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Helical coil steam generator has the advantages of compact structure, high heat transfer efficiency, strong resistance to thermal expansion stress, and has been widely applied in energy and power engineering, chemical industry and other fields. As the energy transfer facility between firstsecond loops and the isolation barrier for radioactive working medium, the inner structure of helical coil steam generator is extremely complicated, hence its structural integrity and operation reliability are necessary guarantee for the nuclear power plant safety. In this paper, the porous media method was adopted to simplify the complex structure of the multilayer helical coil domain in heat exchange assemblies, a shell side working fluid flow heat transfer characteristics analysis model was established, and the tube side watersteam two phase flow boiling heat transfer characteristics analysis model was established based on the homogeneous flow hypothesis. The gridnode data mapping method was applied to realize the coupled heat transfer simulation between shell side and tube side, and a three-dimensional full-scale thermalhydraulic characteristics analysis code HeTAF for the helical coil steam generator was developed based on the open source CFD platform OpenFOAM. The validation was performed against flow boiling heat transfer experiment of helical tube by Santini, and the calculation results of heat transfer coefficient variation with quantity are in good agreement with the measured data, indicating that the adopted model package are capable for accurate prediction under high mass flux rate and heat flux experimental condition. The helical coil oncethrough steam generator in high temperature gas cooled reactorpebble module was selected as the research object. The simulation of single heat transfer assembly under full power operating condition was performed using HeTAF. The distributions of thermalhydraulic parameters including tube side and shell side fluid temperatures, heat transfer coefficient, heat transfer power, void fraction and equilibrium quantity along tube length were obtained, and the transition process of each phase state and dominant heat transfer mechanism in the helical tube was predicted. The calculation results of helium and steam outlet temperature are fixed well with the design value with absolute errors of 5.29 K and 5.76 K respectively, which illustrates that the HeTAF can effectively predict the thermalhydraulic characteristics of both shell side and tube side of single heat transfer assembly. The work in this paper has significance reference for the design and safety analysis of helical coil steam generator. In the future, based on the existing methodology and simulation strategy, the fullscale coupled thermalhydraulic characteristics analysis of the helical coil steam generator will be conducted, and supplementary validation and subsequent optimization of HeTAF code will be carried out continuously.

Liquid metal reactor (LMR), with the great advantages of high safety and good economic benefits, has obvious advantages and broad application prospects in the fourth generation nuclear power systems. Helical coil steam generator is one of the most important equipment for liquid metal reactors which have compact structure and high heat transfer efficiency. Natural frequency of tube bundle is an important parameter in flow induced vibration (FIV) analysis. In this paper, the natural frequency of helical coil steam generator tube bundle was studied. Based on simplifying constraints at both ends of the heat transfer tubes to simple support, the computational fluid dynamics (CFD) simulation was carried out to reveal the effect mechanism of helix angle β, number of supports S and coil radius R, on natural frequency of heat transfer tubes in air. The relative error between the CFD simulation results and experimental values is within 5%. Considering the accuracy of actual processing and manufacturing, the numerical simulation settings have great engineering practicability. The result shows that the increase of β- and R will induce the reduction in natural frequency, and the increase of S will lead to the adverse result. Therefore, we can improve the stability of the heat transfer tubes by increasing β and S or reducing R. Based on CFX simulation calculation, the influence mechanism of tube bundle structure parameters on the natural frequency of heat transfer tubes in liquid metal environment was studied. The increase of layer pitch ratio a, the same layer pitch ratio b, will lead to the increase of natural frequency, and the increase of β will lead to the adverse result. The natural frequencies of heat transfer tubes in liquid metal environment were obtained, and the interaction table was established based on orthogonal experimental design to investigate the effect of the three structural parameters layer pitch ratio a, the same layer pitch ratio b and the helix angle β, on the added mass coefficient. The results of orthogonal analysis show that a and b have a great influence on the added mass coefficient CM1 in the out-of-plane direction and the added mass coefficient CM2 in the in-plane direction of the helical coil tube, respectively. And the effect of β and the coupling effect between various factors can be ignored. Then, the added mass coefficient curve was drawn. This research provides data reference for the prediction of natural frequency of heat transfer tubes and the study of FIV of tube bundles, which are of great importance for avoiding the failure of heat transfer tubes.

Due to the compact structure, high heat transfer efficiency and strong reliability, helical coil once-through steam generator (HCSG) is widely used in advanced small reactors. In HCSG, the liquid in the tube side is heated by the helical coils so that subcooled water in the tube side is transferred into superheated steam, and the entire heat transfer regime is covered. Moreover, the evolution mechanism of thermalhydraulic behaviors is complex because it is affected by the helical geometry, the centrifugal force and the secondary flow. Hence, the development of advanced HCSG was limited due to the lack of more accurate models of heat transfer and regime transition. With the financial support of the three major nuclear power groups in China, experimental and theoretical research on heat and mass transfer behaviors in helical coils was carried out systematically. Different helical coils were investigated and comprehensive parametric analysis of heat transfer was conducted to provide a better understanding of different heat transfer regimes. According to our research, a fundamental database of heat transfer and flow resistance in helical coils with a wide range of geometric dimensions and thermalhydraulic parameters was established. In addition, the transition pattern of the circumferential nonuniform heat transfer mechanism was clarified. Due to the secondary flow, it consequently leaded to the nonuniform distribution of flow field. The heat transfer and flow resistance characteristics were notably affected by the special behaviors of liquid in the helical coils. Hence, based on mechanism analysis, several models were proposed to construct a high precision library of allregime prediction model, such as a threeregion dryout quality model, a postdryout heat transfer model based on dryness gradient and a widerange model for twophase frictional multiplier factor. For the model of dryout quality, it takes the relative intensity of gravity, buoyancy and centrifugal force into consideration. Since different dominant forces lead to different heat transfer behaviors, a piecewise correlation is established to give more accurate predictions. As for the postdryout heat transfer model, it considers the influence of dryness gradient and achieves a more accurate prediction. For the twophase pressure drop model, the modified frictional multiplier factor is adjusted according to our database. Then, a prediction model was proposed which was also validated by other researchers and had great prediction accuracy in a wide range. In all, this work includes part of our investigation on the heat transfer of helical coils and provides a highprecision prediction in the entire heat transfer regime, which meets the design requirement of HCSG for advanced reactors.

A simple but accurate mathematical model is crucial for dynamic simulations and controller design of helical coil once-through steam generator (OTSG). This paper presents a three-region movable boundary dynamic model of the helical coil OTSG. Based on the secondary side fluid conditions, the OTSG is divided into subcooled region (two control volumes), two-phase region (two control volumes) and superheated region (three control volumes) with movable boiling boundaries between each region. The nonlinear dynamic model is derived based on mass, energy and momentum conservation equations. And the linear model is obtained by using the transfer function and state space transformation, which is a 37-order model of five input and three output. Validations are made under full-power steady-state condition and four transient conditions. Results show good agreements among the nonlinear model, linear model and the RELAP5 model, with acceptable errors. This model can be applied to dynamic simulations and controller design of helical coil OTSG with constant primary-side flow rate.

The manufacturing process of heating systems involves incorporating various heat exchangers, each with distinct characteristics. Among these, the helical heat exchanger stands out due to its space-efficient design and enhanced heat transfer rate compared to other variants. Recently, heat exchangers have witnessed novel nanofluid explorations aiming to replace conventional working fluids. Nanofluids possess unique properties that hold the potential for substantial improvements, consequently influencing the efficiency of heat exchangers employing them. The effectiveness of these heat exchangers is intrinsically tied to the properties of the employed nanofluids. Recent years have witnessed remarkable strides in comprehending the distinct traits exhibited by diverse nanofluids. This comprehensive study amalgamates findings from multiple investigations focused on helical-tube heat exchangers utilizing nanofluids as the primary medium. Notably, it underscores the existence of varying conclusions and perspectives among different researchers. This variance arises from the complexity of nanofluid behavior and its interactions within heat exchangers. Consequently, the efficacy of helical heat exchangers leveraging nanofluids hinges on the specifics of the chosen nanofluid and its characteristics. This subject continues to stimulate vigorous research and discussions among scholars. In summation, the dynamic landscape of heat exchanger innovation has brought the spotlight onto helical heat exchangers and their integration with nanofluids, showcasing the intricate interplay between fluid properties and efficient heat exchange.

In the present study, an experimental study and a numerical method are used to simulate the effect of utilizing finned helical coil heat exchanger horizontally oriented with and without internal hollow core inside the shell and monitoring the heat transfer intensification behavior and performance enhancement, by using ANSYS FLUENT 2019R3 package. The working fluid in the inlet side of the coil will be superheated vapor refrigerant (R410a) after the compression stage of the air conditioner (1TR) split type, the working fluid in the shell side is water with various flow rates (1,2 and 3)LPM. Found that when using a heat exchanger with internal hollow core reduces the time needed to reach the steady-state outlet temperature and directly proportional to the size of the core by 20% and slightly increasing the water outlet temperature by 5%.

Due to the special structure, helical coil once-through steam generators (HCOTSGs) can withstand greater thermal expansion stress, have a larger heat exchange area, and cause the secondary flow phenomenon to improve the heat transfer capacity. Thus, it is inevitable to further study the thermal-hydraulic characteristics of the HCOTSG, a vital component of reactors. The optimal physical models were selected for different heat transfer areas by detailed investigation and comparison, to adopt in the TACS, a self-developed thermal-hydraulic analysis code that is accurate and widely-used in HCOTSG simulation. After verification with experiments of Santini, taking the IRIS reactor as the object, the TACS was employed to briefly study the thermal-hydraulic performances of the HCOTSG system at first, and then discuss the influences of thermal and geometric parameters on the HCOTSG. The analysis results showed that: the variation of the primary flow rate greatly affects the heat transfer coefficient of the primary side, while the maximum value of the heat transfer coefficient of the secondary side only changes drastically with the secondary flow rate; when the primary side flow drops to 70%, superheated steam is not generated on the secondary side; when the secondary mass flow rate decreases to a certain extent, the steam superheat degree increases by a small amplitude; the primary side inlet temperature has a little influence on the primary temperature difference, but significant influence on the two-phase zone length of the secondary side; the secondary inlet temperature has very little influence on the HCOTSG system; the inner diameter and the outer diameter of helical tubes have obvious influences, while the helical diameter has not.

Helical coil accelerators are a recent development in laser-driven ion production, acting on the intrinsically wide divergence and broadband energy spectrum of laser-accelerated protons to deliver ultra-low divergence and quasi-monoenergetic beams. The modularity of helical coil accelerators also provides the attractive prospective of multi-staging. Here we show, on a proof-of-principle basis, a two-stage configuration which allows optical tuning of the energy of the selected proton beamlet. Experimental data, corroborated by particle tracing simulations, highlights the importance of controlling precisely the beam injection. Efficient post-acceleration of the protons with an energy gain up to ∼16 MeV (∼8 MeV per stage, at an average rate of ∼1 GeV m ^−1 ) was achieved at an optimal time delay, which allows synchronisation of the selected protons with the accelerating longitudinal electric fields to be maintained through both stages.

This study focused on investigating the impact of α-Al2O3 nanoparticles on heat transfer in shell and helical coiled tube heat exchangers. The objective was to analyze the influence of various geometrical characteristics, specifically the coil pitch, on the Nusselt numbers of both sides using a combination of numerical simulations and experimental methods. The working fluid for the hot side was water. The research encompassed an examination of the friction factor for three different coils, exploring the effects of pitch spacing on heat transfer, and assessing the influence of nanoparticles on heat transfer on the inner side of the coil. The findings of the current work indicated significant improvements in heat transfer parameters when employing water-α-Al2O3 nanoparticles as the cold fluid. Comparing this heat exchanger to one without the inclusion of α-Al2O3 nanoparticles revealed a remarkable efficiency enhancement of 7.68 percent. This increase strongly suggests a notable acceleration in the rate of heat transmission within the heat exchanger. Overall, this study provides valuable insights into the utilization of α-Al2O3 nanoparticles in enhancing heat transfer in shell and helical coiled tube heat exchangers. The results highlight the potential benefits of incorporating nanoparticles into such systems, leading to improved performance and more efficient heat exchange processes.

The heat transfer, flow resistance and entropy generation characteristics of micro-fin helical coil tubes (MFHCTs) are investigated numerically. MFHCT with different fin numbers (2≤N≤6), coil pitches (150mm≤P≤450mm), coil diameters (600mm≤D≤1200mm) and Reynolds numbers (10945≤Re≤30845) are examined. The effects of these geometric parameters on the Nusselt number (Nu), friction factor (f) and improved entropy generation number (Ns′) are discussed. The performance of MFHCT is then compared to that of a smooth helical coil tube (SHCT). The results show that MFCHT always performs better than SHCT, especially in the lower Reynolds number region. Moreover, artificial neural networks (ANNs) are established to predict Nu, f and Ns′, which are trained by simulation data. This model fits the simulation results better than the multiple linear regression, and the maximum error is no greater than 8%. With the prediction of the network, the micro-fin helical coil tubes are optimized by the entropy minimization method and NSGA-III algorithm. Through optimization, the distribution of design variables is examined. The results demonstrate that a higher Reynolds number and a larger coil diameter and coil pitch lead to a better performance. Additionally, the optimal Pareto points can be utilized to guide the design and operation conditions of micro-fin helical coil tubes.

The thermal performance enhancement of a vertical helical coil heat exchanger using distilled water-based copper oxide-graphene hybrid nanofluid has been analyzed experimentally. Accordingly, the focus of this study is the preparation of CuO-Gp (80-20%) hybrid nanoparticles-based suspensions with various mass fractions (0% ≤ wt ≤ 1%). The volume flow rate is ranged from 0.5 L·min−1 to 1.5 L·min−1 to keep the laminar flow regime (768 ≤ Re ≤ 1843) and the supplied hot fluid’s temperature was chosen to equal 50 °C. To ensure the dispersion and avoid agglomeration an ultrasound sonicator is used and the thermal conductivity is evaluated via KD2 Pro Thermal Properties Analyzer. It has been found that the increment in nanoparticles mass fraction enhances considerably the thermal conductivity and the thermal energy exchange rate. In fact, an enhancement of 23.65% in the heat transfer coefficient is obtained with wt = 0.2%, while it is as high as 79.68% for wt = 1%. Moreover, increasing Reynolds number results in a considerable augmentation of the heat transfer coefficient.