What is wet net worth

What is wet steam throttling?

The throttling of the moist steam is also associated with the maintenance of the enthalpy. In this case, reducing the pressure increases the quality of the steam. Thermal engineering

Throttling Process - Isenthalpic Process

A.throttling process is athermodynamic process, in which the enthalpy of the gas or medium remains constant (h = const). In fact, thethrottling process is one ofisenthalpic processes. During the throttling processno work is done by or on the system (dW = 0), and usually there is no heat transfer (adiabatic) from or into the system (dQ = 0). On the other the throttling process cannot be isentropic, it is afundamentally irreversible process. Characteristics of the throttling process:

  1. No work transfer
  2. No heat transfer
  3. Irreversible Process
  4. Isenthalpic Process

A throttling of the flow causes significant reduction in pressure, because a throttling device causes alocal pressure loss. A throttling can be achieved simply by introducing a restriction into a line through which a gas or liquid flows. This restriction is commonly done by means of a partially open valve or a porous plug. Such pressure losses are generally termedminor losses, although they often account for a major portion of the head loss. The minor losses are roughly proportional to thesquare of the flow rate and therefore they can be easily integrated into the Darcy-Weisbach equation throughresistance coefficient K.

A partially open valve or a porous plug can be used to reduce the pressure in a system.

Throttling of Wet Steam

Wet steam is characterized by thevapor quality, which ranges from zero to unity - open interval (0,1). Throttling of the wet steam is also associated withconservation of enthalpy. Enthalpy is conserved because no work is done by or on the system (dW = 0), and usually there is no heat transfer (adiabatic) from or into the system (dQ = 0). But in this case areduction in pressure causes onincrease in vapor quality. As the pressure drops some of the liquid in the wet steam vaporizes and increases the vapor quality (i.e. dryness fraction). This process take place, because thesaturation temperature is lower at the lower pressure. The lower temperature, lower pressure, higher quality steam contains the same enthalpy as the original steam.

Example: Throttling of Wet Steam

A high-pressure stage of steam turbine operates at steady state with inlet conditions of 6 MPa, t = 275.6 ° C, x = 1 (point C). Steam leaves this stage of turbine at a pressure of 1.15 MPa, 186 ° C and x = 0.87 (point D). Determine the vapor quality of the steam when throttled from 1.15 MPa to 1.0 MPa. Assume the process is adiabatic and no work is done by the system.

See also: Steam Tables


The enthalpy for the state D must be calculated using vapor quality:

HD, wet = hD, vapor x + (1 - x) hD, liquid  = 2782 . 0.87 + (1 – 0.87) . 790 = 2420 + 103 = 2523 kJ / kg

Since it is an isenthalpic process, we know the enthalpy for point T. From steam tables we have to find the vapor quality using the same equation and solving the equation for vapor quality, x:

HT, wet = hT, vapor x + (1 - x) hT, liquid

x = (HT, wet - HT, liquid) / (HT, vapor - HT, liquid) = (2523 – 762) / (2777 – 762) = 0.874 = 87.4%

In this case of the throttling process (1.15MPa to 1MPa) the vapor quality increases from 87% to 87.4% and the temperature decreases from 186 ° C to 179.9 ° C.

Throttling of wet steam usually causes an increase in vapor quality, increase in entropy and decrease in temperature


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