Applied Mechanics and Materials Vol. 751

Abstract: The purpose of this study was to identify possible causes of longitudinal surface cracks found during early stages of ingot breakdown. However, these cracks need not necessarily form during forging or as a result of poor quality of the surface in metallurgical terms. Under certain conditions, they may occur even as the ingot is being heated in the furnace to the forging temperature. The cracks probably form within a few minutes after placing the ingot in the furnace as a result of the temperature gradient, which is most severe on the ingot surface. A numerical model was created to represent the case of three ingots in a furnace. Upon casting, the ingots are cooled down to no more than 600°C and then placed in a furnace at 1,100 - 1,200°C. Numerical simulations were used to analyse their internal stresses and temperatures.

Abstract: Influence of the dual twisted tapes (DTs) on the heat transfer enhancement in a circular tube is reported. The effects of twist ratio (y/w = 2.0, 3.0 and 4.0) on the heat transfer rate, friction factor, and thermal performance factor in a tube under constant wall heat flux were investigated in turbulent regions. Computations, based on a finite volume method, and the SIMPLE algorithm, were carried out by QUICK schemes. From the numerical results, heat transfer rate and pressure loss increased as twist ratio of tape (y/w) decreased. Based on the same pumping power consumption, the optimum thermal performance was achieved by the use of the tapes with twist ratio of 3.0. In addition, the predictions of flow-thermal phenomena (streamline, velocity vector, TKE and local Nusselt number) are also described.

Abstract: The effects of loose-fit twisted tape (LFT) on the heat transfer rate, friction factor, fluid phenomena and thermal performance of a tube under constant wall temperature are examined. It is observed that apart from the rise of Reynolds number, the reduction of the clearance ratio (c/D) leads to an increase in the heat transfer and pressure loss. According to the numerical results, the heat transfer and friction factor in the tubes with loose-fit twisted tape (LFT) for the smallest clearance ratio of c/D = 0.05 are higher those other clearance ratios. In addition, the thermal performances of clearance ratio c/D = 0.05 are found to be higher than those other clearance ratios (c/D) for all Reynolds numbers examined.

Abstract: An experimental study on heat transfer enhancement in a heat exchanger square-duct fitted diagonally with 45° V-ribbed tapes has been conducted. The tested duct has a square section and uniform heat-fluxed walls and the flow rate of air used as the test fluid is presented in terms of Reynolds number from 4000 to 25,000. The insertion of the V-ribbed tape is performed with a rib-pitch to duct-height ratio, (P/H=PR=0.75 and 2) at the rib attack angle of 45° with respect to the main flow direction. The V-ribbed tape inserted diagonally in the duct is expected to generate a longitudinal vortex flow pair in each tape side through the heated duct. Influences of four rib-to-duct height ratios (e/H=BR=0.1, 0.15, 0.2 and 0.25) on the heat transfer and pressure drop in terms of respective Nusselt number and friction factor are investigated. The experimental result indicates that the BR and PR of the V-ribs provide a significant effect on the thermal performance of the test duct. The results reveal that at smaller PR, the V-rib with BR=0.25 provides the highest heat transfer and friction factor but the one with BR=0.2, PR=0.75 yields the best thermal performance.

Abstract: Preliminary study of thorium based fuel utilization with the addition of Pa-231 on tight lattice boiling water reactor (BWR) has been performed. In previous studies, the use of fuel composition Th-232 and U-233 as well as the use of protactinium as burnable poisons with hexagonal tight lattice fuel cell geometry has resulted the reactor life time of 30 years without refueling [1]. In this study, power flattening has been conducted on the reactor core by using radially heterogeneous fuel. Addition of the Pa-231 is expected to extend lifetime of the BWR core By optimizing the composition of the fuel elements (Th and Pa) at low moderation conditions (tight lattice) it can be obtained the reactor core which can be opeprated over 30 years without refueling or fuel shuffling. The Reactor core has a volume of 17,635.8 liter, power of 620 MWt, operating life of 30 and a maximum excess reactivity value of 0.384% dk/k, could be achieved by using a composition of U-233 enrichment of 8.1 to 11% and the addition of Pa-231 as much as 6.16 to 11.13% with a power density of 35.2 watts/cc.

Abstract: In post Fukushima nuclear accidents inherent safety capability is necessary against some standard accidents such as unprotected loss of flow (ULOF), unprotected rod run-out transient over power (UTOP), unprotected loss of heat sink (ULOHS). Gas cooled fast reactors is one of the important candidate of 4th generation nuclear power plant and in this paper the safety analysis related to unprotected loss of flow in small long life gas cooled fast reactors has been performed. Accident analysis of unprotected loss of flow include coupled neutronic and thermal hydraulic analysis which include adiabatic model in nodal approach of time dependent multigroup diffusion equations. The thermal hydraulic model include transient model in the core, steam generator, and related systems. Natural circulation based heat removal system is important to ensure inherent safety capability during unprotected accidents. Therefore the system similar to RVACS (reactor vessel auxiliary cooling system) is investigated. As the results some simulations for small 60 MWt gas cooled fast reactors has been performed and the results show that the reactor can anticipate complete pumping failure inherently by reducing power through reactivity feedback and remove the rest of heat through natural circulations.

Abstract: The failure of the secondary side in Gas Cooled Fast Reactor system, which may contain co-generation system, will cause loss of heat sink (LOHS) accident. In this study accident analysis of unprotected loss of heat sink due to the failure of the secondary cooling system has been investigated. The thermal hydraulic model include transient hot spot channel model in the core, steam generator, and related systems. Natural circulation based heat removal system is important to ensure inherent safety capability during unprotected accidents. Therefore the system similar to RVACS (reactor vessel auxiliary cooling system) is also plays important role to limit the level of consequence during the accident. As the results some simulations for small 60 MWt gas cooled fast reactors has been performed and the results show that the reactor can anticipate the failure of the secondary system by reducing power through reactivity feedback and remove the rest of heat through natural circulations based decay heat removal (RVACS system).

Abstract: In this paper a finite element analysis (FEA) of machining for AISI1045 is presented. In particular, the thermodynamical constitutive equation (T-C-E) in FEA is applied for both workpiece material and tool material. Cutting temperature and tool wear depth are predicted. The comparison between the predicted and experimental cutting temperature and tool wear depth are presented and discussed. The results indicated that a good prediction accuracy of both principal cutting temperature and tool wear depth can be achieved by the method of FEA with thermodynamical constitutive equation.

Abstract: The article mainly introduced the design and implementation of food cold chain monitoring system, Introduces the realization method of ZigBee, GPS, GPRS, GIS, embedded system and remote database and remote access technology based on the network, Realized the environment real-time monitoring and real-time location information records to the cold chain transportation of refrigerator truck, and can access it from the remote network.

Abstract: Owing to the dynamic and competitive business environment, manufacturing companies take real-time monitoring and rapid decision making based on RFID applications, which brings huge volume of information and events generated in the defined manufacturing workflows. Complex Event Processing (CEP) is introduced to solve the problems mentioned above. CEP is applied to handle diverse and large amount of low-level multiple data and primitive events for the purpose of identifying meaningful event patterns. It is very important to integrate the CEP technology to the manufacturing workflows. In this paper, we provide a novel framework of RFID-based complex event processing system for assembly manufacturing applications like cars and high-speed trains. It bridges the hardware in workshops and enterprise applications. The Complex Event Management System (CEMS), which is the kernel of the framework, can filter the irrelevant events and work with uncertain data. Furthermore, a concrete example is used to describe the framework and validate the feasibility in assembly monitoring of the car manufacturing.