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。     

基于13X沸石分子筛/MgCl_2的复合吸附剂性能实验研究

复合吸附剂的吸附性能是吸附制冷循环过程中的一个重要参数,基于测试整体成型复合吸附剂吸附性能的需要,本文设计搭建了一种整体成型吸附剂性能测试装置,对复合吸附剂MgCl_2-13X进行了吸附性能测试实验。结果表明:该实验装置中吸附床外侧底部的温度变化速率较接近吸附床内部底部吸附剂的温度变化速率,二者温度变化速率相差0.01~1.9℃/min,整个吸附和脱附过程二者温度的平均值相差约3.24%,能够满足吸附剂性能测试实验的要求。吸附剂性能测试实验及电镜下吸附剂的微观结构表明:浸泡法制备的复合吸附剂的吸附性能与MgCl_2溶液的浓度有关,MgCl_2能够改善13X沸石分子筛的吸附性能,本实验测得当MgCl_2溶液的浓度为15%时所制得复合吸附剂MX3性能最优,其最大吸附量为0.32 g/g,最大吸附速率0.59 g/min,相比单一吸附剂13X沸石分子筛提高了20%。     

非平衡吸附特征的吸附床传热传质特性

建立椰壳活性炭-甲醇吸附式制冷系统吸附床传热传质数学模型,应用该模型进行具有非平衡吸附特性的吸附床传热传质研究,利用数值方法对数学模型进行求解,讨论了吸附床在冷却过程中吸附剂温度、吸附速率、吸附量、制冷系数以及单位质量吸附剂制冷功率与时间的关系,吸附床在加热过程中吸附剂温度、脱附速率及脱附量与时间的关系.研究结果表明:吸附床在整个吸附过程中的吸附速率存在一个峰值0.001 2 ks/s,吸附床在整个脱附过程中的脱附速率存在一个峰值0.001 7ks/s,吸附剂温度变化率在换热阶段趋于平缓,制冷系数值在吸附阶段近似呈线性增长,而单位质量吸附荆制冷功率在吸附阶段存在一个峰值35 kW/kW.     

水合盐热化学储热材料的研究概述

热化学储热材料是通过化学反应过程中化学键的破坏与重组来实现热能的储存与释放.与其他储热材料相比,热化学储热材料具有储热密度高、长周期稳定储热等优势.水合盐热化学储热材料可以高效储存太阳能和工业余热等中低温热源,在热化学储热领域具有很高的关注度.纯水合盐材料(如LiCl、LiBr、CaCl2)液解相对湿度较低,水合(脱水)反应包含固-气水合(脱水)反应、气-液-固三相液解(结晶)、液-气吸收三个过程,这种循环过程可显著提高水合盐的储热密度.若吸水量控制不佳则易引起严重的传质和腐蚀问题.对于液解相对湿度较高、储热密度较高的水合盐,如SrBr2和MgSO4,其传热性能差、孔隙率和渗透率低.将水合盐嵌入多孔基质中形成多孔基质水合盐复合储热材料可进一步强化其传热,并同时解决水合盐的潮解结块问题.近年来,人们对多孔基质水合盐复合储热材料进行了深入研究,获得了多种储热密度高、具有良好循环稳定性的复合储热材料.多孔基质水合盐复合储热材料设计过程中,多孔基质的选择尤为重要.目前研究的热点主要集中于膨胀石墨、沸石、蛭石、硅胶、活性氧化硅等.将LiCl和膨胀石墨(EG)制成的复合材料用于10 kWh的低温热化学吸附储热装置中,系统的储热密度高达3142 kJ/kg;以活性氧化铝(AA)为多孔基质、LiCl为嵌入盐制得了一种新型复合材料(AL),其中AL25(盐含量为14.68％,质量分数)复合材料的结构稳定,储热性能最优,具有最高的储热密度为1041.5 kJ/kg,充热温度为120℃;在不使用多孔基质的条件下,MgCl2·MgSO4二元水合盐在超过50次循环实验后,仍保持良好的性能,说明其具有非常高的循环稳定性.本文基于反应动力学、平衡吸附量和化学反应平衡等理论,从传热和传质性能、循环稳定性和储热密度等方面综述了水合盐热化学储热材料的研究成果,探讨了水合盐热化学储热材料存在的问题,以期为开发高效水合盐热化学储热材料提供参考.     

低温驱动沸石-水吸附式制冷机的性能研究

本文研究的合成沸石-水吸附式制冷机采用FAMZ01沸石作为吸附剂,吸附床选择翅片涂抹式吸附床,通过实验研究该制冷机的制冷功率、制冷性能系数(COP)随热源温度、冷冻水进口温度的变化规律。结果表明,该吸附式制冷机在55℃的热源下就可以稳定输出制冷量,并在驱动热源为65℃左右展现其较佳的性能。     

再吸附制冷系统的性能测试及研究

针对热驱动的制冷方式,建立再吸附制冷试验台。该试验台主要包括4种再吸附制冷系统,每个系统具有高温吸附床与低温吸附床：MnCl2／BaCl2系统、NiCl2／BaCl2系统、NiCl2／NaBr系统以及MnCl2／NaBr系统。在室温环境自然制冷的情况下对比分析这4种工质对的工作性能,并通过对该试验台制冷输出冷水温度参数的记录,估算制冷量及制冷性能系数。由于再吸附系统产生的冷量大部分消耗在系统显热上,其制冷性能系数COP较低。实验结果发现MnCl2／NaBr系统有相对较高的制冷效率,从而为再吸附工质对的选择提供了参考。该简易实验台还可用于本科生教学实验。     

沸石分子筛吸附式制冷 Ⅱ吸附式制冷的循环系统

利用自制的沸石分子筛,在自行设计的吸附式制冷模拟装置上,对吸附剂5A、NaY、CaY、13X及CaX等沸石分子筛和制冷剂水系统进行了制冷效果的测定;讨论了吸附速度、脱附温度对制冷效果的影响;通过吸附等温线的测定,计算了制冷循环系统中水的循环量,并测得分子筛再生时开始脱附的温度Ts值和再生后开始吸附的温度Ts’值。实验结果表明每公斤所研究的分子筛在单级吸附—解吸循环系统中能够产生制冷量为62—100千卡(Tev=0℃,Tcond=Tads=14.5℃,Treg=120℃)。     

循环周期对吸附制冷管性能的影响与分析

设计制作了一种类似于热管、以13X分子筛-水为工质对的吸附制冷单管,吸附制冷单管直径为19 mm,吸附制冷单管由吸附床段和蒸发\冷凝段组成,其中吸附床段长800 mm,蒸发冷凝段长260 mm。吸附制冷系统由吸附制冷单管、管式电炉和数据采集装置组成,利用本装置对影响吸附制冷单管性能的循环周期、吸/脱附时间比进行了一系列实验研究,并利用数值模拟对分析结果进行了理论分析。研究表明:当吸附时间和脱附时间相等时,在不同脱附温度下,循环周期存在一个相应的最佳值,脱附温度越高,相应的最佳循环周期越长;适当增加一个循环周期内吸附时间所占比例可有效提高单元管制冷功率。对于此吸附单元管,在脱附温度为310℃时,吸附时间35 min、脱附时间25 min时,吸附制冷单管制冷功率达到最大值4.97 W,其单位质量吸附剂的制冷功率SCP为57.73W/kg,比吸附时间和脱附时间均为30 min时的制冷功率提高6.65%。     

氯化钙/膨胀硫化石墨复合吸附剂非平衡吸附性能

研究中采用膨胀硫化石墨作为基质,研制了一种新型氯化钙复合吸附剂,研究中测试了氯化钙复合吸附剂的非平衡吸附性能。研究表明：当冷凝温度由25℃变化到35℃,蒸发温度由-10℃变化到15℃时,密度为400kg/m3、质量分数为80%的氯化钙复合吸附剂样品的吸附量变化范围是0.4015kg/kg~0.4585kg/kg,与采用膨胀石墨为基质的复合吸附剂相比,吸附量变化不大。实验中氯化钙/膨胀硫化石墨的吸附/解吸时间约为3300s,与采用普通膨胀石墨相比,循环时间缩短了33%。在冷凝温度为30℃条件下,密度为400kg/m3、质量分数为80%氯化钙复合吸附剂最大SCP(单位质量吸附剂制冷功率)为65.75 W/kg,与采用普通膨胀石墨相比,SCP提高了48%。     

吸附制冷用吸附剂性能测试及实验研究

研究吸附工质对的性能对于吸附式干燥、除湿、制冷具有重要作用,而吸附剂的吸附量、导热系数和吸附材料的性质、温度、压力等许多因素有关,因此用实验来测定就变得十分的有必要。本文以3A作为吸附剂,水作为制冷剂,组成吸附式制冷工质对,通过液位法对工质对的吸附制冷性能进行了研究。结果表明:它的最大吸附量为24.5g,最大吸附率为0.112g/g。本实验吸附床中3A沸石分子筛的量为218.5g,在脱附温度为260℃,吸附环境温度为25℃时,根据已有的对太阳能冷管的改进实验,选用同样材料的太阳能冷管计算时,可得其制冷量为147.864J,制冷系数COP为0.116。     

Thermodynamic study of a combined double-way solid–gas thermochemical sorption refrigeration cycle

A combined double-way thermochemical sorption refrigeration thermodynamic cycle was proposed and tested. Both adsorption refrigeration and resorption refrigeration processes were combined in order to improve the system performance. Two different consolidated composite materials were used as the reactive sorbents and ammonia was used as the refrigerant. Experimental results showed that a system operating with such proposed cycle can have two useful cold productions during one cycle at the expense of only one heat input at high temperature. The average specific cooling power (SCP) during the adsorption refrigeration phase was 301 W kg^?1. Analysis of the experimental data showed that the driving equilibrium drop during the resorption process was much lower than that during the adsorption process, when the cold production temperature was similar. The proposed combined double-way sorption cycle has a larger cooling capacity per unit of heat input and the maximum theoretical coefficient of performance (COP) is 1.24 when MnCl₂ and BaCl₂ are used as the reactive sorbents.     

A combined double-way chemisorption refrigeration cycle based on adsorption and resorption processes

An innovative combined double-way chemisorption refrigeration cycle based on adsorption and resorption processes is presented. Two different reactive salts were used as sorbents and ammonia was utilized as the refrigerant in the proposed cycle. The useful cold was obtained from the evaporation heat of the refrigerant during the adsorption process and from the reaction heat of the low-temperature salt during the resorption process. The proposed combined double-way cycle has a distinct advantage of higher coefficient of performance (COP) in comparison with conventional adsorption cycle or resorption cycle. Experimental verification indicated that the advanced combined double-way cycle is feasible for refrigeration application, and the ideal COP of the basic cycle was about 1.24. Theoretical results showed that the proposed combined double-way cycle could improve COP by 167% and 60% when compared with conventional adsorption cycle and resorption cycle, respectively.     

Experimental study on a combined double-way chemisorption refrigeration system

A combined double-way chemisorption refrigeration system was described and investigated, and the experimental test unit was built, which consists of two adsorption beds: one high-temperature salt bed (HTS bed), which is filled with manganese chloride; and one low-temperature salt bed (LTS bed), which is filled with barium chloride. Moreover, the working performance of double-way chemisorption refrigeration cycle was studied. This cycle uses only one heat input to get two cold outputs, one of which comes from the evaporation heat produced by the refrigerant during the adsorption process, and another of which is from decomposition reaction heat consumed by LTS during the resorption process. The experimental results showed that the coefficient of performance (COP) and specific cooling power (SCP) were 0.703 and 225 W kg⁻¹ respectively at the refrigeration temperature of 15 °C, regeneration temperature of 160 °C and heat sink temperature of 30 °C. Also, the relation between the average global conversion and the COP value were found and analyzed. And the choice of salts and optimum reaction time were discussed either.     

锌基-MOFs对氨吸附制冷性能的分子模拟研究

本文采用巨正则蒙特卡洛(grand canonical Monte Carlo, GCMC)方法,基于UFF(universal force field)和TraPPE(transferable potentials for phase equilibria)力场,对ZIF-8(Zn)吸附NH₃进行了分子模拟研究,并结合分子模拟结果和吸附式制冷热力学循环模型,研究了ZIF-8(Zn)/NH₃工质对的吸附性能和制冷性能。研究表明：在等温条件下,ZIF-8(Zn)对NH₃的吸附量随压力的增大而提高,298 K和398 K下饱和吸附量分别达到0.305 g/g和0.231 g/g;同一温度下的总吸附热也随压力的增大而上升,这主要归因于NH₃分子间相互作用产生吸附热的增加,而ZIF-8(Zn)与NH₃相互作用的吸附热维持在较稳定的状态;NH₃在ZIF-8(Zn)中的吸附密度分布结果表明NH₃在金属位点处被大量吸附,难以通过ZIF-8(Zn)部...     

Mapping of optimum operating condition for LiBr–water refrigeration cycles

In this work, optimum operating condition maps are generated covering wide ranges of refrigeration and sink temperatures for single- and double-effect LiBr–water vapour absorption refrigeration cycle. These optimum condition maps will be useful to choose optimum operating conditions while designing LiBr–water cycle for desired applications. Methodology for generating such maps is discussed in detail, which can also be used for other absorption refrigeration cycles with various working fluids. Three configurations of LiBr–water absorption refrigeration cycles, single effect, double-effect series flow and double-effect parallel flow, are analysed with the most accurate thermodynamic property correlation available in the literature. Sensitivity of cycle performance to various operating variables such as generator, absorber and condenser temperatures is determined. Second law analysis shows that when a higher temperature heat source is available, double-effect cycles are more effective over single effect as they have higher coefficient of performance.     

A novel ejector-absorption combined refrigeration cycle

This paper presents a novel ejector-absorption combined refrigeration cycle. When the temperature of the heat source is high enough, this cycle will work as a double-effect cycle. If the temperature of the heat source is lower than required temperature of heat source used to drive conventional double-effect absorption refrigeration cycle but much higher than required temperature of heat source used to drive conventional single-effect absorption refrigeration cycle, the COP of new cycle will also be higher than that of conventional single-effect absorption refrigeration cycle. Simulation results show that the COP of the cycle is 30% higher than that of the conventional single-effect absorption refrigeration cycle at some working conditions even in the later case.     

以硫化石墨为吸附剂基质的再吸附制冷性能分析

相比于传统的吸附式制冷,再吸附制冷作为一种新型的制冷方式,其结构更加简单,并且其制冷性能系数也比相同条件下的吸附式制冷系统要高,故有较好的应用前景。但受到吸附剂的传热传质性能的限制,难以实现高效的再吸附制冷。本文利用硫化石墨作为吸附剂的基质,对其导热系数以及渗透率进行了测试比较,优选吸附剂。并且针对再吸附制冷系统建立了相关数学模型,分析不同工况条件下吸附剂工质对的性能。对整个再吸附制冷过程进行模拟仿真,从而得到不同工况下的制冷性能。结果表明,采用新型复合吸附剂的再吸附系统,COP最大可达到0.3以上,SCP最大可达到161 W/kg。     

燃料电池汽车余热驱动吸附制冷系统方案研究

使用环保型制冷工质和节能是汽车空调发展的必然趋势，燃料电池汽车余热驱动的吸附式制冷系统正好符合这一趋势。本文通过综合比较，选择活性炭-甲醇工质对作为吸附工质对，采用两床连续回质循环方式，并初步确定了燃料电池汽车余热驱动的吸附式制冷系统方案。     

新型太阳能冷管制冷热力循环分析计算

根据固体吸附制冷原理,利用太阳辐射能作为热源,研究了一种新型太阳能冷管。该新型冷管利用硅胶—水作为制冷工质对,通过理论分析计算可以得出:在平均太阳辐射强度为686.1 W/m2,冷凝温度与蒸发温度分别为40℃、10℃的条件下,该冷管在上海地区典型夏季气候中的制冷量与COP在一个循环周期(24 h)分别为524 kJ和0.414。     

两级双效溴化锂制冷-热泵复合循环

在热电冷联产系统中,溴化锂吸收式制冷机在制冷过程中排放了大量的废热,这些废热品味低,难以直接回收利用。在此提出了两级双效溴化锂制冷-热泵复合循环,该循环具有冷凝温度较高的特点,便于直接回收冷凝排放热。系统以背压汽轮机的背压蒸汽为热源,制冷的同时利用循环所排出的废热加热锅炉补充水至较高温度。以具有相同功效的双效溴冷机与单效溴化锂热泵联合运行作为对比循环,制冷-热泵复合循环系统省去了一台蒸发器与冷凝器,减少了两个换热温差,并且通过热力计算、能量分析和分析表明,该循环的能量利用率与效率均有很大的提高,效率比对比循环提高了45%。