Extending “Assessment of Tesla Turbine Performance” Model for Sensitivity-Focused Experimental Design

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Matthew J. Traum ◽  
Fatemeh Hadi ◽  
Muhammad K. Akbar
Keyword(s):  
Reynolds Number ◽  
Power Output ◽  
Performance Model ◽  
Nozzle Geometry ◽  
Design Parameters ◽  
Working Fluid ◽  
Extended Model ◽  
Number Range ◽  
Nozzle Height ◽  
Turbine Performance

The analytical model of Carey is extended and clarified for modeling Tesla turbine performance. The extended model retains differentiability, making it useful for rapid evaluation of engineering design decisions. Several clarifications are provided including a quantitative limitation on the model’s Reynolds number range; a derivation for output shaft torque and power that shows a match to the axial Euler Turbine Equation; eliminating the possibility of tangential disk velocity exceeding inlet working fluid velocity; and introducing a geometric nozzle height parameter. While nozzle geometry is limited to a slot providing identical flow velocity to each channel, variable nozzle height enables this velocity to be controlled by the turbine designer as the flow need not be choked. To illustrate the utility of this improvement, a numerical study of turbine performance with respect to variable nozzle height is provided. Since the extended model is differentiable, power sensitivity to design parameters can be quickly evaluated—a feature important when the main design goal is maximizing measurement sensitivity. The derivatives indicate two important results. First, the derivative of power with respect to Reynolds number for a turbine in the practical design range remains nearly constant over the whole laminar operating range. So, for a given working fluid mass flow rate, Tesla turbine power output is equally sensitive to variation in working fluid physical properties. Second, turbine power sensitivity increases as wetted disk area decreases; there is a design trade-off here between maximizing power output and maximizing power sensitivity.

Some Aspects of the Outline Design Specification of a 0.5 kW Stirling Engine for Domestic Scale Co-Generation

1996 ◽  
Vol 210 (1) ◽  
pp. 25-33 ◽  
Author(s):  
D H Rix
Keyword(s):  
Power Output ◽  
High Volume ◽  
Combined Heat And Power ◽  
Stirling Engine ◽  
Specific Power ◽  
Design Parameters ◽  
Working Fluid ◽  
Design Specification ◽  
Specific Power Output ◽  
Chp System

This paper describes the design considerations that were involved in the production of a prototype Stirling engine, primarily intended for use in a domestic scale combined heat and power (CHP) system. These are discussed in terms of the specification of basic design parameters—configuration, working fluid, etc. First the particular requirements of this application are considered, primarily a power output of 1 kW or less, suitability for high-volume mass production, ultra long life and as high an efficiency as possible. The design that emerges is relatively simple, of low specific power output and with rather conservative operating parameters—temperature, pressure and speed.

Experimental Analysis of Microchannel Entrance Length Characteristics Using Microparticle Image Velocimetry

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Tariq Ahmad ◽  
Ibrahim Hassan
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Entrance Region ◽  
Working Fluid ◽  
Parallel Plates ◽  
Entrance Length ◽  
Number Range ◽  
Micro Piv ◽  
Image Velocimetry ◽  
Microparticle Image Velocimetry

The study of the entrance region of microchannels and microdevices is limited, yet important, since the effect on the flow field and heat transfer mechanisms is significant. An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of microparticle image velocimetry (micro-PIV), a nonintrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data are obtained for three different microchannel hydraulic diameters of 500 μm, 200 μm, and 100 μm, all of which have cross-sectional aspect ratios of 1. The working fluid is distilled water, and velocity profile data are acquired over a laminar Reynolds number range from 0.5 to 200. The test-sections were designed as to provide a sharp-edged microchannel inlet from a very large reservoir at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100 to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier–Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts or parallel plates, depending on the Reynolds range, and minimal influence of dimensional scaling between the investigated microchannels was observed. New entrance length correlations are proposed, which account for both creeping and high laminar Reynolds number flows. These correlations are unique in predicting the entrance length in microchannels and will aid in the design of future microfluidic devices.

Passive Control and Enhancement of Low Reynolds Number Slot Jets Through the Use of Tabs and Chevrons

2016 ◽  
Author(s):  
Andrew Sexton ◽  
Jeff Punch ◽  
Nicholas Jeffers ◽  
Jason Stafford
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Optical Networks ◽  
Passive Control ◽  
Low Reynolds Number ◽  
Hydraulic Diameter ◽  
Nozzle Geometry ◽  
Critical Element ◽  
Number Range ◽  
Low Reynolds

Optical networks are a critical element of contemporary communications infrastructure, due to their efficacy in transmitting high-speed data over large distances. Photonic integrated circuits (PICs) offer compelling advantages in terms of performance and miniaturization, but the increase in power density of these components, coupled with shrinking packaging restrictions, presents a significant thermal management challenge. This has driven the need for the integration of liquid-based microfluidic cooling artefacts into next generation PIC packages. Liquid micro-jets are emerging as candidate primary or secondary heat exchangers for such packages, however the thermal behavior of confined, low Reynolds number liquid slot jets is not comprehensively understood. This investigation utilized a hot foil technique to experimentally determine the influence of implementing jet outlet modifications — in the form of tabs and chevrons — as techniques for passive control and enhancement of single-phase convective heat transfer. The investigation was carried out for slot jets in the laminar flow regime, with a Reynolds number range, based on the conventional slot jet hydraulic diameter, of 100 to 500. The investigation was carried out with a slot jet aspect ratio of 4, and a fixed confinement height to hydraulic diameter ratio (H/Dh) of 1. It was found that all outlet modifications increased local and area-averaged Nusselt number compared to a conventional slot jet. Modifications to the major axis (or long edge) of the slot jet were most effective, achieving increases in area-averaged Nusselt number of up to 61%. It was also determined that the location and magnitude of Nusselt number peaks within the slot jet stagnation region, could be passively controlled and enhanced through the application of outlet tabs at varying locations, allowing for more flexible targeted hotspot cooling. Therefore, it was concluded that enhancements in an integrated microjet cooling artefact can be achieved through passive geometry devices, without compromising the stringent packaging restrictions of such systems, such as confinement height and nozzle geometry.

CFD Simulation of an Alfa-Stirling Engine to Study the Geometrical Parameters on the Engine Performance

2019 ◽  
Author(s):  
Ana C. Ferreira ◽  
Senhorinha F. C. F. Teixeira ◽  
Ricardo F. Oliveira ◽  
José C. Teixeira
Keyword(s):  
Heat Exchanger ◽  
Power Output ◽  
Cfd Simulation ◽  
Engine Performance ◽  
Stirling Engine ◽  
Operating Conditions ◽  
Design Parameters ◽  
Working Fluid ◽  
Cold Temperatures ◽  
Temperature Heat

Abstract An alpha-Stirling configuration was modelled using a Computational Fluid Dynamic (CFD), using ANSYS® software. A Stirling engine is an externally heated engine which has the advantage of working with several heat sources with high efficiencies. The working gas flows between compression and expansion spaces by alternate crossing of, a low-temperature heat exchanger (cooler), a regenerator and a high-temperature heat exchanger (heater). Two pistons positioned at a phase angle of 90 degrees were designed and the heater and cooler were placed on the top of the pistons. The motion of the boundary conditions with displacement was defined through a User Defined Function (UDF) routine, providing the motion for the expansion and compression piston, respectively. In order to define the temperature differential between the engine hot and the cold sources, the walls of the heater and cooler were defined as constant temperatures, whereas the remaining are adiabatic. The objective is to study the thermal behavior of the working fluid considering the piston motion between the hot and cold sources and investigate the effect of operating conditions on engine performance. The influence of regenerator matrix porosity, hot and cold temperatures on the engine performance was investigated through predicting the PV diagram of the engine. The CFD simulation of the thermal engine’s performance provided a Stirling engine with 760W of power output. It was verified that the Stirling engine can be optimized when the best design parameters combination are applied, mostly the regenerator porosity and cylinders volume, which variation directly affect the power output.

Wavy-Channel for Microscale Heat Transfer in Macro Geometries

2017 ◽  
Author(s):  
Kai Xian Cheng ◽  
Zi Hao Foo ◽  
Kim Tiow Ooi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Performance Index ◽  
Heat Transfer Performance ◽  
Cnc Machining ◽  
Hydrodynamic Performance ◽  
Working Fluid ◽  
Transfer Performance ◽  
Number Range ◽  
Reynolds Number Range

Microscale heat and fluid flow in macro geometries have been made practical in terms of cost and fabrication, by superimposing two macro geometries which are fabricated using readily-available CNC machining methods. Wavy-profile has been proposed to enhance heat transfer performance in the microchannel owing to the simplicity of geometry and feasibility to be fabricated using simple turning process. Experimental studies were conducted on single-phase, forced convective heat transfer using water as the working fluid for the Reynolds number range of 1300 to 4600, for a constant heat flux of 53.0 W/cm2. Three sinusoidal waves with different wavelength and same amplitude are studied to examine the effect of the total number of waves on the heat transfer and hydrodynamic performance within constant microchannel length. The maximum performance index, which evaluates heat transfer performance per unit pumping power, is 1.39, achieved by wavy profile with the shortest wavelength at Reynolds number of 2800. The performance index for all the enhanced microchannels peaks at the Reynolds number range of 2500 to 2800. Beyond that, the performance index is not a strong function of the wavelength. At lower Reynolds numbers, profile with the shortest wavelength achieves substantially higher performance indices, as the increment in pressure drop is accompanied by a comparable increment in heat transfer. Future work includes the introduction of correlations for the implementation of such geometries in industrial heat exchangers.

A Novel Pinch Point Design Methodology Based Energy and Economic Analyses of Organic Rankine Cycle

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Jahar Sarkar
Keyword(s):  
Heat Source ◽  
Power Output ◽  
Capital Cost ◽  
Design Parameters ◽  
Working Fluid ◽  
Pinch Point ◽  
Component Size ◽  
Unit Power ◽  
Isentropic Efficiency ◽  
Source And Sink

A generalized methodology for pinch point design and optimization of subcritical and transcritical organic Rankine cycles (ORCs) using both wet and dry fluids is adopted in this study. The presented algorithm can predict the pinch point location in evaporator and condenser simultaneously and optimize the evaporator pressure for best performance with various heat source and sink conditions. Effects of pinch point temperature difference (PPTD), isentropic efficiency, subcooling, superheating and regenerator on the energy and economic performances are discussed for selected working fluids. System yields similar optimum design for both maximum power generation and minimum capital cost per unit power. At optimum condition, ammonia is best in terms of higher thermal efficiency and lower component size, R152a is best in terms of higher net power output and heat recovery efficiency (11.1%), and toluene is best in terms of lower capital cost and cost per unit power output (7060 $/kW). Effect of heat source and sink parameters on both energy and economic performances is significant. Contour plots are presented to select the best ORC design parameters for available heat source condition. PPTD and expander isentropic efficiency have significant effect on performances. However, the effect of subcooling, superheating and regenerator depends on working fluid.

The Effect of Design Parameters on the Performance of Flagellar Propeller at Low Reynolds Number

2011 ◽  
Author(s):  
Hyejin Jeon ◽  
Yoon-Cheol Kim ◽  
Eun Goh ◽  
Dongwook Yim ◽  
Songwan Jin ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Rotational Speed ◽  
Low Reynolds Number ◽  
Stereoscopic Particle Image Velocimetry ◽  
Macroscopic Model ◽  
Maximum Efficiency ◽  
Design Parameters ◽  
Working Fluid ◽  
Inertia Force ◽  
Low Reynolds

To drive a small object which swims in low Reynolds number situation, we need a new type of propeller which is optimized for low Reynolds number usage since the flow at low Reynolds numbers is dominated by viscous force instead of inertia force. Propeller in a shape of bacterial flagellum can be a strong candidate for propeller of small swimming object. In this paper, we visualized velocity field induced by flagellar shaped propeller using stereoscopic particle image velocimetry. We also have experimentally evaluated the effect of pitch and rotational speeds on the performance of flagellar shaped propeller inspired by flagellum of E.coli using macroscopic model. Silicone oil whose viscosity is 100 times larger than water is used as working fluid to make low Reynolds number situation using macroscopic model. Thrust, torque and velocity were measured as a function of pitch and rotational speed, and efficiency was calculated using measured results. We found that the maximum efficiency of flagellar propeller reaches where the pitch angle is about 40°. However, the effect of rotational speed on the efficiency is relatively smaller than that of pitch. And the flow pattern behind the rotating propeller was altered by pitch of the propeller.

Generalized Parameters for Selection of Turbines and Working Fluids for OTEC Power Systems

1980 ◽  
Vol 102 (1) ◽  
pp. 215-222 ◽  
Author(s):  
D. D. Rosard
Keyword(s):  
Power Systems ◽  
Power Output ◽  
Design Parameters ◽  
Working Fluid ◽  
Working Fluids ◽  
Economy Of Scale ◽  
Scaling Parameters ◽  
Design Characteristics ◽  
Generalized Parameters ◽  
Ocean Thermal Energy

The choice of working fluid has a significant impact on the size and design characteristics of turbines for closed cycle OTEC (Ocean Thermal Energy Conversion) power systems. This paper examines turbine sizes and speeds for various candidate working fluids. The turbine performance and design limits are strongly influenced by blade stress criteria which have been ignored by previous investigators. Illustrative design parameters are given for a turbine using ammonia and scaling parameters are listed to compare the power outputs of turbines using other fluids. The design of a turbine for open-cycle OTEC power systems is largely dictated by the very high specific volume of the exhaust steam at a pressure of about 0.14 psia. In order to minimize the cost of turbines and generators through economy of scale, it is desirable to maximize the power output of a single turbine, and this leads to very large diameters and blade lengths. This paper explores the considerations which influence the choice of turbine size, blade length, speed, power output and efficiency.

scholarly journals Numerical Investigation of Thermal Hydraulic Performance of Printed Circuit Heat Exchanger of Periodic Diamond Channel Shape

2022 ◽  
Vol 961 (1) ◽  
pp. 012010
Author(s):  
Ali M Aljelawy ◽  
Amer M Aldabbagh ◽  
Falah F Hatem
Keyword(s):  
Reynolds Number ◽  
Heat Exchanger ◽  
Numerical Investigation ◽  
Hydraulic Performance ◽  
Operating Conditions ◽  
Design Parameters ◽  
Working Fluid ◽  
Channel Design ◽  
Printed Circuit ◽  
Pitch Length

Abstract One of the most recently important heat exchangers is the Printed circuit heat exchanger especially in the nuclear power plant and aerospace applications due to its very compact geometry and small print foot. This paper presents a 3D numerical investigation on the thermo-hydraulic performance of PCHE with new non-uniform channel design configuration. The new channel design is a rectangular cross section with repeated converging diverging sections or periodic diamond shape. The influence of three design parameters on the heat exchanger performance was studied and optimized, pitch length (p), length ratio (β) and the converging diverging angle (α). The computational models investigated in this study based on the operating conditions of the intermediate heat exchanger of very high temperature gas cooled reactor with helium as the working fluid under operating pressure of 3Mpa and inlet temperature of 800 K. The Reynolds number varied from 200 to 2000. Different Pitch lengths were used (1.59, 3.18, 6.36, and 12.73) mm, and different C-D angle (0, 4.5, 6, 7.5, 9, 10.5 and 12) and also different length ratios were used (0.2, 0.25 and 0.333). Three performance parameters were studied the Nusselt number, friction factor and the overall performance evaluation factor. Results show that the thermal performance enhanced with decreasing the pitch length and with increasing C-D angle and it was shown that this enhancement was found only at high Reynolds number above 1400. The best performance obtained at p=3.18, α=6 and β=0.25 based on the overall evaluation performance.

scholarly journals A New RANS Correction to Account for Varying Viscosity Effects

2021 ◽  
Author(s):  
Victor Coppo Leite ◽  
Elia Merzari
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Design Parameters ◽  
Working Fluid ◽  
Production Term ◽  
High Heat Transfer ◽  
Proposed Model ◽  
Varying Viscosity

Abstract It has previously been shown that by increasing the Reynolds number across a channel by spatially varying the viscosity does not cause an immediate change in the size of turbulent structures and a delay is in fact observed in both wall shear and friction Reynolds number (Coppo Leite, V, & Merzari, E., Proceedings of the ASME 2020 FEDSM, p. V003T05A019). Furthermore, it is also shown that depending on the length in which the flow condition changes, turbulence bursts are observed in the turbulence field. For the present work we propose a new version of the standard Reynolds Averaged Navier Stokes (RANS) k–τ model that includes some modifications in the production term in order to account for these effects. The new proposed model may be useful for many engineering applications as turbulent flows featuring temperature gradients and high heat transfer rates are often seen in heat exchangers, combustion chambers and nuclear reactors. In these applications, thermal and viscous properties of the working fluid are important design parameters that depend on temperature; hence it is likely to observe strong gradients on these scalars’ fields. To accomplish our goal, the modifications for the k–τ model are implemented and tested for a channel flow with spatial varying viscosity in the streamwise direction. The numerical simulations are performed using Nek5000, a spectral-element code developed at Argonne National Laboratory (ANL). Finally, the results considering a turbulence channel using the proposed model are compared against data obtained using Direct Numerical Simulations from the earlier work.

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