Pitch Ratio Research Articles

Numerical modeling and optimization of perforated twisted tape insert based on hybrid ANSYS‐RSM approach

AbstractHeat exchangers have a wider scope in numerous applications, such as space heating, chemical industries, power stations, and so on. Due to heat loss and the thermal properties of the materials involved, the overall performance of a heat exchanger is questionable. Therefore, studies related to heat transfer techniques are appreciated in the research community. Thus, the present study numerically investigates the heat transfer performance of a horizontal heat pipe equipped with hexagonal perforated twisted tape inserts. Further, the numerical solutions of Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF) are optimized with the help of response surface methodology (RSM). The parameters investigated in this study are Reynolds number (Re), which varies between 500 and 1500, input heat supply (Q) between 100 and 1000 W, and pitch ratio (3.2, 4, and 5.2). ANSYS fluid flow fluent was used to perform flow simulations for three different twisted tape inserts: horizontal, vertical, and alternate hexagon perforations. Optimum solutions are obtained at 1000 W heat supply, 1500 Re, and p/di = 4 from alternatively perforated twisted tape inserts. The optimum Nu, f, and TPF achieved are 119.545, 0.437, and 1.82, respectively. Also, the proposed RSM optimization method is evidenced with a maximum of 2.673% error during the confirmatory test.

A weather optimal heading-based incremental feedback control for dynamic positioning of ships

In this brief, the weather optimal heading-based incremental feedback control algorithm is built for dynamic positioning (DP) of ships in the presence of model uncertainties and unknown environmental disturbances induced by wind, waves and currents. The proposed control algorithm has two parts, i.e., the weather optimal heading portion and the control portion. An improved ZPC-W approach with the deviation of the lateral control force is designed in order to enhance the convergence rate of the desired weather optimal heading and avoid overshoot as well. In addition, based on the iterative sliding mode function, a concise incremental feedback control scheme is designed with the pitch ratio of the thruster as the control input. It is measurable in the practical plant and has nothing to do with ship models with good stability and strong robustness. Lastly, simulation studies are performed to illustrate the performance and the superiorities of the proposed control algorithm.

Heat transfer enhancement through pitch ratio optimization of butterfly inserts in minichannel heat sinks

Thermohydraulic characteristics of square minichannel heat sinks (MHS) with butterfly inserts are computationally studied for Reynolds numbers between 200–900 for two hydraulic diameters (Dh) of 2mm and 2.6mm and varied pitch distances (P). The present investigation examines the effect of pitch ratio (P∗=P/Dh) of butterfly inserts on overall thermal performance of MHS to discern its optimal value for the best possible overall performance. Since inserts result in a concurrent rise in both pressure drop and heat transfer rate, this overall thermohydraulic performance is measured using Performance Evaluation Criteria (PEC), which incorporates the simultaneous effects of change in hydraulic and thermal performance. In the present study, PEC values for all analyzed configurations are found to be above unity, which indicates the adequacy and efficacy of the employed butterfly inserts. The study also corroborates the literature-reported finding that the pitch ratio of butterfly inserts significantly alters the thermohydraulics of MHS. Heat transfer performance is found to improve drastically when pitch ratio is reduced from 5 to 1.5, showing a Nusselt number enhancement of 29.57% to 78.47% for Dh=2mm and 27.73% to 63.47% for Dh=2.6mm for the tested range of Reynolds numbers. However, further reduction in pitch ratio is found to deteriorate the thermohydraulic performance of these inserts. The highest PEC value is obtained for P∗=1.5 for both the studied hydraulic diameters, leading to the conclusion that P∗=1.5 is the optimal pitch ratio of butterfly inserts when employed within rectangular MHS.

The interaction between cross-flow induced vibration and convection heat transfer in tube bundle at subcritical Reynolds number

This work numerically investigates the interaction between flow-induced vibration (FIV) and forced convection heat transfer in tube bundle with a pitch ratio of 1.5 at subcritical Reynolds number (Re = 5 × 103-3 × 104). The range of reduced velocity is 0.53 ≤ Vr ≤ 2.71. The mass-damping parameter of coupling system is 0.07. The three-dimensional refined FIV simulation considering fluid viscous damping has been validated by the literature experiment to capture three continuous FIV mechanisms, namely turbulence-induced vibration, vortex-induced resonance and fluidelastic instability. The heat transfer and pressure drop in tube bundle are validated by the experiment. The coupling of Navier-Stokes equations, energy equations and vibration equations is solved by under-relaxation algorithm. The results of vibration response, the change of damping for the coupling system, flow field and temperature field, heat transfer and pressure drop are presented and delineated in this paper. The results show that for the low velocity turbulence-induced vibration, the interaction between FIV and flow heat transfer is negligible due to the weak fluid–solid interaction. In vortex-induced resonance region, the wall heating makes each row tube be out of phase by affecting the vortex shedding and reduces the positive feedback of resonance, which reduces the amplitude. The wall heating reduces the damping of coupling system, which causes an earlier transition from vortex-induced resonance to fluidelastic instability and a faster increase of amplitude in fluidelastic instability. In both vortex-induced resonance and fluidelastic instability, the vibration of tube bundle dominates the vortex shedding by the natural frequency, and further dominates the change of heat transfer. The best performance of enhanced heat transfer induced by FIV is located in vortex-induced resonance region, in which the time–space averaged Nusselt number is increased by 8.83%. Due to the redistribution of flow field and the elimination of deflective flow pattern, compared with vortex-induced resonance, the increasing ratio of heat transfer induced by FIV is lower and the increasing ratio of pressure drop induced by FIV is higher in the fluidelastic instability.

Effect of triangular perforated flat cone-shaped inserts on performance of double-tube heat exchanger

This study investigated the effect of triangular perforations with flat conical inserts in a double-tube heat exchanger. Triangular perforations with flat cone-shaped inserts were placed inside the inner tube to enhance the heat transfer coefficient. The experiments were conducted for a number of flat conical strips (m) and pitch ratios (P = p/di) for flows varying from Re = 3000 to 9000 at a constant attack angle (α = 20°). The results showed that a triangular perforation with flat cone-shaped inserts remarkably increases the heat transfer factor, in contrast to flat conical inserts. The rise in the coefficient of heat was attributed to the creation of turbulence and disturbance of the boundary layer caused by perforated inserts. Furthermore, it was observed that the heat transfer coefficient increased with the Reynolds number, indicating that the effect of the inserts was more significant at higher fluid velocities. Correlations were developed to compare and analyze the results of the Nusselt number and friction factor. The developed correlation results are in good agreement with the experimental results. The findings obtained from this study can be implemented to enhance the performance and optimize the design parameters of industrial heat exchangers.

Experimental and numerical analysis of intermetallics in Al–Mg friction stir welds

In this research work, it was aimed to analyse the thermal behaviour during FSW in order to understand the diffusion behaviour of Al (AA6061)-Mg (AZ31B) dissimilar joints. Three heat input levels at different weld pitch ratios (WPR) of 0.087, 0.068 and 0.051 are accounted for the analysis. Finite element modelling (FEM) is employed to predict temperature evolutions. From the FEM results and fundamental diffusion equations, the intermetallic thickness and the diffusion behaviour between the Al and Mg material were analyzed and found that the Al-rich intermetallic phases Al3Mg2 grow faster and wider than the Mg-rich phase Al12Mg17. Tensile test demonstrates that a lower welding pitch ratio (WPR) leads to the formation of thicker intermetallic layers, resulting in reduced tensile strength and joint efficiency. In contrast, a higher WPR (0.087) minimizes intermetallic thickness, yielding superior tensile properties (138mpa). Microhardness measurements at the stir zone reveal a broad range from 70 to 164 HV, signifying mechanical heterogeneity. Microstructural reveals that a complex interplay between Al and Mg materials, resulting in fine equiaxed grains, intermetallic compounds, and distinct flow patterns in the stir zone.

Air Bubble Effect on Heat Transfer Enhancement in 90° Ribbed Parallel Channels Based on Photovoltaic-Thermal Collector Cooling

The effect of entrained air bubbles on heat transfer enhancement inside 90° ribbed parallel channels has been experimentally studied to improve electrical efficiency inside future solar panels. In this work, the Reynolds number was measured from 200 to 600. The essential ratios of channel aspect, rib height, and rib pitch were all set to 0.4, 0.18, and 10, respectively. The volumetric flow fraction for all test conditions varied from 0.0 to 0.5. The overall heat transfer distributions on the surface were captured using an infrared thermography camera. The main finding showed that the average heat transfer rate and the thermal performance gained beyond 25–81% and 7–82% compared with the smooth wall. In addition, the volumetric flow fraction of 0.5 at the Reynolds number of 200 became the best.

Optimized geometric designs of desiccant wheels with metal-organic frameworks considering dehumidification capacity and energy

With the increasing demand for handling dehumidification loads and energy savings in air-conditioning systems, solid-desiccant dehumidification systems have been implemented in passive and zero-energy buildings. Although novel metal-organic frameworks (MOFs) have been introduced to improve the performance of desiccant wheels, previous studies have mainly focused on silica gel-based desiccant rotors (DRs). This study aimed to optimize the geometric design of MOF DRs to achieve enhanced dehumidification and energy performance. A numerical model for estimating the performance characteristics of MOF DRs was developed using the adsorption isotherm curves measured in this study. The numerical model was validated by comparing the predictions with the experimental data. The dehumidification and energy performance of the MOF DRs were analyzed in terms of the coating amount, channel pitch, rotor thickness, and process-regeneration area ratio. Accordingly, the optimized geometric designs of the MOF DRs were determined to achieve the maximum dehumidification capacity and minimum energy consumption. Compared to the baseline MOF DR, the capacity-optimized MOF DR exhibited a 47.4 % higher moisture removal capacity, whereas the energy-optimized MOF DR exhibited a 48.6 % lower sensible energy ratio.

The influence of geometrical and operational parameters on thermofluid performance of discontinuous colonial self‐swirl‐inducing baffle plate in a tubular heat exchanger

AbstractAn exploratory investigation was conducted to analyze a tubular heat exchanger's turbulent heat transfer characteristics using an innovative baffle plate design. The design incorporated a perforated conical baffle plate and an adjustable rectangular deflector. The strategic placement of this baffle plate at the heat exchanger inlet facilitated a swirling flow downstream. To assess the impact of this design, three baffle plates with varying pitch ratios (l/D) were positioned in the direction of the flow. The study examined the effects of pitch ratio (ranging from 0.6 to 1.2), deflector inclination angle (ranging from 30° to 50°), and Reynolds numbers (ranging from 16,500 to 29,500). Moreover, the size of the conical baffle plate (H/D) was altered (from 0.25 to 0.15). The findings highlighted the substantial influence of pitch ratio, inclination angle, and height ratio on the heat exchanger's performance. Notably, the configuration featuring an inclination angle of 50° and height ratio of 0.15 exhibited an average performance improvement of 22% compared to other height ratios, inclination angles, and pitch ratios.

The effect of swallow-shaped bionic ribs on the thermal-hydraulic performance of heat exchanger tubes

This paper combines the bionic structure and multi-vortex longitudinal swirl to enhance the heat transfer in the heat exchanger tube while reducing the increase in flow resistance. The design of the enhanced tube with swallow-shaped bionic ribs is inspired by the aerodynamic profile of the swallow flight process to improve the comprehensive performance. The SST k-ω model is selected for numerical simulation. The study of the effect of TCR (triangular concave rib) bionic rib and TVR (triangular convex rib) bionic rib on the flow field characteristics and thermal–hydraulic performance, and the analysis of the effect of pitch ratio (P*) on the thermal–hydraulic performance of TCR tube. The results show that both types of bionic ribs promote the formation and development of multi-vortex longitudinal swirl and transverse swirl in the tube, strengthening the mixing of hot and cold fluids in the tube, improving the synergy of velocity and temperature fields, and making the temperature distribution in the tube more uniform. When P* = 0.75, Nusselt number of the TCR and TVR enhanced tubes is increased by 52.3 %–65.8 % and 43.3 %–57.9 %, respectively, and friction factor is increased by 92.7 %–202.3 % and 78.7 %–263.9 %, respectively, over the smooth tubes. The effect of P* on the thermal–hydraulic performance of the TCR tube is studied, and the PEC value increases as P* decreases. Compared to smooth tubes, TCR enhanced tubes have improved Nusselt number by 26.4 %–95.6 %, friction factor by 50.4 %-345.8 %, and PEC can reach 1.335 when the pitch ratio P* = 0.5. Consequently, the enhanced tube obtains the good comprehensive performance.

Impact of vortex generator, magnetic field, and magnetic two-phase hybrid nanofluid on the performance of a dual-tube heat exchanger: Hydrodynamic and exergy analyses

In this study, a three-dimensional model of a counter-flow dual-tube heat exchanger is developed. The heat exchanger is equipped with a vortex generator, and the working fluid used is a hybrid nanofluid consisting of water and iron-copper oxide. The effects of using the hybrid nanofluid and pure water are investigated. Turbulent flow conditions are assumed within a Reynolds number (Re) range of 30,000 to 48,000, employing the realizable k-ε turbulence model. The coupled algorithm is employed to solve the velocity and pressure equations, and the equations are discretized using the least square method. The vortex generator is utilized with various pitch ratios (Ω). Furthermore, the magnetic field affects the middle section of the inner tube, with Hartmann numbers (Ha) of 35, 65, 95, and 125. The study reveals that an increase in the volume fraction (φ) positively impacts the exergy of the heat exchanger, while an enhancement in Ω negatively influences it. Furthermore, the energy efficiency improves with increasing Re. By applying the magnetic field, the maximum power of the system in producing work corresponds to Re = 36,000 because ηex is reduced when Re > 36,000. At all values of Re, the increase in Ha improves ηex.

A case study on thermal performance of solar air heater with down apex position of open trapezoidal ribs with gaps

This study aims to experimentally explore the impact of multiple open trapezoidal ribs with gaps (MOTRG) on the thermal efficiency of a rectangular duct in a solar air heater (SAH). The designed parameters of ribs i.e. relative limb length (L/w), relative pitch ratio (p/e), relative gap ratio (g/e) and relative rib height (e/Dh) are varied as 0.2–1.0, 6–12, 1–5 and 0.023–0.056, respectively. The experiments have been conducted for Reynolds number (Re) span of 2000–16000. Since then, open trapezoidal rib designs have made significant improvements to SAH performance. A highest value of 78.86% of thermal efficiency has been observed corresponding to α = 60°, g/e = 1, L/w = 0.8, p/e = 10, W/w = 6, and e/Dh = 0.043. The global best values of enhancement factors of 3.032, 2.726 and 2.496 have been found for insolation values of 1000 W/m2, 800 W/m2 and 600 W/m2. The findings demonstrate that, when compared to other roughened SAH ducts, the MOTRG roughened duct provides superior thermal performance.

Experimental investigation on jet impingement heat transfer analysis in a channel flow embedded with V-shaped patterned surface

ABSTRACT Heating and cooling systems benefit from jet impingement as it increases efficiency while reducing operating costs. The combined methodology, integrating jet impingement and passive heat transfer through the use of roughened surfaces, offers significant potential for improving heat transfer. This research presents the results of an experimental study on a channel flow commonly used for air heating, known as a solar air heater (SAH), with impinging air on the heated surface. The surface is embedded with V-shaped ribs as turbulence promoters, and it receives a continuous heat flow of 1,000 W/m2. Various design combinations were tested experimentally, including streamwise pitch ratio X/Dh = 0.866, spanwise pitch ratio Y/Dh = 0.866, jet diameter to hydraulic diameter ratio Dj/Dh = 0.065, and an angle of attack (α) ranging from 45° to 90°. During these experiments, the Re varied from 3,500 to 18,000. The optimal improvement was observed at values of X/Dh = Y/Dh = 0.866, Dj/Dh = 0.065, and α = 60°. This paper presents novel findings demonstrating that incorporating V-shaped rib patterns in SAHs can yield Nusselt numbers up to 5.2 times higher than those in smooth duct SAHs, offering substantial potential for enhanced energy efficiency. When the entering jet impacts and flows along the ribs of the absorber, the findings suggest that the V-shaped ribs accelerate the flow, resulting in enhanced heat transfer. All datasets were also analyzed for their thermo-hydraulic performance, with the maximum value recorded as 3.301 within the constraint range used in this analysis.

The time-averaged aerodynamic performance of three circular columns arranged inline at a subcritical Reynolds number

This study conducted a series of wind tunnel tests to present the time-averaged aerodynamic performance of three equidistant circular columns arranged inline at various incidence angles and center-to-center pitch ratios under a subcritical Reynolds number of 6.4 × 104. The incidence angle α and pitch ratio L/D change in the range of 0°–90° and 1.2–4.0, respectively. The results show that the time-averaged aerodynamic performance of the three columns varies significantly with α as well as L/D. Based on the pitch ratio, the time-averaged aerodynamic coefficients can be approximately classified into four types: minimum pitch ratios (1.2≤L/D < 1.4), small pitch ratios (1.4≤L/D < 2.5), medium pitch ratios (2.5≤L/D < 3.5), and large pitch ratios (3.5≤L/D ≤ 4.0). The aerodynamic interference of the time-averaged aerodynamic coefficients under these four types is discussed by comparing the results obtained for the three columns with those for a single one. The time-averaged drag coefficient mainly experiences a reducing effect at the minimum and small pitch ratios and a certain extent of amplifying effect at the medium pitch ratios. The time-averaged lift coefficient appears non-zero values at some incidence angles, the range of which depends on the pitch ratio. The mechanism of the aerodynamic interference is also discussed by analyzing the time-averaged wind pressure distribution.

Effectiveness of a tubular heat exchanger and a novel perforated rectangular flow-deflector type baffle plate with opposing orientation

Purpose The purpose of this experimental research was to examine a novel axial heat exchanger featuring swirling air movement over heated tubes. This apparatus is designed with perforated circular baffle plates complemented by rectangular air deflectors operating at different inclination angles. The tubes were arranged in a consistent layout parallel to the longitudinal airflow. The deflector’s heightened air-side turbulence initiates the frenzied motion, escalating the surface heat transfer rate. Design/methodology/approach The tubes maintained a constant heat flux condition over the surface. In each baffle plate, eight deflectors with identical inclination angles were devised in a reverse position, forming a rotation of air inside a circular duct that held tubes (carrying hot water) which elevated air-side turbulence, thereby enhancing the rate of heat transference on the surface. The baffle plates were equally situated from each other at changing pitch ratios. The Reynolds quantity was preserved in the scope of 16,000–30,000. The performance of the heat exchanger considering pitch ratios and inclination angles was examined. Findings The research indicates that when examined under similar conditions, an exchanger with a deflector baffle plate shows a strong dependence on the pitch ratio and inclination angle with a mean rise of 0.19 times in thermal enhancement factor at an inclination angle of 30° and a pitch ratio of 1.2 contrasted with an exchanger with segmental baffle plates. Originality/value The result shows the dependence of pitch ratio, Reynolds number and inclination on the heat transfer and friction factor rate.

Numerical Investigation of Reversed Flow Solar Air Heater Roughened With Circular- and Triangular-Shaped Tubes

Abstract The roughness geometry has been introduced to improve the rate of heat transfer in a solar air heater duct. In the current work, circular and triangular shape geometries are used as roughness elements in the rectangular channel to enhance the thermal performance of reversed flow solar air heater (RFSAH). The important parameters selected for the research are Reynolds number (Re = 5000–18,000 (5 values)), pitch ratio (P/e = 4–12 (5 values)), and height ratio (e/D = 0.0392–0.1571 (4 values)). A 2D-computational fluid dynamics (CFD) model was developed using ansys (fluent 2022r1), and simulation was performed using the k−ε (RNG) turbulence model and validated with one set of experimental results for smooth duct and previous research. The findings revealed that the highest value of heat transfer was augmented about 2.18 times and 2.35 times for circular and triangular roughness geometry, respectively, as compared to the smooth channel at a Reynolds number of 12,000. The thermohydraulic performance factor (TPF) is 1.58 and 1.7 at pitch ratios of 6 and 5 for circular and triangular roughness geometry respectively, at Re of 12,000.

Effect of jet angle and jet pitch on the Thermo-Hydraulic performance of solar air heater having absorber plate with jet impingement

This numerical investigation focuses on enhancing the heat transfer characteristics and thermo-hydraulic performance of a solar air heater by employing jet impingement over the absorber plate. The study explores the influence of two geometrical parameters, namely jet pitch ratio (P/Dh) and jet angle ratio (α/90), on the heat transfer, frictional losses, and overall performance of the solar air heater with jet impingement (SAHJI) under various flow conditions, represented by Reynolds numbers (Re) ranging from 3500 to 17500. The simulations are conducted using the RNG k-ɛ model with second-order upwind discretization. A comparative analysis is performed between the SAHJI system and a conventional smooth solar air heater (SPSAH) configuration, revealing a significant enhancement in thermal–hydraulic performance with the use of jet impingement. The investigation identifies the maximum thermo-hydraulic performance parameter, reaching a value of 4.12. This peak performance is achieved at specific values of jet pitch ratio (P/Dh) of 1.30 and jet angle ratio (α/90) of 0.094, respectively, at a Reynolds number of 7500. These findings demonstrate the potential of jet impingement as a heat transfer enhancement technique in solar air heaters, contributing to improved overall system efficiency.

Influence of Design Parameters on Mechanical Behavior of Multi-Bolt, Countersunk C/SiC Composite Joint Structure.

Aerospace vehicle connection constructions are in urgent need of joint structures with excellent aerodynamic profiles and environmental adaptability. To address issues such as poor aerodynamic profile, material thermal expansion coefficient mismatch, and limited joint structure evaluation indexes, a multi-bolt, countersunk C/SiC composite joint structure is presented in this study. The development of a 3D Hashin progressive damage model and its dedicated solver code is presented. The validity of the model is confirmed by comparing simulation results with experimental data. Three evaluation indexes are proposed, peak load, weight increment efficiency, and bolt load distribution, to thoroughly evaluate the mechanical performance of multi-bolt, countersunk C/SiC composite joint structures. Using the proposed model and evaluation indices, we evaluate sixteen different designs of multi-bolt, countersunk C/SiC composite joint structures and analyze how design parameters affect their mechanical properties and damage patterns. The results show that the best mechanical properties of the joint structure are achieved when the ratio of bolt pitch to through hole diameter is 3, the ratio of bolt spacing between columns to through hole diameter is 4, the ratio of the distance between the free edge of the substrate to through hole diameter is 1.5, the ratio of through hole diameter to specimen thickness is 1.7, and the ratio of the distance between the edge of the substrate to through hole diameter is 1.5.

Heat transfer and pressure drop characteristic research of sine wavy flying-wing fins

In recent years, heat transfer enhancement of heat exchange equipment has attracted more and more attention. In this paper, the heat transfer and pressure drop characteristics of sine wavy flying-wing fins are studied by numerical method. The objective is to improve the integrated heat transfer and pressure drop performance of sine wavy flying-wing fins. The degrees of freedom of fin sizes include fin pitch to fin height ratio fp/fh, fin height to fin wavelength ratio fh/W, fin amplitude to fin pitch ratio 2A/fp and fin inclined angle α. The results show that among the calculated 17 flying-wing fins, the optimal values of fp/fh, fh/W, 2A/fp, and α are 0.5, 0.4, 1.9 and 70° respectively. The optimized SWFWF simulation model is established, and the average JF factor is 1.307, which is about 10.9% higher than that of Fin 05 (JF = 1.18). Multiple linear regression is used to obtain the correlations of flow and heat transfer characteristics of flying-wing fins. The average deviation of the correlations for j and f are 0.85% and 4.9% respectively. The correlations can be used for the design and optimization of sine wavy flying-wing fins.

Discharge behavior of spherical and rock chip mucks by screw conveyors in TBM: Physical model experiments and DEM simulations

The discharge of muck through a screw conveyor system plays a crucial role in ensuring safe and cost-effective tunneling with earth pressure balance tunnel boring machines (EPB-TBM). However, the discharge mechanism of chip-type rocky mucks through a screw conveyor has not been well examined. Therefore, this study investigates the discharge behavior of rock chips through a screw conveyor by using a 3D discrete element model (DEM). Numerical simulations are conducted with rock chip particles of various sizes, as well as spherical particles, while varying the inclination angle, screw pitch length, and rotational speed of the screw conveyor. The simulation results show that the relative size between the muck particles and pitch has a significant effect on the discharge rate, and an optimal ratio of pitch to flight diameter is suggested. The particle-level analysis reveals distinctive particle discharge paths and a velocity distribution of muck particles along the screw axis. The study proposes the ratio of the screw pitch to the maximum particle size as the primary design parameter to predict the discharge rate. This is because large particles play a critical role in determining the discharge rate. The study highlights the usefulness of 3D DEM-based simulation as a tool to investigate discharge behavior of particulate materials through a screw conveyor. Moreover, it advances our understanding of rock chip-type muck discharge behavior during TBM excavation, providing guidance for screw conveyor design and feedback during TBM operation.