Bi-directional Turbine Research Articles

Acoustic characterization of a bi-directional turbine

A thermoacoustic engine converts thermal energy into acoustic energy, which can then be converted into electricity using an alternator. The conversion of acoustic-to-electric energy in thermoacoustic electricity generators usually relies on electromagnetic transducers. A bi-directional turbine coupled to a DC motor offers a plausible alternative due to its simplified mechanical design, cost-effectiveness, and relatively good performance. Efficient coupling of a bi-directional turbine with a thermoacoustic engine requires a comprehensive understanding of its operating behavior. This study aims to extend existing research by carrying out experimental characterization of a bi-directional turbine. This will involve measuring its transfer matrix and impedance under various acoustic conditions. The experimental results are then analyzed and compared with the predictions of an electro-acoustic model.

Central motor output does not interact with muscle metaboreceptors input for ventilation regulation during dynamic exercise in health humans

INTRODUCTION: The muscle metaboreflex typically does not contribute to ventilation regulation when activated in isolation at rest via post-exercise circulatory occlusion (PECO), but it might synergistically interact with other mechanisms operating during voluntary exercise. Efferent signals from brain areas involved in the motor control of appendicular skeletal muscles to the medulla (i.e., central command) supposedly contribute to ventilation regulation during voluntary exercise. Therefore, we sought to test the hypothesis that central motor output interacts with muscle metaboreceptor input, generating a greater ventilatory response to PECO during voluntary exercise than electrically-induced involuntary exercise. METHODS: Thirteen healthy adults (4 women, age: 26 ± 5 years) participated in the study. Each participant completed four experiments in random order. Two experiments were accomplished per visit at 30-minute intervals. The interval between visits was at least two and at most seven days. The muscle metaboreflex was activated by rhythmic handgrip exercise with the dominant hand at 60% of the maximal voluntary contraction force with a 2-s duty cycle. Then, the muscle metaboreflex remained active for a 4-minute recovery period via PECO, or it was inactivated via free circulation to the exercised arm. During the last 2-minutes of the handgrip exercise recovery, participants either performed unilateral voluntary plantar flexion with the dominant leg to generate central motor output or the dominant leg’s calf was involuntarily activated by electrical stimulation not to have central motor output. Voluntary and involuntary calf contractions were performed at the same external workload. A rebreathing circuit maintained isocapnia throughout all experiments. A bidirectional turbine measured breath-by-breath airflow. Heart rate was measured via ECG, and arterial pressure by auscultation in a resting arm. RESULTS: Ventilation, heart rate, and arterial pressure increased during handgrip exercise similarly in all experiments. PECO-induced muscle metaboreflex activation maintained ventilation (Δ = 5.4 ± 5.2 l/min, P = 0.003), heart rate (Δ = 6.6 ± 8.0 bpm, P = 0.011) and systolic arterial pressure (Δ = 28.4 ± 14.8 mmHg, P < 0.001) elevated above the control handgrip exercise recovery with free circulation to the exercised arm. The ventilation response to voluntary plantar flexion was greater when PECO was present in the arm than when it was absent (Δ = 8.3 ± 5.6 l/min vs. 4.5 ± 2.7 l/min, P = 0.006), reproducing previous findings. However, the ventilation response to voluntary and involuntary plantar flexion with a PECO background was similar (Δ = 8.3 ± 5.6 l/min vs. 8.2 ± 6.3 l/min, P = 1.000). CONCLUSION: The data do not support that an interaction between central motor output and muscle metaboreceptors input is obligatory to generate a ventilatory response to PECO during voluntary exercise. FINANCIAL SUPPORT: grant 2023/07135-0, São Paulo Research Foundation (FAPESP); Scientific production award from the National Council for Scientific and Technological Development (CNPq; Process: 310110/2019-0). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A 3D Printed bi-directional Turbine for Thermoacoustic Standing Wave Environment at an Atmospheric Pressure

This paper reports a study on the use of an in-house 3D printed bi-directional turbine for energy conversion in a standing wave thermoacoustic environment that is operated at an atmospheric pressure. The 3D printed turbine was placed at two locations along the resonator and the data were recorded for several range of flow frequency and flow amplitude. It is found that maximum output is achieved when flow is not at resonance. Resonance of the standing wave inside the rig was found at 106 Hz but the bi-directional turbine performs better at a lower frequency of 85 Hz.

Design and Development of Power Generation System for Thermo-Acoustically Driven Devices

This paper explores the emerging field of thermo-acoustic devices, specifically focusing on developing robust bidirectional turbines. Amidst growing concerns about climate change, rising energy demands, and the urgent need for alternative solutions, the study highlights the underexplored domain of bidirectional turbines within thermo-acoustic systems, offering a crucial pathway toward cleaner and more sustainable technologies, thereby providing commercialization potential. It identifies a significant gap in dedicated investigations regarding the interaction, efficiency, and challenges associated with bidirectional turbines and adopts a comprehensive methodology integrating analytical modelling, computational fluid dynamics simulations, and practical experimentation. An axial bidirectional turbine is carefully selected, designed, and optimized using advanced tools such as MATLAB R2016a and CAD software, including PTC Creo 5.0 and Solidworks 2023. The validity of the CAD model is verified through ANSYS 16.2 CFX simulations, followed by experimental validation to corroborate and enhance theoretical insights. The conclusions drawn from this study offer valuable recommendations for further research and practical implementations.

Exploration of a Model Thermoacoustic Turbogenerator with a Bidirectional Turbine

Abstract The utilisation of the thermal emissions of modern ship power plants requires the development and implementation of essentially new methods of using low-temperature waste heat. Thermoacoustic technologies are able to effectively use low-temperature and cryogenic heat resources with a potential difference of 500–111 K. Thermoacoustic heat machines (TAHMs) are characterised by high reliability, simplicity and environmental safety. The wide implementation of thermoacoustic energy-saving systems is hampered by the low specific power and the difficulties of directly producing mechanical work. An efficient approach to converting acoustic energy into mechanical work entails the utilisation of axial pulse bidirectional turbines within thermoacoustic heat engines. These thermoacoustic turbogenerators represent comprehensive systems that consist of thermoacoustic primary movers with an electric generator actuated by an axial-pulse bidirectional turbine. The development of such a thermoacoustic turbogenerator requires several fundamental issues to be solved. For this purpose, a suitable experimental setup and a 3D computational fluid dynamics (CFD) model of a thermoacoustic engine (TAE) with bidirectional turbines were created. The research program involved conducting physical experiments and the CFD modelling of processes in a TAE resonator with an installed bidirectional turbine. The boundary and initial conditions for CFD calculations were based on empirical data. The adequacy of the developed numerical model was substantiated by the results of physical experiments. The CFD results showed that the most significant energy losses in bidirectional turbines are manifested in the output grid of the turbine.

Delta EC Simulation on Influence of Resonator Length in Close-Open Standing Wave Thermoacoustic Engine

<p class="Abstract"><em><span lang="EN-US">Many applications of thermoacoustic engines in engineering. With its pressure of it, the energy can be harvested and can be converted to many other needs of energies like electrical energy. Energy in thermal form is converted to become acoustic energy and subsequently used to activate a bidirectional turbine. The resonator is very influential toward the power of the thermoacoustic engines. Simulation study with Delta EC fit to make predictions acoustic power as representative performance in thermoacoustic engine with close-open type and standing wave of oscillation. In this study, the material of the resonator is made from a stainless-steel duct with a diameter size of 50.8 mm with three variations of the length. The Standing-Wave Thermoacoustic Engine (SWTE) generates acoustic energy from a temperature gradient of 315 – 993 K. </span></em><em><span lang="IN">In this simulation, Acoustic Power decreased when the resonator length was extended. The shortest resonator had an acoustic power of 50.4 W, and the longest resonator had an acoustic power of 35.7 W.</span></em></p>

Investigating the impact of multi-rotor structure shadowing on tidal stream turbine performance

As the tidal stream energy sector develops, reducing the Levelised Cost of Energy (LCOE) is essential to sustain commercialisation. Modular multi-rotor foundations, with bi-directional turbines, reduce offshore operational complexity through smaller turbine diameters and lift weight, in turn reducing the device Operational Expenditure (OpEx). With the introduction of modular, multi-rotor foundations, the wake-induced impacts that these structures have on turbine performance must be investigated to better estimate energy yield, loading, and fatigue life. This study sets the scene for investigating the relationship between the turbulent wake generated by a modular ballast weighted foundation and 2-bladed Horizontal Axis Tidal Turbine (HATT) motivated by the HydroWing multi-rotor device concept. The presented work aims to determine the broader magnitude and severity of the loads and establish a robust methodology to be followed with further high-fidelity modelling. Initially, a transient RANS Computational Fluid Dynamics (CFD) simulations environment with a sliding mesh is configured and validated against experimental data. A turbine in free-stream isolation is simulated as a benchmark case with the modular foundation sequentially introduced to analyse the impact of the structure. Key findings suggest that operating turbines downstream of the multi-rotor foundation could cause a 20% fluctuation in thrust loading at a 1.82 Hz frequency resulting in a mean Cp reduction of 8% over a revolution.

Analysis of the viability of a radial Double Decker Turbine for application in Oscillating Water Column devices

Oscillating Water Column (OWC) devices are the most widespread among the different systems developed to harness the wave energy available on our coasts. Air turbines, normally used as Power Take Off (PTO) in these devices, are their most controversial part. Unidirectional turbines were first used with rectifying valves to take advantage of both characteristic operating stages of the OWC: exhalation and inhalation. The use of valves was quickly discarded and bidirectional turbines, which rotate in the same direction regardless whence the flow comes, were adopted as the most common solution despite reaching lower efficiencies than unidirectional ones. The Twin Turbine Configuration (TTC), based on the use of two unidirectional turbines, emerged then as a promising system, its main drawback being the duplicity of the equipment. The Double Decker Turbine (DDT) concept has been recently introduced to overcome these limitations since it combines in a single design the two typical solutions: self‐rectifying behaviour and the use of unidirectional turbines. In this work, the performance of a radial DDT, composed of an InFlow Radial (IFR) turbine and an OutFlow Radial (OFR) turbine, is assessed. A CFD model is used to design and optimize an IFR turbine to be mounted in combination with an OFR turbine taken from the literature. Finally, a non‐steady analysis is carried out assuming sinusoidal flow conditions. Results demonstrate that this radial version of the DDT could compete with its axial version and with other alternatives.

Analysis of data from the full-scale prototype testing of the WASP – A novel wave measuring buoy.

To assess the viability of locations for wave energy farms, and design effective coastal protection measures, knowledge of local wave regimes is required. Current regime-measuring devices are expensive, and the aim of the WASP Project is to develop a low-cost, self-powering wave-measuring device. The Wave-Activated Sensor Power Buoy (WASP) comprises a floating body with a moonpool. The relative motion of the water level in the moonpool to the buoy will pressurise and depressurise the air above the water column, which will be used to drive a bidirectional turbine in the manner of an oscillating water column, which will operate in conjunction with a generator to recharge an on-board battery pack. It has previously been demonstrated through tank testing of scale-models that a sea-state may be estimated from measurements of the pressure within the air above the water column under controlled conditions [1]. Important statistical parameters relating to the sea state, such as the significant wave height, zero-cross period et cetera. may then be estimated from the spectral moments of the wave spectrum [2].
 This paper seeks to validate the use of measurements taken of the pressure in a volume of air contained in a chamber above an oscillating water column (OWC) (which is in communication with the ocean) to estimate the sea state which induces motion of the water column.
 The WASP was deployed from March to July 2019 at the Smart Bay test facility in Galway Bay, Ireland. The ¼ Scale test site was previously characterised by B Cahill UCC 2011 [3] using data captured by the Marine Institute Datawell WaveRider buoy from 2006 to 2011. Pressure signal data recorded by the WASP at a frequency of 8Hz was processed in to 30-minutes blocks to reflect the presented data from the WaveRider buoy, from which the WASP was moored a distance of 400m from during deployment. Power Density Spectra for 6,500 thirty-minute sea states were generated and an inverse transfer function between the WASP and the WaveRider produced. This allowed for the calculation of the associated significant wave height, Hs, and zero-crossing period, Tz, from the WASP pressure data for each thirty-minute block of data. At this time, outliers and bimodal spectra were removed to simplify the analysis, and the data was binned based on Hs and Tz ranges. For each bin, average inverse transfer functions were generated. A Bretschneider Spectrum [4] was produced using the Hs and Tz values from the WaveRider data for the respective binned WASP data. An average transfer function was then generated between the Bretschneider models and the corresponding sea states for the WASP. Using this final transfer function, a scatter plot of Hs and Tz for the test site was generated and compared against the previously produced scatter plot from the initial resource characterisation of the Galway Bay Test Site in 2011 in order to determine if the WASP is capable of measuring sea-states through measurement of time series pressure signals in the volume of air above the water column in the OWC.

Sustainable production of green hydrogen, electricity, and desalinated water via a Hybrid Solar Chimney Power Plant (HSCPP) water-splitting process

This work presents a novel sustainable approach to producing desalinated water (Wdes), green hydrogen (GH2) and electrical energy (Eelc) using Hybrid Solar Chimney Power Plant (HSCPP) coupled with a water-splitting (WatSp) process. The HSCPP consists of a collector, absorber, chimney, bidirectional turbine outfitted with a seawater pool, and water electrolysis (Watelc) cell. The HSCPP harnesses solar energy to heat the air under the collector creating air movement within the structure, passing the bidirectional turbine, and producing Eelc. Sprinklers were fitted within the structure to operate the HSCPP as a cooling tower (CT) in the absence of solar radiation (Solirr). The Watelc cell directly uses the produced Eelc for the production of Hydrogen (PH2) and oxygen (PO2), while the condensed water at the chimney's inner walls was also collected as Wdes. Results revealed that the continuous operation of the HSCPP has an average annual Eelc of 633 ± 10 MWh that could be efficiently used to generate 21,653 kg of GRH2, 173,244 kg of O2 as well as 190,863 tons of Wdes. The overall efficiency of the HSCPP for the PH2 was found to be 18.5%, which is higher than Solar PV (max∼ 6%) and geothermal Rankine (max∼ 15%). These high efficiencies rank this technology as competitive with other renewable hydrogen production technologies. In conclusion, HSCPP has a promising future as a novel and sustainable solar tower technology to produce hydrogen.

Design method for a bidirectional ducted tidal turbine based on conventional turbomachinery methods

Renewable energy sources include solar, wind, hydro, geothermal and biomass. Furthermore, ocean energy is being rapidly harnessed worldwide. In this study, to establish a suitable design method for various bidirectional ducted tidal turbines, instead of using blade element momentum theory and CFD, which have been used previously, the method used for turbomachinery was used for designing the turbines. A bidirectional turbine optimises the equipment design and reduces manufacturing and maintenance costs. Using the turbine power as the design condition, the difference in the tangential velocity between the front and rear of the turbine was calculated using Euler’s equation, and the blade stagger angle was determined based on the potential flow theory. To incorporate the effect of duct geometry into this design method in the future, the effect on the internal flow of the duct was experimentally investigated using three ducts with different maximum cross-sectional areas. Performance tests showed that the duct geometry had a negligible effect on the flow rate through the turbine. Therefore, the larger the maximum diameter of the duct, the greater the flow rate into the outside of the duct. The pressure difference between front and rear of the turbine and the inflow energy into the duct were different due to the energy conversion as the flow turned outside of the duct. To improve the accuracy of the design method, the effect of flow at the duct inlet and the energy conversion should be incorporated, and a review of the estimation method for the axial velocity ratio and the selection method for the design representative value should be conducted.

Triple-renewable energy system for electricity production and water desalination

This work presents a novel triple-renewable energy system (TRES) that is based on integrating the photovoltaic panels (PVPs), conventional solar chimney (CSC), and cooling tower (CT) in one structure. The ultimate objective of the proposed TRES system is to produce electrical power (Pelc), desalinated water (Dw), and if required cooling utilities. The components of the system include a chimney tower, collector, base, PVPs, water pool, bi-directional turbine, and water sprinklers. The TRES system can be operated as CSC during the daytime and CT at night providing 24-h operation. The PVPs were integrated within the structure to increase the Pelc production and enhance the process performance by heating the air inside the system. The TRES structure increased the efficiency to 0.860% in comparison with the CSC (0.313%). The annual Pelc production from the TRES system was found to be 792 MWh compared with only 380 MWh generated by the CSC achieving 2.1 folds overall improvement. The CSC-PV and CT contributed to 47% (494 MWh) and 24% (253 MWh) of the Pelc production, respectively. The annual Dw production was found to be 1.2-fold higher (163,142 tons) higher than the CSC (139,443 tons). The newly developed TRES system offers a great potential to produce Pelc and Dw and save fossil fuel consumption while reducing the emissions of greenhouse gasses (GHGs) to the atmosphere.

Analysis of an optimized radial impulse turbine for an OWC wave energy converter

Abstract OWC concept is one of the most spread technologies among wave energy converters due to several reasons. However, this technology has always deal with the problem of the inherent bidirectional flow. Many solutions have been adopted such as a flow rectification system combined with a unidirectional turbine, several types of bidirectional turbines such as Wells turbine or impulse turbine. In this work, it is shown the performance of an optimized geometry for a radial impulse turbine, which improvement is based on the re-designing of the blades and settling angles of the vanes. A CFD model, validated against results from the bibliography, has been used to simulate both a new and a previous geometry taken as reference. The results of both turbines have been analysed in terms of the loss coefficients for each element in order to analyse the advantages of the new geometry. It has been found that the new geometry exceeds the efficiency of the previous geometry by 5%, being this gain based on the fact that sacrificing the rotor’s efficiency could lead to a great improvement in the performance of the guide vanes, reducing their loss and, in turn, lifting the turbine’s efficiency despite reducing the rotor’s one.

Numerical investigation on flow collector with guide vane for tidal energy conversion

Abstract In ocean-based renewable energies, such as wave motion, ocean current, tidal current and ocean thermal energy, many studies have been conducted on the wave energy conversion system and they have been tested in many countries. In this study, a tidal current energy is focused. Collecting a tidal flow is very important because it is generally known that a power available from a stream of water is proportional to the cube of the free stream velocity of the current. In this research, a bi-directional turbine system is investigated for a tidal flow that changes the direction periodically. Numerical investigations are conducted on a bi-directional flow collector with guide vane to collect the flow, in which the effects of vane skew angle and blade number are investigated. Calculated results showed that the collector with eight guide vanes was the highest angular moment at turbine inlet. The axial velocity at turbine inlet was larger for smaller value of the vane skew angle, whereas the tangential velocity at the turbine inlet was larger for larger value of the vane skew angle. As the results of both the profiles of axial and tangential velocity, the angular moment took the local maximum value at around the angle of 180 deg. in this study.

Repeatability and reproducibility of changes in thoracoabdominal compartmental volumes and breathing pattern during low-, moderate- and heavy-intensity exercise.

To determine how repeatable thoracoabdominal compartmental contributions to tidal volume (VT) are across different intensities of exercise, and to examine if the pattern of breathing for a given minute ventilation (V̇E) is reproducible between constant-load and ramp exercise tests. Ten healthy adults (age: 27 ± 6yr, peak oxygen uptake: 42 ± 5mLmin-1kg-1) completed a 25W·min-1 ramp cycling test to exhaustion and two repetitions of a step cycling test on separate days. VT, breathing rate (BR), and V̇E were assessed using a bi-directional turbine, and thoracic and abdominal contributions to VT were measured using respiratory inductance plethysmography. Repeatability (step vs. step) and reproducibility (step vs. ramp) of responses were assessed using the intra-class correlation coefficient (ICC). The relative compartment contributions to VT during step exercise were highly repeatable for low (ICC = 0.87, p = 0.003), moderate (ICC = 0.89, p = 0.002) and heavy (ICC = 0.93, p = 0.001) exercise. Inter-individual differences in response to higher intensity exercise were observed, as two participants had significant relationships between VT and their percent compartmental contributions to VT, but five others did not. No differences were identified between ramp and step exercise tests for VT (main effect: p = 0.61) or BR (main effect: p = 0.77) at matched V̇E for each intensity, and the pattern of breathing was reproducible for each intensity. These findings suggest the way young healthy adults breathe for a given V̇E is repeatable day-to-day and reproducible between different exercise protocols.

Bidirectional Impulse Turbine With Spiral Flow Collector for Tidal Energy Conversion

Abstract In order to make use of ocean renewable energy, a combination system of a bidirectional impulse turbine and a bidirectional flow collector for tidal current energy conversion is investigated in this paper. It is the advantage that this turbine system does not need an operation of orientation change according to the reversal of regular tidal orientation when fixed on the seabed. The experimental investigations by using both a circulating water tank and a towing tank showed that the turbine power output could be increased by adopting the flow collector proposed in this study. Then the flow collector with a fixed spiral vane named spiral flow collector was investigated by both a circulating water tank test and computational fluid dynamics (CFD) analysis. The experimental result of the spiral flow collector showed that the performance improvement was found on the increase of axial velocity in the turbine which contributed to the increase of the turbine power output. The results of CFD analysis showed that 180 deg of the skew angle of the fixed spiral vane was suitable in view of the angular moment at the turbine inlet in this case.

Экспериментальное исследование двунаправленной импульсной турбины в постоянном потоке газа

Экспериментальное исследование двунаправленной импульсной турбины в постоянном потоке газа

Research on the Blade Motion of a Bidirectional Energy-Generating Turbine under Integrated Wave and Tidal Current Action

An integrated wave-tidal current power turbine is affected by both wave and tidal current forces, and its energy efficiency is closely related to the velocity and direction of the two forces. To improve the probability of the horizontal axis turbine reaching maximum energy efficiency under real-time changing sea conditions, we performed the following investigations in this study. Based on the actual application scenario of Lianyungang port, a time series prediction model of tidal current (velocity and flow direction) and wave (mean wave direction, mean wave period, and significant wave height) data for the past year was established. The changes in waves and tidal currents within 24 h after the cutoff point of the existing data were predicted. The integrated wave-tidal current mechanism was studied, and the superposition of wave energy and tidal current energy was transformed into the equivalent velocity vector of wave-tidal current integration. The conversion coefficient between waves and equivalent flows was determined by a numerical wave flume simulation. According to the historical wave and tidal current data, the equivalent velocity range of the integrated action of waves and tidal currents in Lianyungang was determined. The influence of different blade motions on the energy harvesting efficiency of the turbine under the corresponding flow conditions was studied using the Computational Fluid Dynamics (CFD) method to determine the blade motion law of the turbine. The blade motion law of the prototype was verified in a sea trial experiment. The experimental results were basically consistent with the simulation results for the blade motion law designed according to the wave and tidal current prediction law. This design scheme can provide a reference for engineering design for the development and utilization of new marine energy.

Turbin Hibrid Bi-Directional Sebagai Pemanen Energi pada Thermoacoustic Engine

Bi-directional turbines that are commonly applied to convert wave energy into motion energy are the types of Impulse turbines and Wells turbines. Both types of turbines each have advantages and disadvantages. In this research, hybrid turbine type is designed and made to bridge the weaknesses in impulse turbine and turbine wells. Hybrid turbines are made by placing impulse turbines on the outside while turbine wells placed on the inside. In this research, the variation of hybrid bi-directional turbine design aims to find out the most optimal design of this turbine type. Six variations were carried out including a hub to tip ratio of 0.5 with 4 and 5 Wells blades, a hub to tip ratio of 0.6 with 4 and 5 Wells blades, and a hub to tip ratio of 0.7 with 4 and 5 Wells blades. From the test results on thermoacoustic engine media, based on the hub to tip ratio, the most optimal hub to tip ratio is in the order of 0.7 then 0.6, and 0.5. Whereas based on the number of Wells blade, obtained the number of Wells blade 5 is more optimal than the number of Wells blade 4.

Repeatability of Thoracoabdominal Wall Compartmental Contributions to Tidal Volume during Low‐, Moderate‐ and Heavy‐Intensity Exercise

The patterns of breathing and the thoracoabdominal wall compartmental contributions to tidal volume at different exercise intensities are typically assessed during a single laboratory visit, where individuals complete progressively higher intensity stages of exercise. The relative contributions of the thoracic and abdominal compartments have been reported to be invariant across exercise intensities; however, inter-individual differences have been observed. Therefore, the purpose of this study was to assess the repeatability of the compartmental contributions to tidal volume during low-, moderate-, and heavy-intensity exercise. It was hypothesized that the inter-individual differences in the compartmental contributions would be repeatable day-to-day for each intensity. Seven healthy adults (2 female, age: 28±7 yr, peak oxygen uptake: 45±5 ml·min-1·kg-1) completed two step exercise tests on separate days, consisting of low-, moderate-, and heavy-intensity stages for each individual based on their ramp exercise responses. Tidal volume and breathing rate were assessed using a bi-directional turbine, and thoracic and abdominal contributions to tidal volume were measured by respiratory inductance plethysmography. Day-to-day repeatability was evaluated using the intra-class correlation coefficient (ICC). With increasing exercise intensity, the tidal volume (p<0.001) and breathing rate (p<0.001) increased, but no differences in tidal volume (p=0.97; low: 1.14±0.21 L vs. 1.22±0.48 L, moderate: 2.02±0.49 L vs. 1.92±0.54 L, heavy: 2.51±0.60 L vs. 2.54±0.59 L) or breathing rate (p=0.94; low: 18±4 breaths·min-1 vs. 17±6 breaths·min-1, moderate: 22±8 breaths·min-1 vs. 23±7 breaths·min-1, heavy: 37±9 breaths·min-1 vs. 37±10 breaths·min-1) were observed between testing days. The relative contribution of the thoracic (low: 64±12% vs. 63±15%, moderate: 66±12% vs. 64±14%, heavy: 67±11% vs. 67±12%) and abdominal (low: 36±12% vs. 37±15%, moderate: 34±12% vs. 36±14%, heavy: 33±11% vs. 33±12%) compartments did not differ significantly between test days (p=0.59), or exercise intensities (p=0.38). However, there were inter-individual differences in how the compartmental contribution to tidal volume changed with exercise intensity, as the relative contribution of the thoracic compared to abdominal compartment increased with higher intensity exercise for 3 subjects, decreased for 1 subject, and remained relatively constant for 3 subjects. These inter-individual differences to increasing exercise intensity do not appear random, as the test-retest repeatability of the compartmental contribution to tidal volume was good to excellent for low (ICC=0.87, p=0.003), moderate (ICC=0.89, p=0.002) and heavy (ICC=0.93, p=0.001) exercise. Future work should seek to identify factors contributing to the observed inter-individual differences in compartmental contribution to tidal volume with increasing exercise intensity and whether these impart functional consequences.