一、實(shí)驗(yàn)?zāi)康?掌握干燥曲線和干燥速率曲線的測(cè)定方法。 學(xué)習(xí)物料含水量的測(cè)定方法。 加深對(duì)物料臨界含水量Xc的概念及其影響因素的理解。 學(xué)習(xí)恒速干燥階段物料與空氣之間對(duì)流傳熱系數(shù)的測(cè)定方法。 學(xué)習(xí)用誤差分析方法對(duì)實(shí)驗(yàn)結(jié)果進(jìn)行誤差估算。二、實(shí)驗(yàn)內(nèi)容 每組在某固定的空氣流量和某固定的空氣溫度下測(cè)量一種物料干燥曲線、干燥速率曲線和臨界含水量。 測(cè)定恒速干燥階段物料與空氣之間對(duì)流傳熱系數(shù)。三、實(shí)驗(yàn)原理1. 干燥速率的測(cè)定U=dWSdWS (7-1)式中：U干燥速率，kg /（m2h）；S干燥面積，m2；時(shí)間間隔，h；W時(shí)間間隔內(nèi)干燥氣化的水分量，kg。2. 物料干基含水量X =G-GCGc （7-2）式中：X物料干基含水量，kg水/ kg絕干物料；G固體濕物料的量，kg；Gc絕干物料量，kg。3. 恒速干燥階段，物料表面與空氣之間對(duì)流傳熱系數(shù)的測(cè)定Uc = dWSd = dQrtwSd = (t-tw)rtw （7-3）=Ucrtwt-tw （7-4）式中：恒速干燥階段物料表面與空氣之間的對(duì)流傳熱系數(shù)，W/（m2）；Uc恒速干燥階段的干燥速率，kg/（m2s）；tw干燥器內(nèi)空氣的濕球溫度，；t干燥器內(nèi)空氣的干球溫度，；rtwtw下水的氣化熱，J/ kg。 4. 干燥器內(nèi)空氣實(shí)際體積流量的計(jì)算由節(jié)流式流量計(jì)的流量公式和理想氣體的狀態(tài)方程式可推導(dǎo)出：Vt=Vto273+t273+t0 （7-5）式中：Vt干燥器內(nèi)空氣實(shí)際流量，m3/ s；t0流量計(jì)處空氣的溫度，；Vt0常壓下t0時(shí)空氣的流量，m3/ s；t干燥器內(nèi)空氣的溫度，。VT0 =C0A02P （7-6）A0 =4d02 （7-7）式中：C0流量計(jì)流量系數(shù)，C0=0.67A0節(jié)流孔開(kāi)孔面積，m2； d0節(jié)流孔開(kāi)孔直徑， d0=0.050 m；P節(jié)流孔上下游兩側(cè)壓力差，Pa；孔板流量計(jì)處t0時(shí)空氣的密度，kg/m3。四、實(shí)驗(yàn)裝置圖1干燥速率曲線測(cè)定實(shí)驗(yàn)裝置圖1離心風(fēng)機(jī)； 2-孔板流量計(jì)； 3-孔板流量計(jì)顯示儀； 4，11重量傳感器顯示儀； 5干燥物料； 6電加熱器； 7干球溫度計(jì)； 8，14濕球溫度計(jì)顯示儀； 9洞道干燥室； 10廢氣排出閥； 11廢氣循環(huán)閥； 12新鮮空氣進(jìn)氣閥； 13-電加熱控制； 15溫度顯示儀； 16孔板流量計(jì)壓差變送器和顯示儀。五、 操作流程1、將干燥物料放入水中浸濕。2、調(diào)節(jié)送風(fēng)機(jī)吸入口的蝶閥12到全開(kāi)的位置后啟動(dòng)風(fēng)機(jī)。3、 用廢氣排出閥10和廢氣循環(huán)閥11調(diào)節(jié)到指定的流量后，開(kāi)啟加熱電源。在智能儀表中設(shè)定干球溫度，儀表自動(dòng)調(diào)節(jié)到指定的溫度。4、在空氣溫度、流量穩(wěn)定的條件下，用重量傳感器測(cè)定支架的重量并記錄下來(lái)。5、 把充分浸濕的干燥物料5固定在重量傳感器4上并與氣流平行放置。6、在穩(wěn)定的條件下，記錄干燥時(shí)間每隔2分鐘干燥物料減輕的重量。直至干燥物料的重量不再明顯減輕為止。7、變空氣流量或溫度，重復(fù)上述實(shí)驗(yàn)。8、 關(guān)閉加熱電源，待干球溫度降至常溫后關(guān)閉風(fēng)機(jī)電源和總電源。9、實(shí)驗(yàn)完畢，一切復(fù)原。六、實(shí)驗(yàn)數(shù)據(jù)記錄表表 1 操作條件與物料性質(zhì)記錄表備注：表2 干燥速率曲線測(cè)定原始數(shù)據(jù)記錄表序號(hào)時(shí)刻/min總質(zhì)量/g序號(hào)時(shí)刻/min總質(zhì)量/g1262273284295306317328339341035113612371338143915401641174218431944204521462247234824492550七、數(shù)據(jù)處理1、操作條件數(shù)據(jù)計(jì)算干燥面積（帆布面積）S=2ab=2*0.157*0.08=0.02512m2 ；絕干物料重量 27.5g； 支架重量（80.5+81.3）/2=80.9g ；進(jìn)口溫度（35.5+44.5）/2=40.0 ；此時(shí)空氣密度空氣=1.128kg/m3；濕球溫度（27.0+28.2）/2 =27.6； 干球溫度（60.0+60.0）/2=60.0；空氣流量計(jì)壓差讀數(shù)：0.89 kPa；孔板流量計(jì)孔徑d0=0.0450m， A0 =4d02 = 4*0.04502 = 1.59010-3m2；VT0 =C0A02P = 0.671.59010-320.891031.128 = 0.0423m3/s；Vt=Vto273+t273+t0 = 0.0423273+60.0273+40.0 = 0.0450 m3/s；u =VtA =Vtbh =0.04500.125*0.180=2.000m/s。2、實(shí)驗(yàn)數(shù)據(jù)整理計(jì)算表3 干燥速率曲線測(cè)定數(shù)據(jù)整理表序號(hào)時(shí)刻/min總質(zhì)量/g失重/gU/（kg/(m2h）G/gX (kg水/ kg絕干物料)X (kg水/ kg絕干物料)12177.096.102.49524175.91.11.31495.002.4552.47536174.71.21.43393.802.4112.43348173.51.21.43392.602.3672.389510172.31.21.43391.402.3242.345612171.31.01.19490.402.2872.305714170.11.21.43389.202.2442.265816169.01.11.31488.102.2042.224918168.01.01.19487.102.1672.1851020166.91.11.31486.002.1272.1471122165.81.11.31484.902.0872.1071224164.71.11.31483.802.0472.0671326163.71.01.19482.802.0112.0291428162.61.11.31481.701.9711.9911530161.51.11.31480.601.9311.9511632160.51.01.19479.601.8951.9131734159.31.21.43378.401.8511.8731836158.21.11.31477.301.8111.8311938157.30.91.07576.401.7781.7952040156.11.21.43375.201.7351.7562142155.20.91.07574.301.7021.7182244154.11.11.31473.201.6621.6822346153.01.11.31472.101.6221.6422448152.01.01.19471.101.5851.6042550150.91.11.31470.001.5451.5652652149.81.11.31468.901.5051.5252754148.81.01.19467.901.4691.4872856147.71.11.31466.801.4291.4492958146.71.01.19465.801.3931.4113060145.61.11.31464.701.3531.3733162144.61.01.19463.701.3161.3353264143.51.11.31462.601.2761.2963366142.51.01.19461.601.2401.2583468141.41.11.31460.501.2001.2203570140.41.01.19459.501.1641.1823672139.31.11.31458.401.1241.1443774138.40.91.07557.501.0911.1073876137.31.11.31456.401.0511.0713978136.50.80.95555.601.0221.0364080135.41.11.31454.500.9821.0024182134.41.01.19453.500.9450.9644284133.31.11.31452.400.9050.9254386132.40.91.07551.500.8730.8894488131.41.01.19450.500.8360.8554590130.31.11.31449.400.7960.8164692129.21.11.31448.300.7560.7764794128.40.80.95547.500.7270.7424896127.41.01.19446.500.6910.7094998126.31.11.31445.400.6510.67150100125.31.01.19444.400.6150.63351102124.40.91.07543.500.5820.59852104123.31.11.31442.400.5420.56253106122.40.91.07541.500.5090.52554108121.50.91.07540.600.4760.49355110120.51.01.19439.600.4400.45856112119.70.80.95538.800.4110.42557114118.80.91.07537.900.3780.39558116118.10.70.83637.200.3530.36559118117.40.70.83636.500.3270.34060120116.80.60.71735.900.3050.31661122116.30.50.59735.400.2870.29662124115.80.50.59734.900.2690.27863126115.50.30.35834.600.2580.26464128115.10.40.47834.200.2440.25165130114.70.40.47833.800.2290.23666132114.40.30.35833.500.2180.22467134114.10.30.35833.200.2070.21368136113.80.30.35832.900.1960.20269138113.50.30.35832.600.1850.19170140113.20.30.35832.300.175080.40.47831.900.1600.16772144112.50.30.35831.600.149030.20.23931.400.142070.60.71730.800.120010.60.71730.200.0980.10976152110.80.30.35829.900.0870.09377154110.60.20.23929.700.0800.08478156110.30.30.35829.400.0690.07579158110.00.30.35829.100.0580.06480160109.80.20.23928.900.0510.05581162109.50.30.35828.600.0400.04582164109.40.10.11928.500.0360.03883166109.20.20.23928.300.0290.03384168109.00.20.23928.100.0220.02585170109.00.00.00028.100.0220.02286172108.90.10.11928.000.0180.020計(jì)算舉例：以第二組為例，失重W=Wn-Wn+1 = W1-W2= 177.0=175.9=1.1g；干燥速率U = dWSd WS = 1.110-30.02512(260) = 1.314kg/(m2h)；濕物料重量G=W-支架重 = 175.9 - 80.9 = 95.0g；干基含水量X =G-GCGc = 95.0-27.527.5=2.495 kg水/ kg絕干物料；平均含水量X=（X1+X2）/2=（2.495+2.455）/2=2.475 kg水/ kg絕干物料。3、根據(jù)以上數(shù)據(jù)畫(huà)出圖形如下：4、恒速干燥段，物料表面與空氣間對(duì)流傳熱系數(shù)計(jì)算tw =27.6時(shí)，水的汽化熱rtw=2437.8kJ/kgUC =1.314看過(guò)/（m2h），t=t干 =60.0 =Ucrtwt-tw = 1.3142437.810360-27.613600=27.46287W/(m2)八、誤差分析尺寸相對(duì)誤差D(a）=D(b)=0.5mm；Er(a)=D(a)|a| = 0.5157=3.18510-3；Er(b)=D(b)|b| = 0.580=6.25010-3D(S)=D(2ab)= 2bD(a)2+2aD(b)2=(20.080.0005)2+(20.1570.0005)2 =0.176210-3Er(S)=D(S)|S|=0.176210-30.02512=0.701410-3時(shí)間相對(duì)誤差D()=0.5s, =2min=120s,D()=2D()2=20.52=0.7071s,Er()=D()|=0.7071120=5.892610-3失重相對(duì)誤差W=W1-W2,由儀器參數(shù)，D（W）=(200-0)0.2%=0.4g,D(W)= 2D(W)2=20.42=0.5656gW=UcS=1.3140.02512260103=1.100g Er（W）=D(W)|W| =0.56561.100=0.51418干濕球溫差相對(duì)誤差D(t)=D(tw)=1500.5%=0.75, D(t-tw)= D(t)2+D(tw)2=20.752=1.0607Er(t-tw)=D(t-tw)|t-tw|=1.060760-27.6=0.03274rtw是常數(shù)，誤差為0Er()=Er2S+Er2+Er2W+Er2(t-tw) =(0.701410-3)2+(5.892610-3)2+0.514182+0.032742=0.51526則D()=Er()|=0.51526*27.46=14.148915 W/(m2)故=3101 15 W/(m2)各因素在其中占的比例：Er2(S)Er2()=(0.701410-3)20.515262 =0.0001854%； Er