Microchannels Heat Exchanger

Research on heat transfer characteristic inside microchannels has become important topic as the advancement in the field of micro-scale technology such as micro electro-mechanical system. The impacts of miniaturization of the system involving high heat transfer processes create challenges for better system’s thermal management which can only be solved by enhancement of the performance and efficiency of applied heat exchanger devices. Microchannels have been considered as the potential solution for such devices due to their high thermal performance characteristic with low space requirements.

As for current development, the fabrication methods of microchannels, which limit the microchannels applications in the early developments, have emerged beyond the ability to model the thermal system on the microchannels of such scale. Micromachining of silicon wafers, micro-extrusion of aluminum elements [1], anisotropic wet chemical etching and sawing, anisotropic dry etching, hybridization and system-on-chip integration [2] are examples of micro-fabrication methods capable of manufacturing microchannels.

Early research in microchannels heat exchanger can be traced back to works by Tuckerman and Pease [3] for a very-large-scale-integrated circuits cooling. In fact, microchannels application can be found in cooling devices for computer’s microprocessors and electronic components, laser diodes, radar and aviation components, and microchemical reactors. For larger system, microchannels have been employed in compact heat exchanger for air conditioning system in automotive and domestic applications. Various microchannel configurations are used in these applications, including important feature of refrigerant headers which provide minimum effects on the upstream flow during two-phase flows inside the microchannel passages.

Despite the extensive applications of microchannels in heat exchanger devices, as for current applications, the devices are being implemented based on extensive testing which are expensive and time consuming. There has not been a fully-reliable thermal design methods for such applications due to the limited understanding in thermal-hydraulic phenomena occurred in micro-scale channels, importantly for two-phase flow boiling heat transfer mechanism.

Important issues on microchannels include two-phase flow patterns, flow boiling heat transfer mechanism and model developments, two-phase pressure drop and prediction methods, and critical heat flux.

References:
[1] Thome, John R., 2004. Boiling in microchannels: a review of experiment and theory, Int. J. Heat and Fluid Flow 25 pp. 128-139
[2] Kandlikar, Satish G. and Grande, William J., 2003. Evolution of Microchannel Flow Passages-Thermohydraulic Performance and Fabrication Technology, Heat Transfer Eng. 24(1) pp. 3 – 17
[3] Tuckerman, D.B. and Pease, R.F., 1981. High Performance Heat Sinking for VLSI, IEEE E. Device Letters, EDL-2 pp. 126-129

Refrigeration and AC contribution to Climate Change

Refrigeration and air conditioning (RAC) system contribute to climate change through their greenhouse gases emission by two means.

First, they emit refrigerant gases from leak and losses in charging/discharging processes. Some of these refrigerants are not only ozone depleting substances regulated in Montreal Protocol, but also greenhouse gases listed in Kyoto Protocol. For example chlorofluorocarbon, CFC. CFC-11 and CFC-12, which are phased out under Montreal, have Global Warming Potential, GWP 1400 and 4100, respectively. These GWPs are based on CO2 which GWP is defined as 1.

However this contribution is relatively low. The bigger contribution for climate change, accounts for 80% of their contributions, come from carbon dioxide emissions which are released from their energy uses. These emissions are associated with the amount of greenhouse gases emission from the sources of power to run the RAC systems, generally from electric power generators for industrial and domestic uses, and some from combustion engines for automotive air conditioning and local uses.

So, the RAC industry roles in curbing the climate change issues should be focused on reducing the energy consumption of their equipments and systems. It can be achieved through increasing their systems’ energy efficiency and developing new technology.
The research and development of alternative refrigerants as the replacement of phased out refrigerants are still needed to be done, due to their importance on keeping the ozone layer safe. However there should be considerations that the replacement should also be associated with maintaining or increasing their systems’ energy efficiency. Reducing RAC systems’ efficiency is simple not an option.

Finally, as an RAC engineers, these are the challenges we need to face today, and these are the ways you can do to contribute for the solution of climate change.

Climate Change: Voices from Yeosu

‘I’m worry,’ said Kyeong-ran, a middle school teacher in Yeosu when asked about her first impression on ‘climate change’. Her opinion was also shared with Yun-jeong, a Yeosu City public servant and Hyun-mi, a university student studying English.

The topic of climate change and global warming warmed the atmosphere of the discussion that night, even it was a pretty cold night in the middle of autumn in Yeosu.It is interesting to hear what people of Yeosu say about climate change. A relatively small city lying about midway along the southern coast of South Korea, beautiful sea and coasts with more than 300 islands and rich of seafood and fish resources, Yeosu is vulnerable with the impacts of climate change. Beside that, Yeosu is also the place of Yeochon industrial complex, including oil and petrochemical plants, claimed as big contributors of greenhouse gases.

However, not everyone in the room was familiar with climate change issues. At least that what I thought when Yang-hyon, a consultant in machinery supplier, and Mi, a final year student majoring in statistic, said ‘I have no idea,’ prior to the discussion. At the beginning, we read a short article about climate change which I had prepared before. Discussion continued with the climate change impacts to their life. Hyun-mi said the temperature was higher these days, even during the winter, compared to the past. The snow was hardly seen again, the spring and autumn periods were much shorter now. Yang-hyon told the story about an industry plant which had to be closed due to environmental concerns. Yun-jeong, who works in agriculture government office, and Hye-sung said about heavy rain and storm which were more frequent nowadays. Even though they were not sure whether the cause was climate change or something else, but they all agreed that human activities had done negative impacts on the environment and we should do something about it.

Those brought our discussion into what efforts are needed to address the negative impacts above. Yang-hyon and Yun Mi argued that the government role is significant to educate the people about climate change issues. Yun Mi stressed the importance of such education on children and young generation to raise their awareness. Yun-jeong suggested active participation of the community members to get informed and to disseminate the information through public advertisements or campaigns. Yang-hyon added the need to apply stricter regulations and penalties for industries, while Hye-sung said about research and development to improve industry process and products’ energy efficiency such as electric or hybrid car in automotive industry. In the short article, I also included individual efforts that can contribute to the solution of climate change problems.

The discussion then continued on such individual efforts and their willingness to do them. They said the importance of each of us to get informed and learn about climate change issues, for example through this discussion and other sources.Energy efficiency in daily life was also brought to our attention. Through lowering electric bill and the use of energy-efficient utilities in the household e.g. fluorescent lamp, freezer, and air conditioning equipments. We also discussed the efforts on limiting the greenhouse gases emission such as using fuel-efficient vehicle and joining carpool or mass transportation. Hye-sung said he planned to change his car into gas-fuelled with higher fuel efficiency and lower emission. Or even into electric or hybrid car but, he complaint, they were too expensive for him. Other efforts which also came to light during the discussion were the 3R steps, reduce, reuse and recycle waste. They agreed these could be applied in daily life and they were willing to do them.

The discussion had to end because it was already late. I, personally, hope that the discussion could benefit them through the information and opinion we shared. One thing which was encouraging from the discussion, was that everyone wanted to contribute to the solution of the climate change problems. Their arguments were not only limited to the government and industry leader roles, but also their own roles and efforts to get the solutions. They are willing to do the efforts, even if they have to change their individual habit or lifestyles. As Yang-hyon said, ‘it’s inconvenient for us to change, but we have to do it’.

Finally, as the recent international poll said that most people are ready to change their lifestyle to curb the climate change problems, I can proudly say, the voices I heard from Yeosu are parts of them.

What you can do:Climate change is a global issue. It is everyone’s problem, wherever you live, no matter who you are. It affects all of us. So it is our responsibility to curb the climate change problems. It is not as difficult as you think; in fact, you can do it in your daily life. Here are some suggested actions:

1. Reduce, Reuse, and Recycle what you use.The steps reduce greenhouse gases released during waste processes.
2. Be energy efficientLower your electricity use, turn of unused heater or air conditioner, utilize energy-efficient utilities e.g. fluorescent lamp.
3. If you want to buy a car, choose one that is highly fuel efficient. And when you have one, don’t use it too often, join a carpool, and take mass transit, walk, or ride a bike — anything that reduces the amount of gasoline you burn.
4. Eat wisely. Choose foods that are local, organic and low on the food chain whenever possible. Make the most of seasonal foods.
5. Educate yourself. Get informed about climate change, sustainable living, participate actively in forum etc.

If those activities seem too hard for you to do, let’s think this way. Those efforts are not only for us, but they are for our next generations, our own children and grandchildren. They will thank us in the future.

For GwangjuNews, Dec 07

Local Entrepreneurship: Bring the Best from Our Home to the World

There is one question which always comes up when you are a student in the last year of your study in the university: what company do you plan to work?

In today’s world, the competition to get a job in big companies is harder than ever. The requirements for employment are higher every times, demanding students to master many qualifications suitable for the jobs.  For example is the ability in English language. Almost all big companies ask their employees to have English proficiency, since it is used in the global business environment.

The competition is exacerbated by centralized businesses and industries spread in the capital and big cities. These have become magnets which pull almost all the best human resources from the regions. Inevitably, the condition cause the imbalance development between the centers and other regions which responsible in social welfare inequity within the societies. Yet the resources which are needed by the businesses and industries come from these regions.

Each region has unique resources, natural and cultural, which are not found in other regions. Let us examine our local resources, in our ’home’; there are abundant potentials which are waiting to be exploited for the benefit of society. Let see Yeosu for example. We have such strategic geographic location for international hub in business and industrial trade. The ocean and its contents can provide enormous natural resources, yet they have not been developed optimally. The cultures, with many beautiful and historical places, can be great potentials for tourism. And the most important resources are its people, including the students as young generation. They are the driving forces for the development.

The question then is, how all of those resources can be actualized and bring the benefit for the society, especially for Yeosu people and all the country. At this point, we badly in need of science and technology. And to master them, we need education. Here is the point where university role is the most important. In fact, the university is the only appropriate institution which responsible to answer the challenges.

 Change of Mindset

To take the students interest back to their own local development, we need changes in our mindset. Having a carrier in big companies is not the only choice for works. There are bigger challenges and probably higher benefits offered than employment in big cities. And the most important, their works are highly needed by and give more values to the society they are living with. We may call the choice ‘local entrepreneurships’

It is not true that local businesses and industries are less challenging and not competitive. In fact, experiences form industrialized countries indicate that big companies which are well-known globally today came from small and local business units which develop into what they are today. Microsoft Corporation which is owned by the richest man in the world today, Bill Gates, was started by him and his partner Paul Allen from small company in Albuquerque, New Mexico. Or, Pizza Hut which came from small kiosk in Wichita, Texas and brought to almost every countries in the world today by Dan and Frank Chaney. Furthermore, the local entrepreneurships, which most of them are small and medium enterprises are the backbone of the economy and help many countries, including Korea to recover from their economy crisis a decade ago.

At this point, the students should change their mindset and may proudly pronounce them as ‘student today, entrepreneur tomorrow’, and we may see the bright future, not only for them, but also for the societies they are living with.

 The Role of Local Universities

The local universities, with embedded capacity in understanding potentials of their regions, should take the central role to develop local entrepreneurship. These universities have the best resources to do the function. They are the place for science and technology research and development. They have the best human resources, their professors, researchers and the students, infrastructure supports and scientific cultures to actualize the potentials through collaborative efforts. With all the abilities, local universities should identify local potentials which can be developed into competitive business units, not only in local or national levels, but also in the world.

The local universities are the focal point in the efforts to develop students’ abilities in local entrepreneurship. In fact, the students will be the future local entrepreneurs. To perform this function, the universities should encourage their students to enhance their competitiveness, in term of entrepreneurship. Integration of entrepreneurship skills, project managements, and business analysis to their curriculum is one of the efforts.

Empowerment of students in the creation of technology innovation for local industries by means of internship programs is another way to take. The existing internship programs with big industries which have been widely applied can be established also with local industries. Innovations created by the internship students with the guidance of university’s researchers are more accepted and easier to be implemented in local industries with more flexible operations than they are in big industries. Fresh and creative ideas from the internship students can lead to innovation and improvement of the business processes. And of course, these programs promote entrepreneurship among the students who able to learn more comprehensive business processes in local industries than in big industries.

From the academic point of view, the collaboration between local universities and industries requires the universities to perform science and technology research and development. The focus of these efforts should be given to appropriate science and technology development, suitable with local needs and resources. However, notes should be taken that local science and technology development does not always mean practical science or low technology. Instead, they can take form in advance and cutting-edge science and technology, as long as they are in accordance with local industries demand and resources. Silicon Valley and Stanford University is one of good examples. The development may also be synchronized with local or central government policy for the region, such as New University for Regional Innovation program in Korea. Again, the students can take benefit from this function. Through their involvements in the research and development activities, students can get the opportunity to enhance their expertise in their respective fields, which in turn will increase their competitiveness.

The functions of local universities to enhance students’ competitiveness in term of entrepreneurship addressed above require cooperation from all parties, i.e. the universities, industries, government, the society, and the most important, the students themselves. Now, is our turn, as students, to enhance our competitiveness, to answer the problems facing our society today, to take the challenge: will you be an entrepreneur? Will you bring the best from our home to the world? I will.

For Chonnam Tribune, Dec 07