Comparison of swirl tube and hypervapotron for cooling of ITER divertor

The ITER divertor will have a peak steady state heat flux of 5 MW/m/sup 2/ and a heat flux of 15 MW/m/sup 2/ for up to 10 s duration. Cooling will be provided by water at an inlet temperature of 150/spl deg/C and a pressure of 4 MPa. A heat transfer enhancement technique is required in order to achieve a sufficient margin on critical heat flux at a reasonable flow velocity. Hypervapotron (KV) and swirl tube (ST) are under consideration as enhancement methods. There are many fundamental differences between these two devices, such as: (a) The ratio of surface heat flux to coolant channel heat flux, (b) the flow area per unit heat flux area, (c) critical heat flux (CHF) and (d) the pressure drop. This paper presents new CHF correlations for ST and HV concepts and compares them to the available experimental data. The friction factor correlation for ST is well known. A new friction factor correlation for HV based on existing data is presented. A comparison of the two concepts was performed for ITER conditions based on equal heat flux area. The comparison shows that the pumping power required for HV is slightly higher (about 10%) and the incident critical heat flux (ICHF) is slightly lower (8%) for HV compared to ST at similar flow conditions. These differences are small enough and uncertainties in data large enough so that the choice between the two concepts should be based on other considerations such as: (1) cost and ease of fabrication, (2) ease of brazing and (3) volume and reliability of available experimental data: These considerations lead to the conclusion that the choice of concept will depend on the particular application. For ITER, both of these concepts could be used in different areas of the divertor.