Modeling of a novel spool compressor with multiple vapor refrigerant injection ports

A model of a novel rotary spool compressor has been developed to explore the effect of multiple injection ports on compressor and cycle performance. The thermodynamic model includes the effects of heat transfer and leakage and is numerically solved to predict the compressor power consumption and mass flow rate. Saturated vapor injection is modeled assuming that the injection pressures and the timing of the injection process can be controlled.The model predicts that adding a single injection port will provide a 12% increase in the cycle coefficient of performance (COP) when the compressor runs at 1907 rpm with R-22 evaporating at ?7 °C, condensing at 49 °C, and 15 °C of superheat. Adding a second, non-optimized injection port increases the COP by 16% compared to the cycle without injection. The model is used to investigate the effect of injection pressure, port location, and port diameter on cycle performance.     

Theoretic study of backmixing in simulated moving-bed adsorption process with multiple equilibrium stages between ports

A theoretic analysis of the simulated moving-bed process operated as a packed-bed with multiple equilibrium stages between external process ports is undertaken. A model has been proposed that correctly describes the time-averaged movement of individual process streams within the process. Axial mixing is incorporated into the model using the concept of mobile phase backmixing. The number of equilibrium stages between external process ports is shown to be an important parameter when considering design and operation of the simulated moving-bed process as a packed bed.     

Bionanocomposite hybrid polyurethane foam reinforced with empty fruit bunch and nanoclay

Bionanocomposite hybrid polyurethane (BHPU) foams that exploit the tribute of natural fibers and nanoclay in green PU foam can lead to the new imminent in engaging the nanoclay and natural fibers. PU filled empty fruit bunch (EFB), PU filled silane treated EFB (sEFB) and PU filled organo montmorillonite (oMMT) have been prepared as control, and the hybridization has carried out for ¼, ½ and ¾ ratios between EFB/oMMT and sEFB/oMMT. The hybridization of these natural fibers and oMMT permit to retain the strength without compromise the stiffness of BHPU. The hybridization also improves the barrier and thermal properties of these BHPU. Microscopic studies shows that the hybridization of these natural fibers and nanoclay provide initial evidence of the possibilities on the insertion of nanoclay into the natural fibers, thus open the opportunities to exploit this behavior to another hybrid system.     

MRP lot sizing with variable production/purchasing costs: formulation and solution

The research on lot sizing is extensive; however, no author in the literature reviewed to date provides an optimal solution algorithm to a prevalent problem which is found in manufacturing. A multi-level, general product-structure, variable-cost model is presented which follows the procedure of a closed-loop material requirements planning (MRP) system, and incorporates many conditions that production and material managers find in practice. A branch and bound (B&B7) algorithm is developed. The efficiency of B&B is derived from effective lower bounds and solution procedures which are determined on the basis of the space-time structure of the MRP lot-sizing problem and its non-convex total-cost function. This path-dependent lower bound is computationally efficient and guarantees an optimal solution. The B&B algorithm is tested on problems and compared to heuristics in the literature.     

Underground production scheduling with ventilation and refrigeration considerations

Underground mine production scheduling determines when, if ever, activities associated with the extraction of ore should be executed. The accumulation of heat in the mine where operators are working is a major concern. At the time of this writing, production scheduling and ventilation decisions are not made in concert. Correspondingly, heat limitations are largely ignored. Our mixed-integer program maximizes net present value subject to constraints on precedence, and mill and extraction capacities with the consideration of heat using thermodynamic principles, while affording the option of activating refrigeration to mitigate heat accumulation. In seconds to hours, depending on the problem size (up to thousands of activities and 900 daily time periods), a corresponding methodology that exploits the mathematical problem structure provides schedules that maintain a safe working environment for mine operators; optimality gaps are no more than 15% and average less than half that for otherwise-intractable instances.

     

Positioning and immobilization of individual quantum dots with nanoscale precision

We demonstrate a technique for the precise immobilization of nanoscale objects at accurate positions on two-dimensional surfaces. We have developed a water-based photoresist that causes nanostructures such as colloidal quantum dots to segregate to a thin layer at surfaces. By combining this material with electroosmotic feedback control, we demonstrate the ability to position selected, individual quantum dots at specific locations and to immobilize them with 130 nm precision via localized UV exposure.     

Design considerations with zinc coated steel and zinc castings

Zinc castings and the various types of zinc coated steel all have different design considerations. Thick coatings applied by hot dipping, by sheradizing or by spraying are usually a final operation after fabrication. Continuously coated sheet or wire has virtually the same design flexibility as the uncoated steel but with longer life to first maintenance treatment. With zinc castings, technical development in the pressure die casting process — notably the ability to make thin and complex thin dimensional shapes — means that a zinc die casting can often economically replace an assembly of steel pressings. This article describes some of the design considerations for each group of materials with examples from practice.     

Optimal heat exchanger network synthesis with operability and safety considerations

Research on the optimal design of heat exchanger networks (HENs) has primarily revolved around trading off technical design requirements for aspects of economy, such as capital cost of heat exchangers and utilities. As a result, considerations for safety, operability, and flexibility have received much less attention. This study presents a Pinch Analysis-based methodology that considers the inherent safety and operability aspects of an optimal HEN design. The procedure begins with data extraction, followed by utility targeting that gives due consideration to how each process stream impacts the inherent safety of the HEN. This is made possible via the use of a hot and cold Stream Temperature versus Enthalpy Plot (STEP) that prioritises the inherent safety index (ISI) on top of the heat capacity flow rate (CPs) during simultaneous targeting and design of the HEN. The Pinch temperatures and minimum utilities were determined using STEP. At the same time, the hot and cold stream pairs with higher ISIs and those with lower ISIs were matched together so that safety considerations could be emphasised and precautions taken with a particular heat exchanger. The disturbance propagation path through the HEN and the affected streams were also analysed. Network modification was performed using the downstream path concept in order to reduce disturbance propagation downstream of the HEN. The ?T _min violations and energy penalties from network changes were assessed. Flexibility and structural controllability of each network option were compared. The highest percentage of change in every stream of the network indicates that network is the most flexible, while the index of structural controllability closest to 1 demonstrates that the network is most controllable. Application of this method within an illustrative case study showed that network 3 was the most flexible as it yielded the highest percentage of change at 22 %. It was also the most controllable as it had a controllability index closest to 1.0, i.e. at 0.917.     

Effective moduli and failure considerations for composites with periodic fiber waviness

A finite element micromechanical model for fibrous materials introduced in a previous work [J. Compos. Mater. 38 (4) (2004) 273] is used to further study the effects of periodic and localized fiber waviness. A periodic unit cell based on hexagonal fiber packing and sinusoidal fiber waviness was assumed as a representative volume element. Equivalent to this wavy-shaped unit cell, a straight unit cell but with wavy material-orientation is introduced. This type of homogenized continuum modeling simplifies the analysis since the wavy geometry with details of constituent materials is avoided. Thus, stiffness parameters associated with individual lamina with waviness are estimated when subject to the constraining effects of neighboring isotropic or straight fiber material layers. It is shown that the shear constraint of the added layers increases the effective moduli of the wavy layer by inhibiting the fiber straightening deformation mechanism. The local stress distribution is also examined and the potential for material failure is investigated. The methodology provides a platform to study the behavior of wavy fiber composites in a systematic manner.     

Development of a production inventory model with uncertainty and reliability considerations

This paper addresses a problem of an imperfect production system under fuzzy demand and inventory holding cost. Production process reliability is considered because of the imperfect production process. In this problem, reliability of the system in regards to producing defective and non-defective items is considered as a decision variable. The objective is to maximize the graded mean integration value (GMIV) of the expected average profit while considering revenues as well as any other relevant costs. The developed model belongs to the class of a geometric programming. We have developed a simple mathematical methodology to solve the model. Genetic algorithm and simulated annealing algorithms are also applied to solve and validate the results. A numerical example has been presented to interpret the solutions.     

JIT mixed-model sequencing with batching and setup considerations via search heuristics

This research addresses the problem of sequencing items for production when it is desired that the production sequences result in minimal usage rates–surrogate measures for flexibility in a JIT environment. While seeking sequences with minimal usage rates, the number of required setups for the sequences is also considered, along with feasible batch-sizing combinations. The general intent is to find minimum usage-rate sequences for each associated number of setups and total batches. This multiple objective problem is addressed via a three-dimensional efficient frontier. Because the combinatorial nature of sequencing problems typically provides an intractable search space for problems of ‘real world’ size, the search heuristics of simulated annealing and genetic algorithms are presented and used to find solutions for several problem sets from the literature. Experimentation shows that the simulated annealing approach outperforms the genetic algorithm approach in both objective function and CPU performance.     

A genetic algorithm for manufacturing cell formation with multiple routes and multiple objectives

This paper presents a genetic algorithm (GA) approach to the machine-component grouping problem with multiple objectives: minimizing costs due to intercell and intracell part movements; minimizing the total within cell load variation; and minimizing exceptional elements. Manufacturing cells are formed based on production data, e.g. part routing sequence, production volume and workload. Also, we will discuss the implication of part alternative routings and the method we suggest to deal with it. Special genetic operators are developed and multiple experiments are performed. Finally, the results obtained with the proposed algorithm on the tested problems are compared with those of others.     

High-performance metal-induced lateral-crystallization polysilicon thin-film transistors with multiple nanowire channels and multiple gates

In this study, pattern-dependent nickel (Ni) metal-induced lateral-crystallization (Ni-MILC) polysilicon thin-film transistors (poly-Si TFTs) with ten nanowire channels and multigate structure were fabricated and characterized. Experimental results reveal that applying ten nanowire channels improves the performance of an Ni-MILC poly-Si TFT, which thus has a higher ON current, a lower leakage current, and a lower threshold voltage (V/sub th/) than single-channel TFTs. Furthermore, the experimental results reveal that combining the multigate structure and ten nanowire channels further enhances the entire performance of Ni-MILC TFTs, which thus have a low leakage current, a high ON/OFF ratio, a low V/sub th/, a steep subthreshold swing, and kink-free output characteristics. The multigate structure with ten-nanowire-channel Ni-MILC TFTs has a few poly-Si grain boundary defects, a low lateral electrical field, and a gate-channel shortening effect, all of which are associated with such high-performance characteristics.     

Discussion related to Watson and Evans: “Resonant frequencies of a fluid in containers with internal bodies”

Some recent authors have studied sloshing frequencies of fluid in a container, but have ignored the well-established literature on the asymptotic structure of the modes of linear oscillations. The present discussion draws attention to the more efficient solution methods thus suggested and relates the results to known asymptotic forms.     

A single-product network design model with lead time and safety stock considerations

Most existing network design and facility location models have focused on the trade-off between the fixed costs of locating facilities and variable transportation costs between facilities and customers. However, operational performance measures such as service levels and lead times are what motivates customers to bring business to a company and should be considered in the design of a distribution network. While some previous work has considered lead times and safety stocks separately, they are closely related in practice, since safety stocks are often set relative to the distribution of demand over the lead time. In this paper we consider a two-stage supply chain with a production facility that replenishes a single product at retailers. The objective is to locate Distribution Centers (DCs) in the network such that the sum of the location and inventory (pipeline and safety stock) costs is minimized. The replenishment lead time at the DCs depends on the volume of flow through the DC. We require the DCs to carry enough safety stock to maintain the prescribed service levels at the retailers they serve. The explicit modeling of the relationship between the flows in the network, lead times and safety stocks allows us to capture the trade-off between them. We develop a Lagrangian heuristic to obtain near-optimal solutions with reasonable computational requirements for large problem instances.     

An efficient method for dynamic-demand joint replenishment problem with multiple suppliers and multiple vehicles

How to improve competitive edges to meet rapidly changing market environment and dynamic customer needs is critical for the survival and success of firms these days. A good supply chain and inventory management is a necessity in the intensive competitive market. This paper considers a dynamic-demand joint replenishment problem with multiple vehicle routing. The problem is first formulated as a mixed integer programming model with an objective to minimise total costs, which include ordering cost, purchase cost, production cost, transportation cost and holding cost, under a prerequisite that inventory shortage is prohibited in the system. A particle swarm optimisation model is proposed next to solve large-scale problems which are computationally difficult. A case study of a touch panel manufacturer is presented to examine the practicality of the models.     

A viewpoint on material and design considerations for oesophageal stents with extended lifetime

Journal of Materials Science - Oesophageal stents are meshed tubular implants designed to maintain patency of the oesophageal lumen and attenuate the symptoms of oesophageal cancer. Oesophageal...     

Scanning and surface alignment considerations in chemical imaging with desorption electrospray mass spectrometry

The effects of surface scanning mode (raster vs unidirectional scanning) and the constancy of spray tip-to-surface and atmospheric sampling interface capillary-to-surface distances on chemical image quality using desorption electrospray ionization mass spectrometry were investigated. Unidirectional scanning was found to provide a spatially and a quantitatively more precise chemical image of the surface as compared to raster scanning. Maintaining constant spray tip-to-surface and atmospheric sampling interface capillary-to-surface distances during an imaging experiment was found to also be critical. An automation process was implemented using a custom image analysis software (HandsFree Surface Analysis) to keep these distances constant during the surface sampling experiment. Improved chemical image quality afforded through this software control was illustrated by imaging printed objects on normal copy paper.