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Structural and Thermal Calculation for Recuperative Heat Exchanger

Structural and Thermal Calculation for Recuperative Heat Exchanger. Presented by -- Jinying Zhu. Review:. The size of duct: 200μm*200μm Duct number: 200*200 Material: SS 304. Allowable stress (MPa) : 206.84 Young’s Modulus (GPa) : 193.05.

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Structural and Thermal Calculation for Recuperative Heat Exchanger

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  1. Structural and Thermal Calculation for Recuperative Heat Exchanger Presented by -- Jinying Zhu

  2. Review: • The size of duct: 200μm*200μm • Duct number: 200*200 • Material: SS 304 Allowable stress (MPa) : 206.84 Young’s Modulus (GPa) : 193.05 Structural calculation result: (the weakest part--connector) Thickness(μm) max. stress (MPa) max.displacement(μm) 200 215 2.23 300 190 2.80

  3. Thermal calculation: Thickness (μm ) Length (cm) Effectiveness 200 30 90.31% 300 30 90.00% • Analysis: • Relatively high thermal conductivity of SS 304 (12.31W/mK) leads to low effectiveness. • To use other materials with low thermal conductivity and high strength (LTCC is our choice)

  4. Low temperature co-fired ceramic -- LTCC Characteristics: • Soft, pliable and easily dissolved and abrade in the green state. • After the material is fired and fully sintered, it becomes tough and rigid. • Relatively high strength and wide range of conductivity • Easy to machine the tape in the green state with the size of 10 μm to 10 mm • Layer number can be high

  5. Micromachining of LTCC tape • Conventional method: punch and die process (the line with the width of 25 μm has been machined) • Numerically controlled (CNC) milling method (It has been used and obtain the feature size of 100 μm) • Chemical machining: jet vapor etching (The technique allows to manufacture a wide variety of shapes, and holes with the diameter of 25 μm have been obtained) • Laser machining

  6. Low temperature co-fired ceramic (LTCC): Industry LTCC material with their corresponding material properties: material Flexural Strength Young’s Modulus Thermal conductivity (MPa) (GPa) (W/mK) G55* 200 110 2.5 951* 320 152 3.0 A6* 210 92 2.0 A473 314 265 16.7 AN242 400 320 150

  7. Optimization analysis: • The thicker the walls are, the narrower the channels are. • As far as the smooth of channel is concerned, we hope a wider channel. • Considering the limitation of machining of LTCC tape, we also hope a wider channel. • The wall cannot be too thin due to stress and displacement. • Base on the above consideration, we choose the material 951, and use the wall with the thickness of 200 µm.

  8. LTCC fabrication process: Pre-condition (machining registration hole and via hole Layer n Layer 1 Layer 2 Structure formation Structure formation Structure formation Via filling Via filling Via filling Collating and stacking laminating Co-firing inspection

  9. Thermal calculation result: Thermal conductivity Length T (cold side out) T(hot side out) effectiveness 3 W/mK 25cm 296.96 K 78.036 K 97.8%

  10. Structural calculation result: (for connector) Material flexural strength Thickness max. stress max. displacement (MPa) (μm) (MPa) (μm) 951 320 200 215 2.95

  11. Structural calculation result: (for main heat exchanger part) Material flexural strength Thickness max. stress max. displacement (MPa) (μm) (MPa) (μm) 951 320 200 5.96 2.95*10-3

  12. Future work: ? Check the thermal calculation ? Check the structural calculation ? Structure design in detail

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