Hydraulic Length Research Articles

Selection of Heat Transfer Promoters for Heat Exchanger Retrofit

From the thermal point of view, the main operational problems conventional heat exchangers of the tubular type face are the prevalence of the laminar sublayer on the surface immediately adjacent to the heat transfer surface that is responsible for low heat transfer coefficients. A passive means of disrupting this layer is using mechanical inserts known as turbulence promoters. The search for new geometries with better thermohydraulic performance has increased the number of designs available in the open literature. In sight of the large number of different options available for use in design, the selection of the right type of insert for a given application is the focus of this paper and introduces an alternative approach for the selection of turbulence promoters based on the thermal and hydraulic lengths. The approach allows for a quick comparison of the thermo-hydraulic performance in design and retrofit. It considers the effect of the magnitude of the heat transfer coefficient of the opposing stream as well as the effect of viscosity on the selection. Some turbulence promoters out of the many that have been published are used to demonstrate the methodology. This work confirms that the two conditions that result in a greater impact of the turbulence promoter on the overall heat transfer coefficient are when the tube-side presents the higher thermal resistance and when a highly viscous fluid flows through the tubes.

Thermal-hydraulic analysis of the CFETR TF coils when subject to nuclear heat load

China Fusion Engineering Test Reactor (CFETR) has received much attention over the past several years, aiming at bridging the gap between the International Thermonuclear Experimental Reactor (ITER) and the Demonstration Fusion Reactor (DEMO). The toroidal field (TF) coils play an important role in the tokamak, which provide the main magnetic field to confine the plasma. In order to evaluate the feasibility of superconducting magnets used in CFETR, it is important to predict the magnet performance in terms of temperature margin during normal operation conditions. The simulations confirm the need to increase the mass flow rate, or decrease the hydraulic length of high field windings. The results show that the proposed reduction of hydraulic length is more effective to increase the minimum temperature margin.

Comparative Study on Thermos-Hydraulic Performance of Different Cross Section Shapes of Microchannels with Supercritical CO2 Fluid

The influence of the cross section shape of microchannels on the thermos-hydraulic performance of the supercritical CO2 fluid is an important issue in the design of industrial compact heat exchangers, but few studies have been conducted about this issue. In this paper, comparative studies of the flow and heat transfer performance of SCO2 fluid in horizontal microchannels with circular, semicircular, rectangle, and trapezoidal cross sections were conducted numerically. The comparison is based on the same hydraulic diameter and length for all channel types and is carried out under the same mass flux, outlet pressure, and wall heat flux. The fluid bulk temperature in this analysis ranges from 285 K to 375 K, which covers the pseudocritical point of SCO2. The results show that the circular channel has the highest average heat convection coefficient, while the trapezoidal channel has the worst convective heat transfer performance under the same hydraulic diameter and boundary conditions. The results also indicate that the effect of cross section shape on the heat convection coefficient is significantly greater than that on the channel pressure drop, and the existence of the corner region in the cross section, especially the acute angle, will weaken the heat transfer performance.

Prototipe double acting cylinder transparan sebagai media pembelajaran sistem hidrolik

Double acting cylinders in its application are widely used in the industry and are often applied in maintenance or repair instruments. The purpose of this research is to design and make a double acting cylinder so that the movement of the hydraulic cylinder its fluid flow can be seen clearly and easily implemented in the movement process, especially in the learning process. The research employs experimental method by directly design a transparent double acting cylinder. This transparent double acting cylinder will later be applied to the hydraulic trainer. The steps taken were determining the transparent material, making material samples for tensile tests, designing and making hydraulic cylinders, conducting hydraulic cylinder tests using Autodesk Inventor 2019. From the test results of hydraulic cylinders made from acrylic using Autodesk Inventor 2019, the minimum pressure that occurs is 1,456 MPa and the maximum pressure that occurs is 6,573 MPa, in operation, the recommended pressure 1,456 to 5,551 MPa, double acting transparent cylinder which has a transparent hydraulic cylinder length of 250 mm, thickness 11.4 mm, hydraulic cylinder inner diameter 32 mm, hydraulic cylinder locking uses 4 bolts with size M8, design pressure 23 kg/cm².Keywords: hydraulic system, double acting cylinder, transparent.

A New Approach to Embed Complex Fracture Network in Tight Oil Reservoir and Well Productivity Analysis

Accurate modeling of the distribution of induced fractures and pre-existing natural ones in unconventional reservoirs is essential for the analysis of the productivity of horizontal wells after fracturing. A novel approach is proposed here to establish a three-dimensional geological model of induced fractures, natural fractures and the horizontal well using a discrete random distribution method, based on micro-seismic data and natural fracture properties from the S oilfield. Taking the stress sensitivity into consideration, a coupled model calculating the fluid flow in the horizontal wellbore, the reservoir matrix and fractures were established to simulate the productivity of the S oilfield. This model was calibrated by the production data in the S oilfield, and the productivity of horizontal well under different natural fracture intensities, hydraulic fracture spacing and lengths was analyzed. The results show that the area without stimulation in the tight oil reservoir can rarely be exploited. The fluid pressure in the horizontal wellbore cannot be treated as uniform, especially when the production pressure keeps decreasing; otherwise, the cumulative production will be larger than the actual one. Increasing the hydraulic fracture length and natural fracture intensity and decreasing the fracture spacing are all beneficial to the daily and cumulative oil production. However, these methods accelerate the decline of the daily production. The production decline rate with higher natural fracture intensity was about 4 times that of lower natural fracture intensity. The natural fracture intensity and the fracture spacing are factors that are more influential to the productivity compared to the fracture length.

Modeling research on the extreme hydraulic extension length of horizontal well: impact of formation properties, drilling bit and cutting parameters

Horizontal well can increase well productivity and improve the economic benefit, which significantly promotes the development of shale gas, tight oil and heavy oil. Moreover, it plays an important role in the development of natural gas hydrate. Horizontal extension ability is one of the key indexes of horizontal well, but it is always impacted by formation properties and well structure. Therefore, a model is established to analyze the impact of formation properties and well structure as comprehensive as possible, which considers not only traditional influencing factors, like formation pressure and drilling bit parameters, but also other key factors, including cutting particle size, wellbore diameter and cross section. Based on the analysis, some advises are proposed for field application. The analysis indicates that horizontal well has stronger extension ability in the formation with low formation pressure and high fracture pressure, but it is still limited by pump pressure. Under-balanced drilling can strength the extension ability in high formation pressure by reducing drilling mud density. The natural fractures in formation should be noted when drilling long horizontal well. The extension length increases and then decreases with the cutting particle size, so cutting particle has optimal size for the horizontal extension length, which can be adjusted by the rate of penetration and rotation speed. The extension length increases first and then decreases with the gap between drilling string and hole. Considering the demand of rock breaking and cutting sweeping around drilling bit, it is not recommended to adjust the drilling bit parameters. Both the cutting bed height and drilling string eccentricity have impact on horizontal extension length by changing minimum cutting-carry pump rate and annular pressure drop. Under different combinations of above two parameters, minimum cutting-carry pump rate and horizontal extension length are determined by different factors and can be divided into three parts, including acceptable cutting bed height, cutting lifting efficiency, pump pressure and total circulation pressure loss and well bottom pressure and formation fracture pressure. The findings of this study can help for better understanding of horizontal well hydraulic extension length and optimization method.

Alternative PF Coil Winding Pack Design for the EU DEMO

The EUROfusion DEMO machine is at its pre-conceptual stage. The design of the magnet system for this machine is being developed in collaboration with several European research centers. The Poloidal Field (PF) coils proposed by the Swiss Plasma Center (SPC) use a multiple-in-hand Pancake winding technique. A design based on updated plasma scenarios (2018) was recently proposed. The Winding Pack (WP) aspect ratio was kept close to one, similar to the baseline design in the EUROfusion 2018 DEMO baseline document. In this publication, we study the effects of changing WP aspect ratio. A vertically elongated WP cross-section is beneficial in the reduction of the peak magnetic field at WP cross-section, the machine radial extent, and the hydraulic lengths. However, it increases the bending stress on the WP. An updated PF design is presented. The dimensioning and allocation of materials is based on 3-dimensional electromagnetic calculations. Mechanical performance is evaluated against both dynamic fatigue stress and static stresses. The static stresses are evaluated through 3-dimensional finite element simulations to take into account also the ripple effect of TF coils and increase in bending stresses due to the elongation of the WP cross-section. The thermal-hydraulic analysis verifies a temperature margin of 1.5 K and confirms sufficient coolant flow for the prescribed pressure drop. The quench analysis determines the hot-spot temperatures during various quench scenarios.

Use of the thermal and hydraulic length for the screening selection of turbulence promoters in tubular heat exchangers

This paper presents an alternative approach for the selection of the most suitable turbulence promoter for the intensification of heat transfer in tubular heat exchangers. The approach uses the thermal and hydraulic lengths that are determined based on the two main design objectives in a heat exchanger, the heat duty and the pressure drop. Exchanger dimension in the form of plots of the exchanger length are produced to identify the device that results in the smaller equipment size within the constraints imposed by the pressure drop. The length plots are produced for various types of turbulence promoters under fixed design specifications such as heat duty, pressure drop, mass flow rate and tube diameter. The results indicate that from a set of 25 different types of turbulence promoters studied, those that exhibit the largest heat transfer enhancement with the lowest pressure drop are the V-cut twisted tape, the square-cut twisted tape, and the straight tape with center wings. The benefits of the use of heat transfer enhancement on the stream that controls heat transfer on a practical heat exchanger design is analysed on a case study.

Thermohydrodynamic Performance Evaluation of Recharging, Interrupted and Simple Microchannels: A Comparative Study

Abstract In this study, a three-dimensional numerical investigation on the thermohydrodynamic performance of a recently proposed recharging microchannel (RMC) is carried out. In this design, a straight microchannel is split into more than one smaller length channels (having individual inlet and outlet) placed end to end. This design enhances overall heat transfer and maintains temperature uniformity across the substrate length. The comparison of fluid flow and heat transfer performance of RMC, interrupted microchannel (IMC) and straight microchannel (SMC) with the same hydraulic diameter and substrate length are presented to explore the effect of geometrical configuration on heat transfer enhancement. The parametric variations include the number of channels (n), transverse wall length (Ltw), channel aspect ratio (α), and flow Reynolds number. The results reveal that recharging microchannel shows better thermal performance compared to simple and interrupted microchannel with a maximum performance factor of 1.80. The results also indicate that the performance factor of RMC increases with an increase in the number of small channels, transverse wall length, and channel aspect ratio. The outcome of this study indicates the possible use of recharging microchannel heat sinks for high heat flux removal applications such as electronic cooling.

Design of DEMO PF Coils Based on Cable-in-Conduit Conductor

The poloidal field (PF) coils are designed based on the requirements defined by the EUROfusion 2015 DEMO baseline. The conductors are forced flow, NbTi cable-in-conduit. The design addresses the dimensioning of the winding pack, the electromagnetic field calculation and mechanical load. The cross sections of the cable, i.e., superconductor, copper and helium are allocated to fulfill the design criteria for the temperature margin and pressure drop in the operation. The conductors have rectangular cross section and are layer wound, multiple-in-hand, to minimize the hydraulic length (1 single turn can be as long as 100 m). The orientation of the wide side parallel to the main field component minimizes the ac loss. The larger radius compared to international thermonuclear experimental reactor (ITER) PF coils calls for larger electromagnetic load and hence much larger cross section for the structural support, which must be added on top of the conductor conduit to avoid unmanageable thick conduit walls. For PF1 and PF6 coils, a design option with Nb3Sn conductor may need to be considered due to the effective magnetic field in excess of 6.2 T.

Development of lag time and time of concentration for a tropical complex catchment under the influence of long-term land use/land cover (LULC) changes

Lag time (tL) and time of concentration (Tc) are essential time parameters used in hydrological flood-flow design methods for estimating peak discharge and flood hydrograph shape. They form the basis of a number of hydrological models used among the scientists. Kelantan River basin, Malaysia, is a tropical catchment receiving heavy monsoon rainfall coupled with intense land use/land cover (LULC) changes making the area consistently flood prone thereby deteriorating water balance in the area. The most recent is that of December 2014 flood which lead to catastrophic loss of huge amount of properties worth millions of Malaysian ringgit. In view of this, the current research was conducted with the aim of developing (1) tL and Tc based on 1984, 2002, and 2013 LULC conditions; (2) a relationship between tL and tL parameters; and (3) a relationship between tL and Tc among different LULC conditions. Kelantan River basin was first delineated into four major catchments, viz., Galas, Pergau, Lebir, and Nenggiri, due to its large size (approximately 13,100 km2). Soil map and LULC change maps corresponding to 1984, 2002, and 2013 were used for the calculation of CN values while NRCS lag equation was used for the estimation of tL and Tc. The results showed that deforestation for logging activities and agricultural practices were the dominant LULC changes across the watershed. Low values of both tL and Tc were obtained across the catchment which are typical for a tropical monsoon catchment characterized with high runoff and short peak discharge. Results of tL and Tc in this study are not affected by LULC changes in the basin. Slope was observed to be highly correlated with tL. Correlation coefficient was used to determine the relationship between tL and tL factor, and hydraulic length and slope (L√S). The results showed high correlation in all the catchments from 1984 to 2013 except for Lebir catchment where a moderate correlation was observed. The findings of this study may be useful to water resource planners in controlling water loss for future planning.

Performance Analysis and Tube Inlet Orifice Length Evaluation of a Once–Through Steam Generator

A numerical study is conducted for performance analysis and secondary side screw-type tube inlet orifice design of a once–through steam generator (OTSG). Various tube plugging conditions and power levels are considered, and the secondary coolant flow rate is adjusted to maintain a constant thermal power. Comprehensive numerical solutions are acquired to evaluate the OTSG thermal–hydraulic performance and minimum orifice length under various operating conditions. The OTSG performance is analyzed according to the tube plugging condition in terms of the OTSG thermal power, steam outletsuperheat degree, and secondary coolant pressure drop. The results obtained show that a constant thermal power canbe maintained by properly adjusting the secondary coolant flow rate with a variation ofthe steam outlet superheat degree and secondary coolant pressure drop when the OTSG operates at high power level. The required minimum orifice length to suppress the flow oscillation below the allowablelevelis evaluated. The lowest power level results in the highest minimum orifice length, and non-plugging condition provides a limiting case for the orifice length criterion.

Cost effective measuring technique to simultaneously quantify 2D velocity fields and depth-averaged solute concentrations in shallow water flows

This paper presents a cost-effective methodology to simultaneously measure mixing processes and surface velocity fields in shallow flows using multiple, synchronized low cost cameras and lighting. Velocity fields and depth averaged concentration of a soluble fluorescent tracer are obtained over a 4.8 × 1.22 m2 measurement area using the new techniques and the results verified against traditional point probe measurements in a laboratory flume. An example of simultaneous velocity/concentration measurement is presented for an instantaneous release of tracer into flow around an obstruction. The method will help to improve the understanding of mixing processes in shallow open channel flows. It is anticipated that the technique will be useful in physical modelling studies where the mixing and hydraulic length scales under investigation are in the order of 1–10 m, for example in compound channels and partially vegetated streams.

Influence of helix twisted tape on heat transfer and friction factor in forced circulation V-trough solar water heater

ABSTRACTThe effect of helix twisted tape with several twist ratios (Y = 3, 4, 5 and 6) in a V-trough solar water heater for enhancing heat transfer, thermal performance and the friction factor has been examined experimentally in forced circulation with the Reynolds number ranging from 3000 to 23,000. The experimental results of plain V-trough solar collector (PVT) fitted with the standard equations and the variation in the Nusselt number are ±7.23% and the variation in friction factor is about ±5.91%. The PVT has been compared with plain flat plate (PFP) collector. The obtained result shows that the average Nusselt number of PVT performs better than PFP by 8.4%. This is owing to the additional reflectors, reflection of the solar incident rays to the receiver plate, which tend to rise in the temperature gradient of water inlet and outlet of the system. The thermal performance has been increased further by inserting the helix twisted tape with several twist ratios and the results are also presented. The minimum twist ratio 3 provides a higher heat transfer rate and friction factor owing to the increase in the hydraulic length and swirl flow. The experimental Nusselt number and friction factor are correlated and the deficiency falls ±6.44% and ±11.91%, respectively.

Thermohydraulic Analyses on CEA Concept of TF and CS Coils for EU-DEMO

In the framework of the European fusion program for energy, EUROfusion funds the studies for the future fusion power demonstrator reactor DEMOnstration fusion reactor (DEMO). Commissariat a l'energie atomique et aux energies alternatives (CEA) is involved in the conceptual design of the superconducting conductors for the toroidal field (TF) and central solenoid (CS) magnets. The CEA design proposal corresponds to wind and react Nb3Sn pancake-wound coils using cable-in-conduit conductors cooled at about 4.5 K by forced flow of supercritical helium. This paper presents the latest thermal-hydraulic analyses performed on both TF and CS conductors. Two TF conductor designs have been analyzed, with nominal currents of 111 kA and 88 kA, respectively. The analyses were performed in normal (burn) and off-normal (quench) conditions. Burn simulations focused on the central and lateral pancakes with heat load corresponding to neutron heating. The central pancake is the most critical one regarding the magnetic field, while the lateral one receives a more important heat load from the casing. The influence of case cooling on temperature margin (ΔTma) was analyzed by means of a dedicated 2D Cast3M model. The ΔTma sensitivity to driving parameters such as conductor friction factor correlations was analyzed. The impact of interturn thermal coupling on temperature margin was also assessed. Quench studies were performed on the TF conductor, considering a quench initiated either on the innermost turn or at the middle of hydraulic length. Regarding the CS conductor, burn scenario was led on the latest design featuring a nominal current of 53.7 kA, focusing on the impact of ac losses and of dwell duration.

Impact of river network type on the time of concentration

Time of concentration (T c) is one of the frequently used parameters to characterize the response of a drainage basin to a rainfall event. Conceptually, it is the time runoff travels from the hydraulically most distant location in a basin to its outlet. T c was found to vary depending on river basin characteristics such as slope, soil infiltration, and flow path. In this study, we investigate if the drainage network type information can be used as an input to hydrological models, by estimating the time of concentration separately for different network types. Sixty-eight basins which have areas ranging from 24 to 965 km2 in arid and non-arid regions of the USA are compared and the effect of climate is also analyzed. It is found that the slope of the linear relationship between T c and the maximum hydraulic length of flow path shows different correlation coefficients ranging from 0.80 to 0.98 for different network types. It is observed that the slope of the regression line between T c and the maximum hydraulic length of flow path is the lowest for dendritic networks (slope of 0.26), while pinnate networks have the steepest slope of the regression line (slope of 0.59). This indicates that the drainage network type has a direct impact on the hydrological behavior of the basin and can represent a direct input in hydrological modeling.

Effect of articulated frame steering on the transient yaw responses of the vehicle

The directional performance characteristics of articulated frame steering vehicles are known to be strongly coupled with the kinematic characteristics and the dynamic characteristics of the steering system. The reported studies on articulated frame steering generally focus on the yaw divergence behaviour or the snaking tendency of the vehicle based on its free-yaw-oscillation response, while neglecting important contributions due to the kinematics and the dynamics of the steering system. This study characterizes both the free-yaw-oscillation response and the transient steering response of an articulated frame steering mining vehicle, considering the kinematics of the steering struts together with the dynamics of the flow volume-regulated steering valve and the actuating system. The validity of the analytical vehicle and steering system model is demonstrated using the measured data acquired for the vehicle. The free-oscillation behaviour of the articulated frame steering is characterized in terms of the yaw-mode natural frequency and the yaw damping ratio. The transient responses of the articulated frame steering are assessed in terms of the steering gain, the rate of articulation and the articulation overshoot. The effects of the variations in the various articulated frame steering parameters on the free response and the transient response are subsequently investigated and discussed so as to seek guidance for the design of the articulated frame steering system. It is shown that a higher bulk modulus of the hydraulic fluid and longer steering-arm lengths yield a higher yaw stiffness of the articulated frame steering system and thereby a higher frequency of the yaw oscillations. Higher leakage flows and higher viscous seal friction cause a higher yaw damping coefficient but decrease the steering gain and the articulation rate of the vehicle.

Characteristics of Hydraulic Jump in U-Shaped Channels

A hydraulic jump is the rapid transition from a supercritical to subcritical flow. This transition is characterized by large-scale turbulence and energy dissipation. Despite the importance of understanding the hydraulic jump to design hydraulic structures, few studies have aimed on hydraulic jumps in U-shaped channels. In this paper, the 3D pattern of hydraulic jumps in U-shaped channels is studied numerically. The variations of the flow free surface are predicted using the volume of fluid scheme. Also, the flow field turbulence is simulated using the standard $$k-\varepsilon $$ and RNG $$k-\varepsilon $$ turbulence models. According to the numerical modeling results, the standard $$k-\varepsilon $$ turbulence model estimates the flow characteristics with more accuracy. A comparison between the laboratory and numerical results shows that the numerical model simulates the flow field characteristics with good accuracy. For example, in the hydraulic jump model with a relative discharge $$({q=Q/{\sqrt{( {gD^{5}})}}})$$ equal to 0.321 and a Froude number $$({{F}_1})$$ equal to 4.85, the values of MAPE, RMSE and $${R}^{2}$$ are calculated 7.617, 0.022 and 0.989, respectively. Next, 45 numerical models are simulated in different hydraulic conditions and some relationships are provided for calculating the sequent depth $$({{h_2 }/{h_1 }})$$ , hydraulic length $$({{L_\mathrm{j}}/{h_1}})$$ and roller length $$({{L_\mathrm{r} }/{h_1}})$$ ratios by analyzing their results.

Bypass Flow Resistance in Prismatic Gas-Cooled Nuclear Reactors

Available computational fluid dynamics (CFD) predictions of pressure distributions in the vertical bypass flow between blocks in a prismatic gas-cooled reactor (GCR) have been analyzed to deduce apparent friction factors and loss coefficients for nuclear engineering systems and network codes. Calculations were performed for vertical gap spacings “s” of 2, 6, and 10 mm — representing 1, 3, and 5 mm in a GCR design, horizontal gaps between the blocks of 2 mm and two flow rates, giving a range of vertical gap Reynolds numbers ReDh of about 40–5300. The present focus is on the examination of the flow in the vertical gaps. Horizontal gaps are treated in CFD calculations but their flows are not examined. Laminar predictions of the fully developed friction factor ffd were about 3–10% lower than the classical infinitely wide channel. In the entry region, the local apparent friction factor was slightly higher than the classic idealized case, but the hydraulic entry length Lhy was approximately the same. The per cent reduction in flow resistance was greater than the per cent increase in flow area at the vertical corners of the blocks. The standard k–ϵ turbulence model was employed for flows expected to be turbulent. Its predictions of ffd and flow resistance were significantly higher than direct numerical simulations (DNS) for the classic case; the value of Lhy was about 30 gap spacings. Initial quantitative information for entry coefficients and loss coefficients for the expansion–contraction junctions between blocks is also presented. The present study demonstrates how CFD predictions can be employed to provide integral quantities needed in systems and network codes.

Scaling Roughness Effects on Pressure Loss and Heat Transfer of Additively Manufactured Channels

Additive manufacturing (AM) with metal powder has made possible the fabrication of gas turbine components with small and complex flow paths that cannot be achieved with any other manufacturing technology presently available. The increased design space of AM allows turbine designers to develop advanced cooling schemes in high-temperature components to increase cooling efficiency. Inherent in AM with metals is the large surface roughness that cannot be removed from small internal geometries. Such roughness has been shown in previous studies to significantly augment pressure loss and heat transfer of small channels. However, the roughness on these channels or other surfaces made from AM with metal powder has not been thoroughly characterized for scaling pressure loss and heat transfer data. This study examines the roughness of the surfaces of channels of various hydraulic length scales made with direct metal laser sintering (DMLS). Statistical roughness parameters are presented along with other parameters that others have found to correlate with flow and heat transfer. The pressure loss and heat transfer previously reported for the DMLS channels studied in this work are compared to the physical roughness measurements. Results show that the relative arithmetic mean roughness correlates well with the relative equivalent sand grain roughness. A correlation is presented to predict the Nusselt number of flow through AM channels, which gives better predictions of heat transfer than correlations currently available.