Quenching Experiment on Vertical Surface using Carbon Nanotube (CNT) Nano-fluids

ABSTRACT
Quenching experiment on vertical surface using Carbon Nanotube (CNT) nanofluids were conducted to see the effect of using CNT nanofluids on the quenching speed. Homogeneous and stable CNT nanofluids have been produced by suspending well dispersible CNT nano-particle into water base fluid. CNT nanofluids (0.0001 vol.% and 0.01 vol.%) were prepared for experiments. From zeta potential results our CNT nano-fluids has a good stability. The test section was an annular channel with a concentric inner rod made of stainless steel SUS316 and an outer tube made of quartz glass. The experimental data obtained show that quenching speed using CNT nanofluids enhanced compare to water.

Keywords: film boiling; Nanofluids; CNT nanofluids , quenching

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Characteristics of Pool Boiling Heat Transfer of Stabilized Colloidal Single walled Carbon Nano Tube (SW-CNT) and Multi walled Carbon Nano Tube (MW-CNT

ABSTRACT
Heat transfer and Critical heat flux (CHF) in pool boiling of single-walled and multi-walled CNT nanofluids were investigated using horizontal surface. Homogeneous and stable nanofluids have been produced by suspending well dispersible single-walled carbon nanotubes (S-CNTs) and multi-walled carbon nanotubes (M-CNTs) into water base fluid. S-CNTs nanofluids (0.0001, 0.001, and 0.01 vol.%) and M-CNTs nanofluids (0.0001, 0.001 vol.%) were prepared for experiments. From zeta potential results our CNTs nano-fluids has a good stability, it was constant for more than one month. The experimental data obtained show that there were a significant enhancement of CHF using nano-fluids compare to water. Our findings indicate that have collective influence on the CHF enhancement of CNT nanofluids.

Keywords: CHF; Nanofluids; Single-walled CNT; Multi-walled CNT; Pool boiling; CHF enhancement; SEM; AFM; contact angle; zeta potential

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Reflooding Experiment on Vertical Surface using Al2O3 Nano-fluids

ABSTRACT
Reflooding experiment on vertical surface using Al203 nanofluids were conducted to see the effect of using Al203 nanofluids on the quenching speed. Homogeneous and stable nanofluids have been produced by suspending well dispersible Al203 nano-particle into water base fluid. Al203 nanofluids (0.0001 vol.% and 0.01 vol.%) were prepared for experiments. From zeta potential results our Al203 nano-fluids has a good stability. The test section was an annular channel with a concentric inner rod made of stainless steel SUS316 and an outer tube made of quartz glass. The experimental data obtained show that quenching speed using nanofluids enhanced compare to water.

Keywords: film boiling; Nanofluids; Al203 nanofluids , reflooding, quenching

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A study on Stabilized Colloidal Fullerene (C-60) Nanoparticles for Pool Boiling Heat Transfer Applications

ABSTRACT
We report the first Critical Heat Flux (CHF) experiment in pool boiling conditions using Fullerene (C60) nanofluids. Fullerene (C-60) nanofluids (0.0001, 0.001, and 0.01 vol.%) were prepared for experiments. We observe that maximum CHF enhancement up to ~108% was observed at volume concentration 0.01% Fullerene (C-60) nanofluids compare to pure waters. The heat transfer coefficient also found enhanced, the boiling curves observed shifted to the right. After experiment we found there was nanoparticle deposited on the heater surface, several investigations have been performed to discover the porous layer on the heater surface. The mechanisms of pool boiling CHF and heat transfer coefficient enhancement using Fullerene (C60) nanofluids also been discussed.

Keywords: CHF; Nanofluids; Fullerene; C60; Pool boiling; CHF enhancement; SEM; AFM; contact angle; zeta potential

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An Overview Enhancement of Critical Heat Flux at Pool Boiling and Flow Boiling condition using nanofluids

ABSTRACT
The most important thermal-hydraulic parameter in heat transfer system design and safety analysis is Critical Heat Flux (CHF). Many research have been conducted to investigate CHF enhancement technique such as by surface roughening, surface coating, by adding soluble addictive, and by adding nanofluids. Nanofluids have been attracting significant attention since it found be able give a significant CHF enhancement. This article summarizes the recent research in experimental study on CHF enhancement at Pool boiling and Flow boiling conditions using nanofluids, and identifies the challenges and opportunities for future research.

Keywords: CHF; CHF enhancement; Nanofluids; Pool boiling; Flow boiling

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“NUCLEAR POWER: LOOKING FOR THE FUTURE,THE 4TH KEY ISSUES OF NUCLEAR POWER TODAY”

“NUCLEAR POWER: LOOKING FOR THE FUTURE,THE 4TH KEY ISSUES OF NUCLEAR POWER TODAY”

A. Introduction

The most important constraints on economic growth and development are the availability of energy. Nuclear power is the best source of energy for support the economic growth and development. There are four key issues for nuclear power to continue to be viable as a source of energy now and in the future: the economic of nuclear power, nuclear safety, spent fuel and radioactive waste management, and nuclear non-proliferation.

B. 4th Key Issues of Nuclear Power Today

1. The Economic of Nuclear Power

There is generally increasing pressure on nuclear power to be genuinely economically competitive with other large-scale energy sources, such as coal, oil and gas. To make nuclear power competitively economics, we need some strategy whether for the current nuclear power plant and for the new nuclear power plant. Here are certain strategies to improve the economics of nuclear power:

a. The economics of current nuclear power plants

The overall picture with current nuclear plants is very clear. They are operating more and more efficiently and operating costs are generally low relative to those of alternative generating technologies. These improvements have now become routine and will be integrated into the construction of new nuclear plants. Here are in detailed the economic improvement of the current plant (the existing plant):

a.1. High Plant Performance by High plant availability and Capacity Factor

The current plant have been operated more and more efficiencies and have more output is being achieved with each reactor through improved availability / capacity up-rates and operation will continue for many years in the future, backed by the necessary investment in refurbishment.

a.2. Operating Cost

OECD2 /NEA3 studies from 1983-2005 (OECD-NEA/IEA 2005 and earlier) [table1] show relative stability in the overall generating cost of nuclear power plants. This has resulted essentially from two different factors: Nuclear fuel costs have fallen due to lower uranium and enrichment prices together with new fuel designs allowing higher burnups, while O&M costs have now stabilized at levels competitive with other base-load generation.

a.3. Capacities Up rates

Up-rating the power output of nuclear reactors is recognized as a highly economic source of additional generating capacity. The refurbishment of the plant turbo generator combined with utilizing the benefits of initial margins in reactor designs and digital instrumentation and control technologies can increase plant output significantly, by up to 15-20%. There are many examples of this throughout the world, but it is a particular focus in Sweden, the United States and East European countries.

a.4. Licensing Extensions

The extending the lifetime of plants may allow the owner to reduce their annual depreciation charge thereby spreading decommissioning charges over an extended lifetime and further improving profitability. Existing well maintained NPPs have become valuable assets with excellent safety performance. Those effect wich result reducing the cost.

b. The economics of new nuclear power plants

The future of all reactors will depend on whether they can be economically built and operated. One of the major impediments to new nuclear construction is the capital cost due in large part to the length of construction time and complexity of the plant. Here are in detailed the economic improvement of the new nuclear power plant:

b.1. Reducing the capital cost of nuclear power

OECD-NEA (2000), highlights several areas where vendors have identified specific steps to reduce capital costs to a range they regard as feasible: $1000-1400 per kW of installed gross capacity. Key areas of cost reduction include the following:

  1. Larger unit capacities provide substantial economies of scale, suggesting that nuclear plants should, for economic reasons, use higher-capacity reactors.
  2. Replicating several reactors of one design on one site can bring major unit cost reductions.
  3. Standardization of reactors and construction in series will yield substantial savings over the series.
  4. Learning-by-doing can save substantial capital costs, both through replication at the factory for components and at the construction site for installation.
  5. Simpler designs, some incorporating passive safety systems, can yield sizeable savings, as can improve construction methods.
  6. A predictable licensing process can avoid unexpected costs and facilitate getting the new plant up to safety and design requirements at an early date to start electricity – and revenue – generation.

b.2. Low interest charge and the shorten the construction periods

Construction interest costs can be an important element of total capital costs but this depends on the rate of interest and the construction period. The low interest charge can reduce the cost of new plant. Since nuclear power projects are very much capital intensive, shortening the construction period is important to the interest charges during construction period. Construction period may be reduced through: (a) parallel construction technology; (b) increased composite modularization; (c) increased prefabrication; (d) better communication through information technology; and replication.

2. Safety of Nuclear Power

Second important key issue in nuclear power is nuclear safety. The TMI accident in 1979 and the Chernobyl accident in 1986 was clearly a setback to nuclear power. Many lives were lost. Thousands suffered major health impacts, and there were significant environmental and social impacts. The accident was the result of less than optimal reactor design, compounded by gross safety mismanagement. But ironically, this event also prompted major improvements in an approach to nuclear safety.

A key change was the development of a so-called international “nuclear safety regime”. The IAEA updated its body of safety standards to reflect best industry practices. International conventions were put in place, creating legally binding norms to enhance the safety of nuclear activities. A systematic analysis of risk was used to ensure that safety upgrades would be made in areas that would bring the greatest safety return. And, importantly, both the IAEA and the World Association of Nuclear Operators created international networks to conduct peer reviews, compare safety practices, and exchange operating information to improve safety performance.

The international nuclear safety regime has been demonstrating its effectiveness for two decades. But it would be a misunderstanding to regard nuclear safety as something that can be “fixed.” As IAEA Report, “Every [nuclear] operator must establish and maintain a ´safety culture´ in which management demonstrates that safety is the overriding priority and in which every member of staff recognizes his or her individual responsibility for safety.”

A key aspect of an effective safety culture is taking full advantage of operating experience. Experts note that serious nuclear safety events are almost always preceded by less serious “precursor” events. By taking prompt action based on the “precursors”, the probability of a serious accident can be reduced. But to do this effectively requires a number of things:

1. careful analysis of the root causes of events;

2. mechanisms that facilitate sharing this information with other nuclear operators worldwide; and

3. a commitment to transparency by all nuclear power countries and operators – including making use of peer review safety missions – as part of an ongoing process of mutual learning.

In that regard, many countries have requested an Integrated Regulatory Review Service to IAEA. This new service combines a number of elements ranging from nuclear safety and radiation safety to emergency preparedness and nuclear security. It includes a self-assessment aspect, and permits a comprehensive, participatory approach to evaluating a country’s safety performance.

3. Spent fuel and Nuclear Waste Management

The management of spent fuel and disposal of high level radioactive waste remain a challenge for the nuclear power industry. The amount of spent nuclear fuel produced annually – about 10 000 tonnes – is actually small when contrasted with the 25 billion tonnes of carbon waste from fossil fuels that is released directly into the atmosphere. Experts agree that the geological disposal of high level radioactive waste is safe and technologically feasible. But public opinion will likely remain skeptical – and nuclear waste disposal will likely remain a topic of controversy – until the first geological repositories are operational and the disposal technologies fully demonstrated.

The greatest progress on deep geological disposal has been made in Finland, Sweden and the United States. But it will still be more than a decade before the first such facility is operational.

In the meantime, the trend has been to construct and use above-ground interim storage facilities, and many countries are exploring the feasibility of interim storage for 100 years or more. An increasing number of countries are also interested in ensuring waste retrievability for future flexibility. Research is also progressing on the use of fast reactors and accelerator driven systems to incinerate and transmute long lived waste, in order to reduce the volume and radiotoxicity of waste to be sent to geologic repositories.

For some time, many countries start to consider the multinational approaches to the management of spent fuel and disposal of high level radioactive waste. More than 50 countries have their spent nuclear fuel stored in temporary sites, awaiting disposal or reprocessing. Many countries do not have the technology or appropriate sites for geological disposal, and the costs for countries with small nuclear programmes would be prohibitive.

4. Nuclear Non-Proliferation and Safeguards for peaceful uses of nuclear energy

Nuclear security has also become a major concern in recent years.Perhaps the most serious concern relates to the proliferation of nuclear weapons. At the same time that we are seeing rising expectations for nuclear power, we are also witnessing concerns regarding the spread of sensitive nuclear technology. Particularly sensitive are nuclear operations such as enrichment and spent fuel reprocessing – activities that are part of a peaceful nuclear programme, but also can be used to produce the high enriched uranium and plutonium used in nuclear weapons. Countries that have such operations are only a short step away from a nuclear weapons capability.

There are four critical aspects of the nuclear non-proliferation regime that must be strengthen – addressing both symptoms and root causes – if we are to avoid a cascade of nuclear proliferation, and our ultimate self-destruction.

First, develop a more effective approach for dealing with proliferation threats. The Nuclear Non-Proliferation Treaty and the IAEA Statute make clear the reliance of the international community on the IAEA to verify States´ adherence to their non-proliferation obligations, and on the United Nations Security Council to act in cases of non-compliance. The present system offers an array of measures ranging from dialogue to sanctions to enforcement actions. But judging by our record in recent years, these measures have not been applied effectively to deal with proliferation issues. Second, secure existing nuclear material stockpiles and tighten controls over the transfer and production of nuclear material. Effective control of nuclear material is the “choke point” for preventing the production of additional nuclear weapons. Third, strengthen the verification authority and capability of the IAEA. Effective verification has four elements: adequate legal authority; state-of-the-art technology; access to all relevant information and locations; and sufficient human and financial resources. Fourth, urgently need to find a way for disarmament to be given the prominence and priority it deserves. Article VI of the NPT requires parties to the Treaty to pursue negotiations in good faith “on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament”. It is now 37 years since the Treaty entered into force. Should we not be well past the date when States party should be developing new nuclear weapons?

C. Key Issue Advantage for Renaissance Nuclear Power In the Future

After we know the key issue and how to improve those key important issues, we will be able to answer the challenge of nuclear power renaissance in the future. Knowing the important issue will make us have “A NEW PARADIGM”: A New Nuclear Economic Paradigm, A New Nuclear Safety Paradigm, A New Nuclear Waste Management Paradigm and A New Nuclear Security Paradigm.

By having a new nuclear economic paradigm the existing and future of all reactors will be economically built and operated. By having a new nuclear safety paradigm the existing and future of all reactors will be maintain in safety condition and no more nuclear incident and accident. By having a new nuclear waste management paradigm the existing and future of all reactors waste will be manageable and public doesn’t have to worry about the waste of nuclear power.  By having a new nuclear security paradigm the existing and future of all reactors will secure from misused.

Those key issues are challenge for the nuclear society now, and those key issues will be solved by the international cooperation strategy. Now we have the Gen IV Cooperation and much other International collaboration, that cooperation are one of the step to answer the key important issue challenge in near future.

D. Conclusion

Nuclear power now in the crossroad to nuclear renaissance, to ensure that nuclear renaissance will be coming and nuclear power comeback as favorite energy source option are by answering 4 (four) key important issue today: : the economic of nuclear power, nuclear safety, spent fuel and radioactive waste management, and nuclear non-proliferation. Those key issues are challenge for the nuclear society now, and those key issues will be solved by the international cooperation strategy.

E. Reference

1. www.nrc.gov.

2. www.world-nuclear.org

3. www.iea.org

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An Experimental study of Fullerene (C60) Nano-fluids on Pool Boiling Conditions

An Experimental study of Fullerene (C60) Nano-fluids on Pool Boiling Conditions

1. Introduction

Critical heat flux (CHF) is directly related to the performance of the system since CHF limits the heat transfer of a heat transfer system. Significant enhancement of CHF allows reliable operation of equipment with more margins to operational limit and more economic cost saving. The previous results show that the nano-fluids significantly enhanced pool boiling CHF compared to pure water. It was supposed that CHF enhancement was due to increased thermal conductivity of fluids, change of bubble shape and behavior, and nano-particle coating of the boiling surface. The previous researches also show that mainly the pool boiling experiment was employed metal particles. Fullerene (C60) is a novel carbon allotrope that was first discovered in 1985 by a winner noble “Sir Harold W.Kroto, Richard E. Smalley and Robert F.Curl Jr”. In this study we report the first CHF experiment in pool boiling conditions using Fullerene (C60) nanofluids.

2. Experiment

2.1. Preparations of nanofluids

The C60 particles are nearly water insoluble in water, because of their strong hydrophobicity and van der Waals attractions. As a way alternative to such chemical synthesis, water dispersion of C60 itself has recently attracted increasing interest for practical applications. Some methods based on reprecipitation, solvent replacement, and ultrasonications have been introduced to prepare the dispersion, and surfactant, polymer, or other detergents are often added.
In this study we use acid treatment as our method to have water dispersible Fullerene (C60).The fullerene [C60] used in this work was 99.99% pure from Sigma Aldrich. All the solvents and chemical reagents were from Aldrich.

2.2. Zeta Potential Measurements

The dispersion and stability of fullerene (C60) nanofluids were checked by measuring zeta potential. Zeta potential is an abbreviation for electrokinetic potential in colloidal system. In other words, zeta potential is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle. The significance of zeta potential is that its value can be related to the stability of colloidal dispersions. The zeta potential of Fullerene nanofluids were found in the range of mV . The zeta potential of nanofluids was constant for more than one month .

3. Boiling experimental facility and procedure

The CHF of deionized pure water and nanofluids was measured in the apparatus , which basically consists of horizontal flat surfaces heater submerged in the test fluid at atmospheric pressure.

4. Results and Discussions

4.1. CHF with fullerene (C60) nanofluids

For the prediction of CHF of pure fluids, Zuber’s (1959) correlation, has been used widely for the past years. The CHF for flat plate is predicted as 1110 kW/m2 by Zuber’s model for water under atmospheric pressure. The results data for CHF of pure water was approximately 50% lower than Zuber prediction, however the main focus of this present work is to investigate CHF enhancement using nano-fluids relative to CHF of pure water, the experimental CHF value of pure water in present work can be used as standar for subsequent CHF comparisons of nano-fluids. It was also reported by N. Barkhu and J.H. Lienhard that the prediction of zuber equation is not valid.
Significant CHF enhancement is observed for all concentrations content Fullerene (C60) nanofluids compare to pure water. CHF enhancement as compared to pure water occurs up to 108% for 0.01vol% fullerene (C60) nanofluids, up to 46% for 0.001vol% fullerene (C60) nanofluids, and up to 22% for 0.0001vol% fullerene (C60) nanofluids.

4.2. Heat Transfer Coefficients with fullerene (C60) nanofluids

The boiling curves in Fullerene nanofluids are shifted to the left of boiling curve in water. Its means the heater surface boiling in Fullerene nanofluids will generally have a higher nucleation site density causing this shift to the left.

5. Conclusions

The critical heat flux in pool boiling conditions is experimentally evaluated for Fullerene (C60) nanofluids. It is found several significant findings such as:
1. The zeta potential of Fullerene nanofluids were in the range of 41 mV. The zeta potential of nanofluids was constant for more than one month. It concludes that the treatment has been succeeded produces water dispersible Fullerene (C60) nanofluids with good stability.
2. Enhanced (~108.9%) CHF was observed for solutions with Fullerene (C60) nanofluids with concentration 0.01%.
3. The pool boiling HTCs of Fullerene (C60) nanofluids are higher than those of pure water in the entire nucleate boiling regime.

REFERENCES

[1] I.C. Bang, S.H. Chang, Boiling heat transfer performance and phenomena of Al2O3–water nano-fluids from a plain surface in a pool, Int. J. Heat Mass Transfer 48 (2005) 2407–2419.
[2] N. Zuber, Hydrodynamic aspects of boiling heat transfer, AEC Report AECU-4439, Physics and Mathematics, 1959.
[3] J.H. Lienhard, A heat transfer textbook, Prentice-Hall, p. 404, 1981.

[4] U.S Choi, Developments and Applications of Non-Newtonian Flows, ASME FED-Vol. 231/MD, vol. 66, (1995), PP. 99-105.

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