Optimal Allocation of Heat Transfer Area for a Heat Engine

2005 ◽  
Vol 21 (1) ◽  
pp. 1-4 ◽  
Author(s):  
Y. C. Hsieh ◽  
J. S. Chiou
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Optimal Allocation ◽  
Heat Engine ◽  
Thermal Conductance ◽  
Heat Transfer Area ◽  
Internal Irreversibility ◽  
Optimal Area ◽  
Special Case

AbstractFor an endoreversible heat engine operates steadily between two fixed temperatures, Bejan found the engine's best performance can be obtained if the total thermal conductance is evenly divided for hot-end and cold-end heat exchangers. In this study, a heat by-pass model is used to represent the losses due to internal irreversibilities, and the more general formulations are derived for both the optimal area allocation and the maximum thermal efficiency. The results calculated from the present formulations when there is no internal irreversibility(a special case) are consistant with that obtained by Bejan.

Efficiency Optimizations of an Irreversible Brayton Heat Engine

1998 ◽  
Vol 120 (2) ◽  
pp. 143-148 ◽  
Author(s):  
C.-Y. Cheng ◽  
C.-K. Chen
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Heat Engine ◽  
Thermal Conductance ◽  
Working Fluid ◽  
Reservoir Temperature ◽  
Temperature Ratio ◽  
Conductance Ratio ◽  
Internal Irreversibility

A steady-flow approach for finite-time thermodynamics is used to calculate the maximum thermal efficiency, its corresponding power output, adiabatic temperature ratio, and thermal-conductance ratio of heat transfer equipment of a closed Brayton heat engine. The physical model considers three types of irreversibilities: finite thermal conductance between the working fluid and the reservoirs, heat leaks between the reservoirs, and internal irreversibility inside the closed Brayton heat engine. The effects of heat leaks, hot-cold reservoir temperature ratios, turbine and compressor isentropic efficiencies, and total conductances of heat exchangers on the maximum thermal efficiency and its corresponding parameters are studied. The optimum conductance ratio could be found to effectively use the heat transfer equipment, and this ratio is increased as the component efficiencies and total conductances of heat exchangers are increased, and always less than or equal to 0.5.

Design and Test of a Thermoelectric Ground-Source Heat Engine

2007 ◽  
Author(s):  
James W. Stevens
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
High Reliability ◽  
Heat Engine ◽  
Acoustic Emissions ◽  
Extended Period ◽  
Transfer Coefficients ◽  
Night Time ◽  
Ground Source

The daily variation in air temperature is large compared with the temperature changes a short distance below the surface of the ground. In theory, a heat engine can be arranged to produce electricity from this temperature difference. In practice, the thermal efficiency of such a device will be low because of the small temperature differences involved. One example of such an energy harvesting device that can produce a small amount of electrical power uses a thermoelectric generator operating between the air and ground temperatures. The low thermal efficiency means that accurately predicting thermal resistances throughout the device and at the air-side and ground-side heat exchangers is critical to the creation of a useful device. Advantages of this device include high reliability, no acoustic emissions, low visibility, significant night-time power production, ruggedness, and long life. With appropriate external power conditioning components, the device could be used to power remote sensors and communications systems. The design of a pair of milliwatt-scale ground source heat engines is described. The devices were fabricated using custom heat exchangers and off-the-shelf thermoelectric modules and other supplies. Both systems were tested over an extended period in order to quantitatively assess effects of sunlight and precipitation on system performance and life. Exhaustive analysis of air-side average heat transfer coefficients, system thermal resistances, and ground-side thermal resistances provide quantitative design information for future applications. Finned and unfinned versions of the device permit assessment of fin performance on both ground-side and air-side heat transfer.

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.

Transient Temperature Response of Variable Flow Heat Exchangers in a Marnoch Heat Engine

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
P. Saneipoor ◽  
G. F. Naterer ◽  
I. Dincer
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Heat Engine ◽  
Heat Transfer Model ◽  
Transient Temperature ◽  
Transfer Model ◽  
Gas Temperature ◽  
Variable Flow ◽  
Flow Heat ◽  
Shell And Tube

Within a Marnoch heat engine (MHE), a water/glycol mixture transfers heat from the heat source into a set of variable flow heat exchangers and removes heat from adjoining cold heat exchangers. The compressed dry air is used as the working medium in this heat engine. The MHE has four shell and tube heat exchangers, which operate transient and variable flow conditions. A new transient heat transfer model is developed to predict this transient behavior of the heat exchangers for different flow regimes and temperatures. The results from the model are validated against experimental results from an MHE prototype. The heat transfer model shows 85% agreement with measured data from the MHE prototype for the individual heat exchangers. This model can be used for similar shell and tube heat exchangers with straight or U-shaped tubes. The heat transfer model predicts the gas temperature on the shell side, when a step change is imposed on the liquid entering the tubes.

scholarly journals Plate heat exchanger design software for industrial and educational applications

2017 ◽  
Vol 71 (5) ◽  
pp. 439-449
Author(s):  
Nikola Zlatkovic ◽  
Divna Majstorovic ◽  
Mirjana Kijevcanin ◽  
Emila Zivkovic
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Plate Heat Exchanger ◽  
Heat Transfer Area ◽  
Transfer Coefficients ◽  
Plate Heat ◽  
Two Fluids ◽  
Heat Exchanger Design ◽  
Educational Applications

Plate heat exchanger is a type of heat exchanger that uses corrugated metal plates to transfer heat between two fluids. The plate corrugations are designed to achieve turbulence across the entire heat transfer area thus producing the highest possible heat transfer coefficients while allowing close temperature approaches. Subsequently, this leads to a smaller heat transfer area, smaller units and in some cases, fewer heat exchangers. In this work, an application for thermal and hydraulic computations of plate heat exchangers had been developed using Sharp Develop, an open source programming platform. During the development process, several literature methods and correlations for calculation of heat transfer coefficient and pressure drop in a plate heat exchanger have been tested and the selected four methods: Martin, VDI, Kumar and Coulson and Richardson have been incorporated into the software. The structure of the software is visually presented through several windows: a window for inserting input data, windows for showing the results of computation by each of the methods, a window for showing comparative analysis of the most important computation results obtained by all of the used methods and a help window for demonstrating the working principle of plate heat exchanger.

scholarly journals Multi-objective optimization of CuO based organic Rankine cycle operated using R245ca

2019 ◽  
Vol 116 ◽  
pp. 00062 ◽  
Author(s):  
Parth Prajapati ◽  
Vivek Patel
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Waste Heat ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Working Fluid ◽  
Multi Objective Optimization ◽  
Multi Objective ◽  
Source Fluid

The present work deals with multi objective optimization of nanofluid based Organic Rankine Cycle (ORC) to utilise waste heat energy. Working fluid considered for the study is R245ca for its good thermodynamic properties and lower Global Warming Potential (GWP) compared to the conventional fluids used in the waste heat recovery system. Heat Transfer Search (HTS) algorithm is used to optimize the objective functions which tends to maximize thermal efficiency and minimize Levelised Energy Cost (LEC). To enhance heat transfer between the working fluid and source fluid, nanoparticles are added to the source fluid. Application of nanofluids in the heat transfer system helps in maximizing recovery of the waste heat in the heat exchangers. Based on the availability and cost, CuO nanoparticles are considered for the study. Effect of Pinch Point Temperature Difference (PPTD) and concentration of nanoparticles in heat exchangers is studied and discussed. Results showed that nanofluids based ORC gives maximum thermal efficiency of 18.50% at LEC of 2.59 $/kWh. Total reduction of 7.11% in LEC can be achieved using nanofluids.

scholarly journals Modelling of Polymeric Shell and Tube Heat Exchangers for Low-Medium Temperature Geothermal Applications

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2737
Author(s):  
Francesca Ceglia ◽  
Adriano Macaluso ◽  
Elisa Marrasso ◽  
Maurizio Sasso ◽  
Laura Vanoli
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Power Plants ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Working Fluid ◽  
Heat Transfer Area ◽  
Geothermal Fluid ◽  
Shell And Tube

Improvements in using geothermal sources can be attained through the installation of power plants taking advantage of low and medium enthalpy available in poorly exploited geothermal sites. Geothermal fluids at medium and low temperature could be considered to feed binary cycle power plants using organic fluids for electricity “production” or in cogeneration configuration. The improvement in the use of geothermal aquifers at low-medium enthalpy in small deep sites favours the reduction of drilling well costs, and in addition, it allows the exploitation of local resources in the energy districts. The heat exchanger evaporator enables the thermal heat exchange between the working fluid (which is commonly an organic fluid for an Organic Rankine Cycle) and the geothermal fluid (supplied by the aquifer). Thus, it has to be realised taking into account the thermodynamic proprieties and chemical composition of the geothermal field. The geothermal fluid is typically very aggressive, and it leads to the corrosion of steel traditionally used in the heat exchangers. This paper analyses the possibility of using plastic material in the constructions of the evaporator installed in an Organic Rankine Cycle plant in order to overcome the problems of corrosion and the increase of heat exchanger thermal resistance due to the fouling effect. A comparison among heat exchangers made of commonly used materials, such as carbon, steel, and titanium, with alternative polymeric materials has been carried out. This analysis has been built in a mathematical approach using the correlation referred to in the literature about heat transfer in single-phase and two-phase fluids in a tube and/or in the shell side. The outcomes provide the heat transfer area for the shell and tube heat exchanger with a fixed thermal power size. The results have demonstrated that the plastic evaporator shows an increase of 47.0% of the heat transfer area but an economic installation cost saving of 48.0% over the titanium evaporator.

The Variation in Effectiveness of Low-Finned Tubes Within a Shell-and-Tube Heat Exchanger for Supercritical CO2

2012 ◽  
Author(s):  
Patrick M. Fourspring ◽  
Joseph P. Nehrbauer
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Exchanger ◽  
Thermal Conductance ◽  
Heat Transfer Area ◽  
Shell Side ◽  
Additional Heat ◽  
Tube Heat Exchanger ◽  
Finned Tubes ◽  
Shell And Tube

Low-finned tubes can be effective in baffled flow heat exchangers, if the heat transfer coefficients on either side of the heat exchanger differ greatly and therefore limit the thermal conductance of the heat exchanger. Low-finned tubes can increase thermal conductance by providing additional heat transfer area on the limiting side. The height and the spacing of the low-fins must be greater than the thickness of the thermal boundary layer on the low-finned side of the heat exchanger. Otherwise, the effectiveness of the additional area that the low-finned tubes provide will be reduced. The boundary layer thickness is dependent on the velocity and the thermophysical properties of the fluids. Therefore, in a standard shell-and-tube heat exchanger, the number of heat exchanger shell-side baffles needs to be properly considered to provide the correct shellside velocity without introducing too much pressure drop. Testing of a shell-and-tube heat exchanger containing low-finned tubes varied the flow rate and pressure of the supercritical CO2 on the shell side as water provided the cooling on the tube side. The testing maintained the temperature and pressure of the CO2 above the critical point in order to determine the changes in the effectiveness of the low-finned tubes and thus the heat transfer rate of the heat exchanger. The results show that the additional heat transfer area provided by the low-finned tubes will remain fully effective, even as the supercritical fluid nears its critical point or a pseudo-critical temperature. This result also supports (but is not sufficient to prove) the guidance to limit the estimated thickness of the thermal boundary layer to the fin height and twice the fin spacing to ensure the additional heat transfer area provided by the low-finned tubes remain effective.

scholarly journals Shell and Tube Heat Exchanger – the Heat Transfer Area Design Process

2017 ◽  
Vol 67 (2) ◽  
pp. 13-24
Author(s):  
Štefan Gužela ◽  
František Dzianik ◽  
Martin Juriga ◽  
Juraj Kabát
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Nuclear Reactors ◽  
Design Calculation ◽  
Heat Transfer Area ◽  
Fast Reactors ◽  
Tube Heat Exchanger ◽  
Commercial Operation ◽  
Shell And Tube

AbstractNowadays, the operating nuclear reactors are able to utilise only 1 % of mined out uranium. An effective exploitation of uranium, even 60 %, is possible to achieve in so-called fast reactors. These reactors commercial operation is expected after the year 2035. Several design configurations of these reactors exist. Fast reactors rank among the so-called Generation IV reactors. Helium-cooled reactor, as a gas-cooled fast reactor, is one of them. Exchangers used to a heat transfer from a reactor active zone (i.e. heat exchangers) are an important part of fast reactors. This paper deals with the design calculation of U-tube heat exchanger (precisely 1-2 shell and tube heat exchanger with U-tubes): water – helium.

Thermal Design of Heat Exchanger With Fins Inside and Outside Tubes

2006 ◽  
Author(s):  
G. N. Xie ◽  
Q. Y. Chen ◽  
M. Zeng ◽  
Q. W. Wang
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Total Pressure ◽  
Thermal Design ◽  
Operating Pressure ◽  
Heat Transfer Area ◽  
Tube Heat Exchanger ◽  
Total Pressure Drop

Compact heat exchangers such as tube-fin types and plate-fin types are widely used for gas-liquid or gas-gas applications. Some examples are air-coolers, fan coils, regenerators and recuperators in micro-turbines. In this study, thermal design of fin-and-tube (tube-fin) heat exchanger performance with fins being employed outside and inside tubes was presented, with which designed plate-fin heat exchanger was compared. These designs were performed under identical mass flow rate, inlet temperature and operating pressure on each side for recuperator in 100kW microturbine as well as specified allowable fractions of total pressure drop by means of Log-Mean Temperature Difference (LMTD) method. Heat transfer areas, volumes and weights of designed heat exchangers were evaluated. It is shown that, under identical heat duty, fin-and-tube heat exchanger requires 1.8 times larger heat transfer area outside tubes and volume, 0.6 times smaller heat transfer area inside tubes than plate-fin heat exchanger. Under identical total pressure drop, fin-and-tube heat exchanger requires about 5 times larger volume and heat transfer area in gas-side, 1.6 times larger heat transfer area in air-side than plate-fin heat exchanger. Total weight of fin-and-tube heat exchanger is about 2.7 times higher than plate-fin heat exchanger, however, the heat transfer rate of fin-and-tube heat exchanger is about 1.4 times larger than that of plate-fin heat exchanger. It is indicated that, both-sides finned tube heat exchanger may be used in engineering application where the total pressure drop is severe to a small fraction and the operating pressure is high, and may be adopted for recuperator in microturbine.

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