BS 4485-2-1988 Water cooling towers - Methods for performance testing《水冷却塔规范 第2部分 性能试验方法》.pdf

1、BSI BS*4YB5 PART*Z BB = Lb24667 0007bOL B I BS 4485 : Part 2 : 1988 UDC 66.045.5.001.4 British Standards Institutiq. No part of this publication may be photocopied or otherwise reproduced without the prior permission in writing of BSI Brit ish Standard Water cooling towers Part 2. Methods for perfor

2、mance testing Tours,de refroidissement par leau Partie2. Mthodes dessai de fonctionnement Wasserkh Itrme Teil 2. Funktionsprfung British Standards Institution BSI BS*Ky485 PART*2 88 Lb2Kybb 0007602 T W BS 4485 : Part 2 : 1988 Foreword This Part of BS 4485, which has been prepared under the direction

3、 of the Civil Engineering and Building Structures Standards Committee, deals with the performance testing of industrial mechanical draught and natural draught water cooling towers. This Part of BS 4485 is a revision of BS 4485 : Part 2 : 1969 which is withdrawn, The principal difference between this

4、 Part of BS 4485 and the 1969 edition is the introduction of the option of using a computer to do the calculation of thermal performance capability rather than carrying it out manually. The performance of a cooling tower is dependent upon a number of factors, such as conditions of the atmosphere, co

5、nditions of the cooling water flow, conditions of equipment and conditions of the site, and the object of this Part of BS 4485 is to describe methods for the accurate determination of thermal performance. In addition, methods are described for the functional testing of equipment necessary for the sa

6、tisfactory operation of a cooling tower. This Part of BS 4485 also includes a description for the performance test procedure, the computation and evaluation of results, and the appendices provide worked examples for establishing the L/G ratio for natural draught cooling towers, and also the cooling

7、tower characteristic KaVIL. The other Parts of BS 4485 are as follows. Part 1 Glossary of terms Part 3 Code of practice for thermal and functional design Part 4 Code of practice for the structural design of Where necessary, definitions have been included in the revisions of BS 4485 : Parts 2, 3 and

8、4 so that when they have all been published BS 4485 : Part 1 can be withdrawn. Compliance with a British Standard does not of itself confer immunity from legal obligations. cooling towers BSI BS*4485 PART*k2 8 W Lb24bb 0007b03 L W BS 4485 : Part 2 : 1988 Contents Foreword Committees responsible Page

9、 Inside front cover Back cover Methods 1 Scope 2 Definitions 3 Symbols and units 4 4.1 General 4.2 Conditions of site 4.3 Conditions of equipment 4.4 Conditions of atmosphere 4.5 Conditions of inlet water 4.6 Variation from design conditions 5 5.1 Measurement of wind velocity 5.2 Measurement of air

10、temperature 5.3 Measurement of water temperature 5.4 Measurement of water flow 5.5 Water analysis 5.6 Measurement of tower pumping head 5.7 Measurement of power input to the fan driver 5.8 Measurement of drift loss 5.9 Measurement of tower noise 6 Test checks and readings 6.1 Functional test 6.2 Per

11、formance test 7 Performance test procedure 7.1 Preparation for test 7.2 Preliminary tests 7.3 Test procedure 8 Computation of results 8.1 Reduction of test readings 8.2 Computation of inlet water temperature 8.3 Computation of recooled water temperature with make-up and purge flows shut off 8.4 Comp

12、utation of recooled water temperature with make-up and purge flows operating Conditions of validity of tests Instruments and methods of measurement 2 2 2 2 2 2 2 4 4 4 4 4 4 5 5 6 6 6 6 6 6 6 7 7 7 7 8 8 8 8 8 9 - 8.5 Computation of tower pumping head 8.6 computation of thermal lag 8.7 Computation o

13、f fan power 9 Evaluation of thermal performance Appendices A Matters to be agreed between purchaser and supplier B Guidance on precipitation rates and determination of droplet size for the evaluation of drift nuisance C Methods for evaluating test results D Computer program for calculating performan

14、ce capabi I ity E Determination of test value of LIG for natural draught towers F Example of determination of cooling tower capability from calculation of KaVIL value Tables 1 Symbols and units 2 Frequency of readings 3 Precipitation rates for droplet diameters 100 pm- 4 Guide to nuisance effects fo

15、r precipitation rates 5 Enthalpy of saturated air to 2000 pm of 0.05 mm/h to 0.0005 mm/h Figures 1 Determination of droplet diameter 2 Graph for determination of density difference at 3 Determination of relation between G, and 4 Determination of cooling tower capability design conditions G, for natu

16、ral draught cooling towers Page 9 9 9 9 10 11 13 17 27 32 3 8 12 13 15 12 29 31 33 1 BSI BSm111185 PART*Z 88 W Lb211669 0007604 3 W BS 4485 : Part 2 : 1988 Methods 1 Scope This Part of BS 4485 describes methods for the determina- tion of the performance of industrial mechanical draught and natural d

17、raught water cooling towers. This Part of BS 4485 can also be applied to other forms of coo I ing towers. NOTE 1. The matters to be agreed between purchaser and supplier are listed in appendix A. NOTE 2. The titles of the publications referred to in this standard are listed on page 33. 2 Definitions

18、 For the purposes of this Part of BS 4485 the following definitions apply. 2.1 air flow. Total quantity of air, including associated water vapour flowing through the tower. 2.2 ambient wet (dry) bulb temperature. Wet (dry) bulb temperature of air measured windward of the tower and free from the infl

19、uence of the tower. 2.3 approach. Difference between recooled water temperature and nominal inlet air wet bulb temperature. 2.4 inlet water flow. Quantity of hot water flowing into the tower. 2.5 cold water basin. Device underlying the tower to receive the cold water from the tower and direct its fl

20、ow to the suction line or sump. 2.6 cooling range. Difference between the hot water temperature and the recooled water temperature. NOTE. The term range is also applied to this definition, but is regarded as a non-preferred term. 2.7 drift loss. Water lost from the tower as liquid droplets entrained

21、 in the outlet air. 2.8 heat load. Rate of heat removal from the water within the tower. 2.9 hot wbter temperature. Temperature of inlet water. 2.10 inlet air wet (dry) bulb temperatures. Average wet (dry) bulb temperatures of the inlet air; including any recirculation effect. NOTE. This is an essen

22、tial concept for purposes of design, but is difficult to measure. 2.11 make up. Water added to the circulating water system to replace water loss from the system by evaporation, drift, purge atid leakage. 2.12 nomirial inlet air wet (dry) bulb temperatures. Arithmetical for crossflow see appendix C.

23、 tAll enthalpies relate to 1 kg of dry air. Units kJ/kg kg/m2 .s.(kg/kg)l kg/(m2 -SI - m3 Is m3 /s m3 /s OC OC OC OC OC OC “C m3 /m2 m3 W kg/m3 kJ/kg K kg/m3 - - - ES1 BS*lili85 PART*2 88 W Lb2libbS 0007bob 7 rn BS 4485 : Part 2 : 1988 4.4 Conditions of atmosphere The tests shall be carried out duri

24、ng stable weather conditions and within the following limitations. (a) Wind velocity readings averaged over the test period shall not exceed 5.0 m/s, with readings averaged over 1 min not exceeding 7.0 m/s, when measured at a height of 1.5 m to 2,O m above local ground level. (b) The inlet wet bulb

25、temperature shall be within i 5 K of the design wet bulb temperature, but shall not fall below 3 “C. Readings may fluctuate but the rate of change in average wet bulb temperature shall not exceed 1 K/h. (c) In the case of natural draught towers, the relative humidity shall not fall below 40 %. (d) N

26、atural draught towers shall not be tested under conditions of atmospheric inversion. Where doubt exists as to the presence of a normal lapse rate, additional readings of air temperature shall be taken at a height of 8 m to 10 m to confirm a positive lapse (see 5.2). The tests shall be carried out du

27、ring daylight hours for reasons of safety and accuracy of measurements except that under certain circumstances it may be necessary to carry out noise tests at night. 4.5 Conditions of inlet water The total dissolved solids in the inlet water shall be within 500 mg/L of the design value and oil, tar

28、or other fatty substances shall not exceed 10 mg/L. 4.6 Variation from design conditions The following variations of average test readings from design conditions are permissible. (a) Inlet water flow not more than 10 % below or 10 % above the design value. (b) Cooling range not more than 20 % below

29、or 20 % above the design value. (cl Heat load not more than 20 % below or 20 % above . the design value. During the hour selected in accordance with 7.3.1 as being representative of the test conditions, the difference between maximum and minimum readings of the inlet water flow, cooling range and he

30、at load, shall not exceed 5 %. 5 Instruments and methods of measurement 5.1 Measurement of wind velocity Instruments shall be calibrated before use. Measurement shall be made in an open and unobstructed location to the windward of the equipment at a horizontal distance sufficient to eliminate the in

31、fluence of the upstream effects of the equipment, and, where possible, a vertical distance of 1.5 m to 2.0 m above local ground level. NOTE 1. The instrument recommended for the measurement of wind velocity is either the rotating cup or rotating vane anemometer. NOTE 2. If such a location is inacces

32、sible, a suitable location for wind measurement should be agreed between the test personnel (see appendix A). NOTE 3. The frequency of readings taken should increase with wind speed and gust effect, in order to arrive at a representative average result. 5.2 Measurement of air temperature 5.2.1 Gener

33、al. The number of stations at which measure- ments are to be taken depends upon the size of the cooling tower and the existence of neighbouring influences. In the case of multi-cell mechanical draught and natural draught cooling towers, a minimum of three stations shall be used, whereas one station

34、may suffice for a single-cell cooling tower. 5.2.2 Measurement of nominal inlet air temperatures. The nominal inlet wet bulb and dry bulb temperature shall be determined as the arithmetical average of the measure- ments taken within 1.5 m of the air inlets and between 1.5 m and 2.0 m above the basin

35、 kerb elevation on both sides of the cooling tower so as to bracket substantially the air flow to the tower. In the case of natural draught towers, it is likely that the ambient and nominal inlet air temperatures will be identical, in which case the tests can be carried out using the ambient tempera

36、ture measurements only in accordance with 5.2.- 5.2.3 Measurement of ambient temperatures. The ambient wet bulb and dry bulb temperatures shall be determined as the arithmetic average of measurements taken, where possible, approximately 1.5 m to 2 m above ground level, and not less than 15 m or more

37、 than 100 m to windward of the equipment, and equally spread along a line substantially bracketing the flow of air to the equipment. NOTE. If such a location is inaccessible, or the area surrounding the equipment contains elements which can affect the ambient wet bulb and dry bulb temperatures, a su

38、itable location for these measure- ments should be mutually agreed (see appendix A). 5.2.4 Measurement of wet bulb and dry bulb temperatures. The instrument for the measurement of the wet bulb and dry bulb temperature shall be a mechanically aspirated psychrometer complying with the following. (a) T

39、he temperature-sensitive element shall be in accordance with 5.3.1. (b) Temperature-sensitive elements shall be shielded from the direct rays of the sun or from any other sources of radiant heat. Shielding devices shall be substantially at the dry bulb temperature. (c) The wick covering the bulb of

40、the wet bulb thermometer shall be kept clean at all times and maintained in a saturated condition. It shall be a snug fit over the bulb and at least 25 mm in length. *. (d) The temperature of the distilled water used to wet the wick shall be at approximately the wet bulb temperature to be measured.

41、BSI BSU4q85 PART*:ZI 88 m Lb24b67 0007607 7 BS 4485 : Part 2 : 1988 NOTE 1. This can be obtained in practice by allowing adequate ventilated wick between the water supply and the temperature- sensitive element. (e) The air velocity over the temperature-sensitive elements shall be between 3.0 m/s and

42、 6.0 m/s. At least three successive readings, separated by 10 s, shall be taken at any given location and averaged after the psychrometer has reached equilibrium. NOTE 2. The instrument will usually reach equilibrium in 2 min. 5.3 Measurement of water temperature 5.3.1 General. The method used to me

43、asure water temperature shall be accurate to 1.0.05 OC. NOTE. The instrument preferred for water temperature measure- ment is the mercury in glass thermometer with divisions etched on the glass at intervals not greater than 0.1 OC. Other officially calibrated instruments may be used by mutual agreem

44、ent (see appendix A). The instrument used for the test shall have been checked against a reference thermometer calibrated by an approved calibrating authority prior to the test, but not more than 6 months before the test in the case of a first calibration of the same instrument. Certificates of exam

45、ination shall be made available for inspection. The locations of the temperature measuring instruments shall be such that theeverage tempehfreTthe hGt-and- the recooled water flows are determined. Where various streams of different temperatures combine, the point of measurement shall be located to e

46、nsure complete mixing without stratif ication. If stratification is evident, the weighted average water temperature shall be determined by a survey of a selected section using simultaneous temperature and water flow measurements at each ooint. 5.3.2 Hot water temperature. A suitable location for the

47、 measuring instrument for hot water temperature is the common supply conduit to the tower. 5.3.3 Recooled water temperature. The recooled water temperature can be measured directly at the point where the water is discharged from the basin, the average cold water temperature being determined by simul

48、taneous test readings, where possible, across the selected section. Where stratification is evident, a suitable point of measure- ment is at the outlet of the circulating water pump. Allowance shall also be made for the rise in temperature due to energy losses in the pump (see 8.4). When the tempera

49、ture of the circulating water in the basin is the mixed temperature of both circulating water and make-up water, the recooled water temperature shall be determined indirectly by heat balance calculation taking into account the temperature and quantity of make-up and purge and other heat added or removed between the tower and the point of measurement (see 8.4). 5.3.4 Make-up water and purge temperatures. Temperature readings shall be taken at the spill over weir or in the piping immediately adjacent to the cooling tower. 5.4 Measurement of water flow 5.4.1 Measurement 5.4.1.