Maximum Power From Fluid Flow: Results From the First and Second Laws of Thermodynamics

2012 ◽  
Author(s):  
German Amador Diaz ◽  
John Turizo Santos ◽  
Elkin Hernandez ◽  
Ricardo Vasquez Padilla ◽  
Lesme Corredor
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Power Output ◽  
Power Plants ◽  
Cross Sectional Area ◽  
Maximum Power ◽  
Sectional Area ◽  
Cross Sectional ◽  
Maximum Power Output ◽  
Piston Cylinder

The heat transfer principle of power maximization in power plants with heat transfer irreversibilities was cleverly extended by Bejan [1] to fluid flow, by obtaining that the energy conversion efficiency at maximum power is ηmax = 1/2(1 − P2/P1). This result is analog to the efficiency at maximum power for power plants, ηmax = 1 − (T2/T1)1/2 which was deduced by Curzon and Ahlborn [2]. In this paper, the analysis to obtain maximum power output delivered from a piston between two pressure reservoir across linear flow resistance is generalized by considering the piston cylinder friction, by obtaining relations of maximum power output and optimal speed of the piston in terms of first law efficiency. Expressions to relate the power output, cross sectional area of the chamber and first law efficiency, were deduced in order to evaluate the influence of the overall size constraints and fluid regime in the performance of the piston cylinder system. Flow in circular ducts and developed laminar flow between parallel plates, are considered to demonstrate that when two pressure reservoirs oriented in counterflow, with different and arbitrary cross sectional area, must have the same area in order to maximize the power output of the system. These results introduce some modifications to the results obtained by Bejan [1] and Chen [3]. This paper extends the Bejan and Chen’s work by estimating under turbulent regime the lost available work rate associated with the degree of irreversibilities caused by the flow resistances of the system. This analysis is equivalent to evaluate the irreversibilities in an endoirreversible Carnot heat engine model caused by the heat resistance loss between the engine and its surrounding heat reservoirs. This paper concludes with an application to illustrate the practical applications by estimating the lost available work of an actual steady-flow turbine and the layout pipes upstream and downstream of the same device.

Convective Heat Transfer and Contact Resistances Effects on Performance of Conventional and Composite Thermoelectric Devices

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
B. V. K. Reddy ◽  
Matthew Barry ◽  
John Li ◽  
Minking K. Chyu
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Conversion Efficiency ◽  
Power Output ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Transfer Coefficients ◽  
Cross Sectional ◽  
Heat Transfer Coefficients

The performance of Π shaped conventional and composite thermoelectric devices (TEDs) applied to waste heat recovery by taking the Fourier heat conduction, Joule heating, and the Peltier and Thomson effects in TE materials is investigated using analytical solutions. The TE legs built with semiconductor materials bonded onto a highly conductive interconnector material in a segmented fashion is treated as the composite TED, whereas the legs merely made from semiconductors is treated as the conventional TED. The top and bottom surfaces of TEDs are subjected to convective heat transfer conditions while the remaining surfaces exposed to ambient are kept adiabatic. The effects of contact resistances, convective heat transfer coefficients, and TE leg heights L on TEDs' performance are studied. An increase in electrical and/or thermal contact resistance and a decrease in heat transfer coefficients are resulted in a decrease in power output P0 and conversion efficiency η. Depending on the contact resistances and convective heat transfer loads, the optimum L where a maximum Po occurs is obtained typically in the range of 1–4 mm. For TE leg size greater than optimum L and TED operating under higher convective heat transfer conditions, the composite design exhibited better power output and lower conversion efficiency compared to conventional design. The effects of interconnector lengths and cross-sectional area on the composite TED's characteristics are also investigated. An increase in a length and a decrease in a cross-sectional area of the interconnector decreases the composite TED's performance. However, based on the increase of the interconnector's electrical resistance in relation to the device's total internal resistance, the composite TED exhibited both negligible and significant change behavior in P0.

scholarly journals Numerical Investigation of a two-inlet PVT air collector

2019 ◽  
Vol 136 ◽  
pp. 05014
Author(s):  
Zhangyang Kang ◽  
Zhaoyang Lu ◽  
Xin Deng ◽  
Qiongqiong Yao
Keyword(s):  
Heat Transfer ◽  
Single Channel ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Thermal Characteristics ◽  
Area Ratio ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Maximum Heat

A numerical study of heat and mass transfer characteristics of a two-inlet PV/T air collector is performed. The influence of thermal characteristics and efficiency is investigated as the area ratios of inlet and outlet of the single channel with two inlets are changed. The design of the two-inlet PV/T air collector can avoid the poor heat transfer conditions of the single inlet PV/T air collector and improve the total photo-thermal efficiency. When the inlet/outlet cross-sectional area ratio is reduced, the inlet air from the second inlet enhances the convection heat transfer in the second duct and the temperature distribution is more uniform. As the cross-sectional area of the second inlet increase, the maximum heat exchange amount of the two-inlet PV/T air collector occurs between the inlet and outlet cross-sectional area ratio L=0.645 and L=0.562.

The Efficiency at Maximum Power Output of a Carnot Engine with Heat Leak

1995 ◽  
Vol 23 (2) ◽  
pp. 157-165 ◽  
Author(s):  
F. Moukalled ◽  
R. Y. Nuwayhid
Keyword(s):  
Heat Transfer ◽  
Power Output ◽  
Maximum Power ◽  
Heat Leak ◽  
Suggested Model ◽  
Maximum Power Output ◽  
Transfer Processes ◽  
Newton’S Law ◽  
New Formulation ◽  
Special Case

Endoreversible thermodynamics are used for studying the performance of Carnot engines with heat leak. This is done by adding a heat leak term into a variation of the model suggested by DeVos [1]. Heat transfer across the engine is assumed to occur via a conduction/convection mechanism and Newton's law of cooling is employed to model the heat transfer processes. The efficiency at maximum power output is found to be deeply affected by the rate of heat leak. Moreover, the Curzon-Ahlborn relation [2] is shown to represent a special case of the new formulation. Since the suggested model allows more flexibility in predicting actual engines' performance, its use is recommended in thermodynamics courses.

scholarly journals Row Resolved Heat Transfer Variations in Pin-Fin Arrays Including Effects of Non-Uniform Arrays and Flow Convergence

1986 ◽  
Author(s):  
D. E. Metzger ◽  
W. B. Shepard ◽  
S. W. Haley
Keyword(s):  
Heat Transfer ◽  
Cross Sectional Area ◽  
Experimental Program ◽  
Internal Cooling ◽  
Sectional Area ◽  
Order Unity ◽  
Cross Sectional ◽  
Turbine Engine ◽  
Pin Fin ◽  
Pin Fin Arrays

Measured streamwise (longitudinal) heat transfer variations, spanwise (transverse) averaged and resolved to single row spacings, are presented for large aspect ratio ducts containing staggered arrays of circular pin fins which span the entire duct height. A number of different array geometries have been investigated in an experimental program, including uniformly spaced arrays in constant cross sectional area ducts with streamwise row spacings over the range 1.5 to 5.0 pin diameters. Such arrays, with pin length-to-diameter ratio of order unity, are often used to enhance heat transfer in internal cooling passages of gas turbine engine airfoils. The effects of various length interruptions in the pin pattern and of abrapt changes in pin diameter are presented for constant cross sectional area ducts. In addition, results are presented for the effect of duct convergence, a common situation in the cooled turbine airfoil application. A concise summary of all the observed behavior is given, useful for predicting the performance of arbitrarily spaced pin fin arrays that may be specified to produce a particular cooling distribution. Predictions are compared with two final test, configurations which combine aspects of all of the effects investigated in the experimental program.

scholarly journals Modeling and Analysis of a Piezoelectric Energy Harvester with Varying Cross-Sectional Area

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Maiara Rosa ◽  
Carlos De Marqui Junior
Keyword(s):  
Experimental Verification ◽  
Power Output ◽  
Optimization Problems ◽  
Load Resistance ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Beam Shape ◽  
Piezoelectric Energy ◽  
Tip Mass

This paper reports on the modeling and on the experimental verification of electromechanically coupled beams with varying cross-sectional area for piezoelectric energy harvesting. The governing equations are formulated using the Rayleigh-Ritz method and Euler-Bernoulli assumptions. A load resistance is considered in the electrical domain for the estimate of the electric power output of each geometric configuration. The model is first verified against the analytical results for a rectangular bimorph with tip mass reported in the literature. The experimental verification of the model is also reported for a tapered bimorph cantilever with tip mass. The effects of varying cross-sectional area and tip mass on the electromechanical behavior of piezoelectric energy harvesters are also discussed. An issue related to the estimation of the optimal load resistance (that gives the maximum power output) on beam shape optimization problems is also discussed.

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