Eco-friendly alternative refrigeration systems

Refrigeration applications at the domestic, commercial and industrial levels are becoming an integral part of the present day living. The demand and supply of refrigeration systems is increasing day by day with the changing lifestyle. The existing compressor-based refrigeration (i.e., mechanical refrigeration) system has reached the maximum level of innovation. For the last few decades, there has not been any significant increase in the efficiency (i.e., coefficient of performance, COP) of the system. Moreover, with the increasing awareness of environmental degradation, the production, use and disposal of ChloroFluoro Carbons (CFCs) and HydroChloroFluoroCarbons (HCFCs) as refrigerants in mechanical refrigeration system has become a subject of great concern. However, such systems are being developed using more ecofriendly refrigerants viz., air, CO₂, NH₃, etc. Besides, efforts are being directed to develop other types of refrigeration technologies e.g., magnetic refrigeration, thermoelectric refrigeration (discussed in Part 1) and thermoacoustic refrigeration (discussed in Part 2), which will be moreecofriendly, cost effective, efficient, simple in design, convenient and reliable.     

机载小功率热电制冷系统的性能分析

在设定飞机参数的条件下,以现有的实验模型为研究平台,提出了一种机载小功率热电制冷系统的设计优化方法.考察了该系统在3种不同飞行高度运行时制冷量与制冷系数的变化曲线.然后,利用熵产最小法评估了系统的性能,并计算出系统的代偿损失.通过电功率实验,得出了制冷系统的功耗变化曲线,其峰值小于机载装备可提供的最大电量,由此证明了小功率热电制冷系统应用于机载设备的可行性.制冷系数、制冷量及系统熵产与飞行高度和电流有关,通过分析这些变化数据,得出工作状态下制冷系数的最优值,并提出可最大程度利用热电制冷系统优势的优化方案.     

氨水吸收/压缩复合制冷循环性能分析(英文)

针对氨水吸收/压缩复合制冷循环的方式不同,结合Schulz氨水溶液状态方程,分别对压缩机处于系统高压区和低压区2种不同的组合方式进行了理论分析计算.分析了在给定中间压力下,蒸发温度Te、热源温度Th和冷却水温度Tw对2种组合方式下压缩机当量热耗量qCW、热源耗热量qG和循环性能系数COP的影响.结果表明:压缩机当量热耗量对循环性能系数的影响要低于热源耗热量的影响;压缩机处于系统高压区时循环的一次用能量要明显高于压缩机处于系统的低压区;压缩机处于系统低压区时循环性能要优于压缩机处于系统的高压区.当中间压力给定时,存在一个最佳热源温度,使得氨水吸收/压缩复合制冷循环的性能系数取得最大值.     

System design and analysis of the trans-critical carbon-dioxide automotive air-conditioning system

As an environmentally harmless and feasible alternate refrigerant, CO₂ has attracted worldwide attention, especially in the area of automobile air-conditioning (AAC). The thermal property of CO₂ and its trans-critical refrigeration cycle is very different from that of the traditional CFC or HCFC system. The detailed process of CO₂ system thermal cycle design and optimization is described in this paper. System prototype and performance test bench were developed to analyze the performance of the CO₂ AAC system.     

Experimental adsorption equilibrium study and comparison of zeolite with water and ethanol for cooling systems

INTRODUCTION In the past few decades, adsorption processes have been used exclusively for gas separation and purification purposes. It is only recently that this phenomenon has been exploited to produce cooling and heating. As regulations aiming at phasing out the CFCs are being implemented, thermally driven sorp-tion refrigeration machines are emerging as an at-tractive alternative to electrical vapor compression machines that produce no harmful effect on the en-vironment since their w…     

The Electrochemical Performance of Ml0.7Mm0.3Ni3.7Co0.7Mn0.4Al0.2 Nanocrystalline Hydrogen Storage Alloy as Metal Hydride Electrode

Ml0.7Mm0.3Ni3.7Co0.7Mn0.4Al0.2 nanocrystalline hydrogen storage materials are prepared by melt-spinning(MS).X-ray diffraction is used for the measurement of the nanocrystalline size.Compared to the electrode of polycrystalline alloys,the property of activation MH9metal hydride)electrode of the alloys with nanometer scale became worse and the inital discharge capacity decreased.It may be ascribed to the decrease of the total amount of rare earth metals and the increase of oxygen on the surface from the analysis of components of the alloys.After heat-treatment,the electrochemical performance of MH electrode of as-spun alloys could be improved,which could be attributed to the alleviation of the lattice strain.     

新型太阳能吸收式制冷循环系统性能分析

在传统两级溴化锂吸收式制冷循环的基础上,从增大热源可利用温差考虑,提出了一种由太阳能驱动的新型吸收式制冷循环,分析计算了低压发生器压力(中间压力)和中间溶液浓度变化对系统热力系数COP和热源可利用温差的影响。结果表明,在发生热源温度85℃~95℃的范围内,中间压力在1.6KPa (12mmHg)和2.2KPa (16.5mmHg)之间取值新型循环有较高的热力系数和较大的热源可利用温差。     

Study of transport behavior for Fe-doping La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> perovskite manganese

Systematic studies of the transport properties of La_0.67Ca_0.33Mn_1?xFe _x O₃ (x=0–0.3) systems showed that with increasing Fe-doping contentx the resistance increases and the insulator-metal transition temperature moves to lower temperature. For small doping content, the transport property satisfies metal transport behavior below the transition temperature, and above the transition temperature it satisfies the small polaron model. This behavior can be explained by Fe³⁺ doping, which easily forms Fe³⁺?O^2??Mn⁴⁺ channel, suppressing the double exchange Mn³⁺?O^2??Mn⁴⁺ channel and enhancing the spin scattering of Mn ions induced by antiferromagnetic clusters of Fe ions.     

渔船尾气驱动的氨水溶液冷却吸收式制冷

提出了一种溶液冷却吸收的氨水吸收式制冷循环方案,即利用来自吸收器的浓溶液冷却吸收过程的前半部分以回收部分吸收热.由于进入溶液热交换器的浓溶液温度提高,在其出口浓溶液将部分沸腾,因而可减少外界热源的消耗.计算结果显示,在典型条件下改进循环的性能系数（COP）比传统循环提高约28.3%,而该循环所有换热器所需的总换热面积则比传统循环略有减少.在同等条件下与吸附式制冷方案相比,改进循环的制冷量可增加1倍多.渔船采用改进循环的制冷机后用其自身柴油机废气足以提供渔品保鲜用的制冷量.     

Thermal Response Test by Improved Test Rig with Heating or Cooling Soil简

An improved test rig providing both the heat and cold source was used to perform thermal response test(TRT), and the line source model was used for data analysis. The principle of determining the temperature difference between the inlet and outlet of test well can keep the heating or cooling rate constant, along with a reduced size of test rig. Among the influencial factors of the line source model, the temperature difference was determined as the most important, which agreed with the test results. When the gravel was taken as the backfill material, the soil thermal conductivities of heating and cooling at the test place were 1.883 W/(m·K) and 1.754 W/(m·K), respectively, and the deviation of TRT between heating and cooling soil was 6.8%. In the case of fine sand, the thermal conductivities of heating and cooling were 1.541 W/(m·K) and 1.486 W/(m·K), respectively, and the corresponding deviation was 6%. It was also concluded that different velocities of water had less influence on TRT than the temperature difference.     

Experimental performance of moderate and high temperature heat pump charged with refrigerant mixture BY-3

Theoretical and experimental analysis of a new refrigerant mixture BY-3 was conducted based on a single-stage vapor compression refrigeration system. The water-water heat pump system used BY-3 to produce hot water when the low temperature was 20 ℃. The following results were obtained: the highest temperature at the condenser outlet reached about 85 ℃; when the difference between the water temperatures at the condenser outlet and the evaporator inlet was less than 40 ℃, the coefficient of performance (COP) was larger than 4; when the difference reached 55 ℃, the COP still kept 3; the discharge temperature of BY-3 was lower than 100 ℃, and the refrigerant vapor pressure kept lower than 1.8 MPa. When the water temperature at the condenser outlet reached over 85 ℃, nearly a 5 ℃ superheating temperature was maintained.     

In-situ characterization of gas-liquid precipitation reaction in a spray using rainbow refractometry

Gas-liquid precipitation reactions in terms of a spray exist widely in energy, chemical, and environmental engineering. In this paper, a rainbow refractometry-based method is used to measure the reaction process of these spray-based gas-liquid precipitation reactions in a non-intrusive way. Rainbow refractometry can simultaneously provide information on thermochemical and physical properties of droplets. A global rainbow measurement system was built to characterize a CO₂ absorption reaction. Rainbow signals of spray droplets of Ca(OH)₂ solutions before and after CO₂ absorption were recorded and processed. Results indicated that the average refractive index of saturated H₂O-Ca(OH)₂ solution was 1.335 69, which accorded with the Abbe measurement. After the absorption reaction, the refractive index of droplets decreased to 1.335 17 which is close to that of water. The reaction extent was therefore reflected in the change of the refractive index of droplets. An extra experiment of CO₂ absorbed by Ba(OH)₂ solutions was conducted. The refractive index of droplets decreased with the reaction process, which acted well as an evolution indicator of the reaction. A heat transfer analysis of the reaction was also carried out. Due to the high heat dissipation performance of fine droplets, the temperature increase in the measurement volume was estimated to be less than 0.61 K, which has almost no effect on the measured results. The rainbow refractometry-based method shows good potential for in-situ characterization of a gas-liquid precipitation reaction.     

Effects of nucleating agents on crystallization of arc-molten slag from incinerator fly ash

Glass-ceramics obtained from the electric arc furnace molten slag of incinerator fly ash was produced by applying nucleation and crystallization through heat treatment process. The effects of nucleating agent (TiO₂ and Cr₂O₃)on the crystallization kinetics and heat treatment schedule of the slag were investigated. The results show that the nucleating agents changed the crystallization phase and morphology of the obtained glass-ceramics. The optimum heat treatment schedule of the glass with TiO₂ was determined as nucleation at 952 K for 1.5 h and crystal growth at 1258 K for 1.5 h, while those values with Cr₂O₃ were estimated at 971 K for 2 h and at 1 238 K for 2 h. TiO₂ acting as nucleating agent could decrease the activation energy of the slag and shorten the total thermal treatment time in comparison with Cr₂O₃. The glass-ceramics obtained under the optimum heat treatment condition was environment-friendly and had remarkable physical/mechanical properties and chemical durability.     

Metal Oxide/Nitrogen-Doped Carbon Catalysts Enables Highly Efficient CO2 Electroreduction

The metal oxide/nitrogen-doped carbon (NC) compounds zirconium oxide/NC (ZrO₂/NC) and cerium oxide/NC (CeO₂/NC) were synthesized via the pyrolysis of polyaniline on the metal oxide surface. The characterization of the ZrO₂/NC and CeO₂/NC catalysts showed more active CO₂ reduction reaction activity than that of NC catalyst without metal oxide. Gas chromatography analysis revealed that CO and H₂ were the primary products, and no liquid-phase products were detected via proton nuclear magnetic resonance spectroscopy or high-performance liquid chromatography. The maximum Faraday efficiency of ZrO₂/NC reached 90% at − 0.73 V (vs. RHE), with the current density of CO at 5.5 mA/cm²; this Faraday efficiency value was higher than that of NC (41%), with the current density of CO at 3.1 mA/cm². The interaction between the metal oxide and carbon allowed the efficient formation of defect sites, especially imine-type nitrogen, strengthening the adsorption of the key reaction intermediate CO₂^•− and thus promoting the CO₂ reduction reaction.

     

Kinetics of the reaction between boron trifluoride methanol complex and sodium methoxide to produce enriched <Superscript>10</Superscript>B methylborate

The relation of boron trifluoride concentration with conductivity in boron trifluoride methanol solution (BF₃-CH₃OH)was power exponent fitted in low concentration range. The kinetics of the reaction between boron trifluoride methanol complex and sodium methoxide to produce enriched ¹⁰B methylborate was proposed based on a detailed mechanism study, and was verified by acid-base titration method and conductivity method. It was found that this reaction is first order reaction and the rate constant is 0.022 min^?1 at 338 K(65 °C), the activity energy is 65 kJ/mol. In addition, it was found that the conductivity method is more feasible to measure the kinetic curve than acid-base titration method.     

Measurement of the thermal transport properties of dielectric thin films using the micro-Raman method

The micro-Raman method is a non-contact and non-destructive method for thermal conductivity measurement. To reduce the measurement error induced by the poor fit of the basic equation of the original micro-Raman method, we developed a new basic equation for the heat source ofa Gaussian laser beam. Based on the new basic equation, an analytical heat transfer model has been built to extend the original micro-Raman method to thin films with submicrometer- or nanometer-scale thickness. Experiments were performed to measure the thermal conductivity of dielectric thin films with submicrometer- or nanometer-scale thickness. The thermal resistance of the interface between dielectric thin films and their silicon substrate was also obtained. The obtained thermal conductivity of silicon dioxide film is 1.23 W/（m.K）, and the interface thermal resistance between silicon dioxide film and substrate is 2.35×10^-8 m^2.K/W. The thermal conductivity and interface thermal resistance of silicon nitride film are 1.07 W/（m.K） and 3.69×10^-8 m^2.K/W, respectively. The experimental results are consistent with reported data.     

V2O5-CaCo3-Nb2O5掺杂对低损耗功率Mn-Zn铁氧体的影响

Effect of the content of dopants in the manganese-zinc ferrites on the low power loss is studied by measuring magnetic properties and observing the grain boundary structures. The Mn0.738Zn0.206Fe2.066O4 composition powders were prepared by using conventional ceramic powder processing technique. The microstructure of grain boundary was observed by scanning electron microscope （SEM）. It has been found that power loss is greatly dependent upon the content of the additives.     

Mn3+～甲苯非均相体系的氧化反应动力学

The reaction kinetics of the heterogeneous oxidation oftoluene with Mn^3 was studied by considering the effects of disproportionation of Mn^3 in reaction system,a “parallel”modulus was set up.And then the concentration of Mn^3 in disproportionation and the concentration of benzaldehyde in oxidation were respectively determined in turn.the rate constant,order and pseudo-activation energy of the heterogeneous oxidation were obtained by mathematical deduction and the kinetic equation was concluded.In addition,the reaction mechanism was analyzed.It shows that the results are completely consistent with modulus.     

HNCO hydrolysis performance in urea-water solution thermohydrolysis process with and without catalysts

The thermolysis of urea-water solution and its product, HNCO hydrolysis is investigated in a dual-reactor system. For the thermal decomposition below about 1073 K, the main products are ammonia (NH3) and isocyanic acid (HNCO) whereas at higher temperatures the oxidation processes take effect and the products include a low concentration of nitric oxide (NO) and nitrous oxide (N2O). The gas HNCO is quite stable and a high yield of HNCO is observed. The ratio of NH3 to HNCO increases from approximately 1.2 to 1.7 with the temperature. The chemical analysis shows that H radical is in favor of HNCO hydrolysis by instigating the reaction HNCO+H·→·NH2+CO and high temperature has positive effect on H radical. The hydrolysis of HNCO over an alumina catalyst made using a sol-gel process (designated as γ-Al2O3) is investigated. The conversion of HNCO is high even at the high space velocities (6×105 h-1) and low temperatures (393–673 K) in the tests with catalysts, which enhances HNCO hydrolysis and raises the ratio of NH3 to HNCO to approximately 100. The pure γ-Al2O3 shows a better catalytic performance than CuO/γ-Al2O3. The addition of CuO not only reduces the surface area but also decreases the Lewis acid sites which are recognized to have a positive effect on the catalytic activity. The apparent activation energy of the hydrolysis reaction amounts to about 25 kJ/mol in 393–473 K while 13 kJ/mol over 473 K. The overall hydrolysis reaction rate on catalysts is mainly determined by external and internal mass-transfer limitations.     

Occurrence of the Bunsen side reaction in the sulfur-iodine thermochemical cycle for hydrogen production

This study aimed to establish a closed-cycle operation technology with high thermal efficiency in the thermochemical sulfur-iodine cycle for large-scale hydrogen production. A series of experimental studies were performed to investigate the occurrence of side reactions in both the H₂SO₄ and HI _x phases from the H₂SO₄/HI/I₂/H₂O quaternary system within a constant temperature range of 323–363 K. The effects of iodine content, water content and reaction temperature on the side reactions were evaluated. The results showed that an increase in the reaction temperature promoted the side reactions. However, they were prevented as the iodine or water content increased. The occurrence of side reactions was faster in kinetics and more intense in the H₂SO₄ phase than in the HI _x phase. The sulfur or hydrogen sulfide formation reaction or the reverse Bunsen reaction was validated under certain conditions.