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      日光溫室裝配式土質(zhì)夾心墻體熱濕遷移及蓄放熱性能

      2019-02-20 13:37:44王少杰張廣鵬劉福勝胡玉秋
      關(guān)鍵詞:日光溫室熱量裝配式

      王少杰,張廣鵬,劉 鑫,吳 昆,3,劉福勝,魏 珉,胡玉秋

      ·農(nóng)業(yè)生物環(huán)境與能源工程·

      日光溫室裝配式土質(zhì)夾心墻體熱濕遷移及蓄放熱性能

      王少杰1,2,張廣鵬1,劉 鑫1,吳 昆1,3,劉福勝1,魏 珉2,胡玉秋1

      (1. 山東農(nóng)業(yè)大學(xué)水利土木工程學(xué)院,泰安 271018;2. 山東農(nóng)業(yè)大學(xué)園藝科學(xué)與工程學(xué)院,泰安 271018;3. 山東交通職業(yè)學(xué)院,濰坊 261206)

      為研究日光溫室裝配式土質(zhì)夾心墻體的熱濕遷移及蓄放熱性能,通過可控式墻體熱濕耦合試驗(yàn)臺(tái)控制墻體兩側(cè)溫度、相對(duì)濕度的不同,實(shí)測(cè)墻內(nèi)溫度、相對(duì)濕度的穩(wěn)態(tài)分布及瞬態(tài)變化,并對(duì)墻體的蓄放熱性能進(jìn)行定量計(jì)算與分析。結(jié)果表明:該層狀異質(zhì)結(jié)構(gòu)復(fù)合墻體,熱濕遷移存在耦合但并不明顯;墻內(nèi)填土始終保持高濕狀態(tài),有利于墻體蓄放熱,是該墻體的主要蓄放熱體;外側(cè)墻板保溫隔熱效能明顯,室外環(huán)境變化對(duì)墻體保溫蓄熱性能影響較小,且能使墻內(nèi)熱量主要向室內(nèi)單向釋放;墻內(nèi)熱量釋放存在滯后效應(yīng),最長(zhǎng)可持續(xù)6 d+6.5 h,但以快速放熱期(4 d+8 h內(nèi))所釋放熱量為主,約占總放熱量的85.64%~91.21%;所建立的數(shù)值分析方法可為不同厚度的同類墻體設(shè)計(jì)與建造提供參考,具有指導(dǎo)生產(chǎn)意義。該新型墻體設(shè)計(jì)理念先進(jìn),蓄放熱性能優(yōu)越,且能夠快速裝配、重復(fù)利用、就地還田,適于在中國(guó)大面積推廣應(yīng)用。

      日光溫室;墻體;溫度;土質(zhì)夾心;熱濕遷移;蓄放熱性能;裝配式墻體

      0 引 言

      日光溫室是中國(guó)獨(dú)有的一種溫室類型,其通過后墻吸收太陽能實(shí)現(xiàn)蓄放熱,維持棚內(nèi)溫度以滿足蔬菜作物生長(zhǎng),能有效解決中國(guó)北方地區(qū)冬季果蔬供應(yīng)問題[1-4]。當(dāng)前,中國(guó)日光溫室墻體仍以就地取材、成本低廉、保溫蓄熱性能良好的土墻為主,但由于墻體穩(wěn)定和蓄熱保溫的需要,土墻普遍較厚且易坍塌,土地利用效率低,施工緩慢且受季節(jié)性影響。研究表明,一般日光溫室墻體應(yīng)具有保溫和儲(chǔ)放熱2種功能,隨著技術(shù)發(fā)展,采用聚苯乙烯板材或型磚作為墻體室外側(cè)保溫層、使用土壤作為墻體室內(nèi)側(cè)蓄熱層的新型復(fù)合墻體在實(shí)際生產(chǎn)中已經(jīng)得到了推廣和應(yīng)用[5],但其保溫蓄熱層特別是建造方式仍無法滿足工業(yè)化建造、多次重復(fù)利用的現(xiàn)實(shí)技術(shù)需求。為解決上述不足,研發(fā)了裝配式土質(zhì)夾心異質(zhì)復(fù)合墻體[6],該墻體以輕質(zhì)節(jié)能保溫板為墻體室外側(cè)保溫層,以土和普通鋼筋混凝土板為蓄熱層,同時(shí)內(nèi)外兩側(cè)墻板通過筋材或立柱進(jìn)行連接,提高其結(jié)構(gòu)穩(wěn)定性與抗災(zāi)能力,土質(zhì)夾心層厚度可根據(jù)不同作物對(duì)溫度的不同需求靈活調(diào)整,外側(cè)保溫板可有效阻隔熱量傳遞。該類型墻體施工建造方便快捷,蓄放熱性能優(yōu)越,內(nèi)外墻板可重復(fù)利用,內(nèi)部夾心土可原位還田,綜合性能優(yōu)越,有關(guān)技術(shù)已在山東煙臺(tái)、濰坊、臨沂等地區(qū)日光溫室建造時(shí)推廣和應(yīng)用。

      圍繞層狀異質(zhì)復(fù)合墻體及單一材質(zhì)墻體的熱濕遷移及蓄放熱性能,在現(xiàn)場(chǎng)試驗(yàn)方面,史宇亮等[7-8]研究表明土墻白天蓄積熱量的43%用于改善夜間溫室內(nèi)的熱環(huán)境;武國(guó)峰等[9]計(jì)算分析了3種不同墻體結(jié)構(gòu)日光溫室各組成元素的熱工性能,結(jié)果表明土質(zhì)墻體在保溫蓄熱方面優(yōu)于秸稈塊墻體;陳超等[10]研究了制作方式對(duì)日光溫室蓄熱材料熱性能的影響。國(guó)內(nèi)學(xué)者還通過數(shù)值分析方法對(duì)墻體熱工性能進(jìn)行了研究[5,11-17],其中,李明等[5]計(jì)算得到土墻蓄熱層厚度為38.5 cm,佟國(guó)紅等[17]對(duì)比分析了復(fù)合墻和土墻保溫蓄熱能力的差異。上述研究表明日光溫室復(fù)合墻體具有更好的蓄放熱性能,僅通過增加墻體厚度提高蓄熱效率非常有限[18],其建造應(yīng)向輕量化、現(xiàn)代化、標(biāo)準(zhǔn)化、工業(yè)化方向發(fā)展[19-24]。對(duì)異質(zhì)復(fù)合墻體的熱濕性能研究還表明,濕遷移會(huì)影響墻體保溫蓄熱能力,熱遷移影響濕遷移進(jìn)而改變墻體熱工性能[25-28]。與現(xiàn)場(chǎng)試驗(yàn)、數(shù)值模擬相比,室內(nèi)模型試驗(yàn)?zāi)芡ㄟ^精準(zhǔn)調(diào)控室內(nèi)熱濕環(huán)境,深入系統(tǒng)研究墻體的熱濕遷移及蓄放熱性能,尤其是有利于揭示墻內(nèi)填土對(duì)溫度變化響應(yīng)存在的滯后效應(yīng)[29],該領(lǐng)域的研究相對(duì)較少且十分必要。

      本文以自主研發(fā)的可控式墻體熱濕耦合試驗(yàn)臺(tái)[30]為基礎(chǔ),通過試驗(yàn)和理論方法系統(tǒng)研究日光溫室裝配式土質(zhì)夾心墻體的熱濕遷移及蓄放熱性能;在試驗(yàn)研究基礎(chǔ)上,修正建立該層狀異質(zhì)復(fù)合墻體的熱工性能數(shù)值分析方法,旨在為不同土質(zhì)夾心層厚度的同類型墻體提供蓄放熱性能計(jì)算方法,為該新型墻體推廣應(yīng)用提供技術(shù)依托。

      1 試驗(yàn)概況

      1.1 試驗(yàn)墻體

      試驗(yàn)墻體系層狀異質(zhì)復(fù)合墻,室內(nèi)模型試驗(yàn)段長(zhǎng)1.2 m、高0.6 m,總厚度600 mm,示意圖如圖1所示。其中,室外側(cè)采用山東和悅生態(tài)新材料科技有限責(zé)任公司生產(chǎn)的裝配式CF蒸壓瓷粉加氣混凝土板,厚100 mm,具有優(yōu)良的保溫隔熱特性,能有效阻止室內(nèi)側(cè)熱量向外側(cè)傳輸;墻內(nèi)填土采用泰安當(dāng)?shù)馗赜猛梁粚?shí),厚440 mm,就地取材,蓄熱放熱性能好;室內(nèi)側(cè)采用60 mm厚普通鋼筋混凝土板,能在有效支擋墻內(nèi)填土的同時(shí),因?qū)嵯禂?shù)大能快速傳熱。為保證試驗(yàn)過程中熱量在墻體中一維傳遞,以避免邊際效應(yīng),在墻體上下左右四周均采用聚苯保溫板(對(duì)應(yīng)的熱阻為10.26 ℃/W)進(jìn)行封裝,試驗(yàn)墻體對(duì)應(yīng)的實(shí)測(cè)熱阻為3.53 ℃/W,熱阻值前者遠(yuǎn)大于后者能實(shí)現(xiàn)熱量在墻體中一維傳遞。試驗(yàn)墻體所用材料對(duì)應(yīng)的各項(xiàng)參數(shù)詳見表1。

      圖1 試驗(yàn)墻體及測(cè)點(diǎn)布置示意圖

      表1 試驗(yàn)墻體所用材料各項(xiàng)參數(shù)

      注:填土質(zhì)量含水率為13.14%,對(duì)應(yīng)最佳含水率。

      Note: The fill water quality moisture content is 13.14%, corresponding to the optimum moisture content.

      1.2 試驗(yàn)儀器

      通過課題組研發(fā)的可控式墻體熱濕耦合試驗(yàn)臺(tái)調(diào)控墻體兩側(cè)溫濕度,如圖2所示。該試驗(yàn)臺(tái)主要由2個(gè)可控式恒溫恒濕箱組成,用于模擬實(shí)際環(huán)境的溫濕度工況,提供試驗(yàn)要求的溫濕度環(huán)境,當(dāng)將箱體開敞一側(cè)與墻體密封時(shí),溫度值可以設(shè)定在10~100 ℃,偏差不超過±0.5 ℃;相對(duì)濕度值可以設(shè)定在30%~95%,偏差值不超過±2%。數(shù)據(jù)采集采用上海搜博實(shí)業(yè)有限公司生產(chǎn)的SLHT1溫濕度傳感器、SM1210B溫濕度采集模塊及SV3000環(huán)境狀態(tài)監(jiān)測(cè)系統(tǒng)。

      圖2 墻體試驗(yàn)

      1.3 測(cè)點(diǎn)布置

      為得到墻體內(nèi)部溫度、相對(duì)濕度的穩(wěn)態(tài)分布和動(dòng)態(tài)遷移情況,在墻體內(nèi)部共布設(shè)8個(gè)溫濕度測(cè)點(diǎn),如圖1所示,8個(gè)測(cè)點(diǎn)在空間上形成一條沿墻體厚度方向的水平直線。其中,1、2、3號(hào)測(cè)點(diǎn)沿CF蒸壓瓷粉加氣混凝土板厚度方向按間距為50 mm等分布設(shè)于板的兩側(cè)和中點(diǎn)處;4、5、6號(hào)測(cè)點(diǎn)沿墻內(nèi)填土厚度方向按間距為110 mm等分布設(shè);7、8號(hào)測(cè)點(diǎn)沿室內(nèi)側(cè)普通鋼筋混凝土板厚度方向分別布設(shè)于板兩側(cè),所有測(cè)點(diǎn)沿長(zhǎng)度、高度方向均布設(shè)于中心位置。數(shù)據(jù)采樣時(shí)間間隔為5 min。

      1.4 工況設(shè)計(jì)

      為研究墻體兩側(cè)溫度、相對(duì)濕度變化對(duì)墻體熱濕遷移及蓄放熱性能的影響,綜合考慮日光溫室室內(nèi)外實(shí)際對(duì)應(yīng)的熱濕環(huán)境和試驗(yàn)臺(tái)的技術(shù)參數(shù),設(shè)計(jì)2個(gè)試驗(yàn)組共7種工況(表2),每種工況以墻體內(nèi)溫度、相對(duì)濕度達(dá)到相對(duì)穩(wěn)定并維持12 h以上,由此進(jìn)入下一工況。

      表2 試驗(yàn)組列表

      為研究日光溫室內(nèi)部溫度變化對(duì)墻體熱濕性能的影響,試驗(yàn)組1設(shè)置為室外側(cè)溫度、相對(duì)濕度不變,室內(nèi)側(cè)相對(duì)濕度不變、溫度以5 ℃為梯度由30 ℃降至15 ℃,分別對(duì)應(yīng)工況1-1至工況1-4;為研究室外側(cè)溫度、相對(duì)濕度變化對(duì)墻體熱濕性能的影響,以工況1-2為基準(zhǔn),設(shè)置試驗(yàn)組2開展對(duì)比試驗(yàn),其中,工況2-1為室外側(cè)溫度不變、相對(duì)濕度變化;工況2-2為室外側(cè)溫度變化、相對(duì)濕度不變;工況2-3為室外側(cè)溫度、相對(duì)濕度均變化。

      2 結(jié)果與分析

      2.1 室內(nèi)溫度變化時(shí)墻體的熱濕性能

      2.1.1 墻體溫度及相對(duì)濕度穩(wěn)態(tài)分布

      試驗(yàn)組1各工況對(duì)應(yīng)的所有測(cè)點(diǎn)溫度、相對(duì)濕度達(dá)到穩(wěn)定后,取穩(wěn)定后12 h內(nèi)的平均值作為各測(cè)點(diǎn)的溫度、相對(duì)濕度值,以測(cè)點(diǎn)1對(duì)應(yīng)位置為橫軸坐標(biāo)0點(diǎn)作圖,試驗(yàn)組1各工況對(duì)應(yīng)的溫度、相對(duì)濕度沿墻厚度方向的分布分別如圖3、圖4所示。

      注:數(shù)字為各測(cè)點(diǎn)的對(duì)應(yīng)代碼,下同,以墻室外表面為“0”點(diǎn)。

      由圖3可知,試驗(yàn)組各工況對(duì)應(yīng)溫度均由室內(nèi)高溫側(cè)(600 mm)向室外低溫側(cè)(0 mm)傳遞,普通鋼筋混凝土板對(duì)熱量的阻隔作用較小,可實(shí)現(xiàn)室內(nèi)與墻內(nèi)熱量的快速交換;墻內(nèi)填土能在有效阻礙熱量向外傳遞的同時(shí)蓄集熱量,室內(nèi)溫度越高、對(duì)應(yīng)溫度梯降越大;各工況中1、3號(hào)測(cè)點(diǎn)溫差均較大,即CF蒸壓瓷粉加氣混凝土板可有效阻礙墻內(nèi)熱量向外部的傳遞,保溫隔熱作用明顯。

      圖4 試驗(yàn)組1相對(duì)濕度-墻厚曲線

      由圖4可知,各工況墻內(nèi)填土均處于高濕狀態(tài)(測(cè)點(diǎn)3~6的相對(duì)濕度維持在99%以上),基本不向兩側(cè)傳遞,室內(nèi)溫度變化對(duì)墻內(nèi)濕度的影響亦較小,基本規(guī)律是伴隨室內(nèi)溫度的降低墻內(nèi)濕度略有增加。分析可知,墻內(nèi)填土處于高濕狀態(tài)下,相比于干燥狀態(tài)的傳統(tǒng)土墻,含濕量大的土傳熱介質(zhì)以土和水為主導(dǎo),從而具有較大的比熱容與導(dǎo)熱系數(shù),使得熱收益增加、蓄熱循環(huán)周期縮短[31],即該特性更有利于墻體在白天吸收太陽輻射蓄集更多的熱量,從而可在夜間或連陰天向溫室內(nèi)釋放更多的熱量,對(duì)日光溫室內(nèi)熱環(huán)境的營(yíng)造是有利的。

      2.1.2 墻體溫度瞬態(tài)遷移規(guī)律

      1)溫度變化率

      為獲得各測(cè)點(diǎn)的溫度有效下降時(shí)間,以1 h為間隔求出溫度下降過程中各測(cè)點(diǎn)的溫度變化率,具體方法為:以墻內(nèi)夾心土層對(duì)應(yīng)的中點(diǎn)即測(cè)點(diǎn)5為例,對(duì)其溫度變化曲線求導(dǎo)得到測(cè)點(diǎn)5的溫度變化率曲線,對(duì)應(yīng)溫度及溫度變化率曲線如圖5所示,溫度變化率大于0為升溫、小于0為降溫,當(dāng)溫度趨于相對(duì)穩(wěn)定時(shí)溫度變化率會(huì)在0值處上下波動(dòng),找出溫度變化率此時(shí)對(duì)應(yīng)的時(shí)間點(diǎn),即為溫度保持相對(duì)穩(wěn)定的時(shí)間點(diǎn),并將該點(diǎn)標(biāo)示在對(duì)應(yīng)的溫度—時(shí)間曲線上,該段時(shí)間即為測(cè)點(diǎn)的溫度有效下降時(shí)間。依據(jù)該方法可以在試驗(yàn)組1各工況對(duì)應(yīng)的溫度—時(shí)間曲線上厘清各測(cè)點(diǎn)在各工況的溫度變化開始及結(jié)束點(diǎn),如圖6所示;定量結(jié)果匯總見表3。實(shí)測(cè)結(jié)果表明,由于墻體內(nèi)部測(cè)點(diǎn)存在溫度滯后效應(yīng),故定義以溫度率先達(dá)到穩(wěn)定態(tài)的測(cè)點(diǎn)8所需要的時(shí)間為快速放熱期。

      圖5 測(cè)點(diǎn)5各階段溫度變化及其溫度變化率

      圖6 試驗(yàn)組1各測(cè)點(diǎn)溫度-時(shí)間曲線

      表3 各階段各測(cè)點(diǎn)溫度有效下降時(shí)間及下降幅度

      注:測(cè)點(diǎn)1受室外側(cè)溫度(維持在10 ℃上下)影響較大,且溫度變化不大,故未列入表中。

      Note: Measurement point 1 is greatly affected by the outdoor side temperature (maintained at 10 ℃), and the temperature does not change much, so it is not listed in the table.

      2)空間遷移規(guī)律

      分析圖6可知,空間上沿墻體厚度方向,各階段各測(cè)點(diǎn)溫度有效下降時(shí)間由墻體內(nèi)側(cè)至外側(cè)依次變長(zhǎng);溫度下降開始時(shí)間率先從墻內(nèi)側(cè)開始,越靠近外側(cè)溫度開始下降的時(shí)間越晚,導(dǎo)致這種現(xiàn)象的原因是墻內(nèi)填土對(duì)溫度變化的響應(yīng)存在滯后效應(yīng),內(nèi)側(cè)普通鋼筋混凝土板較外側(cè)CF蒸壓瓷粉加氣混凝土板具有更高的熱擴(kuò)散率。熱擴(kuò)散率是指在一定的熱量得失情況下,物體溫度變化快慢的一個(gè)物理量,相當(dāng)于物體的蓄熱能力,是一個(gè)在非穩(wěn)態(tài)導(dǎo)熱過程中非常重要的參數(shù)。物體的熱擴(kuò)散率越大,表明熱量由物體表面向深層或者由深層向物體表面擴(kuò)散的能力越強(qiáng),普通鋼筋混凝土板、CF蒸壓瓷粉加氣混凝土板對(duì)應(yīng)的熱擴(kuò)散率分別為2.101×10-7、0.499×10-7m2/s。

      3)時(shí)間遷移規(guī)律

      為便于分析,以試驗(yàn)組1對(duì)應(yīng)4個(gè)工況為界,將溫度-時(shí)間曲線分為3個(gè)階段,如圖6所示標(biāo)注。從時(shí)間角度可明顯看出,各測(cè)點(diǎn)溫度達(dá)到相對(duì)穩(wěn)定所用的時(shí)間在第1階段(室內(nèi)外溫差為20 ℃)最短,第2階段(室內(nèi)外溫差為15 ℃)次之,第3階段(室內(nèi)外溫差為10 ℃)最長(zhǎng)。其原因是墻體兩側(cè)溫差越大,墻體材料的熱傳導(dǎo)就越快,溫度達(dá)到相對(duì)平衡的速度就越快,單位時(shí)間熱量損失的越大,從而達(dá)到溫度相對(duì)穩(wěn)定的時(shí)間也就越快,這一特性有利于極端天氣下室內(nèi)氣溫驟降時(shí)墻體向室內(nèi)快速釋放熱量,減小室內(nèi)溫度下降幅度。

      更進(jìn)一步的由圖6和表3綜合量化分析可知,由測(cè)點(diǎn)5至測(cè)點(diǎn)8,即室內(nèi)側(cè)280 mm厚的墻體在3 d+11 h至4 d+15.5 h內(nèi)溫度達(dá)到相對(duì)穩(wěn)定,且下降幅度較大;靠近墻外側(cè)厚320 mm的墻體最晚可在6 d+6.5 h后達(dá)到相對(duì)穩(wěn)定。即在連續(xù)陰天,當(dāng)日光溫室內(nèi)部氣溫下降時(shí),墻內(nèi)側(cè)厚280 mm的墻體可持續(xù)在4 d+15.5 h內(nèi)快速向室內(nèi)釋放熱量,墻外側(cè)厚320 mm的墻體最大可持續(xù)6 d+6.5 h向室內(nèi)釋放熱量,但溫度變化幅度縮小即放熱能力較快速放熱期減弱。

      2.2 室外溫濕度變化時(shí)墻體的熱濕性能

      對(duì)比試驗(yàn)組2各工況與工況1-2,可知室外溫濕度變化時(shí)墻體熱濕性能遷移規(guī)律,如圖7所示。對(duì)比工況1-2與2-1,即當(dāng)室外相對(duì)濕度增大時(shí),試驗(yàn)組2-1中靠近室外側(cè)的測(cè)點(diǎn)1~3的溫度明顯低于工況1-2,而測(cè)點(diǎn)4~8的溫度基本相同;室外側(cè)相對(duì)濕度的提高導(dǎo)致測(cè)點(diǎn)1相對(duì)濕度增加,進(jìn)而使導(dǎo)熱系數(shù)變大,降低該處保溫性能,使測(cè)點(diǎn)1~3處溫度下降明顯,而對(duì)墻內(nèi)填土及室內(nèi)側(cè)影響不大。對(duì)比工況1-2與2-2,可明顯看出室外側(cè)溫度提高對(duì)墻體相對(duì)濕度影響不大,對(duì)墻體的溫度影響較大,測(cè)點(diǎn)1~8溫度均有所提升,但越靠近室內(nèi)側(cè)溫度變化越小,以測(cè)點(diǎn)1的溫度所受影響最大。對(duì)比工況1-2與2-3,即當(dāng)室外側(cè)溫度、相對(duì)濕度同時(shí)提高時(shí),首先室外側(cè)溫度的升高使墻內(nèi)溫度整體提高,但由于室外相對(duì)濕度提高使靠近室外的測(cè)點(diǎn)1~3溫度提升幅度較工況2-2低,該段曲線形狀更接近于工況2-1;上述現(xiàn)象說明無論室外高溫或低溫,室外高濕環(huán)境都會(huì)降低室外側(cè)210 mm厚墻體的溫度,但影響深度有限。

      圖7 室外溫濕度變化時(shí)墻體的熱濕性能

      2.3 墻體蓄熱、放熱性能分析

      2.3.1 墻體蓄、放熱量計(jì)算

      墻體蓄集、釋放熱量的過程是墻體內(nèi)能增加、減少的過程,可以通過墻體內(nèi)溫度的變化計(jì)算得到蓄、放熱量。物體熱量與溫度的換算公式為

      =D(1)

      式中D為物體的溫度變化值,℃;為物體所吸收或釋放的熱量(D為正值時(shí)表示吸收熱量、為負(fù)值時(shí)表示釋放熱量),kJ;為物體比熱容,kJ/(kg·℃);為物體質(zhì)量,kg。

      裝配式土質(zhì)夾心墻體為層狀異質(zhì)復(fù)合墻體,水平方向由3種不同材料組成,其比熱容各不相同,根據(jù)試驗(yàn)測(cè)點(diǎn)沿墻厚方向的分布,以測(cè)點(diǎn)1~8對(duì)應(yīng)的在墻厚方向上的距離將墻體離散為7層,每一層墻體可以看作是穩(wěn)態(tài)導(dǎo)熱,其傳熱過程可認(rèn)為是沿墻體厚度方向的一維穩(wěn)態(tài)導(dǎo)熱[11],第層墻體的蓄、放熱量計(jì)算公式為

      墻體整體蓄、放熱量計(jì)算公式為

      2.3.2 室內(nèi)溫度變化時(shí)墻體的蓄放熱性能

      由公式(2)~(4)計(jì)算可知試驗(yàn)組1各工況墻體各層的蓄、放熱量,如圖8所示。分析可知,墻體主要蓄、放熱體為墻內(nèi)填土,且越靠近室內(nèi)一側(cè)蓄集的熱量越多,各工況及工況間各階段墻內(nèi)填土平均蓄、放熱占比分別為75.81%、75.38%;室內(nèi)側(cè)普通鋼筋混凝土板次之,各工況及工況間各階段平均蓄、放熱占比分別為21.92%、21.90%;室外側(cè)CF蒸壓瓷粉加氣混凝土板蓄放熱量最小,主要起隔熱作用,這對(duì)墻體向室內(nèi)側(cè)單向釋放熱量是有利的。

      由公式(2)~(5)計(jì)算比較了試驗(yàn)組1各工況所有測(cè)點(diǎn)溫度相對(duì)穩(wěn)定時(shí)墻體的蓄熱量和對(duì)應(yīng)各階段快速放熱期結(jié)束時(shí)以及各階段結(jié)束時(shí)墻體的放熱量,如圖9所示。由圖9可明顯看出,各階段放熱率隨著墻體兩側(cè)溫差的減小不斷提高,第1階段結(jié)束時(shí)放熱量占工況1-1穩(wěn)定時(shí)蓄熱量的26.57%,第2階段結(jié)束時(shí)放熱量占工況1-2穩(wěn)定時(shí)蓄熱量的29.97%,第3階段結(jié)束時(shí)放熱量占工況1-3穩(wěn)定時(shí)蓄熱量的60.62%??焖俜艧崞谒尫艧崃空几麟A段放熱量的絕大比例,其中第1、第2、第3階段快速放熱期所釋放的熱量分別占總放熱量的88.64%、85.64%和91.21%,用時(shí)分別是3 d+11 h、3 d+16 h和4 d+ 8 h(見表3),即伴隨墻體兩側(cè)溫差減小,快速放熱期的時(shí)長(zhǎng)、放熱率均提高。

      圖8 試驗(yàn)組1各層蓄放熱量

      圖9 試驗(yàn)組1各時(shí)期墻體蓄放熱量

      2.3.3 室外溫濕度變化時(shí)墻體的蓄放熱性能

      計(jì)算試驗(yàn)組2各工況墻體各層蓄熱量并求得與對(duì)比工況1-2的熱量變化值,如圖10所示。分析圖10可知,當(dāng)室外相對(duì)濕度提高時(shí)(工況2-1),墻體第1~3層蓄熱量下降。由工況2-2、工況2-3的熱量變化均為正值可知,由于室外側(cè)溫度提高,使墻體溫度升高,墻體內(nèi)能增加而蓄集更多熱量;對(duì)比工況1-2與工況2-1、工況2-2與工況2-3可明顯看出,墻體外側(cè)相對(duì)濕度提高使墻體第1~3層熱量流失、而第4~7層熱量并無明顯變化,結(jié)合2.2節(jié)的分析可知,室外相對(duì)濕度提高不僅降低了室外側(cè)210 mm厚墻體的蓄熱性能,而且使熱量由墻內(nèi)向室外側(cè)單向流失,即可以通過進(jìn)一步提高外側(cè)墻板的熱阻和防水性能改善墻體熱環(huán)境。

      圖10 試驗(yàn)組2與工況1-2各層蓄熱量變化值

      3 數(shù)值分析方法

      3.1 數(shù)值建模

      通過有限元軟件ANSYS和APDL參數(shù)化語言,采用2維4節(jié)點(diǎn)熱分析單元PIANE55建立裝配式土質(zhì)夾心墻體的數(shù)值模型,對(duì)普通鋼筋混凝土板、墻內(nèi)填土、CF蒸壓瓷粉加氣混凝土板分別賦予不同的建模參數(shù)(表1),網(wǎng)格尺寸為10 mm,采用熱分析第一類邊界條件,即物體邊界上溫度已知且為定值,對(duì)室內(nèi)外兩側(cè)施加溫度荷載并提取試驗(yàn)測(cè)點(diǎn)對(duì)應(yīng)路徑上的溫度,通過數(shù)值分析方法研究墻體熱工性能。試驗(yàn)實(shí)測(cè)結(jié)果表明土的相對(duì)濕度始終處于高濕狀態(tài)(99%以上),且相對(duì)十分穩(wěn)定,對(duì)導(dǎo)熱系數(shù)的變化無明顯影響;故為了建立簡(jiǎn)單實(shí)用高效的數(shù)值分析方法,本文在進(jìn)行數(shù)值模擬時(shí)考慮了相對(duì)濕度的影響但沒有考慮相對(duì)濕度變化的影響,所采用的導(dǎo)熱系數(shù)為土在高濕狀態(tài)下對(duì)應(yīng)的導(dǎo)熱系數(shù)。

      3.2 試驗(yàn)驗(yàn)證

      選取具有代表性的工況1-2、2-1,開展數(shù)值計(jì)算與實(shí)測(cè)結(jié)果的對(duì)比分析,如圖11所示。

      圖11 模擬與實(shí)測(cè)溫度對(duì)比圖

      可明顯看出,各測(cè)點(diǎn)溫度實(shí)測(cè)值均較為均勻的分布在模擬曲線兩側(cè),且數(shù)值計(jì)算結(jié)果與實(shí)測(cè)結(jié)果變化趨勢(shì)一致,均由高溫側(cè)傳向低溫側(cè),模擬曲線的斜率變化體現(xiàn)為墻體各材料的不同;定量分析表明,各測(cè)點(diǎn)除工況2-1中測(cè)點(diǎn)2誤差為1.34 ℃以外,其他各測(cè)點(diǎn)的誤差均在1.00 ℃以內(nèi),數(shù)值計(jì)算與實(shí)測(cè)結(jié)果的良好吻合為后續(xù)定量研究土質(zhì)夾心層厚度不同的同類型墻體的熱工性能提供了高效方法。

      4 討 論

      日光溫室是農(nóng)業(yè)生產(chǎn)中應(yīng)用最廣泛的果蔬園藝設(shè)施之一,其墻體是日光溫室的主要蓄放熱體,本研究結(jié)合實(shí)際生產(chǎn)需求,以最新研發(fā)的日光溫室裝配式土質(zhì)夾心墻體為研究對(duì)象,在材料選擇與結(jié)構(gòu)布置上以普通鋼筋混凝土板和具有一定水分的土為蓄熱材料,以CF蒸壓瓷粉加氣混凝土板為室外側(cè)隔熱保溫材料,試驗(yàn)結(jié)果表明該設(shè)計(jì)理念可行且有利于營(yíng)造、維持溫室內(nèi)的溫度。本文所研究墻體適于中國(guó)北方地區(qū)種植草莓、葡萄等,尤以種植草莓可趕上春節(jié)茬口上市,經(jīng)濟(jì)效益十分明顯。為兼顧墻體的保溫蓄放熱能力與快速建造、節(jié)約土地資源,本文墻厚為600 mm,墻內(nèi)填土為440 mm,若要進(jìn)一步滿足對(duì)室內(nèi)熱量要求較高的果蔬生長(zhǎng),廣泛使用的方法為增加墻體厚度,但目前研究表明僅通過增加溫室墻體厚度來提高墻體保溫蓄熱效果非常有限,且墻體的熱量釋放路徑并非一維單向傳遞,后續(xù)可在提高單位土體蓄熱量、采取墻體外保溫措施、優(yōu)化墻體熱量傳遞路徑等方面開展研究。

      不同于現(xiàn)場(chǎng)測(cè)試,本文通過控制變量的方法,研究了墻體兩側(cè)溫度、相對(duì)濕度對(duì)墻體熱濕遷移的影響,墻體不受雨、雪、風(fēng)、光照及棚內(nèi)作物、土壤等因素影響,得到了墻體在工況所設(shè)環(huán)境下最終穩(wěn)定時(shí)的溫濕度分布情況及遷移過程;同時(shí)工況設(shè)置未模擬晝夜循環(huán)情況下的溫度,后續(xù)研究在考慮墻體保溫蓄熱性能影響因素的同時(shí),宜加強(qiáng)晝夜溫度變化對(duì)墻內(nèi)溫度波動(dòng)影響的研究。

      本文試驗(yàn)數(shù)據(jù)主要采集了溫度與相對(duì)濕度,較準(zhǔn)確地獲得了墻內(nèi)的熱濕分布與遷移變化情況,對(duì)于墻體蓄、放熱量的計(jì)算與評(píng)價(jià)主要以理論推導(dǎo)為主,試驗(yàn)結(jié)果與數(shù)值模擬結(jié)果表明墻內(nèi)有關(guān)墻體保溫蓄熱性能的參數(shù)(如導(dǎo)熱系數(shù)等)并非固定不變,會(huì)因墻體兩側(cè)溫濕度環(huán)境的變化而受到不同程度影響,鑒于墻體保溫蓄熱性能影響因素的復(fù)雜性,如何實(shí)時(shí)監(jiān)測(cè)、獲得墻體各項(xiàng)熱工性能參數(shù),更加準(zhǔn)確計(jì)算墻體蓄、放熱量,后續(xù)研究應(yīng)予以加強(qiáng)。

      5 結(jié) 論

      1)日光溫室裝配式土質(zhì)夾心墻體熱濕遷移存在耦合,但并不明顯;墻內(nèi)填土始終保持高濕狀態(tài),有利于墻體蓄熱和放熱;室外環(huán)境變化對(duì)墻體保溫蓄熱性能影響有限,其中室外相對(duì)濕度變化僅會(huì)使室外側(cè)210 mm厚墻體的溫度產(chǎn)生變化。

      2)日光溫室裝配式土質(zhì)夾心墻體主要蓄放熱體為墻內(nèi)填土,室內(nèi)側(cè)普通鋼筋混凝土板次之;CF蒸壓瓷粉加氣混凝土板則主要起保溫隔熱作用,能使墻內(nèi)熱量主要向室內(nèi)單向釋放。室內(nèi)側(cè)280 mm厚墻體對(duì)室內(nèi)溫度變化響應(yīng)迅速且可在4 d+15.5 h內(nèi)持續(xù)向室內(nèi)釋放熱量;墻體在快速放熱期4 d+8 h內(nèi)所釋放熱量占總放熱量的85.64%~91.21%。

      3)日光溫室裝配式土質(zhì)夾心墻體具有優(yōu)良的保溫蓄熱性能,墻內(nèi)熱濕遷移對(duì)墻體蓄放熱為有利影響,對(duì)室外環(huán)境變化有一定抵御能力。該新型層狀異質(zhì)結(jié)構(gòu)復(fù)合墻體符合室外側(cè)為保溫隔熱層、內(nèi)側(cè)為蓄放熱層的設(shè)計(jì)理念,且實(shí)現(xiàn)了快速裝配、節(jié)能環(huán)保,具有一定推廣價(jià)值。數(shù)值分析方法與實(shí)測(cè)結(jié)果吻合良好,可為不同地區(qū)不同作物所需不同蓄放熱量日光溫室墻體的設(shè)計(jì)與建造提供參考,具有指導(dǎo)生產(chǎn)意義。

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      Heat and moisture transfer and heat storage and release performance of assembled soil sandwich wall in solar greenhouse

      Wang Shaojie1,2, Zhang Guangpeng1, Liu Xin1, Wu Kun1,3, Liu Fusheng1, Wei Min2, Hu Yuqiu1

      (1.,,271018,;2.,,271018,;3.,261206,)

      Solar greenhouse is a unique type of greenhouse in China. It can absorb solar energy through the back wall to achieve heat storage and release, maintain the temperature in the greenhouse to meet the growth of vegetable crops, and effectively solve the problem of winter fruit and vegetable supply in northern cold region of China. In order to solve the problems of excessive thickness, easy collapse and low land-use efficiency of traditional soil wall, an assembled heterogeneous composite soil sandwich wall was developed. Prefabricated ordinary reinforced concrete slabs and light energy-saving thermal insulation slabs were used on both sides of the wall, respectively. The thickness of the soil sandwich layer could be flexibly adjusted according to the different needs of different crops for temperature. The interior and exterior wall panels are backfilled with soil and tied with reinforcements. The exterior insulation panels can effectively prevent heat transfer. In order to deeply and systematically study the heat and moisture transfer and heat storage and release performance of assembled soil sandwich wall in solar greenhouse, and reveal the hysteretic effect of filling on the response of temperature change, indoor model tests were carried out. The test wall is 1.2 m long and 0.6 m high with a total thickness of 600 mm. CF autoclaved ceramic powder aerated concrete slab with excellent heat preservation and insulation characteristics is used outdoors with a thickness of 100 mm. The filling material in the wall is taken locally, and the cultivated land with good heat storage and heat release performance is tamped, with a thickness of 440 mm. The indoor side is made of ordinary reinforced concrete slab with a thickness of 60 mm, which is effectively supported and retained. While supporting the wall, it has high thermal conductivity and fast heat transfer. Considering the actual indoor and outdoor hygrothermal environment of solar greenhouse and the technical parameters of the self-developed controllable coupled heat and moisture test bench, two test groups were designed under seven cases. The temperature and relative humidity changes of the indoor and outdoor walls were accurately controlled by the test bench, and the temperature and humidity sensors embedded in the wall were used in advance. The data acquisition system is used to measure and analyze the steady-state distribution and transient change of temperature and relative humidity in the wall. The thermal storage and release performance of the wall is calculated and analyzed quantitatively through theoretical formula deduction. On the basis of experimental research, the numerical analysis method of thermal performance of the layered heterogeneous composite wall is revised and established. The results show that the heat and moisture transfer of the composite wall with layered heterogeneous structure is coupled but not significant; the filling in the wall keeps high humidity (more than 90%) all the time, which is conducive to the heat storage and release of the wall, and is the main heat storage and release body of the wall; the thermal insulation efficiency of the outer wall panel is remarkable, and the change of the outdoor environment affects the thermal insulation and storage performance of the wall. The heat release in the wall has a lag effect in time and space, the longest lasting time is 6 days and 6.5 hours, but the heat release in the fast exothermic period (within 4 days and 8 hours) accounts for 85.64% to 91.21% of the total heat release, and the 280 mm thick wall on the indoor side responds quickly to the change of indoor temperature. The numerical analysis method can provide reference for the design and construction of similar walls with different thickness, and has guiding significance for production. The new wall design concept is advanced. The outer wall is thermal insulation layer and the inner wall is heat storage and release layer. It has excellent heat storage and release performance, and it can be quickly assembled, reused and returned to the field in situ. It is suitable for wide application in China.

      solar greenhouse; walls; temperature; soil sandwich; heat and moisture migration; heat storage and release performance; assembled wall

      王少杰,張廣鵬,劉 鑫,吳 昆,劉福勝,魏 珉,胡玉秋. 日光溫室裝配式土質(zhì)夾心墻體熱濕遷移及蓄放熱性能 [J]. 農(nóng)業(yè)工程學(xué)報(bào),2019,35(23):209-217.doi:10.11975/j.issn.1002-6819.2019.23.026 http://www.tcsae.org

      Wang Shaojie, Zhang Guangpeng, Liu Xin, Wu Kun, Liu Fusheng, Wei Min, Hu Yuqiu. Heat and moisture transfer and heat storage and release performance of assembled soil sandwich wall in solar greenhouse[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2019, 35(23): 209-217. (in Chinese with English abstract) doi:10.11975/j.issn.1002-6819.2019.23.026 http://www.tcsae.org

      2019-07-13

      2019-11-06

      中國(guó)博士后科學(xué)基金面上項(xiàng)目(2017M622239);國(guó)家大宗蔬菜產(chǎn)業(yè)技術(shù)體系項(xiàng)目(CARS-23-C04);國(guó)家重點(diǎn)研發(fā)計(jì)劃政府間國(guó)際科技創(chuàng)新合作重點(diǎn)專項(xiàng)項(xiàng)目(2017YFE9135300、SQ2017YFNC060047)

      王少杰,副教授,博士,主要從事農(nóng)業(yè)建筑與結(jié)構(gòu)、結(jié)構(gòu)安全與防災(zāi)診治等研究。Email:tumuwsj@sdau.edu.cn

      10.11975/j.issn.1002-6819.2019.23.026

      S625.1; TU111.2

      A

      1002-6819(2019)-23-0209-09

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