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NA62 CO 2 Cooling - Microchannels Analysis-

NA62 CO 2 Cooling - Microchannels Analysis-. Boundary Conditions. 2-Phase correlation is valid for heat fluxes within the range of 1.8 to 46kW/m 2 and tube diameters of 0.6 to 10mm Sensor h eat flux = 4W/cm 2 = 40kW/m 2 Sensor dimensions = 6 x 60mm Maximum channel h eight = 250 μ m

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NA62 CO 2 Cooling - Microchannels Analysis-

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  1. NA62 CO2Cooling- Microchannels Analysis- João Noite PH-CMX-DS

  2. Boundary Conditions • 2-Phase correlation is valid for heat fluxes within the range of 1.8 to 46kW/m2 and tube diameters of 0.6 to 10mm • Sensor heat flux = 4W/cm2 = 40kW/m2 • Sensor dimensions = 6 x 60mm • Maximum channel height = 250μm • Evaporator thickness = 380μm • Calculated square channel sizes: 250, 200, 150 and 100μm • Equivalent diameter sizes: 0.28, 0.22, 0.17 and 0.11mm • Channel length = 40mm (to save space for manifold). João Noite PH-CMX-DS

  3. 250 μm Channel • Observations: • Stratified wavy flow regime has low HTC. • Low HTC increases the temperature gradually along channel length. • ΔT is more than 5°C due to low HTC. • Mass flow of 0.008g/s has to be increased to be able to reach annular flow. João Noite PH-CMX-DS

  4. 250 μm Channel • Observations: • Flow increased to 0.016g/s. • Although the Annular flow regime is now present, it’s very close to Stratified-Wavy flow. • Maximum ΔT across the channel is 3.21°C due to HTC. João Noite PH-CMX-DS

  5. 200 μm Channel • Observations: • Decreasing the size of the channel from 250 to 200μm doesn’t seem to affect the ΔP. • The flow regime is now clearly Annular. • Maximum ΔT across the channel is 3.21°C due to CO2 HTC. • ΔT along the length of the channel is negligible, due to very low ΔP. • This is a good example for the channel size. João Noite PH-CMX-DS

  6. 150 μm Channel • Observations: • Decreasing the size of the channel from 200 to 150μm shows a ΔT along the length of about 1°C due to increased ΔP. • The flow regime is still clearly Annular. • Maximum ΔT across the channel is slightly increased to 3.27°C due to CO2 HTC. João Noite PH-CMX-DS

  7. 100 μm Channel • Observations: • As said, decreasing the size of the channel increases ΔP. • When ΔP increases the evaporator temperature gradient increases and it can also can be flooded with sub cooled liquid. • The presence of liquid will increase the temperature in the first section of the channel until it starts boiling. João Noite PH-CMX-DS

  8. Conclusions • This is a preliminary study. • Inlet restriction for flow balance has not been done. Inlet ΔP should not be considered in this exercise. • Annular flow regime has optimum HTC. • Required mass flow should be enough for the presence of this regime. • Increasing mass flow to assure the presence of this regime will reduce vapor quality and in some cases increase ΔP. This has to be carefully tuned to avoid the presence of sub-cooled liquid in the evaporator. Sub-cooled liquid has a low HTC when compared with 2-phase. • Increasing ΔP will therefore increase ΔT. • Depending on the size, the heat flow on each channel will be between 0.56 and 1.41W. • Channel size of 200x200μm shows good performance. • 200x200μm channel results in 14 parallel channels per evaporator. João Noite PH-CMX-DS

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