NSTX OH Coil Optimization Ali Zolfaghari Amir Salehzadeh

Optimization Parameters: Coolant channel diameter –Large coolant diameter leads to: Higher resistance and ohmic heating. Higher coil voltage and turn-to-turn voltage gradients. More efficient cooling –Smaller coolant diameter leads to: Lower resistance and ohmic heating. Higher coil voltage and turn-to-turn voltage gradients. Longer cooling time

Possible Approaches: 0D analysis with closed form formulas for turbulent flow and heat transfer. Crude method, but useful for trade-off study. Got the Mathcad files from Mike Kalish. Finite section (node) transient simulation of flow parameters and cooling along the conductor length. Fcool program from Fred Dahlgren. Coupled 3D CFD/Heat transfer simulation of coolant flow and conjugate heat transfer. We started with this approach.

Coupled CFD/Heat Transfer Ansys multiphysics/CFD is used to model the turbulent flow and heat transfer as well as heat conduction in solid. Initial conditions for the solid to be cooled are simulated first using the pulse current profile as energy source. Copper will be heated and will reach a temperature profile. This serves as the initial condition for the transient CFD/Heat transfer simulation of cooling.

NSTX OH Coil Optimization Coil geometry was brought into Ansys from Pro/E using STEP format. It was determined that for meshing simplicity and with negligible loss of accuracy the coil can be modeled as a straight conductor.

t=200 sec Coil temperature profile

t=500 sec

t=800 sec

t=1800 sec

Fcool program results for the same case

Fcool program results for CSU with in. hole diameter

Fcool program results for CSU with 0.25 in. hole diameter

Fcool results for CSU with 0.25 in. hole diameter, 480 PSI

What is next: Need to know the trade offs and parameter limits. –Pump Gallon per Minute –Pressure drop –Total coil voltage vs. the supply –Interaction of R and L (e.g. decay time) –Turn-turn voltage stress limit –Acceptable and desired cooling time