Log entry time 18:53:05 on March 25, 2014

Entry number 387546

Followups:

• 387596 03/26/14 11:54 covrig target pump mass flow assumption correction

The lh2 pump in loop 1 was briefly (4 minutes) ran at 60 Hz to try to estimate its flow with the help of the HPH. The formula used was

where ṁ is the lh2 mass flow, c_p is lh2 specific isobaric heat at 26 psia and T ~ 19.1 K, ΔT is the temperature difference across the HPH (T7 seems to be heater out and T5 seems to be heater in) and Power_hph is the power put out by the HPH.

Averages over three minutes of (stable) data from the Archiver are: Power_HPH ~ 62.8 W, ΔT = T5 - T7 = 19.081 - 19.025 = 0.056 K, c_p (from a NIST table) ~ 9036 J/kg.K, which gives ṁ ~ 124 g/s or Ṽ ~ 1.7 liters/s (lh2 density 72.48 kg/m³ at 19 K, 26 psia). The pump ran at f ~ 62.1 Hz. All averages were made over about 60 readings from the Archiver. The lh2 pump mass flow estimate at 31 Hz is 70.2 g/s (P_HPH ~ 94.3 W, ΔT ~ 148 mK). Typically the mass flow varies with the square of the pump frequency (if the pump efficiency is constant with frequency, for these pumps it usually drops), which means that based on the mass flow at 31.22 Hz the predicted mass flow at 62.1 Hz should be 261 g/s, but it seems to be 124 g/s (efficiency drop, temperature sensors are a not precise enough etc.).

If I compare the estimate of 1.7 l/s with the expected volume flow at 62 Hz of 8.1 l/s the pump is about 21% efficient, which is low even for a vane-axial pump.

The caveats are the calibrations of the temperature sensors and their offsets (if any), the calibration of the HPH and so on.

Figure 1