ASHRAE OR-10-030-2010 Thermal Environment around Strong Heat Source with Single-Sided Natural Ventilation《带有单面自然通风的强热源周围的热环境》.pdf

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1、284 2010 ASHRAEABSTRACTA test model has been built in order to analyze how a strongheat source (SHS) influences its surrounding thermal environ-ment with single-sided natural ventilation. Through a studyabout how the air temperature distributes around the heatsource, particularly when the heat sourc

2、e was located in threelocationsin the center of the test model room, near the inletand comparatively far away from the inlet, a conclusion canbe drawn that three factors, heat release rate of the SHS, airdistribution with single-sided natural ventilation and the loca-tion of the heat source, have a

3、great impact on the surroundingthermal environment. Furthermore, if the heat release rate ofthe heat source is fixed, the other two above-mentioned factorswould take in charge instead. Furthermore, the air-tempera-ture in the leeward side appears a little higher than that in thewindward side. Combin

4、ed the experiment and some fieldworkresults, it is easy to draw the conclusion that when the heatsource is located comparatively far away from the inlet, thetemperature around the heat source would rise approximatelylinearly with height. The result is consistent with the CFDsimulation.INTRODUCTIONIt

5、 is common that a SHS exists in the workshop of electricpower or metallurgical industries. The heat emitted by theSHS has greatly influenced the indoor thermal environmentand workers health and thus directly relates to work effi-ciency. The steel rolling workshop typically represents thiskind of wor

6、kshops. A cold rolling workshop of one steelfactory in Shanghai, China, has been used to researchsurrounding thermal environment of the working area. Therolling furnace did not cover a broad area and yet was morethan the half of the total height of the workshop high. Aroundthe furnace wall there are

7、 footpaths for regular operation andexamination. A workshop is next to the cold rolling workshopon one side, so only the windows on the other side could beopen. So here comes the problem: if we choose natural venti-lation as our venting pattern, the single-sided natural ventila-tion would serve as t

8、he only way. Thus the heat released by thefurnace would bring about many negative effects on the indoorenvironment. In this case, under single-sided natural ventila-tion, issues, such as how the SHS will work on the surroundingenvironment and what the characteristics of the air distributionare, shou

9、ld be resolved. This paper primarily discusses theseproblems, based on the test model studies, where the single-sided natural ventilation is motivated by thermal pressuredifferences.SIMILARITY CRITERIONThe height of the test model cell is 2 m (6.56ft), but theindustry workshop with SHS is usually a

10、large space above 10m (32.81ft) height. Considered that the indoor airflow is simi-lar to the flow in the ducts, so according to the similaritytheory, if the air flow is in the self-simulation area of Reyn-olds number, the air flow in the test model is similar to the airflow in the industry workshop

11、. Generally, if the Reynoldsnumber fulfills (1), we think that the air flow is in the self-simulation area of Reynolds number, which means the fric-tion resistance is dependent of Reynolds number.Re = vd/ 2000 (1)Through the measurements, we have1. the average inlet velocity of the test model cell i

12、s 0.2 m/s(0.7 ft/s).Thermal Environment around Strong Heat Source with Single-Sided Natural VentilationDong Liu, PhD Siwei Li Qing MiaoDong Liu is associate professor and Siwei Li and Qing Miao are graduate students in the Department of Mechanical Engineering, TongjiUniversity, Shanghai China.OR-10-

13、030 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without

14、ASHRAEs prior written permission. ASHRAE Transactions 2852. the hydraulic diameter of the inlet is 0.28 m (0.92 ft).3. the air viscosity coefficient at the temperature of 24C(75.2F) is 16.1106.So according to Equation (1), we get that the Reynoldsnumber equals 3.7 103and fulfill Equation (1). The ai

15、rflowin the test model cell is similar to the airflow in the industryworkshop. Details of similarity criterion between the mock-upand the prototype was described fully elsewhere 3 and 4.Define the temperature differences scale CATto be 1, sowhen the outside temperature of the mock-up is kept the sam

16、eas of the prototype, the temperature scale CAwas also 1. Ignorethe atmosphere pressure difference between the mock-up andthe prototype, we haveCQ= CG= Cl5/2CV= Cl1/2whereCl= geometry scale;CQ= heat quantity scale;CG=air volume scaleCV= velocity scale.Through calculation, a conclusion can be drawn t

17、hat theminimum air velocity should be greater than a certain value tomeet the requirements of self-simulation area of Reynoldsnumber. Table 1 shows the corresponding relation betweenscales and the minimum velocity.Geometry scale as 1:25 has finally been chosen in orderto avoid any inaccuracy caused

18、by the inconvenience due to thelow air velocity. Thus the dimension of the test model is 2 2 2 m (6.56 ft) since dimension of the workshops is almost 50 50 50 m (164.04 ft).THE SHS MODELThe SHS cell is a single room with a floor area of 2 m(6.56 ft) 2 m (6.56 ft), 2 m (6.56 ft) high and is located i

19、n aHVAC laboratory which stands 3.2 m (10.5 ft) high in TongjiUniversity, Shanghai China (Figure 1). The cell is made ofsteel plates which are painted in grey. In order to simulate theworkshop situation, the plates on the top and two sides of thecell are fixed with screws so they can easily be taken

20、 down.There are an observation window on one facade and a door onthe opposite side for researchers. The resistance wires acts asthe heat source, with the high temperature resistant materialwrapped outside. The heat source with an area of 800 mm(2.62 ft) 400 mm (1.31 ft), 30 mm (1.18 in.) thick is li

21、ke arectangular plate. Its surface heats evenly and its input poweris adjustable from 0-3000 W.DATA COLLECTIONType T thermocouples are used to measure the surround-ing air temperature and Type K thermocouples (2 to 200C)(4 to 392F) are used to measure the surface temperature ofthe heat source. All t

22、hermocouples are connected to thecomputer through a data collecting block, so it is more conve-nient to collect and analyze the data. The probes of Type Tthermocouples are wrapped by aluminum radiation-proofshield during the measurement in order to avoid the influenceof the radiation from the heat s

23、ource. Before the measurement,all of the thermocouples are calibrated by the standard ther-mometer.Thermal electric anemometer type QDF-3 is used tomeasure the inlet airflow velocity. The measurement instru-ment ranges from 0.05 m/s (0.16 ft/s) to 3 m/s (9.84 ft/s) andhas an accuracy of 5% (full ran

24、ge).THE PLACEMENT OF THE SHSThe SHS plate hung with a steel wire and fixed in threedifferent positions: A. the centre of the cell; B. near the inletand 500 mm (1.64 ft) away from the centre of the cell; C. awayfrom the inlet and 500 mm (1.64 ft) away from the centre of thecell. As it is shown in Fig

25、ure 2, the plate was 300 mm (0.98 ft)higher than the bottom of the cell and 900 mm (2.95 ft) lowerthan the roof.Table 1. Corresponding Relation Between Scales and Minimum VelocityGeometry scale 1:10 1:15 1:20 1:25Heat quantity scale 1:316 1:871 1:1789 1:3125Velocity scale 1:3.16 1:3.87 1:4.47 1:5The

26、 minimum inlet velocity, m/s (ft/s)0.38 (1.25)0.46 (1.51)0.54 (1.77)0.6 (1.97)Figure 1 The SHS cell. 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional repr

27、oduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. 286 ASHRAE TransactionsHEAT TRANSFER RATE CALCULATION OF THE SHSWhen the input power of the SHS was 1500 W, the outputpower of the SHS has been calculated to be 2107 W/m

28、2according to the actual size of the plate. Besides, the averagetemperature of the plates surface is measured to be Tw =118.6C (245.48F), and the inner surface temperature of thecell is T0 = 29C (84.2F). So emissive power W of the plateis given by 1:Wrad= (Tw4 T04) = 0.96 5.67 108 (118.6 + 273)4 (29

29、 + 273)4 = 827 W/m2where = total hemispherical emissivity; = Stefan-Boltzmann constant (5.67 108W/m2K4)About 40% of the heat is emitted by radiation. It meansthat the raise of the surrounding air temperature is due to therest of the heat, about 900 W, which heats the air through ther-mal convection.

30、Under a certain natural ventilation condition, when theinput power of the SHS changes from 1000 W, 1500 W to3000 W, the relationship between the surface temperature ofthe SHS and the input power is shown in (a) of Figure 3. (b)of Figure 3 shows the relationship between the air tempera-tures at the p

31、oint which is along the outer normal of the SHScenter and 40 mm away from center and the input power.As it is shown in Figure 3, the surface temperature ofthe SHS increases linearly with the input power, and simul-taneously also obviously increases the surrounding airtemperature. So a conclusion can

32、 be drawn that the heattransfer rate of the SHS acts a decisive part in the surround-ing thermal environment around the SHS. The paper belowwill focus on the situation with 1500 W input power.Figure 2 Placements of the SHS (a) and the test pointsaround the SHS (b).Figure 3 Relationships between the

33、surface temperature ofthe SHS and the Input Power (a) and therelationships between the air temperature aroundthe SHS and the input power (b). 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part

34、1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. ASHRAE Transactions 287NEUTRAL PRESSURE LEVELThe area of the underside inlet:(2)The area of the top outlet:(3)whereG1= air mass

35、flux of the inlet, kg/s;G2= air mass flux of the outlet, kg/s; 1= flow coefficient of the inlet;2= flow coefficient of the outlet;h1= the height difference between the underside inlet centre and the neutral pressure level, m;h2= the height difference between the top exhaust window and the neutral pr

36、essure level, m;np= air density in the cell at the average temperature, kg/m3;w= inlet air density, kg/m3;p= exhaust air density, kg/m3.The physical principle that mass is conserved, whenapplied to this model of the airflow, simply states that the airmass flux of the inlet equals the air mass flux o

37、f the exhaustwindow, it means G1 = G2. From the Equations (2) and (3), wehave(4)Here we denote the inlet and the exhaust window have thesame configuration, so 1= 2.Substituting 1= 2 into Equation (4), we have(5)Denote H = h1+ h2, here H is the height difference be-tween the centre of the inlet and t

38、he exhaust window.With this and wapproximates to p, Equation (4)becomes (6)(7)In this experiment, substitutingF1 = 0.15 1.91 = 0.29 m2(3.12 ft2), F2= 0.246 1.91 =0.47 m2 (5.06 ft), H = 1.93 m (6.33 ft) into Equations (6) and(7), we have h1= 1.4 m (4.59 ft)h2 = 0.53 m (1.74 ft)Thus the result indicat

39、es that the neutral pressure level has a height of 1.4 m (4.59 ft).AIR TEMPERATURE DISTRIBUTION AROUND THE SHSThis chapter studies how the air temperature on both sidesof the SHS distributes according to the different locations ofthe SHS, through experiments, under single-sided naturalventilation.A.

40、 The SHS was located in the centre of the cell.The SHS was located at A as it is shown in Figure 2. Inorder to see about how the air temperature distributes near theSHS, test points were set up at a distance of 40 mm (1.57 in.)and 80 mm (3.15 in.) from the SHS, as it is shown in Figure 2.The input p

41、ower is fixed at 1500W, the surface heatrelease rate is 2107 W/m2and the inlet air temperature is 24C(75.2F).When the system becomes stable, starts the datacollection. And the result is shown in Figure 4.Examining Figure 4, we see that1. With the same height and equal distance from the SHS,the air t

42、emperatures at the leeward points are higher thanthose at the windward points, 2.9C (37.22F) higher onaverage.2. The air temperatures at the leeward points which were80 mm (3.15 in.) away from the SHS are close to those atF1G112gh1wnp()w-=F2G122gh2wnp()p-=F112gh1wnp()wF222gh2wnp()p=h1h2-F22pF12w-=h1

43、F22F12F22+- H=h2F12F12F22+- H=Figure 4 Comparison of leeward and windward airtemperature when the SHS was located in thecenter. 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For persona

44、l use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. 288 ASHRAE Transactionsthe windward points which were 40 mm (1.57 in.) awayfrom the SHS, even exceed at the height of 1.1 m (3.61 ft).B. The S

45、HS was located near the inlet.The location of the SHS as B and the test points around theSHS has been shown in Figure 2. And also the input power ofthe SHS, the surface heat release rate and the inlet air temper-ature remain the same. Figure 5 shows the experiment results.Analyzing Figure 5, we have

46、 that1. When the test points are 40 mm (1.57 in.) away from theSHS, the air temperatures at the leeward side and those atthe windward side dont have obvious difference.2. When the test points are 80 mm (3.15 in.) away from theSHS, the air temperatures at the windward side are gener-ally higher than

47、those at the leeward side.C. The SHS was located away from the inlet.The SHS was located at C as it is shown in Figure 2. Theother conditions are the same as A and B. Figure 6 shows themeasurement results.Examining Figure 6, we have that1. When the test points are 40 mm (1.57 in.) away from theSHS,

48、the air temperatures at the windward side are lowerthan those at the leeward side.2. When the test points are 80 mm (3.15 in.) away from theSHS, the air temperatures at the windward side are lowerthan those at the leeward side.3. When the test points are 40 mm (1.57 in.) away from theSHS, the air te

49、mperatures at the windward side have alinear increasing trend with the height.The summary of the air temperature distribution is tabu-lated in Table 2.FACTORS THAT INFLUENCE THE AIR TEMPERATURE DISTRIBUTION AROUND THE SHSThe heat release rate from the SHS is the dominant factorin arousing the air temperature increase around