Compare the frictional pressure drop due to the vapor flow to that due to the liquid flow through the wick for a heat pipe using ammonia as the working fluid. Assume that the ratio of dynamic viscosities of ammonia is µI/µV = 3.0, the inside diameter of the wick is 2 cm and the annular area of the wick is 0.65 cm^2. The wick is phosphor-bronze.
What will be an ideal response?
This problem is best approached using Equation 9-62 or the two previous equations 9-
57 and 9-58. The Equation 9-57 defines the vapor flow pressure drop and Equation 9-58
the liquid flow pressure drop. These two terms are the first and second terms in 9-62.
The effective length and the mass flow are the same for the liquid and the vapor, and
the density of the saturated liquid is about 2,000 times (as a rough approximation for
many substances) more than that for the saturated vapor. From Table 9-5 the
permeability for the wick and liquid flow is about 0.296 x 10^-12 m^2 or 0.296 x 10^-8cm^2. For
the vapor, the hydraulic diameter is about 2 cm and the annular area for the liquid flow
is given as 0.65 cm^2. The ratio of the liquid pressure drop to the vapor pressure drop is
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