孔板流量计算公式

孔板流量计的测定与计算在孔板流量计的前后端测出压差后可按以下两种方法进行计算；（一）、可按公式计算出瓦斯流量。计算公式：Q混=Kb(Δh)1/2δpδT（1）Q纯=Q混X式中：Q混——抽放的瓦斯混合量，m3/min；Q纯——抽放的瓦斯纯量，m3/min；K——实际孔板流量特性系数，计算见（2）式；b——瓦斯浓度校正系数，计算见（3）式；δp——气压校正系数，计算见（4）式；δT——温度校正系数，计算见（5）式；Δh——在孔板前后端所测之压差，mmH2O；X——混合气体中瓦斯浓度，%。K=189.76a0md2（2）式中：a0——标准孔板流量系数；m=（d1/D）2m——截面比；D——管道直径，米；d1——孔板直径，米；b=[1/（1－0.00446X）]1/2（3）δp=（PT/760）1/2（4）式中：PT——孔板上风端测得的绝对压力，mmHg；PT=测定当地压力（mmHg）+[该点管内正压（正）或负压（负）（mmH2O）]/13.6760——标准大气压，mmHg；δT=293°/（273°+t°）（5）式中：t°——瓦斯管内测点温度，℃；293°——标准绝对温度，℃；四寸管路d1=49.50mmD=98.28mm则：m=0.2536查（表一）得a0=0.6327K=0.3001六寸管路d1=74.68mmD=151.20mm则：m=0.2439查（表一）得a0=0.6294K=0.6718（二）、在计算过程中为加快计算速度，可把公式中的各项数值表格化，查表得出b、δp、δT。瓦斯浓度校正系数b值表二；瓦斯浓度(%)012345678901020304050607080901001.0001.0241.0481.0741.1031.1341.1681.2061.2471.2921.3441.0021.0261.0501.0771.1061.1371.1721.2101.2511.2971.0041.0281.0531.0801.1091.1411.1761.2141.2561.3021.0071.0311.0561.0821.1131.1441.1791.2201.2601.3081.0091.0321.0581.0851.1161.1481.1821.2221.2631.3131.0111.0351.0601.0881.1191.1511.1861.2251.2691.3181.0141.0381.0631.0911.1221.1541.1901.2291.2741.3241.00161.0401.0661.0951.1251.1581.1941.2341.2781.3281.0191.0431.0681.0971.1281.1621.1981.2381.2831.3341.0211.0451.0711.1001.1311.1641.2021.2431.2871.339气压校正系数δp值表三；压力(mmHg)δp压力(mmHg)δp压力(mmHg)δp压力(mmHg)δp压力(mmHg)δp1501551601651701751801851901952002052102152202252302352402452502552602652702752802850.4440.4520.4580.4660.4720.4800.4880.4930.5000.5060.5130.5190.5250.5320.5380.5440.5500.5560.5620.5680.5740.5790.5850.5900.5960.6010.6070.6122902953003053103153203253303353403453503553603653703753803853903954004054104154204250.6170.6230.6290.6330.6390.6430.6490.6540.6590.6630.6690.6740.6780.6830.6890.6930.6980.7020.7070.7120.7160.7200.7250.7290.7340.7390.7430.7484304354404454504554604654704754804854904955005055105155205255305355405455505555605650.7520.7560.7610.7650.7690.7740.7780.7820.7860.7910.7940.7990.8030.8070.8110.8150.8190.8230.8270.8310.8350.8390.8430.8470.8500.8540,8580.8625705755805855905956006056106156206256306356406456506556606656706756806856906957007050.8660.8700.8740.8780.8810.8860.8890.8920.8960.9000.9030.9070.9100.9140.9180.9220.9250.9280.9320.9350.9390.9420.9460.9490.9530.9560.9600.9637107157207257307357407457507557607657707757807857907958008058108158208258308358408450.9670.9700.9730.9770.9800.9840.9870.9900.9930.9971.0001.0031.0061.0091.0131.0161.0191.0231.0261.0291.0311.0341.0371.0401.0431.0471.0501.053温度校正系数δT值表四；温度℃0123456789403020100-0-10-20-30-400．9680．9831．0001．0171．0351．0351．0561．0761．0981．1220．9660．9820．9981．0161．0341．0371．0581．0781．0991．1230．9640．9800．9971．0141．0331．0391．0591．0801．1031．1260．9630．9790．9951．0121．0321．0411．0611．0831．1051．1290．9610．9770．9931．0101．0291．0431．0631．0851．1081．1310．9600．9750．9921．0081．0271．0451．0661．0861．1091．1330．9580．9740．9901．0071．0251．0471．0681．0891．1151．1390．9570．9720．9881．0051．0231．0491．0701．0911．1151．1390．9550．9710．9871．0031．0211．0521．0721．0941．1171．1410．9540．9690．9851．0011．0191．0541．0741．0951．1191．143例题：某钻场瓦斯支管路D=25.4mm，孔板直径d1=12.7mm，在井下实测，测得压差为30mmH2O，瓦斯浓度30%，测得大气压力1.01×105pa，管内负压0.07Mpa,瓦斯管内温度为20℃，求瓦斯流量？解：由公式Q混=K*b*(Δh)1/2*δp*δT求K值m=(d1/D)1/2=(12.7/25.4)1/2=0.25查表一得：a0=0.6417K=0.0190b值查表二得：b=1.074求δp值PT=1.01*105/(9.8*13.6)-0.07*106/(9.8*13.6)=232.6mmHg求δp查表三得：δp=0.556求δT查表四得：δT=0.983则Q混=0.019*1.074*301/2*0.556*0.983=0.061m3/minQ纯=Q混*X=0.061*30%=0.0183m3/min（举例）YD-2型孔板流量计的应用与计算孔板流量计用以测定瓦斯管路中的瓦斯流量（如下图）。抽放瓦斯管路中孔板流量计的安装与使用：（1）、在抽放瓦斯管路中安装孔板时，孔板的孔口必须与管道同心，其端面与管路轴线垂直，偏心度<1～２％；（2）、安装孔板的管道内壁，在孔板前后距离2D的范围内，不应有凸凹不平，焊缝和垫片等。（3）、孔板流量计的上游（前端），管道直线长度》20D，下游（后端）长度》10D；（4）、要经常清理孔板前后的积水和污物，孔板锈蚀要更换；（5）、抽放瓦斯量有较大变化时，应根据流量大小更换相应的孔板。应用孔板流量计与计算管道内的瓦斯流量时，必须同时测量的参数：（1）、孔板前后端的压差值（△h）；（2）、测量地点的大气压力（PD）；（3）、管道内的气体压力（PG），正压或负压；（4）、管道内的气体温度（t）;（5）、管道内的瓦斯浓度（x）。抽放的混合瓦斯量计算：式中：QH--------抽放的混合瓦斯量，m3/min;K-------孔板系数，取实际校正值；0.3072b--------瓦斯浓度校正常数；x-------混合瓦斯中的瓦斯浓度，%；δT--------------温度校正系数；δT=293/(273+t)t--------管道内的气体温度，℃；δP------压力校正系数；δP=(Pt/101.325)1/2Pt----孔板前端管道内的绝对压力，Kpa;Pt=PDPD---------测量地点的大气压力；PG---------观测点管道内的压力，正压取(+),负压取(-),Kpa;101.325----------标准大气压，Kpa。抽放的纯瓦斯量计算Qc=QHX/100式中Qc-----抽放的纯瓦斯量，m3/