Evaluation of additively manufactured stacks for thermo-acoustic devices

2021 ◽  
Vol 263 (2) ◽  
pp. 4376-4387
Author(s):  
Samarjith Biswas ◽  
Zack Krawczyk ◽  
James M. Manimala
Keyword(s):  
Scaling Laws ◽  
Ambient Pressure ◽  
Volume Ratio ◽  
Software Tool ◽  
Acoustic Energy ◽  
Working Fluid ◽  
Mechanical And Thermal Properties ◽  
Acoustic Effect ◽  
Acoustic Waveguides ◽  
Material Length

The thermo-acoustic effect provides a means to convert acoustic energy to heat and vice versa without the need for moving parts. This is especially useful to construct mechanically-simple and robust energy harvesting devices, although there are limitations to the power-to-volume ratio achievable. The mechanical and thermal properties as well as geometry of the porous stack that forms a set of acoustic waveguides in thermo-acoustic devices are key to its performance. In this study, we evaluate various additively manufactured polymer stacks against more conventional ceramic stacks using a benchtop thermos-acoustic refrigerator rig that uses air at ambient pressure as its working fluid. Influence of stack parameters such as material, length, location, porosity and pore geometry are examined using experiments and correlated to simulations using DeltaEC, a software tool based on Rott's linear approximation. Structure-performance relationships are established by extracting scaling laws for power-to-volume ratio and frequency-thermal gradient dependencies. It is found that additively manufactured stacks can deliver performance comparable to ceramic stacks while being more affordable and customizable for thermo-acoustic transduction applications.

Empirical Models for a Screw Expander Based on Experimental Data From Organic Rankine Cycle System Testing

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Vamshi Krishna Avadhanula ◽  
Chuen-Sen Lin
Keyword(s):  
Experimental Data ◽  
Power Output ◽  
Pressure Ratio ◽  
Organic Rankine Cycle ◽  
Volume Ratio ◽  
Rankine Cycle ◽  
Empirical Models ◽  
Working Fluid ◽  
Work Output ◽  
Experimental Values

The screw expander discussed in this work was part of a 50 kW organic Rankine cycle (ORC) system. The ORC was tested under different conditions in heat source and heat sink. In conjunction with collecting data for the ORC system, experimental data were also collected for the individual components of the ORC, viz. evaporator, preheater, screw expander, working fluid pump, and condenser. Experimental data for the screw expander were used to develop the two empirical models discussed in this paper for estimating screw expander performance. As the physical parameters of the screw expander discussed in this article are not known, a “black-box” approach was followed to estimate screw expander power output, based on expander inlet and outlet pressure and temperature data. Refrigerant R245fa was used as the working fluid in the ORC. The experimental data showed that the screw expander had ranges of pressure ratio (2.70 to 6.54), volume ratio (2.54 to 6.20), and power output (10 to 51.5 kW). Of the two empirical models, the first model is based on the polytropic expansion process, in which an expression for the polytropic exponent is found by applying regression curve-fitting analysis as a function of the expander pressure ratio and volume ratio. In the second model, an expression for screw expander work output is found by applying regression curve-fitting analysis as a function of the expander isentropic work output. The predicted screw expander power output using the polytropic exponent model was within ±10% of experimental values; the predicted screw expander power output using the isentropic work output model was within ±7.5% of experimental values.

Analysis and Comparison of the Performance of an Inverted Brayton Cycle and Turbo-Compounding With Decoupled Turbine and CVT Driven Compressor for Small Automotive Engines

2016 ◽  
Author(s):  
P. Lu ◽  
C. Brace ◽  
B. Hu ◽  
C. Copeland
Keyword(s):  
Fuel Consumption ◽  
Power Output ◽  
Heat Recovery ◽  
Power Plants ◽  
Waste Heat ◽  
Ambient Pressure ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Partial Load ◽  
Exhaust Heat

For an internal combustion engine, a large quantity of fuel energy (accounting for approximately 30% of the total combustion energy) is expelled through the exhaust without being converted into useful work. Various technologies including turbo-compounding and the pressurized Brayton bottoming cycle have been developed to recover the exhaust heat and thus reduce the fuel consumption and CO2 emission. However, the application of these approaches in small automotive power plants has been relatively less explored because of the inherent difficulties, such as the detrimental backpressure and higher complexity imposed by the additional devices. Therefore, research has been conducted, in which modifications were made to the traditional arrangement aiming to minimize the weaknesses. The turbocharger of the baseline series turbo-compounding was eliminated from the system so that the power turbine became the only heat recovery device on the exhaust side of the engine, and operated at a higher expansion ratio. The compressor was separated from the turbine shaft and mechanically connected to the engine via CVT. According to the results, the backpressure of the novel system is significantly reduced comparing with the series turbo-compounding model. The power output at lower engine speed was also promoted. For the pressurized Brayton bottoming cycle, rather than transferring the thermal energy from the exhaust to the working fluid, the exhaust gas was directly utilized as the working medium and was simply cooled by ambient coolant before the compressor. This arrangement, which is known as the inverted Brayton cycle was simpler to implement. Besides, it allowed the exhaust gasses to be expanded below the ambient pressure. Thereby, the primary cycle was less compromised by the bottoming cycle. The potential of recovering energy from the exhaust was increased as well. This paper analysed and optimized the parameters (including CVT ratio, turbine and compressor speed and the inlet pressure to the bottoming cycle) that are sensitive to the performance of the small vehicle engine equipped with inverted Brayton cycle and novel turbo-compounding system respectively. The performance evaluation was given in terms of brake power output and specific fuel consumption. Two working conditions, full and partial load (10 and 2 bar BMEP) were investigated. Evaluation of the transient performance was also carried out. Simulated results of these two designs were compared with each other as well as the performance from the corresponding baseline models. The system models in this paper were built in GT-Power which is a one dimension (1-D) engine simulation code. All the waste heat recovery systems were combined with a 2.0 litre gasoline engine.

Study of Gas/Liquid Behavior Within an Aeroengine Bearing Chamber

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Budi Chandra ◽  
Kathy Simmons ◽  
Stephen Pickering ◽  
Steven H. Collicott ◽  
Nikolas Wiedemann
Keyword(s):  
Film Thickness ◽  
High Speed ◽  
Flow Behavior ◽  
Ambient Pressure ◽  
Current Model ◽  
Test Chamber ◽  
Experimental Program ◽  
Working Fluid ◽  
Rotating Shaft ◽  
Significant Difference

Aeroengine bearing chambers typically contain bearings, seals, shafts and static parts. Oil is introduced for lubrication and cooling and this creates a two phase flow environment that may contain droplets, mist, film, ligaments, froth or foam and liquid pools. Some regions of the chamber contain a highly rotating air flow such that there are zones where the flow is gravity dominated and zones where it is rotation dominated. The University of Nottingham Technology Centre in Gas Turbine Transmission Systems, is conducting an ongoing experimental program investigating liquid and gas flow behavior in a relevant highly rotating environment. Previously reported work by the UTC has investigated film thickness and residence volume within a simplified chamber consisting of outer cylindrical chamber, inner rotating shaft and cuboid off-take geometry (termed the generic deep sump). Recently, a more aeroengine relevant bearing chamber offtake geometry has been studied. This geometry is similar to one investigated at Purdue University and consists of a “sub-sump” region approached by curved surfaces linked to the bearing chamber. The test chamber consists of an outer, stationary cylinder with an inner rotating shaft. The rig runs at ambient pressure and the working fluid (water) is introduced either via a film generator on the chamber wall or through holes in the shaft. In addition to visual data (high speed and normal video), liquid residence volume within the chamber and film thickness were the two numerical comparators chosen. Data was obtained for a number of liquid supply rates, scavenge ratios and shaft rotation speeds. The data from the current model is compared to that from the earlier studies. The data shows that in contrast to the previously reported generic deep sump study, the residence volume of the curved wall deep sump (CWDS) designs is far less sensitive to shaft speed, liquid supply rate and scavenge ratio. The method of liquid supply only makes a significant difference at the lowest scavenge ratios. Residence volume data for the Nottingham CWDS is comparable, when appropriately scaled, to that for the Purdue design. The film thickness data shows that at the lower shaft speeds investigated the flow is gravity dominated whereas at higher shaft speeds shear dominates.

scholarly journals Basic Potential of Carbon Nanotubes in Tissue Engineering Applications

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Hisao Haniu ◽  
Naoto Saito ◽  
Yoshikazu Matsuda ◽  
Tamotsu Tsukahara ◽  
Yuki Usui ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Tissue Engineering ◽  
High Surface ◽  
High Surface Area ◽  
Volume Ratio ◽  
Medical Application ◽  
Mechanical And Thermal Properties ◽  
Biological Responses

Carbon nanotubes (CNTs) are attracting interest in various fields of science because they possess a high surface area-to-volume ratio and excellent electronic, mechanical, and thermal properties. Various medical applications of CNTs are expected, and the properties of CNTs have been greatly improved for use in biomaterials. However, the safety of CNTs remains unclear, which impedes their medical application. Our group is evaluating the biological responses of multiwall CNTs (MWCNTs)in vivoandin vitrofor the promotion of tissue regeneration as safe scaffold materials. We recently showed that intracellular accumulation is important for the cytotoxicity of CNTs, and we reported the active physiological functions CNTs in cells. In this review, we describe the effects of CNTsin vivoandin vitroobserved by our group from the standpoint of tissue engineering, and we introduce the findings of other research groups.

scholarly journals Experimental characterization of the COndensation PArticle counting System for high altitude aircraft-borne application

2008 ◽  
Vol 1 (1) ◽  
pp. 321-374 ◽  
Author(s):  
R. Weigel ◽  
M. Hermann ◽  
J. Curtius ◽  
C. Voigt ◽  
S. Walter ◽  
...  
Keyword(s):  
High Altitude ◽  
Ambient Pressure ◽  
Particle Diameter ◽  
The Arctic ◽  
Working Fluid ◽  
Counting System ◽  
Dual Channel ◽  
Particle Counting ◽  
Condensation Particle Counting

Abstract. This study aims at a detailed characterization of an ultra-fine aerosol particle counting system for operation on board the Russian high altitude research aircraft M-55 "Geophysica" (maximum ceiling of 21 km). The COndensation PArticle counting Systems (COPAS) consists of an aerosol inlet and two dual-channel continuous flow Condensation Particle Counters (CPCs). The aerosol inlet, adapted for COPAS measurements on board the M-55 "Geophysica", is described concerning aspiration, transmission, and transport losses. The counting efficiencies of the CPCs using the chlorofluorocarbon FC-43 as the working fluid are studied experimentally at two pressure conditions, 300 hPa and 70 hPa. Three COPAS channels are operated with different temperature differences between the saturator and the condenser block yielding smallest detectable particle sizes (dp50 – as 50% detection "cut off" diameters) of 6 nm, 11 nm, and 15 nm, respectively, at ambient pressure of 70 hPa. The fourth COPAS channel is operated with an aerosol heating line (250°C) for a determination of the non-volatile number of particles. The heating line is experimentally proven to volatilize pure H2SO4-H2O particles for a particle diameter (dp) range of 11 nm<dp<200 nm. Additionally this study includes investigation to exclude auto-nucleation of the working fluid inside the CPCs. An instrumental inter-comparison (cross-correlation) has been performed for several measurement flights and mission flights in the Arctic and the Tropics are discussed. Finally, COPAS measurements are used for an aircraft plume crossing analysis.

Analysis of a FAME/MLL Screw Multi-Stage Compressor for High Temperature, High Pressure Vapor Compression Refrigeration Cycle

2020 ◽  
Author(s):  
Kevin R. Anderson ◽  
Trevor Steele
Keyword(s):  
Elevated Temperatures ◽  
Cooling System ◽  
Acid Methyl Ester ◽  
Volume Ratio ◽  
Working Fluid ◽  
Analysis And Design ◽  
Working Cycle ◽  
Multi Stage ◽  
Vapor Compression Refrigeration Cycle ◽  
Compressor Power

Abstract This paper presents the analysis and design of a compressor for application to a Fatty Acid Methyl Ester (FAME) Methyl Linoleate (MLL) bio-refrigerant cascade working cycle. This working fluid is being used in the topping cycle of an active electronics payload cooling system design to operate at elevated temperatures and pressures such as those witnessed by a Venus lander. The twin-screw, three-stage compressor operates at escalated temperatures of approximately 520 °C (960 °F). The total compressor power of 143.4 W is shared as 43.5 W, 47.7 W, and 53.3 W over stages 1, 2, and 3, respectively. The screw compressor is baselined with a D = 1 inch diameter rotor and an L/D (stroke/bore) ratio of L/D = 2 per stage. The compression ratio corresponds to a volume ratio of 6.5. The swept volume for a 4+6 rotor configuration is estimated to be 1.13 CFM at 2000 RPM with an asymmetric profile and no leakage. The volumetric efficiency of the compressor is estimated to be on the order of 80% due to the higher molecular weight of the FAME/MLL working fluid. The SCORG turbomachinery software is used to verify the thermodynamics analysis and affords a volumetric displacement of 0.025 L/rev at 2000 RPM and 80% adiabatic efficiency.

Study of Gas/Liquid Behaviour Within an Aeroengine Bearing Chamber

2012 ◽  
Author(s):  
Budi Chandra ◽  
Kathy Simmons ◽  
Stephen Pickering ◽  
Steven H. Collicott ◽  
Nikolas Wiedemann
Keyword(s):  
Film Thickness ◽  
High Speed ◽  
Flow Behavior ◽  
Ambient Pressure ◽  
Current Model ◽  
Test Chamber ◽  
Experimental Program ◽  
Working Fluid ◽  
Rotating Shaft ◽  
Significant Difference

Aeroengine bearing chambers typically contain bearings, seals, shafts and static parts. Oil is introduced for lubrication and cooling and this creates a two phase flow environment that may contain droplets, mist, film, ligaments, froth or foam and liquid pools. Some regions of the chamber contain a highly rotating air flow such that there are zones where the flow is gravity dominated and zones where it is rotation dominated. The University of Nottingham Technology Centre in Gas Turbine Transmission Systems, is conducting an ongoing experimental program investigating liquid and gas flow behavior in a relevant highly rotating environment. Previously reported work by Chandra et al [1, 2] has investigated film thickness and residence volume within a simplified chamber consisting of outer cylindrical chamber, inner rotating shaft and cuboid off-take geometry (termed the generic deep sump). Recently a more aeroengine relevant bearing chamber offtake geometry has been studied. This geometry is similar to one investigated by Chandra [3] at Purdue University and consists of a “sub-sump” region approached by curved surfaces linked to the bearing chamber. The test chamber consists of an outer, stationary cylinder with an inner rotating shaft. The rig runs at ambient pressure and the working fluid (water) is introduced either via a film generator on the chamber wall or through holes in the shaft. In addition to visual data (high speed and normal video), liquid residence volume within the chamber and film thickness were the two numerical comparators chosen. Data was obtained for a number of liquid supply rates, scavenge ratios and shaft rotation speeds. The data from the current model is compared to that from the earlier studies [1, 2, & 3]. The data shows that in contrast to the previously reported generic deep sump study, the residence volume of the curved wall deep sump (CWDS) designs is far less sensitive to shaft speed, liquid supply rate and scavenge ratio. The method of liquid supply only makes a significant difference at the lowest scavenge ratios. Residence volume data for the Nottingham CWDS is comparable, when appropriately scaled, to that for the Purdue design. The film thickness data shows that at the lower shaft speeds investigated the flow is gravity dominated whereas at higher shaft speeds shear dominates.

Experiments on Thermosyphon Loops for Low-Temperature Waste-Heat Recovery

2014 ◽  
Vol 6 (4) ◽  
Author(s):  
Koji Matsubara ◽  
Suguru Tachikawa ◽  
Itaru Kourakata ◽  
Yusaku Matsudaira
Keyword(s):  
Thermal Resistance ◽  
Heating Rate ◽  
Waste Heat ◽  
Volume Ratio ◽  
Pressure Head ◽  
Working Fluid ◽  
Heating Rates ◽  
Different Temperatures ◽  
Flow Circulation ◽  
Flow Map

We tested a thermosyphon loop with water as the working fluid using heating rates between 100 W and 400 W. Four kinds of core blocks were installed in the evaporator and tested: a hollow block, and blocks with narrow holes: Φ 2.2 mm × 90; Φ 2.5 mm × 55; and Φ 4.0 mm × 30. The temperature distribution indicated stable flow circulation inside the thermosyphon at low volume ratios but was unstable when the volume ratio was increased higher than 30%. The characteristics of the flow pattern are summarized as a flow map showing the heating rate versus the volume ratio. The recovered heat and the thermal resistance of the thermosyphon loop were clearly improved by using the core blocks with narrow holes instead of hollow blocks for the treated volume ratios from 20% to 80%. The thermal resistance increased when the volume ratio reached high values, suggesting that the effects from the abnormality of the flow circulation affected thermal resistance. The velocity of the gas stream in the thermosyphon was estimated by assuming an isothermal state, and it is diagrammed showing the heating rate at different temperatures. The current experiment of the thermosyphon loop is plotted in this diagram, which indicates the need for a wide margin due to the limitations of the sonic velocity and the pressure head at the full height of the heat pipe.

Unsteady Two-Phase Flow Analysis on Water Retarder Performance Using Sliding Mesh Technique and VOF Method

2015 ◽  
Author(s):  
Wonju Lee ◽  
Nahmkeon Hur
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Volume Fraction ◽  
Volume Ratio ◽  
Working Fluid ◽  
Water Volume ◽  
Phase Flow ◽  
Two Phase ◽  
Sliding Mesh ◽  
Mesh Technique

Hydraulic retarders are used as auxiliary brake system in heavy vehicles and high speed trains. A hydraulic retarder is composed of two parts, a rotor and a stator. When the system is activated, the working fluid is injected into the wheel and circulates between the rotor and stator vanes using the resisting torque of the stator to slow down the vehicle. The purpose of this research is to investigate a water retarder system and the details of flow characteristics of the water, and to investigate the device performance as well. The water retarder is basically composed of a rotor and a stator. In the present research, the rotor rotating speed is fixed at 2000 rpm. Since the performance characteristic of the water retarder is dependent upon the water volume ratio, different volume ratios have been investigated. In this paper water retarder simulations are carried out using CFD using sliding mesh technique. To capture the unsteady effects, the cases have been solved as transient simulations using standard k-ε turbulence model. The simulations have been solved as two phase flow, water and air. The results are compared for different water volume ratios. The result show that the air particles are accumulated in the center of the wheels forming a tube shape (doughnut shape) and water particles are at the outside, wrapping the air particles. In addition, torque values are sensitively dependent upon water volume fraction.

A high-performance fully nanostructured individual CdSe nanotube photodetector with enhanced responsivity and photoconductive gain

2017 ◽  
Vol 5 (28) ◽  
pp. 7057-7066 ◽  
Author(s):  
Qinwei An ◽  
Xianquan Meng ◽  
Ke Xiong ◽  
Yunlei Qiu
Keyword(s):  
Vapor Deposition ◽  
Physical Vapor Deposition ◽  
High Performance ◽  
Ambient Pressure ◽  
Volume Ratio ◽  
Deposition Process ◽  
Single Crystalline ◽  
Photoconductive Gain ◽  
One Step ◽  
Physical Vapor Deposition Process

Single-crystalline CdSe nanotubes with a perfect hollow tubular architecture and higher surface-to-volume ratio were synthesized via a simplified one-step ambient pressure physical vapor deposition process and utilized to fabricate an individual CdSe nanotube photodetector with enhanced responsivity and photoconductive gain.

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