Comparative Exergetic Analysis Research Articles

Exergy Analysis of a Vapour Compression Heat Pump Using Environmentally Friendly Refrigerants

The paper presents the comparative exergetic analysis of heat pumps using refrigerants with different ozone depletion potential and global warming potentials. Globally, the air conditioning of houses is seen as a major energy challenge as the economic development of countries, the majority situated in hot climates, will lead to a growing demand for chilling. Added to this is the increasingly widespread use of heat pumps in areas with a temperate climate to increase energy efficiency. As a result, the environmental impact of refrigerants from ozone depletion potential and global warming potential point of view cannot be overlooked. On the other hand, an environmental benefit of high energy efficiency is the reduction of greenhouse gas emissions from fossil fuel combustion for various purposes. The purpose of this approach is to highlight how the use of different types of refrigerants will impact the exergy efficiency of heat pumps.

Comparative Exergetic Analysis of Two Biodiesel Production Routes

Biofuels, such as biodiesel has obtained more and more relevance in the national scenario, because of the current concerns related to the burning of fossil fuels, besides of laws in force that determine the increase of biodiesel blend in common diesel each year. Thus, in this study a comparative exergetic analysis was carried out between the biodiesel production from soybean oil via basic homogeneous catalysis, case 1, where sodium hydroxide (NaOH) was used as a catalyst, and by means of supercritical alcohol, case 2, in which methanol was led to critical state. For that, two production plants were simulated in Aspen HYSYS® V9 software accepting the same amount of main feedstock, in this case soybean oil. After the simulations, the exergetic efficiency of each process was calculated through to a global control volume (CV), having as result 94.01 and 93.50 % to the Case 1 and 2, respectively. These results confirm the feasibility of biodiesel production and the little exergetic difference was caused principally by the conditions of temperature and pressure that were imposed in the methanol supercritical case.

Exergetic Analysis between a First-Generation Bioethanol Production Plant and a Second-Generation Plant Coupled to Conventional Process

Large consumption of non-renewable fuels in the world has strongly encouraged the search for biofuels, due to inevitable shortage of fossil energy sources and catastrophic problems generated by their use. Under these circumstances the so called second generation biofuel production has been highlighted, where lignocellulosic materials such as sugarcane bagasse are used to produce bioethanol, unlike the traditional first-generation process, whose feedstock is sugarcane. Therefore, this work aimed to perform a comparative exergetic analysis between first and second-generation bioethanol production processes, in order to evaluate from the exergetic point of view, which of these processes is the most feasible. It was found an overall exergetic efficiency of 60.89 % for the exclusively first-generation plant, whereas for the integrated plant, it was obtained 41.58 %. In this way, insertion of new stages in production process, required by the second generation, has caused consequently an increase of irreversibilities and losses.

Comparative Exergetic Analysis of Solar Integration and Regeneration in Steam Power Plants

AbstractNowadays, many health, environmental, and economic concerns are associated with fossil fuel use, and therefore the improvement of new and advanced technologies and the use of renewable fuel...

The substitution of R134a with R744: An exergetic analysis based on experimental data

This paper deals with the problem of R314a substitution with a natural refrigerant fluid. A comparison is performed between R134a and R744 (CO2). R134a is a hydrofluorocarbon with a large direct warming impact (GWP), whereas the R744 contribution is negligible. A comparative exergetic analysis, carried out with experimental tests, has been presented. This paper compares a commercial R134a refrigeration plant and a prototype R744 system working in a trans-critical cycle. Based on the experimental data an exergetic analysis has been carried out on the overall plant and on each device. The overall exergetic performances of the classical vapour compression plant working with R134a are consistently better than that of R744 (from a minimum of 20 to a maximum of 44%). The performance of the individual components of the plant has been analyzed, in order to pinpoint those contributing most to the decrease in the exergetic performance of R744.

Exergy analysis of a hydrogen fired combined cycle with natural gas reforming and membrane assisted shift reactors for CO2 capture

Hydrogen production from fossil fuels together with carbon capture has been suggested as a means of providing a carbon free power. The paper presents a comparative exergetic analysis performed on the hydrogen production from natural gas with several combinations of reactor systems: (a) oxy or air fired autothermal reforming with subsequent water gas shift reactor and (b) membrane reactor assisted with shift catalysts. The influence of reactor temperature and pressure as well as operating parameter steam-to-carbon ratio, is also studied exergetically. The results indicate optimal power plant configurations with CO2 capture, or hydrogen delivery for industrial applications.

An exergetic analysis of R22 substitution

This paper deals with the substitution of R22 in an experimental vapour compression plant with the most widely used drop-in substitute, i.e. the zeotropic mixture R407C. A comparative exergetic analysis, carried on with experimental tests, has been presented. The experimental tests are performed in a vapour compression plant working with water and air as secondary fluids in the condenser and in the evaporator, respectively. The overall exergetic performance of the plant working with R22 is consistently better than that of its candidate substitute. The performance of the individual components of the plant has been analysed, in order to pinpoint those contributing most to the decrease in the exergetic performance of R407C.