T.T. Wong

Experimental study of developing turbulent flow and heat transfer in ribbed convergent/divergent square ducts

Abstract The local heat transfer and pressure drop characteristics of developing turbulent flows of air in three stationary ribbed square ducts have been investigated experimentally. These are: ribbed square duct with constant cross-section (straight duct), ribbed divergent square duct and ribbed convergent square duct. The convergent/divergent duct has an inclination angle of 1°. The measurement was conducted within the range of Reynolds numbers from 10xa0000 to 77xa0000. The heat transfer performance of the divergent/convergent ducts is compared with the ribbed straight duct under three constraints: identical mass flow rate, identical pumping power and identical pressure drop. Because of the streamwise flow acceleration or deceleration, the local heat transfer characteristics of the divergent and convergent ducts are quite different from those of the straight duct. In the straight duct, the fluid flow and heat transfer become fully developed after 2–3 ribs, while in the divergent and convergent ducts there is no such trend. The comparison shows that among the three ducts, the divergent duct has the highest heat transfer performance, the convergent duct has the lowest, while the straight duct locates somewhere in between.

A study of wear resistance of plasma-sprayed and laser-remelted coatings on aluminium alloy

Abstract Two kinds of alloys Ni–Cr–B–Si and Ni–Cr–B–Si+WC were plasma sprayed onto aluminium alloy. The coatings were remelted successively with a CO 2 laser. A comparison of the wear resistance properties of both laser-treated and plasma-sprayed samples with those of aluminium alloy was conducted. A scanning electron microscope (SEM) was used to analyse wear phenomena of samples. Experimental results showed that the laser-treated and plasma-sprayed samples demonstrated, in general, good wear resistance. The laser remelted Ni–Cr–B–Si sample exhibited the highest wear resistance, and the laser remelted samples were much better than the as-sprayed samples. The plasma-sprayed Ni–Cr–B–Si+WC sample had better wear resistance than the sample without WC. However, the laser-treated Ni–Cr–B–Si+WC sample did not enhance its wear resistance compared with laser-treated Ni–Cr–B–Si sample. The worn surface analysis showed that the alloyed layer of the laser-treated samples was very compact, the worn surface was smooth and granular peeling was hardly observed. The worn surface of the plasma-sprayed sample was rather loose and there was granular peeling on the worn surface.

Microstructure and character of laser remelting of plasma sprayed coating (Ni-Cr-B-Si) on Al-Si alloy

Abstract In this paper, a plasma sprayed coating (Ni-Cr-B-Si) on an Al-Si alloy surface was remelted by a 5 kW CO 2 laser. Structure and chemical composition of different parts of the laser melted zone were investigated. Hardness distribution in the laser melted zone was measured. Experimental results showed that chemical composition of the sample is not a well-distributed gradient because there is compositional segregation in the laser melted zone. In the surface of the laser-melted zone, a concentration of aluminium exists; and there is a concentration of Fe, Cr and Ni in the sub-surface of this zone. Corresponding to chemical compositional segregation, a aluminium-rich phase Al 3 Ni emerges in the surface and the nickel-rich phases AlNi and AlNi 3 are found in the sub-surface. There are some amorphous regions with super-hardness in the sub-surface of the laser-melted zone. Owing to the tempering effect of laser scanning heat transfer, many nano-crystallites of AlNi 3 separate out from the amorphous structure. The hardness distribution in the laser-melted zone corresponds with the structure and solidification conditions. The highest hardness is in the amorphous and nano-crystallite regions. The higher hardness is in the Al + Al 3 Ni eutectic structure region that is in the rapidly solidified surface and is in the fine needle-like Al 3 Ni 2 structure region that is adjacent to the amorphous region. The thick needle-like Al 3 Ni 2 structure has lower hardness.

Neural-fuzzy modeling of plastic injection molding machine for intelligent control

Abstract Neural network and fuzzy logic reasoning can complement each other to form an integrated model which capitalizes on the merits and at the same time offsets the pitfalls of the involved computational intelligence technologies. This article presents a neural-fuzzy model which consists of a neural network for suggesting the change of process parameters, together with a fuzzy reasoning mechanism for acquiring modified parameter values based on the induced parameter values from the neural network. This model is particularly useful in parameter-based control situations where there may be multiple inputs and multiple outputs involved. This model, which serves to learn from sample data and allows to extract rules which are then fuzzified prior to fuzzy inference, is implemented for the dimensional control of injection molding parts, the dimensions of which are primarily determined by the molding process parameters such as injection time and cooling temperature.

Enhanced forced-convection from ribbed or machine-roughened inner surfaces within triangular ducts

An experimental investigation has been conducted to study the steady-state forced-convection heat-transfer characteristics of the hydrodynamic fully-developed turbulent flow in air-cooled horizontal equilateral triangular ducts (i.e. of 60° apex angle), which were each fabricated with the same length of 2.4 m and hydraulic diameter of 0.44 m. The inner surfaces of the triangular ducts were roughened by a milling process, shaping process or fixing uniformly-spaced parallel square ribs orthogonal to the mean air flow. The average surface roughness of the inner surfaces, which were produced by milling and shaping processes, were 3.0 and 11.5 [mu]m, respectively. The square-sectioned ribs, adopted to produce the roughened surface, had different protrusions of 6.35, 9.525 and 12.7 mm, and the uniform separation between the centre lines of two successive ribs was kept constant at 57.15 mm. Both the triangular ducts and the square ribs were fabricated out of duralumin. The experiments were performed with the hydraulic-diameter based Reynolds numbers ranging from 4000 to 15000. The entire inner wall of the duct was heated uniformly, while its outer surfaces were thermally well insulated. By comparing the heat-transfer performances with those of a smooth triangular duct (i.e. average inner-surface roughness of less than 1.0 [mu]m) having the same geometry, it was found that forced convection was enhanced by the roughened surfaces. In addition, a much enhanced forced convection was obtained by fixing uniformly-spaced parallel square ribs, rather than by fabricating random roughness on its inner surfaces by machining. However, the heat-transfer enhancement was not proportional to the rib size; the maximum forced convection heat-transfer augmentation was obtained using the smallest (i.e. 6.35 mm) ribs of those tested. Non-dimensional expressions for the determination of the steady-state heat-transfer coefficient of the equilateral triangular ducts, which were fabricated with the various kinds of artificial inner-surface roughness, were also developed.

Turbulent convection of air-cooled rectangular duct with surface-mounted cross-ribs

Abstract Experimental and numerical studies were conducted to investigate the forced convection and flow friction of a turbulent airflow in a horizontal air-cooled rectangular duct, with square-sectioned cross-ribs mounted on its bottom surface. Cross-sectional dimensions of the cross-ribs were 6.37 mmxa0×xa06.37 mm. Reynolds number of the fully turbulent flow was maintained constant at 12,380. Heat was supplied uniformly to the airflow via bottom surface of the duct only. Effects of varying the angle formed by the cross-ribs between 30° and 120° on the forced convection and flow friction were studied. It was found that an optimum angle corresponding to the highest heat transfer coefficient occurred between 60° and 70°. Computational predictions of forced convection and flow friction of the same rectangular duct mounted with cross-ribs were performed with the zonal k– e model, the stability-guaranteed second-order difference scheme and the block implicit method. A comparison with the experimental results indicated that a reasonably good agreement had been achieved. Existence of an optimum angle formed by the cross-ribs between 60° and 70° was also indicated, except the numerical predictions were lower than the experimental findings by approximately 2–10%. However, the flow friction had been slightly over-estimated by 2–11% with the numerical model. It was shown that forced convection could be enhanced sufficiently by mounting cross-ribs on the internal surfaces of a rectangular duct, especially when the optimum angle was used.

Wear resistance of laser-clad Ni–Cr–B–Si alloy on aluminium alloy

Using a 5 kW CO2 laser, two kinds of plasma-sprayed coatings, Ni‐Cr‐B‐Si and Ni‐Cr‐B‐SiaWC alloys, were remelted on aluminium alloy. The wear resistance of both laser-treated samples and plasma-sprayed samples were investigated using a pin-on-disc sliding friction wear tester. A scanning electron microscope (SEM) was used to analyse the abrasion phenomena of the samples and a transmission electron microscope (TEM) was used to study the microstructure of the laser-clad zone. Experimental results showed that the laser-clad samples had double the wear resistance of the plasma-sprayed samples, and that the laser-clad Ni‐Cr‐B‐Si sample exhibited the highest wear resistance. The results of wear surface analysis showed that the microstructure of the alloyed layer of the laser-clad samples was quite compact and the surfaces were also very smooth, and there was less peeling phenomenon of the granules. The microstrucutre of the plasma-sprayed sample was rather loose and there were a lot of granular peelings left on the worn surface. A study of the microstructure showed extensive amorphous and ultra-crystalline structures in the laser-clad zone, to which the increase in hardness and wear resistance may be attributed. # 2000 Elsevier Science S.A. All rights reserved.

Fulfillment of Retailer Demand by Using the MDL-Optimal Neural Network Prediction and Decision Policy

Prediction of demand plays a critical role in replenishment, in supply chain management. Accurate prediction of demand is a fundamental requirement and is also a great challenge to demand prediction models. This has motivated the research team to develop the minimum description length (MDL)-optimal neural network (NN) which can accurately predict retailer demands with various time lags. Moreover, a surrogate data method is proposed prior to the prediction to investigate the dynamical property (i.e., predictability) of various demand time series so as to avoid predicting random demands. In this paper, we validate the proposed ideas by a full factorial study combining its own decision rules. We describe improvements to prediction accuracy and propose a replenishment policy for a Hong Kong food wholesaler. This leads to a significant reduction in its operation costs and to an improvement in the level of retailer satisfaction.

Forced convection and pressure drop in a horizontal triangular-sectional duct with V-grooved (i.e. orthogonal to the mean flow) inner surfaces

An experimental investigation has been performed to study the forced convection and pressure-drop characteristics fully-developed steady turbulent flows in air-cooled, horizontal, equilateral-triangular ducts. These ducts were constructed of duralumin, each of the same axial length and hydraulic diameter. The inner surfaces of each duct were either plane or machined with uniformly-spaced parallel, identical V-grooves. For each tested duct, these grooves had a depth of 1 mm, but were all of the same apex angle, [theta], where 0[less-than-or-equals, slant][theta]

Incorporating machine intelligence in a parameter-based control system: a neural-fuzzy approach

Abstract The capabilities of the two computational intelligence technologies including neural network and fuzzy logic can be synergized through the formation of an integrated and unified model which capitalizes on the benefits and concurrently offsets the flaws of the involved technologies. In this paper, a neural-fuzzy model, which is characterized by its ability to suggest the appropriate change of process parameters in a relatively complex parameter-based control situation involving multiple parameters, is presented. This model is particularly useful in multiple input and multiple output situations where complex mathematical calculations are required if conventional control approach is adopted. In particular, it serves to acquire knowledge from the information base for extracting rules, which are then fuzzified based on fuzzy principle. To validate the feasibility of this approach, a test has been conducted based on the neural-fuzzy model with the objective to achieve heat transfer enhancement in rectangular ducts using transverse ribs. This paper describes the roadmap for the deployment of this hybrid model to enhance machine intelligence of a complex system with the description of a case study to exemplify its underlying principles.