弹热制冷技术的发展现状与展望

弹热制冷是由应力场驱动弹热材料相变而产生制冷效应的固态制冷技术,特点是无任何环境破坏作用,具有较高的理论制冷效率和制冷功率密度。近年来,欧美多个研究机构对弹热制冷技术进行了持续性研究,使该技术得到快速发展,已有多个可实际工作的弹热制冷原型机。本文从热力学理论基础、弹热工质、原型机开发和系统性能仿真等方面展开分析与讨论,为国内同行开展弹热制冷相关领域的研究提供参考。根据文献资料,现阶段弹热制冷机的制冷效率可达14%的热力完善度(外部参数),且有潜力在未来达到30%的热力完善度,从长远来看,材料层面的热力完善度可达80%,在系统层面还有较大性能提升空间。因此,可以持谨慎乐观的态度认为,弹热制冷技术在今后将得到更快、更广泛的发展和应用。     

不同温度下天然橡胶扭拉热效应分析

弹热制冷是由应力场驱动弹热材料相变而产生制冷效应的固态制冷技术.天然橡胶由于价格低廉,弹性模量较小而备受关注.本文在0℃以上的环境温度对硫化天然橡胶进行拉伸-加捻-解捻-回缩循环消除Mullins效应,并在环境温度为-30～40℃范围内对消除了Mullins效应的天然橡胶进行循环加载,采用红外热像仪记录循环过程中天然橡...     

橡胶弹热效应的研究现状与展望

弹热制冷因具有较高的制冷效率和比制冷功率等特点,被认为是最有希望替代传统蒸气压缩技术的新型高效制冷技术之一。本文从橡胶弹热效应的热力学基础、动力学理论、橡胶工质及以橡胶为制冷工质的制冷循环进行分析与讨论,为国内外开展橡胶弹热效应的研究提供参考。根据文献资料可知,天然橡胶的弹热性能最好,在0℃的环境温度下应变为6,可实现的最大温变为12 K。对天然橡胶加捻-解捻过程可以实现更高的温度变化,缩小制冷系统的体积,当应变为3时,实现的最大温变为12.9 K,是未加捻橡胶的5.4倍。目前,对橡胶弹热效应的理论研究已经相对成熟,但原型机的开发有限,需进一步开发推进以天然橡胶为工质的弹热制冷技术的实际应用。因此,本文谨慎的认为天然橡胶在弹热制冷技术应用中存在很大潜能。     

水冷式半导体冰箱制冷性能的研究

研究了水冷式散热方法对半导体冰箱制冷性能的提高.以常用的半导体小冰箱为实例,分别测试了在风冷、循环水和恒温水条件下小冰箱的制冷性能.结果表明,水冷制冷效果明显优于传统风冷式,且其制冷性能与冷却水的温度有关.水温越低,半导体制冷器的制冷效率越高,制冷温度越低.当冷却水温度为171 ℃时,水冷半导体小冰箱很快达到冷冻.建立了水冷式半导体冰箱的制冷模型,计算分析了在不同恒定冷却水温度下半导体制冷器冷端温度随时间的变化关系,并将理论结果与实验测量结果进行了拟合分析,发现理论模型与实验测量结果一致.研究结果为水冷式半导体冰箱制冷性能的提高提供了实验和理论依据.     

多级热电制冷器的制冷性能及主要影响因素分析

目前对多级热电制冷器的研究较少,且对制冷性能的报导尚不统一。为研究多级热电制冷器的确切性能,本文利用商用热电材料的物性参数,建立了一级至六级热电制冷器的多物理场耦合仿真模型,并通过实验验证了模型的准确性。然后从多级热电制冷器的设计角度出发,研究了外部驱动电路及内部结构参数对其制冷性能的影响。结果表明：在热端为27℃时,六级热电制冷器在电串联、电并联和独立电源驱动电路下可分别获得113.32、71.84和129.78℃的最大制冷温差。进一步探究了不同驱动电路的最佳应用场合,分析了不同驱动电路下多级热电制冷器的制冷性能出现差距的原因。并以六级热电制冷器为例,研究了各层级热电臂的高度的影响,结果表明最高层级的臂高是最主要的影响因素。     

冰箱回热毛细管内部流动特性研究

通过对冰箱回热毛细管的“六段流阻”模型物理意义的描述,模拟了3种不同工况对冰箱回热毛细管运行性能的影响,即:不同的冷凝器温度、不同的蒸发器温度及不同的回热段相对位置。从仿真结果可以看出冷凝温度的变化对毛细管内部流动特性的影响最大,并对此进行了初步的实验验证。从对比结果可以看出,该模型能够较好地描述冰箱回热毛细管内部的流动特性。     

半导体制冷床垫睡眠热平衡系统模拟与性能分析

通过营造局部非均匀空调环境,可以实现人体睡眠热舒适与节能的双重目的。本文提出并搭建了基于半导体制冷床垫的睡眠热平衡系统,通过半导体制冷与人体热负荷耦合传热模型,对半导体制冷床垫系统的热特性进行了参数化分析、优化设计与节能性评价。结果表明：通过增加制冷床垫的半导体数量,减小电流输入,可以扩大室内允许的舒适空气温度范围,同时降低结露风险。半导体制冷床垫系统的节能率与室内温度、半导体工作电流以及房间面积直接相关。通过对比参考工况（空调设定26 ℃）、工况1（空调设定27 ℃）与工况2（空调设定28 ℃）,可知工况1与工况2可实现最高10.26%与23.37%的节能率。     

半封闭活塞式制冷压缩机低温工况应用R404A的实验研究

通过对大连三洋压缩机有限公司生产的半封闭活塞式制冷压缩机C—L150M82，分别应用R404A与R22在低温工况下的对比实验研究，来分析使用环保型制冷剂R404A替换R22的可行性。实验研究表明：第一，半封闭活塞式制冷压缩机在保持配置不变的条件下，在低温工况下，保持冷凝温度不变，使用R404A比使用R22制冷量有明显提升，随着蒸发温度的降低制冷量可提升10％～30％；第二，在冷凝温度不变条件下，使用R404A可以达到-45℃蒸发温度；第三，使用R404A后压缩机排气温度比R22有明显降低；第四，过冷过热循环对R404A系统都有明显的性能改善。     

基于热电原理的过冷器在家用空调中应用的实验研究

在蒸气压缩制冷系统中,增加系统的过冷度可以提高系统的制冷量及其性能系数。本文设计了一种基于热电制冷原理来增加系统过冷度的空调系统,并在最小制冷,额定制冷和最大制冷三种工况下,对运行过冷装置前后的空调系统的性能进行实验对比。结果表明:采用设计的过冷器后,冷凝器出口的过冷度分别提高了2.3℃、1.9℃和1.5℃,系统的制冷量分别提高了3.6%、3.2%和4%,系统的性能系数分别提高了3.7%、3.1%和4.2%。在下一步的实验中可通过优化热电制冷片的运行工况,进一步提高系统的性能。     

低温热源驱动的二级吸附冷冻循环实验研究与性能分析

在冷冻应用方面,传统的吸附式制冷工质对在热源温度低于90℃、冷凝温度高于25℃的条件下,很难实现-10℃以下的冷冻。为了实现100℃以下的太阳能或废热利用,这里提出了二级吸附式制冷循环,建立了性能测试实验台。采用CaCl2-BaCl2-NH3作为工质对,利用85℃热源驱动,测试不同蒸发温度与冷凝温度下吸附剂的吸附与解吸性能。结果表明,二级吸附式制冷能够实现-20℃下的冷量输出,同时,冷却水温度为25℃时,氯化钙的循环吸附量、二级吸附式制冷COP与SCP分别为0.598kg/kg,0.24,106.6W/kg。     

Development and performance of steam ejector refrigeration system operated in real application in Thailand

This paper presents the design and construction of a prototype steam ejector refrigeration system which can be operated under the actual condition of Thai environment, which is rather hot and humid. The prototype refrigerator was designed to produce a cooling capacity of approximately 3 kW. Water was selected to be used as the working fluid. The steam boiler used was a vertical fire tube type and it was designed to be used with LPG compact gas burner. The condenser was cooled by water obtained from a conventional cooling tower. The prototype refrigerator was used to produce chilled water which was used to cool a small tested room. It was observed that the room temperature of 24.2 °C was obtained at the cooling load of 3000 W. The cooling water was supplied to the condenser at about 30 °C. The COP obtained was 0.45. This prototype refrigerator is proven to be practical and can be used in actual environment of Thailand.     

一种变频空调电控箱体降温模块的研究

本文根据变频热泵机组系统特点和制冷循环热传导原理设计了一种变频空调电控箱体的降温模块,该降温模块的U型散热装置与制冷剂配管接触弧度为3/4圆弧结构,接触点切线成45°斜角,放置在空调系统中出储液器到进入电子膨胀阀之间的管路部分,使制冷剂经过该散热装置的温度处于40℃～50℃之间最佳温度范围。在环境温度43℃、出水温度15℃的制冷工况下,通过实验分析和验证了增加该散热装置和自然冷却两种状态下系统的性能。结果表明:加装制冷剂散热装置机组运行时变频器功率器件产生的热量可以通过制冷剂散热装置带走,降温效果较为明显。同时,通过理论计算和实验测试对比了变频器功率发热部件温度与制冷剂进口温度之间温度差变化情况,验证了加装制冷剂散热装置的效果。     

Performance characterisation of a small milk cooling system with ice storage for PV applications

The presented work proposes a calculation method to estimate the transient performance of a small on-farm milk cooling system for PV applications. The system employs 3 kg ice for fast cooling of 17 L milk in conventional 20-L-milk-cans. Two units of a commercial DC refrigerator operate at −10 °C and at 4 °C for ice production and milk preservation respectively. The development of milk temperature and energy consumption during a cooling event was studied experimentally at different ambient temperatures of 20 °C, 30 °C and 40 °C. A computational model was developed and validated where thermal resistances and COP were adjusted with experimental data. The results between 20 °C and 40 °C ambient temperature show a COP reduction of around 30% and a total daily energy consumption increase of around 100%. The specific total energy consumption of the system per litre milk was between 30 Wh/L and 58 Wh/L for the studied ambient temperature range. The suggested model can be used for the optimisation of photovoltaic stand-alone systems at specific locations.     

Design and performance of a room-temperature hybrid magnetic refrigerator combined with Stirling gas refrigeration effect

The experimental prototype described in this work is a hybrid refrigerator that combines the active magnetic refrigeration effect with the Stirling gas regenerative refrigeration effect. In this prototype, gadolinium sheets are packed in the regenerator matrix for both Stirling and active magnetic regenerative refrigeration. Experimental tests were carried out to measure the cooling performance of this hybrid prototype. The influence of the phase angle on the cooling performance was investigated, and a reasonable phase angle of 90° was determined to obtain optimal cooling performance. By combining the two refrigeration effects, a minimum cooling temperature without heat load of 3.5 °C was reached, which is lower than that of 6.5 °C for the pure Stirling refrigeration effect without the magnetic cooling effect. The results of this study show that the cooling performance is improved by 24% for the hybrid effects compared with that exploiting only the Stirling gas refrigeration effect.     

Design and Properties of Thermal Barrier Coatings for advanced turbine engines

The efficiency and performance of advanced aircraft turbines can be markedly increased if higher gas temperatures are used. Although the highly loaded blades and vanes in the high pressure turbine are heavily cooled, today's substrate materials are unable to provide sufficient strength in the temperature range up to 1500°C and above. If thermal barrier coatings (TBCs) are applied on superalloy turbine blades a substantial temperature drop of the parts can be achieved. The resulting increase in efficiency comes from reduced cooling and/or increased gas turbine inlet temperatures of up to 150°C. TBCs are either processed by plasma spraying (PS) or electron beam physical vapour deposition (EB-PVD). While PS is lower in cost EB-PVD leads to superior strain and thermoshock tolerant coatings. Furthermore, cooling hole closure of turbine blades and vanes is prevented and aerodynamic design maintained. Finally, future research and development needs in TBC technology are stressed.     

Thermal-Driven Soft-Contact Triboelectric Nanogenerator for Energy Harvesting and Industrial Cooling Water Monitoring

In this paper, a quaternary dielectric soft-contact rotary triboelectric nanogenerator (QDSR-TENG) of low frictional resistance is fabricated for combining TENG with a shape memory alloy (SMA) engine. The introduction of rabbit fur brush and FEP brush results in charge pumps with a partially soft contact structure. Benefiting from the low friction loss of the structure, the QDSR-TENG can operate stably and continually for 100k cycles without significant output degradation. The SMA engine exhibits thermally induced phase transformation and super-elasticity and can be utilized for harnessing waste heat energy. The thermal-driven QDSR-TENG can operate with a water source of 43 °C with a distinguishable response to the variation of temperatures. Such a low starting temperature not only promotes the harvesting of low-grade thermal energy, but also results in a self-monitoring industrial cooling water system. The coupled elastocaloric power and cooling cycle proposed in the thermal-driven QDSR-TENG opens a new paradigm for the application in energy harvesting and smart sensing.