Fin Convection Experiment

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1 Fin Convection Experiment Thermal Network Solution with TNSolver Bob Cochran Applied Computational Heat Transfer Seattle, WA ME 331 Introduction to Heat Transfer University of Washington November 1, 2016

2 2 / 29 Outline Fin Convection Experiment Math Model Thermal Network Model Analysis Calculations

3 Fins to be Studied Fin Convection Experiment Four uniform cross section fins will be studied Steady state, forced and natural convection Three are circular,, and one is diamond shaped p (a square, rotated 45 ) Fin Material Dimensions k (W/m-K) Aluminum Alloy 6061-T6 0.5 X L Copper Alloy X L Copper Alloy X 6.77 L Stainless Steel Alloy X L / 29

4 Test Fixture Assembly Fin Convection Experiment 4 / 29

5 5 / 29 Measurements Fin Convection Experiment The following measurements are made: Base temperature of the fin Heater power Ambient air temperature Fin temperatures along the length of the fin Thermocouples are located at the center line of the fin Flow velocity for forced convection A typical data set is shown for the aluminum fin, for both forced and natural convection.

6 Temperature (C) 6 / 29 Aluminum Fin - Forced Convection Fin Convection Experiment Heater Power = W Aluminum Fin - Forced Convection Base = (C) TC1 = (C) TC2 = (C) TC3 = (C) TC4 = (C) TC5 = (C) TC6 = (C) Ambient = (C) Time

7 Temperature (C) 7 / 29 Aluminum Fin - Natural Convection Fin Convection Experiment Heater Power = W Aluminum Fin - Natural Convection Base = (C) TC1 = (C) TC2 = (C) TC3 = (C) TC4 = (C) TC5 = (C) TC6 = (C) Ambient = (C) Time

8 8 / 29 Math Model Overview Math Model Conduction Forced Convection Correlations Natural or Free Convection Correlations Surface Radiation

9 9 / 29 Heat Conduction: Cartesian Coordinates (Plane Wall) Math Model The rate of heat transfer, Q ij, due to conduction, between the two temperatures T i and T j, separated by a distance L and area A, is: Q ij = ka ( ) Ti T j L The heat flux, q ij, is: q ij = Q ij A = k ( ) Ti T j L where k is the thermal conductivity of the material.

10 10 / 29 Convection Correlations Math Model The convection heat flow rate is: Q = ha(t s T ) where h is the heat transfer coefficient, T s is the surface temperature and T is the fluid temperature

11 External Forced Convection over a Cylinder Math Model Correlation is (Equation (17.69), page 504 in [KK58]): Nu D hd k = CRem 1/3 D Pr where D is the diameter of the cylinder and the Reynolds number is Re D = ρvd/µ = VD/ν. Re D C m , ,000 40, , , Table 17-5, page 505 in [KK58] 11 / 29

12 12 / 29 External Forced Convection over a Noncircular Cylinder Math Model For the case of a gas flowing over noncircular cylinders in crossflow (see [SAT04]): Geometry Re D C m p D = 2H 2 6,000 60, g D = H 5,000 60, Note that the fluid properties are evaluated at the film temperature, T f : T f = T s + T 2

13 13 / 29 External Natural Convection over a Horizontal Cylinder Math Model Correlation is (see [CC75]): Nu D = hd k = Ra 1/6 D [1 + (0.559/Pr) 9/16] 8/27 valid for Ra D 10 12, Pr 0.7, where D is the diameter of the cylinder and the Rayleigh number, Ra, is: Ra D = GrPr = gρ2 cβd 3 (T s T ) kµ = gβd3 (T s T ) να Note that the fluid properties are evaluated at the film temperature, T f : T f = T s + T 2 2

14 14 / 29 Surface Radiation Math Model Radiation exchange between a surface and large surroundings The heat flow rate is (Equation (1.32), p. 32 in [LL16]): Q = σɛ s A s (T 4 s T 4 sur ) where σ is the Stefan-Boltzmann constant, ɛ s is the surface emissivity and A s is the area of the surface. Note that the surface area, A s, must be much smaller than the surrounding surface area, A sur : A s A sur Note that the temperatures must be the absolute temperature, K or R

15 15 / 29 Radiation Heat Transfer Coefficient Math Model Define the radiation heat transfer coefficient, h r (see Equation (2.29), p. 74 in [LL16]): Then, Note: h r = ɛσ(t s + T sur )(T 2 s + T 2 sur ) Q = h r A s (T s T sur ) h r is temperature dependent h r can be used to compare the radiation to the convection heat transfer from a surface, h (if T sur and T have similar values)

16 h r (W/m 2 -K) 16 / 29 Range of Radiation Heat Transfer Coefficient Math Model Radiation Heat Transfer Coefficient, h r, for T 1 = 25 C s = s = s = s = " T = T s - T 1 (C)

17 17 / 29 Thermal Network Terminology Thermal Network Model Analysis Geometry Control Volume Volume property, V = dv V Node:, T node = T (x V i)dv Control Volume Surface Area property, A = da A Surface Node:, T surface node = T (x A i)da Material properties Conductors Conduction, convection, radiation Boundary conditions Boundary node:

18 TNSolver Input Files Thermal Network Model Analysis The supplied TNSolver input files for each fin model: Fin Forced Convection Natural Convection Aluminum, Al fin FC.inp Al fin NC.inp Round Copper, 6.77 Cu fin FC.inp Cu fin NC.inp Square Copper, sqcu fin FC.inp sqcu fin NC.inp Stainless Steel, SS fin FC.inp SS fin NC.inp Edit each file to set appropriate boundary conditions (Tc, Tr and base) and flow velocities (forced convection models) for your specific experimental data set 18 / 29

19 19 / 29 TNSolver Input Files for Estimating h Thermal Network Model Analysis The supplied TNSolver input files for each fin model to be used with ls fin h.m: Fin Aluminum, Round Copper, 6.77 Square Copper, Stainless Steel, Convection Al fin C.inp Cu fin C.inp sqcu fin C.inp SS fin C.inp Edit each file to set appropriate boundary conditions (Tc, Tr and base) for your specific experimental data set

20 20 / 29 Running a TNSolver Model Thermal Network Model Analysis The MATLAB/Octave command to run the aluminum fin, forced convection model is: >>tnsolver( Al fin FC ); Note that you supply the base of the input file name (AL fin FC, in this example), without the.inp extension The results output file will be the base name with the extension.out (Al fin FC.out, in this example)

21 21 / Fin Thermal Network Model Thermal Network Model Analysis For the long fin, there are six thermocouples: Tc base tip 127 Tc Tr Tr

22 22 / Fin Thermal Network Model Thermal Network Model Analysis For the 6.77 long fin, there are four thermocouples: Tc base tip 125 Tc Tr 221 Tr

23 23 / 29 Surface Radiation Properties Thermal Network Model Analysis Fin Material Emissivity, ɛ (dimensionless) Aluminum Alloy 6061-T Copper Alloy Stainless Steel Alloy See Table 10.1, page 530, in [LL16]

24 24 / 29 Verification with Analytical Solution Thermal Network Model Analysis Table 3.4, page 161 in [BLID11], Temperature distribution and heat loss for fins with a uniform cross section Case Tip Condition Temperature, θ/θ b Fin Heat Transfer Rate, Q A Convection cosh m(l x)+(h/mk) sinh m(l x) sinh ml+(h/mk) cosh ml cosh ml+(h/mk) sinh ml M cosh ml+(h/mk) sinh ml cosh m(l x) cosh ml M tanh ml (θ L /θ b ) sinh mx+sinh m(l x) sinh ml M cosh ml (θ L/θ b ) sinh ml B Adiabatic C Specified T D L = e mx M θ = T T m = hp/ka c θ b = θ(0) = T b T M = ( hpka c )θ b For circular fins: P = πd and A c = π(d/2) 2 For square/diamond fins: P = 4H and A c = H 2

25 Temperature (C) 25 / 29 Comparison with TNSolver Network Model Thermal Network Model Analysis 50 1/2" Diameter Fin, Case A Tip, h = 55.0 W/m2 -K SS, Q = W Aluminum, Q = W Copper, Q = W TNSolver SS, Q = 1.14 W TNSolver Al, Q = 5.1 W TNSolver Cu, Q = 7.7 W x (m)

26 26 / 29 Calculations Calculations For the four forced convection experimental data sets: 1. Using forced convection correlations, determine h and h r for each fin EFCcyl and EFCdiamond conductors 2. Using least-squares fit, estimate ɛ, using forced convection correlations ls fin emiss.m function 3. Using least-squares fit, estimate h, using estimated ɛ and forced convection correlations ls fin h.m function How does the estimated h compare to the correlation? How does the estimated ɛ compare to the material property table value?

27 27 / 29 Calculations (continued) Calculations For four free convection experimental data sets: 1. Using free convection correlations, determine h and h r for each fin ENChcyl conductor 2. Using least-squares fit, estimate ɛ, using free convection correlation ls fin emiss.m function 3. Using least-squares fit, estimate h, using estimated ɛ and free convection correlation ls fin h.m function How does the estimated h compare to the correlation? How does the estimated ɛ compare to the material property table value?

28 28 / 29 Least Squares Estimation Calculations Least squares estimation of a parameter θ, for n data points, is: R = n i=1 ( ) 2 θexp i θmodel i The closest model parameter is determined by the index i, of the minimum R Function to estimate emissivity, ɛ, is: ls fin emiss.m Function to estimate convection coefficent, h, is: ls fin h.m

29 29 / 29 Conclusion Fin convection experiment overview Conduction, convection and surface radiation math model Thermal network model analysis Calculations using the experimental data Questions?

30 Appendix 30 / 29

31 31 / 29 Heat Transfer Analysis Thermal Network Model Energy conservation: control volumes Identify and sketch out the control volumes Use the conductor analogy to represent energy transfer between the control volumes and energy generation or storage Conduction, convection, radiation, other? Capacitance Sources or sinks State assumptions and determine appropriate parameters for each conductor Geometry, material properties, etc. Which conductor(s)/source(s)/capacitance(s) are important to the required results? Sensitivity analysis What is missing from the model? - peer/expert review

32 32 / 29 Thermal Network Terminology Thermal Network Model Geometry Control Volume Volume property, V = dv V Node:, T node = T (x V i)dv Control Volume Surface Area property, A = da A Surface Node:, T surface node = T (x A i)da Material properties Conductors Conduction, convection, radiation Boundary conditions Boundary node:

33 33 / 29 Thermal Network Analysis Thermal Network Model For the long fin, there are six thermocouples: Tc base tip 127 Tc Tr Tr

34 34 / 29 Thermal Network Analysis Thermal Network Model For the 6.77 long fin, there are four thermocouples: Tc base tip 125 Tc Tr 221 Tr

35 35 / 29 Control Volume Geometry Thermal Network Model Scale drawing of thermocouple locations and control volume lengths: base tip Fin Dimensions (m) base tip Fin Dimensions (m) Note that the control volume boundaries are located midway between the thermocouple locations

36 Round Fin, Long, Conduction Geometry Thermal Network Model Axial conduction in the fin, L = = m D = 0.5 = m and r = 0.25 = m: L = distance between TC A = πr 2 Conductor Length (m) A (m 2 ) / 29

37 Round Fin, Long, Convection Geometry Thermal Network Model Surface convection area: D = 0.5 = m A = L CV P = L CV πd Conductor L CV (m) A (m 2 ) / 29

38 Round Fin, 6.77 Long, Conduction Geometry Thermal Network Model Axial conduction in the fin, L = 6.77 = m D = 0.5 = m and r = 0.25 = m: L = distance between TC A = πr 2 Conductor Length (m) A (m 2 ) / 29

39 Round Fin, 6.77 Long, Convection Geometry Thermal Network Model Surface convection area: D = 0.5 = m A = L CV P = L CV πd Conductor L CV (m) A (m 2 ) / 29

40 Square Fin, Long, Conduction Geometry Thermal Network Model Axial conduction in the fin, L = = m, H = 0.5 = m L = distance between TC A = H 2 Conductor Length (m) A (m 2 ) / 29

41 Square Fin, Long, Convection Geometry Thermal Network Model Surface convection area: H = 0.5 = m A = L CV P = L CV 4H Conductor L CV (m) A (m 2 ) / 29

42 42 / 29 Conduction Conductor Thermal Network Model Q ij = ka L (T i T j ) Begin Conductors! label type nd_i nd_j k L A 100 conduction base 1 x.x conduction 1 2 x.x conduction 2 3 x.x conduction 3 4 x.x conduction 4 5 x.x conduction 5 6 x.x conduction 6 tip x.x End Conductors

43 43 / 29 Convection Conductor Thermal Network Model Q ij = ha(t s T ) = ha(t i T j ) Begin Conductors! label type nd_i nd_j h A 121 convection 1 Tc x.x convection 2 Tc x.x convection 3 Tc x.x convection 4 Tc x.x convection 5 Tc x.x convection 6 Tc x.x convection tip Tc x.x End Conductors

44 44 / 29 Forced Convection Over Cylinder Conductor Thermal Network Model Heat transfer coefficient, h, is evaluated using the correlation. Begin Conductors! label type nd_i nd_j fluid V D A 121 EFCcyl 1 Tc air x.x EFCcyl 2 Tc air x.x EFCcyl 3 Tc air x.x EFCcyl 4 Tc air x.x EFCcyl 5 Tc air x.x EFCcyl 6 Tc air x.x EFCcyl tip Tc air x.x End Conductors Note that Re, Nu and h are reported in the output file.

45 45 / 29 Forced Convection Over Diamond Conductor Thermal Network Model Heat transfer coefficient, h, is evaluated using the correlation. Begin Conductors! label type nd_i nd_j fluid V D A 121 EFCdiamond 1 Tc air x.x EFCdiamond 2 Tc air x.x EFCdiamond 3 Tc air x.x EFCdiamond 4 Tc air x.x EFCdiamond 5 Tc air x.x EFCdiamond 6 Tc air x.x EFCdiamond tip Tc air x.x End Conductors Note that Re, Nu and h are reported in the output file.

46 46 / 29 Natural Convection Conductor Thermal Network Model Heat transfer coefficient, h, is evaluated using the correlation. Begin Conductors! label type nd_i nd_j fluid D A 121 ENChcyl 1 Tc air ENChcyl 2 Tc air ENChcyl 3 Tc air ENChcyl 4 Tc air ENChcyl 5 Tc air ENChcyl 6 Tc air ENChcyl tip Tc air End Conductors Note that Ra, Nu and h are reported in the output file.

47 47 / 29 Surface Radiation Conductor Thermal Network Model Q ij = σɛ i A i (T 4 i T 4 j ) Begin Conductors! label type nd_i nd_j emissivity A 221 surfrad 1 Tr x.xx surfrad 2 Tr x.xx surfrad 3 Tr x.xx surfrad 4 Tr x.xx surfrad 5 Tr x.xx surfrad 6 Tr x.xx surfrad tip Tr x.xx End Conductors Note that h r is reported in the output file.

48 48 / 29 Boundary Conditions Thermal Network Model Begin Boundary Conditions! type Tb Node(s) fixed_t x.xx Tc! fluid T fixed_t x.xx Tr! surrounding radiation T fixed_t x.xx base! fin base T End Boundary Conditions

49 TNSolver Input Files Thermal Network Model The supplied TNSolver input files for each fin model: Fin Forced Convection Natural Convection Aluminum, Al fin FC.inp Al fin NC.inp Round Copper, 6.77 Cu fin FC.inp Cu fin NC.inp Square Copper, sqcu fin FC.inp sqcu fin NC.inp Stainless Steel, SS fin FC.inp SS fin NC.inp Edit each file to set appropriate boundary conditions (Tc, Tr and base) and flow velocities (forced convection models) for your specific experimental data set 49 / 29

50 50 / 29 Running a TNSolver Model Thermal Network Model The MATLAB/Octave command to run the aluminum fin, forced convection model is: >>tnsolver( Al fin FC ); Note that you supply the base of the input file name (AL fin FC, in this example), without the.inp extension The results output file will be the base name with the extension.out (Al fin FC.out, in this example)

51 51 / 29 Screen Output When Running TNSolver Thermal Network Model ********************************************************** * * * TNSolver - A Thermal Network Solver * * * * Version 0.2.0, October 28, 2014 * * * ********************************************************** Reading the input file: Al_fin_FC.inp Initializing the thermal network model... Starting solution of a steady thermal network model... Nonlinear Solve Iteration Residual e e-09 Results have been written to: Al_fin_FC.out All done...

52 52 / 29 View TNSolver Output File For Results Thermal Network Model Open Al fin FC.out in your favorite text editor ********************************************************** * * * TNSolver - A Thermal Network Solver * * * * Version 0.2.0, October 28, 2014 * * * ********************************************************** Model run finished at 10:05 AM, on October 29, 2014 *** Solution Parameters *** Title: Aluminum Fin - Forced Convection Type = steady Units = SI Temperature units = C Nonlinear convergence = 1e-008 Maximum nonlinear iterations = 15 Gravity = (m/sˆ2) Stefan-Boltzmann constant = e-008 (W/mˆ2-Kˆ4)

53 53 / 29 View TNSolver Output File For Results (continued) Thermal Network Model *** Nodes *** Volume Temperature Label Material (mˆ3) (C) N/A N/A N/A N/A N/A N/A Tc N/A 0 25 Tr N/A 0 25 base N/A tip N/A

54 54 / 29 View TNSolver Output File For Results (continued) Thermal Network Model *** Conductors *** Q_ij Label Type Node i Node j (W) conduction base conduction conduction conduction conduction conduction conduction 6 tip EFCcyl 1 Tc EFCcyl 2 Tc EFCcyl 3 Tc EFCcyl 4 Tc EFCcyl 5 Tc EFCcyl 6 Tc EFCcyl tip Tc surfrad 1 Tr surfrad 2 Tr surfrad 3 Tr surfrad 4 Tr surfrad 5 Tr surfrad 6 Tr surfrad tip Tr

55 55 / 29 View TNSolver Output File For Results (continued) Thermal Network Model *** Conductor Parameters *** surfrad: Surface Radiation h_r label (W/mˆ2-K) EFCcyl: External Forced Convection - Cylinder h label Re Number Nu Number (W/mˆ2-K)

56 56 / 29 References I [BLID11] T.L. Bergman, A.S. Lavine, F.P. Incropera, and D.P. DeWitt. Introduction to Heat Transfer. John Wiley & Sons, New York, sixth edition, [CC75] [KK58] Stuart W. Churchill and Humbert H.S. Chu. Correlating equations for laminar and turbulent free convection from a horizontal cylinder. International Journal of Heat and Mass Transfer, 18(9): , J. G. Knudsen and D. L. Katz. Fluid Dynamics and Heat Transfer. McGraw-Hill, New York, 1958.

57 57 / 29 References II [LL16] J. H. Lienhard, IV and J. H. Lienhard, V. A Heat Transfer Textbook. Phlogiston Press, Cambridge, Massachusetts, fourth edition, Available at: [SAT04] Ephraim M. Sparrow, John P. Abraham, and Jimmy C.K. Tong. Archival correlations for average heat transfer coefficients for non-circular and circular cylinders and for spheres in cross-flow. International Journal of Heat and Mass Transfer, 47: , 2004.

Fin Convection Experiment

Fin Convection Experiment Thermal Network Solution with TNSolver Bob Cochran Applied Computational Heat Transfer Seattle, WA TNSolver@heattransfer.org ME 331 Introduction to Heat Transfer University of