1、BRITISH STANDARD BS ISO 8778:2003 Pneumatic fluid power Standard reference atmosphere ICS 23.100.01 BS ISO 8778:2003 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 21 March 2003 BSI 21 March 2003 ISBN 0 580 41437 X National foreword This Bri
2、tish Standard reproduces verbatim ISO 8778:2003 and implements it as the UK national standard. The UK participation in its preparation was entrusted to Technical Committee MCE/18, Fluid power systems and components, which has the responsibility to: A list of organizations represented on this committ
3、ee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facilit
4、y of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations.
5、aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages
6、This document comprises a front cover, an inside front cover, the ISO title page, pages ii to v, a blank page, pages 1 to 10, an inside back cover and a back cover. The BSI copyright date displayed in this document indicates when the document was last issued. Amendments issued since publication Amd.
7、 No. Date Comments Reference number ISO 8778:2003(E)INTERNATIONAL STANDARD ISO 8778 Second edition 2003-03-15 Pneumatic fluid power Standard reference atmosphere Transmissions pneumatiques Atmosphre normalise de rfrence BSISO8778:2003IS:8778 O3002(E) DPlcsid Fremia ihTs PDF file may ctnoian emdebt d
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12、 tsopale 65 eneG 1121-HC 02 av leT.+ 2 142 11 10 947 xaF 74 90 947 22 14 + E-mailc oirypthgiso.o gr Wew bww.is.o gro Pulbisdehi n Switlrez dnaii BSISO8778:2003 iiiContents Page Foreword iv Introduction v 1 Scope 1 2 Normative references . 1 3 Terms and definitions. 1 4 Standard reference atmosphere
13、1 5 Identification statement (Reference to this International Standard) 2 Annex A (informative) Alternative reference atmospheres and determination of humidity and density 3 Annex B (informative) Development of equations for relative humidity, density and error analysis. 5 Bibliography . 10 BSISO877
14、8:2003iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for
15、which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on al
16、l matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are
17、circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held res
18、ponsible for identifying any or all such patent rights. ISO 8778 was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee SC 5, Control products and components. This second edition cancels and replaces the first edition (ISO 8778:1990), which has been technically revised. BS
19、ISO8778:2003 vIntroduction In pneumatic fluid power systems, power is transmitted and controlled through a gas, most commonly compressed air, under pressure within a circuit. When presenting characteristics of pneumatic components, equipment or systems that use compressed air, it is necessary to hav
20、e a standard reference atmosphere to permit comparison of data obtained under various pressure conditions. BSISO8778:2003INTENRATIONAL TSANDADR IS:8778 O3002(E)1Pneumatic fluid power Standard reference atmosphere 1 Scope This International Standard specifies a standard atmospheric reference value to
21、 be used in pneumatic fluid power technology for stating the performance data of components and systems. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the
22、 latest edition of the referenced document (including any amendments) applies. ISO 5598, Fluid power systems and components Vocabulary 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 5598 and the following apply. 3.1 atmosphere ambient conditions def
23、ined by one or more of the following parameters: temperature, relative humidity, pressure 3.2 reference atmosphere agreed atmosphere to which conditions determined in other atmospheres may be related by using suitable conversion factors NOTE 1 The term “other atmospheres” can mean pressurized or vac
24、uum conditions. NOTE 2 See Annex A for a discussion of alternative reference atmospheres. 3.3 standard reference atmosphere atmosphere whose pressure has been approximated to be nearly that at sea level, whose temperature is typically considered to be room temperature and whose relative humidity is
25、arbitrarily established 4 Standard reference atmosphere 4.1 The standard reference atmosphere shall be as defined in Table 1. BSISO8778:20032 Table 1 Definition of standard reference atmosphere Pressure Temperature Relative humidity 100 kPa (1 bar) 20 C 65 % NOTE This is the same reference atmospher
26、e as that given in ISO 8778:1990. 4.2 For gases, when the quantity is expressed as free gas, the abbreviation ANR (standard reference atmosphere), in parentheses, shall follow the unit, not the value, for example: q V= x m 3 /s (ANR) 5 Identification statement (Reference to this International Standa
27、rd) Manufacturers are strongly recommended to use the following statement in their catalogues, test reports and sales literature when electing to comply with this International Standard: “Standard reference atmosphere conforms to ISO 8778:2003, Pneumatic fluid power Standard reference atmosphere.” B
28、SISO8778:2003 3Annex A (informative) Alternative reference atmospheres and determination of humidity and density A.1 Introduction This annex provides two additional categories of reference atmospheres for informative purposes only. In addition, equations for calculating humidity and density are also
29、 included. A.2 Description and application of alternative reference atmospheres A.2.1 Conversion reference atmosphere The conversion reference atmosphere is a reference atmosphere whose pressure is considered to be atmospheric pressure at sea level, whose temperature is typically considered to be ro
30、om temperature and whose relative humidity is calculated to be equivalent to that existing at the conditions at which the conversion originates (see Table A.1). The conversion reference atmosphere is considered to be the most accurate for pressure conversions and density calculations. A.2.2 Engineer
31、ing reference atmosphere The engineering reference atmosphere is a reference atmosphere whose pressure is rounded off to a number that provides for very convenient calculations, whose temperature is typically considered to be room temperature and whose relative humidity is assumed to be 0 %. The eng
32、ineering reference atmosphere is typically used in cases where the effect of relative humidity is ignored. A.3 Specification of alternative reference atmospheres The conversion reference atmosphere and engineering reference atmosphere are as defined in Table A.1. Table A.1 Definitions of conversion
33、reference atmosphere and engineering reference atmosphere Type of alternative reference atmosphere Pressure Temperature Relative humidity Conversion reference atmosphere (ACR RH %) 760 mm Hg absolute 100,96 kPa a(1,009 6 bar) 20 C Equivalent to that existing at the conditions at which the conversion
34、 originates Engineering reference atmosphere (AER) 100 kPa (1 bar) 20 C 0 % a The value of 100,96 kPa is a conversion from 760 mm Hg, using the density of Hg at 20 C. BSISO8778:20034 A.4 Determination of equivalent relative humidity and density at atmospheric conditions A.4.1 Symbols and constants T
35、he following symbols and constants are used in determining equivalent relative humidity and density at atmospheric conditions. NOTE All pressures are absolute. p 0= atmospheric pressure p 1= pressure of the compressed state p s0= saturation pressure of the water vapour at atmospheric temperature p s
36、1= saturation pressure of the water vapour at the temperature of the compressed state R a= 287 m 2 /s 2 K (gas constant for dry air) R w v= 461,45 m 2 /s 2 K (gas constant for water vapour) T 0= absolute temperature of the atmosphere 0 = relative humidity of the air at atmospheric conditions if it c
37、ontains all the water vapour from the compressed state 1= relative humidity of the air in the compressed state A.4.2 Equivalent relative humidity A relationship between the relative humidity in the compressed state and the relative humidity at atmospheric conditions, assuming that none of the water
38、vapour is condensed, can be stated as follows: 0s 1 01 1s 0 pp pp = If the result is greater than 100 %, water vapour has condensed and the calculation is limited to 100 %. A.4.3 Density at atmospheric conditions The density of air expanded to atmospheric conditions from a pressurized state (line co
39、nditions), including the relative humidity at line conditions carried to atmospheric conditions (assuming that none of the water vapour condenses) is: 00 s 1 01 a0 1 0 a w v 11 pp p RT p T R R = A.5 Analysis of errors The simplification of pressure in the engineering reference atmosphere can introdu
40、ce an error of about 1 %. However, this is to be assessed in applications where use of the pressure term may be non-linear, as in flow and thermodynamic calculations. Annex B describes the errors introduced from relative humidity considerations. BSISO8778:2003 5Annex B (informative) Development of e
41、quations for relative humidity, density and error analysis B.1 Statement of the problem When compressed air in a container or conduit is equated to its atmospheric equivalent, the water vapour content is often ignored in the calculation process. However, the change of state will affect the density a
42、t atmospheric conditions. Although the density change may not affect an equivalent-state calculation (pressure and temperature), the water content could be important in those calculations where the change affects system calculations, such as a dehumidifying process. The following analysis develops e
43、quations for determining the relative humidity and density at atmospheric conditions for a mixture of air and water vapour at pressurized conditions. B.2 Symbols and constants Symbols and constants used in the following equations: NOTE All pressures and temperatures are absolute. M a= 28,967 g/mole
44、(molecular weight of dry air) M w v = 18,016 g/mole (molecular weight of water vapour) m = mass of mixture m a= mass of dry air m w v= mass of water vapour p 0= pressure of the atmosphere (mixture of air and water vapour) p 1= pressure of mixture of air and water vapour in the compressed state p a0=
45、 partial pressure of the dry air at atmospheric conditions p a1= partial pressure of the dry air in the compressed state p w v1= partial pressure of the water vapour in the compressed state p w v0= partial pressure of the water vapour at atmospheric conditions, if it contained all the water vapour f
46、rom the compressed state p s0= saturation pressure of the water vapour at atmospheric temperature p s1= saturation pressure of the water vapour at the temperature of the compressed state R a= 287 m 2 /s 2 K (gas constant for dry air) R w v= 461,45 m 2 /s 2 K (gas constant for water vapour) T 0= temp
47、erature of the atmosphere T 1= temperature of the compressed state V = volume of mixture BSISO8778:20036 0= relative humidity of the air at atmospheric conditions if it contained all the water vapour from the compressed state 1= relative humidity of the air in the compressed state 0 = arbitrarily sp
48、ecified relative humidity of the air at atmospheric conditions 0= density of the mixture at atmospheric conditions with relative humidity equivalent to the compressed state 0 = density of the mixture at atmospheric conditions with arbitrary relative humidity B.3 Relative humidity In general, the pre
49、ssure of an air/water vapour mixture is the sum of its two partial pressures: p mixture= p dry air+ p water vapour Using the symbols and constants given above, the following can be stated for both compressed and atmospheric conditions: p a1= p 1 p w v1and p a0= p 0 p w v0(B.1) From the definition of relative humidity (at compressed and at atmospheric conditions): 1= p w v1 /p s1and 0= p w v0 /p s0The partial
