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

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

Hydrodynamics investigation of pepper drying in a swirling fluidized bed dryer with multiple-group twisted tape swirl generators

The present work aims to investigation the behavior of drying peppers in a swirling fluidized bed dryer (S-FBD) fitted with multiple twisted tape swirl generators. A multiple-group twisted tape swirl generator was located at the air inlet at the bottom of the bed. The effects of the superficial air velocity (U*=U/Umf = 1.0, 1.1 and 1.2) on the moisture content (MC), moisture content ratio (MR) and drying rate (DR) were examined. The experimental results showed that the S-FBD can reduce the moisture content of peppers more rapidly than a conventional fluidized bed dryer (FBD). The S-FBD gave a higher DR and decreased drying time compared to that of a FBD. The results also indicated that operation at higher superficial air velocities resulted in a greater DR, especially at the beginning stage of the drying process. For the S-FBD, the reduced of MC, MR and DR at a high superficial air velocity (U*=U/Umf = 1.2) was better than at low superficial air velocities (U* = 1.0 and 1.1). Furthermore, five different drying models were evaluated to predict the performance of the S-FBD. Keywords: Drying, Swirl flow, Conventional fluidized bed dryer (FBD), Drying rate (DR), Swirling fluidized bed dryer (S-FBD), Peppe

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

Multi-Objective Optimization of Tio2-Water Nanofluid Flow in Tubes Fitted With Multiple Twisted Tape Inserts in Different Arrangement

In this paper, experimentally derived correlations of heat transfer and pressure drop are used in a Pareto based Multi-Objective Optimization (MOO) approach to find the best possible combinations of heat transfer and pressure drop of TiO2-water nanofluid flow in tubes fitted with multiple twisted tape inserts in different arrangement. In this study there are four independent design variables: the number and arrangement of twisted tape inserts (N), TiO2 volume fraction (φ), Reynolds number (Re) and Prandtl number (Pr). Seven twisted tape arrangement in three different categories are investigated. The objectives are maximizing the non-dimensional heat transfer coefficient (Nu) and minimizing the non-dimensional pressure drop (f Re). It is shown that some interesting and important relationships as useful optimal design principles involved in the thermal performance of nanofluid flow in tubes fitted with multiple twisted tape inserts in different arrangement can be discovered by Pareto based multi-objective optimization approach

Performance Assessment in a Heat Exchanger Tube with Opposite/Parallel Wing Twisted Tapes

The thermohydraulic performance in a tube containing a modified twisted tape with alternate-axes and wing arrangements is reported. This work aims to investigate the effects of wing arrangements (opposite (O) and parallel (P) wings) at different wing shapes (triangle (Tri), rectangular (Rec), and trapezoidal (Tra) wings) and on the thermohydraulic performance characteristics. The obtained results show that wing twisted tapes with all wing shape arrangements (O-Tri/O-Rec/O-Tra/P-Tri/P-Rec/P-Tra) give superior thermohydraulic performance and heat transfer rate to the typical twisted tape. In addition, the tapes with opposite wing arrangement of O-Tra, O-Rec, and O-Tri give superior thermohydraulic performances to those with parallel wing arrangement of P-Tra, P-Rec, and P-Tri around 2.7%, 3.5%, and 3.2%, respectively