孔板流量計(jì)算公式

孔板流量計(jì)的測定與計(jì)算在孔板流量計(jì)的前后端測出壓差后可按以下兩種方法進(jìn)行計(jì)算；（一）、可按公式計(jì)算出瓦斯流量。計(jì)算公式：Q混=Kb(Δh)1/2δpδT（1）Q純=Q混X式中：Q混——抽放的瓦斯混合量，m3/min；Q純——抽放的瓦斯純量，m3/min；K——實(shí)際孔板流量特性系數(shù)，計(jì)算見（2）式；b——瓦斯?jié)舛刃Ｕ禂?shù)，計(jì)算見（3）式；δp——?dú)鈮盒Ｕ禂?shù)，計(jì)算見（4）式；δT——溫度校正系數(shù)，計(jì)算見（5）式；Δh——在孔板前后端所測之壓差，mmH2O；X——混合氣體中瓦斯?jié)舛龋?。K=189.76a0md2（2）式中：a0——標(biāo)準(zhǔn)孔板流量系數(shù)；m=（d1/D）2m——截面比；D——管道直徑，米；d1——孔板直徑，米；b=[1/（1－0.00446X）]1/2（3）δp=（PT/760）1/2（4）式中：PT——孔板上風(fēng)端測得的絕對(duì)壓力，mmHg；PT=測定當(dāng)?shù)貕毫Γ╩mHg）+[該點(diǎn)管內(nèi)正壓（正）或負(fù)壓（負(fù)）（mmH2O）]/13.6760——標(biāo)準(zhǔn)大氣壓，mmHg；δT=293°/（273°+t°）（5）式中：t°——瓦斯管內(nèi)測點(diǎn)溫度，℃；293°——標(biāo)準(zhǔn)絕對(duì)溫度，℃；四寸管路d1=49.50mmD=98.28mm則：m=0.2536查（表一）得a0=0.6327K=0.3001六寸管路d1=74.68mmD=151.20mm則：m=0.2439查（表一）得a0=0.6294K=0.6718（二）、在計(jì)算過程中為加快計(jì)算速度，可把公式中的各項(xiàng)數(shù)值表格化，查表得出b、δp、δT。瓦斯?jié)舛刃Ｕ禂?shù)b值表二；瓦斯?jié)舛?%)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氣壓校正系數(shù)δp值表三；壓力(mmHg)δp壓力(mmHg)δp壓力(mmHg)δp壓力(mmHg)δp壓力(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溫度校正系數(shù)δT值表四；溫度℃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例題：某鉆場瓦斯支管路D=25.4mm，孔板直徑d1=12.7mm，在井下實(shí)測，測得壓差為30mmH2O，瓦斯?jié)舛?0%，測得大氣壓力1.01×105pa，管內(nèi)負(fù)壓0.07Mpa,瓦斯管內(nèi)溫度為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則Q混=0.019*1.074*301/2*0.556*0.983=0.061m3/minQ純=Q混*X=0.061*30%=0.0183m3/min（舉例）YD-2型孔板流量計(jì)的應(yīng)用與計(jì)算孔板流量計(jì)用以測定瓦斯管路中的瓦斯流量（如下圖）。抽放瓦斯管路中孔板流量計(jì)的安裝與使用：（1）、在抽放瓦斯管路中安裝孔板時(shí)，孔板的孔口必須與管道同心，其端面與管路軸線垂直，偏心度<1～２％；（2）、安裝孔板的管道內(nèi)壁，在孔板前后距離2D的范圍內(nèi)，不應(yīng)有凸凹不平，焊縫和墊片等。（3）、孔板流量計(jì)的上游（前端），管道直線長度》20D，下游（后端）長度》10D；（4）、要經(jīng)常清理孔板前后的積水和污物，孔板銹蝕要更換；（5）、抽放瓦斯量有較大變化時(shí)，應(yīng)根據(jù)流量大小更換相應(yīng)的孔板。應(yīng)用孔板流量計(jì)與計(jì)算管道內(nèi)的瓦斯流量時(shí)，必須同時(shí)測量的參數(shù)：（1）、孔板前后端的壓差值（△h）；（2）、測量地點(diǎn)的大氣壓力（PD）；（3）、管道內(nèi)的氣體壓力（PG），正壓或負(fù)壓；（4）、管道內(nèi)的氣體溫度（t）;（5）、管道內(nèi)的瓦斯?jié)舛龋▁）。抽放的混合瓦斯量計(jì)算：式中：QH--------抽放的混合瓦斯量，m3/min;K-------孔板系數(shù)，取實(shí)際校正值；0.3072b--------瓦斯?jié)舛刃Ｕ?shù)；x-------混合瓦斯中的瓦斯?jié)舛龋?；δT--------------溫度校正系數(shù)；δT=293/(273+t)t--------管道內(nèi)的氣體溫度，℃；δP------壓力校正系數(shù)；δP=(Pt/101.325)1/2Pt----孔板前端管道內(nèi)的絕對(duì)壓力，Kpa;Pt=PDPD---------測量地點(diǎn)的大氣壓力；PG---------觀測點(diǎn)管道內(nèi)的壓力，正壓取(+),負(fù)壓取(-),Kpa;101.325----------標(biāo)準(zhǔn)大氣壓，Kpa。抽放的純瓦斯量計(jì)算Qc=QHX/100式中Qc-----抽放的純瓦斯量，m3/