Optimal Efficiency-Power Tradeoff for an Air Motor/Compressor With Volume Varying Heat Transfer Capability

2011 ◽  
Author(s):  
Andrew T. Rice ◽  
Perry Y. Li
Keyword(s):  
Heat Transfer ◽  
High Efficiency ◽  
Linear Optimization ◽  
Air Motor ◽  
Transfer Capability ◽  
Compression And Expansion ◽  
Optimal Efficiency ◽  
Method Of Lagrange Multipliers ◽  
The Heat Transfer Coefficient

This paper presents the pressure-volume trajectories that yield the optimal tradeoff between efficiency and power during the compression and expansion of air. These results could benefit applications such as compressed air energy storage where both high efficiency and power density are required. Earlier work established solutions for the simple case in which hA, the product of the heat transfer coefficient and heat transfer surface area, is constant. This paper extends that analysis by allowing hA to vary with air volume. Solutions to the constrained, non-linear optimization problem are developed utilizing the method of Lagrange multipliers and Karush-Kuhn-Tucker (KKT) conditions. It is found that the optimal trajectory takes the form “fast-slow-fast” where the fast stages are adiabatic and the temperature change during the slow stage is proportional to the inverse root of the hA product. A case study predicts a 60% improvement in power over the constant-hA solution when both trajectories are run at 90% efficiency and hA = hA(V). Compared to linear- and sinusoidal-shaped trajectories, also at 90% efficiency, power gains are expected to be in the range of 500–1500%.

scholarly journals Optimal Efficiency-Power Tradeoff for an Air Compressor/Expander

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Andrew T. Rice ◽  
Perry Y. Li ◽  
Caleb J. Sanckens
Keyword(s):  
Heat Transfer ◽  
Ad Hoc ◽  
Expansion Chamber ◽  
Compression Efficiency ◽  
Air Compressor ◽  
Air Volume ◽  
Compression And Expansion ◽  
Optimal Efficiency ◽  
The Heat Transfer Coefficient

An efficient and power dense high pressure air compressor/expander (C/E) is critical for the success of a compressed air energy storage (CAES) system. There is a tradeoff between efficiency and power density that is mediated by heat transfer within the compression/expansion chamber. This paper considers the optimal control for the compression and expansion processes that provides the optimal tradeoff between efficiency and power. Analytical Pareto optimal solutions are developed for the cases in which hA, the product of the heat transfer coefficient and heat transfer surface area, is either a constant or is a function of the air volume. It is found that the optimal trajectories take the form “fast-slow-fast” where the fast stages are adiabatic and the slow stage is either isothermal for the constant-hA assumption, or a pseudo-isothermal (where the temperature depends on the instantaneous hA) for the volume-varying-hA assumption. A case study shows that at 90% compression efficiency, power gains are in the range of 500−1500% over ad hoc linear and sinusoidal profiles.

Combustion and Heat Transfer in 300MW Oxy-Fired CFBB

2011 ◽  
Vol 354-355 ◽  
pp. 369-375
Author(s):  
Chun Bo Wang ◽  
Xiao Fei Ma ◽  
Jiao Zhang ◽  
Jin Gui Sheng ◽  
Hong Wei Li
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Particle Diameter ◽  
External Heat ◽  
Transfer Model ◽  
Heat Transfer Characteristics ◽  
Operation Condition ◽  
Transfer Capability ◽  
The Heat Transfer Coefficient

A combustion and heat transfer model in oxy-fired CFBB was set. Particle diameter, voidage of the bed ,etc, was analyzed with 30%, 50%, and 70% oxygen. Take a 300MW CFBB for example, the heat transfer characteristics in furnace were numerical simulated. In the sparse zone, heat transfer coefficient is proportional to oxygen concentration at the same voidage of the bed; under the same operation condition, the heat transfer coefficient in CFB increases with the voidage of the bed at first, then it decreases. It was found the heat transfer capability decrease due to the higher concentration of oxygen. It is necessary to set an external heat exchanger to keep a normal combustion

Effect of High Coolant Velocity on Heat Transfer in Compact Heat Exchangers

2006 ◽  
Author(s):  
P. L. Sathyanarayanan ◽  
N. Venkateswaran ◽  
R. Ramprabhu
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
High Efficiency ◽  
Fluid Velocity ◽  
Small Diameter ◽  
Space Applications ◽  
Compact Heat Exchangers ◽  
Military Vehicle ◽  
Transfer Capability ◽  
Lower Fluid

Compact Heat Exchangers were developed to have very high efficiency in transfer of heat within a very small space or volume and are being used in the automotive, aircraft and space applications. In order to obtain much higher heat transfer, these Heat Exchangers uses closely packed fins, narrow or small diameter passages and turbulators or turbulence promoters. Though these arrangements result in much higher pressure drop for the fluids, this disadvantage is expected to be off-set with a larger increase in heat transfer capability. Generally it is known that turbulence enables better mixing of the fluid and results in enhancing the heat being transferred. However in practice it has been observed that there is a limit to this enhancement and the heat transfer does not improve beyond certain turbulence levels. The higher turbulence level probably results in carrying the heat away along with the fluid without transferring all the heat to the cooling medium. The presence of turbulence promoters was found to be beneficial at a lower fluid velocity level, where they conduct the heat away more by surface conduction than by convection in the fluid. Detailed experimental investigation and findings of this phenomenon using a compact heat exchanger for a military vehicle is described in this paper.

Numerical Investigation of Thermal Resistance in a Rectangular Flux Channel With Non-Uniform Heat Convection in the Sink Plane

2015 ◽  
Author(s):  
Masood Razavi ◽  
Alireza Dehghani-Sanij ◽  
Yuri S. Muzychka
Keyword(s):  
Heat Transfer ◽  
Thermal Analysis ◽  
Heat Transfer Coefficient ◽  
Thermal Resistance ◽  
Transfer Coefficient ◽  
Numerical Study ◽  
Commercial Software Package ◽  
Volume Method ◽  
The Heat Transfer Coefficient

Thermal analysis of electronic devices is essential for designing thermal management systems and for assuring a perfect working condition. In order to have a precise thermal analysis, thermal spreading resistance should be calculated. In this paper, a numerical study is conducted on the thermal resistance of a 2D flux channel with a non-uniform convection coefficient in the heat sink plane. For this purpose, the Finite Volume Method (FVM) is used. As a case study, a 2D flux channel with a discrete specified heat flux and convection edges is assumed. Also, the heat transfer coefficient in the sink boundary condition is determined symmetrically using a hyperellipse function. This function can model a wide variety of different distributions of a heat transfer coefficient from a uniform cooling to the most intense cooling in the central region. All results are compared and validated with the COMSOL commercial software package. The proposed method is useful for thermal engineers for modeling different flux channels with different properties and boundary conditions such as the variable heat transfer coefficient.

scholarly journals Application of sensitivity and uncertainty analyses in the calculation of the heat transfer coefficient of a window

2012 ◽  
Vol 20 (3) ◽  
pp. 27-34
Author(s):  
Pavol Hrebík
Keyword(s):  
Heat Transfer ◽  
Sensitivity Analysis ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Random Variable ◽  
Realistic Model ◽  
Sensitivity Analyses ◽  
The Heat Transfer Coefficient ◽  
Selection Of

AbstractThe type of analysis we choose to use depends on exactly what we intend to explore. TheMonte Carlo (MCA) method, which can be applied to a sensitivity analysis (SA) and anuncertainty analysis (UA), is based on the random selection of a random variablegenerated by all the input parameters X. This paper discusses a realistic model ofa window and is focused on the uncertainties of the input and a sensitivity analysis of theoutput parameters - a window is a heat transfer coefficient. A case study is described toevaluate the necessity of the use of uncertainty and sensitivity analyses.

Optimal Efficiency-Power Relationship for an Air Motor-Compressor in an Energy Storage and Regeneration System

2009 ◽  
Author(s):  
Caleb J. Sancken ◽  
Perry Y. Li
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Pressure Ratio ◽  
Compressed Air ◽  
Power Relationship ◽  
Regeneration System ◽  
Trade Off ◽  
Air Motor ◽  
Transfer Capability ◽  
Heat Transfer Capability

Compressing air from atmospheric pressure into high pressure storage and expanding the compressed air in reverse is a means of energy storage and regeneration for fluid power systems that can potentially improve energy density by an order of magnitude over existing accumulators. This approach, known as the “open accumulator” energy storage concept, as well as other applications such as compressed air powered cars, rely on the availability of efficient and power-dense air motor/compressors. Increasing power is typically accompanied by reducing efficiency with the trade-off being determined by the heat transfer capability. In this paper, the authors present the Pareto optimal trade-off between the efficiency and power for a given heat transfer capability and ambient temperature in an air motor/compressor to achieve a given pressure ratio. It is shown that the optimal frontier is generated by an air motor/compressor that compresses and expands the air via a sequence of adiabatic, isothermal, and adiabatic processes. For the same efficiency of 80%, such an optimal volume trajectory achieves 3–5 times increased power over ad-hoc volume trajectories. It is also shown that approximating the infinitely fast adiabatic portions by finite time processes do not significantly reduce the effectiveness of the optimal operating strategy.

Evaporation of lignin-lean black liquor

TAPPI Journal ◽  
2015 ◽  
Vol 14 (7) ◽  
pp. 441-450
Author(s):  
HENRIK WALLMO, ◽  
ULF ANDERSSON ◽  
MATHIAS GOURDON ◽  
MARTIN WIMBY
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Black Liquor ◽  
Salt Content ◽  
Solubility Limit ◽  
Lignin Removal ◽  
Kraft Black Liquor ◽  
Black Liquors ◽  
The Heat Transfer Coefficient

Many of the pulp mill biorefinery concepts recently presented include removal of lignin from black liquor. In this work, the aim was to study how the change in liquor chemistry affected the evaporation of kraft black liquor when lignin was removed using the LignoBoost process. Lignin was removed from a softwood kraft black liquor and four different black liquors were studied: one reference black liquor (with no lignin extracted); two ligninlean black liquors with a lignin removal rate of 5.5% and 21%, respectively; and one liquor with maximum lignin removal of 60%. Evaporation tests were carried out at the research evaporator in Chalmers University of Technology. Studied parameters were liquor viscosity, boiling point rise, heat transfer coefficient, scaling propensity, changes in liquor chemical composition, and tube incrustation. It was found that the solubility limit for incrustation changed towards lower dry solids for the lignin-lean black liquors due to an increased salt content. The scaling obtained on the tubes was easily cleaned with thin liquor at 105°C. It was also shown that the liquor viscosity decreased exponentially with increased lignin outtake and hence, the heat transfer coefficient increased with increased lignin outtake. Long term tests, operated about 6 percentage dry solids units above the solubility limit for incrustation for all liquors, showed that the heat transfer coefficient increased from 650 W/m2K for the reference liquor to 1500 W/m2K for the liquor with highest lignin separation degree, 60%.

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