The performance and economics of a dairy refrigeration heat recovery unit

The results of a series of experiments on a refrigeration heat recovery unit designed to provide 300 1 of 60°C water from a 2·25 kW refrigeration system cooling 21001 of milk per day are presented. The unit was inserted between the compressor and condenser of the refrigeration plant and tested with two condenser systems (air and water), four condenser pressures (6·5 bar, 7·5 bar, 10 bar and 12 bar), two milk inlet temperatures (23°C and 18°C), and two milk final temperatures (4°C and 7°C). In addition, tests on receiver pressure and suction superheat were performed to determine their effect on the overall system performance.Increasing condenser pressure caused the gross heat recovery to rise from 15·1 MJ (4·2 kWh) d⁻¹ m⁻³ to 29·2 MJ (8·1 kWh) d⁻¹ m⁻³ of milk for the water cooled system, while water outlet temperatures rose from 45°C to 64°C. The corresponding ranges for the air cooled condenser were 13·7 MJ (3·8 kWh) d⁻¹ m⁻³ to 23·8 MJ (6·6 kWh) d⁻¹ m⁻³, and 38°C to 55°C. Changing milk inlet and final temperatures gave a proportional change in cooling times and total heat recovery, but had no effect on C.O.P. or heat recovery rates. Suction superheating increased the total heat recovery by approximately 3·2 MJ (0·9 kWh) d⁻¹ m⁻³, and water outlet temperatures by 5°C. Although increasing condenser pressure resulted in an increase in gross heat recovery, these gains were offset by the additional compressor power required. The net heat recovery varied between 13·7 MJ (3·8 kWh) d⁻¹ m⁻³ at 6·5 bar, to 19·1 MJ (5·3 kWh) d⁻¹ m⁻³ at 12 bar for the water cooled system. For the air cooled condenser system the net heat recovery remained fairly constant at approximately 11·5 MJ (3·2 kWh) d⁻¹ m⁻³.Based on these figures, the annual savings have been calculated under various conditions. At 10 cents per kWh, the heat recovery unit used in a system with a water cooled condenser operating at 12 bar, with suction superheat, on a farm producing 2100 1 per day, could save $NZ453 per annum. For a 210 cow dairy farm, such a system would cost around $NZ5000 (including the cost of the water cooled condenser), making the installation marginally uneconomic. However, heat recovery systems on larger farms are likely to be more attractive financially, because the increase in return is not matched by a similar increase in cost. The optimum operating conditions may vary if the electricity tariffs are altered. Methods of increasing the net heat recovery are considered and other techniques for reducing hot water power consumption are discussed.     

Thermal properties of gram

Values of specific heat, thermal conductivity and thermal diffusivity of rewetted whole grain were found. The specific heat of the grain shows a nonlinear relationship both with temperature and moisture content in the range of 292 to 308 K and 12·4 to 32·4% d.b. respectively, resulting in a second-order multiple regression equation. Bulk thermal conductivity increases both with increase in temperature and moisture content in the ranges 283 to 312 K and 11·5 to 27·2% respectively and was found to vary from 0·114 to 0·247 W/m K. Thermal diffusivity increases with increase in moisture content and decreases with increase in temperature in the temperature and moisture ranges of 293 to 307 K and 12·5 to 26·5% respectively, and its value lies between 9·46 × 10⁻⁸ to 16·35 × 10⁻⁸ m²/s.     

卧式柴油机冷却水套结构优化与流动特性分析

针对卧式柴油机结构特点,设计了强制冷却闭式循环系统水套结构,在不同工况下对水套入口流量及关键点的温度和压力进行了测试与分析.利用计算流体动力学软件对冷却水套的流场、压力场和换热系数分布进行了分析,并对原水套结构进行了优化.结果表明:原水套平均流速为1.00 m/s,平均换热系数为7 767 W/( m2· K),压力损失为0.027 MPa,基本符合工程设计要求;但各缸冷却水流速和传热系数不均匀,在公共水腔中部、二缸缸体水套上部出现大的漩涡,二缸鼻梁区、两个排气道下方局部区域存在流动死区.结构优化后,水套平均流速达到1.35 m/s,平均换热系数达到9 826 W/(m2·K),较原方案分别提高了35％和26.5％.在热负荷最大的缸盖鼻梁区,冷却水平均流速达到1.33 m/s,提高了41.5％,换热系数都在5000 W/( m2· K)以上,没有出现原方案中的局部流动死区和大的漩涡.     

装载机散热器模块进出口位置匹配试验

为提高车辆冷却系统中多散热器模块匹配的性能，对某装载机散热器模块在风洞测试平台上进行试验研究。试验散热器模块第1排是中冷器和液压油冷却器，第2排为水箱，第3排是变矩器油冷器。在风洞上对模块原型和在原型基础上互换变矩器油冷器进出油口位置的变型进行对比试验。试验结果表明，调整进出油口位置，能提高总的散热量，且对模块中单个散热器的性能影响更大。在设计中可以合理布置散热器进出油口位置，使得模块性能更加优异。     

生鲜乳快速冷却装置监测系统的设计

为了快速、准确地获取生鲜乳冷却过程的温度、流量，设计了一种生鲜乳快速冷却装置监测系统。该系统采用Pt100热电阻和阿尔泰DAM-3047N模块测量板式换热器冷却水进、出口和生鲜乳进、出口等位置的温度，采用智能涡轮流量传感器监测生鲜乳的瞬时流量和累积流量，采用MCGS开发监测软件，通过Modbus RTU协议与热电阻模块和流量传感器建立通讯联系，实现对生鲜乳冷却过程相关参数的实时监测、数据存储和报警信息输出等功能，为生鲜乳高效生产提供依据。      

湿冷换热器的计算与试验

为克服普通冷库保鲜果蔬时半冷时间长和冷却排管结霜等缺点，采用湿冷系统保鲜果蔬。探讨了湿冷保鲜系统中湿冷换热器的设计计算方法。试验表明，设计方法合理．系统运行正常，适合预冷,保鲜效果明显。     

The behaviour of tractor drive tyres at low inflation pressures when reacting high side forces

One option for reducing soil surface compaction resulting from the passage of lightly loaded vehicles is to reduce the inflation pressure of conventional tyres below the minimum currently recommended by tyre manufacturers. This paper describes an investigation of one potential problem, collapse of a tyre when subjected to large side forces, which might result from this approach.Three types were towed sideways on concrete at inflation pressures down to 0·4 bar (6 lb/in²) at constant radial tyre deflection while the side force generated and tyre sidewall deflection were monitored.There was no tendency for the tyres to collapse but the trailing sidewall did buckle. It may therefore be concluded that from the safety aspect that the tyre is insensitive to this type of loading. The effects of large tyre deflections on the vehicle stability as well as the effect of side forces on a rolling tyre should be investigated before any recommendation is made on the safety of using conventional tyres at pressures below the minimum currently recommended.     

简化Kalina循环系统的热力学分析

提出了一种简化Kalina循环发电系统,该系统以净功率、电力产率、热效率和换热面积比率为性能指标,分析了氨水溶液质量分数、循环倍率、热源温度、冷源温度和换热器端部温差对性能指标的影响。结果表明,氨水溶液的质量分数可以改变循环系统的性能;循环系统存在最佳的循环倍率约为4,对应的氨水溶液质量分数差范围为12%~13%;提高溶液换热器端部温差,可使电力产率增加,但系统热效率降低。     

基于太阳能的小型降温系统研发设计

在“双碳”背景下,结合我国西北地区太阳能资源丰富且炎热干旱的气候条件,研发了基于太阳能的1 kW小型降温系统。系统以水为介质,采用超声波将水雾化为1～5 μm云雾喷洒在房屋周围,通过蒸发吸热的原理对房屋周围环境进行降温加湿,通过设计光伏系统、电源与控制系统及水箱管道系统并在50 m2的房屋周围进行试验测试,结果表明此小型降温系统平均可降低环境温度6 °C,可使湿度达42.9%,验证了该系统对我国西北农村庭院家庭夏季降温增湿的有效性。      

YN04型生物质燃气脱焦机的研制

作者对YN0 4型生物质燃气脱焦机所采用的干式 (间接换热冷却 )快速冷凝悬浮脱焦工艺技术及脱焦机的设计计算进行了介绍。该脱焦机经实地运行试验和测试 ,结果表明 :YN0 4型生物质燃气脱焦机正常运行的平均脱焦率达 91% ,常压固定床生物质气化机组所产燃气中焦油含量平均为12 4mg·m- 3,优于国内一搬常压固定床生物质气化机组净化装置的工作效率 ,且不带来水的二次污染。同时 ,该脱焦机还具有体积小 ,造价低 ,操作简单 ,工作可靠等优点。     

The yield,quality and profitability of annual forage,perennial pasture and perennial forage systems under irrigation

Intensive fodder production systems were compared under irrigation in western New South Wales. The three basic systems studied were:

• 1.(1) Annual forages (Sorghum bicolor × S. sudanense plus Avena sativa).
• 2.(2) Perennial pasture (Paspalum dilatatum).
• 3.(3) Perennial forage (Medicago sativa).

The first two systems included nitrogen fertilizer or legume options, while the last had the option of including a perennial sorghum.Dry matter production was highest in the annual forage system (maximum of 30·5 tonnes ha⁻¹ year⁻¹), although annual establishment costs were higher than for perennial systems. The perennial pasture yielded 21·5 tonnes ha⁻¹ year⁻¹ but, like the annual forage system, 250 kg N ha⁻¹ year⁻¹ was required to obtain this yield. The perennial forage yielded 19·8 tonnes ha⁻¹ year⁻¹ without nitrogen fertilizer. Furthermore, it yielded more digestible dry matter and nitrogen than any other system.Although the annual forage system was the most profitable when based upon a set price for hay, the best system for grazing was difficult to determine; factors relating to grazing management are discussed.     

非道路用柴油机缸体水套CFD分析及优化改进

利用AVL F ire软件对SNH4102Z柴油发动机的缸体水套进行了冷却水的流动分布、压力损失及换热性能的CFD分析,然后在原机的基础上进行了优化改进。结果表明:原机缸体水套存在背水侧冷却强度不足、冷却均匀性差的缺点,不能满足缸套冷却要求。而提出的改进方案明显提高了缸体水套背水侧的冷却强度,改善了缸体冷却的均匀性。     

High-rate anaerobic digestion of screened dairy manure

Laboratory-scale fixed-film reactors were used for the high rate production of methane from screened dairy manure under mesophilic temperatures. The active biomass, growing on the support structures, enabled the reactors to withstand high organic loadings as well as very short hydraulic retention times down to 1 h. Screened dairy manure (3·25% VS) was added intermittently at loading rates ranging from 2·25 to 778 gram volatile solids per litre per day (g VS 1⁻¹ d⁻¹) for fixed-film reactors. The maximum methane production rate was 6·20 litre methane per litre reactor per day (6·20 1 CH₄ 1⁻¹ d⁻¹) when operated at a loading rate of 259 g VS 1⁻¹ d⁻¹ with a 3 h hydraulic retention time. The fixed-film reactor was capable of sustaining a loading rate of 778 g VS 1⁻¹ d⁻¹ (1 h hydraulic retention time). The data illustrated the advantages of fixed-film reactors. The results obtained with reactors of varying sizes, and different fixed-film support materials are discussed.     

Estimation of Moisture Diffusivity Coefficient and Thermal Properties of Alfalfa Pellets

Heat and mass transfer characteristics of alfalfa pellets are needed in the optimization of coolers for freshly-made pellets and in managing storage schedules of the pellets in silos and bins. Moisture diffusivity and thermal properties are important parameters used to characterize the heat and mass transfer ability of a material. In this study, experimental thin-layer data on (a) moisture desorption, (b) moisture absorption and (c) rate of heating of alfalfa pellets were collected. By applying the inverse theory and using second order mass transfer and heat transfer equations in cylindrical coordinates, the moisture absorption and desorption data were used to estimate the moisture diffusivity as a function of moisture content of the pellets while the heating rate data were used to estimate the thermal properties (thermal conductivity and specific heat) as a function of pellet temperature.Better estimates were obtained when moisture diffusivity of the pellets was exponentially related to moisture content in comparison with a linear relation between moisture diffusivity and moisture content. Moisture diffusivity during desorption (2·40×10^-9to 4·12×10^-9 m²/s) was about three times that of the values of diffusivity during moisture absorption (7·50×10^-10to 1·26×10^-9 m²/s). A good fit to the experimental heating rate data was obtained when thermal conductivity and specific heat of the pellets were linearly related to temperature. Over a temperature range of 2 to 110°C, estimated particle thermal conductivities and specific heats of the pellets were in the range of 0·04 to 0·19 W/m K and from 962 to 2114 J/kg K respectively.     

The Influence of Cement Content and Water/Cement Ratio on the Durability of Portland Cement Concretes exposed to Silage Effluent

This paper outlines the findings of a study on the influence of cement content (275–425 kg/m³) and water/cement ratio (0·45 to 0·75) on the durability of concrete exposed to silage effluent. The test facility exposed concrete specimens to a controlled flow of effluent such that the volume of effluent in each 28 day cycle of exposure simulated one year's volume and expected period of effluent flow at the front of a well-drained 200 t horizontal silo. The relative performance of the concrete mixes was assessed over 10 cycles through measurement of saturated mass loss and surface depth change. The saturated mass loss measurement gave more consistent results. Optimum performance was recorded in concretes of cement content 325 and 375 kg/m³with water/cement ratios of 0·55 and 0·50, respectively. The studies indicate that water/cement ratio is a more critical variable than cement content. Deterioration increased significantly when the water/cement ratio exceeded 0·5. Increasing the cement content beyond the minimum recommended value in current national specifications (350 kg/m³) did not lead to a reduction in mass loss rate. The benefits of high cement content concretes is questioned, therefore, not least because of the increased risk of early-thermal cracking. It is postulated that specifications should limit the maximum water/cement ratio and both maximum and minimum cement content.     

横流式混合换热器中传质系数与压降的数学模型

果蔬贮藏保鲜是保持其品质和商品价值的一种重要方法,湿冷保鲜技术有其独特的保鲜优势,具有非常好的应用前景.为此,以湿冷系统中混合换热器内的传热与传质作为研究对象,系统地分析和研究了横流接触式情况下混合换热器的传递性能及流动阻力,通过理论和实验分析,获得了可靠实用的传质系数和过帘压降的数学模型.该数学模型可作为湿冷系统中混合换热器设计的依据.     

冷水机组在泵站冷却系统中的应用

泵站的水冷却方式大多存在着冷却水杂质多、冷却器容易堵塞、管路复杂、系统耗电量大和成本高等问题。为了解决这些问题，在泗阳第二抽水站机组冷却系统中采用MFLS—10型模块化风冷冷水空调机组，采用循环清洁水、单管道、水温调节、断续运行、远程控制等措施。新系统的开发应用大大提高了主机泵冷却系统的可靠性，取得了较好效益。     

电网中换热器提高效率的方法研究

文章针对电厂汽机及给水泵的冷换设备陈旧,在夏季被迫掺用或直接用工业水(地下水)进行冷却的情况,认为利用新型先进换热器进行改造,增加换热面积,提高换热效果,能达到优化全厂水平衡和节水的目的。     

气调保鲜液氮充注沉浸式汽化器工作特性研究

针对液氮充注气调方式液氮温度较低,直接充注将对果蔬产生冻害问题,为提高液氮汽化器出口温度的控制精度,提高冷量利用率,设计了一种蓄冷液氮充注沉浸式汽化器并搭建试验平台,研究盘管长度、蓄冷剂类型和液氮流量等因素对汽化器工作特性的影响。基于传热理论建立了汽化器出口温度计算模型。计算得到的汽化器出口温度与试验值基本一致,相对误差为2.01%和8.06%。试验结果表明:盘管长度、蓄冷剂类型和液氮流量都对汽化器工作特性有显著影响,盘管长度和液氮流量与充注时间呈线性关系,随着盘管长度增加或液氮流量减小,相关系数升高;当盘管长度为3 m、液氮流量为0.0075 kg/s和蓄冷剂类型为水时,汽化器的换热性能较佳,而当盘管长度为3 m、液氮流量为0.01 kg/s和蓄冷剂类型为水时,汽化器的蓄冷效率较佳。     

复合发电系统的沼气热泵供能特性研究

建立了包括沼气发动机模型、压缩机模型、换热器模型、膨胀阀模型、发电机模型的沼气热泵复合发电系统各部件数学模型,利用该模型,研究了不同转速下的热泵系统特性、发电系统特性以及整体性能.计算和实验结果均表明,复合发电系统的沼气热泵系统最高总制热性能系数在5.0以上,并且在低转速下,制冷和制热系数较高,具有较好的部分负荷特性和节能环保效果.系统的发电电压为28.8V,其发电能够满足自身用电需求.