Standards The book of ASTM standards is a collection of published experiments that have been used for a considerable period of time and which have gained wide acceptance in the scientificengineering community as an acceptable method for evaluating the parameter of interest It is available in the engineering library and is a very good place to begin when attempting to measure a material property There is a guide to the ASTM standards included at the end of this writeup You will be required to provide a summary of an applicable ASTM standard for this experiment A basic literature review on the subject can also be effective There is a variety of information available in the library on possible search strategies and the databases available You will be required to submit a list of three papers that are relevant to the determination of transmissivity NOTE you are not required to formally review these papers however you do need to 18 ME 412 Heat Transfer Laboratory Fall 2010 examine them enough to determine whether or not they are relevant to the topic and be able to summarize that relevancy And finally a patent search can provide useful insight into applications of the parameter being studied You will be required to submit a relevant patent or patent application These can be found in the library or with a Google Scholar search Provide a summary of one patent TASK The student team is to design an experiment that will permit the determination of transmissivity of several nonopaque materials This experiment will be conducted over a two week period By Friday October 29I 2010 the following must be submitted Proposed procedure Including literature review ASTM Standard patent search The proposed procedure must be approved before the group will be allowed to run the experiment Much of the work involved can be performed outside of the lab The lab lecture will review some basic research strategies and will introduce you to the equipment that may be utilized It will be the student s responsibility to review the fundamentals of radiation theory and how it relates to the determination of material properties such as transmissivity and to subsequently develop an experiment that can adequately measure this property A worksheet is included that must be completed and turned in at the beginning of lab lecture The student group will also be expected to justify the merits and validity of this experiment using collected data which might include reproducibility studies comparison to standards and sensitivity to other variables An error analysis will be required to indicate the accuracy of the experiment These tests will be conducted in groups of 23 during the week of November 2I 2010 TA s will be available during the regular labtime to answer questions about equipment however the development of the experiment will be the charge of the student group Students will be schedule to come into lab in shifts the week of November 2I 2010I provided that the groups proposal has been approved This will not necessarily be during the regular laboratory time Some equipment in the lab that may prove useful includes various square metal plates with attached thermocouple A thermopile A hot plate An infrared thermometer A heat flux plate heater Along with these instruments is documentation that may be helpful in designing your experiment 28 ME 412 Heat Transfer Laboratory Fall 2010 Various Metal Plates These square plates are comprised of different textures and colors These plates have a thermocouple attached to one side to allow for temperature measurement The reference end of the thermocouple can be attached to an electronic thermometer that converts the differential voltage reading directly to a temperature Hot Plate This device is simply a flat heater The temperature of the hot plate can be set and the plates placed on top This is the simplest way to raise the temperature of the plate A good starting point for the temperature setting would be 200 C The draw back to using this method is that once the plate is removed it begins to cool resulting is a transient effect which may or may not add complications to designing an experiment Thermopile The thermopile is conical in shape as shown in the Fig 1 and has a heat meter situated at the back end of the cone Heat Meter Figure 1 Sketch of Thermopile Simplistically the heat meter consists of a thin slab of material with thermocouples attached to either side In steady state Fourier s law of heat conduction can be used to show that a linear relationship exists between the temperature difference or voltage difference which can be measured by a multimeter across the slab and the heat flux through the slab This is shown in Fig 2 VtP khmAT tp am but AT olt th sothat X tp if Figure 2 Schematic of Heat Meter 38 ME 412 Heat Transfer Laboratory Fall 2010 Hence the voltage reading from the thermopile is proportional to the heat flux delivered to the back end of the cone By utilizing a cone we have eliminated the possibilities of convection and conduction and thus any heat flux which reaches the heat meter must be radiation Infrared Thermometer The infrared thermometer is a measurement device which allows the emissivity of a surface to be calculated This device will work on any surface but is most reliable for surfaces with high emissivities greater than 09 This thermometer works by measuring the radiation heat flux from a surface It assumes that this surface is a gray surface completely surrounded by black surrounds with the infrared thermometer part of the surrounds By using the gray surface radiation expression qfad 80Tstrface 39 Tstnomds 2 The temperature reading displayed by the infrared thermometer is calculated from this equation using the emissivity set on the device By separately measuring the temperature of the surface say with a thermocouple the emissivity of the surface can be estimated by adjusting the emissivity setting on the infrared thermometer until the temperature reading of the infrared thermometer is equal to the true temperature of the surface Similarly if the emissivity of the surface is known then the radiation heat flux may be calculated from equation 2 using the temperature reading displayed by the infrared thermometer when the emissivity setting is at the true value It is important that the infrared thermometer be aligned to approximately the same spot the surface temperature was recorded To reiterate this device should only be used for surfaces with emissivities greater than 09 to obtain accurate results Heat Flux Plate Heater This device supplies a constant heat flux from a 6quotx 6quot heating unit To operate this device one must turn the powerstat switch and the plate heaterquot switch to on Now the heater is online and can be set to the desired flux level by simply turning the powerstat dial to the left of the switches This dial ranges from 0 to 100 with the setting reflecting a percentage of the maximum heat flux In this case the maximum heat supplied from the heater is 350 watts During lab lecture the equipment available for use will be reviewed and the procedure for operating these devices discussed You should take the opportunity to familiarize yourself with the equipment during this time Several nonopaque testing materials will be provided to guide the development of the experiment Groups must use at least 3 different materials in testing PROCEDURE 1 Before lab lecture read through the experimental write up the sections of the ME 410 textbook indicated above and complete the radiation worksheet The radiation worksheet is to be turned in at the beginning of lab lecture The worksheet will count for maximum of ten points on the technical memo 2 Using online library literature search resources identify 3 three papers associated with the measurement and determination of transmissivity Record and summarize these 3 three citations 48 ME 412 Heat Transfer Laboratory 0 1 U1 0 Fall 2010 Review the use of the ASTM Standards that are attached Go to the library and identify one ASTM standard that is relevant to the measurement of transmissivity You are to provide a brief summary no more than two paragraphs in your own words of the standard Perform a patent search and provide a summary of one relevant patent After reviewing the literature and equipment available design an experimental procedure that can be used to determine the transmissivity of nonopaque materials Draft this procedure prior to experimentation The draft should include group members names TA s name 3 citations and summary of relevant work 1 citation and summary of ASTM standard 1 citation and summary of patent search the step by step procedure Including proposed data to be taken analysis error analysis It must be submitted via email by Friday October 29I 2010 to Dr Genik for review 7 I Go to the lab and try out your experimental procedure and compare your results to anticipated values for transmissivity Record all uncertainties associated with your measurements and perform an error analysis Final memorandum which includes the approved version of step 6 will be due to the TA no later then Monday November 8I 2010 SUGGESTIONS FOR DISCUSSIONS 1 1 Evaluate your experimental design What were the flaws in your experiment What sort of reproducibility does your experimental procedure yield How might you reduce the uncertainty in the determined transmissivities 58 ME 412 Heat Transfer Laboratory Fall 2010 ME 412 Heat Transfer Laboratory Radiation Transmissivity Experiment Grading Sheet Name Name Worksheet 10 Discussion of basic theory 10 Definition of radiative heat transfer transmissivity Clear statement of the problem Procedure 20 Clearly written procedure for conducting the experiment AnalyticalExperimental 30 Results for test run Reproducibility Error analysis Control observations Justification of experimental method chosen Library Search 20 Summary of ASTM Standard Mini literature review 3 citations Patent search Overall Quality 10 Total 100 Comments 68 ME 412 Heat Transfer Laboratory Fall 2010 Radiation Worksheet To Be Completed and Turned In at the Beginning of Lab Lecture will count for maximum of ten points on the technical memo Student Name 1 l O 4 01 O l What is a photon 1 pt Underwhat conditions is radiation heat transfer important 1 pt Write an equation that represents the StefanBoltzman law 1 pt What is transmissivity 1 pt A radiant heater may be considered a gray surface and the room it is occupying may be considered black surrounds If the heater is at 200 C with emissivity 085 and the room walls are at 22 C determine the radiative heat flux away from the heater 2 pts Solar radiation of 300 Wm2 is incident the outside surface of a window with solar transmissivity of 078 What is the value of the radiation heat flux the leaves the inside surface of the window 2 pts What types of measurements will need to be made to determine the transmissivity of a nonopaque material 2 pts 78 Natural Convection Experiment Measurements from a Vertical Surface OBJECTIVE 1 To demonstrate the basic principles of natural convection heat transfer including determination ofthe convective heat transfer coef cient 2 To demonstrate the boundary layer character of external natural convection BACKGROUND Since the density of most uids vary with temperature temperature gradients within a uid medium will give rise to density gradients If these density gradients are such that the fluid is in an unstable situation heavy uid on top of light uid the uid will begin to move This motion is termed natural convection Newton39s law of cooling governs this physical process which states that the heat transfer from the surface is directly proportional to the temperature difference between the surface and the uid far away from the surface or q 0c Tsurface 39 T uid 1 Introducing the convective heat transfer coef cient as the constant of proportionality we have q he Tsurface 39 T uid 2 It is clear that the major obstacle in utilizing Eq 2 for convective heat transfer calculations is the evaluation of the convective heat transfer coef cient There are three standard methods used to evaluate he The rst involves a mathematical solution to the conservation equations in differential form For problems where these equations are too complicated to be solved analytically we can employ the second method a computational solution Finally for problems that are so complicated that we cannot even write the appropriate conservation equations we must go into the laboratory and make measurements in employing an experimental solution Before we contemplate employing one of these solution methods it is useful to use our intuition to gure out upon what the convective heat transfer coefficient depends Our intuition tells us that the three major factors associated with the calculation of hC should be i uid mechanics ii uid transport properties iii geometry Starting with the uid mechanics we recognize there are a variety of ways to characterize the ow We can consider what is driving the ow and classify it as forced or natural convection Next we consider how many boundaries the uid flow interacts with and classify it as external or internal ow Recall that the difference between internal ows and external flows is often one of perspective A third way to characterize the ow is by the presence or absence of turbulence An important consideration in the handling of convective heat transfer coef cients is the notion of dynamic similarity It is found that certain systems in uid mechanics or heat transfer are found to have similar behaviors even though the physical situations may be quite different Recall the uid mechanics of ow in a pipe What we are able to do is to take data as shown in Fig 1 for different uids and pipe diameters and by appropriately scaling collapse these curves into one curve 16 Pressure Drop Friction Factor Veocity Reynolds Num ber Figure 1 Dynamic Similarity for Pipe Flow In convective heat transfer we may apply dynamics scaling to make a parallel transformation Tem perature Difference Rayleigh Num ber Nusslet Number Convective Heat Transfer Coefficient Figure 2 Dynamic Similarity for Convective Heat Transfer We have defined a dimensionless convective heat transfer coef cient called the Nusselt number as th k Nu 3 where he convective heat transfer coef cient L characteristic length k thermal conductivity ofthe M The characteristic length is chosen as the system length that most affects the uid flow For ow along a flat plate our characteristic length is the plate length L and we write th Nu D k 4 The Rayleigh number is indicative ofthe buoyancy force that is driving the flow and is given by 3 2 gain TfL VOL Ra 5 26 where acceleration due to gravity 3 uid thermal expansion coef cient Ts surface temperature Tf uid temperature L characteristic length v uid kinematic viscosity 0c uid thermal diffusivity Another important feature introduced by the fluid mechanics is the local nature of the convective heat transfer coef cient If as the uid flows over different regions of the surface the uid mechanics change then the convective heat transfer coefficient will change For natural convection over a vertical at plate we will have the boundary layer ow shown in Fig 3 Figure 3 Flat Plate Boundary Layer Development As the boundary layer thickness grows the uid mechanics change significantly so that the convective heat transfer coef cient will vary along the length of plate and we will have a local convective heat transfer coefficient hcx Then we may also define local Nusselt and Rayleigh numbers as h NuX 01 X 6 3 Ra gBITsltxgt Tflx 7 VOL Though local heat transfer conditions can be extremely important an average heat transfer coef cient over the entire surface length is often desirable By de nition we have h hcx dx 8 cavg with an average Nusselt Number given as 36 h L NHLavg 9 The dimensionless parameter which is used to represent the affect of uid properties is the Prandtl number Pr X 10 or The in uence of geometry may be seen in a couple of ways First for those configurations that have two length dimensions such as a cylinder we introduce a dimensionless geometric parameter D X L 11 The second way in which we see geometrical in uences is through the functional form of the Nusselt number correlation In general we may write Nu fnRaPrX 12 For simple situations these may often be written as power law relationships Nu a Ran Prm 13 where the constants a m and n will change for different geometries In this experiment the student will develop the relationship among the Nusselt number and other dimensionless parameters for natural convection from a vertical at surface The students will determine local heat transfer coefficients which are indicative ofa boundary layer phenomena These local measurements will then be averaged and compared to published correlations Natural convection heat transfer from a vertical surface will be investigated using an electrically heated flat plate A schematic ofthe apparatus is shown in Figure 4 46 Rotary Selection Switch Power Supply Flat Plate Voltage DMlVl Test Section Current DMM TC DMlVl Figure 4 Schematic of Experimental Apparatus Assuming the heating is uniform the heat ux at any location on the plate is given by 39quot 39 14 q 2WL where V and l are the electric voltage and current supplied to the plate and w and L are the width and length of the heated surface Temperature measurements are made along the length of the plate with thermocouple embedded beneath the heated surface The local heat transfer coef cient the heat transfer coef cient at a certain distance from the leading edge is then calculated as lt1 h cX TSXTf 15 Since in most engineering applications the interest would be in an average heat transfer coef cient for the entire surface we use the mathematical de nition 1 L h0 j l lcX dX 15 L 0 Now substituting and recognizing that the thermocouple is designed to read the temperature difference directly we have 56

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