HEM_example

# HEM_example - ∂vol v /∂p along the saturated vapor...

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Working with the HEM 1 1. (Solved on the board) Compute the pressure gradient for a saturated 1 kg s - 1 steam-water ﬂow at 7 MPa and a quality of 0.1 in a smooth 2.5 cm diameter pipe using the homogeneous equilibrium model. f TP is to be taken as f lo Assume the ﬂow direction is upward, there is no change in quality with axial distance, and ignore the eﬀects of gas compressibility. We’ll need to know viscosities and densities for both phases to complete this problem. These can be obtained from steam tables: ρ f = 740 kg m - 3 (1) ρ v = 36 . 5 kg m - 3 (2) μ f = 9 . 55 × 10 - 5 Pa s (3) μ v = 1 . 90 × 10 - 5 Pa s (4) 2. Use Equation 11-79b to compute the friction factor, employing each of the three estimates for μ TP (Equations 11-80a through 11-80c), and then use this to compute the pressure gradient. How important is the selection of the friction factor or the viscosity model to the computed pressure loss? 3. Compute the gas compressibility factor (denominator of RHS of Equation 11-78). Estimate
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Unformatted text preview: ∂vol v /∂p along the saturated vapor line. Is it a reasonable engineering assumption to neglect this eﬀect in this system? 4. Now, the pipe is heated at a constant rate to produce a linear quality proﬁle ( i.e., x = 0 at the inlet, 1 at the outlet, 0.5 halfway up [5 m], etc.) Assume that the two-phase friction factor is equal to the liquid-only friction factor and that the properties of steam and water can be estimated at their saturated states at 7 MPa throughout the pipe. Neglect vapor compressibility and analytically integrate Equation 11-78 to compute the total pressure loss from saturated liquid to saturated vapor. 5. Is assuming constant properties is a good engineering simpliﬁcation for this system? In your answer, consider how much eﬀort accounting for variations in properties with pressure would be....
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## This note was uploaded on 10/22/2011 for the course ENU 4134 taught by Professor Schubring during the Fall '11 term at University of Florida.

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