scholarly journals Optimization and Entropy Production: Application to Carnot-Like Refrigeration Machines

2018 ◽  
Author(s):  
Camelia Stanciu ◽  
Michel Feidt ◽  
Monica Costea ◽  
Dorin Stanciu
Keyword(s):  
Heat Transfer ◽  
Second Law Of Thermodynamics ◽  
Operating Conditions ◽  
Optimum Operating ◽  
System Parameters ◽  
Linear Heat ◽  
Operation Conditions ◽  
Sensitivity Studies ◽  
Actual Operation ◽  
Magnitude Sensitivity

Several optimization models of irreversible reverse cycle machines have been developed based on different optimization criteria in the literature, most of them using linear heat transfer laws at the source and sink. This raises the issue how close to actual operation conditions they are, since the heat transfer law on the phase-change processes is dependent on ΔT3. This paper addresses this issue by proposing a general model for study and optimization of thermal machines with two heat reservoirs applied to a Carnot-like refrigerator, with non-linear heat transfer laws and internal and external irreversibility. The optimization was performed using First and Second Law of Thermodynamics and Lagrange multipliers method. Thus, several constraints were imposed to the system, also different objective functions were considered, allowing finding the optimum operating conditions, as well as the limited variation ranges of the system parameters. Results show that the nature of the heat transfer laws affects the optimum values of system parameters for obtaining maximum performances and also their magnitude. Sensitivity studies with respect to system several parameters are presented. The results contribute to the understanding of the system limits in operation under different constraints and allow choosing the most convenient variables in given circumstances.

scholarly journals Optimization and Entropy Production: Application to Carnot-Like Refrigeration Machines

Entropy ◽  
2018 ◽  
Vol 20 (12) ◽  
pp. 953 ◽  
Author(s):  
Camelia Stanciu ◽  
Michel Feidt ◽  
Monica Costea ◽  
Dorin Stanciu
Keyword(s):  
Heat Transfer ◽  
Second Law Of Thermodynamics ◽  
Operating Conditions ◽  
Optimum Operating ◽  
System Parameters ◽  
Linear Heat ◽  
Operation Conditions ◽  
Sensitivity Studies ◽  
Actual Operation ◽  
Magnitude Sensitivity

Several optimization models of irreversible reverse cycle machines have been developed based on different optimization criteria in the literature, most of them using linear heat transfer laws at the source and sink. This raises the issue how close to actual operation conditions they are, since the heat transfer law on the phase-change processes is dependent on ΔT3. This paper addresses this issue by proposing a general model for study and optimization of thermal machines with two heat reservoirs applied to a Carnot-like refrigerator, with non-linear heat transfer laws and internal and external irreversibility. The optimization was performed using First and Second Law of Thermodynamics and the Lagrange multipliers method. Thus, several constraints were imposed to the system, also different objective functions were considered, allowing finding the optimum operating conditions, as well as the limited variation ranges of the system parameters. Results show that the nature of the heat transfer laws affects the optimum values of system parameters for obtaining maximum performances and also their magnitude. Sensitivity studies with respect to system several parameters are presented. The results contribute to the understanding of the system limits in operation under different constraints and allow choosing the most convenient variables in given circumstances.

Second Law Analysis and Synthesis of Solar Collector Systems

1981 ◽  
Vol 103 (1) ◽  
pp. 23-28 ◽  
Author(s):  
A. Bejan ◽  
D. W. Kearney ◽  
F. Kreith
Keyword(s):  
Heat Transfer ◽  
Solar Collector ◽  
Second Law Of Thermodynamics ◽  
Ambient Air ◽  
Operating Conditions ◽  
Optimum Operating ◽  
Second Law ◽  
Second Law Analysis ◽  
Analysis And Synthesis ◽  
Minimum Heat

The second law of thermodynamics is used to analyze the potential for exergy conservation in solar collector systems. It is shown that the amount of useful energy (exergy) delivered by solar collector systems is affected by heat transfer irreversibilities occurring between the sun and the collector, between the collector and the ambient air, and inside the collector. Using as working examples an isothermal collector, a nonisothermal collector, and the design of the collector-user heat exchanger, the optimum operating conditions for minimum heat transfer irreversibility (maximum exergy delivery) are derived.

Portable pilot plant for evaluating marine biofouling growth and control in heat exchangers-condensers

2003 ◽  
Vol 47 (5) ◽  
pp. 99-104 ◽  
Author(s):  
J.F. Casanueva ◽  
J. Sánchez ◽  
J.L. García-Morales ◽  
T. Casanueva-Robles ◽  
J.A. López ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Pilot Plant ◽  
Economic Cost ◽  
Automatic Monitoring ◽  
Operating Conditions ◽  
Optimum Operating ◽  
Indirect Measure ◽  
Transfer Equations ◽  
And Control

Biofouling frequently involves a serious impediment to achieving optimum operating conditions in heat exchangers-condensers. The economic cost and energy losses associated with this phenomenon are significant and the environmental impact of biocides must satisfy stringent regulations. A portable pilot plant has been designed in order to carry out in-situ experimental study as biofilm is formed under thermal and hydrodynamically controlled conditions. The pilot plant has an automatic monitoring, control and data acquisition system, which automatically processes data from indirect measure of fouling in terms of increased fluid frictional and heat transfer resistances. A particular method is used and proposed for direct measuring and biofilm characterization. Once we know the actual film thickness, we can calculate the effective thermal conductivity of the layer by using the appropriate heat transfer equations.

Electro-Mechanical Coupling Performances of a Piezoelectric Bimorph

2007 ◽  
Vol 336-338 ◽  
pp. 327-330
Author(s):  
Shao Ze Yan ◽  
Fu Xing Zhang ◽  
Shi Zhu Wen
Keyword(s):  
Strong Dependence ◽  
Operating Conditions ◽  
Step Response ◽  
Optimum Operating ◽  
Piezoelectric Bimorph ◽  
Force Output ◽  
Mechanical Coupling ◽  
Operation Conditions ◽  
Series Of Experiments ◽  
Set Up

The influence of electro-mechanical operation conditions on the actuation capabilities of the piezoelectric bimorph is investigated in this paper. The objective is to compare the performance of the piezoelectric bimorph in different operation conditions and to determine the optimum operating conditions. An experimental set-up is built, and a series of experiments are presented to investigate the static and dynamic characteristics of the bimorph, including tip displacements of the bimorph under different preloads, dynamic response at different drive frequencies, step response and creep. Some properties such as displacement output, force output and hysteresis of the piezoelectric bimorph under different operating conditions are evaluated. Experimental results indicate strong dependence of both elastic and piezoelectric properties of the bimorph on the operating conditions.

Thermal Management of Single- and Dual-Tank Fuel-Flow Topologies Using an Optimal Control Strategy

2018 ◽  
Vol 10 (4) ◽  
Author(s):  
P. G. Huang ◽  
D. B. Doman
Keyword(s):  
Heat Transfer ◽  
Optimal Control ◽  
Control Strategy ◽  
Linear Quadratic Regulator ◽  
Operating Conditions ◽  
Adjoint Equations ◽  
Linear Quadratic ◽  
Optimal Control Strategy ◽  
Flow Topology ◽  
Operation Conditions

The effect of fuel topology and control on thermal endurance of aircraft using fuel as a heat transfer agent was studied using an optimal dynamic solver (OPT). The dynamic optimal solutions of the differential equations governing the heat transfer of recirculated fuel flows for single- and dual-tank arrangements were obtained. The method can handle sudden jumps of operating conditions across different operating zones during mission and/or situations when control parameters have reached their physical limits. Although this method is robust in providing an optimal control strategy to prolong thermal endurance of aircrafts, it is not ideal for practical application because the method required iterative procedures to solve expensive nonlinear equations. The linear quadratic regulator (LQR), the feedback controller, can be derived by linearizing the adjoint equations at trim points to offer a simple control strategy, which can then be implemented directly in the feedback control hardware. The solutions obtained from both OPT and LQR were compared, and it was found two solutions were almost identical except in regions having sudden jump of operation conditions. Finally, a comparison between single- and dual-tank arrangements was made to demonstrate the importance of the flow topology. The study shows the dual-tank arrangement allows flexibility in how energy is managed and can release energy faster than a single-tank topology and hence provides improved aircraft thermal endurance.

Investigation of the System Parameters Affecting the Runtime of a Freezer Compartment

2012 ◽  
Author(s):  
Husnu Kerpicci ◽  
Onur Poyraz ◽  
Tolga N. Aynur ◽  
Ismail Teke
Keyword(s):  
Experimental Data ◽  
Energy Consumption ◽  
Empirical Model ◽  
Operating Conditions ◽  
Optimum Operating ◽  
Experimental Setup ◽  
Airflow Rate ◽  
System Parameters ◽  
Evaporation Temperature ◽  
Wide Range

In this study, an experimental setup was built to evaluate the energy consumption of a freezer compartment by varying the runtime (i.e. the ratio of the compressor ON time to the total cycle time) of the system with the evaporation temperature and the airflow rate. Evaporation temperature and the normalized airflow rate were varied from −25°C to −28°C and from 0.8 to 1.4, respectively, thus the effects of these parameters on the runtime of the freezer were evaluated in a wide range of operating conditions. In addition, an empirical model that estimates the runtime within ± 4% compared to the experimental data was presented. By using the empirical model, optimum operating conditions (i.e. evaporation temperature and airflow rate) for the freezer were found with an energy saving of %13.8.

Optimum Operating Conditions for Subcritical/Supercritical Fluid-Based Natural Circulation Loops

2016 ◽  
Vol 138 (11) ◽  
Author(s):  
Ajay Kumar Yadav ◽  
Souvik Bhattacharyya ◽  
M. Ram Gopal
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Power Plants ◽  
Natural Circulation ◽  
Operating Conditions ◽  
Optimum Operating ◽  
Reduced Pressure ◽  
Optimum Operating Condition ◽  
Maximum Heat

Natural circulation loop (NCL) is simple and reliable due to the absence of moving components and is preferred in applications where safety is of foremost concern, such as nuclear power plants and high-pressure thermal power plants. In the present study, optimum operating conditions based on the maximum heat transfer rate in NCLs have been obtained for subcritical as well as supercritical fluids. In recent years, there is a growing interest in the use of carbon dioxide (CO2) as loop fluid in NCLs for a variety of heat transfer applications due to its excellent thermophysical environmentally benign properties. In the present study, three-dimensional (3D) computational fluid dynamics (CFD) analysis of a CO2-based NCL with isothermal source and sink has been carried out. Results show that the heat transfer rate is much higher in the case of supercritical phase (if operated near pseudocritical region) than the subcritical phase. In the subcritical option, higher heat transfer rate is obtained in the case of liquid operated near saturation condition. Correlations for optimum operating condition are obtained for a supercritical CO2-based NCL in terms of reduced temperature and reduced pressure so that they can be employed for a wide variety of fluids operating in supercritical region. Correlations are also validated with different loop fluids. These results are expected to help design superior optimal NCLs for critical applications.

Entropy Generation Rate in Forced Convection Flow About Inclined Surfaces in a Porous Medium

2011 ◽  
Author(s):  
Bourhan Tashtoush ◽  
B. S. Yilbas
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Pressure Drop ◽  
Forced Convection ◽  
Entropy Generation ◽  
Operating Conditions ◽  
Generation Rate ◽  
Optimum Operating ◽  
Entropy Generation Rate ◽  
Thermal System

Entropy generation rate has been the attraction of research, since it provides information on the thermodynamic irreversibility associated with the thermal systems. The exergy distraction in the thermal system increases entropy generation rate while lowering the second law efficiency of the thermal system. The heat transferring devices, such as heat exchangers, operates better when temperature difference between the transferring device and the heat sink is maintained high. In addition, the use of porous material in these devices enhances the heat transfer rates due to the achievement of high heat transfer coefficients. However, the presence of the porous material also increases the pump power because of the high pressure drop in the flow system. This increases the operational costs. Consequently, entropy generation rate due to pressure drop needs to be minimized to reduce the cost; however, heat transfer rates from the thermal system needs to be enhanced to improve the thermal performance of the heat transferring device. Therefore, a balance between the entropy generation rates due to pressure drop and heat transfer needs to be attained to achieve optimum operating conditions of such devices. To investigate the optimum operating conditions, the forced convection problem about inclined surfaces (or wedges) in saturated porous medium is considered. The flow in the porous medium is described by the Darcy-Brinkman momentum equation. An exact analytical solution of the governing equations using Kummer function is developed for the velocity, temperature, Nusselt Number, and entropy generation rate for the case where the free stream velocity and wall temperature distribution of the inclined surface vary according to the same power function of distance x, along the plate. It is demonstrated that the entropy generation number is weakly dependent on the Brinkman-Darcy number for forced convection flow, which is particularly true near the wall region.

scholarly journals Methyl-Tert-Butyl-Ether Synthesis Reactor Modelling and Optimization Using an Aspen Custom Modeler

2017 ◽  
Vol 45 (2) ◽  
pp. 1-7
Author(s):  
Zeeshan Nawaz
Keyword(s):  
Heat Transfer ◽  
Homogeneous Model ◽  
Operating Conditions ◽  
Effectiveness Factor ◽  
Packed Bed Reactor ◽  
Methyl Tert Butyl Ether ◽  
Optimum Operating ◽  
Process Data ◽  
Butyl Ether ◽  
Aspen Custom Modeler

Abstract A pseudo-homogeneous model of methyl-tert-butyl-ether (MTBE) synthesis in a multi-tubular packed-bed reactor has been developed using an Aspen Custom Modeler (ACM) for selecting optimum operating strategies, for the maximization and enhancement of MTBE production, and isobutylene consumption, respectively. The model accounts for mass, energy and momentum balances; and the effectiveness factor is evaluated in a onedimensional pseudo-homogeneous model. The kinetic investigation contains kinetic rate expressions as given by the effectiveness factor for accounting the resistance of pellets in terms of mass and heat transfer. An activity coefficient can be used in order to systematically obtain a new steady-state solution. The model used literature-based correlations for the estimation of heat transfer coefficients. The value of the coefficient for gascoolant heat transfer can be adjusted by using a tuning coefficient in order to enrich the process data. Reasonable agreement was found between model predictions and data under similar conditions. The studies concerning model sensitivity compute the optimum temperature, pressure, feed flow rate, methanol/isobutylene ratio, heat removal rate, etc. of the reactor and suggest optimum operating conditions of the reactor.

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