余热制冷用氯化钙_硅胶复合吸附剂的制备及性能研究

为了开发出利用余热进行吸附制冷的高性能吸附剂,采用浸渍法在真空下将氯化钙担载于粗孔硅胶上,制备了硅胶/氯化钙复合吸附剂,测试了复合吸附剂的吸附等温线和吸附速率,测试结果表明:浸渍法得到的复合吸附剂对水具有更大的吸附能力,在20%的湿度下,复合吸附剂在2h的吸附量为15.64 g/100 g吸附剂,是单一硅胶在相同条件下吸附量的8.06倍。用制备的复合吸附剂制作了一台小型吸附制冷机并进行了测试,当热源温度为90℃,冷却水温度为35℃时,在整个循环周期内(15 min),制冷功率为0.705kW,单位质量吸附剂的制冷功率(SCP)为70.51 W/kg,COP为0.25。     

采用复合吸附剂和高效吸附床的吸附制冷机性能测试

利用平行流换热器和自制的硅胶/氯化钙复合吸附剂研制了一台小型吸附式制冷样机,并对样机进行了试验测试。测试结果表明:相对于硅胶吸附制冷样机,复合吸附剂吸附制冷样机的COP和制冷功率都有了明显的提高;在热源温度为90℃,冷却水温度为35℃,冷冻水进口温度为16.5℃、出口温度为14.4℃,吸附10min,脱附5 min的运行工况下,在整个循环周期内(15 min),制冷功率为1.03 kW,SCP为128.3 W/kg,COP为0.29;在吸附周期内(10 min),制冷功率为1.54 kW,SCP为192.4 W/kg,样机的能量密度为10.3 kW/m3,平行流换热器的换热系数为472.3 W/(m2.K)。     

新型复合吸附剂SiO2·xH2O·yCaCl2与常用吸附剂空气取水性能的对比实验研究

提出了一种便携式吸附空气取水器 ,并为其提出了一种新型复合吸附剂SiO2 ·xH2 O·yCaCl2 。介绍了这种吸附剂的配制方法 ,分析了它吸附湿空气中水蒸气的原理。通过实验表明 :在空气温度恒为 2 5℃、相对湿度 4 0 %的条件下 ,这种复合吸附剂的平衡吸附量we(H2 O干吸附剂 )可达 0 .4 ,是粗孔球形硅胶的 5 .7倍、细孔球形硅胶的 2 .1倍、人工沸石 13X的 1.9倍、椰壳活性炭的 6 .8倍。通过对比分析它们的吸附速度曲线表明 :这种复合吸附剂的吸附特点是吸附量大、吸附速度快。分析结果表明 :采用这种复合吸附剂的空气取水器即使在我国西北地区 7月份的干燥气候条件下也能够有很高的出水量。而且这种复合吸附剂的解吸温度低 (6 0～ 80℃ ) ,可用太阳能加热解吸 ,是一种理想的取水用吸附剂     

基于湿差法太阳能空气取水用吸附剂吸附性能测量的实验研究

吸附剂的开式吸附性能是指其在大气中对水蒸气的吸附能力。为了研究细孔硅胶和金属有机骨架MIL-101的开式吸附性能,文章基于湿差法等测量了这两种吸附剂的吸附量、吸附速率等参数。实验结果表明:对于质量为50 g的细孔硅胶,利用湿差法和重量法测得其平衡吸附量分别为10.00 g和10.13 g,二者之间的差值(0.13 g)为该吸附剂对干空气的吸附量;当环境温度为10～25℃时,MIL-101和细孔硅胶的吸附速率与环境温度均呈正相关,当环境温度为25～35℃时,MIL-101和细孔硅胶的吸附速率与环境温度均呈负相关;当环境温度为25℃时,MIL-101的平衡吸附量为0.334 kg/kg,相对于细孔硅胶,增加了25.6%;MIL-101的最大吸附速率为456 g/(kg·h),为细孔硅胶最大吸附速率的5.6倍。     

炭化活化温度对活性炭-CaCl2复合吸附剂性能的影响

为研究并开发高性能的吸附剂,本文以CaCl₂和杉木木屑为原料,采用炭化活化造孔的方法制备复合吸附剂,考察了炭化活化温度对复合吸附剂性能的影响,炭化活化温度分别选择400℃、500℃、600℃和700℃。扫描电镜照片和元素分布图表明,复合吸附剂具有发达的孔隙结构而且CaCl₂分布均匀。NH₃吸附性能实验表明,吸附剂4 h的NH₃吸附量随炭化活化温度的升高而增加。而对于吸附制冷而言,500℃炭化活化温度下制备的复合吸附剂具有最好的性能,其30 min的吸附量达到0.488 g/g。     

SAPO-34与ZSM-5沸石的动态吸附特性

采用称重法对颗粒状的SAPO-34和条状的ZSM-5在恒温恒湿箱中对水的吸附特性进行实验研究。将2种沸石的动态吸附特性曲线和吸附等温线进行拟合。实验结果表明,在同一温度下两种沸石的吸附率均随相对湿度的增加而增大,但是SAPO-34在空气相对湿度70%~80%范围内变化较敏感,而ZSM-5在相对湿度60%~70%范围内变化较敏感。它们的吸附速度是时间的减函数,但是随温度和相对湿度的增加而增大。与ZSM-5相比,SAPO-34作为吸附剂可以缩短循环吸附时间。另外比较2种沸石的吸附等温线发现,SAPO-34的冷凝温度较高,对环境的要求较低,因此更适于夏季空调、制冷系统。     

硅胶及硅胶-氯化锂复合材料蓄能特性实验与分析

通过将硅胶浸泡在氯化锂溶液中制成硅胶-氯化锂复合材料,并对硅胶及复合吸附材料的平衡吸附量进行测试,利用材料的平衡吸附模型分析材料在不同再生温度和再生湿度条件下的再生特性以及材料的最大蓄能特性,结果表明:复合材料的平衡吸水量约为硅胶的2.3倍,且其最大蓄能密度可以达到1723 k J/(kg吸附剂),约为硅胶的1.65倍。材料在不同的处理空气入口温度与湿度条件下,分析材料释放热量的特点以及在利用材料进行除湿供暖时,吸湿量每增加2 g/(kg干空气)时,出口空气温度平均升高5℃。     

太阳能吸附制冷用复合吸附剂制备及其吸附机理探讨

以乙醇为吸附质，选取13X分子筛、凹凸楱土和氯化锶等为主要吸附材料．通过混合法制备了一系列有着优良吸附能的复合吸附剂。测定了乙醇在主要吸附材料和自制复合吸附剂上的吸附量，用TG-DTA法对主要吸附材料的热稳定性和自制吸附剂DTA脱附乙醇峰端温度进仃了分析.对吸附剂原料复合比例和扩孔剂种类等制备条件进行了实验研究。结果表明：自制复合吸附剂比单一吸附材料对乙醇确着更大的吸附能力；DTA分析的脱乙醇峰端温度明显低于单一吸附材料；加入扩孔剂E1或E2，可增加自制复合吸附剂孔容和孔径，改善其吸附性能；自制复合吸附剂对乙醇的吸附量显著高于活性炭。其中，M4-0003和M1-0001复合吸附剂对乙醇的平衡吸附量约为活性炭的2．5～4倍；M1-0001—乙醇工质对的吸附制冷量是活性炭—乙醇的2～6倍。对吸附剂复合的机理初步探讨表明：增加复合吸附剂弱吸附中心数，可降低其脱附温度。     

吸附式太阳能水管空气取水的特性研究

基于开式空气吸附基本原理,在直径50 mm的不锈钢管内填充硅胶-氯化钙复合吸附剂,制备了太阳能水管;利用吸附床内的复合吸附剂吸附空气中的水分,并利用太阳能加热吸附床使之脱附,通过冷凝器冷凝成液态水。理论计算显示,在环境湿度为40%时,单只水管一昼夜可获得水量为700 ml左右。将多支水管组合起来,有望在沙漠或荒岛上建立小型饮水站,也可以在干旱地区发展滴灌式大棚种植业。     

矿物基硫酸镁热化学吸附材料的制备与性能评价北大核心CSCD

本工作以凹凸棒土、硅藻土和膨胀蛭石三种矿物材料为载体,采用等体积浸渍法制备了矿物基硫酸镁热化学吸附材料。通过X射线衍射(XRD)、扫描电子显微镜(SEM)和比表面积与孔结构测试表征了矿物载体与矿物基硫酸镁复合材料的微观结构,并基于热失重(TG)、动态水蒸气吸附(DVS)和差示扫描量热(DSC)测试对复合材料的吸附/脱附动力学性能和储热性能进行了评价。研究发现,硅藻土的圆盘形微观结构有利于复合材料获得更快的脱附/吸附反应速率和更高的储热能力,其脱附反应热可达557.1 kJ/kg。此外,环境温度25℃、相对湿度85%为矿物基硫酸镁复合材料的最佳吸附反应条件。     

Effect of internal cooling/heating coil on adsorption/regeneration of solid desiccant tray for controlling air humidity

Thermal performances of solid desiccant tray having internal cooling/heating coil for air humidity adsorption and desiccant regeneration are investigated. Three units of desiccant tray each of 48 cm × 48 cm cross‐sectional area and 2.5 cm thickness filled with silica gel are tested in a wind tunnel. For adsorption process, an air stream is flowing through the desiccant trays and the air humidity is captured by the silica gel. Approximately 10–40% of air humidity could be adsorbed more in case of the internal cooling. Besides, the outlet air temperature increases only slightly. In regeneration process, a hot air stream is used to repel the moisture in the silica gel. With the internal heating, the regeneration time is shorter compared with that without internal water heating. In addition, a correlation for calculating the adsorption/regeneration performance of the silica gel trays is developed and the results from the model agree well with the experimental data. Copyright © 2008 John Wiley & Sons, Ltd.     

Experimental and theoretical performance analysis of the silica gel,LiCl with water,methanol multifunction adsorption system

The world is facing the ever‐worsening issues of global warming. The results show that the physical‐/chemical‐adsorbent water can improve the adsorption capacity of 1.22 kg/kg. If water is used as the adsorbate, the adsorbent has a serious issue of corrosion. So, methanol is utilized. However, methanol just can be heated by low‐temperature heat, because methanol will be broken down in above 140°C adsorption system. The multifunction adsorption system can produce one cold effect output and two power generation outputs. The results show that the silica gel/LiCl‐methanol multifunction adsorption system has a higher cooling exergy efficiency of 0.25 and a higher total system exergy efficiency of 0.87 compared with that of the silica gel‐water system.     

Experimental investigation of the silica gel–water adsorption isotherm characteristics

In designing adsorption chillers that employs silica gel–water as adsorbent-adsorbate pair, the overriding objective is to exploit low temperature waste-heat sources from industry. This paper describes an experimental approach for the determination of thermodynamic characteristics of silica gel–water working pair that is essential for the sizing of adsorption chillers. The experiments incorporated the moisture balance technique, a control-volume-variable-pressure (CVVP) apparatus and three types of silica gel have been investigated, namely the Fuji Davison Type A, Type 3A and Type RD. As evidenced by the experimental results, the Henry-type equation is found to be suitable for describing the isotherm characteristics of silica gel–water working pair at the conditions of adsorption chiller. The regeneration of adsorbent depends on the correct allocation of temperature as well as the amount of regeneration time. From the experiments, the isotherm characteristics of silica gel–water in the low- to high-pressure regimes and hence, its isosteric heat of adsorption will be determined. Key parameters for optimizing the amount of heat recovery such as the cycle and switching time of chiller can also be implied from the measured results.     

The heat and mass transfer performance of facile synthesized silica gel/carbon-fiber based consolidated composite adsorbents developed by freeze-drying method

A series of experimental investigations had been performed to analyze the heat and mass transfer performance for two novel types of silica-based consolidated composite adsorbents developed by the freeze-drying method. The first type of adsorbent is silica gel consolidated with carboxymethyl cellulose (CMC) (SC), while the other is silica gel consolidated with CMC and carbon fiber powder (SCC). Results indicate that the thermal conductivity of consolidated composite adsorbents increases with the mass proportion of carbon fiber powder, while it decreases with the increasing moisture content in the preparation process of the adsorbents. When the mass ratio of silica gel, CMC, and carbon fiber powder is 4:1:4, the highest thermal conductivity of consolidated composite adsorbent obtained from experiments reaches 1.66 W m^?1 K^?1, which is 13.4 times greater than that of pure silica gel. Furthermore, the results of macroporous properties analysis of typical samples including SC20 and SCC20 (where the 20 means that the undried samples have a water content of 20% by mass during the preparation process) show that heat transfer additives effectively improve the macroporous porosity and permeability of the consolidated composite adsorbents. The study on adsorption dynamic performance indicates that the freeze-drying method helps to improve the adsorption performance including adsorption rate and equilibrium water uptake. The experimental results also show that the mass transfer coefficient K of the two typical samples are approximately stable at 5 × 10^?3 s^?1 when the adsorption temperature is ranged between 30 and 40°C, which are almost twice the corresponding values of the samples developed by heating–drying method. Therefore, the proposed approach which is the consolidation with heat transfer additives combined with freeze-drying method is effective for simultaneously enhancing the heat and mass transfer performance of the silica gel adsorbents.     

Comparative study on adsorbent characteristics for adsorption thermal energy storage system

The adsorption performance of the thermal energy storage (TES) system changes depending on the material properties of the adsorbent itself, but the change of the hardware structure can also substantially change the adsorption characteristics. In this study, a laboratory‐scale adsorption‐based TES system was constructed, and the adsorption performance of three adsorbents was evaluated in the same system to compare the adsorption performance between adsorbents. The adsorption characteristics of silica gel, zeolite 13X, and 4A, which are the most preferred adsorbents in the physical adsorption‐based TES system, were selected for evaluation. Experiments with each adsorbent were performed, including heat recovery to evaluate the heat transfer effect and the amount of heat recoverable in the actual TES system. Experimental results have identified several key characteristics of the adsorption and performance of each adsorbent in the TES system, as well as operating parameters that determine the influence of adsorption performance on the TES system. The actual energy storage density of the adsorbent is affected not only by the enthalpy of adsorption of the material itself but also by other factors. These factors include the difference in thermal conductivity that causes a difference in temperature distribution and the magnitude of mass transfer resistance due to the shape of the adsorbent particle and the actual TES system reactor structure. If the reaction heat generated during the adsorption reaction cannot be effectively released, the adsorption performance is significantly lowered due to the increased temperature of the reactor inside. This phenomenon was commonly observed in adsorbents examined in the present study. The uptake amount, X [g/g], was increased by allowing the inside of the reactor to be maintained at a lower temperature through heat recovery. In case of silica gel, the temperature rise during adsorption reaction is not high due to the difference of isotherm characteristics compared with zeolites, but it is possible to absorb more amount of adsorbate and to recover heat for a longer time. The energy storage density is affected by the temperature increase effect and the uptake amount of adsorbate during the adsorption reaction. The experimental results show that the energy storage density of zeolite 13X is 15% and 28.7% higher than that of silica gel and 4A, respectively, and the temperature rise due to heat generation during adsorption reaction is also high, which is advantageous in adsorption TES system performance.     

Performance study of new adsorbent for solid desiccant cooling

The properties of 13x, silica gel, DH-5 and DH-7 adsorbents proposed by authors in solid desiccant cooling system were investigated. The adsorption isotherms of adsorbents were obtained. Cooling capacity as functions of time had been determined in the experimental device, which accomplished the behavior of adsorbent desiccant cooling. The performance parameters such as adsorption capacity, air humidity, regeneration temperature and cooling capacity were discussed. The results show: (1) the properties of DH-5 and DH-7 adsorbents on desiccant cooling are superior to those of commonly used desiccant (i.e., silica gel and 13x molecular sieve); (2) the maximum adsorption capacity of water on DH-5 and DH-7 reaches 0.72 and 0.73 kg/kg, respectively; (3) the desiccant cooling capacity of DH-5 and DH-7 are 2.2 and 1.3 times that of silica gel and 13x, respectively, after 100 °C regeneration; (4) the cooling capacity per mass unit of DH-5 is 1.9 times larger than that of 13x; (5) DH-5 and DH-7 are suitable for the desiccant cooling cycle, which is operated by low-temperature or low-grade waste heat.     

Adsorption cooling cycles for alternative adsorbent/adsorbate pairs working at partial vacuum and pressurized conditions

This article presents the performance analysis of both ideal single-stage and single-effect double-lift adsorption cooling cycles working at partially evacuated and pressurized conditions. Six specimens of adsorbents and refrigerant pairs, i.e., ACF (A-15)/ethanol, ACF (A-20)/ethanol, silica gel/water, Chemviron/R134a, Fluka/R134a and MaxsorbII/R134a have been investigated. The relationships between equilibrium pressures, adsorbent temperatures and equilibrium adsorption concentrations (Dühring diagram) are presented. Parametric analyses have been carried out with various regeneration (desorption) and evaporation temperatures. Theoretical analysis for adsorption cycles working in single-stage mode shows that ACF (A-20)/ethanol can achieve a specific cooling effect (SCE) of 344 kJ/kg_ads, which is followed by the silica gel/water pair with 217 kJ/kg_ads at a regeneration temperature of 85 °C. On the other hand, when the regeneration temperature is below 70 °C, single-effect double-lift cycle has a significant advantage over single-stage cycle, at which the SCE is higher due to the reduction in adsorption bed pressure in single-effect double-lift cycle.     

Investigation on water vapor adsorption performance of LiCl@MIL-100(Fe) composite adsorbent for adsorption heat pumps

MIL-100(Fe) with good hydrothermal stability and high hydrophilicity is considered to be a potential adsorbent for adsorption heat pumps (AHPs). However, its water vapor adsorption performance at low relative humidity needs to be improved. In this study, composite adsorbent LiCl@MIL-100(Fe) was synthesized by impregnating LiCl aqueous solution in MIL-100(Fe). The effects of the LiCl loading in the composite on the crystal structure, morphology, composition, pore structure as well as the vapor adsorption/desorption performance of the composites were carefully studied. The results showed that on the premise of ensuring no leakage, the LiCl loading in the composite was up to 32.9 wt%. At 20% relative humidity (RH), the saturated adsorption ratio of the composite (0.260 g/g) was higher than that of original MIL-100(Fe) (0.054 g/g). Meanwhile, the water adsorption rate of the new composite adsorbent was faster than pristine MIL-100(Fe). Moreover, after 50 cycles of vapor adsorption/desorption, the composite adsorbent showed a satisfactory stability. All these indicate that the new LiCl@MIL-100(Fe) composite adsorbent will be a prospective candidate for high-efficiency AHPs.