On the Thermodynamic Cycle of a MEMS-Based External Combustion Resonant Engine

2010 ◽  
Author(s):  
H. Bardaweel ◽  
R. Richards ◽  
C. Richards ◽  
M. Anderson
Keyword(s):  
Heat Transfer ◽  
Heat Engine ◽  
Fluid Motion ◽  
Thermodynamic Cycle ◽  
Working Fluid ◽  
Thermal Mass ◽  
Compression Pressure ◽  
Heat Addition ◽  
Irreversible Effects ◽  
Micro Heat Engine

In this work we investigate the thermodynamic cycle of a resonant, MEMS-based, micro heat engine. The micro heat engine is made of a cavity encapsulated between two membranes. The cavity is filled with saturated liquid-vapor mixture working fluid. Heat is added/rejected from the engine at a frequency equal to its resonant frequency. Both pressure-volume and temperature-entropy diagrams of the resonant engine are used to investigate the thermodynamic cycle of the resonant micro heat engine. The results show that the thermodynamic cycle of the engine consists of four major processes: heat addition, expansion, heat rejection, and compression. pressure-volume and temperature-entropy diagrams are bounded by two constant temperature processes and two constant volume processes. The temperature-entropy and pressure-volume diagrams show deviations from this ideal description and are rounded due to the presence of irreversible effects. Major sources of irreversibility in the engine are heat transfer over finite temperature differences during heat addition and rejection, heat transfer into and out of engine thermal mass and viscous losses due to liquid working fluid motion. The measured second law efficiency of the micro heat engine is about 16%.

A Micro Heat Engine Executing an Internal Carnot Cycle

2008 ◽  
Author(s):  
Eli Lurie ◽  
Abraham Kribus
Keyword(s):  
Strong Dependence ◽  
Heat Engine ◽  
Thermodynamic Cycle ◽  
Maximum Power ◽  
Working Fluid ◽  
Carnot Cycle ◽  
Heating And Cooling ◽  
Engine Design ◽  
Power Point ◽  
Micro Heat Engine

A micro heat engine, based on a cavity filled with a stationary working fluid under liquid-vapor saturation conditions and encapsulated by two membranes, is described and analyzed. This engine design is easy to produce using MEMS technologies and is operated with external heating and cooling. The motion of the membranes is controlled such that the internal pressure and temperature are constant during the heat addition and removal processes, and thus the fluid executes a true internal Carnot cycle. A model of this Saturation Phase-change Internal Carnot Engine (SPICE) was developed including thermodynamic, mechanical and heat transfer aspects. The efficiency and maximum power of the engine are derived. The maximum power point is fixed in a three-parameter space, and operation at this point leads to maximum power density that scales with the inverse square of the engine dimension. Inclusion of the finite heat capacity of the engine wall leads to a strong dependence of performance on engine frequency, and the existence of an optimal frequency. Effects of transient reverse heat flow, and ‘parasitic heat’ that does not participate in the thermodynamic cycle are observed.

Micro Thermal Engines: Is There Any Room at the Bottom?

1999 ◽  
Author(s):  
Richard B. Peterson
Keyword(s):  
Heat Transfer ◽  
Scaling Laws ◽  
Critical Role ◽  
Heat Engine ◽  
Engine Performance ◽  
Characteristic Size ◽  
Operating Efficiency ◽  
Simple Scaling ◽  
Small Structure ◽  
Micro Heat Engine

Abstract Richard P. Feynman introduced the field of microscale and nanoscale engineering in 1959 by giving a talk on how to make things very small. Feynman’s premise was that no fundamental physical laws limit the size of a machine down to the microscopic level. Is this true for all types of machines? Are micro thermal devices fundamentally different than mechanically-based machines with respect to their scaling laws? This paper demonstrates that micro thermal engines do indeed suffer serious performance degradation as their characteristic size is reduced. A micro thermal engine, and more generally, any thermally-based micro device, depends on establishing a temperature difference between two regions within a small structure. In this paper, the performance of a micro thermal engine is explored as a function of the characteristic length parameter, L. In the development, the important features of thermal engines are discussed in the context of developing simple scaling laws predicting the dependency of the operating efficiency on L. After this is accomplished, a general model is derived for a heat engine operating between two temperature reservoirs and having both intrinsic and extrinsic sources of irreversibility, i.e. thermal conductances and heat leakage paths for the heat flow. With this model and typical numerical values for the conductances, micro heat engine performance is predicted as the characteristic size is reduced. This paper demonstrates that under at least one particular formulation of the problem, there may indeed be some room at the bottom. However, heat transfer does play a critical role in determining micro engine performance and depending on how the heat transfer through the engine is modeled, vanishingly small efficiencies can result as the characteristic engine size goes to zero.

Performance Optimization and Parametric Analysis of a Class of Solar-Driven Heat Engines

2010 ◽  
Author(s):  
Houcheng Zhang ◽  
Lanmei Wu ◽  
Guoxing Lin
Keyword(s):  
Heat Transfer ◽  
Heat Loss ◽  
Performance Optimization ◽  
Solar Collector ◽  
Heat Engine ◽  
Working Fluid ◽  
Convection Heat ◽  
Combined System ◽  
Heat Engines ◽  
Internal Irreversibility

A class of solar-driven heat engines is modeled as a combined system consisting of a solar collector and a unified heat engine, in which muti-irreversibilities including not only the finite rate heat transfer and the internal irreversibility, but also radiation-convection heat loss from the solar collector to the ambience are taken into account. The maximum overall efficiency of the system, the optimal operating temperature of the solar collector, the optimal temperatures of the working fluid and the optimal ratio of heat transfer areas are calculated by using numerical calculation method. The influences of radiation-convection heat loss of the collector and internal irreversibility on the cyclic performances of the solar-driven heat engine system are revealed. The results obtained in the present paper are more general than those in literature and the performance characteristics of several solar-driven heat engines such as Carnot, Brayton, Braysson and so on can be directly derived from them.

Low Frequency Operation of the P3 Micro Heat Engine

2002 ◽  
Author(s):  
Scott A. Whalen ◽  
Michael R. Thompson ◽  
Cecilia D. Richards ◽  
David F. Bahr ◽  
Robert F. Richards
Keyword(s):  
Combustion Engine ◽  
Thermal Power ◽  
Electrical Power ◽  
Heat Engine ◽  
Low Frequency ◽  
Thermodynamic Cycle ◽  
Mechanical Power ◽  
Peak Voltage ◽  
Macro Scale ◽  
Micro Heat Engine

The development and low frequency testing of a micro heat engine is presented. Production of electrical power by a dynamic micro heat engine is demonstrated. The prototype micro heat engine is an external combustion engine in which thermal power is converted to mechanical power through a novel thermodynamic cycle. Mechanical power is converted into electrical power through the use of a thin-film piezoelectric membrane generator. This design is well suited to photolithography-based batch fabrication methods and is unlike any conventionally manufactured macro-scale engine. A peak-to-peak voltage of .84 volts, and power output of 1.5 microwatts have been realized at operating speeds of 10 Hz. Measurements are also presented for the engine operating at resonant conditions. Cycle speeds up to 240 Hz have been obtained, with peak-to-peak voltages of 70 millivolts.

scholarly journals Two-Dimensional Model of a Space Station Freedom Thermal Energy Storage Canister

1994 ◽  
Vol 116 (2) ◽  
pp. 114-121 ◽  
Author(s):  
T. W. Kerslake ◽  
M. B. Ibrahim
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Free Convection ◽  
Phase Change ◽  
Thermal Energy ◽  
Heat Engine ◽  
Space Station ◽  
Working Fluid ◽  
Two Dimensional ◽  
Liquid Salt

The Solar Dynamic Power Module being developed for Space Station Freedom uses a eutectic mixture of LiF-CaF2 phase-change salt contained in toroidal canisters for thermal energy storage. This paper presents results from heat transfer analyses of the phase-change salt containment canister. A two-dimensional, axisymmetric finite difference computer program which models the canister walls, salt, void, and heat engine working fluid coolant was developed. Analyses included effects of conduction in canister walls and solid salt, conduction and free convection in liquid salt, conduction and radiation across salt vapor-filled void regions, and forced convection in the heat engine working fluid. Void shape and location were prescribed based on engineering judgment. The salt phase-change process was modeled using the enthalpy method. Discussion of results focuses on the role of free convection in the liquid salt on canister heat transfer performance. This role is shown to be important for interpreting the relationship between ground-based canister performance (in 1-g) and expected on-orbit performance (in micro-g). Attention is also focused on the influence of void heat transfer on canister wall temperature distributions. The large thermal resistance of void regions is shown to accentuate canister hot spots and temperature gradients.

Characterization of the Thermodynamic Working Cycle in a MEMS-Based Micro Heat Engine

2003 ◽  
Author(s):  
S. A. Whalen ◽  
L. W. Weiss ◽  
C. D. Richards ◽  
D. F. Bahr ◽  
R. F. Richards
Keyword(s):  
Mechanical Energy ◽  
Michelson Interferometer ◽  
Heat Engine ◽  
Working Fluid ◽  
Resistance Thermometer ◽  
Working Cycle ◽  
Displacement Profile ◽  
Micro Heat Engine ◽  
Center Deflection

This work examines the conversion of thermal to mechanical energy in a micro heat engine by characterizing the heat engine’s working cycle. Results are given for dynamic measurements of pressure, volume, and temperature throughout the working cycle of the engine. Engine pressure is determined from the deformation of the two membranes in contact with the working fluid. A Michelson interferometer is used to measure the center deflection and displacement profile of both of these membranes. Pressure is determined from the membrane deflection using experimental static pressure-deflection curves. Engine temperature is measured using electrical resistance thermometry, via a micro resistance thermometer fabricated on the surface of a silicon membrane exposed to the working fluid in the engine cavity.

Development of Scaling Model for a MEMS-Based Micro Heat Engine

2010 ◽  
Author(s):  
H. Bardaweel ◽  
B. S. Preetham ◽  
R. Richards ◽  
C. Richards ◽  
M. Anderson
Keyword(s):  
Combustion Engine ◽  
Heat Engine ◽  
Working Fluid ◽  
Thin Membranes ◽  
Micro Heat Engine ◽  
Heat Of Evaporation ◽  
Major Factors ◽  
Engine Components ◽  
External Combustion ◽  
Thermal Physical Properties

In this work we investigate issues related to scaling of a MEMS-based resonant heat engine. The engine is an external combustion engine made of a cavity encapsulated between two thin membranes. The cavity is filled with saturated liquid-vapor mixture working fluid. We use both model and experiment to investigate scaling of the MEMS-based resonant heat engine. The results suggest that the performance of the engine is determined by three major factors: geometry of the engine, speed of operation, and thermal physical properties of engine components. Larger engine volumes, working fluids with higher latent heat of evaporation, slower engine speeds, and compliant expander structures are shown to be desirable.

Finite Time Thermodynamics: Realizability Domain of Heat to Work Converters

2019 ◽  
Vol 44 (2) ◽  
pp. 181-191 ◽  
Author(s):  
M. A. Zaeva ◽  
A. M. Tsirlin ◽  
O. V. Didina
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Energy Conversion ◽  
Conversion Efficiency ◽  
Finite Time ◽  
Heat Engine ◽  
Energy Conversion Efficiency ◽  
Maximum Power ◽  
Working Fluid ◽  
Finite Time Thermodynamics

Abstract From the point of view of finite time thermodynamics, the performance boundaries of thermal machines are considered, taking into account the irreversibility of the heat exchange processes of the working fluid with hot and cold sources. It is shown how the kinetics of heat exchange affects the shape of the optimal cycle of a heat engine and its performance, with a focus on the energy conversion efficiency in the maximum power mode. This energy conversion efficiency can depend only on the ratio of the heat transfer coefficients to the sources or not depend on them at all. A class of kinetic functions corresponding to “natural” requirements is introduced and it is shown that for any kinetics from this class the optimal cycle consists of two isotherms and two adiabats, not only for the maximum power problem, but also for the problem of maximum energy conversion efficiency at a given power. Examples are given for calculating the parameters of the optimal cycle for the case when the heat transfer coefficient to the cold source is arbitrarily large and for kinetics in the form of a Fourier law.

Experimental Investigation Into the Heat Transfer Mechanism of Oscillating Heat Pipes Using Temperature Sensitive Paint

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Matthew Francom ◽  
Jungho Kim
Keyword(s):  
Heat Transfer ◽  
Latent Heat ◽  
Fluid Motion ◽  
Heat Pipes ◽  
Transfer Mechanism ◽  
Working Fluid ◽  
Temperature Sensitive ◽  
Heat Transfer Mechanism ◽  
Experimental Apparatus ◽  
Temperature Sensitive Paint

Abstract Oscillating heat pipes (OHPs) represent a promising passive mechanism for the removal or spreading of heat. While simple to construct, the fluid and thermodynamics of these devices are still poorly understood. There is debate over whether the primary heat transfer mechanism is due to sensible heating of the liquid phase or due to latent heat transfer through phase change. To answer this question, an experimental apparatus was constructed to provide time- and space-resolved temperature and heat transfer data across the face of an operating OHP with HFE-7000 as the working fluid. This experiment utilized temperature sensitive paint (TSP) alongside visual recording of the fluid motion in order to determine the relative latent and sensible contribution to the overall heat transfer. The OHP was tested with input powers ranging from 2.6 W to 10.1 W. It found that latent heat transfer was the dominant heat transfer mechanism, accounting for between 65% and 83% of the total heat transferred in all cases.

Thermally Actuated Pumping of a Fluid With a Free Interface Using Surface Asymmetry

2008 ◽  
Author(s):  
Myeong Chan Jo ◽  
Vinod Narayanan
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Heat Source ◽  
Fluid Velocity ◽  
Fluid Motion ◽  
Working Fluid ◽  
Thermal Structures ◽  
Loop Channel ◽  
Interfacial Temperature ◽  
Thermally Actuated

An experimental study of thermally actuated pumping of a single-component fluid is presented in the context of thermal management of a heat source. The prominent feature of this pumping method is that the very heat that is to be removed from the heat source causes a net fluid motion. Surface tension is the dominant driving force for convection in this study. An asymmetry in this force is created by the use of a surface with repeated asymmetric triangular structures. Silicone oil was used as the working fluid. Independent parameters that were varied consisted of the channel surface-to-ambient temperature difference and the fluid thickness. A dye-tracking imaging method was developed to determine the fluid interfacial velocity. The flow results were corroborated with interfacial temperature measurements obtained using infrared thermography. Dye tracking experiments indicate that the direction of net fluid motion is from the less-steep side of the ratchet towards its steeper side, resulting in a clockwise flow direction in the closed loop channel for all three liquid depths of 0.5 mm, 1.0 mm and 2.7 mm. The range of the net flow velocities varies from 0.18 mm/min to 0.86 mm/min. A fluid height of 1 mm results in a maximum net fluid velocity at both surface-to-ambient temperatures studied. Interfacial temperature contour maps indicate the presence of thermal structures that are indicative of convection cells, and that an optimum thickness exists for maximum heat transfer coefficient. Difference in streamwise gradients of temperature (and hence surface tension) on either side of the thermal structures causes a net streamwise surface tension gradient in the direction of net fluid motion. An optimal fluid thickness for heat transfer as well as net interfacial fluid velocity is suggested by the results.

Sign in / Sign up

Export Citation Format

Share Document