Effects of Heat Transfer and Friction on the Performance of a Miller Cycle Diesel Engine with Considerations of Variable Specific Heats of the Working Fluid

2013 ◽  
Vol 311 ◽  
pp. 211-216
Author(s):  
Jiann Chang Lin ◽  
Shuhn Shyurng Hou
Keyword(s):  
Heat Transfer ◽  
Diesel Engine ◽  
Power Output ◽  
Thermal Efficiency ◽  
Friction Loss ◽  
Working Fluid ◽  
Miller Cycle ◽  
Temperature Dependent ◽  
Specific Heats ◽  
Negative Effect

The objective of this study is to analyze the effects of friction and heat transfer with considerations of variable specific heats of working fluid on the performance of a Miller cycle Diesel engine. The variations in power output and thermal efficiency with compression ratio, and the relations between the power output and the thermal efficiency of the Miller cycle Diesel engine are presented. The results show that the power output as well as the efficiency where maximum power output occurs will decrease with the increase of heat loss. The temperature-dependent specific heats of working fluid have a significant influence on the performance. The power output and the working range of the Miller cycle Diesel engine increase with the increase of specific heats of working fluid, while, the efficiency decreases with the increase of specific heats of working fluid. The influence of the parameter b related to the friction loss has a negative effect on the performance. Therefore, the power output and efficiency of the cycle decrease with increasing b. Note that the effects of heat transfer with considerations of variable specific heats of working fluid and friction loss on the performance are significant and should be considered in practice cycle analysis.

scholarly journals Numerical study of flow patterns and heat transfer in mini twisted oval tubes

2015 ◽  
Vol 26 (12) ◽  
pp. 1550140 ◽  
Author(s):  
Amin Ebrahimi ◽  
Ehsan Roohi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Critical Role ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Working Fluid ◽  
Transfer Performance ◽  
Temperature Dependent ◽  
Overall Performance

Flow patterns and heat transfer inside mini twisted oval tubes (TOTs) heated by constant-temperature walls are numerically investigated. Different configurations of tubes are simulated using water as the working fluid with temperature-dependent thermo-physical properties at Reynolds numbers ranging between 500 and 1100. After validating the numerical method with the published correlations and available experimental results, the performance of TOTs is compared to a smooth circular tube. The overall performance of TOTs is evaluated by investigating the thermal-hydraulic performance and the results are analyzed in terms of the field synergy principle and entropy generation. Enhanced heat transfer performance for TOTs is observed at the expense of a higher pressure drop. Additionally, the secondary flow generated by the tube-wall twist is concluded to play a critical role in the augmentation of convective heat transfer, and consequently, better heat transfer performance. It is also observed that the improvement of synergy between velocity and temperature gradient and lower irreversibility cause heat transfer enhancement for TOTs.

Thermodynamic Analysis of a Novel Ammonia-Water Cogeneration System for Maritime Diesel Engines

2020 ◽  
Author(s):  
Ziyang Cheng ◽  
Yaxiong Wang ◽  
Qingxuan Sun ◽  
Jiangfeng Wang ◽  
Pan Zhao ◽  
...  
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
System Performance ◽  
Mass Fraction ◽  
Ammonia Concentration ◽  
Working Fluid ◽  
Fluid Temperature ◽  
Kalina Cycle ◽  
Ammonia Water ◽  
Cogeneration System

Abstract This paper proposes a novel cogeneration system based on Kalina cycle and absorption refrigeration system to meet the design requirements of China State Shipbuilding Corporation, which is efficiently satisfy the power and cooling demands of a maritime ship at the same time. Unlike most of the combined systems, this cogeneration system is highly coupled and realizes cogeneration without increasing the system complexity too much. The basic ammonia mass fraction of this novel system is increased, so that the ammonia concentration of ammonia-water steam from the separator can be higher, which contributes to lower refrigerating temperature and thus less heat loss in the distillation process. In addition, higher ammonia concentration solution makes overheating easier, which improves the thermal efficiency. Moreover, the system has two recuperators to make further improvement of the thermal efficiency. Thermodynamic models are developed to investigate the system performance and parametric analysis is conducted to figure out the effects of including working fluid temperature at the outlet of the evaporator, working fluid temperature at superheater outlet, mass fraction of ammonia in basic solution, turbine inlet pressure, temperature of cooling water at the inlet of condensers and the refrigeration evaporation temperature on the system performance. Furthermore, the cogeneration system is optimized with genetic algorithm to obtain the best performance, which achieves 333.00kW of net power output, 28.83 kW of cooling capacity and 21.81% of thermal efficiency. Finally, the performance of the proposed system is compared with an optimized recuperative organic Rankine cycle (ORC) system and an optimized Kalina cycle system 34 (KCS34) using the same heat source. The results show that the thermal efficiency and power output of the novel cogeneration system is 3.89% and 1.05% higher than that of the recuperative ORC system and KCS34 system respectively.

scholarly journals Effect of Porous Medium and Copper Heat Sink on Cooling of Heat-Generating Element

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2538 ◽  
Author(s):  
Marina Astanina ◽  
Mikhail Sheremet ◽  
U. S. Mahabaleshwar ◽  
Jitender Singh
Keyword(s):  
Energy Transport ◽  
Cooling System ◽  
Variable Viscosity ◽  
Optimal Number ◽  
Working Fluid ◽  
Heat Conducting ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Negative Effect ◽  
Dependent Viscosity

Cooling of heat-generating elements is a challenging problem in engineering. In this article, the transient free convection of a temperature-dependent viscosity liquid inside the porous cavity with copper radiator and the heat-generating element is studied using mathematical modeling techniques. The vertical and top walls of the chamber are kept at low constant temperature, while the bottom wall is kept adiabatic. The working fluid is a heat-conducting liquid with temperature-dependent viscosity. A mathematical model is developed based on dimensionless stream function, vorticity, and temperature variables. The governing properties are the variable viscosity, geometric parameters of the radiator, and size of thermally insulated strip on vertical surfaces of the cavity. The effect of these parameters on the energy transport and circulation patterns are analyzed numerically. Based on the numerical results obtained, recommendations are given on the optimal values of the governing parameters for the effective operation of the cooling system. It is shown that the optimal number of radiator fins for the cooling system configuration under consideration is 3. In addition, the thermal insulation of the vertical walls and the increased thickness of the radiator fins have a negative effect on the operation of the cooling system.

scholarly journals Thermal performance analysis of organic flash cycle using R600A/R601A mixtures with internal heat exchanger

2020 ◽  
pp. 296-296
Author(s):  
Guidong Huang ◽  
Songyuan Zhang ◽  
Zhong Ge ◽  
Zhiyong Xie ◽  
Zhipeng Yuan ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Power Output ◽  
Thermal Efficiency ◽  
Electricity Generation ◽  
Internal Heat ◽  
Working Fluid ◽  
Cycle System ◽  
Internal Heat Exchanger ◽  
Generation Costs ◽  
Net Power Output

In this study, the thermal performance of an internal heat exchanger-organic flash cycle system driven by geothermal water was investigated.R600a/R601a mixtures were selected as the working fluid. The effects of the mole fraction of mixtures on the heat absorption capacity of the heater, the temperature rise of cold working fluid in the internal heat exchanger, net power output, thermal efficiency, and electricity generation costs were analyzed. The net power outputs, electricity generation costs, and thermal efficiency of the internal heat exchanger-organic flash cycle and simple organic flash cycle systems were compared. Results showed that the system using theR600a/R601a mixtures (0.7/0.3mole fraction) has the largest net power output, which increased the net power output by 3.68% and 42.23% over the R601a and R600a systems, respectively. WhentheR600a mole fraction was 0.4, the electricity generation costs reduction of the internal heat exchanger-organic flash cycle system was the largest (1.77% compared with the simple organic flash cycle system).The internal heat exchanger can increase the thermal efficiency of organic flash cycle, but the net power output does not necessarily increase.

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 Assessing the optimum combustion under constrained conditions

2018 ◽  
Vol 21 (5) ◽  
pp. 811-823 ◽  
Author(s):  
Pablo Olmeda ◽  
Jaime Martín ◽  
Ricardo Novella ◽  
Diego Blanco-Cavero
Keyword(s):  
Heat Transfer ◽  
Diesel Engine ◽  
Heat Release ◽  
Engine Speed ◽  
Direct Injection ◽  
Pressure Rise ◽  
Maximum Pressure ◽  
Low Load ◽  
Negative Effect ◽  
Constrained Conditions

This work studies the optimum heat release law of a direct injection diesel engine under constrained conditions. For this purpose, a zero-dimensional predictive model of a diesel engine is coupled to an optimization tool used to shape the heat release law in order to optimize some outputs (maximize gross indicated efficiency and minimize NO x emissions) while keeping several restrictions (mechanical limits such as maximum peak pressure and maximum pressure rise rate). In a first step, this methodology is applied under different heat transfer scenarios without restrictions to evaluate the possible gain obtained through the thermal isolation of the combustion chamber. Results derived from this study show that heat transfer has a negative effect on gross indicated efficiency ranging from −4% of the fuel energy ( ṁfHv), at high engine speed and load, up to −8% ṁfHv, at low engine speed and load. In a second step, different mechanical limits are applied resulting in a gross indicated efficiency worsening from −1.4% ṁfHv up to −2.8% ṁfHv compared to the previous step when nominal constraints are applied. In these conditions, a temperature swing coating that covers the piston top and cylinder head is considered obtaining a maximum gross indicated efficiency improvement of +0.5% ṁfHv at low load and engine speed. Finally, NO x emissions are also included in the optimization obtaining the expected tradeoff between gross indicated efficiency and NO x. Under this optimization, cutting down the experimental emissions by 50% supposes a gross indicated efficiency penalty up to −8% ṁfHv when compared to the optimum combustion under nominal limits, while maintaining the experimental gross indicated efficiency allows to reduce the experimental emissions 30% at high load and 65% at low load and engine speed.

scholarly journals Comparison of single and double stage regenerative organic rankine cycle for medium grade heat source through energy and exergy estimation

2019 ◽  
Vol 8 (2) ◽  
pp. 141 ◽  
Author(s):  
Ghalya Pikra ◽  
Nur Rohmah
Keyword(s):  
Heat Source ◽  
Flow Rate ◽  
Power Output ◽  
Thermal Efficiency ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Exergy Efficiency ◽  
Working Fluid ◽  
Energy And Exergy ◽  
Net Power Output

Regenerative organic Rankine cycle (RORC) can be used to improve organic Rankine cycle (ORC) performance. This paper presents a comparison of a single (SSRORC) and double stage regenerative organic Rankine cycle (DSRORC) using a medium grade heat source. Performance for each system is estimated using the law of thermodynamics I and II through energy and exergy balance. Solar thermal is used as the heat source using therminol 55 as a working fluid, and R141b is used as the organic working fluid. The initial data for the analysis are heat source with 200°C of temperature, and 100 L/min of volume flow rate. Analysis begins by calculating energy input to determine organic working fluid mass flow rate, and continued by calculating energy loss, turbine power and pump power consumption to determine net power output and thermal efficiency. Exergy analysis begins by calculating exergy input to determine exergy efficiency. Exergy loss, exergy destruction at the turbine, pump and feed heater is calculated to complete the calculation. Energy estimation result shows that DSRORC determines better net power output and thermal efficiency for 7.9% than SSRORC, as well as exergy estimation, DSRORC determines higher exergy efficiency for 7.69%. ©2019. CBIORE-IJRED. All rights reserved

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