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小型稻谷干燥机——风运动提升部分的设计,小型,稻谷,干燥机,运动,提升,部分,设计
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科技论文及翻译Experiment research on grain drying process in the heat pump assisted fluidized bedsJing Yang，Li Wang，FiXiang，Lige Tong，andHua Su MechanicEngineering School，University of Science and Technology Beijing，Beijing 100083，ChinaAbstract：A heat pump assisted fluidized bed grain drying experimental system was developedBased on this systema serial of experiments was performed under four kinds of air cycle conditionsAccording to the experimental analysis，an appropriate drying mediumair cycle for the heat pump assisted fluidized bed drying equipment was decidedwhich is difierent from the commonly usedheat pump assisted drying systemThe experimental results concerning the drying operation perform ance of the new system show that the averaged coefi cient of perform ance fCOP1 can reach more than 25The economical evaluation was perform ed and the power consumption for removing a kilogram water from grains was about 0485 kWhkg(H，0)，which shows its reasonable commercialefi ciency and great application potentiality in future markeKey words：heat pump，fluidized bed，grain，drying，air recycle1 IntroductionNowadays there 1s an urgent need for the development of high capacity and high quality grain drying equipment in the agriculture of China1As the society and agriculture develop quickly，it is of important practical value to develop the efi cient，energy saving， nonpollution and even movable drying equipment to match the mechanization harvestry 2Traditional methods of drying involve the direct combustion of fossil fuel together with controlled ventilationSuch methods are obviously ineficient，with efficiencies never exceeding 20 ，not to mention the fact that expensive primary energy is depleted only to produce low grade heat3The traditional drying methods have been prevailing domestically up to now,not only for grain drying，but also for other matedals such as wood，cement，ceramics and medicine etcAs the power supply structure improved greatly by the hydropower and nuclear power development policy of the government of China，the research on the heat pump assisted drying system is of special meanings，due to the fact that a portion of power usually can supply more than 2 portions of heat energy for drying by using a heat pumpRecently there are quite a few scholars48findin their interests in heat pump assisted drying area and the great potentiality in future for heat pump applications in drying areaHowever the researches9，1 0mostly concentrate on the low temperature heat pump with the hot medium temperature lower than 55。CThere was still a blank in the high temperature heat pump assisted drying system with temperatures above 70。C and especially for the system with grain drying and heat pump working together,which is the great motivation of the present paperBesides the gassolid fluidized beds have obtained widely applications in drying area with so obvious advantages such as high gassolid contact surface，high heat and mass transferrates，easy to be mechanically operated，usually with great continuous production capability and high quality of drying due to its uniform temperature field11，121This paper combined the both advantages of heat pump and fluidized bed to develop a new type of graindrying experimental systemBased on this system，aserial of experiments was perform ed under different conditionsAccording to the experimental analysis，an appropriate drying mediumair cycle for the new type heat pump assisted fluidized bed drying equipment was decidedwhich is different from the traditional heat pump assisted drying systemTh e research results also show the optimistic future and the potential market competition ability of this new equipment2 Experiment In a drying system with a heat pump and a fluidized bed togetherthere are three material flows：the grain flow，the refrigerant flow and the dry ing mediumAir flowThis air flow relates the grain flow to be dried and the refrigerant flow of the heat pump together and become the medium transferring the moisture and heat between the both，in which the flow ratetemperaturevelocitv and humidity of the air influence the working condition of the heat pump，whereas the working condition of the heat pump also afects the temperature and humi dity of the air and further influences the drying processHere the air circulation jn the systemis vital not only to the working performance of the heat pump and the dry ing process but also to the final structure of the whole equipmentHence the experimental system was designed as shown in figure 1which includes mainly four parts：fluidized bed drying room，heat pump，tube connection and several valvesThis system can realize four types of air circulation by adjusting difierent valvesType one：close valves 1，2，4，5 and open valves 3，6，7，in which the air discharged from the fluidized bed flows only through the evaporator of the heat pump and then the condenser where it is heated and finally into the fluidized bedperforming a close circuit circulationType two：close valves 2，3，6 and open valves 1，4，5，7，in which the air discharged from the fluidized bed flows directly through the condenser and then into the fluidized bedperformi ng a close circulation，and the air from circumstance flows through the evaporator of the heat pumpType 3：close valves 1，3，5 and open valves 2，4，6，7，in which the air discharged from the fluidized bed flows completely through the evaporator and then into the ambientwhereas the ambient air is absorbed through the condenser by the ventilator and then flows into the fluidized bedperforming an open circulationType 4：open all the valves and adjusting their turndown ratioin which the air discharged from the fluidized bed splits into two parts，one mixing with some ambient air flows into the evaporator and then into the ambient，the other mi xing with the ambient air flows into the condenser and then into the fluidized bed，performing an half close and half open air circulation3 Parameter measurements and principlesIn this experiment，the parameters need to be measured are the temperatures at the inlet and the outlet of the fluidized bed and the evaporator and the condenser,the flow quantities of the air through the evaporator，the condenser and the fluidized bed respectively，the high and the low pressures of the refrigerantAll the temperature measurements adopted digital temperature sensors which were calibrated by the liquid in the glass therm ometer from 0 to l 00。CThe hot spherical wind velocity meter was used to measure the flow velocity and then to get the flow quantityThe power of the compressor was calculated based on its phase current measured by a multimeterThe refrigerant pressures were measured by elastic tube manometersThe performance parameters of the system can be calculated based on these measured parameters by following formulaeThe air flow quantity：v=(u/N) A3600,m3/h；The refrigerating output from the evaporator：Qe=VcairC（toe-tie）/3600,KW ；The heating output from the condenser：Qe=VcairC（toe-tie）/3600,KW；The compressor power：P=3IpVp=(I1+I2+I3)220/1000,KW；The coeficient of the performance(COP)of theheat pump：COP=QC/PThe flow rate of refrigerant：X=cP/W,kg/s The theoretical refrigerating output from the evaporator：LQe=Xqe,KW；The theoretical heating output from the condenserLQc=xqc, KW；The theoretical coefi cient of the performance ofthe heat pump：LCOP= LQc/pHere the theoretical cycle refers to the ideal thermodynamic cycle corresponding to the high and low pressures measured in the experiment4 Experimental results and analysis41 Efects of air circulation typeIn order to get the effect from different air circulations on the drying process，we conducted four types of air circulation experimentskeeping all the other conditions the same，such as the air flow quantity and the inlet temperatures etcand found that the temperature at the inlet of the fluidized bed is the highest in type 2，that in type l is the lowest and that in type 3 is slightly higher than that in type l，that in type 4 is between that in types 2 and 3This is because in type 2，the air circulates only through the condenser and the heat wasted is comparatively small resulting in the high temperature at the outlet of the condenserThe humidity of the air at the inlet of the fluidized bed was also higher，since the air discharged from the fluidized bed did not remove its moistureHowever,in fact the connection tube was not closely sealed，therefore there was some fresh air from ambient flowed into the condenserThat is like such a circulation：close valves 36 and open all the other valvesin which the air discharged from the fluidized bed，mi xing with the ambient air flowed through the condenser and then into the fluidized bed，meanwhile some air from the fluidized bed flowed into the ambient through the interspacebetween the fluidized bed and its blastcapIn this experiment system1 0一20 fresh air was estimated mi xing into the flow in air circulation between the condenser and the fluidized bedHence type 2 with a certain fresh air ratio can be chosen as the best air circulation used in the following experiments42 Efects of air flow quantity through the evaporator Two experiments were performedIn one experiment1 00 k2 grains were put into the fluidized bed with a moisture of about 25 fits denominator contains no water)，and then the system was started and the airflow through the evaporator was kept relatively low at about 500 m hThe performances of the heat pump are shown in figures 2-4In the other experiment，the system was started firstly and the airflow through the evaporator was kept high at about 2500 m3h after the temperature at the outlet of the condenser reached about 70。C 100 kg grains with a moisture of 27 were put into the fluidized bedThe heat pump performances are shown in figures 5-7The air flow through the condenser is about the sameof 1 650 m3h for both experimentsFigure 2 Pressure variation of the refrigerant in the dry ing process at v=soo mahFigure 3 Performance of the heat pump in the drying process at v=5oo mahFigure 4 COPoftheheatpump atv=5ooIll3，l1Figure 5 Pressure variation of the refrigerant in the drying process at v=25oo mahIn figures 3，4 and 6，7，the theoretical results are all calculated from the ideal refrigeration circulation respectively coresponding to the high and low pres。sures of the refrigerant in figures 2 and 5The comparison between figures 3 and 6 shows that the heat output from the condenser greatly increases by in creasing the air flow through the evaporator and the COP is much closer to the idea1 value in figure 7 than that in figure 4Thus the airflow quantity through the evaporator is very important to the performance of the heat pumpIn fact，the growing of the air flow quantity through the evaporator greatly enhances the heat transfer rate between the air and the surface of the evaporator resulting the worldng medium in it absorb more heat at the same temperature differenceTh e theoretical analysis also show that as the airflow increases further,the heat absorbed by the evaporator will reach its peak and then level offFigure 6 Performance of the heat pump in the drying process atv,=25oom3hFigure 7 COP of the heat pump at v=2soo m3h43 Drying process of the heat pump assisted fluidized bed grain dryerFigure 8 shows the temperature variations at the inlet and the outlet of the fluidized bed during the drying process under the same condition to the experiment at Ve=2500 m hIt shows that both the temperatures rise gradually with timeAt such temperature variation，the wheat drying process is shown in figure 9，which displays the wet moisture(the fraction of the water quantity contained in the grains to its total quantity)and dry moisture(the fraction of the water quantity contained in the grains to its absolute dry quantity)variations of wheat wifh drying timeW e can see that it takes about 60 min for the wheat to drv from a wet moisture of 21-3 to 13 Figure 8 Temperature variations at the inlet and outlet of the fluidized bed during the drying process at v,=2500m3hFigure 9 W heat moisture variations during the dry ingprocess at v,=2500 m3h44 Economical evaluationThe factors afecting the commercial eficiency of the drying system are the drying time，the COP and power consumption of the heat pumpHowever the drying time mainly depends on the air temperature at the inlet of the fluidized bedIn order to analyze the com ercial efficiency of the systemwe assume that the wheat is continuously dried bv the system as it was done by the most dryers in industry，the temperature at the inlet of the fluidized bed is about 70。C which wasobtained in the experimentIn such assumptions，we can obtain that the drying time needed for wheat to dry from its wet moisture of 20 t0 13 is about 35min，which is deduced from another experiment2and will not be presented hereAccording to the known parameters mentioned above and the heatpump power consumption in figure 6，including the blower power consumption in the system，the averaged power consumption of the system is gotten (about 55 kW)during the drying processConsidering the capability of the fluidized bed is about 100 kg，we can conclude its totally power consumption per unit grain output is about 00321 kW hkg or that per unitwater removed from the grain is 0458 kW hkg(H20)5 Conclusions(1)Th e appropriate air cycle for drying grain is that the air discharged from the fluidized bed directly flows into the condenser of the heat pump with 10 一20 flesh air where it is heated and then flows into the fluidized bed to form a circulation(2)The airflow through the evaporator is very important to the perform ance of the heat pumpThe higher the flow quantity，the beaer the perform ance ofthe heat pump(3)Th e economical evaluation shows that if the system working at continuous state，its power consumption for removing a kilogram water from the grains is about 0485 kWhkg(H2O)and shows great potentiality in the future marketNomenclatureV,Ve,Vc:Th e flow quantities for the fluidized bed，the evaporator and the condenser,respectively；u:The air velocity at the measured pointms；N:Th e number of the measured points；A：Th e tube across area，m ；Qe,Qc:Th e refrigerating and heating outputs of the heat pump，kW ；rair:Th e air density，kgm ；C:Th e air specific heat capacity，kJ(kg。c)；toe,tie:Th e temperatures at the inlet and the outlet of the evaporator，。C：toc,tic:Th e temperatures at the inlet and the outlet of the condenser,。C：Ip:Th e averaged phase current of the compressor,A;Vp:Th e phase voltage，V；X：Th e mass flow rate of refrigerantkgs；c：Th e compressor efficiency，about 09 here；W：Th e theoretical compressor work per unit masskJkg；LQe,LQc: Th e theoretical refrigerating and heating output of the heat pump，kW ；qe,qc:Th e refrigerating and heating outputs from theoretical cycle per unit mass refrigerant，kJkg；COP,LCOP:Th e practical and theoretical coefficients of the perform ance of the heat pumpReferences1XHZhu and WCGuo，The situation and development of the grain drying equipment in our countryJI AgricFood Mach(in Chinese)，No4，1998，P22JYang and LWang，Heat Pump Assisted Fluidized Bed Grain Drying Technology Research (in Chinese) R，Technical Report Submitted to Educational Department of China (00020)，University of Science and Technology Beijing，20023 Manuel SV Almeida，CMarcio，Gouveia，Suzana RZdebsky,an d Jose Alberto RParise，Performan ce an alysis of a heat pump assisted drying system J，Int Energy Res，14(1990)，p3974RKLei and JMBunn，Evaluation of a solar-driven absorption heat pump J，TransASAE，37(1994)，No4，p13095YZhang，QsLiu，and YCLi，Development and application of heatpump technologyJI Energy Eng(in Chinese)，2001，No4，p326GC Gao，JF Wang，and YE Feng，Further studying on the perform ance of heat pump drying unitsJ，Food Sci(in Chinese)，16(1995)，No5，P597XDLi and JMa，Brief introduction to hot pump drying technologyJ，ChemEngDes(in Chinese)，7(1 997)，No6，p408KMYu and QWang，Development and its application foreground of heat pump drying technologyJ，Energy Techno1(in Chinese)，21(2000)，No1，p_369BHWang and XZWang，Heat pump drying unitsJ，ChemWorld(in Chinese)，38(1997)，No7，p343l0Y Ma，JHZhang，and YI Ma，Th e optimal analysis of the drying heat pump system J，Acta EnergySoL Sin(in Chinese)，2 l(2000)，No2，p208llXLHuai，LWang，and XZNi，Heat and mass transfer during granular materials dryingJ， UnivSciTechno1Beijing(in Chinese)，20(1998)，No5，p484l2XLHuai，LWang，and ZY Qu，Mathematical model for the drying process of granular materials in a fluidized bedJI UnivSciTechno1Beijing，7(2000)，No4，p296关于用带有热泵辅助流化床在谷粒烘干过程中的实验研究Jing Yang，Li Wang，FiXiang，Lige Tong，and Hua Su摘要：一种热泵辅助流动床谷物干燥实验系统已经开发。基于这系统，在四种不同的空气周期条件下进行了一系列的实验。根据实验分析，为热泵辅助流动床烘干设备制定了一个适当的干燥空气介质循环，它完全不同于普通使用的带有烘干系统的热泵。关于新系统的烘干操作系统性能的实验结果表明：平均性能系数超过2.5。进行经济评估，从谷粒中去除一千克水的消耗能量大约是0.485kw.h/kg，它显示合理的经济效益和在在未来的市场上有着巨大应用潜力。关键字：热泵，流化床，谷物，烘干，空气循环1.引言现在，在中国农业里急需发展高容量和高质量的谷粒烘干设备1.随着社会和农业快速地发展，为了匹配机械化收割，提高效率、节能、不污染和甚至可移动的烘干设备有着重要的实际价值2。传统的烘干方法涉及到连同控制空气流通的直接石化燃气的消耗。这种方法的效率明显不高，效率从来不超过20%，更不用说：昂贵的基本能量大大减少，它仅仅来生产低阶段的热量3。到目前为止，传统的烘干方法在国内很流行，不仅为谷粒烘干而且为其它材料例如木材、水泥、陶瓷和药等等。因为中国政府氢能和核能的发展政策大大地提高了电源结构，关于带有热系统的热泵研究具有特殊的意义，由于一部分动力通常能提供大于2%由热泵烘干的热能量。近来相当多的学者4-8对促进干旱地区的热泵有兴趣并且发现：在干旱地区热泵在未来具有很大的应用潜力。然而，研究者9,10大部分关注低于55适中的温度的低温热泵。对带有温度超过70烘干系统的热泵仍然是一片空白，尤其是带有谷物烘干和热泵一起工作的系统，它对目前的论文具有很大的动力。除此之外，由于它具有明显地优势例如数量大地气固接触面、高的热量、质量转移率、容易机械操作、由于它有一致的温度通常有着连续产量能力和高的烘干质量，气固流化床在干旱地区获得广泛地应用11，12.论文结合热泵和流化床两者优势发展了一种新的烘干实验系统。基于这种系统，在不同的条件下执行了一系列的实验。根据实验分析，执行了为带有流化床的烘干设备的一种适中的烘干的中等空气周期，它完全不同于带有烘干系统的传统热泵。研究结果也表明：未来很乐观并且这种新设备具有市场竞争潜力。2实验在有热泵和流化床的烘干系统里，有三种材料流动：谷物流动，制冷流动，烘干适中空气流动。空气流动把谷物流动和热泵的制冷流动联系在一起并且变成两者之间转移湿度和热度的工具，流速、温度和空气的速度和湿度影响热泵的工作条件，然而热泵的工作条件也影响空气的速度和湿度并且进一步影响烘干过程。在这一点上系统的空气流通是至关重要的，不仅对热泵的工作性能和烘干有影响而且对整个设备最终结构有影响。因此按照图一设计了实验系统，它主要包括了四部分：流化床烘干室、热泵、管联接和几个阀门。图一：带有热泵辅助流化床谷物烘干实验系统的电路原理图这系统通过调整不同的阀门能实现四种类型的空气流通。类型一：关闭阀门1，2，4，5同时打开阀门3，6，7，从流化床释放的空气仅仅通过热泵的蒸发器然后通过它被加热的冷凝器最终流入流化床，它叫闭合的电路循环。类型二：关闭阀门2，3，6同时打开阀门1，4，5，7，从流化床释放的空气直接通过蒸发器然后流向流化床。它叫闭合循环。类型三：关闭1，3，5同时打开2，4，6，7，从流化床释放的空气完全通过蒸发器然后流进周围的空气，然而通过通风设备周围空气被冷凝器吸收然后流入流化床。它叫开放循环。类型四：打开所有的阀门并且调整降低的比率，从流化床释放的空气分成两部分，混合着周围空气的一部分流入蒸发器然后流入周围空气；混合周围空气的另一部分流入冷凝器然后流入流化床，它叫半闭半开的空气循环。3参数测量和公式 在这个实验中，必须测量的参数：流化床、蒸发器和冷凝器的出口和进口的温度，通过蒸发器、冷凝器和流化床各自的流动空气的数量，制冷剂的高压和低压。所有温度测量采纳数字温度传感器，它是从0到100通过液体用玻璃温度计来校准的。热的球形风速仪表被用来测量流速然后得到流数量。基于外用表测量的阶段气流来测量压气机的动力。用弹性管压力计测量制冷压力。通过下列公式这些测量参数可以计算系统的性能参数。空气流数： v=(u/N) A3600,m3/h来自蒸发器的制冷输出功率： Qe=VcairC（toe-tie）/3600,KW来自冷凝器的热输出功率： Qc= VcairC（toc-tic）/3600,KW压缩机功率：P=3IpVp=(I1+I2+I3)220/1000,KW热泵的性能指数：COP=QC/P;制冷剂的流量：X=cP/W,kg/s来自蒸发器的理论制冷输出功率：LQe=Xqe,KW来自冷凝器的理论热输出功率：LQc=xqc, KW热泵的理论性能指数：LCOP= LQc/p;在此，理论周期指的是理想的热力学周期，它相应于在试验中测量的高压和低压。4.实验结果和分析4.1空气流通类型的效应为了获得从在干燥过程中不同空气循环的效应，我们进行了四种类型的空气流通实验.保持所有其他条件相同，如空气流动量和入口温度等。并发现，型号2在流化床入口的温度是最高的，型号1中是最低的，而且，型号3略高于在型号1，型号4在型号2和型号3之间。这是因为， 在型号2中空气流通只能通过冷凝器并且余热比较少地造成在冷凝器出口处的高温。空气相对湿度在流化床入口也较高，因为空气从流化床排出没有去掉其水分。然而事实上，连接管并不完全密封，因此，有一些新鲜的空气从环境中流入冷凝器。这就是像这样一个循环：关闭阀门3,6和开放的所有其他阀门.其中的空气排出流化床，与流经冷凝器的空气混合，然后进入到流化床，同时一些流化床里的空气通过流化床及其风帽之间空隙流入周围环境。在这个实验系统，在冷凝器和流化床之间估计有1 0 一20 的新鲜空气混合到流动的空气流通之中。因此，具有一定的新鲜空气的比例的型号2可以作为最佳的空气流通在下面的实验中使用。4.2通过蒸发器的空气流量效应我们进行了两个实验，在一项实验中，含水分约25 的1 00千克谷物放入到流化床（其母体不包含水分）。然后系统启动和通过蒸发器气流保持相对较低的速度约以500米/小时。热泵的工作情况是显示数字2-4。在令一个实验中，该系统首先启动和气流保持以高约2500 立方米/小时的速度通过蒸发器。在冷凝器出口处的温度达到约70度后将水分含量为27 的100公斤放入到流化床。热泵的工作情况是显示数字5-7 。这两个实验中，气流都是以相同的1 650立方米/小时的速度通过冷凝器。图2制冷剂在以500立方米/小时的干燥过程中压力变化。图3.热泵在以500立方米/小时的干燥过程中的工作情况。图4，热泵以500立方米/小时的性能指数图5. 制冷剂在以2500立方米/小时的干燥过程中压力变化。在图3，4和6，7中，理论计算结果都是从理想的制冷循环计算出来的。它分别对应图2和5中制冷剂的高，低压力。比较图3和6表明，从冷凝器的热输出大大增加通过增加空气流经蒸发器和在图7的性能指数比在图4中更接近理想状态。因此，通过蒸发器的气流数量对热泵的工作情况非常重要。事实上，通过蒸发器的气流量的增加大大提
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