Unsteady Discharging of Wet Vapor From a Vessel

Abstract

A saturated liquid-vapor mixture discharging from a pressurized thermal-insulated vessel through a nozzle or a valve is considered as an unsteady-flow problem. It is shown that in the case of relatively small energy losses a valve may be modeled as a converging nozzle. After losses exceed certain value a condition of constant enthalpy typical for throttling devices is applicable to a valve. On the basis of such consideration, the step by step calculation method for small time intervals or pressure drops is developed. The proposed approach allows obtaining all characteristics of the discharging process as functions of time. The expression defining the speed of sound in the case of discharging of wet vapor is derived. A special technique is proposed to calculate and correct the usually recommended value of critical pressure ratio. A numerical example of calculation is provided. To estimate the accuracy and limits of the applicability of the results presented in the paper a comparison with corresponding experimental data is needed.

Vapor quality measurement by a discharging calorimeter

“…As such example in [7] is studied discharging of a wet vapor from cylindrical vessel of size 24 cm × 40 cm (the volume V = 0.01810 m 3 ) in atmosphere through a valve with efficiency η = 0.62. The vapor of quality x 0 = 0.9 is pressured to 0.45 MPa.…”

“…Using the pressure step p 0 = −0.05, we find the parameters inside the vessel after the first step for the pressure: The computing results for all steps are presented in adopted from [7] Table 2.…”

“…In the paper [7], the calculation method of the vapor discharging from a vessel is developed. Using this approach, the vapor characteristics inside the vessel and in the exit flow can be obtained as functions of time.…”

“…To calculate the second approximation of the critical pressure, we use calculations for two arbitrary selected pressures at the exit. First we assume that this pressure is p (1) = 0.2 Then, the isentropic parameters inside the vessel are calculated: To determine the speed of sound we use the formula [7]: The mass flow rate is determined using the velocity and the specific volume:…”