Numerical Investigation of Thermal Hydraulic Performance of Printed Circuit Heat Exchanger of Periodic Diamond Channel Shape

One of the most recently important heat exchangers is the Printed circuit heat exchanger especially in the nuclear power plant and aerospace applications due to its very compact geometry and small print foot. This paper presents a 3D numerical investigation on the thermo-hydraulic performance of PCHE with new non-uniform channel design configuration. The new channel design is a rectangular cross section with repeated converging diverging sections or periodic diamond shape. The influence of three design parameters on the heat exchanger performance was studied and optimized, pitch length (p), length ratio (β) and the converging diverging angle (α). The computational models investigated in this study based on the operating conditions of the intermediate heat exchanger of very high temperature gas cooled reactor with helium as the working fluid under operating pressure of 3Mpa and inlet temperature of 800 K. The Reynolds number varied from 200 to 2000. Different Pitch lengths were used (1.59, 3.18, 6.36, and 12.73) mm, and different C-D angle (0, 4.5, 6, 7.5, 9, 10.5 and 12) and also different length ratios were used (0.2, 0.25 and 0.333). Three performance parameters were studied the Nusselt number, friction factor and the overall performance evaluation factor. Results show that the thermal performance enhanced with decreasing the pitch length and with increasing C-D angle and it was shown that this enhancement was found only at high Reynolds number above 1400. The best performance obtained at p=3.18, α=6 and β=0.25 based on the overall evaluation performance.

Research on Tool Presetting and Tool Deviation in CNC Lead Screw Grinding Process

In the process of tool presetting for an CNC lead screw grinding, when A-axis rotating and Z-axis shifting synchronously according to the screw pitch length, L, of the lead screw workpiece, the handwheel corresponding to X-axis and Z-axis, respectively, is operated to align the grinding wheel with the middle of the screw groove. Then, the coordinates of Z-axis, A-axis and X-axis of the current position are recorded, and the coordinates of the grinding start position and grinding end position of the lead screw workpiece are calculated accordingly.However, due to the mutual following error of Z-axis and A-axis in the synchronous movement process, tool deviation typically occurs when the grinding wheel moves from the grinding start position to the grinding end position to grind the lead screw workpiece. More specifically, the grinding wheel slightly deviates from the middle of the screw groove to the left or right of the screw groove.To offset this deviation, the root cause for creating the deviation is analyzed, and a method to correct the tool deviation is proposed: First, the CNC system sends out grinding instructions, according to the requirements of grinding process, to make the A-axis and the Z-axis move synchronously. In the meantime, the CNC system measures and records the current coordinates of A-axis and Z-axis, and calculates the tool deviation caused by the mutual following error between Z-axis and A-axis. As a result the grinding start position and the grinding end position are adjusted in light of the value of tool deviation in the subsequent grinding process, so as to address the tool deviation issue.

Study of patterned GaAsSbN nanowires using sigmoidal model

This study presents the first report on patterned nanowires (NWs) of dilute nitride GaAsSbN on p-Si (111) substrates by self-catalyzed plasma-assisted molecular beam epitaxy. Patterned NW array with GaAsSbN of Sb composition of 3% as a stem provided the best yield of vertical NWs. Large bandgap tuning of ~ 75 meV, as ascertained from 4 K photoluminescence (PL), over a pitch length variation of 200–1200 nm has been demonstrated. Pitch-dependent axial and radial growth rates show a logistic sigmoidal growth trend different from those commonly observed in other patterned non-nitride III–V NWs. The sigmoidal fitting provides further insight into the PL spectral shift arising from differences in Sb and N incorporation from pitch induced variation in secondary fluxes. Results indicate that sigmoidal fitting can be a potent tool for designing patterned NW arrays of optimal pitch length for dilute nitrides and other highly mismatched alloys and heterostructures.

Enhancement of Mixing Performance of Two-Layer Crossing Micromixer through Surrogate-Based Optimization

Optimum configuration of a micromixer with two-layer crossing microstructure was performed using mixing analysis, surrogate modeling, along with an optimization algorithm. Mixing performance was used to determine the optimum designs at Reynolds number 40. A surrogate modeling method based on a radial basis neural network (RBNN) was used to approximate the value of the objective function. The optimization study was carried out with three design variables; viz., the ratio of the main channel thickness to the pitch length (H/PI), the ratio of the thickness of the diagonal channel to the pitch length (W/PI), and the ratio of the depth of the channel to the pitch length (d/PI). Through a primary parametric study, the design space was constrained. The design points surrounded by the design constraints were chosen using a well-known technique called Latin hypercube sampling (LHS). The optimal design confirmed a 32.0% enhancement of the mixing index as compared to the reference design.

HELIOTRON MAGNETIC SYSTEM OF A FUSION NEUTRON SOURCE

Numerical calculations have been carried out on magnetic field of heliotron magnetic system with a region of stellarator and mirror-type magnetic field superposition. Formation of a region of magnetic field superposition takes place in the gap between two helical coil sections which have reduced pitch length L in comparison with pitch length L0 of the heliotron helical coils, L=L0/3.

Manipulating the Pitch Size Constrains the Players’ Positioning during Unbalanced Soccer Small-Sided Games Played by Different Age Groups

We aim to investigate the impact of variable soccer pitch sizes on the position of players during unbalanced small-sided games (SSGs) and compare the responses of players from two different age groups. Forty-eight young players (n = 24 under-13 and n = 24 under-14) took part in the study and played 3 vs. 3 + 1 SSGs on two different pitch sizes (smaller: 36 x 27 m / 139m2 per player; and larger: 40 x 29 m / 166 m2 per player). Players’ positions on the pitch (length, width, length-to-width ratio, stretching index, and spatial exploration index) were assessed by the positional data provided by global position system devices and were compared within age groups and between game formats using a two-way analysis of variance. Results showed higher values of spatial exploration index in the larger SSGs than in the smaller format (p<.001). Moreover, a higher length (p<0.001) and length-to-width ratio (p<.001) was observed in the younger group. Finally, the larger format presented higher values of SEI and stretching index, independent of the age group (p<.001). In the smaller format, U-14 players presented a higher stretching index, while in the larger format U-13 players presented higher values in the same variable. We conclude that enlarging the pitch size constrains players’ behaviour during SSGs, and older players are more able to deal with this more complex task context than younger ones.

Numerical study on the impact of particles filling pattern and screw parameters on the mixing uniformity of wheat grains in a screw mixer

The presence of moisture content in a silo makes the preservation of a grain stock challenging especially when dealing with a large stock. This made it as a major concern for engineers to preserve large crops of grains and avoid huge losses. By installing a screw inside of a silo, the moisture problem could be avoided by stirring the loaded granular bed alongside aeration, also it could be effective to mix different types of loaded materials. The present work has sought to develop predictive models of discrete element method for mixing uniformity assessment when mixing wheat granules in a hopper-bottom screw mixer. The different factors being investigated are: initial configuration of particles, screw rotational direction, screw pitch length, screw diameter and screw rotational velocity. Findings regarding bed homogeneity were calculated using the nearest neighbor’s method. The best mixture was obtained when considering a side-wise filling type of particles ahead mixing and using a 20 mm screw diameter, 30 mm screw pitch and rotating the screw at 80 rpm speed.