In this paper, the effect of a fixed twisted-tape placed in the inner tube of a double-pipe heat exchanger is investigated using numerical simulation. A twisted-tape with three and four blades with different twist ratios is placed in the inner tube of the heat exchanger, and the Nusselt number, friction coefficient, and overall performance coefficient of the heat exchanger are studied. The flow velocity in the outer tube is considered constant, but the Reynolds number of the flow at the inlet of the inner tube is changed in the range of 5000 to 12000. The results showed that in all cases, placing a twisted-tape inside increases the Nusselt number and friction coefficient. The highest increase of these two parameters is 244 and 490 percent, respectively. By increasing the Reynolds number, the friction coefficient and the overall performance coefficient decreased, while the Nusselt number increased. This increase reaches about 80% in the case that has a twisted-tape with a twist ratio of 4. Also, reducing the twist ratio increases the turbulence of the flow and thus increases the Nusselt number, pressure drop, friction coefficient, and the overall performance coefficient. The maximum increase in the friction coefficient due to the reduction of the twist ratio from 8 to 4 was equal to 43%, occurred in the Reynolds number of 5000 and the three-bladed twisted-tape. Increasing the number of blades of the twisted tape has a direct effect on the pressure drop and friction coefficient and causes a decrease in the overall performance coefficient.

In this study, forced convective heat transfer characteristics of /water nanofluid flowing through a double pipe heat exchanger with plain twisted tape and cut twisted tape inserts is investigated experimentally to reveal the effect of cut twisted tape and nanofluid concentration on heat transfer. Experiments are conducted in a turbulent flow regime with Re number ranging from 4000-34000 and in the particle volume concentration range of 0<φ<0.1%.The results of thermal studies showed enhancement of convective heat transfer with nanofluids compared with flow of water. Also it was found that in higher Reynolds numbers the nanofluid has better heat transfer capability. The effects of twisted tape with and without cuts on edges on heat transfer coefficient and rate were investigated. It was found that the twisted tape with cut edges could enhance heat transfer rate better than twisted tape without cut edges. The pressure drop was investigated for flow of nanofluid and water. The results showed that there is a little difference between pressure drops in these cases. Friction factor and pressure drop in tube with plain twisted tape and cut twisted tape inserts are increased due to increasing flow resistance and contact surface between fluid and flow passage.

Inactive methods of enhancing heat transfer in the shell and tube heat exchangers, such as using micro-fins and helically coiled tubes and employing nanofluids as the working fluid, are investigated experimentally. Experiments are carried out to measure the pressure drop and the heat transfer coefficient of the Al2O3-water nanofluid flowing in the shell and helically coiled micro-finned as well as smooth tube heat exchangers. The performed experiments are for the Dean number ranging from 500 to 4000, the fin helix angle between 18 and 25º, and the nanofluid volume fractions of 0, 0.5 1%. The overall heat transfer coefficients of the heat exchangers are calculated using the Wilson plot method. Empirical correlations are proposed for the heat transfer coefficient of nanofluid through the tube-side in terms of the Dean number, the fin helix angle, the fin height and the volume fraction of nanofluid. Based on the experimental results, the microfining of the coiled tube and increasing the microfin helix angle and using nanofluid enhance the heat transfer and increase the pressure drop.

In order to study the tendency of amino acid neighbors in helical structures, proteins with known structures were carefully analyzed. The studied helical positions: N, Ncap, N1, N2, N3, N4, M, C4, C3, C2, C1, Ccap, C and their doublet counterparts: N Ncap, NcapN1, N1N2, N2N3, N3N4, M1M2, M2M3, C4C3, C3C2, C2C1, C1Ccap, CcapC were carefully analyzed. The propensity for all amino acids in different helical positions and also the propensity for all 400 different doublet positions were calculated and compared. For this purpose, a databank of 3705 helices was designed and used. In this database helices were longer than 7 amino acid residues and were derived from 696 non-homologous proteins with less than 25% identity. SLP(Single Local Propensity) for each 20 amino acid in different helical positions was calculated. Furthermore, DLPo or the observed Doublet Local Propencity which is based upon prefered occurrence of paired amino acids in different doublet positions of alpha helices and DLPe or the expected Doublet Local Propensity calculated directly using SLPs was also calculated. If the propensity of a particular doublet in a specific alpha helical positon or DLPo becomes more than the calculated single positions in alpha helices, in other words, DLPo>>DLPe it indicates that this particular doublet has a tendency in staying as neighbors in that particular helical position. Results showed that doublets in which DLPo>>DLPe are as follows: Met-Thr for N’Ncap position, Glu-Pro in NcapN1, Pro-Arg at N1N2, Lys-His in C2C1, Thr-Gly in C1Ccap, and Gln-Pro in CcapC’. It was also seen that Gly in Ccap position has a tendency to neighbor on a hydrophobic amino acid at C’ position. Studying the tendency of amino acids in neighboring each other in alpha helices can be used in designing novel helical structures and can also be used in modifying existing helical structures in proteins.

The objective of this paper is to experimentally investigate the effects of Shchelkin spiral geometry in the transition from deflagration to detonation on the quality of the produced detonation. Deflagration to detonation transition (DDT) is required in cases where ignition energy release is less than the critical ignition energy required for a direct detonation initiation. A stoichiometric mixture of hydrogen–oxygen has been used in a tube of 25 mm diameter and 700 mm length. Spiral coils have been mounted at the ignition-end of the tube to facilitate DDT. Keeping spiral coil diameter fixed at 22mm, the coil length, pitch and thickness were varied to produce desirable detonation waves. Spiral coil selection was based on several criteria including; the pressure and velocity jump across the wave at the beginning of the tube, and the percentage of successful tests in each batch. The results indicate that the spiral coil pitch has the greatest influence on minimizing the DDT length and obtaining a desirable detonation.

One of the main problems in SWATH ship is the excessive increase of the wet surface due to the presence of the hulls below. Increasing the wet surface increases the resistance force and as a result the use of powerful engines in this type of ship. The purpose of this paper is to investigate the effect of spiraling the lower bodies and its effect on reducing the resistance force in a completely submerged state. In this paper, first, the effect of spiraling the lower bodies using a numerical method is compared. After proving the effectiveness of the proposed method, various parameters of the spiral body such as spiral depth, spiral length and rotation angle were examined. By integrating the optimized state of each of the parameters, a new spiral body was presented in which the resistance force was significantly reduced compared to the initial state.By reducing fuel consumption by spiraling submerged hulls, a new step will be taken to optimize Swath vessels.

Ash content of concentrates of cyclone-spiral units at the Zarand coal washing plant was higher than the allowable limit (11%) mainly. The main reason was due to the presence of particles smaller than 150 µm containing high amount of ash. The removal of this size fraction by installing a screen with aperture of 0. 5 mm increased the quality of the concentrate. The stream passing the screen (removed fraction) used to be sent to the cyclone-spiral unit at the flotation section for further processing. Since the spiral concentrate of this unit had low quality (ash content of 18%) it was sent to the screening unit. The under screen stream used to be sent again to the cyclone-spiral unit at the flotation section. This procedure created a non-beneficial circulating load with the amount of 56% of the spiral concentrate. By modification in the dewatering process، this amount was reduced to 5%. In order to increase the quality of the final concentrate، a two-stage separation unit where the spiral concentrate instead of entering the screening unit was fed to another spiral was installed. Finally، by determining optimum values of 40 for solids concentration and 2 t/h for the feed to spiral، the amount of final concentrate and capacity were increased by 11 and 14 t/h، respectively. Furthermore، the final spiral concentrate ash decreased from 18 to 11%.

The increasing rate of construction activities in urban areas is accompanied by excavation in the vicinity of existing structures and urban utilities. This issue has highlighted the importance of constructing protecting structures in order to control displacements and prevent damage to structures and their neighboring area. Among the important widely used wall stabilization techniques, one can name nailing and grouted anchors. However, these methods suffer some drawbacks such as annoying noise and vibration during the drilling, implementation difficulties below the water table, grouting problem, installation of strands and bars in the borehole in porous and collapse soils, and long curing time for the grout of post-tension anchors. Since the helical anchor method lacks many of the mentioned problems, it is now widely used in many applications.In the present work, a laboratory model of helical anchor stabilized wall is presented and evaluated. For this purpose, four types of anchors at 20° back slope are designed in a sandy soil and the effect of helix configuration (in term of its diameter and number of blades) is investigated. Considering the laboratory scale of the designed model, the results obtained using helical anchor were compared with numerical results of soil nailing wall by applying the particle image velocimetry (PIV) analyses.

The test box designed in this work is made of a metal plate with a thickness, length, width, and depth of 1.5 mm, 100 cm, 60 cm, and 30 cm, respectively, and a Plexiglas in its opposing side with a thickness of 50 mm. The soil used in the experiments was the dry sand of Soufian region in east Azerbaijan province of Iran. The soil is classified as SP according to USCS classification. The helical anchors were fabricated by welding the helical pitches to a metal shaft. The end part of the shafts is screw threaded such that to fasten a bolt to them. To start the experiment, the empty box was completely cleaned using the detergents to remove any pollution or soil on the Plexiglas and metal surface. Afterward, the sandy soil was poured on the wall floor and the facing was placed inside the box vertically. Again, the sandy soil was poured from both sides of the facing up to the installation height of the helices. Helices were installed in the assigned holes and their angle was adjusted through the pre-fabricated stencils. The soil height was increased up to the next row assigned for helices installation. These steps were repeated until reach the wall crest. After preparation of the physical model, its behavior during the preparation must be modeled. We first filled both sides of the model and then modeled the stability behavior of the helical anchor wall through excavating its facing opposed side. Overall, the wall was built through eight excavation steps.

The maximum displacement is related to the anchor type 1, which does not have enough bearing capacity under surcharge conditions. By changing the anchor type and increasing the number of helices, shear strains and their expansion in the wall back decline. The decrease in displacement rate by changing the anchor from type 1 to type 2 is 18%, which is due to the low bearing capacity of type 2 anchor compared to the type 1 anchor. Increasing the number of pitches from one to two (changing the type 1 anchor to type 3 anchor) showed a considerable decrease (i.e., 43%) in displacement rate. Increasing the number of pitches from 1 to 3 (changing the anchor from type 1 to type 3) resulted in a 62% decrease in wall crest displacement. This displacement decrease rate seems to decline with an increase in the number of helixes.The displacement rate for all four anchors is almost similar in two excavation steps, which probably is because of the need for displacement for activation of the anchors. One strategy to deal this issue in the sensitive projects and control the displacement is to apply post-tension helical anchors. Then, in stages 4 to 6, the displacement was almost constant due to four main reasons including wall rigidity, the presence of reinforcements, formation of pre-step displacement-induced tension force, and enough capacity of anchors to face with more displacement. In stages 6 to 8, type 1 and 2 anchors showed growing displacements due to the reduction and ending the wall rigidity and lower bearing capacity. In type 3 and 4 anchors, the maximum displacement was related to 4 initial stages. In type 1 and 2 anchors, which have two helical plates, almost a similar behavior was observed until stage 6 of excavation, but eventually type 3 anchors showed better performance because of higher bearing capacity to overall displacement.

In the present study, a physical model was designed to investigate the effect of helical anchors’ geometry on displacement rate of helical anchor wall and compare it with a nail wall. Overall, comparing the results obtained by conducting these experiments on a helical anchor stabilized wall and a nail wall revealed that:- Wall crest displacement is affected by the diameter and number of helices and decreases by an increase in bearing capacity. The increase in the number of pitches from one to two (single-pitch to double-pitch anchor) has a higher effect on displacement control compared to the case of changing the double-pitch to triple-pitch anchor. So, it can be stated that a further increase in the number of anchor pitches results in a declined performance of the anchors. All anchors need a slight displacement for activation. This issue cannot be resolved by changing the type of helical anchors. Hence, when the displacement required for activation of the anchors exceeds the allowable wall crest displacement, use of post-tensioned helical anchors is recommended.A comparison between nailing and helical anchor results revealed that the relative density of the wall stabilized with the helical anchor is less than that of the nail wall; and wall crest displacement in the helical anchor wall was very lower than that of nail wall. Thus, the helical anchor wall stabilization is preferred when other economic and technical requirements are met.

In today’s world, roads are considered the main arteries of the global community. One of the most typical methods to build these routes is stabilizing the excavations on two sides of the roads. Using multiple helical anchors in excavation stabilization is one of the means recently used by many road and geotechnical engineers. The increasing use of multiple helical anchors has led to several laboratories, numerical, and field studies. Therefore, this study employed the FLAC 3D software also a three-dimensional numerical investigation of bearing capacity under different inclination angles in sandy soil. In the present study, the effect of soil installation, which is caused by installing helical anchors in the soil, has been studied on the load-bearing capacity of these helical anchors. For this purpose, first, a verification test is done to validate the modeling approach. Then, by performing a parametric analysis, the effect of different inclination angles, as well as the installation effect on the bearing capacity of the multiple helical anchors, are studied. The present study results show that the maximum bearing capacity of the helical anchors is achieved by the angle of 5 and 10 degrees. In addition, by investigating the installation effect, the bearing capacity of the helical anchors has been significantly reduced with respect to the number of helical plates and the density of soil.

In this research, hydrothermal performance of boehmite alumina nanofluid based on water in a cylindrical heat sink with helical minichannels is investigated numerically. The design factors were selected at four levels including the helix angle of minichannels, the Reynolds number, the nanoparticles shape and volume fraction of nanoparticles. To perform sensitivity analysis of design factors, the Taguchi method with L16 orthogonal array and statistical analysis of variance are used.The Nusselt number, the Fanning friction factor and the total thermal performance factor were computed as the output parameters. The obtained results showed that the helix angle of minichannels and the nanoparticles shape have a vital role in the Nusselt number and the Fanning friction factor with the sum of the contribution ratios of the two factors 85.21% and 96%, respectively. Also, the helix angle of minichannels has a 47.93% contribution in the total thermal performance factor.The optimal combination for the Nusselt number and the total thermal performance factor is acquired as A1B4C4D4. Overall, the helical minichannel with boehmite alumina nanofluid can be useful as a preferred cooling for the cylindrical heat sources.