PROBLEM 1 Problem 13.11. Helium, at an inlet pressure of 10 bar and an inlet temperature of 220 K, flows through a rectangular channel with very small cross-section aspect ratio, and leaves with an average temperature of 245 K. The channel is assumed to be subject to a constant surface heat flux. Helium velocity at inlet is 5 m/s. Find the size of the channel that defines the threshold between continuum and slip flow regimes Consider a channel whose hydraulic diameter is 1/2 of the threshold calculated in part (a), and has a length-to-hydraulic diameter ratio of 150. Calculate the pressure drop and heat flux assuming fully-developed flow and neglecting the compressibility effect. c) Repeat part (b) this time neglecting rarefaction effect as well. Assume a = ath = 1.0. a) b)

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