Design of Recuperative Heat Exchanger Presented by -- Jinying Zhu

Review: The material: LTCC (may use Dupont 951) Properties: - Flexural Strength: 320 MPa - Young’s Modulus: 152 GPa - Thermal Conductivity: 3 W/mK The size of recuperative heat exchanger - about 8cm×8cm×25cm

Review: 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: Material flexural strength Thickness max. stress max. displacement (MPa) (μm) (MPa) (μm)

The bonding concept for LTCC: 700 °C --- transition temperature of glass 800 °C --- the glass begin to flow and surround the grains of ceramic, joining them together 850 °C ---the glass will completely surround the grains and bond them strongly

The bonding concept for LTCC:

Problems and shortcoming: It is difficult for the vapor produced during heating to escape It is difficult to heat the recuperator uniformly because of the large size The wall thickness was chosen to be 200 μm because of the high differential pressure of JT - This maybe unnecessary Axial heat conduction is playing an important role for the 200 μm wall

Problems and shortcoming: Temperature along the length for 200μm wall thickness

Solution: Wall thickness: 50μm (using thinner wall will also reduce the size of the recuperator) Δp: 4 bars (lower due to the lower differential pressure of the centrifugal compressor) It is very important to reduce axial conduction. To reduce the axial conduction: Grid number: 100×100 Size: about 2.5cm × 2.5cm × 8cm To reduce the size:

Calculation results: Structural calculation: -- Max. stress: 200 MPa -- Max. displacement: 5.02 μm Thermal calculation: dT (K) T cold side out (K) T hot side out (K) efficiency (%)

Calculation results: Temperature along the length:

Future Work: To confirm the validity of structure design To work with Dr. An in fabricating the LTCC recuperator