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Calculation principles of humid air in a reversed Brayton cycle

Abstract

The article presents a calculation method for reversed Brayton cycle that uses humid air as working medium. The reversed Brayton cycle can be employed as an air dryer, a heat pump or a refrigerating machine. In this research the use of humid air as a working fluid has an environmental advantage, as well. In this method especially the expansion process in the turbine is important because of the condensation of the water vapour in the humid air. This physical phenomena can have significant effects on the level of performance of the application. The expansion process differs physically from the compression process, when the water vapour in the humid air begins to condensate. In the thermodynamic equilibrium of the flow, the water vapour pressure in humid air cannot exceed the pressure of saturated water vapour in corresponding temperature. Expansion calculation during operation around the saturation zone is based on a quasistatic expansion, in which the system after the turbine is in thermodynamical equilibrium. The state parameters are at every moment defined by the equation of state, and there is no supercooling in the vapour. Following simplifications are used in the calculations: The system is assumed to be adiabatic. This means that  More>>
Authors:
Backman, J [1] 
  1. Lappeenranta Univ. of Technology (Finland). Dept. of Energy Technology
Publication Date:
Dec 31, 1997
Product Type:
Conference
Report Number:
TKK-MK-1; CONF-9706306-
Reference Number:
SCA: 330103; PA: FI-99:003111; EDB-99:069909; SN: 99002078276
Resource Relation:
Conference: 4. international colloquium on process simulation, Espoo (Finland), 11-13 Jun 1997; Other Information: PBD: 1997; Related Information: Is Part Of The 4th international colloquium on process simulation. Proceedings; Jokilaakso, A. [Helsinki Univ. of Technology, Otaniemi (Finland). Dept. of Materials Science and Metallurgy]; PB: 621 p.
Subject:
33 ADVANCED PROPULSION SYSTEMS; BRAYTON CYCLE POWER SYSTEMS; AIR; WATER VAPOR; CALCULATION METHODS; THERMODYNAMICS; GAS TURBINES; EXPANSION; ADIABATIC PROCESSES; HUMIDITY
OSTI ID:
357217
Research Organizations:
Helsinki Univ. of Technology, Otaniemi (Finland)
Country of Origin:
Finland
Language:
English
Other Identifying Numbers:
Other: ON: DE99735414; ISBN 951-22-3574-9; TRN: FI9903111
Availability:
OSTI as DE99735414
Submitting Site:
FI
Size:
pp. 233-247
Announcement Date:
Aug 12, 1999

Citation Formats

Backman, J. Calculation principles of humid air in a reversed Brayton cycle. Finland: N. p., 1997. Web.
Backman, J. Calculation principles of humid air in a reversed Brayton cycle. Finland.
Backman, J. 1997. "Calculation principles of humid air in a reversed Brayton cycle." Finland.
@misc{etde_357217,
title = {Calculation principles of humid air in a reversed Brayton cycle}
author = {Backman, J}
abstractNote = {The article presents a calculation method for reversed Brayton cycle that uses humid air as working medium. The reversed Brayton cycle can be employed as an air dryer, a heat pump or a refrigerating machine. In this research the use of humid air as a working fluid has an environmental advantage, as well. In this method especially the expansion process in the turbine is important because of the condensation of the water vapour in the humid air. This physical phenomena can have significant effects on the level of performance of the application. The expansion process differs physically from the compression process, when the water vapour in the humid air begins to condensate. In the thermodynamic equilibrium of the flow, the water vapour pressure in humid air cannot exceed the pressure of saturated water vapour in corresponding temperature. Expansion calculation during operation around the saturation zone is based on a quasistatic expansion, in which the system after the turbine is in thermodynamical equilibrium. The state parameters are at every moment defined by the equation of state, and there is no supercooling in the vapour. Following simplifications are used in the calculations: The system is assumed to be adiabatic. This means that there is no heat transfer to the surroundings. This is a common practice, when the temperature differences are moderate as here; The power of the cooling is omitted. The cooling construction is very dependent on the machine and the distribution of the losses; The flow is assumed to be one-dimensional, steady-state and homogenous. The water vapour condensing in the turbine can cause errors, but the errors are mainly included in the efficiency calculation. (author) 11 refs.}
place = {Finland}
year = {1997}
month = {Dec}
}