1、- STD-BSI BS EN 30h-ENGL 1777 Lh24hb7 ObLib.508 3h7 BRITISH STANDARD Heat exchangers - Methods of measuring the parameters necessary for establishing the performance The European standasd EN 306 : 1997 has the status of a British Standard ICs 27.060.30 BS EN 306 : 1997 NO COPYING WITHOUT BSI PERMISS
2、ION EXCEPT AS PERMITTED BY COPYRIGHT LAW STD-BSI BS EN 306-ENGL 1777 m Lb24669 Db4b507 2T3 m AmdNo. Date BS EN 306 : 1997 Text affected Committees responsible for this British Standard The following BSI references relate to the work on this standard committee reference RHEX30 Draft for comment ENV 3
3、06 DC ISBN O 680 27983 9 The preparation of this British Sandard was entrusted to Technical Committee RHE30, Heat exchangers, upon which the following bodies were represented _ British Refngeration Association Building Services Research and Information Association Federation of Environmental We Asso
4、ciations WAC Association Waterheater Manufacturers Association This British Standad, having been prepared under the direction of the Engineering Sector Board, was published under the authority of the Standards Board and comes into effect on 15 October 1997 3 BSI 1997 STD-BSI BS EN 306-ENGL 1797 Lb24
5、bb7 Ob+b51D TL5 W BS EN 306 : 1997 National foreword This British Standard has been prepared by Technical Committee RW30, and is the English language version of EN 306 : 1997 Heat exchmgers - Methods of rneasufiw the parameters necessary for Rstablishiw the pe?$omnce, published by the European Commi
6、ttee for Standasdization (CEN). Cross-references EN Is0 9000 Publication referred to Corresponding British Standard BS EN IS0 goo0 Qualitg management and quditg assurance standards BS EN IS0 5167 Measurement ofjluidjlow by meam of diflrentid pressure Part 1 : 1997 %fke plates, rwzzles, and venturi t
7、ubes inserted in circuhr cross-section conduits running full Compliance with a British Standard does not of itself confer immunity from legal obligations. IS0 5167 Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, the EN title page, pages 2 to 26, an insi
8、de back cover and a back cover. O ES1 1997 i EN 306 February 1997 ICs 27.060.30 Supersedes ENV 306 : 1990 Descriptors: Heat transfer, heat exchangers, definitions, thermodynamic properties, measurements, flow measurements, pressure measurements, temperature measurements English venion Heat exchange=
9、 - Methods of measuring the parameters nec- for estab- the performance Echangem thermiques - Mthodes de mesurage des paramtres ncesahes l?valuation des performances Wrmeaustauscher - Messungen und Messgenauigkeit bei der kistungsbestimmung This European Standard was approved by CEN on 199741-10. CEN
10、 members are bound to comply with the CENKENELEC Internal Regulations which stipulate 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 national standards may be obtained on appii
11、cation to the Central Secretariat or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has t
12、he same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, bce, German% Greece, Iceland, Ireland, Ita is a characteristic dimension of the system in which the flow occurs expressed in metres; is the kinematic viscmity of the fluid ex
13、pressed in square metre per second 3.3 Measurement of pressure 3.3.1 pressure Mo of force and area. 3.3.2 static pressure Pressure caused by the random motion of fluid particles. In fluid flows static pressure is determined in such a way that the flow does not afect the determination of static press
14、ure. 3.3.3 dMnumic pressure Pressure caused by the systematic motion of fluid particles in a fluid flow. 3.3.4 total pressure The sum of static pressure and dynamic pressure in a fluid flow (equivalent to the ratio of mechanical energy and volume). 3.3.5 stagnation pressure Sum of the static pressur
15、e and the dynamic pressure. It characterizes the state of the fluid when its flow energy is completely transformed into pressure. For an element of fluid at rest, the static pressure and the stagnation pressure have the same numerical value. 3.3.6 Uectve (gauge) pressure The difference between the l
16、ocal absolute pressure of the fluid and the atmospheric pressure at the place and time of the measurement. 3.3.7 pressure loss The static pressure loss caused by the presence of a heat exchanger in the conduit. i) The steady flows observed in conduits are in practice flows in which quantities such a
17、s velocity, pressure, mass density and temperature vary in time about mean values independent of time; these are actuaUy statistically steady flows 1 Two types of pulsating flow are found - periodic pulsating flow - random pulsating flow 3, The time interval being considered is to be long enough to
18、exclude from this definition the random components of the turbulent flow itself 4, For a circular conduit running fuil, the hydraulic diameter is equal to the diameter of the conduit 6, Laminar flow may be unsteady but is completely free from turbulent mixing. Poiseuille flow is an example of steady
19、 laminar flow in a circula conduit As a guide, the Reynolds number for the transition flow of a Newtonian fluid, when referred to the conduit diameter, is generally between a lower limit of 2 O00 and upper limit which varies between 7 O00 and 12 O00 according to the conduit roughness and other facto
20、rs 7, When specifying a Reynolds number, one should indicate the characteristic dimension on which it has been based (for example diameter of the conduit, diameter of the differential pressure device, diameter of a Pitot tube head, etc.) O BSI 1997 STD-BSI BS EN 30b-ENGL 1777 W Lb24bb9 Ob4bSlb 433 W
21、 Page 6 EN 306 : 1997 3.3.8 piezometer ring A pressure eqmblion enclosure linking together two or more pressure tappings instaled on one cross-section, and to which a pressure transducer can be connected. It can either lie outside or be integral with the conduit. 3.3.9 annular chamber Piezometer rin
22、g integral with the conduit or the primaqy device. This implies the use of annular pressure tappings. 3.3.10 wall ressure) tapping Annular or circular hole drilled in the wail of a conduit in such a way that, its edge is flush with the intemal surface of the conduit, the tapping being such that the
23、pressure within the hole is the static pressure at that point in the conduit. 3.4 Measurement of fluid quality 3.4.1fluid quality (x) Rrm describing multicomponent fluids or multi-phase fluis by the mass ratio of a particular component of fluid phase and the fluid mixture. For example: x, is the vap
24、our ratio of humid air expressed as mass of vapour per mass of dry aU; XR is the vapour ratio of refigerants expressed as mass of vapour phase per total mass of refrigerant. Measuring fluid quality also includes other quantities which can affect the perormance of the heat exchanger. 3.6 General defi
25、nitions 3.6.1 iqtluence quantity Quantity which is not the object of the measurement but which can affect the result of a measurement 3.6.2 measurement Procedure in order to determine the value of a given 3.6.3 inaccuracy of measurement The inaccuracy expressed by the totality of the overall imiting
26、 errors of measurement including ail the systematic errors as well as the limiting random errors. 3.6.4 repeatability of measurements The closeness of the agreement between the results of successive measurements of the same quantity carried out by the same method, by the same observer, with the same
27、 measuring instsuments, in the same aboratom, at quite short inkrvaJs of time. 3.6.6 reproducibility of measurements The closeness of the agreement between the results of measurements of the same quantity, where the individual measurements are made: guantis - by different methods, with different mea
28、swring instruments, - by Merent observers, in different laboratories; - after quite long intervas of time compared with the duration of a single measurement under Werent normal conditions of use of the instnun ents employed 3.6.6 error of measurement The discrepancy between the result of the measure
29、ment and the true value of the quantity measured. This can be expressed as an absolute error, or as a relative error Ea =M-T Er= - (M-T) 100% T where: Ea E, M T is an absolute error of measurement; is a relative error of measurement in percent; is the value as result of a measurement; is the true or
30、 as true considered value. 3.6.7 measuring instrument Technical device for measuring a quantity. 3.6.8 measuring transducer Device which converts the value of one quantity to a value of another quantity or to a different value of the same quanti. 3.6.9 sensor Part of a measuring instrument which rec
31、eives information about a quantity. The sensor is the first element of a measuring transducer. 3.6.10 sensing element Sensing part of sensor which is under direct influence of a quantiiy to be measured. 3.6.11fluid Iiquid, gas or vapour. In this standard priority is given to water, air, steam or any
32、 fluid used for heat transfer. 3.6.12 primary fluid Fluid acting as the heat source. 3.6.13 secondary fluid Fluid acting as the heat sink. 3.6.14 single-phase fluid A fluid in single-phase can be liquid or gas. 3.6.16 multi-phase fluid A fluid with two or more phases can be liquid and gas. 3.6.16 pr
33、imary rwgerant Fluid producing low temperature by absorbiig heat during evaporation at low pressure and rejecting heat during condensation at a high pressure. 3.6.17 secondary refigerant Fluid conveying heat from the low temperature source to the evaporating primary refrigerant. O BSI 1997 - - STD-B
34、SI BS EN 30b-ENGL 1797 m 1b24bb9 Ob4b517 37“ m 4 sampling 4.1 Sampling frequency The sampling kequency or the time between two consecutive readings shall be sufficient for the medium around the measuring points to have changed. The following formula can be used as a guidehe for the sampling period:
35、M is the total medium mass in the system expressed in kilograms; is the mass flow expressed in kilograms per second. This corresponds to about ten measurements in a period corresponding to the exchange rate of the volume of the system. Considerably higher sampling frequency may be required for the p
36、erformance of the regulating system. 4.2 Measuring sampling period Measurements shall continue for a sufficient length of time to give statkticaily satisfactory results. The measurements performed shall also indicate the stabiiity of the test point 4.3 Simultaneous reading of measurements On each me
37、asuring occasion the transducers shall be read off as rapidly as possible. The measurement shali provide an instantaneous picture of the heat exchanger. The following formula provides a guideline for simultaneous measurements with respect to time (t). M ts t - looq, =io where: t M qm is the time, ex
38、pressed in seconds; is the sampling period expressed in seconds, is the total medium mass in the system expressed in kilograms; is the mass flow expressed in kilograms per second 4.4 Mean value calculation Several measurements are carried out at each point in order to decrease the Statistacal error,
39、 The performance of the heat exchanger shall be calculated on the basis of the mean value for the respective measurement dueS. The mew due shall be calculated with the instantaneous measurement dues so that lack of hearity in conversions between si and measurement values does not influence the mean
40、value. In the case of heat exchangers which are fouled or frozen, special instructions concerning the evaluation shall be followed. See the relevant Parts in the European Standards for various branch applications. Page 7 EN 306 : 1997 5 Temperature measurement 6.1 Purpose in a single-phase system th
41、e change in the medium temperature through the measurement object and the thermal capacity is sufficient to determine the change in enthalpy through the heat exchanger. Absolute temperatures are needed in a two-phase or multi-phase system, and a further quantity must be measured in order to determin
42、e the change in enthalpy See clause 8. The requirements for the temperature measurements for various applications are presented in the European Stan - accuracx - chemical resistance; - thed ageing. When measuring with a thermocouple, the reference point temperature must be known. The uncertainty in
43、the determination of the reference temperature influences the uncertainty of the temperature measurement when measuring with a thermocouple. 6.3 Preparations 63.1 Instdlation The temperature sensor shall be installed so that it does not disturb the medium flow and/or cause secondary effects such as
44、medium leakage. For practical reasons, the sensor is often installed in measurement pockets since the medium flow takes place in pipes. In such cases it is possible to install and remove a sensor without influencing the medium flows. Measurement pockets also protect the sensor against mechanid and c
45、hemical damage. The temperature sensor shail be installed and insulated so that heat leakage through the sensor does not influence the performance of the heat exchanger or the measured temperature. satisfactory thermal contact between the sensor and medium is essential. Thm contact can be obtained w
46、ith the aid of heat-transferring paste, iarge heat-sensing surfaces, turbulent medium flows etc. In multi-phase systems, pressure changes can influence the phase state and thus also the enthalpy content in meia. This shall be taken into account K I Nickelchromehickel-aluminium I - 210 to 1372 O BSI
47、1997 If a risk of temperature stsatifcation occurs, several sensors shali be installed in one measurement plane. These can be installed in accordance with the figure below The mean value of the temperatures is formed and is used as inputioutput temperature. If considerable deviations in temperature
48、occur between different sensors in the same measurement plane, the temperatures should be weighted with regard to the local flow velocity of the measurement point to obtain the correct heat quantity. The following formula shall be used where: T, n q va, Tk is the weighted mean temperature in the mea
49、surement plane expressed in “C; is the number of temperature measurement pointq is the flow velocity at measurement point No. k expressed in metres per second; is the mean value of the flow velocity expressed in metres per second; is the temperature at measurement point No. k expressed in “C. Alternatively, the flow can be mixed to obtain the correct mean temperature. Page 9 EN 306 : 1997 6.3.2 Location The temperature sensors shail be so located that oniy temperature changes caused by the heat exchanger are measured. A boundary shall theref
