the counterflow cooling arrangement the liquid nitrogen flows through the HTS cable
former, providing cooling to the terminations as well as the cable and returns in the annulus
between the outside of the cable and the inner cryostat wall as illustrated in FIGURE 1. In
contrast, for the parallel flow arrangement, liquid nitrogen flows in the same direction
through the cable former and the annulus. The liquid nitrogen is returned through a
separate vacuum-insulated line.
The advantages of counterflow-cooled cable systems include compact size, low heat
load, and lower cost since only one vacuum insulated line is required. An analysis
challenge is present from the thermal short circuiting between the coolant streams from a
finite radial thermal conductance of the HTS cable. The inter-stream thermal conductance
is defined as the amount of heat transfer radially through a cable for a given temperature
difference between the coolant streams. The literature dealing with the radial heat transfer
in coaxial cables does not present experimental data for comparison with calculated cable
temperature profiles [1, 3, 4]. So data is needed to benchmark any analysis of long length
cable systems.
Measurements of cable temperature profiles for a parallel flow HTS cable
configuration were conducted by Superpower for the Albany cable system [7].
Temperature profiles at various times during the cooling process were measured by optical
fiber in the cryostat along the cable. This type of measurement provides a combination of
the coolant and cable temperature since it cannot be precisely known whether the
temperature is measured at the cable surface or in the flow.