Optimasi Kinerja Termohidrolik Model Konseptual Shell-and-Tube Heat Exchanger dengan Baffle Perforasi pada Molten Salt Fast Reactor Berbasis Computational Fluid Dynamics

Gian Fadhlurrahman, Prof. Dr. Ir. Andang Widi Harto, M.T., IPU., ASEAN Eng.; Ir. Kutut Suryopratomo, M.T., M.Sc.

2026 | Skripsi | TEKNIK NUKLIR

Molten salt menawarkan stabilitas termal tinggi sebagai fluida kerja, seperti pada Molten Salt Fast Reactor (MSFR) dengan bahan bakar dan pendingin, LiF–ThF4–UF4 dan LiF–NaF–KF. Shell-and-tube heat exchanger (STHE) sebagai konfigurasi umum, krusial terhadap desain daya MSFR dan sangat dipengaruhi oleh rancangan baffle yang mengatur pola aliran sisi shell. Tujuan studi ini adalah mengetahui efek baffle berperforasi pada model konseptual dan menentukan kompromi terbaik antara nilai perpindahan kalor dan pressure drop (Delta-p).

Penelitian CFD menggunakan ANSYS Fluent dengan solver k-epsilon realizable pada geometri STHE 20 tube. Studi independensi mesh dilakukan hingga perubahan Tout-shell sudah tidak signifikan dan kualitas mesh baik. Untuk verifikasi model dilakukan dengan metode Kern dan Bell-Delaware. Variasi utama adalah baffle segmental dengan 24 perforasi berdiameter 4, 5, dan 6 mm dengan laju alir massa divariasikan 2, 5, dan 10 kg/s dalam rejim turbulen.

Hasil menunjukkan perforasi secara efektif mengurangi area dead zone dan Delta-p dengan penalti termal kecil. Pada 10 kg/s, Delta-p turun 49% (4 mm), 62% (5 mm), dan 73% (6 mm), sementara h-shell hanya turun sekitar 23%. Indeks kinerja termohidrolik (Q/PP)m/(Q/PP)/b tertinggi konsisten pada modifikasi perforasi 6 mm sebesar 3,5 relatif terhadap non-perforasi baseline sehingga menjadikannya desain optimum.

Molten salts offer high thermal stability as working fluids, as in the Molten Salt Fast Reactor (MSFR) employing fuel and coolant salts LiF–ThF4–UF4 and LiF–NaF–KF, respectively. The shell-and-tube heat exchanger (STHE), as a common configuration, is crucial for MSFR power design and is strongly influenced by the baffle arrangement that controls the shell-side flow pattern. This study aims to investigate the effect of perforated baffles in a conceptual STHE model and to determine the best compromise between heat transfer performance and pressure drop (Delta-p).

3D CFD simulations were carried out in ANSYS Fluent using the realizable k-epsilon turbulence model on an STHE geometry with 20 tubes. A mesh-independence study was performed until changes in shell outlet temperature were negligible and the mesh quality was satisfactory. Model verification was conducted using the Kern and Bell–Delaware methods. The main variations are segmental baffles with 24 perforations of 4, 5, and 6 mm in diameter, at mass flow rates of 2, 5, and 10 kg/s in turbulent regime.

The results show that perforations effectively reduce dead-zone regions and Delta-p with only a minor thermal penalty. At 10 kg/s, Delta-p decreases by 49% (4 mm), 62% (5 mm), and 73% (6 mm), while h-shell decreases by around 23%. The highest thermohydraulic performance index, defined as (Q/PP)m/(Q/PP)b, is consistently obtained for the 6 mm perforated baffle with a value of 3.5 relative to the non perforated baseline, making it the optimum design.

Kata Kunci : baffle perforasi, CFD, kinerja termohidrolik, molten salt, penukar kalor