Effect of perforated twisted-tapes with parallel wings on heat tansfer enhancement in a heat exchanger tube

AbstractThis article reports an experimental investigation on heat transfer and pressure drop characteristics of turbulent flow n a heating tube equipped with perforated twisted tapes with parallel wings (PTT) for Reynolds number between 500 and 20500. The design of PTT involves the following concepts: (1) wings induce an extra turbulence near tube all and thus efficiently disrupt a thermal boundary layer (2) holes existing along a core tube, diminish pressure losswithin the tube. The parameters investigated were the hole diameter ratio (d/W = 0.11, 0.33 and 0.55) and wing depthratio (w/W = 0.11, 0.22 and 0.33). A typical twisted tape was also tested for an assessment. Compared to the plain ube, the tubes with PTT and TT yielded heat transfer enhancement up to 208% and 190%, respectively. The valuation of overall performance under the same pumping power reveal that the PTT with d/W = 0.11 and w/W = .33, gave the maximum thermal performance factor of 1.32, at Reynolds number of 5500. Empirical correlations of he heat transfer, friction factor and thermal performance for tubes with PTTs were also developed. In addition, the wirling/axial flow patterns of tube with PTT were visualized using dye injection technique

Assessment, Management and Future Directions for Coastal Fisheries in Asian Countries

Abstract The biomass of 40 ecological groups, the diet composition of prey and predators, production/biomass (P/B) and consumption/biomass (Q/B) ratios, and catches were used as basic input to parameterize an Ecopath model of the Gulf of Thailand. Following construction of a mass-balance ecosystem model, a time-dynamic simulation model (Ecosim) was used to simulate the impact of change in fishing effort. This was done using time series data to validate the historic fisheries development in the Gulf of Thailand prior to using the model for forward-looking simulations. The time series data used in the analyses were catch and effort data from research vessel trawl surveys and landings data for six groups of fishing gear operating in the Gulf during the period 1973 to 1993. The fish market price and fixed and variable costs of each fleet (as well as profit) were also used as input for the time-series simulations using Ecosim. The results depict changes in biomass and trophic interactions in time (Ecosim) and space (Ecospace). The model was also used to investigate management options or measures for the fisheries of the Gulf of Thailand. Recommendations for future studies using Ecopath with Ecosim are also presented

Elevation of the Yields of Very Long Chain Polyunsaturated Fatty Acids via Minimal Codon Optimization of Two Key Biosynthetic Enzymes

Eicosapentaenoic acid (EPA, 20:5Δ5,8,11,14,17) and Docosahexaenoic acid (DHA, 22:6Δ4,7,10,13,16,19) are nutritionally beneficial to human health. Transgenic production of EPA and DHA in oilseed crops by transferring genes originating from lower eukaryotes, such as microalgae and fungi, has been attempted in recent years. However, the low yield of EPA and DHA produced in these transgenic crops is a major hurdle for the commercialization of these transgenics. Many factors can negatively affect transgene expression, leading to a low level of converted fatty acid products. Among these the codon bias between the transgene donor and the host crop is one of the major contributing factors. Therefore, we carried out codon optimization of a fatty acid delta-6 desaturase gene PinD6 from the fungus Phytophthora infestans, and a delta-9 elongase gene, IgASE1 from the microalga Isochrysis galbana for expression in Saccharomyces cerevisiae and Arabidopsis respectively. These are the two key genes encoding enzymes for driving the first catalytic steps in the Δ6 desaturation/ Δ6 elongation and the Δ9 elongation/Δ8 desaturation pathways for EPA/DHA biosynthesis. Hence expression levels of these two genes are important in determining the final yield of EPA/DHA. Via PCR-based mutagenesis we optimized the least preferred codons within the first 16 codons at their N-termini, as well as the most biased CGC codons (coding for arginine) within the entire sequences of both genes. An expression study showed that transgenic Arabidopsis plants harbouring the codon-optimized IgASE1 contained 64% more elongated fatty acid products than plants expressing the native IgASE1 sequence, whilst Saccharomyces cerevisiae expressing the codon optimized PinD6 yielded 20 times more desaturated products than yeast expressing wild-type (WT) PinD6. Thus the codon optimization strategy we developed here offers a simple, effective and low-cost alternative to whole gene synthesis for high expression of foreign genes in yeast and Arabidopsis

Numerical investigation of turbulent swirling flows through an abrupt expansion tube

A numerical investigation of turbulent swirling flows through an abrupt expansion tube is reported.  The TEFESS code, based on a staggered Finite Volume approach with the standard k-ε model and first-order numerical schemes built-in, was used to carry out all the computations. The code has been modified in the present work to incorporate the ASM and two second-order numerical schemes.  The ASM, which includes the non-gradient convection terms arising from the transformation from Cartesian to cylindrical coordinates, was investigated for isothermal flows by applying it to the flow through an abrupt expansion tube with or without swirl flows.  In addition, to investigate the effects of numerical diffusion on the predicted results, two second-order differencing schemes, namely, second-order upwind and the quadratic upstream interpolation, were used to compare with the first-order hybrid scheme.  An abrupt expansion tube with non-swirling flow, predicted results using both the k-ε model and the ASM were in good agreement with measurements.  For swirling flows, the calculated results suggested that the use of the ASM with a second-order numerical scheme leads to better agreement between the numerical results and experimental data, while the k-ε model is incapable of capturing the stabilizing effect of the swirl

Numerical investigation of turbulent swirling flows through an abrupt expansion tube

A numerical investigation of turbulent swirling flows through an abrupt expansion tube is reported.  The TEFESS code, based on a staggered Finite Volume approach with the standard k-ε model and first-order numerical schemes built-in, was used to carry out all the computations. The code has been modified in the present work to incorporate the ASM and two second-order numerical schemes.  The ASM, which includes the non-gradient convection terms arising from the transformation from Cartesian to cylindrical coordinates, was investigated for isothermal flows by applying it to the flow through an abrupt expansion tube with or without swirl flows.  In addition, to investigate the effects of numerical diffusion on the predicted results, two second-order differencing schemes, namely, second-order upwind and the quadratic upstream interpolation, were used to compare with the first-order hybrid scheme.  An abrupt expansion tube with non-swirling flow, predicted results using both the k-ε model and the ASM were in good agreement with measurements.  For swirling flows, the calculated results suggested that the use of the ASM with a second-order numerical scheme leads to better agreement between the numerical results and experimental data, while the k-ε model is incapable of capturing the stabilizing effect of the swirl

Characterization of heat transfer and artificial neural networks prediction on overall performance index of a channel installed with arc-shaped baffle turbulators

Influences of baffle pitch ratio (p/w) and attached angle of arc-shaped baffles (AB) on the overall performance index (OPI) of a channel installed with AB have been carefully studied. In addition, an artificial neural network (ANN) model for predicting the OPI of the channel was reported. The arc-shaped baffle (AB) showed a significant effect on the augmented heat transfer and friction loss penalty as compared to a smooth channel. As the attached arc shaped angle (θ) increased, both Nusselt number and friction factor intensified. The Nusselt number values at θ = 90° were higher than those at θ = 20°, 40°, 60°, and 80° by up to 5.8%, 3.9%, 2.3% and 2.5%, respectively. The Nusselt number increased when the p/w was raised from 4.0 to 8.0 while the opposite trend was observed when the p/w was raised from 8.0 to 12.0. The maximum OPI of 1.43 was achieved by using the baffles with θ = 90° and pitch ratio of 8.0 at Re = 4000. For the development of ANN models for predicting the OPI, it was found that the best predictive performance was (R2) of 0.99843407 for ANN model of 3-50-50-1 with Tanh-Tanh activation function at epoch of 1200

Thermal and fluid flow characteristics in a tube equipped with peripherally-cut dual twisted tapes

This article presents an experimental analysis of the turbulent flow of water in a heat exchanger tube fitted with peripherally-cut dual twisted tapes (PDTs) under a constant wall heat-flux condition. The peripherallycut dual twisted tapes with different cutting pitch ratios (l/y = 0.5, 0.75 and 1.0) were tested for Reynolds numbers in the range of 5400 to 14,000. The experimental results showed thatNusselt number and friction factor of the tubes fitted with PDTswere considerably higher than those of the plain tube and those of the tubes with single twisted tape (ST) and dual twisted tapes (DTs). It was found that PDTs with l/y = 0.5, 0.75 and 1.0 gave higher heat transfer rate than the typical DTs, with average Nusselt numbers greater by 12.1%, 7.8% and 3.8%, respectively. For the range investigated, PDTs with the smallest l/y ratio offered the highest thermal performance factor of 1.14