林磊 王宏付 柯瑩
摘要: ?為揭示電加熱服的材料、加工工藝與熱防護性能之間的關(guān)系,解析電加熱服設計過程中的關(guān)鍵問題,文章首先對金屬、鍍金和非金屬兩個類別的電加熱材料進行分別闡述并分析其各自的優(yōu)缺點;接著介紹了電加熱服的三種加工工藝,分別為直接利用電熱絲制作、放置電加熱片制作和涂覆電熱薄膜或涂層制作。其中,直接利用電熱絲制作電加熱服加熱均勻、直接高效,但工藝復雜;放置電加熱片制作電加熱服方便簡潔,但容易造成加熱不均;涂覆電加熱薄膜或涂層的方式成本低、使用靈活,但服裝透濕透氣性和耐用性不佳。最后從電安全、電熱、熱舒適性三方面對電加熱服的綜合性能進行評價,總結(jié)得出未來電加熱服將會在加熱區(qū)域的設計、加工工藝優(yōu)化、性能評價方式改進和功能升級四方面開展更加深入的研究。
關(guān)鍵詞: ?電加熱服;電加熱材料;加工工藝;熱防護性能;性能評價;熱舒適性
中圖分類號: TS941.71
文獻標志碼: A
文章編號: 1001 7003(2022)03 0068 08
引用頁碼: 031110
DOI: 10.3969/j.issn.1001-7003.2022.03.010 (篇序)
低溫環(huán)境下,人們通常穿著多層服裝以防止熱量散失,但服裝過于厚重會限制著裝者的身體運動,在一些特定場合并不實用。隨著紡織技術(shù)的不斷發(fā)展創(chuàng)新,智能加熱服裝得以廣泛應用,它將傳統(tǒng)保暖服的被動隔熱變?yōu)橹鲃蛹訜?。目前智能加熱服主要有:電加熱服、化學加熱服、相變加熱服、流體加熱服和太陽能加熱服? [1] 。電加熱服以電為能源,將電能通過置入于服裝中的電加熱元件從而轉(zhuǎn)化為熱能,可以在低溫環(huán)境中積極主動地提供熱量,提高穿戴者的舒適性? [2] 。相比其他智能加熱服,電加熱服發(fā)熱時間長、溫度可調(diào)節(jié)、并且能較好地貼合人體。隨著電發(fā)熱系統(tǒng)技術(shù)的逐漸成熟,電加熱服已成為最常見的智能加熱服裝之一? [3] 。本文從電加熱服的材料、加工工藝、性能評價三方面介紹電加熱服的發(fā)展現(xiàn)狀,分析未來電加熱服的發(fā)展趨勢,并提出電加熱服的性能評價流程,為后續(xù)相關(guān)研究提供一定參考。
1 電加熱材料的分類
電加熱材料主要分為金屬、鍍金和非金屬類加熱材
料,如圖1所示。金屬類加熱材料主要有鐵、銅、銀、不銹鋼和鋁等金屬或合金類材料,通常將金屬絲制成導電紗線或包覆紗線,然后將其織入織物或者其他材料中制成電加熱元件。鍍金屬類電加熱材料通過電鍍、化學鍍和真空鍍等方法將純金屬鍍在普通纖維或者紗線上制成,其中鍍金紗線的含量影響電加熱材料的性能。鍍銀紗線導電性能優(yōu)異,阻值穩(wěn)定,延展性好,是目前金屬鍍金類加熱材料中最常用的一種。
非金屬類電加熱材料來源廣泛,主要有碳系發(fā)熱材料、導電高聚物等。相對于金屬類加熱材料,非金屬類電加熱材料模量低,延展性好,便于織造,制成服裝更貼合人體。碳系發(fā)熱材料主要有碳纖維、碳納米材料和石墨烯發(fā)熱材料等,目前使用在電加熱材料中的導電高聚物較多的有聚吡咯(PPy)、聚噻吩及其衍生物和過渡金屬碳化物(MXene)。
雖然電加熱材料的研究取得了相當大的進展,但在實際應用中仍然存在一些具有挑戰(zhàn)性的問題。如表1所示為一些常用電加熱材料性能優(yōu)劣的總結(jié)。石墨烯、碳納米材料和金屬納米線等電加熱材料的能耗減少、加工過程優(yōu)化和經(jīng)濟化生產(chǎn)是未來需要重點發(fā)展的,金屬類加熱材料的柔性化、輕薄化,非金屬加熱材料的耐洗性能、耐磨性能也是需要進一步解決的問題。
2 電加熱服的加工工藝
電加熱服的加工工藝主要有三種:直接通過電熱絲制作、放置電加熱片制作、通過電熱薄膜或者涂層制作。
2.1 通過電熱絲制作
將電熱絲直接縫制到服裝中,或者先縫制到織物上制作電加熱元件,再將其置入電加熱服裝是較早的制作電加熱服的方式,如圖2所示。這種加工工藝的優(yōu)點在于發(fā)熱效率高,加熱位置覆蓋廣。
Leveratt? [25] 將柔性電加熱線縫制到織物上,制成電加熱服裝,包括上衣、褲子、手套和襪子,通過電子控制器控制每根電熱絲的電流,多個電路器控制供應的功率,自動且獨立調(diào)節(jié)服裝加熱功率。Doganay等? [26] 用銀納米線制備了電加熱手套,當施加3.5 V電壓加熱時,手套的溫度分布相當均勻,且溫度上升到70 ℃只需要100 s。Cheng等? [6] 利用銅納米線基復合纖維織成保暖織物,并將其與單片機集成到服裝中,設計了一個可穿戴的智能個人取暖系統(tǒng),實現(xiàn)了取暖織物與智能手機的交互,為行動不便的人提供了一種有效取暖的解決方案。另外,將其固定在護膝和嬰兒模型胸部位置,經(jīng)紅外熱像顯示,加熱織物對相應部位進行了有效的加熱,通過手機APP可以實現(xiàn)溫度監(jiān)測和加熱溫度控制,應用前景較好。
2.2 放置電加熱片制作
電加熱片也是常見的電加熱元件,是目前最常用的制作電加熱服的手段,其結(jié)構(gòu)如圖3所示。通常利用口袋放置電加熱片,或者直接將電加熱片縫制到服裝中。根據(jù)所需要的加熱部位不同,可以在不同位置放置加熱片,根據(jù)用戶要求,可以制作不同形狀、大小的加熱片。研究指出? [27] ,人體保暖不足的部位主要在前胸、肩部、腹部、前臂和小腿,因此加熱片的放置應主要集中在這些區(qū)域。
唐世君等? [28] 研制了一種由背心、電池和加熱載體組成的電加熱服裝,背心前身兩個口袋用來放置電池,發(fā)熱載體布置在后背、前腹部,智能遙控電池有四檔電壓脈沖輸出,電熱服發(fā)熱時間大于3 h,服裝表面溫度高于50 ℃。WU等? [29] 將基于熱舒適控制模型設計得到電加熱片應用于服裝中,通過低溫實驗證明了電加熱片對于人體熱舒適調(diào)節(jié)的舒適性。Udayraj等? [30] 設計出由加熱夾克和褲子組成的電加熱服,放置12個加熱片,兩個在腹部,三個在上背部,三個位于下背部,另外在臀部和骨盆處各有兩個,通過獨立的兩個電池提供電壓,加熱時間分別可達6 h和14.8 h。李佳怡等? [31] 研制了具有智能溫控裝置的新型防寒服,具有多層結(jié)構(gòu),上衣加熱片位于防寒服內(nèi)膽腹部和后腰,褲子加熱片放置在兩側(cè)膝蓋。圖4是對常見電加熱服中加熱片分布情況進行的展示。
在低溫環(huán)境,手指靈活性能會受到很大影響,溫度過低也會導致凍瘡、麻痹,因此手部保暖也很重要。馬妮妮等? [32] 研制了一款輕便、可持續(xù)保暖的溫控電熱防護手套,包括手套本體、加熱元件和智能調(diào)溫裝置,加熱片形狀為五指型,放置在手套背部隔熱層和內(nèi)里之間,通過真人實驗發(fā)現(xiàn)電熱手套能提供較好的保暖性能,提高手指舒適性。
2.3 涂覆電熱薄膜或涂層制作
將電熱薄膜或涂層涂覆在織物表面,也能得到電熱性能良好的電加熱服,制作方便,使用靈活,也常用于電加熱服的制作中。Zhang等? [33] 在織物表面涂覆導電聚合物亞乙基二氧噻吩(PEDOT)涂層, 制備出一款柔軟、質(zhì)輕、透氣的電熱手套,施加電壓幾秒后,佩戴者就能感受到熱量從織物傳遞到手指。有學者將MXene分別涂覆在棉手套、纖維素纖維表面制作了電熱手套和電熱護頸墊,熱性能優(yōu)良,溫度分布均勻? [23-24] 。許冰等? [35] 基于石墨烯電加熱膜研究出一款自動控溫運動服,這種加熱膜可以在10 V電壓下連續(xù)工作500 h,5 000次穩(wěn)定發(fā)熱。
通過電熱絲直接制作電加熱服的方法直接有效,但是制作工藝復雜,簡化制作工藝是一大挑戰(zhàn),如何將其合理地嵌入服裝而不影響服裝舒適性是未來研究重點。外置電加熱片雖然可以根據(jù)人體部位所需進行加熱,但是電加熱服的加熱均勻度得不到保障。除此之外,電加熱片的厚度會影響舒適性,輕薄化電加熱片是未來電加熱服研究的熱點。電加熱片與服裝的結(jié)合方式需要更加完善,以保證電加熱服的舒適性。在織物表面涂覆電熱薄膜或涂層雖然方便經(jīng)濟,但是薄膜和涂層的耐洗性能到目前為止都沒有很好的保障,在長時間使用過后性能下降,且通過這種方式制作的電加熱服,其透濕透氣性能較差。
3 電加熱服的性能評價
3.1 電安全性能
電加熱服的電安全問題是人們一直關(guān)心的問題,到目前為止還沒有關(guān)于電加熱服電安全性能的一套完整評價體系。鄭兆和等? [36] 將電加熱服裝的電安全性能分為移動電源安全性、電器安全性、電磁兼容性、電發(fā)熱安全性、特殊存放安全性的要求。張妍? [37] 研究指出電加熱服一般貼身穿著,所以存在一定安全隱患,應確保輸出電壓低于12 V,輸出電流在2 A以下,同時設置短路保護裝置,確保著裝者人身安全。除此之外,電加熱服應該注意的電安全問題還有:電路封裝得嚴謹,防止出現(xiàn)短路或者意外接觸液體后出現(xiàn)安全問題;電路設計的合理性,防止發(fā)熱溫度過高而對人體造成損傷;電加熱服的防老化性能要好,保證在存放過程中不會造成導線脫膠、裸露等情況。
3.2 電熱性能
電加熱服的電熱性能主要包括電熱元件的熱穩(wěn)定性、加熱均勻度、加熱功率密度和升溫速度等? [38] 。
熱穩(wěn)定性是指在穩(wěn)定狀態(tài)下工作溫度的電阻穩(wěn)定性和加熱功率穩(wěn)定性,是評價電熱服電熱性能的重要指標。其變化越小,說明電加熱服的熱穩(wěn)定性越好。Ou等? [7] 通過紅外熱像系統(tǒng)測試由液態(tài)金屬氧化薄膜制成的加熱服裝的熱性能,其熱像圖顯示在外力作用下,加熱元件的電阻變化率小。
加熱均勻度是指在穩(wěn)定工作狀態(tài)下加熱織物表面溫度的一致性,通常利用紅外熱像儀來進行測評。通過服裝表面溫度分布計算溫度分布系數(shù),其值越小說明溫度分布越均勻。盧俊宇等? [39] 對用鍍銀紗線制作的加熱織物進行了電熱性能測試,通電后織物溫度先上升后穩(wěn)定,當鍍銀紗線與滌綸紗線橫列排列方式為1 ︰ 2時,織物表面溫度分布較為均勻。
加熱功率密度是指單位面積內(nèi)電加熱服的加熱功率,常用數(shù)字萬用表測量功率,除以電加熱服的面積即得到加熱功率密度,其值越大越好。Bhat等? [21] 測試了浸漬聚吡咯而制成的電加熱織物,當施加穩(wěn)定電壓時,其產(chǎn)生的熱量可達 1 000 W/m 2 ,使用9 V便捷式電源就能產(chǎn)生足夠的熱來維持體溫。
升溫速度是指電熱服達到預設溫度的快慢,升溫速度越 高,電加熱服就能更快地對環(huán)境做出反應。隨著電加熱材料
的不斷發(fā)展,電加熱服的升溫速度已經(jīng)有了很大提升,在幾十秒內(nèi)就能達到預設溫度。Zhang等? [33] 測量了PEDOT涂層棉織物的電阻和加熱性能,由其制作的加熱手套只需一節(jié)3 V電池,就能在10~20 s后實現(xiàn)暖手效果。
3.3 熱舒適性能
電加熱服的熱舒適性能通常與電熱性能放在一起進行,一般通過暖體假人實驗、真人著裝實驗和數(shù)值模型構(gòu)建進行測評。暖體假人實驗就是利用人體模型模擬人體與環(huán)境的熱交換過程,在過程中測量電加熱服裝的溫度變化、溫度分布、加熱功率等。真人著裝實驗即通過真人穿著電加熱服裝,在特定環(huán)境下對所穿著服裝的主觀評價,同時記錄人體生理反應。數(shù)值模型構(gòu)建就是通過人體、服裝和環(huán)境之間的熱傳導、對流、輻射等建立理論模型,為電加熱服的優(yōu)化設計提供理論依據(jù),方便調(diào)節(jié)參數(shù)。電加熱服性能評價的流程如圖5所示,表2為電加熱服性能評價的方法比較及實驗結(jié)果。
分析表2可知,暖體假人實驗可以客觀表征服裝的熱阻、熱流量等物理指標,但不能體現(xiàn)人體真實熱感覺。真人著裝實驗客觀地評價穿著服裝時的熱感覺,可結(jié)果受實驗對象影響,且實驗成本高。 數(shù)值模型構(gòu)建可以模擬人體與外界的熱交換,但是受模擬環(huán)境的影響,有些條件模擬時會比較困難,往往會忽略一些外界因素的影響,模擬結(jié)果與實際情況存在一定誤差。
從以上研究來看,在不同條件下電加熱服的熱舒適性能有
所區(qū)別,對影響電加熱服熱舒適性能的研究可以為其設計提供更多依據(jù)。圖6是影響電加熱服加熱性能的因素分析? [46-51] ,在設計過程中應充分考慮這些條件。目前較多研究重點集中在環(huán)境對于電加熱服性能的影響,而關(guān)于電加熱片形狀對電熱性能和熱舒適性能的影響鮮有涉及。電熱服的電熱性能和熱舒適性能已有比較完善的評價體系,但是對于電加熱服的安全性能研究較少,完整的評價方案和標準有待進一步探索。
4 結(jié) 語
電加熱材料包括金屬與鍍金類電加熱材料和非金屬類電加熱材料,通常將其制成電加熱元件集成到服裝中制成電加熱服。本文對制作電加熱服的方式進行了分類,總結(jié)了三種方式的優(yōu)缺點,并提出改進建議。對電加熱服性能評價的指標做了詳細闡述,介紹了性能評價的方法,綜合現(xiàn)階段存在的一些問題,提出了未來電加熱服研究的展望。
1) ?加熱區(qū)域的設計。不同的加熱片放置位置對電加熱服的加熱效率有不同的影響,未來可以研究不同加熱區(qū)域組合對電加熱服熱舒適性能的影響,提高加熱效率的同時節(jié)約能量。
2) 加工工藝的優(yōu)化。將電熱元件置入服裝當中會造成服裝舒適性降低,服裝一體化成型技術(shù)的發(fā)展為電加熱元件的置入提供一種解決方案。在同一件電加熱服裝的不同加熱區(qū)域可以結(jié)合不同的加熱方式,彎曲形變較多的部位可以使用電熱膜,軀干部位用加熱片,足部利用加熱絲等。
3) ?電加熱服的功能升級。目前電加熱服的研究多在提高人整體溫度角度,但是人體各個部位對熱的敏感程度不同,未來的研究應該合理量化電加熱服各局部的熱量,根據(jù)各部位的熱需求進行設計,結(jié)合傳感器技術(shù),實現(xiàn)電加熱服裝的分區(qū)域智能加熱,提高保暖性能。同時在電安全問題上,無線充電技術(shù)的發(fā)展為電加熱服的電源問題提供了新的解決方案,既可以減少導線的使用和線路封裝的安全問題,也能提高電加熱服的輕便性。
4) 性能評價方式改進。目前對于電加熱服的性能測試主要在人工氣候倉中進行,并且溫度設置多為穩(wěn)態(tài)溫度,實際使用中環(huán)境溫度是實時變化的,所以需要對動態(tài)溫度變化下電加熱服的性能進行評價,得出的結(jié)果更加客觀。
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Research status and progress of electrically heated garments
LIN Lei a, WANG Hongfu b, KE Ying b
(a.College of Textile Science and Engineering; b.School of Design, Jiangnan University, Wuxi 214122, China)
????Abstract:
As one of the important components of intelligent heated clothing, the electrically heated garment uses electrical energy as the energy source and converts it into heat energy through the built-in electric heating elements in the clothing to actively supply heat for human body, boasting the advantages of long heating time, adjustable heating temperature and good fit to the human body. In recent years, the positive role of electrically heated garments in the field of cold-proof and thermal clothing has been proved by a lot of studies. The development of electric heating materials and the research of heating body parts have promoted the development of electrically heated garments, providing vital references for the design of electrically heated garments. To reveal the relationship between the materials, processing technology, and thermal protection performance of electrically heated garments, and to analyze the key issues in the process of electrically heated garment design, this paper summarizes the development of electric heating materials. At the same time, this paper introduces the production process of the electrically heated garments, proposes the method of electrically heated garment performance evaluation, and prospects the development of electrically heated garment based on the current research.
The materials used for electrically heated garments are mainly divided into two types: metallic and gold-plated materials and non-metallic materials. Metallic and gold-plated electric heating materials are not readily implanted into clothing despite their high heating efficiency. On the contrary, non-metallic electric heating materials are easy to manufacture electric heating elements so that they are used in electrically heated garments. Although non-metallic electric heating materials are convenient and simple, and cost little for production, they have the drawback of short lifespan, which needs to be improved. There are three main processes for the production of electrically heated garments respectively by using electric heating wires directly, placing electric heating pads, and applying electric heating films or coatings. Among them, the production of electrically heated garments by directly using electric heating wires is direct and efficient, but the process is complex. Placing electric heating pads is convenient and simple, but it would easily cause uneven heating. Despite the low cost and flexible use of coating electric heating film or coating, the clothing moisture permeability, air permeability, and durability are not ideal. As a result, there is still great potential for the research of production process of electrically heated garments.
The electrically heated garment performance evaluation is mainly carried out from three main aspects: electrical safety performance, electrical heat performance, and thermal comfort performance. An objective evaluation of the performance of electrically heated garment could be carried out by combining the three aspects. The current means of testing the performance of electrically heated garments mainly include thermal manikin experiments, real person attire experiments, and numerical model construction. The thermal resistance, heat flow, and other objective physical indicators of electrically heated garments can be characterized by thermal manikin experiments, but they cannot reflect the real thermal sensation of the human body. The performance of electrically heated garments can be evaluated by real person attire experiments based on the objective and subjective feelings of the human body. The results are highly reliable, but the experiment cost is high. The numerical model construction method can simulate the heat exchange between the human body, clothing, and the environment, simulate the application environment of the electrically heated garments by changing the parameters. Because the results from this method have some deviation from the actual operating environment, they finally need to be verified by real person attire experiments.
Graphene and carbon nanotube heating materials as the current hotspots of the research ofelectrical heating materials can be made into coatings or thin films coated on the surface of fabrics to make electric heating elements, which have high heating efficiency and good flexibility. However, the production cost of these materials is high, the process is complicated, and the aging resistance needs to be improved. The research on the electrically heated garment performance evaluation is mainly focused on the electric heating and thermal comfort performance, but there is little research on the electric safety performance. Therefore, a complete system is needed to evaluate the performance of electrically heated garments.
As the research on the electrically heated garments has proven that it has great potential in the field of cold-proof clothing, the development of electric heating materials has also provided the basis for the development of electrically heated garments. Although the research on electric heating materials, cold-proof clothing, and human thermal comfort has accumulated many valuable results for electrically heated garments, it is necessary to carry out more studies on the design of the heating areas of the electrically heated garments. Limited by the production process, the electrically heated garments have not yet been widely popularized, hence optimizing the processing is also a challenge. At the same time, how the performance of the electrically heated garments is evaluated needs to be improved to ensure that users can accurately select an appropriate suit. Technological development will facilitate the functional upgrading of electrically heated garments, ?and integrating wireless charging technology into the design of the electrically heated garments is an effective way to reduce the wiring arrangement. Artificial intelligence can realize separate local heating according to the thermal needs of each body part, thereby meeting meet people’s requirements for thermal comfort in different environments.
Key words:
electrically heated garments; electric heating materials; processing technology; thermal protection performance; performance evaluation; thermal comfort
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