bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupled Dynamic Analysis of Hybrid Offshore Wind Turbine and Wave Energy Converter
Authors: Rony J.S. , Karmakar D.
Published: November 2021

The combined offshore wind and wave energy on an integrated platform is an economical solution for the offshore energy industry as they share the infrastructure and ocean space. The study presents the dynamic analysis of the Submerged Tension-Leg Platform (STLP) combined with a heaving-type point absorber wave energy converter (WEC). The feasibility study of the hybrid concept is performed using the aero-servo-hydro-elastic simulation tool FAST. The study analyzes the responses of the combined system to understand the influence of the WECs on the STLP platform for various operating conditions of the wind turbine under regular and irregular waves. Positive synergy is observed between the platform and the WECs, and the study also focuses on the forces and moments developed at the interface of the tower and platform to understand the effect of wind energy on the turbine tower and the importance of motion amplitudes on the performance of the combined platform system. The mean and standard deviation for the translation and rotational motions of combined wind and wave energy converters are determined for different sea states under both regular and irregular waves to analyze the change in responses of the structure. The study observed a reduction in motion amplitudes of the hybrid floating system with the addition of the wave energy converters around the STLP floater to improve the energy efficiency of the hybrid system. The study helps in understanding the best possible arrangement of point absorber-type wave energy converters at the conceptual stage of the design process.
Experimental Study on CaCO3 Fouling Characteristics During Falling Film Evaporation
Authors: Ding Zhikou , Li Wei , Wang Lei , Zhao Limin , Sherif S. A. , Wang Ru , Kabelac Stephan
Published: November 2021

Falling film evaporation is widely used in solar desalination systems. Fouling is an important problem to be addressed in many applications involving heat transfer including processes involving the utilization of solar energy in desalination applications. In the research upon which this paper partly reports, an experimental investigation was carried out on a vertical tube in falling film evaporation to determine the effects of temperature, velocity, the use of a porous-sintered tube, and the use of Teflon coating on calcium carbonate deposition characteristics. During the fouling experiments, the pressure inside the test tubes was maintained constant at 101.3 kPa, and the inlet temperature was maintained at 373 K, while allowing the water mass velocity to vary from 0.42 to 1.05 kg m−1 s−1. Results show that the fouling in the test tube becomes more serious as the temperature increases and the flowrate decreases. Compared with stainless-steel tubes, porous-sintered tubes can significantly reduce fouling resistance, but at the same time they bring about a decrease in the heat transfer coefficient. The Teflon coating also has anti-fouling performance but does not affect the heat transfer coefficient in stainless-steel tubes. Through the weighing of local fouling deposits, it has been found that the mass of the fouling deposits in the lower part of the tested tubes is greater than that in the upper part.
Hybrid Frequency Response Characteristics of a Low-Frequency Charge-Mode PVDF Curvature Sensor Measured With a Random Vibration Method
Authors: Lloyd George M. , Zhang Ying , Fabo Peter , Wang Ming L.
Published: November 2021

Polyvinylidene fluoride (PVDF) is a semicrystalline polymer exhibiting piezoelectric and pyroelectric properties which has been used for sensing infrared energy and the measurement of high frequency stress and strain, such as shocks. Despite the low material cost, durability, high sensitivity, and fast response, PVDF-based sensors have not been successfully used in sensors for large structures (such as buildings and bridges) with dominant low frequency modes, where these benefits would seem appropriate. One reason is that the low frequency response of the sensor and integrated charge amplifier (the hybrid characteristic of the sensor) has not been adequately measured and modeled. In this paper we report precise measurements of the hybrid frequency response of a charge-mode curvature sensor in the range 0.1–45 (Hz) using a random vibration method in conjunction with a precision displacement stage. The experimentally determined response is compared to a SPICE model. The results show a characteristic high pass response with cutoff in qualitative agreement with the model. However the rolloff appears consistently more rapid, with possible attenuation at high frequencies. These results will be useful for developing more accurate models of the sensor, and to further the use of PVDF in low frequency applications.
Optimizing Stiffness Properties of Tensegrity Structures
Authors: de Jager Bram , Skelton Robert
Published: November 2021

The design of mechanical systems normally exploits numerical analysis and optimization. We make a plea for symbolic computation and give an example where the desired results are symbolic. Geometrical design parameters enter in this computation. The resulting expressions reveal the values which yield desirable properties for, e.g., stiffness or damping. This is applied to repetitive (fractal) mechanical systems, namely tensegrity structures. A set of equations linear in the degrees-of-freedom, but nonlinear in the design parameters, is solved symbolically. A large scale example with 1533 degrees-of-freedom is computed successfully. The results make it possible to optimize the structure with respect to stiffness properties, not only by appropriately selecting (continuous) design parameters like dimensions, but also by selecting the number of stages used to build up the structure (a discrete design parameter).
Modeling of Active Constrained Layer Damping Structures Using a Commercial Finite Element Code
Authors: Lumsdaine Arnold
Published: November 2021

Active Constrained Layer Damping (ACLD), involving a hybrid of active and passive damping elements, has been shown to be a promising method for maximizing vibration damping effectiveness. Active damping can be effective at reducing vibration of a given single mode. Passive damping has dissipative qualities for all modes. There has been much discussion comparing and contrasting the uses of these different methods in the literature. It has been found that using a hybrid ACLD layer can be more effective than just using an active control (AC) approach or a Passive Constrained Layer Damper (PCLD) approach, in some cases.

ACLD structures are characterized in the literature either by the development of analytic equations, or by finite element modeling. In cases where the ACLD structure is modeled using finite elements, the formulation is done by the author in developing a code. This limits the availability of the result beyond a specific application. For the modeling of ACLD structures to be more generally applicable, and available, modeling could be done using a commercial finite element code. A greater variety of different structures could be modeled, and structural optimization could easily be integrated. The study of ACLD structures would be available to an audience without the resources to construct their own elements. To the author’s knowledge, no studies of ACLD structures exist using a generally available finite element code. The ABAQUS commercial finite element code, with certain customizations, is used in this study. Results compare favorably with other sources in the literature.
Freeform Skeletal Shape Optimization of Compliant Mechanisms
Authors: Xu Dong , Ananthasuresh G. K.
Published: November 2021

Compliant mechanisms are elastic continua used to transmit or transform force and motion mechanically. The topology optimization methods developed for compliant mechanisms also give the shape for a chosen parameterization of the design domain with a fixed mesh. However, in these methods, the shapes of the flexible segments in the resulting optimal solutions are restricted either by the type or the resolution of the design parameterization. This limitation is overcome here by focusing on optimizing the skeletal shape of the compliant segments in a given topology. It is accomplished by identifying such segments in the topology and representing them using Bezier curves. The vertices of the Bezier control polygon are used to parameterize the shape-design space. Uniform parameter steps of the Bezier curves naturally enable adaptive finite element discretization of the segments as their shapes change. Practical constraints such as avoiding intersections with other segments and self-intersections, and restrictions on the available space and material, are incorporated into the formulation. A multi-criteria function from our prior work is used as the objective. Analytical sensitivity analysis for the objective and constraints is presented and is used in the numerical optimization. Examples are included to illustrate the shape optimization method.
Narrow-Band Disturbance Rejection Using Semi-Active Control
Authors: Anusonti-Inthra Phuriwat , Gandhi Farhan
Published: November 2021

The present study examines the potential of using a semi-active controllable damper, whose damping coefficient can be modulated in real-time, for narrow-band disturbance rejection applications. A frequency-domain optimal control algorithm is developed for determining the controllable damper input (of twice the disturbance frequency) that minimizes the force transmitted to the support at the disturbance frequency. The effectiveness of both open-loop and closed-loop controllers in rejecting the transmitted disturbances are evaluated. The results of the study indicate that for physically achievable damping coefficient variations, the support force could be reduced by about an additional 30%, beyond the levels due to the passive isolation characteristics (no damping coefficient variation). When the disturbance phase changed during the simulation, the effectiveness of the open-loop controller reduced, while the closed-loop controller was still able to generally reduce vibrations to levels lower than those due to pure passive isolation. Even so, closed-loop control of the semi-active damper was not able to completely maintain the level of reduction in vibration when the disturbance phase changed, suggesting that an adaptive controller may be necessary.
Image-Based Modeling of Dynamic Porous SMA Behavior
Authors: Qidwai Muhammad A. , DeGiorgi Virginia G. , Everett Rick K.
Published: November 2021

Porous shape memory alloys (SMAs) are a relatively new group of materials that are of interest because of their potential use in the design of vibration-control, damping and shock mitigation systems. Essential to the use of these materials is an understanding of their mid to high strain-rate response. The emphasis of this research is to develop a computational methodology that will bridge the microstructural and macrostructural features of porous SMAs. In a first attempt, information obtained from x-ray computed micro tomography (XCMT) images is employed in producing realistic finite element meshes with the help of probabilistic pore generating algorithms. Average constitutive behavior of porous SMA in the intermediate strain rate of 103/s is studied by simulating the compressional split-Hopkinson bar test. Preliminary results are obtained for selected pore volume fractions and distinct trends in material behavior are observed.
Feedback Control of Resonant Modes in Bending Response of Ionic Polymer Actuators
Authors: Mallavarapu Kiran , Leo Donald J.
Published: November 2021

Ionic polymer actuators exhibit large bending response under the application of an electric field but their slow time constant limits the actuation bandwidth. Recent results have demonstrated the ability of feedback control to increase the actuation bandwidth of ionic polymer bender actuators. A critical parameter in the control system is the frequency of the first elastic resonance of the actuator. Longer polymers exhibit a lower frequency resonance which limits the closed-loop performance. In this paper, an empirical model of ionic polymer actuator developed by Kanno (1994) is used for closed-loop control. The empirical model is modified to incorporate the resonant dynamics of the actuator and optimized. The empirical model is based on experimental measurements obtained through a series of open-loop responses for an ionic polymer actuator in a cantilever configuration. The empirical model is optimized and used to design a feedback compensator by state space modeling techniques. Since the ionic polymer actuator has slow settling time in the open-loop, the design objectives are to minimize the settling time and constrain the control voltage to be less than a prescribed value. The controller is designed using Linear Quadratic Regulator (LQR) techniques which reduced the number of design parameters to one variable. Simulations are performed which shows settling times of 0.03 seconds for closed-loop feedback control are possible as compared to the open-loop settling time of 15–20 seconds. The maximum control voltage varied from 1.2 Volts to 3.5 Volts depending on the LQR design parameter. The controller is implemented and results obtained are consistent with the simulations. Closed-loop settling time is observed to be 6–10 seconds and the ratio of the peak response to the steady-state response is reduced by an order of magnitude. Discrepancies between the experiment and the simulations are attributed to the inconsistencies in the resonant frequency of the actuator. Experiments demonstrate that changes in the surface hydration of the polymer result in 6.5%–12.5% variations in the actuator resonance. Variations in the actuator resonance require a more conservative compensator design, thus limiting the performance of the feedback control system.
Large Magnetostriction in Oriented Particle Terfenol-D Composites
Authors: McKnight Geoffrey P. , Carman Gregory P.
Published: November 2021

Magnetostrictive composite materials have been extensively investigated to overcome limitations of the monolithic form such as frequency response and durability, but have previously shown decreased saturation strain as compared to the monolithic materials. This paper attempts to overcome this limitation by manufacturing composites with particle orientation along a specific crystal axis. Shape anisotropy was used during manufacture to orient needle shaped particles along their longest dimension, near the [112] direction. Measurements reveal that the saturation magnetostriction has been increased from ∼1200 ppm for a non-oriented composite (at 12 MPa compressive stress) to over 1550 ppm for a [112] oriented composite (under 12 MPa compressive stress). This is the largest magnetostriction reported as yet for a composite material. A key conclusion of this study is that the dominant influence on the orientation of Terfenol-D particles aligned during manufacture is the shape anisotropy and not the magnetocrystalline anisotropy. Furthermore, the necessary applied fields to reach similar magnetostriction have been reduced in the oriented particle composite as compared to the non-oriented particle composite. In addition, a rule of mixtures model has been used to determine that the composite exhibits nearly the maximum rule of mixtures prediction for magnetostriction.
Control-Oriented Modeling for Smart Mesoflap Aeroelastic Recirculation Control (S.M.A.R.T)
Authors: Tharayil Marina , Alleyne Andrew
Published: November 2021

This paper introduces a novel concept termed Smart Mesoflaps for Aeroelastic Recirculation Transpiration (SMART) to render mass and momentum transfer for controlling shock/boundary-layer interactions (SBLI) in supersonic jet inlets. The SMART concept consists of a matrix of small flaps (sub-millimetric in thickness and of smart material composition), which are designed to undergo local aeroelastic deflection to achieve proper mass bleed or injection when subjected to shock loads. Although positive system performance is achieved using this system, the ‘smart’ part of the SMART is utilized to control the flap deflection to optimize the amount of recirculation (and thus the performance). This Thermally-Activated Smart Material (TASM) design uses NiTi shape memory alloy as an actuator for the flaps to control the amount of circulation. The focus of this paper will be the subsystem modeling of a single flap. After a relatively detailed model is developed, a simpler model is used to approximate the system, and it is shown that this approximation is adequate for control purposes. This model is then validated using step responses as well as closed loop experimental data.
Control of Shape Memory Alloy Actuators Using Pulse Width Pulse Frequency (PWPF) Modulation
Authors: Song G. , Ma N.
Published: November 2021

This paper presents the design and experimental results of control of an SMA actuator using PWPF modulation to reduce the energy consumption by the SMA actuator. An SMA wire test stand is used in this research. Based on results of open-loop testing of the SMA wire actuator and parameter analysis of the PWPF modulator, a PWPF modulator is designed to modulate a Proportional plus Derivative (PD) controller. Experiments demonstrate that control of the SMA actuator using PWPF modulation effectively save actuation energy whiling maintaining same control accuracy as compared to continuous PD control.
Impact Damping With Granular Materials
Authors: Saeki Masato
Published: November 2021

The performance of an impact damper with granular materials in horizontally and vertically vibrating systems is investigated both experimentally and analytically. The motion of the damper is solved by the discrete element method, which is often used in investigations of soil mechanics and powder technology. This method makes it possible to consider the effect of granularity on the damping performance. In this method, the dynamics of the entire system is determined by analysis of the motion of the individual particles. The validity of this numerical method is examined by comparison with the experimental results. The difference in the damping effect in horizontally and vertically vibrating systems is considered.
Static Compressive Study of Metallic Cellular Solids: Aluminium Honeycombs and Foams
Authors: Ruan D. , Lu G. , Chen F. L.
Published: November 2021

In this paper the behaviour of both aluminium honeycombs and closed-cell aluminium foams under static loading was investigated. A comparison was conducted between experimental data of foams with various densities and honeycombs with different cell size and cell wall thickness and previous theoretical analysis. In addition, the finite element numerical simulation of honeycomb was carried out. It was found that the numerical simulation results fitted well with the previous theoretical results.
A Meso-Electro-Mechanical Model for PMN-PT-BT Ceramics Behavior
Authors: Fan Jinghong
Published: November 2021

A three-dimensional, meso-electro-mechanical model has been formulated for description of PMN-PT-BT ceramics. Unlike the experimentally fit models and phenomenological models which are based on state variables and/or empirical relationships, this fully coupled, computational mesomechanics model for polycrystalline PMN-PT-BT ceramics is developed based on considerations of constitutive behavior of single crystals. Specifically, domain wall nucleation and evolution rate equations are proposed in this work to describe the nonlinear hysteresis behavior of these ceramics near the phase transition temperature with maximum permittivity.
Development of a PZT Fiber/Piezo-Polymer Composite Actuator With Interdigitated Electrodes
Authors: Kim Cheol , Koo Kun-Hyung
Published: November 2021

Piezoelectric Fiber Composites with Interdigitated Electrodes (PFCIDE) were previously introduced as an alternative to monolithic wafers with conventional electrodes for applications of structural actuation. This paper is an investigation into the performance improvement of piezoelectric fiber composite actuators by changing the matrix material. This paper presents a modified micro-electromechanical model and numerical analyses of piezoelectric fiber/piezopolymer matrix composite actuator with interdigitated electrodes (PFPMIDE).

Various concepts from different backgrounds including three-dimensional linear elastic and dielectric theories have been incorporated into the present linear piezoelectric model. The rule of mixture and the modified method to calculate effective properties of fiber composites were extended to apply to the PFPMIDE model. The new model was validated comparing with available experimental data and other analytical results. To see the structural responses of a composite plate integrated with the PFPMIDE, three-dimensional finite element formulations were derived. Numerical analyses show that the shape of the graphite/epoxy composite plate with the PFPMIDE may be controlled by judicious choice of voltages, piezoelectric fiber angles, and elastic tailoring of the composite plate.
Design of a Robotic Fish Using Shape Memory Alloy (SMA) Wires
Authors: Penney N. , Barr T. A. , Song G.
Published: November 2021

There are several problems with current electro-mechanical or biomechanical robotic fish. All servomotors emit detectable noises when they are operated. This is a major problem when designing a device that needs to remain undetectable, such as a submarine. The cost of hardware and electronics package that is associated with servo devices are generally very high. Another problem is the underwater reliability of sensitive electronics packages in a fresh or saltwater environment, where the possibility of leaking is a real threat. Finally the duplication of natural fish movement with servomotors is a very complex design.

This paper presents a novel design of a robotic fish actuated by shape memory alloy wires. This fish is constructed using an innovative composite skeleton and shape memory alloy wires for the muscle structure. The skeleton of the fish is designed to duplicate a natural fish like movement. Several working models of this type fish have been fabricated in the Smart Materials and Structures Laboratory at The University of Akron. An off-board electronic control package has been designed to actuate the SMA wires and maneuver the fish. The off-board electronic control package mainly consists of a programmable current amplifier and a real-time control system. Experimental results show that fish-like locomotion can be achieved.

By utilizing shape memory alloys instead of servomotors a robotic fish can become as undetectable as a living fish. Smart memory alloys are cheaper and more reliable than servomotors under harsh environmental conditions; the overall cost of the fish may be reduced. Since this fish can reproduce the natural mobility of a living fish without the noise of servomotors, this fish can be utilized in both the commercial fishing industry and the intelligence field.
Actuation Efficiency and Work Flow in Piezoelectrically Driven Systems
Authors: Shi Yong , Hagood Nesbitt W.
Published: November 2021

Previous study indicts that load coupling has significant influence on the work flow and actuation efficiency in the systems. Theoretical coupled analysis has shown that the actuation efficiency is the highest at the stiffness ratio larger than one and this maximum value is much higher than that predicted by the uncoupled analysis. Moreover, for non-linear systems, the actuation efficiency can be twice as high as that of linear systems. The objectives of this research is to verify the theoretical coupled analysis experimentally and explore the possibility for the mechanical work to be done into the environment. The test results exactly proved out the theoretical prediction of linear and non-linear loading systems. The capability of modeling and testing of non-conservative thermodynamic cycles have also been demonstrated which make it possible to take advantage of the mechanical work out of the systems.
Prediction of Water Circulation Characteristics in a 4-Pass Firetube Boiler With the Non-Symmetric Arrangement of Tube Passes 3 and 4
Authors: Park Hyunjae , Bowman Anthony , Stansfield Tod , Huibregtse Brian , Wilkinson Steve , Ayala Willie
Published: November 2021

Water circulation characteristics, for a newly designed 4-pass 300 BHP (Boiler Horse Power) firetube boiler with a non-symmetric arrangement of tube passes 3 and 4, are investigated in this paper by means of measured furnace wall temperatures for different boiler firing conditions. Vapor production rate and intensity, at each of the 28 temperature measurement nodes, is approximated using the nodal temperature in conjunction with a nucleate boiling heat transfer mode on the water side of the furnace. Defining an attraction force that is proportional to the relative difference of the evaporation intensity between two nodes and inversely proportional to the distance between, the two-dimensional components of the attraction force can be calculated. Integrating all attraction force vectors between a node and the surrounding nodes produces a representative attraction force vector at the node. Similar calculation of the attraction force vectors at all of the temperature nodes on the furnace wall will characterize the water circulation near the boiler furnace. Investigations of the analysis results reveal various complicated non-symmetric water circulation patterns for different boiler firing conditions. Consequently, the analysis methods employed in this paper can be used to predict and improve the water circulation in a firetube boiler, particularly with regard to the placement of the boiler feed-water inlet location.
Study on Wrap Profile Modification Using Symmetrical Circular Involute Plus Dual Line-Segment
Authors: Wang Guoliang , Guo Bei , Zhang Wei , Li Liansheng , Shu Pengcheng
Published: November 2021

The scroll machine’s performance is influenced by its wrap profile. The geometry theory of scroll profile at starting part, which is composed of symmetrical circular involute plus dual line-segment, is proposed. The meshing property of the new modified curve is derived. The formula used to caculate the discharge chamber volume when the modified profiles are in mesh are also given. It is emphasized that the modifacation using symmetrical circular arc (for short, SCA) and that using symmetrical circular arc plus dual line-segment (for short, SCAL) are two special cases of that using symmetrical circular involute plus dual line-segment (for short, SCIL).
Evaluation of Conventional Pump Impeller Design Methods by Means of Numerical Calculations
Authors: Karakas A. Askin , Ayder Erkan
Published: November 2021

Conventional methods for the design of radial pump impellers are evaluated by use of computational approaches. Three dimensional continuity and momentum equations for steady incompressible flows are solved by utilizing an artificial compressibility technique. A finite volume method associated with the explicit fourth order modified Runge-Kutta time marching is developed to study the flow in a three dimensional radial impeller, designed by using a streamline curvature method with adaption of emprical formulas.

The developed flow solver provides detailed pressure and velocity distributions inside the radial pump impellers. The comparison of the computationaly calculated and experimentaly measured impeller heads are in agreement especially at the design point of the impeller. Additionally, calculated impeller exit flow conditions, variations of static pressure, total pressure, meridional component of absolute velocity and absolute flow angle from hub to shroud are compared with those measured experimentally.
The Role of CFD in Turbomachinery Design
Authors: Tsuei Hsin-Hua
Published: November 2021

The use of three-dimensional, Navier-Stokes CFD as a practical tool for turbomachinery design is discussed. For a CFD based design procedure to be practical and efficient, the design engineer is required to make a number of important decisions e.g. the minimum level of physics that is required to be simulated which will impact the design outcome, the appropriate level of grid resolution that will be necessary to model this physics. With judicious decisions for these issues, we illustrate that CFD can be integrated effectively into a design iteration process for problems ranging from single blade row design to multiple stage analysis. A wide range of test cases are presented using the pbCFD code which is built upon Dawes’ BTOB3D code. The examples presented here include a range of centrifugal and axial turbomachines. In most cases, solutions are obtained in the order of 10 minutes on a 1GHz Pentium processor with mass convergence error being within 1 percent. Good comparison is shown with data for the final design illustrating the critical role that CFD can play in the design process.
Validation of Design-Based CFD Calculations for a Centrifugal Pump
Authors: Lee Yu-Tai , Tse Michael , Katz Joseph
Published: November 2021

The use of fully unsteady CFD computations for centrifugal turbomachinery during preliminary design calculations is still infeasible due to the extensive computational efforts required. Most design-based CFD analyses for centrifugal machines are conducted on individual components using steady-state calculations. These steady calculations do not represent the interactions of the components with their neighboring blade rows, including the upstream rotating component. In this paper, commonly accepted CFD procedures for steady-state calculations are applied to the components of a centrifugal pump with a shrouded impeller and a vaned diffuser/volute. Evaluation of the validity of these calculations is conducted by comparing the predicted flow field with detailed measurements at the interface between the rotating impeller and the stationary diffuser and volute.
The Performance of R-407C and R-410B in a Residential Window Air-Conditioner With a Liquid-Suction Heat Exchanger
Authors: Kim Man-Hoe , Shin Jeong-Seob , Kim Kwon-Jin
Published: November 2021

This study presents test results of a residential window air-conditioner using R-22 and two potential alternative refrigerants, R-407C and R-410B. A series of performance tests have been carried out for the basic and liquid-suction heat exchange cycles in a psychrometric calorimeter of which the dry and wet bulb temperatures for the indoor and outdoor chambers are 27/19.5°C and 35/24°C, respectively. For R-407C, the same rotary compressor was used as in the R-22 system. The R-410B system was equipped with a newly designed compressor to provide the similar cooling capacity as the baseline system. The liquid-suction heat exchange cycle with the modified counter-cross flow evaporator was considered to improve the system performance. System characteristics such as cooling capacity, energy efficiency ratio, and suction and discharge pressures and heat exchanger temperature profiles are presented, compared to those for the baseline R-22 system. The modified system with a liquid-suction heat exchanger increased cooling capacity and energy efficiency by up to 5%.
Experimental and Theoretical Study of Microturbine-Based BCHP System
Authors: Fairchild P. D. , Labinov S. D. , Zaltash A. , Rizy D. T.
Published: November 2021

On-site and near-site distributed power generation (DG), as part of a Buildings Cooling, Heating and Power (BCHP) system, brings both electricity and waste heat from the DG sources closer to the end user’s electric and thermal loads. Consequently, the waste heat can be used as input power for heat-activated air conditioners, chillers, and desiccant dehumidification systems; to generate steam for space heating; or to provide hot water for laundry, kitchen, cleaning services and/or restrooms. By making use of what is normally waste heat, BCHP systems meet a building’s electrical and thermal loads with a lower input of fossil fuel, yielding resource efficiencies of 40 to 70% or more.

To ensure the success of BCHP systems, interactions of a DG system — such as a microturbine and thermal heat recovery units under steady-state modes of operation with various exhaust backpressures — must be considered. This article studies the performance and emissions of a 30-kW microturbine over a range of design and off-design conditions in steady-state operating mode with various backpressures. In parallel with the experimental part of the project, a BCHP mathematical model was developed describing basic thermodynamic and hydraulic processes in the system, heat and material balances, and the relationship of the balances to the system configuration. The model can determine the efficiency of energy conversion both for an individual microturbine unit and for the entire BCHP system for various system configurations and external loads. Based on actual data from a 30-kW microturbine, linear analysis was used to obtain an analytical relationship between the changes in the thermodynamic and hydraulic parameters of the system. The actual data show that, when the backpressure at the microturbine exhaust outlet is increased to the maximum of 7 in. wc (0.017 atm), the microturbine’s useful power output decreases by from 3.5% at a full power setting of 30 kW to 5.5% at a one-third power setting (10 kW), while the efficiency of the unit decreases from 2.5 to 4.0%, accordingly.

Tests on the microturbine were conducted at the Cooling, Heating, and Power Laboratory set up at the Oak Ridge National Laboratory’s Buildings Technology Center. Data were collected from the microturbine at power demand settings of 30 kW (full load) to 10 kW in 5-kW increments. For each power demand setting, data measurements were taken over an entire range of microturbine exhaust backpressures. The parameters measured were engine speed, ambient air temperature, air temperature at the microturbine inlet, gas temperature at the turbine outlet, exhaust gas temperature, throttle pressure loss, flow rate of natural gas, and composition of combustion products. The mathematical model provided gas temperature before the turbine, compression rate, and air flow rate, which were determined based on the measured data. The results of these early tests and the computer-based simulation model are in very close agreement.
Experimental Study on Characteristics of an Air-Source Heat Pump Under Frosting/Defrosting Conditions
Authors: Peng Xueyuan , Xing Ziwen , Huang Hu , Shu Pengcheng
Published: November 2021

Applications of air-source heat pump are steadily increasing in South China especially in Yangtze River region. Owing to low temperature and high humidity in these areas, frost formation is liable to occur on the outdoor heat exchanger, thus resulting in reduction in performance of the heat pump and even failure of some components such as the compressor and the motor. In order to improve performance and reliability of the air-source heat pump operating in cold and humid climate, rational defrosting control is important, and this should be based on understanding of characteristics of the heat pump operating under frosting/defrosting conditions. In this paper, operating behavior of an air-source heat pump under frosting/defrosting conditions is investigated experimentally. Recorded are dynamic changes in parameters of the heat pump under frosting/defrosting conditions, including suction and discharge pressure of the compressor, temperature of the fin surface, heating capacity, power consumption, electric current of the fan and thickness of the frost layer. Effect of frost formation on performance and reliability of the heat pump is analyzed. It is shown that there is not a great change in operating state as well as performance of the air-source heat pump until the frost layer is accumulated to some extent, and that performance can be improved by taking proper defrosting measurements. Furthermore, rapid changes in suction pressure and discharge pressure under defrosting conditions may result in failure of the compressor and the motor, and therefore, reducing changes in pressure especially of suction is important for improving reliability of the heat pump.
Heat Transfer and Pressure Drop of Evaporating CO2 in Microchannels and System Design Implications of Critical Heat Flux Conditions
Authors: Nekså Petter , Pettersen Jostein , Skaugen Geir
Published: November 2021

Experimental data on heat transfer and pressure drop during near-critical evaporation of carbon dioxide (CO2) in a microchannel aluminium tube are presented. The test tube had 25 circular ports/channels with 0.79 mm inner diameter. The CO2-side heat transfer coefficient was determined by a modified Wilson plot technique. Measured data were compared to correlations available in the literature. For evaporating heat transfer and pressure drop, common correlations did not correspond well to the test data. Under some conditions, the evaporating heat transfer coefficient dropped significantly as the vapour fraction increased. This critical heat flux effect was most pronounced for high heat and mass flux, and high evaporation temperature. Different system designs able to reduce the possible negative effects of critical heat flux are discussed. Negative effects of the phenomenon may be highly reduced if the effect is taken into account when designing the components and the system.
Improved Performance of Transcritical Carbon Dioxide As a Refrigerant in Army Tactical Environmental Control Units
Authors: Manzione John A. , Calkins Frank E.
Published: November 2021

Commercially available heat pumps have traditionally relied upon fluorocarbon working fluids commonly known as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). These fluids are recognized as substances which destroy the earth’s ozone layer, and they are being phased out of production and use. Hydrofluorocarbons (HFCs) have been proposed as the next industry standard, but HFCs have extremely high global warming potential and, like their predecessors, are subject to regulation by the U.S. Environmental Protection Agency under provisions of the U.S. Clean Air Act. Similar restrictions exist internationally. HFCs are also costly and impose a handling and maintenance logistics burden, and in some cases pose performance limitations in high ambient temperatures. Consequently, they may represent only an interim solution for military air-conditioning and refrigeration needs.

On the other hand, carbon dioxide is inexpensive, safe, widely available, and fundamentally feasible. Operating at substantially higher working pressures, carbon dioxide (CO2) offers the potential of lighter, more compact systems, as well as providing environmental, performance, and logistics advantages that are attractive for military applications. With CO2, the Army sees the potential for smaller, lighter, systems with lower life-cycle costs. The U.S. Army Communications and Electronics Command’s Research, Engineering and Development Center has developed a first prototype packaged-unitary compact CO2 heat pump built within the physical constraints of existing Army ECUs (Environmental Control Units),. The performance of this unit has been further improved by the addition of an internal suction line heat exchanger. The unit is lighter in weight than the current military standard unit. When tested under a range of military operational conditions, it achieves a higher Coefficient of Performance (COP) but a lower capacity, than the military standard unit.

This paper will address the Army’s CO2 Development Program, with emphasis on fabrication and testing of the improved CO2 heat pump.
Evaluation of Fuel Cell Based Combined Heat and Power Systems for Residential Applications
Authors: Gunes M. Burak , Ellis Michael W.
Published: November 2021

Residences in the United States use 10.8 × 109 MJ (10.25 quadrillion Btus) per year, and the resulting energy cost exceeds $5 billion annually. Electricity use accounts for over 30 percent of residential energy needs. This electricity is typically provided by large remote power plants that discharge more than 60 percent of input energy as waste heat to the environment. The advent of fuel cell power systems makes on-site power generation feasible for residential applications. With on-site generation, waste heat can be recovered and used to meet the thermal needs of the residence including space heating and water heating. Combined heat and power (CHP) systems can substantially reduce the energy required for residential applications.

The energy use and economic benefits of fuel cell based CHP systems are investigated for single-family residential applications. Hourly energy use profiles for electricity and thermal energy are determined for typical residential applications. A mathematical model of a residential fuel cell based CHP system is developed. The system incorporates a fuel cell system to supply electricity and thermal energy, a vapor compression heat pump to provide cooling in the summer and heating in the winter, and a thermal storage tank to help match the available thermal energy to the thermal energy needs. The performance of the system is evaluated for different climates.

Results from the study include an evaluation of the major design characteristics of the system, load duration curves, an evaluation of the effect of climate on energy use characteristics, and a comparison of the life cycle cost of the fuel cell based CHP system to the life cycle costs of conventional residential energy systems.
Thermodynamic Diagnosis of a Small Scale Gas Turbine With Neural Networks
Authors: Bidini Gianni , Fantozzi Francesco , Barelli Linda
Published: November 2021

Real time monitoring and the diagnostics of fault critical power plants, such as small scale gas turbine based ones, is proved to increase their availability and rentability. However, the diagnostic tool requires high speed calculators and fast response models to produce time efficient action, therefore encouraging model free application such as Artificial Neural Networks (ANN) techniques.

To this aim, the present paper investigates the performances of an ANN based diagnostic system realized for a small scale commercial gas turbine.

After a data harvesting campaign on two existing installations, a diagnostic tool (DT), provided by the gas turbine manufacturer, was operated to produce a sufficient comprehensive diagnostic data base to be used to training and testing the ANN system. The DT system evaluates performance deterioration causes (i.e. compressor fouling) modifying diagnostic parameters, such as efficiencies and combustion parameters, in order to meet data provided by thermodynamic simulation with data gathered on field therefore requiring a relatively high number of input variables (namely 9).

The results obtained show good agreement with the ones provided by the DT diagnostic tool with a percentage error not exceeding 4%. Moreover, the ANN model utilized in the diagnosis was implemented considering only 3 input parameters therefore resulting in a less complicated system, not considering the dramatic increase in execution time due to the lack of any iterative calculation.

The next step is to extend the monitoring to the overall gas turbine’s components and to integrate the monitoring system with an artificial intelligence based supervising system for diagnostic purposes which derives from ANN outputs damage presence, fault source and evaluation.
Thermal Utility Influence on the Cogenerative Performance of a Below Ambient Pressure Discharge Gas Turbine (BAGT)
Authors: Bianchi M.
Published: November 2021

The use of gas turbine for heat and power production is widespread. Usually, the temperature of the gas exhausted from a gas turbine is greater than that required from the thermal utilities. Therefore, it may results convenient, before gas cooling, to produce additional work expanding the high temperature flue gas below the ambient pressure. Subsequently, a compressor will discharge to the ambient the cooled gas.

In the present paper, a thermodynamic analysis of a gas turbine working with the discharge pressure below ambient pressure (BAGT) is carried out considering different cogenerative applications. It resulted that the BAGT is especially convenient for low thermal utility temperature that strongly increases the gas turbine electric efficiency.

Moreover, in order to obtain high electric performance also with high thermal utility temperature, the employment of an additional heat exchanger (BAGT + cooler) has been taken into account.
Comparison of Exergy, Energy Utilization Factors and CO2 Production of CHP Systems Using Fuel Cell and Engine Power Cycles
Authors: Kowalski Gregory J. , Zenouzi Mansour
Published: November 2021

The following paper develops tools using energy and exergy analysis of heat engine and fuel cell based CHP systems to determine which type should be used to minimize fuel consumption and CO2 production. In the near future, physical plant and energy resource managers will have to decide how to satisfy electrical power requirements and reduce CO2 and other “greenhouse gas” emissions. Preliminary results demonstrate these tools provide useful information and indicate that heat engine based cogeneration devices are more desirable than the fuel cell based devices for systems with a large heat load to require power ratio. Fuel cell cogeneration devices are preferred for systems with a large power requirement as compared to the heat load.
Insulated Pressure Vessels for Vehicular Hydrogen Storage: Analysis and Performance Evaluation
Authors: Aceves S. M. , Martinez-Frias J. , Garcia-Villazana O. , Espinosa-Loza F.
Published: November 2021

Insulated pressure vessels are cryogenic-capable pressure vessels that can be fueled with liquid hydrogen (LH2) or ambient-temperature compressed hydrogen (CH2). Insulated pressure vessels offer the advantages of liquid hydrogen tanks (low weight and volume), with reduced disadvantages (fuel flexibility, lower energy requirement for hydrogen liquefaction and reduced evaporative losses). The work described here is directed at verifying that commercially available pressure vessels can be safely used to store liquid hydrogen. The use of commercially available pressure vessels significantly reduces the cost and complexity of the insulated pressure vessel development effort. This paper describes a series of tests that have been done with aluminum-lined, fiber-wrapped vessels to evaluate the damage caused by low temperature operation. All analysis and experiments to date indicate that no significant damage has resulted. Required future tests are described that will prove that no technical barriers exist to the safe use of aluminum-fiber vessels at cryogenic temperatures. Future activities also include a demonstration project in which the insulated pressure vessels will be installed and tested on two vehicles. A draft standard will also be generated for obtaining certification for insulated pressure vessels.