In this paper, hydrogen management in refineries is examined considering a new perspective to optimize refinery costs. In order to minimize the total annual cost in refineries a mixed-integer non-linear programming (MINLP) model has been developed. Retrofitting the hydrogen network and determining the hydrogen surplus capacity of refineries are the main outputs of the proposed model. Then, to utilize this surplus capacity and increase the profitability of refineries, surplus hydrogen is used to produce electricity and ammonia. The results of a case study showed that retrofitting of the hydrogen network can save 12% in the consumption of fresh hydrogen from hydrogen plants. After retrofitting of the existing hydrogen network, three scenarios for efficient use of hydrogen surplus are defined as electricity production by SOFC fuel cells, electricity production by hydrogen turbines, and ammonia production. The comparison of proposed scenarios showed that the ammonia production scenario has better economic results with a payback period of 3.52 years and 16.81 MUSD/yr. total saving. Furthermore, the sensitivity analysis of electricity prices in two electricity production scenarios was performed, and the results showed that by considering the exporting electricity price, electricity production scenarios are profitable due to having payback periods of about five years.

In this study, a mathematical model associated with genetic algorithms (GM) is developed to optimize the design of process fired heaters where the objective function is the total annual cost. The mathematical model considering operational and geometric constraints is used to design all subsections of a furnace including the radiant chamber, the convection and stack sections. The proposed model allows the economic optimization using the MATLAB genetic algorithm toolbox. This procedure is implemented to design and optimize fired heaters. Two case studies are considered. First, by comparing the results with literature, it is shown that the developed model can be successfully used in design with acceptable accuracy. In the first case study, based on TAC (total annual cost) minimization, two optimization scenarios with two sets of decision variables using GA are applied to determine the optimal economic design. It is demonstrated that by considering the tube diameter as a decision variable (scenario B), the TAC minimization approach does not present a realistic optimal design, because the crude oil pressure drop is out of a permissible range. Finally, by including the pumping cost into the operating cost and modifying the objective function, another optimization approach based on MTAC minimization is applied for the same optimization scenarios. In this case, scenario B results in the economic/realistic optimal design by up to 2.48% cheaper than Original Design.

This paper focuses on a simple method towards optimal sizing of radiant enclosures through thermal resistance analysis and the concept of constructal theory. In this method, a new approach based on constructal theory is presented to optimize the aspect ratio of rectangular radiant enclosures by the aim of maximizing the heat flux on the product surface. Based on constructal theory, the global radiation resistance between all surfaces is minimized by adjusting the aspect ratio of the shape while the volume of the enclosure is fixed. The problem is solved by using a Genetic Algorithm (GA) for delivering the optimal aspect ratio. The performance of the present method is evaluated by solving the problem numerically for a soaking zone in a reheating furnace which is separated from the adjacent zone by a zone divider. It is shown that the maximum of heat flux will occur when the heat transfer area of the zone approaches the square area. Moreover, the optimum size of the soaking zone for various scenarios in terms of retrofit is investigated.

In this study, the relationship among the concepts of entropy generation rate, entransy theory, and generalized thermal resistance to the optimal design of thermal systems is discussed. The equations of entropy and entransy rates are compared and their implications for optimization of conductive heat transfer are analyzed. The theoretical analyses show that based on entropy generation minimization principle by decreasing irreversibility, thermodynamic optimization can be obtained. Significantly, the entransy concept merely describes the heat transfer ability and the minimum and maximum entransy dissipation principle can only lead to thermal optimization. However, due to decreasing thermal resistance both principles are considered as optimization tools for the optimal design of energy and thermal systems. Also, it is shown that the concept of entransy theory is more suitable than the concept of entropy generation for optimizing the performance of heat transfer processes.

In this paper, the potential of combined injection of CNG and gasoline is studied on a 1.7 L turbocharged, port-injected SI engine and the best engine performance point for the best conversion efficiency of the catalytic converters has been investigated. Compressed natural gas (CNG) as an alternative fuel is used in spark ignition engines to improve fuel consumption and exhaust emissions. The improvements gave more advantage in emission but it lowered the performance of the engine. As a substitute, CNG has a higher octane number and knocking resistance than gasoline and hence CNG-dedicated engines can have higher compression ratios and therefore higher indicated efficiencies. Turbocharged bi-fuel, combined CNG and gasoline, injection engine of is a new concept which offers direct benefits with regards to gas or gasoline powered vehicles running separately on each fuels. It also opens very interesting perspectives for meeting future emission regulations using only a three-way catalyst, since the stoichiometry condition of combustion is maintained over the whole engine operating range. Results show that the combined injection of gasoline and CNG is much better than gasoline mode in terms of fuel consumption and raw HC and CO emissions. However, as expected the NO x emission will increase. According to the obtained results at 16.2 bar BMEP, 3000 rpm full load condition with 30% CNG mass fraction, the BSFC, CO and HC emissions are improved by 16, 66 and 50%, respectively, compared to gasoline single mode. It was found that a fuel mixture of 30% CNG mass fraction was the best trade-off point between engine performance and emission production. Also, significant reductions of fuel consumption were observed. Full-load tests carried out with a turbocharged engine enhanced the synergy effect between the two fuels at full-load condition.

In this study, the optimal sizing and performance analysis of a standalone integrated solar power system equipped with different storage scenarios to supply the power demand of a household is presented. One of the main purposes when applying solar energy resource is to face the increasing environmental pollutions resulting from fossil fuel based electricity sector. To this end, and to compare and examine two energy storage technologies (battery and hydrogen storage technology), three storage scenarios including battery only, hydrogen storage technology only and hybrid storage options are evaluated. An optimization framework based on Energy Hub concept is used to determine the optimum sizes of equipment for the lowest net present cost (NPC) while maintaining the system reliability. It was determined that the most cost effective and reliable case is the system with hybrid storage technology. Also, the effects of solar radiation intensity, the abatement potential of CO2 emissions and converting excess power to hydrogen on the system's performance and economics, were investigated and a few noticeable findings were obtained.

The techno-economic and environmental performance of hybrid solar hydrogen energy systems was investigated to provide combined cooling, heating and power (CCHP) demands of a standalone greenhouse in Iran to achieve sustainable agriculture based on an optimization procedure. From the environmental point of view, by deploying hybrid energy systems, 83%, to 100% of emissions can be avoided. Also a sensitivity analysis was performed on the hybrid energy systems in order to study the effect of major parameter variation on the systems justification. It was concluded that hybrid solar systems are economically competitive with conventional systems, for high solar intensity locations with high diesel fuel prices and decreased prices for PV and hydrogen storage technology.

In this study, a focus on geometry & elements is taking place with open expansion tanks (OETs) to reduce the energy loss in the system. A new model based on the inlet and outlet flow control in the tank is developed by a semi-spiral coil. A fully numerical comparison of the proposed new OET and the conventional system is done in assistance with Computational Fluid Dynamic (CFD) modeling that has been utilized by QuickerSim CFD toolbox. In order to approve the data, an experimental set up was installed in the laboratory, which includes: three types of OETs (conventional, optimized twin container, and optimized by the coil). Finally, the economic analysis of the new design tank has been performed. The Net Present Value (NPV) in all the three scenarios (international, without subsidy and with subsidy) for optimized models is more than zero and Internal Rate of Return (IRR) is concluded 38%, 113.3% & 303%, respectively. Furthermore, the value of the Simple Payback (SPB) is half a year accordingly in the international energy price calculation based scenario. The results demonstrate the proposed OET that uses a coil, avoids the energy losses as much as possible. As an overall achievement, the energy losses in the OET with the coil are reduced in the range of 80% to 95%. Additionally, replacement of the conventional models by the new proposed design results in the annual energy saving of 857.1 cubic meters of natural gas per household.

Open expansion tanks are applied vastly in central heating and air-conditioning systems. Central heating systems are subjected to great deals of energy losses, owing to the lack of proper design. In this paper, the structure of Open Expansion Tanks is revised and some modifications for reducing energy and heat loss are made to their elements. Moreover, some common designs available in the market are studied in order to better recognize their defects and capabilities. To reach an efficient design, several scenarios are tested using Computational methods (CFD based). In order to validate the new design, an experimental model was created and heat and energy survey operations were performed. The results of energy auditing were analyzed to show the convergence of numerical and experimental models. Additionally, the proposed model was economically evaluated. The final presented model named “Optimized OET with twin containers” is capable of reducing the energy loss by 85 to 95 percent.

This paper presents thermodynamic investigation and environmental consideration of combined Stirling-organic Rankine cycle (ORC) power cycle. Combined cycle can be assisted by solar energy and an ORC used as an annular cold-side heat rejector for a free piston Stirling cycle. ORC can increase the power output efficiency by 4% to 8% compared to that of a Stirling standard cycle. Operating temperatures of ORC are between 80°C and 140°C. The main objective of this work is to model the combined cycle for performance optimization in respect to the use of several different working fluids with relevant temperature ranges. Total power efficiency in the range of 34% to 42% was observed for different cases. Several working fluids in the ORC were investigated from a thermal, operational, and environmental point of view. Working fluids considered were FC72, FC87, HFE7100, HFE7000, Novec649, n -pentane, n -decane, R245fa, and toluene. Practical issues like thermodynamic cycle efficiency, latent heat, density, toxicity, flammability, ozone depletion potential, global warming potential, and atmospheric lifetime are considered. Considering the cycle efficiency, n -decane shows the best performance at both levels of temperature supposed. However, this fluid has the highest saturated vapor specific volume (resulting in a larger condenser) and the lowest condenser saturation pressure (higher infiltration of non-condensable gases). The best candidates for the cycle regarding all the considered aspects were found to be toluene, HFE7100, and n -pentane. Comparing these three fluids, toluene presents the highest efficiency, the highest impact on the environment, the biggest vapor specific volume, and the minimum mass flow rate in Rankine cycle, therefore decreasing the pump power consumption. N -pentane exhibits the lowest cycle efficiency and vapor specific volume, but this fluid has super-atmospheric saturation pressure advantage. HFE7100 is a good working fluid from environmental and safety point of view.

All rights reserved by www.ijsrd.com 902 Abstract— An internal combustion (IC) engine has a predominant role in a low power generation and a virtual monopoly in mobile applications today. One of the best methods to improve the engine performance and reduce the exhaust emission in a SI engine is by using introduction of twin spark into the combustion chamber. The main purpose of this study is to investigate the effects of twin spark using CNG fuel in SI engine. The performance and emission analysis of an engine are investigated by experiment with CNG kit and gas analyzer. From this study the fuel consumption is reduce in twin spark arrangement for the same power output as compare to single spark using both of the fuel gasoline as well as CNG. Engine emission is considerably reduced using twin spark plug.

There are concerns both about the excess usage of limited fossil fuels reservoirs, and the environmental emissions production of fossil fuels such as CO, CO2, NO X , UHC and particles which may have long term effects on sustainable development and providing welfare and convenience for future generations.Internal combustion engines have caused the largest contribution to these problems.The most common internal combustion engines are gasoline engines which cannot be replaced completely from vehicle fleets due to technical benefits.In this study, a spark ignition engine cycle simulation based on the first law of thermodynamics has been developed.The model effectively described the thermodynamic processes and chemical state of the working fluid by considering a closed cycle containing compression, combustion, ignition delay and expansion processes.The two-zone model was used for simulation of the combustion process and the species including CO2, CO, H2O, H2, N2, O2 , NO and UHC were considered as exhaust gases.The model predicted the trends and tradeoffs of the engine performance characteristics including indicated power, IMEP, ISFC and emissions.Finally, the model has been used to carry out a parametric study of the engine to evaluate the effects of a number of engine parameters.This analysis showed the capability of the model to predict engine performance characteristics over the various ranges of engine parameters.

In this study, a thermodynamic cycle simulation of a conventional four-stroke SI engine has been carried out to predict the engine performance and emissions. The first law of thermodynamics has been applied to determine in-cylinder temperature and pressure as a function of crank angle. The Newton-Raphson method was used for the numerical solution of the equations. The non-differential form of equations resulted in the simplicity and ease of the solution to predict the engine performance. Two-zone model for the combustion process simulation has been used and the mass burning rate was predicted by simulating spherical propagation of the flame front. Also, temperature dependence of specific heat capacity has been considered. The performance characteristics including power, indicated specific fuel consumption, and emissions concentration of SI engine using gasoline and CNG fuels have been determined by the model. The results of the present work have been evaluated using corresponding available experimental data of an existing SI engine running on both gasoline and CNG. It has been found that the simulated results show reasonable agreement with the experimental data. Finally, parametric studies have been carried out to evaluate the effects of equivalence ratio, compression ratio and spark timing on the engine performance characteristics in order to show the capability of the model to predict of engine operation.

Using CNG as an additive for gasoline is a proper choice due to higher octane number of CNG enriched gasoline with respect to that of gasoline. As a result, it is possible to use gasoline with lower octane number in the engine. This would also mean the increase of compression ratio in SI engines resulting in higher performance and lower gasoline consumption. Over the years, the use of simulation codes to model the thermodynamic cycle of an internal combustion engine have developed tools for more efficient engine designs and fuel combustion. In this study, a thermodynamic cycle simulation of a conventional four-stroke spark-ignition engine has been developed. The model is used to study the engine performance parameters and emission characteristics of CNG/gasoline blend fuelled engine. A spark ignition engine cycle simulation based on the first law of thermodynamic has been developed by stepwise calculations for compression process, ignition delay time, combustion and expansion processes. The building blocks of the model are mass and energy conservation equations. Newton-Raphson method has been used to solve the equations numerically and there was no need to solve them analytically. In the quasi-dimensional combustion model, the cylinder is divided into two zones separated by a thin flame front. The flame front propagates spherically throughout the combustion chamber to the point that it contacts the cylinder wall and head. The model effectively describes the thermodynamic processes and chemical state of the working fluid via a closed system containing compression, combustion, and expansion processes. The model predicts the trends and tradeoffs the performance characteristics at various engine speeds. The variation of indicated power, ISFC and emissions are predicted by the model. Experimental data are also presented to indicate the validity of the model. The predicted results based on the model have shown reasonable agreement with the corresponding experimental data.

In this article, helically serrated finned tubes, which are generally used in heat recovery steam generator (HRSG) boilers in combined cycle power plants, are experimentally studied, in order to find their thermal contact resistance (TCR) values in different conditions. Temperature, air velocity and fin-to-tube bonding extent were the variables and a precise methodology was performed to extract the TCR values from the obtained data. The results showed that TCR decreases by increasing the air velocity and the bonding extent, but temperature has a negligible effect on it. Moreover, the TCR values showed a good consistency in order of magnitude when compared to similar systems studied before.

Drying fruit, heating residential buildings and providing a hot water supply in villages all consume energy. Using fossil fuel for these purposes creates pollution and costs too much. In contrast, the use of solar energy in these applications leads to a noticeable decrease both in pollution and investment costs. In this study, a new solar system was designed and tested in order to reduce energy usage in rural residential buildings and the food drying industry. As the peaks of energy consumption in the proposed system are not simultaneous, this new system is very effective in reducing energy consumption, controlling energy peaks and reducing environmental pollution. This system has the ability to provide the required energy in both summer and winter modes. In the summer mode, the energy supply is used for providing hot water and drying agricultural products, while in winter mode it is used for rural residences heating and hot water supply. Drying time has been varied between 51.23 and 42.45 h according to type of application, and average temperature difference between room and ambient is almost nearly 10 degrees C with different air heaters. The system includes energy supply and storage equipment, solar dryers, water collectors and rectangular, triangular, trapezoidal and double-pass with longitudinal fins air heaters. The system was tested in Iran for drying apricots, heating rural residential buildings and supplying hot water for domestic use, meanwhile, the energetic and exergetic efficiency of the system was calculated 37.3-61.3 and 3.2-9.7 respectively for different types of installations. (C) 2011 Elsevier B.V. All rights reserved.

ABSTRACTIn this work, a method for increasing the storage capability of a solar thermal energy system has been discussed. The system includes two tanks with the flexibility in choosing the best storage medium on the basis of the solar collector's outlet temperature. The results show that using such a hybrid storage system, the storable energy can be increased. Comparing the results with those for simple common storage systems, the extent of improvement was calculated.For verification of the results, a small pilot system was assembled. The test apparatus operated during 2008-2009 cold months and the parameters were recorded. Comparison of the theoretical and experimental results showed a good agreement.

In this article, a comparative study is carried out between two equations for the exergy efficiency of photovoltaic thermal (PV/T) air collectors; the first equation is based on net output exergy and the second equation is in terms of exergy losses. The exergy efficiency equation parametrically is dependent on thermal and electrical parameters of PV/T air collector; therefore, improved thermal and electrical models are used to calculate them. Developing an exergy balance for PV/T air collector system, the various exergy components in PV/T system are introduced and two equations for the exergy efficiency of PV/T air collector are derived. A computer simulation program is also developed which is based on the used improved thermal and electrical models. In order to validate the simulation results, a typical PV/T air collector has been built and some experiments have been carried out on it. The results of numerical simulation are in good agreement with the experimental results. Finally, parametric studies have been carried out and the effect of design and climatic parameters on two exergy efficiency equations has been investigated. It is observed that the improved exergy efficiency obtained in this paper is in good agreement with the one given by the previous literature and it is better because it shows the portion of each of exergy losses in the exergy efficiency equation, directly.

With the declining energy resources and increase of pollutant emissions, a great deal of efforts has been focused on the development of alternatives for fossil fuels. One of the promising alternative fuels to gasoline in the internal combustion engine is natural gas [1-5]. The application of natural gas in current internal combustion engines is realistic due to its many benefits. The higher thermal efficiency due to the higher octane value and lower exhaust emissions including CO2 as a result of the lower carbon to hydrogen ratio of the fuel are the two important feature of using CNG as an alternative fuel. It is well known that computer simulation codes are valuable economically as a cost effective tool for design and analysis of the engine operations. In the present work the use of an exiting spark ignition engine to run on both gasoline and CNG is evaluated by thermodynamic simulation of the engine cycle. The stepwise calculations for pressure and temperature of the cylinder at compression process, ignition delay time, combustion and expansion processes have been considered. The first law of thermodynamics is applied for all steps and Newton-Raphson method is used for the numerical solution. Temperature dependent specific heat capacity and as a result specific enthalpy, entropy, internal energy and specific Gibbs functions are calculated in each step. Two zones model for the combustion process simulation has been used and the mass burning rate is predicted by considering the propagation of the flame front spherically. The performance characteristics including power, IMEP, ISFC, thermal efficiency and emissions concentration of SI engine on both gasoline and CNG fuel are determined by the model. In order to validate the model, the results are compared with the corresponding experimental data. It is found that the simulated results show reasonable agreement with the experimental data.