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Mech_HT_18.0_WS04.1_Radiating_System.pdf

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This document describes a workshop analyzing heat transfer in a fin and tube heat exchanger. A 90 degree section of an aluminum fin and tube structure is modeled. The interior tube wall is set to 300C. Both convection and radiation boundary conditions are applied to the exterior surfaces to evaluate their impact on heat losses. The model is meshed, loads are applied, and the solution is obtained and evaluated. Radiation accounts for approximately 2.7% of total heat losses from the system. An extra challenge is provided to convert the radiation boundary condition to a surface-to-surface model.

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1 息 2017 ANSYS, Inc. May 10, 2017 Workshop 04.1: Radiating System 18.0 Release ANSYS Mechanical Heat Transfer
2 息 2017 ANSYS, Inc. May 10, 2017 Problem Description An aluminum section of a fin and tube heat exchanger is to be analyzed. Since the model represents an axially symmetric structure, a 90 degree section will be modeled. The tube carries a contained hot fluid and the interior wall is assumed to be at 300C. The exterior surfaces experience a convective condition. We will add both convection and radiation boundary conditions on the exterior surfaces to evaluate the impact of heat losses due to each mode of heat transfer.
3 息 2017 ANSYS, Inc. May 10, 2017 Open Workbench and specify the unit system: Metric (kg, mm, s, 尊C, mA, N, mV) Choose to Display Values in Project Units Units Setup
4 息 2017 ANSYS, Inc. May 10, 2017 Open the Workbench Project Schematic and choose a Steady State Thermal analysis system from the toolbox. Highlight the Geometry branch, RMB, select Import geometry and Browse ..., to file Fin_Tube_WS04.1.stp. Double Click the Engineering Data cell. Model Setup
5 息 2017 ANSYS, Inc. May 10, 2017 You will be in the Engineering Data Application tab. Activate the Engineering Data Sources toggle and highlight General Materials. Add Aluminum Alloy to the current project by pressing the Add button. Return to Project by pressing the Project tab. Double click the Model cell to open the Mechanical application. Model Setup
6 息 2017 ANSYS, Inc. May 10, 2017 Expand the Geometry branch and highlight the part FinTube. In the details change the material assignment to Aluminum Alloy. A check in engineering data will confirm the aluminums thermal conductivity property is temperature dependent. Preprocessing
7 息 2017 ANSYS, Inc. May 10, 2017 Highlight the mesh branch. Select the 2 symmetry faces, RMB > Insert > Sizing. Set Element Size to 2 mm. Highlight the mesh branch, RMB > Generate Mesh. Preprocessing
8 息 2017 ANSYS, Inc. May 10, 2017 Highlight the Steady State Thermal branch. Highlight the interior wall of the tube section, RMB > Insert > Temperature. In the details for the temperature load enter 300 属C in the Magnitude field. Preprocessing
9 息 2017 ANSYS, Inc. May 10, 2017 Make sure surface select mode is active. In the graphics window, RMB > Select All. Use the control key and unselect the interior, ends and symmetry faces of the fin tube model (5 faces in all). You should have 33 faces selected. RMB > Insert > Convection. Continued . . . Preprocessing
10 息 2017 ANSYS, Inc. May 10, 2017 Enter a Film Coefficient = 5e-4 W/(mm^2-C) . Enter Ambient Temperature = 30C. Repeat selection steps from previous slide (select 33 faces) RMB > Insert > Radiation. Enter Ambient Temperature = 30属C. Leave Emissivity = 1. Leave Correlation = To Ambient. Preprocessing
11 息 2017 ANSYS, Inc. May 10, 2017 Rt Rc Rr = Rtot 4785.2 4657.8 127.43 = -0.03 Solve: Highlight the Temperature, Convection and Radiation loads and drag and drop them into the Solution branch, RMB > evaluate all results: This is a shortcut to setting up reaction probes for boundary conditions. Insert a Chart with these three results selected, then the results will be combined into a single chart & table. Analysis shows we have an energy balance. Reactions show that radiation accounts for roughly 2.7% of heat losses from the system. Solution
12 息 2017 ANSYS, Inc. May 10, 2017 If you have extra time, attempt to convert the To-Ambient radiation thermal boundary condition to Surface-to-Surface (i.e. radiosity solver), as discussed earlier. Hints: a) You will need to establish a Symmetry condition (Periodic Region or Cyclic Region with a cylindrical coordinate system) to achieve the proper view factors. b) The enclosure should be open because the radiative loss to ambient dominates. c) Net loss due to radiation should be similar to the To Ambient results obtained before. Extra Challenge

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Mech_HT_18.0_WS04.1_Radiating_System.pdf

  • 1. 1 息 2017 ANSYS, Inc. May 10, 2017 Workshop 04.1: Radiating System 18.0 Release ANSYS Mechanical Heat Transfer
  • 2. 2 息 2017 ANSYS, Inc. May 10, 2017 Problem Description An aluminum section of a fin and tube heat exchanger is to be analyzed. Since the model represents an axially symmetric structure, a 90 degree section will be modeled. The tube carries a contained hot fluid and the interior wall is assumed to be at 300C. The exterior surfaces experience a convective condition. We will add both convection and radiation boundary conditions on the exterior surfaces to evaluate the impact of heat losses due to each mode of heat transfer.
  • 3. 3 息 2017 ANSYS, Inc. May 10, 2017 Open Workbench and specify the unit system: Metric (kg, mm, s, 尊C, mA, N, mV) Choose to Display Values in Project Units Units Setup
  • 4. 4 息 2017 ANSYS, Inc. May 10, 2017 Open the Workbench Project Schematic and choose a Steady State Thermal analysis system from the toolbox. Highlight the Geometry branch, RMB, select Import geometry and Browse ..., to file Fin_Tube_WS04.1.stp. Double Click the Engineering Data cell. Model Setup
  • 5. 5 息 2017 ANSYS, Inc. May 10, 2017 You will be in the Engineering Data Application tab. Activate the Engineering Data Sources toggle and highlight General Materials. Add Aluminum Alloy to the current project by pressing the Add button. Return to Project by pressing the Project tab. Double click the Model cell to open the Mechanical application. Model Setup
  • 6. 6 息 2017 ANSYS, Inc. May 10, 2017 Expand the Geometry branch and highlight the part FinTube. In the details change the material assignment to Aluminum Alloy. A check in engineering data will confirm the aluminums thermal conductivity property is temperature dependent. Preprocessing
  • 7. 7 息 2017 ANSYS, Inc. May 10, 2017 Highlight the mesh branch. Select the 2 symmetry faces, RMB > Insert > Sizing. Set Element Size to 2 mm. Highlight the mesh branch, RMB > Generate Mesh. Preprocessing
  • 8. 8 息 2017 ANSYS, Inc. May 10, 2017 Highlight the Steady State Thermal branch. Highlight the interior wall of the tube section, RMB > Insert > Temperature. In the details for the temperature load enter 300 属C in the Magnitude field. Preprocessing
  • 9. 9 息 2017 ANSYS, Inc. May 10, 2017 Make sure surface select mode is active. In the graphics window, RMB > Select All. Use the control key and unselect the interior, ends and symmetry faces of the fin tube model (5 faces in all). You should have 33 faces selected. RMB > Insert > Convection. Continued . . . Preprocessing
  • 10. 10 息 2017 ANSYS, Inc. May 10, 2017 Enter a Film Coefficient = 5e-4 W/(mm^2-C) . Enter Ambient Temperature = 30C. Repeat selection steps from previous slide (select 33 faces) RMB > Insert > Radiation. Enter Ambient Temperature = 30属C. Leave Emissivity = 1. Leave Correlation = To Ambient. Preprocessing
  • 11. 11 息 2017 ANSYS, Inc. May 10, 2017 Rt Rc Rr = Rtot 4785.2 4657.8 127.43 = -0.03 Solve: Highlight the Temperature, Convection and Radiation loads and drag and drop them into the Solution branch, RMB > evaluate all results: This is a shortcut to setting up reaction probes for boundary conditions. Insert a Chart with these three results selected, then the results will be combined into a single chart & table. Analysis shows we have an energy balance. Reactions show that radiation accounts for roughly 2.7% of heat losses from the system. Solution
  • 12. 12 息 2017 ANSYS, Inc. May 10, 2017 If you have extra time, attempt to convert the To-Ambient radiation thermal boundary condition to Surface-to-Surface (i.e. radiosity solver), as discussed earlier. Hints: a) You will need to establish a Symmetry condition (Periodic Region or Cyclic Region with a cylindrical coordinate system) to achieve the proper view factors. b) The enclosure should be open because the radiative loss to ambient dominates. c) Net loss due to radiation should be similar to the To Ambient results obtained before. Extra Challenge