Heat exchangers are thermal devices used in several industrial applications. Parallel flow arrangement means that both fluids flow stream is in the same direction. Low thermal conductivity of traditional fluids affects in a negative manner the efficiency of heat exchangers. In order to overcome this drawback, literature recommends the use of nanofluids. This paper deals with a theoretical study of performance enhancement of a double pipe heat exchange with parallel flow arrangement. The analysis consists in a comparison between the situations in which the water and the water base nanofluid (Al2O3-water) are the cooling fluids. The cold fluid is a nanofluid (NF)- represented by Al2O3 nanoparticles added to water. The diameter of nanoparticles is 25 nm and the considered volume concentration is of 0.25%. The hot fluid is water. The nanofluid flows in the outer pipe, while the water flows in the inner pipe; fluids flow with constant inlet temperature: 32°C – for the nanofluid and 58°C – for the water. The volumetric flow rate varies in the range: 0.5÷1.9 L/min. The obtained results show that the average values of the following: heat transfer rate, effectiveness, inner and outer heat transfer coefficients, all for the nanofluid, are about 16%, 10%, 16% and respectively 17% higher in comparison to the base fluid. The analysis will reveal the fact that a better performance of the heat exchanger it is achieved when using Al2O3-water nanofluid as a cooling medium than when using the base fluid (water), due to the higher thermal conductivity of the nanofluid.
Vapour compression refrigeration systems (VCRS) are present in various applications of refrigeration; they work with high power consumption and rise environmental concerns. Important features of VCRS working with R134a are reflected in significant energy consumption and environmental issues. This is why the analysis of performances terms, such as power consumption and Coefficient of Performance (COP), is mandatory. The adoption of nanorefrigerants is a promising step towards new working fluids to be used in refrigeration systems. The environmental issue specific to the traditional R134a can be diminished by replacing it with nanorefrigerants- resulted by adding of nanoparticles to the pure refrigerant (R134a). Traditionally used R134a contributes to the global warming. This problem is associated with the need to improve the efficiency of the plant. The solution is the adoption of a new refrigerant: the nanorefrigerant. This paper focuses on the performance improvement of VCRS working with R134a and R134a/Al2O3. The theoretical comparison is developed considering the evaporator temperature of –10° C and a condensing temperature in the range (30÷50)° C. The performance of the system is analysed in terms of work consumption and COP. Since the adoption of R134a/Al2O3 will reveal a gain in the energy efficiency (13%) when rising the condensing temperature, the analysis will continue with the performance assessment when the concentration of nanoparticles will vary in the range (0.05÷0.50)%. Results indicate that a 10 times increase in Al2O3 concentration will lead to about 77% decrease in work consumption.
KEYWORDS: Nanoparticles, Ozone, Climate change, Aluminum, Safety, Energy efficiency, Thermodynamics, Particles, New and emerging technologies, Space operations
Nanorefrigerants are a new class of refrigerants, resulted by adding nanoparticles in a conventional refrigerant. Vapor compression refrigeration systems play an important role in refrigeration applications, which are sein to be one of the most energy consuming technologies. Improving energy efficiency of these systems is a nowadays challenge, due to environmental benefits. On the other hand, the use of ecological refrigerants (ODP=0 and low GWP) is an actual trend, in accordance with international regulations. This paper focuses on the performance of a vapor compression system in two cases: when the working fluid is a pure refrigerant (R600a) and when the working fluid is a nanorefrigerant (R600a/Al2O3). The nanorefigerant has resulted by adding Al2O3 nanoparticles the environmental friendly refrigerant R600a. The results indicate that the system working with the nanorefrigerant has an enhanced performance; also, it is investigated its behavior when keeping the evaporation temperature constant and the condensation temperature varies.
Contaminants met during marine transportation erode air compressor blades of the gas turbine; the result of this process is sein in the decrement of the performance and the increment of fuel need. Also, there is an energy degradation during the operation of the gas turbines, being required an exergy analysis which is able to provide a plan for this power plant performance enhancement. This paper is discussing the benefits brought by nanotechnology when improving the energy efficiency in gas turbines, more specifically applying erosion resistant nanocoatings to compressor air foils is a way to optimize gas turbine performance. Ceramic matrix composites ensure durability of the components under high operating temperatures. Besides the technology dealing with better coats, the exergy analysis assesses the waste of potential energy – also known to be exergy destruction. Exergy destruction has an impact on the efficiency of the plant; moreover each component part of the thermal system has a contribution to the merit of the gas turbine. This is why are formulated exergy destructions for these components. According to the results of this analysis, it can be stated that the least inefficient component of the gas turbine system is the compressor, followed by the gas turbine itself. The object of this study is a 4,1 MW gas turbine with ceramic matrix composites nanocoating, operating at different loads (60%, 80%, 100%).
It is well known that our times require a high energy demand, resulting in an acute climate change due to carbon dioxide emissions, as well as that fossil fuels are limited and their amount started to be diminished. To cover worldwide energy consumption, mankind should focus on the more intensive use of renewable energy sources, which present a huge potential to ensure the energy supply in the long run. For an affordable renewable energy, it is expected to be seen a significant development of the specific technologies, nanotechnologies being strong contributors to a green energy supply. This paper is discussing about the establishment of a marine renewables network (MRNBSR), having 6 offices in maritime universities from countries that border the Black Sea: Romania, Bulgaria, Ukraine, Russia, Georgia and Turkey. This establishment aims to intensify the role that marine renewables can play in the energy system of coastline countries and also the facilitation of the integration of nanotechnologies into maritime renewables sector in the region, based on the reality that universities are centers of research and innovation. The new formed network will work as a coordinator of the will to increase the deployment of renewable energy use. Will be given the steps to be followed in the setting up of the network. After the establishment, in these offices will work personnel with specific tasks - which will be described in the paper.
A challenge that fishing industry is facing is the improvement of the refrigeration technology on board of fishing vessels. This paper deals with vapor compression refrigeration systems included on board of these ships. In these systems, significant thermodynamic losses are encountered in the expansion valve, during throttling process. Because it is possible to improve a thermodynamic process by decreasing irreversibility, in this paper it is used an ejector in order to reduce throttling irreversibility. A new technology results, the use of an ejector as a refrigerant expander leading to the ejector expansion refrigeration cycle. The theoretical study developed here will reveal a performance improvement of the new cycle. Also, because the traditional refrigerant used in marine refrigeration is R 134a, which presents a high value of its Global Warming Potential, the performance analysis is extended for the case of the use of other more environmentally friendly refrigerants: propane and isobutane.
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