Airflow pattern and temperature distribution in a typical refrigerated truck configuration loaded with pallets

This work is part of a research activity aiming to improve and to optimise air-distribution systems in refrigerated vehicles in order to decrease the temperature differences throughout palletised cargos. This condition is essential in order to preserve the quality, safety and shelf life of perishable products. The present study reports on the numerical and experimental characterization of airflow within a semi-trailer enclosure loaded with pallets. The experiments were carried out on a reduced-scale (1:3.3) model of a refrigerated-vehicle trailer. The performance of ventilation and temperature homogeneity were characterized with and without supply air duct systems. Both configurations are extensively used in refrigerated transport. The numerical modelling of airflow was performed using the Computational Fluid Dynamics (CFD) code Fluent and a second-moment closure, the Reynolds stress model (RSM). The results obtained using the RSM model showed good agreement with the experimental data. Numerical and experimental results clearly show the importance of air ducts in decreasing temperature differences throughout the cargo.     

Airflow patterns in an enclosure loaded with slotted pallets

A reduced scale model and CFD predictions are used to investigate experimentally and numerically the airflow patterns within a refrigerated truck loaded with slotted but empty pallets. Air velocity measurements are carried out on a reduced scale model with a Laser Doppler Anemometer above and inside the pallets. The numerical predictions obtained with Computational Fluid Dynamics package using the RSM turbulence model showed a satisfactory agreement with experimental data in high velocity zones. An approach was developed to evaluate the local ventilation efficiency and the fresh air within the pallets. The flow rate through the last pallet is about 35 times smaller than for the five first pallets. In terms of fresh air the difference is not so high; the equivalent fresh airflow rate through the last pallet is about six times smaller than for the first pallets.     

Measurement and prediction of air movement through doorways in refrigerated rooms

Reducing the amount of air infiltration through the doorways of food storage rooms would improve temperature control and the overall economics of food storage. In the UK a joint government/industry supported LINK project has been set up to look at methods of reducing air infiltration. The project is combining direct experimental measurement with computational fluid dynamics (CFD) modelling. A CFD model of air movement through a doorway has been developed and verified against conventional and laser Doppler anemometry (LDA) measurements. The CFD model has been shown to be generally accurate, however, there are areas where the accuracy is less than perfect. For example the CFD model predicted the shape of the vertical profile accurately, although it under-predicted the maximum velocity by 0.1 m s⁻¹ and it predicted the height at which the airflow changed direction to be 40 mm lower than was measured by the LDA.     

Experimental study on the heat and mass transfer characteristics in a refrigerated truck

An experimental study on the heat and mass transfer characteristics in the body of a refrigerated truck for cases without an air curtain, with a fan air curtain and with a plastic strip curtain have been carried out. The variations in temperature and relative humidity inside the stationary truck during a short duration after the door is opened are the present focus. The average air temperature inside is found to increase to 14, 7 and 8°C from an initial temperature of −10°C, for cases without an air curtain, with a fan air curtain and with a plastic strip curtain, respectively, within 2 min after the door is opened. It is found that using an air curtain can have energy savings up to 40 and 11%, respectively, compared to the cases without an air curtain and using plastic strip curtain. Comparison between the experiment and numerical results also shows reasonable agreement in terms of average temperature inside the body.     

车载信息记录仪硬盘减振缓冲的研究

在车载环境下,冲击和振动会对工作中的硬盘造成传输中断甚至损坏。采用抗冲击振动性能强的硬盘以及合理的减振装置可以使设备稳定地工作。文中通过实验测试出某型号硬盘开启主动保护的激振频率的范围,针对实验数据及车载情况选用钢丝绳减振器,通过简化的动力学模型,确定了减振器型号以及隔振效率,并采用合理的安装方式,设计出结构简单,适应性强的硬盘隔振系统。     

特种平车线路试验加速度异常分析与仿真

在对特种平车(如双层集装箱凹底平车)进行120 km/h线路动力学试验中,多次出现重车下心盘处垂向加速度过大,甚至高于车辆空载时的异常现象,而同时试验的其他敞车或棚车等却没有此问题.在对试验取得的垂向加速度频谱分析后,发现车体振动的主要频率高于车体的低阶弹性自振频率,并且响应主频会随着车速的提高而线性增大,这与之前一些研究认为加速度过大是由线路不平顺激起车体的弹性振动结果不一致.为了解其机理,建立具有刚柔耦合车体的凹底平车整车非线性动力学模型进行仿真,并与C70敞车的仿真结果进行了对比,仿真结果与试验基本一致.结果表明,加速度超标的主要因是:在线路不平顺激扰下,重车时转向架减振斜楔产生较大冲击力作用于凹底平车心盘,而此处的等效被冲击质量偏小,从而在车体心盘处产生较大的垂向加速度.     

R134a汽车空调及整车降温性能仿真优化分析

本文通过KULI仿真软件搭建整车降温模型,计算并分析了中间换热器(又称同轴管,IHX)、后出风吹面装置以及乘员舱衣帽架对乘员舱降温性能的影响,对比了其单一装置及其组合方案对整车降温性能的影响。分析结果显示当取消单一功能配置时,衣帽架对乘员舱降温性能影响较大,平均温度升高2.2~2.4℃;后吹面装置次之,平均温度升高0.6~0.8℃;同轴管的影响最小,平均温度升高0.2~0.4℃。而且衣帽架单一装置对乘员舱降温性能的影响大于同轴管和后出风吹面装置组合对乘员舱降温的影响。通过仿真计算为整车及后续车辆开发提供了一定的理论依据及优化方案。     

用Excel进行空调通风管道阻力计算

介绍用Excel软件编制钢板管道计算表的步骤和要点，在此基础上说明编制空调管路阻力计算表、建立风（水）系统阻力计算书的方法，演示了风管阻力计算，阻力平衡的实例。     

车用制动空气压缩机结构辐射噪声特性研究

针对某公司生产的KYV480型号车用制动活塞式空气压缩机(简称:空压机)运行过程中,振动噪声较大,一定程度上影响了驾驶员和乘客的乘车舒适性和身心健康的情况,文章基于有限元和声学边界元联合求解的方法对空压机的结构表面辐射噪声特性进行研究.在计算得到空压机运行过程中壳体所受载荷的基础上,对空压机壳体表面的振动加速度响应进行...     

Modelling carbon trading and refrigerated logistics services within a fresh food supply chain under carbon cap-and-trade regulation

Carbon cap-and-trade regulation is widely adopted to reduce carbon emissions. Under this regulation, we propose a carbon trading mechanism considering refrigerated logistics services in a fresh food supply chain. In addition to supplying fresh food, the supplier offers refrigerated logistics services and overstocked carbon emission permits to the retailer. We study the decisions on the price of emission permits traded within the supply chain, the retail price and the price of refrigerated logistics services in different carbon trading options, without carbon trade, inner carbon trade, inner and outer carbon trade. Pricing strategies for fresh food, emission permits and refrigerated logistics services are provided for supply chain members. We also reveal the relationship between carbon trading and refrigerated logistics services, and investigate their joint influence on the supplier–retailer cooperative relationship. In addition, it is shown that with the implementation of a transfer payment mechanism, supply chain members are motivated to participate in the carbon trading mechanism, which has advantages including improved resource utilisation and more competitive supply chains.     

Effect of transverse velocity and temperature gradients on sound attenuation in straight annular ducts

Abstract

In this paper, the effects of transverse mean velocity and temperature gradients on the acoustic propagation in a straight annular duct are studied so as to be the basis of further analyzing the sound propagation in nonuniform annular ducts. The wave equation governing this acoustic field is a difficult eigenvalue problem. The eigenvalue is solved by an IMSL package which is proposed to find suitable initial guess. By using the initial guess, in addition to the iterative process, the final results have been found. The results are proved to be of good accuracy by comparing with published data, and the errors are under 2.0%. From this paper we also find that, under the influence of the unsymmetric boundary condition, the attenuations of the axial symmetric radial mode are different from other modes, and this property of the former mode can not be expected by ray acoustic arguments, on the other hand, the attenuations of the lowest mode and the spinning modes can be expected.     

Performance of evacuated calcium phosphate microcarriers loaded with mesenchymal stem cells within a rat calvarium defect

Tissue engineering of stem cells in concert with 3-dimensional (3D) scaffolds is a promising approach for regeneration of bone tissues. Bioactive ceramic microspheres are considered effective 3D stem cell carriers for bone tissue engineering. Here we used evacuated calcium phosphate (CaP) microspheres as the carrier of mesenchymal stem cells (MSCs) derived from rat bone marrow. The performance of the CaP-MSCs construct in bone formation within a rat calvarium defect was evaluated. MSCs were first cultured in combination with the evacuated microcarriers for 7?days in an osteogenic medium, which was then implanted in the 6?mm-diameter calvarium defect for 12?weeks. For comparison purposes, a control defect and cell-free CaP microspheres were also evaluated. The osteogenic differentiation of MSCs cultivated in the evacuated CaP microcarriers was confirmed by alkaline phosphatase staining and real time polymerase chain reaction. The in vivo results confirmed the highest bone formation was attained in the CaP microcarriers combined with MSCs, based on microcomputed tomography and histological assays. The results suggest that evacuated CaP microspheres have the potential to be useful as stem cell carriers for bone tissue engineering.     

Batching and scheduling for a single-machine flexible machining cell with multi-fixturing pallets and controllable processing times

This study addresses an integrated batching and scheduling problem for a single-machine flexible machining cell in which each pallet can load multiple parts, i.e. multi-fixturing pallets, and part processing times can be changed with different processing costs, i.e. controllable processing times. The batching sub-problem is to select the set of parts to be produced in each period of a planning horizon and the resulting scheduling sub-problem is to determine the set of parts to be loaded on each multi-fixturing pallet, the part processing times and the pallet input/processing sequences for the parts selected in each period. A bi-criterion objective is considered that minimises the total tardiness and the total processing cost simultaneously. A solution approach is proposed that consists of three phases from the first to the last period: (a) generating the whole schedule over the planning horizon; (b) selecting the parts to be produced during the current period using the scheduling information; and (c) determining the final schedule for the selected parts. Simulation experiments were done on a number of test instances and the results are reported.     

采用ER流体半主动座椅减振器的车辆平顺性模拟

介绍采用ER流体的筒式半主动座椅减振器车辆的平顺性模拟.建立具有针对系统不确定的内部鲁棒性的滑模控制器,通过控制电场来控制座椅的振动水平.模拟计算结果表明,采用半主动悬架时,在共振频率附近位移和加速度的传输率得到实质性的减小;当汽车驶过不平路面时,从半整车模型的位移和加速度的频率响应的整个频域段来看,采用ER流体半主动悬架汽车的性能得到了很大提高.特别是在1Hz以上频率段,位移和加速度传输率都得到了显著减小.表明通过采用ER流体半主动悬架能够很好地提高车辆的行使平顺性.     

Unstable sinking of spheres at higher air velocity in a gas-solid fluidized bed

Float-sink of large objects (on order of cm) in a gas-solid fluidized bed of powder (on order of 100 s of microns) based on density difference has been utilized for dry density separation in industry. The air velocity u₀/u_mf is one of the important factors operating the fluidized bed, where u₀ and u_mf are the superficial air velocity and the minimum fluidization air velocity, respectively. It is empirically known that the sinking of heavy objects is “occasionally” unstable in the fluidized bed combustor, for which the higher air velocity u₀/u_mf > 4 is used. Unstable sinking means heavy objects that are expected to sink but sometimes do not. However, the precise conditions at which the unstable sinking occurs are not clear. In this study, we investigated the float-sink characteristics at a given air velocity u₀/u_mf = 2–7 using glass beads of size D_gb = 425–600 μm and 600–850 μm as the fluidized powder bed media. The float-sink experiments were carried out at the bed height h_gb = 150 mm and 75 mm using density adjusted spheres (diameter = 30 mm). We found that the spheres stably float or sink based on density difference at D_gb = 425–600 μm & h_gb = 150 mm and at D_gb = 600–850 μm & h_gb = 75 mm. However, the unstable sinking does occur at u₀/u_mf > 4 at D_gb = 600–850 μm & h_gb = 150 mm. These results indicate that the powder size and the bed height are key factors to induce the unstable sinking at the higher air velocity.     

Experimental study of fluctuations of particle velocity in a turbulent flow of air in a pipe

The distribution of longitudinal and normal components of the fluctuation velocity of particles in their motion in a downward turbulent airflow in a pipe is obtained. The effect of the concentration of particles on the intensity of fluctuations of their velocity is studied. A high rise of the longitudinal fluctuation of the velocity of particles in the pipe wall region with an increase in their concentration is revealed.     

Examining the use of dedicated and general purpose pallets in a dedicated flexible manufacturing system

This research describes one example of how the failure to understand the relationships between the flexibility associated with all resources within an FMS can be critical to overall performance. The need for such understanding is clearly spelled out by Jaikumar (1986). This research illustrates that even in situations where the demands placed upon the system are very well defined, tooling resources, such as pallets, may constrain overall system flexibility and subsequent system performance. In this paper, we simulate the operational performance of an existing FMS designed to manufacture a relatively small set of agricultural equipment components (only eight part types) over a known planning horizon using general purpose pallets and dedicated pallets. The simulation model is run under experimental conditions that include levels of: demand mix variability, number of each type pallet available to the system, and incremental loading time and scrap rate when general purpose pallets are used. In most cases, the results indicate a significant increase in system performance when using general purpose pallets. In general, while system performance decreases as the level of demand mix variability increases, relatively higher throughput is obtained using general purpose pallets except where the assumed incremental loading times and scrap rates associated with assembling the pallets are highest. System performance also improves as additional pallets are made available. In addition, overall system investment is impacted as fewer general purpose pallets are required to achieve a given level of performance compared to the use or dedicated pallets. As the overall system investment and scheduling restrictions associated with dedicated pallets would be expected to increase with the number of part types made in the system, the results found in this analysis for a dedicated FMS producing a small number of parts on a regular basis form a relative ‘lower bound’ on the scheduling and investment benefits of using general purpose pallets.     

Towards a standardised information exchange within finished vehicle logistics based on RFID and EPCIS

Finished vehicle logistics is facing different challenges. In order to cope with these challenges this article presents a case study, analysing a concept to improve finished vehicle logistics using radio frequency identification (RFID)-based and electronic product code information services (EPCIS). Within this case study, vehicles were identified automatically by RFID. For sharing, the information generated by RFID the EPCIS-based InfoBroker was developed according to the needs of the automotive industry. By having data available through the InfoBroker, decision support systems (DSS) can make planning and control of finished vehicle logistics decisions more efficiently. The case study was executed within two finished vehicle logistics cases. Based on this article practitioners can estimate the potentials of RFID and EPCIS for finished vehicle logistics. Based on the data made accessible by the presented concept practitioners and researches can develop innovative DSS to improve finished vehicle logistics     

Laser plasma accelerated by an optical discharge moving in air at a hypersonic velocity

The results of computer simulations show that a pulsing optical discharge moving in the atmosphere at a hypersonic velocity creates a plasma stream propagating in the direction opposite to that of the discharge. The plasma is accelerated upon efflux from the high-pressure region into an “evacuated” channel created by the discharge. Analytical expressions were derived to evaluate the stream velocity, density, and radius depending on the discharge parameters.