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.

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%.

Optimal Control Experimentation of Compression Trajectories for a Liquid Piston Air Compressor

2013 ◽  
Author(s):  
Farzad A. Shirazi ◽  
Mohsen Saadat ◽  
Bo Yan ◽  
Perry Y. Li ◽  
Terry W. Simon
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Power Density ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Compression Efficiency ◽  
Air Compressor ◽  
Compression Time ◽  
Liquid Piston

Air compressor is the critical part of a Compressed Air Energy Storage (CAES) system. Efficient and fast compression of air from ambient to a pressure ratio of 200–300 is a challenging problem due to the trade-off between efficiency and power density. Compression efficiency is mainly affected by the amount of heat transfer between the air and its surrounding during the compression. One way to increase heat transfer is to implement an optimal compression trajectory, i.e., a unique trajectory maximizing the compression efficiency for a given compression time and compression ratio. The main part of the heat transfer model is the convective heat transfer coefficient (h) which in general is a function of local air velocity, air density and air temperature. Depending on the model used for heat transfer, different optimal compression profiles can be achieved. Hence, a good understanding of real heat transfer between air and its surrounding wall inside the compression chamber is essential in order to calculate the correct optimal profile. A numerical optimization approach has been proposed in previous works to calculate the optimal compression profile for a general heat transfer model. While the results show a good improvement both in the lumped air model as well as Fluent CFD analysis, they have never been experimentally proved. In this work, we have implemented these optimal compression profiles in an experimental setup that contains a compression chamber with a liquid piston driven by a water pump through a flow control valve. The optimal trajectories are found and experimented for different compression times. The actual value of heat transfer coefficient is unknown in the experiment. Therefore, an iterative procedure is employed to obtain h corresponding to each compression time. The resulted efficiency versus power density of optimal profiles is then compared with ad-hoc constant flow rate profiles showing up to %4 higher efficiency in a same power density or %30 higher power density in a same efficiency in the experiment.

scholarly journals C INVESTIGATION OF HEAT TRANSFER COEFFICIENT AUGMENTATION IN DIVERGENT RECTANGULAR DUCT FOR TWO PHASES FLOW (AIR-WATER)

2020 ◽  
Vol 20 (2) ◽  
pp. 111-121
Author(s):  
Hadi O . Basher ◽  
Riyadh S Al-Turaihi ◽  
Ahmed A. Shubba
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Rate ◽  
Volume Flow Rate ◽  
Volume Flow ◽  
Water Volume ◽  
Maximum Heat ◽  
Air Volume ◽  
The Heat Transfer Coefficient

In this project, the flow distribution for air and water, and the enhancement of the heattransfer coefficient are experimentally studied. Experimental studies have been performed totest the influence of discharge, pitch, the height of ribs at a constant heat flux on thetemperature and pressure distributions. Along the channel of the test and the heat transfercoefficient, the water volume flow rate was about (5-12 L/min), the air volume flow rate wasabout (5.83-16.66 L/min), and heat were (80, 100,120, watt). An experimental rig wasconstructed within the test whole system. On the other hands, the channel has a divergentsection with an angle =15o with vertical axis. The study included changing in the ribs heightby using three values (12, 15, 18 mm) and changing the ribs pitch into three values (5, 8, 10mm).The results indicated an increasing in the local heat transfer coefficient as a result ofincreasing the discharge. While there was an inverse influence for the temperature distributionalong the test channel which drops when the discharge rise. The results also confirm that theincreasing in the pitch distance leads to reduce the heat transfer coefficient. Increasing theribs height increases the coefficient of heat transfer. However, the experiment heat transfercoefficient improves about (15.6 %) when the water volume flow rate increased from (5 to 12L/min), and about (18.7%) when the air volume flow rate increased from (5.83 to 16.66L/min). The best heat transfer coefficient was about (35.6 %) which can be achieved whenthe pitch decreased from (10 to 5mm). The increasing of the height from (12 to 18) mmimproves the heat transfer coefficient about (11.2 %). The best rib dimension was 18 mmheight, and 5 mm pitch, which give a maximum heat transfer coefficient (1212.02 W/m2. oC).

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.

Air Compression Performance Improvement via Trajectory Optimization: Experimental Validation

2016 ◽  
Author(s):  
Mohsen Saadat ◽  
Anirudh Srivatsa ◽  
Perry Y. Li ◽  
Terrence Simon
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Power Density ◽  
Experimental Validation ◽  
Ad Hoc ◽  
Programming Approach ◽  
Trade Off ◽  
Air Compressor ◽  
Compression Time ◽  
Liquid Piston

In an isothermal compressed air energy storage (CAES) system, it is critical that the high pressure air compressor/expander is both efficient and power dense. The fundamental trade-off between efficiency and power density is due to limitation in heat transfer capacity during the compression/expansion process. In our previous works, optimization of the compression/expansion trajectory has been proposed as a means to mitigate this trade-off. Analysis and simulations have shown that the use of optimized trajectory can increase power density significantly (2–3 fold) over ad-hoc linear or sinusoidal trajectories without sacrificing efficiency especially for high pressure ratios. This paper presents the first experimental validation of this approach in high pressure (7bar to 200bar) compression. Experiments are performed on an instrumented liquid piston compressor. Correlations for the heat transfer coefficient were obtained empirically from a set of CFD simulations under different conditions. Dynamic programming approach is used to calculate the optimal compression trajectories by minimizing the compression time for a range of desired compression efficiencies. These compression profiles (as function of compression time) are then tracked in a liquid piston air compressor testbed using a combination of feed-forward and feedback control strategy. Compared to ad-hoc constant flow rate trajectories, the optimal trajectories double the power density at 80% efficiency or improve the thermal efficiency by 5% over a range of power densities.

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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