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The quality of the proton beam produced by target normal sheath acceleration (TNSA) with high-power lasers can be significantly improved with the use of helical coils. While they showed promising results in terms of focusing, their performances in terms of the of cut-off energy and bunching stay limited due to the dispersive nature of helical coils. A new scheme of helical coil with a tube surrounding the helix is introduced, and the first numerical simulations and an analytical model show a possibility of a drastic reduction of the current pulse dispersion for the parameters of high-power-laser facilities. The helical coils with tube strongly increase bunching, creating two collimated narrow-band proton beams from a broad and divergent TNSA distribution. The analytical model provides scaling of proton parameters as a function of laser facility features.

Moving the load peak to consume electrical power is valuable in air conditioning systems. Consequently, the current study presents an experimental thermal investigation of an ice storage system. For this purpose, a twin concentric helical coil (TCHC) is utilized. The coil is submerged in distilled water in an insulated tank. The main aim is to explore the effect of geometrical/operating conditions for the TCHC on percentage energy stored/regained, solidified/melted mass fraction, and average charging/discharging rate. The main parameters are twin coil pitch and tube diameter while keeping the cold heat transfer fluid (HTF) inlet conditions at −12 °C and 10 L/min. The results disclosed that the discharge time increases by about 79% for total energy gained as the coil pitch rises from 30 to 50 mm at a smaller tube diameter of 9.52 mm. At the same time, the discharge time is doubled when the tube diameter is 15.88 mm. Furthermore, the complete solidification needs half the time (time reduced to 50%) to be achieved as the tube diameter increases from 9.52 mm to 15.88 mm (68% increases in diameter) for lower pitch (P = 30 mm).

To effectively enhance the heat transfer of a tube-in-tube helical coil heat exchanger, a novel internal and external-corrugated tube-in-tube helical coil was proposed by improving both the inner and outer tubes. The impact of the corrugation layout on the annular region’s heat transfer property was simulated. The effect of periodically distributed corrugations on flow patterns and the local Nusselt on the inner tube wall was explored. Furthermore, by comparing the fluid’s velocity and temperature field contour in traditional helical coil and novel helical coil, the enhanced heat transfer mechanism was discovered. Finally, the effects of Re, dimensionless depth H, and dimensionless pitch S of corrugations on the annular region’s heat transfer, flow resistance and entropy generation were analyzed. The results showed that annular region’s heat transfer could be improved due to the periodically distributed corrugations. The local Nu distribution on the corrugated inner tube wall was similar to that of ordinary inner tube, while changed periodically due to the continuous influence of corrugations. The number of Nu and f increased by 53% ~72% and 40% ~120% with the dimensionless corrugation depth and dimensionless pitch being 0.15 and 1.5, respectively. The comprehensive heat transfer performance PEC reached 1.2 ~ 1.6, and cross-arranged inner and outer tube corrugations were more favorable for heat transfer than the corresponding arrangement, when Re = 6000, H3 structure has the highest St, Sf and Sgen, which are 0.934W/K, 0.379 W/K and 1.312W/K, respectively. Increasing H and decreasing S could enhance the Nu, f and entropy generation. The values of PEC decreased with increasing S, while with the increment of H, PEC increased and decreased, respectively when Re was in the range of (2000, 4000) and (4000, 6000). In the study range, changing H and S could increase Nu by 40.3%–97.3%, 31.7%–96.8%, and f by 11.7%–176.5%, 16.4%–180.9%, respectively. The final comprehensive heat transfer performance increased by 12.8%-65.9%. Finally, the prediction correlation formulas of Nu and f in NTTHC annular region with high correlation is proposed. [ABSTRACT FROM AUTHOR]

To numerically investigate the flow and heat transfer characteristics of a water/Al 2 O 3 nanofluid in a double-pipe helical coil heat exchanger, we simulated a two-phase Eulerian model to predict the heat transfer coefficient, Nusselt number, and pressure drop at various concentrations (i.e., volume fraction) and under diverse flow rates at the steady state. In this simulation, we used the k-epsilon turbulence model with an enhanced wall treatment method. The performance factor of the nanofluid was evaluated by accounting for the heat transfer and pressure drop characteristics. As a result, the heat transfer was enhanced by increasing the nanofluid concentration. The 1.0 vol.% nanofluid (i.e., the highest concentration) showed a heat transfer coefficient 1.43 times greater than water and a Nusselt number of 1.38 times greater than water. The pressure drop of nanofluids was greater than that of water due to the increased density and viscosity induced using nanoparticles. Based on the relationship between the Nusselt number and pressure drop, the 1.0 vol.% nanofluid was calculated to have a performance factor of 1.4 relative to water, indicating that the enhancement rate in heat transfer performance was greater than that in the pressure drop. In conclusion, the Al 2 O 3 nanofluid shows potential as an enhanced working fluid in diverse heat transfer applications.

Post-acceleration of protons in helical coil targets driven by intense, ultrashort laser pulses can enhance ion energy by utilizing the transient current from the targets’ self-discharge. The acceleration length of protons can exceed a few millimeters, and the acceleration gradient is of the order of GeV/m. How to ensure the synchronization between the accelerating electric field and the protons is a crucial problem for efficient post-acceleration. In this paper, we study how the electric field mismatch induced by current dispersion affects the synchronous acceleration of protons. We propose a scheme using a two-stage helical coil to control the current dispersion. With optimized parameters, the energy gain of protons is increased by four times. Proton energy is expected to reach 45 MeV using a hundreds-of-terawatts laser, or more than 100 MeV using a petawatt laser, by controlling the current dispersion.

The influence of a helical coil turbulence promoter on liquid-solid mass transfer rates in a stirred tank was investigated using a technique that involved measuring the rate of diffusion-controlled copper dissolution in acidified dichromate. The study examined the effects of helical coil tube diameter (d), helical coil pitch (p), impeller rotation speed, impeller geometry (axial and radial), the presence of baffles, and solution physical properties. The presence of the helical coil near the reactor wall significantly enhanced mass transfer rates, with a factor ranging from 1.01 to 2.48. This improvement was accompanied by a corresponding increase in the volumetric mass transfer coefficient (kA), ranging from 2.68 to 4.55, depending on operating conditions. Further analysis revealed that the average mass transfer coefficient increased with decreasing coil tube diameter, while coil pitch had a minimal impact. Additionally, radial flow turbines demonstrated superior mass transfer performance compared to axial flow turbines. The presence of baffles also promoted higher mass transfer rates compared to unbaffled reactors. The experimental data were successfully correlated using dimensionless correlations, emphasizing the significance of these correlations in scaleup and design optimization of catalytic stirred tank reactors with efficient cooling systems. [ABSTRACT FROM AUTHOR]

The application of ground heat exchanger technology in backfill mines can actualize subterranean heat storage, which is one of the most effective solutions for addressing solar energy faults such as intermittence and fluctuation. This paper provides a 3D unsteady heat transfer numerical model for full-size horizontal backfill heat exchangers (BFHEs) with five configurations in a mining layer of a metal mine by using a COMSOL environment. In order to ensure the fairness of the comparative analysis, the pipes of BFHEs studied have the same heat exchange surface area. By comparing and evaluating the heat storage/release characteristics of BFHEs in continuous operation for three years, it was discovered that the helical pipe with serpentine layout may effectively enhance the performance of BFHEs. Compared with the traditional SS BFHEs, the heat storage capacity of the S-FH type is significantly increased by 21.7%, followed by the SA-FH type, which is increased by 11.1%, while the performances of U-DH and SH type are considerably lowered. Also, the impact of the critical structural factors (pitch length and pitch diameter) was further studied using the normalized parameters C1 and C2 based on the inner diameter of the pipe. It is discovered that BFHEs should be distributed in a pipe with a lower C1, and increasing C2 encourages BFHEs to increase the storaged/released heat of BFHEs. By comparatively analysing the effect of thermal conductivity, it is found that the positive effects of thermal conductivity on the performance of SH, U-DH, SA-FH, and S-FH type BFHEs are found to decrease successively. This work proposes a strategy for improving the heat storage and release potential of BFHEs in terms of optimal pipe arrangement.