High Electrical Conductivity

h i g h l i g h t s A comprehensive coverage on carbon materials used in redox flow batteries is given. The influence of nanotechnology and graphene is discussed in detail. The importance of studying RFB degradation mechanisms is emphasised.

The source of fossil fuel is decreasing. The price increased rapidly. Population and demand of energy increased significantly over the years. Carbon pollution and global warming are becoming major issues. The best way to overcome this problem is by changing to renewable source of energy. One of it is solar thermal energy. However, a solar technology is currently still expensive, low in efficiency and takes up a lot of space. Nanofluid is recognized as a solution to overcome this problem. Due to the high thermal conductivity of nanofluids, the thermal efficiency of a solar collector can be increased and thus decreasing the size of the system. This paper analyzes the efficiency of using the Al2O3 nanofluid as absorbing medium in flat-plate solar collector and estimated the potential of size reduction. When applying the same output temperature of Al2O3 nanofluid as with water, it can be observed that the collectors size can be reduced up to 24% of its original size.

In the present work the effect of Al 2 O 3 ewater nanofluid, as working fluid, on the efficiency of a flat-plate solar collector was investigated experimentally. The weight fraction of nanoparticles was 0.2% and 0.4% and the particles dimension was 15 nm. Experiments were performed with and without Triton X-100 as surfactant. The mass flow rate of nanofluid varied from 1 to 3 Lit/min. The ASHRAE standard was used to calculate the efficiency. The results show that, in comparison with water as absorption medium using the nanofluids as working fluid increase the efficiency. For 0.2 wt% the increased efficiency was 28.3%. From the results it can be concluded that the surfactant causes an enhancement in heat transfer.

In this study the effect of MWCNT nanofluid, as absorbing medium, on the efficiency of a flat-plate solar collector was investigated experimentally. The weight fraction of CNTs was 0.2% and 0.4%. The effect of Triton X-100 as a surfactant on the stability of nanofluid was studied. The tests were performed in different mass flow rates of nanofluid from 0.0167 to 0.05 kg/s. ASHRAE standard was used to perform the tests. Results show that by increasing the weight fraction from 0.2% to 0.4%, there is a substantial increase in the efficiency. Also, using the surfactant causes an increase in the efficiency.

For a solar thermal system, increasing the heat transfer area can increase the output temperature of the system. However, this approach leads to a bigger and bulkier collector. It will then increase the cost and energy needed to manufacture the solar collector. This study is carried out to estimate the potential to design a smaller solar collector that can produce the same desired output temperature. This is possible by using nanofluid as working fluid. By using numerical methods and data from literatures, efficiency, size reduction, cost and embodied energy savings are calculated for various nanofluids. From the study, it was estimated that 10,239 kg, 8625 kg, 8857 kg and 8618 kg total weight for 1000 units of solar collectors can be saved for CuO, SiO 2 , TiO 2 and Al 2 O 3 nanofluid respectively. The average value of 220 MJ embodied energy can be saved for each collector, 2.4 years payback period can be achieved and around 170 kg less CO 2 emissions in average can be offset for the nanofluid based solar collector compared to a conventional solar collector. Finally, the environmental damage cost can also be reduced with the nano-fluid based solar collector.

The source of fossil fuel is decreasing. The price increased rapidly. Population and demand of energy increased significantly over the years. Carbon pollution and global warming are becoming major issues. The best way to overcome this problem is by changing to renewable source of energy. One of it is solar thermal energy. However, a solar technology is currently still expensive, low in efficiency and takes up a lot of space. Nanofluid is recognized as a solution to overcome this problem. Due to the high thermal conductivity of nanofluids, the thermal efficiency of a solar collector can be increased and thus decreasing the size of the system. This paper analyzes the efficiency of using the Al 2 O 3 nanofluid as absorbing medium in flat-plate solar collector and estimated the potential of size reduction. When applying the same output temperature of Al 2 O 3 nanofluid as with water, it can be observed that the collector's size can be reduced up to 24% of its original size.

Continuous escalation of the cost of generating energy is preceded by the fact of scary depletion of the energy reserve of the fossil fuels and pollution of the environment as developed and developing countries burn these fuels. To meet the challenge of the impending energy crisis, renewable energy has been growing rapidly in the last decade. Among the renewable energy sources, solar energy is the most extensively available energy, has the least effect on the environment, and is very efficient in terms of energy conversion. Thus, solar energy has become one of the preferred sources of renewable energy. Flat-plate solar collectors are one of the extensively-used and well-known types of solar collectors. However, the effectiveness of the collector's absorber plate to absorb solar energy limits the efficiency of this type of collector, as does the inefficient transfer of the solar energy via heat transfer to the fluid in the collector's flow channels. To improve its efficiency and performance, ''nanofluids," synthesized by mixing solid, nanometer-sized particles at low concentrations with the base fluid, have been used with remarkable effects on the thermophysical properties, such as thermal conductivity. The use of nanofluids as an advanced kind of fluids is a comparatively recent development. In this paper, the previous investigations of the performance of flat-plate solar collectors using nanofluids as working fluids are covered in detail. Then, some conclusions and recommendations are presented concerning the use of nanofluids in flat-plate solar collectors.

At present, literature data on density of nanofluids are still scarce and controversial. In this paper, density data for nanofluids formed by water, as a base fluid, and solid nanoparticles of two different materials are presented. Density was measured by using a Density Meter DA-130N from Kyoto Electronics. The obtain result is compared with previous models and found incompatible for temperature variations.

Using nanofluids as an innovative kind of liquid
blend with a trivial volume fraction (in percent) of
nanometer-sized solid particles in suspension is a
fairly a novel arena or idea. The objective of this
presented review paper is to inspect the performance
of the nanofluid-based solar collector (NBSC). In
past few years for a number of experimental and
industrial thermal engineering systems solar energy
has proven to be the best input energy source. The
scarcity of fossil fuels and environmental
contemplations motivated the researchers to utilize
alternative energy sources such as solar energy, wind
energy, tidal energy etc. Therefore, it is essential to
boost the performance of the solar thermal
engineering systems. Because of better rheological
properties nanofluids are utilized to build up the
performance of conventional solar thermal
engineering systems. Therefore, major part of this
presented review paper lays a main emphasis to
investigate the effects of nanofluids on the
performance of solar collectors. Some proposals are
also given to use the nanofluids for future work in
different solar thermal engineering systems such as
parabolic trough systems (PTS), solar thermoelectric
cells and finally, the challenges of using nanofluids in
solar energy devices are reviewed in brief.

Flat-plate solar collector is the most popular type of collector for hot water system to replace gas or electric heater. Solar thermal energy source is clean and infinite to replace fossil fuel source that is declining and harmful to the environment. However, current solar technology is still expensive, low in efficiency and takes up a lot of space. One effective way to increase the efficiency is by applying high conductivity fluid as nanofluid. This paper analyzes the potential of size reduction of solar collector when MWCNT nanofluid is used as absorbing medium. The analysis is based on different mass flow rate, nanoparticles mass fraction, and presence of surfactant in the fluid. For the same output temperature, it can be observed that the collector's size can be reduced up to 37% of its original size when applying MWCNT nanofluid as the working fluid and thus can reduce the overall cost of the system. © Published under licence by IOP Publishing Ltd.

http://iopscience.iop.org/1755-1315/16/1/012004