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

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

Thermal calculation: Thickness (μm ) Length (cm) Effectiveness % % 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)

Low temperature co-fired ceramic -- LTCC Low temperature co-fired ceramic -- LTCC 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 Characteristics:

Micromachining of LTCC tape 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

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* * A6* A AN

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.

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

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

Structural calculation result: (for connector) Material flexural strength Thickness max. stress max. displacement (MPa) (μm) (MPa) (μm)

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

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