叢 茜，陳廷坤，李 楊，孫成彬，金敬福

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利用相變釋能的農(nóng)產(chǎn)品冷藏設(shè)備主動(dòng)防除冰方法

叢 茜1,2，陳廷坤1，李 楊1，孫成彬1，金敬福1※

（1. 吉林大學(xué)生物與農(nóng)業(yè)工程學(xué)院，長(zhǎng)春 130022； 2. 吉林大學(xué)汽車仿真與控制國(guó)家重點(diǎn)實(shí)驗(yàn)室，長(zhǎng)春 130022）

為減小農(nóng)副產(chǎn)品冷藏設(shè)備表面的結(jié)冰危害，提高部件表面的抗結(jié)冰能力和設(shè)備運(yùn)轉(zhuǎn)效率，該文提出利用相變釋能的主動(dòng)防除冰方法。試驗(yàn)以帶有不同凹坑尺寸的聚甲基丙烯酸甲酯（polymethyl methacrylate,PMMA）和6061鋁合金作為基體材料，凹坑內(nèi)填充氣體或不同冰點(diǎn)的介質(zhì)，表面覆蓋雙向拉伸聚丙烯薄膜（biaxially oriented polypropylene,BOPP）。試驗(yàn)采用水杯制冰法，測(cè)量表面結(jié)冰附著強(qiáng)度，結(jié)合剝離界面的形態(tài)，分析相變時(shí)差對(duì)界面附著強(qiáng)度的影響機(jī)理。結(jié)果表明：相對(duì)于光滑PMMA試樣的表面附著強(qiáng)度169.81 kPa，試樣（凹坑內(nèi)分別填充純凈水和體積分?jǐn)?shù)為6%乙醇溶液）表面的附著強(qiáng)度分別降低了100%和82%；對(duì)比無(wú)凹坑鋁合金試樣表面的附著強(qiáng)度，凹坑內(nèi)填充體積分?jǐn)?shù)為15%乙醇溶液低冰點(diǎn)溶液的試樣表面附著強(qiáng)度可減小76.52%。因此利用不同水溶液的相變時(shí)間差和膨脹釋能可減小試樣表面的附著強(qiáng)度，并且試驗(yàn)表明試樣材料、凹坑尺寸對(duì)附著強(qiáng)度的降低作用影響較小。利用相變時(shí)差和相變膨脹釋能破壞冰在彈性凍結(jié)界面的接觸穩(wěn)定性，達(dá)到降低結(jié)冰表面附著強(qiáng)度的目的，并且水溶液中水的體積分?jǐn)?shù)越大，試樣結(jié)冰表面的附著強(qiáng)度的越小。研究結(jié)果為農(nóng)產(chǎn)品冷藏領(lǐng)域中的防、除冰方法研究和開發(fā)提供參考。

制冷；凍結(jié)；界面；彈性膜；相變；膨脹；附著強(qiáng)度

0 引 言

隨著中國(guó)冷凍、冷藏行業(yè)的迅速發(fā)展，農(nóng)副產(chǎn)品、果蔬等食品對(duì)冷庫(kù)、冷藏機(jī)械的需求逐年增加，如微型冷庫(kù)在未來(lái)20年的保有量將達(dá)到50萬(wàn)左右臺(tái)[1]，而且保鮮冷庫(kù)的制冷效率可影響儲(chǔ)藏物的品質(zhì)[2-3]。因此，制冷設(shè)備高效節(jié)能的運(yùn)轉(zhuǎn)一直是該行業(yè)追求的目標(biāo)，但使用過(guò)程中，由于表面溫度低，空氣中的水蒸氣或雨水易附著在蒸發(fā)器、冷凝管、冷風(fēng)機(jī)等制冷部件表面，發(fā)生結(jié)霜、結(jié)冰現(xiàn)象，降低了制冷器表面的熱交換效率，造成設(shè)備運(yùn)行不穩(wěn)定，嚴(yán)重影響制冷設(shè)備的運(yùn)轉(zhuǎn)效率和制冷速度，增加了用電量和運(yùn)行成本，經(jīng)濟(jì)性差[4-10]。但日常的除冰、除霜效果是影響冷庫(kù)運(yùn)轉(zhuǎn)效率的關(guān)鍵，并且常規(guī)除冰方式效率低且成本高[11-14]。因此，提高制冷設(shè)備表面的防/除冰效果一直是制冷行業(yè)中的重要研究課題。

冰凍結(jié)過(guò)程中必然發(fā)生體積變化，對(duì)農(nóng)業(yè)、南水北調(diào)等領(lǐng)域中的渡槽、溝渠容易造成膨脹損壞[15-19]，能否可以將冰的凍脹力作為破壞力應(yīng)用于有益方向，如作為除冰動(dòng)力進(jìn)行自主破冰、提升制冷設(shè)備表面的防/除冰能力。項(xiàng)目組前期進(jìn)行表面宏觀形態(tài)對(duì)結(jié)冰附著強(qiáng)度的影響試驗(yàn)[20-21]：改變材料表面宏觀形態(tài)、利用冰的相變膨脹影響表面結(jié)冰附著強(qiáng)度，結(jié)果表明網(wǎng)格狀、條紋狀、點(diǎn)狀凹坑等不同形態(tài)對(duì)表面結(jié)冰附著強(qiáng)度的降低效果具有不同程度的影響。根據(jù)項(xiàng)目組提出的“一種防結(jié)冰覆膜”[22]的除冰思路，本文將彈性凍結(jié)界面與凍結(jié)過(guò)程中的相變膨脹釋能進(jìn)行耦合，同時(shí)利用不同凍結(jié)介質(zhì)的相變時(shí)間差異，破壞已凍結(jié)界面的穩(wěn)定性。在耦合作用下，降低表面冰的粘附強(qiáng)度。同時(shí)利用試驗(yàn)方法驗(yàn)證相變釋能進(jìn)行除冰的可行性，并分析相變時(shí)差對(duì)凍結(jié)界面穩(wěn)定性的影響機(jī)理，為開發(fā)新除冰技術(shù)提供試驗(yàn)數(shù)據(jù)和理論支撐。

1 材料與方法

試驗(yàn)測(cè)試?yán)浔砻姹膭冸x強(qiáng)度來(lái)評(píng)價(jià)水溶液相變時(shí)差對(duì)附著強(qiáng)度的影響，通過(guò)剝離后界面的形狀分析相變時(shí)差對(duì)附著強(qiáng)度的影響效應(yīng)。試驗(yàn)測(cè)試前，界面需采用丙酮溶液擦干。

1.1 試樣制備

待測(cè)試樣的材料為聚甲基丙烯酸甲酯（polymethylmethacrylate，PMMA），采用激光雕刻加工直徑30 mm、深3 mm的凹坑，如圖1所示。

制備體積分?jǐn)?shù)分別為6%、8%、10%的乙醇溶液，3種體積分?jǐn)?shù)溶液的冰點(diǎn)分別為：?1.94、?2.6、?3.26 ℃。凍結(jié)介質(zhì)填充凹坑后，表面粘貼雙向拉伸聚丙烯薄膜（biaxially oriented polypropylene，BOPP），作為試樣表面的彈性接觸界面。制備6種待測(cè)試樣，并分別命名為a、b、c、d、e、f，特征如表1所示。

表1 制備的6種PMMA試樣特征

同時(shí)為驗(yàn)證該防除冰思路不受材料導(dǎo)熱性、凹坑尺寸的影響，本文采用導(dǎo)熱性差距較大的6061鋁合金（237 W/(m·k)）和PMMA（0.2 W/(m·k)）作為試驗(yàn)材料，在材料表面制備直徑30 mm、深3.5 mm的凹坑。凹坑內(nèi)分別填充冰點(diǎn)為?6.8 、?10.4 ℃的15%、20%乙醇溶液，并分別命名為i～v，其具體特征如表2所示。

表2 制備的5種試樣特征

1.2 試樣制備

參考ASTM-D3528粘附劑測(cè)試標(biāo)準(zhǔn)及相關(guān)文獻(xiàn)中結(jié)冰表面附著強(qiáng)度測(cè)試方法[23-26]，搭建冰的切向附著強(qiáng)度測(cè)量裝置，如圖2所示。

試驗(yàn)中采用“水杯制冰法”，其中鋁杯內(nèi)徑為32 mm、外徑為39 mm、高度為41 mm，用水量為5 mL純凈水。采用東莞宏展儀器的LP-225U高低溫環(huán)境箱控制?25 ℃的環(huán)境溫度。制冷1 h以后，采用圖2裝置進(jìn)行測(cè)量，每種試樣測(cè)試5次。

2 結(jié)果與分析

2.1 結(jié)冰表面附著強(qiáng)度測(cè)試

2.1.1 試驗(yàn)數(shù)據(jù)

利用自制裝置測(cè)試試樣結(jié)冰的表面附著強(qiáng)度，并通過(guò)SPSS軟件分析試驗(yàn)測(cè)試數(shù)據(jù)的顯著性，如圖3所示。

由試驗(yàn)結(jié)果可知，凹坑試樣表面的附著強(qiáng)度明顯低于光滑試樣表面的附著強(qiáng)度。相對(duì)于光滑試樣表面的附著強(qiáng)度平均值（169.81 kPa），帶有凹坑的b～f試樣表面附著強(qiáng)度分別降低了56%、100%、82%、65%、59%，其中試樣b表面附著強(qiáng)度最大（75.51 kPa），試樣c表面附著強(qiáng)度為0。d~f試樣中，d試樣（6%乙醇溶液）表面的附著強(qiáng)度最小，e和f試樣表面的附著強(qiáng)度值相近。

相同試驗(yàn)條件下，分別測(cè)試i～v試樣表面的附著強(qiáng)度，并利用SPSS軟件分析試驗(yàn)測(cè)試結(jié)果的顯著性，如圖4所示。由試驗(yàn)數(shù)據(jù)可知，帶有凹坑且填充低冰點(diǎn)乙醇溶液的ii~v試樣表面的附著強(qiáng)度明顯低于光滑的鋁合金、PMMA試樣表面的附著強(qiáng)度，其中無(wú)凹坑的鋁合金試樣i表面附著強(qiáng)度略小于PMMA試樣a表面的附著強(qiáng)度。

相對(duì)于無(wú)凹坑鋁合金試樣i表面的附著強(qiáng)度，帶有凹坑的ii、iii試樣表面附著強(qiáng)度明顯的降低了76.52%、74.91%。材質(zhì)為PMMA的iv、v試樣，其表面的凹坑尺寸及填充的介質(zhì)不同于a～f試樣表面的凹坑尺寸和填充的溶液，但其表面的附著強(qiáng)度值（分別為24.76 kPa、26.62 kPa）也顯著減小，明顯低于試樣a、d、e、f表面的附著強(qiáng)度。ii、iii鋁合金試樣表面的附著強(qiáng)度略高于iv、v試樣表面的附著強(qiáng)度。

Fig4. Surface adhesion strength of different thermal conductivity samples

綜合圖3、4的試驗(yàn)數(shù)據(jù)可見，試驗(yàn)材料采用導(dǎo)熱性良好的鋁合金和導(dǎo)熱性差的PMMA作為凍粘基體，利用相變膨脹釋能均明顯的減小了試樣表面的附著強(qiáng)度?；诜澜Y(jié)冰模型中不同溶液的相變時(shí)間差，耦合利用凹坑內(nèi)對(duì)表面附著強(qiáng)度的影響效果與模型中的凹坑尺寸無(wú)關(guān)。

2.1.2 結(jié)冰界面形態(tài)

圖5為剝離后BOPP及結(jié)冰界面的表面形態(tài)，并參照剝離后的界面形態(tài)添加了BOPP膜變形示意圖。表面未經(jīng)任何處理的a試樣，剝離后BOPP膜及冰的凍結(jié)界面未發(fā)生變化。具有凹坑且填充不同介質(zhì)的b～f試樣中，BOPP膜出現(xiàn)了不同程度的變形，如b試樣的凹坑表面BOPP膜出現(xiàn)凹陷現(xiàn)象，c～f凹坑部位BOPP膜呈現(xiàn)膨脹凸起。剝離測(cè)試后，采用數(shù)顯游標(biāo)卡尺測(cè)量c～f表面膨脹凸起高度，平均值分別為3.34、1.25、1.13、1.04 mm，并且由圖5可見，c試樣（凹坑內(nèi)填充純凈水）表面的膨脹凸起最為明顯。

1.剝離后的BOPP膜 2.剝離后的結(jié)冰界面 3.BOPP膜 4.PMMA 5.冰

1.BOPP film after stripping 2.Freezing interface after stripping 3.BOPP film 4.PMMA 5.Ice

注：H、H、H、H、H分別為試樣b~f表面BOPP覆膜的膨脹凸起高度。

Note:H,H,H,H,Hare the expansion deformation height of the BOPP film covered on the samples b-f, respectively.

圖5 剝離后凍結(jié)界面的變形

Fig5. Deformation of freezing interface after stripping

2.2 結(jié)果分析與討論

冷表面水滴的初始形態(tài)近似半球形，從冷表面開始凍結(jié)結(jié)冰，完成后頂端產(chǎn)生膨脹凸起、高度增加，形態(tài)類似于“桃”型[27-30]，如圖6所示。由于凹坑內(nèi)水溶液的冰點(diǎn)，鋁杯的導(dǎo)熱系數(shù)大于PMMA的導(dǎo)熱系數(shù)，延長(zhǎng)了彈性覆膜上下水溶液與水之間的相變時(shí)間差。低溫環(huán)境下，彈性覆膜表面上的水分首先開始凍結(jié)結(jié)冰，形成彈性凍結(jié)界面的同時(shí)，對(duì)凹坑內(nèi)的水溶液形成彈性約束。隨凍結(jié)時(shí)間的延長(zhǎng)，凹坑內(nèi)填充的液體開始相變結(jié)冰，水溶液短時(shí)間內(nèi)釋放相變膨脹能。

眾所周知，水結(jié)冰產(chǎn)生會(huì)釋放大量的能量，如冬季水箱內(nèi)的水結(jié)冰引起水箱的破裂。防結(jié)冰模型中的凹坑只有表面粘貼的覆膜為彈性邊界，釋放的相變膨脹力只能加載于頂部的BOPP覆膜，引起凍結(jié)界面產(chǎn)生不規(guī)則的凹凸變形，破壞了試樣表面的附著穩(wěn)定性，如圖7所示。

由試驗(yàn)結(jié)果及剝離后凹坑表面變形的BOPP覆膜可見，利用不同水溶液的相變時(shí)間差異以及膨脹釋能，彈性凍結(jié)界面發(fā)生膨脹凸起，破壞結(jié)冰界面的連續(xù)性，降低表面的附著強(qiáng)度。試樣凹坑內(nèi)填充的低冰點(diǎn)溶液，水占據(jù)的比例越大，，相變膨脹能越大，對(duì)表面結(jié)冰附著強(qiáng)度的影響越大，如c試樣（凹坑內(nèi)填充純凈水，表面膨脹變形最大）表面附著強(qiáng)度為0 kPa。

實(shí)際環(huán)境中結(jié)冰的或結(jié)霜過(guò)程受諸多復(fù)雜因素的影響，不能僅僅是通過(guò)試驗(yàn)?zāi)M凍結(jié)過(guò)程，需要結(jié)合理論分析開展研究，提出的防除冰方法仍需不斷進(jìn)行開發(fā)。該方法應(yīng)用在工程領(lǐng)域中時(shí)，可采用諸多方式實(shí)現(xiàn)防結(jié)冰部件表面的相變時(shí)差，如表面粘貼容納低冰點(diǎn)液體的覆膜，利用液體邊界約束材料導(dǎo)熱性差異等方式。

3 結(jié) 論

1）通過(guò)試驗(yàn)方法驗(yàn)證了采用彈性覆膜作為結(jié)冰界面，耦合冰自身產(chǎn)生的相變膨脹以及利用不同水溶液的相變時(shí)間差，破壞彈性凍結(jié)界面的穩(wěn)定性，降低表面結(jié)冰附著強(qiáng)度的方法是可行的，并且防結(jié)冰模型中試樣材料、凹坑尺寸對(duì)結(jié)冰附著強(qiáng)度的降低效果的影響較小。

2）試驗(yàn)中采用BOPP彈性覆膜作為凍結(jié)界面，利用不同水溶液的相變時(shí)差，將凍結(jié)過(guò)程中的相變膨脹能作為主動(dòng)除冰動(dòng)力，使彈性接觸界面發(fā)生變形，與結(jié)冰界面之間產(chǎn)生間隙，破壞凍結(jié)界面的連續(xù)性，減小表面結(jié)冰附著強(qiáng)度。

3）冰在凹坑試樣表面的附著強(qiáng)度明顯(＜0.05）低于在光滑試樣表面的附著強(qiáng)度。相對(duì)于光滑試樣a表面的附著強(qiáng)度，c試樣（純凈水）對(duì)表面附著強(qiáng)度為0 kPa；凹坑填充不同體積分?jǐn)?shù)乙醇溶液的試樣中，6%乙醇體積分?jǐn)?shù)表面的附著強(qiáng)度降低了82%。

由于顯微觀察、計(jì)算機(jī)模擬等技術(shù)手段的限制，目前本文僅停留在理論設(shè)想及采用工程材料進(jìn)行試驗(yàn)驗(yàn)證的階段。本文中采用的防、除冰模型對(duì)試樣材料表面附著強(qiáng)度的降低作用顯著，相對(duì)于常規(guī)除冰方式，該模型制備成本低，并為除冰方法的開發(fā)、升級(jí)提供了一種新的技術(shù)思路。

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Active anti-icing method for agricultural product refrigerated equipment based on phase change energy release

Cong Qian1,2, Chen Tingkun1, Li Yang1, Sun Chengbin1, Jin Jingfu1※

(1.130022,;2.130022,)

The application of refrigeration in agricultural and sideline products preservation is getting more and more extensive. However, the surface of refrigeration equipment, such as evaporator, condenser and chiller, is prone to freeze, and ice and frost are easy to occur, which seriously affect the operation efficiency of refrigeration equipment and increase the cost. The formation of ice must be accompanied by the phase expansion. So, why not use the phase transition expansion as the deicing power, and make the refrigeration equipment surface own active control ability of ice? During the test, the polymethyl methacrylate (PMMA) with pit and the aluminum alloy were used as the matrix materials, which were bonded with the biaxially oriented polypropylene (BOPP) elastic film as the freezing interface. The pit of the PMMA was filled with gas or aqueous solution with different freezing point. The test adopted the cup method to make the ice under -25 ℃ temperature. With the same cup, the test directly adopted the measured peeling force as the icing adhesion strength. The experimental results showed that the influence of the freezing medium with different freezing point on the icing adhesion strength was different. Compared with icing adhesion strength on the smooth specimen surface 169.81 kPa, the icing adhesion strength of the sample filled with the pure water in the pit was 0 kPa, decreased by 100%. And the icing adhesion strength of the sample filled with 6% ethanol solution was declined by 82% compared with the smooth specimen. Compared with the aluminum alloy sample surface, the icing adhesion strength of the sample filled with the solution of low freezing point was reduced by 76.52%. The icing adhesion strength of the sample filled with 6% ethanol solution was the smallest among the samples with the pits filled with alcohol solution. After the test, it was found that the expansion bump with different height occurred on the surface of the BOPP film on the surface of the pits, and the maximum height (3.34 mm) was on the surface of the specimen filled with pure water, followed by the sample filled with 6%, 8% and 10% ethanol solution, whose swell bump heights were 1.25, 1.13 and 1.04 mm, respectively. The results showed that the icing adhesion strength would be reduced by the phase expansion energy owing to the time difference of phase change. What was more, the influence of sample material, size of pit and filled solution on the icing adhesion strength decrease was very small. During the test, BOPP elastic film was used as the icing interface, and the rigid freezing interface under normal conditions was transformed into a flexible freezing interface. Due to the different thermal conductivity, the moisture on the film was first frozen, and the water solution in the pit formed the boundary constraints. After the aqueous solution was frozen into ice, the swell was generated and the energy was released. The energy played a role on the BOPP elastic film, and it destroyed the contact stability of the interface and reduced the icing adhesion strength. Therefore, it is feasible to destroy the contact stability of the elastic freezing interface and reduce the surface icing strength by the phase transition expansion caused by the coupled effect of ice itself and time difference of the phase transition using different aqueous solutions. The experimental results could provide a reference for studying and developing of anti-icing during agricultural product refrigeration field.

refrigeration; freezing; interface; elastic film; phase transition; expansion; adhesion strength

10.11975/j.issn.1002-6819.2017.09.036

TB131

A

1002-6819(2017)-09-0276-06

2016-11-20

2017-04-10

吉林省教育廳“十二五”科學(xué)研究項(xiàng)目（2015-473,2015-417）和吉林大學(xué)研究生創(chuàng)新基金項(xiàng)目（2016167）聯(lián)合資助。

叢 茜，女（漢族），吉林長(zhǎng)春人，教授，博士，博士生導(dǎo)師，主要從事工程仿生學(xué)及低溫防凍粘技術(shù)。長(zhǎng)春吉林大學(xué)生物與農(nóng)業(yè)工程學(xué)院 130022。Email: congqian@jlu.edu.cn

金敬福，男（朝鮮族），吉林長(zhǎng)春人，副教授，博士，主要從事工程仿生學(xué)及表面與界面效應(yīng)分析。長(zhǎng)春吉林大學(xué)生物與農(nóng)業(yè)工程學(xué)院 130022。Email: jinjingfu@jlu.edu.cn

叢 茜，陳廷坤，李 楊，孫成彬，金敬福. 利用相變釋能的農(nóng)產(chǎn)品冷藏設(shè)備主動(dòng)防除冰方法[J]. 農(nóng)業(yè)工程學(xué)報(bào)，2017，33(9)：276－281. doi：10.11975/j.issn.1002-6819.2017.09.036 http://www.tcsae.org

Cong Qian, Chen Tingkun, Li Yang, Sun Chengbin, Jin Jingfu. Active anti-icing method for agricultural product refrigerated equipment based on phase change energy release[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2017, 33(9): 276－281. (in Chinese with English abstract) doi：10.11975/j.issn.1002-6819.2017.09.036 http://www.tcsae.org