1、_ STD-BSI BS EN 305-ENGL 1797 W LbZl.rbb7 Ob23111b TBLi BRITISH STANDARD Heat exchangers - Definitions of performance of heat exchangers and the general test procedure for establishing performance of all heat exchangers t * rn ICs 27.060.30 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY CO
2、PYRIGHT LAW BS EN 305 : 1997 STD*BSI BS EN 305-ENGL 1997 LbZLibbS Ob23417 310 BS EN 306 : 1997 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee RHE/30, Heat exchangem, upon which the following bodies were represented: Brit
3、ish Refrigeration Association Building Services Research and Momation Association Federation of Environmental nade Associations HEVAC Association Water Heaters Manufacturem Association This British Standard, having been prepared under the direction of the Engineering Sector Board, was published unde
4、r the authority of the Standards Board and comes into effect on 15 July 1997 O BSI 1997 Amendments issued since publication The foiiowing BSI references relate to the work on this standard Committee reference RW30 ENV 305 ISBN O 680 27624 4 BS EN 306 : 1997 Contents Committees responsible National f
5、oreword page hide front cover ii Foreword Text of EN 305 2 3 O BSI 1997 i I BS EN 305 : 1997 I National foreword This British Stan- has been prepared by Technical Committee RHE/30 and is the English language version of EN 305 : 1997 Heat mhungm - Definitions of pe$mname of heat mhangers and t3te gen
6、eml test procedure for establishing perfomuLnce of aU heat mhangers, published by the European Committee for Standardizon (CEN). EN 305 : 1997 was produced as a resuit of internatiod discussions in the UK took an active part. Compliance with a British Standard does not of itself confer immunity from
7、 iegd obligations. Summary of pages This document comprises a kont cover, an inside front cover, pages i and ii, the EN title page, pages 2 to 14, an inside back cover and a back cover. ii O BSI 1997 - STD-BSI BS EN 305-ENGL 1777 1b2qbb7 Ob23q20 405 EUROPEAN STANDARD EN 305 NORME EUR0PEE”E EUROP- NO
8、RM January 1997 ICs 27.060.30 Descriptors: Heat transfer, heat exchangers, definitions, thermodynamic properties, tests, information Supersedes ENV 305 : 1990 Jkghh version Heat exchangem - Denitions of performance of heat exchangem and the general test pmedure for establishin$ peorrnance of all hea
9、t exchange= Echangem thenniques - Dnitions de la performance des changetus thermiques et procdure gnrale dessai pour la dtemon de la performance de tous les changeus hermiques Wanneaustauscher- BegrBe und allgemeine Festlegungen bei der Prufung zur Leistinigsbestimmung This European Standard was app
10、roved by CEN on 199612-27. CEN members are bound to comply with the CENKENELEC Internai Regulations which stipuiak the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationai stand
11、ards may be obtained on appication to the Cenld Secretariat or to any CEN member. This European Standard errists in three official versions (English, French, German). A version in any other language made by translalion under the responsibility of a CEN member into its own language and notified to th
12、e Central Secretariat has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Denmark, Finand, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN Euro
13、pean Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1060 Brussels O 1997 Copyright reserved to CEN members Ref. No. EN 305 : 1997 E STD-BSI BS EN 305-ENGL 1777 LbZLibbS Ob23LiZ1 3Y1 Page 2 EN 305 : 1997 Foreword
14、This European Standard has been prepared by khnical Commit- - fluid flow rate; - temperature; - temperature Merence; - pressure drop; - heat transfer coefficient; that can be determined by measurement or calc- from measured parametem W Wall 4.1.11 categories of heat exchanger tot total 4 Denitions a
15、nd meaning of performance Classincation of heat exchanger types based on design criteria of physical criteria or both. The categories of heat exchanger in this standard are classified according to the general arrangement of heat transfer specified by heat tsansfer surface types in 4.1 of mEN 247 : 1
16、996. L 4.1 Basic terms For the purposes of this standard, the following denitions apply 4.1.12 recuperative heat excharage Heat transfer from the primary fluid to a secondary fluid, either direct through a wall or indirect through 4.1.1fluid an intermediate medium. transfer of thermal energy (heat).
17、 Two or more types present. 4.1.2 primaryfluk The warmer fluid (heat source). 4.1.3 secondary fluid The cooler fluid (heat sink). 4.1.4 mixture Fluid including two or more components in the same state of phase. w Cleanliness factor Heat power 4.1.18 melting Liquefying a solid by supplying heat. 4.1.
18、19 solwing Phase change in a liquid to solid state by removing heat. 4.1.20 fouling Deposition of a layer of unwanted material of low thermal conductivity on the heat exchanger surface. 4.1.21 pressure drop Loss in total pressure between the inlet and the outlet including channeis for flow distribut
19、ion to and from the heat transfer surface. 4.1.22 stanan inlet point “he inlet point considered most representative of each heat exchanger is chosen by the manufacturer or according to the condition for the installation. 4.1.23 stanan outlet point The outlet point considered most representative of e
20、ach heat exchanger is chosen by the manufacturer or according to the condition for the installati on. 4.2 Parameters characterizing heat exchangers 4.2.1 Derived parameters When using this sandard as a basis for reporting of performance, the parts contained in the European Standards for various bran
21、ch applications shall be used. Cf 6.1.6) P 6.1.6 lhble 1. Parameters used in reporting of performance I Logarithmic mean temperature difference Terminal temperature merence Overall heat transfer coefficient Fouling resistance 6.1.4.1 6.1.4.2 6.1.6.1 6.1.6a) I HGI transfer surface margin I SM 16.1.6b
22、) I I Number of heat transfer units 1 NT 16.2.2 I I Temperature efficiency I ut 15.2.1.3 I - flowrate (mass flow of primary and secondary fluids and any intermediate flows necessary); - pressure (iniet of primary and secondary fluids); - pressure drop (of primary and secondary fluids); - type of med
23、ia; - physical properties and chemical composition of the fluids involved (at standard inlet and/or outlet - clean or fouled heat mnsfer surfaces; - demands on auxiliary equipment (e.g. vents, level controls, pumps, fans, etc.); - demands on environment (e.g. ambient tempe-, humidity, poliution, etc
24、.); - operaling frequency (for regenerative heat exchangers). points); 4.2.3 Rating The performance of the heat exchanger shall be referred to the rating condition of the operating conditions. In order to predict or project the performance at other operating conditions, relevant data may be presente
25、d in the form of curves, tables or equations. 4.2.4 Test condition A condition where the system has been stabiied and reproducible values are attainable. For detailed information on stabiiity criteria, reference is made to the relevant chapters in the European standard on methods of measurement and
26、the European standards on various branch applications of this European Standard. 4.3 Energy balance A balance comparing total energy input and total energy output of a heat exchanger. This balance should be included in ali tests on heat exchangers to verify measured results. “he comparison should ag
27、ree within hits specified for each particular application. For detailed equations, see annex k 4.4 Heat transfer coefficients Heat transfer shall be charactrized by different types of heat tsansfer coefficients, expressing the rate of heat flow per unit heat transfer surface area and unit temperatur
28、e diference. Heat transfer coefficients shall be given separately for the primary and secondary flows or as an overaii heat transfer coefficient. The overaii heat transfer coefficient combines the effects of convection, conduction and radiation between the two flows and the heat transfer surface of
29、the heat exchanger. O BSI 1997 STD-BSI BS EN 305-ENGL 1777 1b2LibbS Ob23925 T97 Page 6 EN305:1997 The conditions relating to the determination of a heat transfer coefficient shall be described, e.g. concerning how the heat txamfer surface area and temperature diference is determined. In this standar
30、d, unless stated otherwise, the overall heat transfer coefficient is used This heat transfer coefficient is calculated using the corrected logarithmic mean temperature difference (see 6.1.4) and the total heat transfer area in contact with one or the other fluid, including nnS or other types of surf
31、ace extensions. For no is the temperature difference between the primary inlet point and the secondary inlet or outlet point, according to figures 1 and 2; is the temperature difference between the primary outlet point and the secondary inlet or outlet point, according to figures 1 and 2. 2)Heat is
32、transferred from a higher to a lower temperature level in accordance with the second thermodynamic law. The significance of this is that the temperature difference is the driving force. If no temperature difference exists no heat transfer will occur. When the two media, separated by a wall in the he
33、at exchanger, pass through the respective channels the temperature of each medium wiii change. O BSI 1997 - STD*BSI BS EN 305-ENGL 1777 = Lb24bb7 Db2342b 723 The temperature differences over the heat tsancfer surface deviate between counter flow and parallel flow types, in accordance with figure 1 a
34、nd figure 2. 51 Figure 1. Counter flow 51 t21 I Figure 2. Parallel flow 42 t22 These gures 1 and 2 are valid for pure counter flow and pure parallel flow. For other types of flow, i.e. cross flow, correction factors for LMTD shall be applied. Such factors (3) can be found in literature and shd be ap
35、plied when calculating heat power. 6.1.4.2 Terminal temperature difference (pinch) shall be determined by the difference between the temperature at the outlet of the primasy circuit and the inlet or the outlet of the secondary circuit, depending on the flow type. For physical reasons the terminal te
36、mperature difference must be positive. Page 7 EN305:1997 6.1.6 Heat power 6.1.6.1 ?i.ansfer of heat power as the basic principle of a heat exchanger is characterized by the transfer of a certain amount of heat per unit time defined by the equation: a) for heat power b) for the overall heat transfer
37、coefficient P = k*A*LMTD*F P A.LMTD.F k= where P is the heat power (in IV); k is the ove A is the reference heat transfer surface an?a (in m2); LMTD is the logarithmic mean temperature difference in accordance with 6.1.4.1; F is the correction fador for LMTD. 6.1.6.2 Siigie phase fluid system of a h
38、eat exchanger (i.e. where both fluids remain in the liquid or vapoudgas states without condensation or vaporization) is characterized by the heat power defined by the equation: where P = (qm*$ hi - tnz I + 4oss) P qm cp t temperature (in OC); n fioss is the heat power (in W); is the mass flow rate (
39、i Ws); is the specific heat at constant pressure (in J-kgK); subscript referring to either side; is the heat loss to or the heat gained from the surrounding environment (i W). Subscript n is referred to the primary or secondary circuit of the heat exchanger. In this relation the heat balance for the
40、 heat exchanger describes that heat given away from the hot fluid is equal to the heat taken up by the cold fluid including losses and gains to/from the sw.-roundlligs. O BSI 1997 Page 8 EN3oEi:1997 6.1.6.3 Multi-phase fluid system of a heat exchanger is characterized by the heat power defined by th
41、e equation: where p = (Qm-h + loss?z P is the heat power (in W); qm is the mass flow rate (in kg/s); h is the specific enthalpy change of the fluid (in J/kg); Plos, is the heat loss to or heat gain from the surrounding environment (i W); n subscript n is referred to either side 6.2 Ratios 5.2.1 Wcie
42、ncg 5.2.1.1 Fin efficiency E is the ratio of the power actually exchanged by the fin to the power which it would exchange if its temperature were uniformly that of the fin base temperature. 5.2.1.2 Finned surface efficiency is the ratio of the power actually exchanged by the finned surface to the po
43、wer which it would exchange if its temperature were uniformly that of the temperature at the base of the fins. Ah X (1 - E) A Eh = 1- where Afin A is the reference heat transfer surface area (in m2); 6.2.1.3 Exchanger efficiency is the ratio of the actual heat power exchanged to the maximum heat pow
44、er which is theoretically possible to exchange with an kop IC, Icf ideal item of equipment using the same fluids at the same flow rates and at the same inlet temperatures. The heat power exchanged is expresed (see 6.1.6.2) a) for fouling resistance SM is the value of the k-value margin3), (in %); Cf
45、 is the cleanliness factor, kop is the operational overail heat transfer coefcient (i whn2.1; k, is the overall heat transfer coefficient under clean conditions (in Wm2-K); cf is the reciproca3 f value (in w/.K). as: P = qmi *Cpi.(tii - ti21 + 4ossi = Qm2ql2 -022 - h1) + Plos2 The power exchanged wi
46、ll be at its maximum if one of the fluids undergoes a temperature variation eqd to the Merence between the inlet temperatures of the two fluids. This maximum vanation is undergone only by the fluid with the lower qmc, (see figures 3 and 4). The maximum exchangeable power is thus: 3)This due may give
47、 a higher or lower pressure drop or a higher or lower temperature difference. O BSI 1997 STD-BSI BS EN 305-ENGL 1997 lb29bb9 Ob23928 7Tb W Page 9 EN 305 : 1997 f i- t ll t22 1 I Figure 3. Counter flow Figure 4. Parallel flow O BSI 1997 STD-BSI BS EN 305-ENGL Page 10 EN305:19!37 Clearly in practice t
48、he efficiency of an exchanger is defined by the useful fluid, i.e. the fluid that is heated or cooled, and for which qm$ is not necessarily the minimum. However, only the efficiency defined by the fluid for which qmc, is the minimum has a physical meaning where: nt P pmax tll t12 hl t22 4m Gp PlOsSi
49、 is the temperature efficiency; is the operational heat power (in W); is the maximum (theoretical) heat power (in W); is the inlet temperature on the primary side (in OC); is the outlet temperature on the primary side (in OC); is the inlet temperature on the secondary side (in OC); is the outlet temperature on the secondary side (in OC); is the mass flow rate (in kg/s); is the specific heat at constant pressure is the heat loss from the surrounding environment on primary side (in W); is the heat loss
