Jumping Droplets Take a Lot of Heat, as Long as It Comes in a Cool Way

Chuan-Hua Chen, foreground, and Jonathan Boreyko. (Credit: Image courtesy of Duke University)

Science Daily  — Microscopic water droplets jumping between surfaces that repel and attract moisture could hold the key to a wide array of more energy efficient products, ranging from large solar panels to compact laptop computers.

These phase-change diodes can transfer over a hundred times more heat in the forward direction compared to the reverse, but with major limitations -- they are dependent on gravity or restricted by a tubular configuration. These limitations severely constrain the application of phase-change thermal diodes, for example, in mobile electronics which require orientation independence or solar panels which require a large surface area.Duke University engineers have developed a new way of producing thermal diodes, devices which regulate heat to preferentially flow in a certain direction, effectively creating a thermal conductor in the forward direction and an insulator in the reverse direction. While thermal diodes can be made from solid materials, these solid-state diodes are not nearly as effective as "phase-change" thermal diodes that rely on vaporization and condensation to transport heat.

The Duke engineers believe they have figured out a way to solve these limitations to existing thermal diodes by exploiting self-propelled water droplets, which can jump from a superhydrophobic (highly water-repellent) surface to a superhydrophilic (highly absorbent) surface, but not the other way around. The results of the Duke experiments were published online in the journal Applied Physical Letters.

Chuan-Hua Chen, assistant professor of mechanical engineering and materials science at Duke's Pratt School of Engineering, and his research group was the first to actually videotape the self-propelled jumping motion of water droplets on a superhydrophobic surface. They found that the droplets literally jumped straight up and off the surface. In their current experiments, a superhydrophilic plate was placed opposite to the superhydrophobic one, creating an asymmetry crucial for the directional transport of heat in their thermal diode.

"When the superhydrophobic surface is colder than the superhydrophilic surface, the heat transport is very effective with phase-change processes, much like sweat taking away body heat; when the superhydrophobic surface is hotter, the heat flow is blocked and the diode behaves like a double-paned window," said Chen. "Because the jumping droplets in our system are very small, gravity has negligible effect on them. Therefore, devices based on this approach can be oriented in any direction without the need to worry about gravity."

Furthermore, Chen said, this approach can be easily scalable, which means technology based on this design can be used for thermal management of devices as small as computer chips and as large as building roofs. The jumping-drop approach uniquely combines large-area scalability, orientation independence, and effective thermal rectification into one device. This combination of properties is extremely useful for thermal diodes but has remained elusive until Chen's invention.

Typical phase-change thermal diodes rely on evaporating water to transfer heat from one surface to another, with gravity pulling the subsequent condensate down to restart the cycle again. For example, these so-called thermosyphons are in use in the Alaskan oil pipeline, in order to keep the heat from the pipes from melting the permafrost.

Chen believes that this new approach could make thermal diodes more practical and effective for a variety of applications. These applications range from energy-efficient solar panels to smart "skins" of thermally adaptive buildings. For example, in the summertime a diode panel on a building could let heat escape out but prevent heat from creeping in. In space vehicles, thermal diodes can be used to regulate diurnal thermal fluctuations in the outer space, or even to harvest solar energy for powering satellites.

Chen's research is supported by the Defense Advanced Research Projects Agency. Other Duke members of the team are and Yuejun Zhao.

Double Or Nothing

“Activity in Krishna consciousness, or acting for the benefit of Krishna without expectation of sense gratification, is the highest transcendental quality of work. Even a small beginning of such activity finds no impediment, nor can that small beginning be lost at any stage.” (Shrila Prabhupada, Bhagavad-gita, 2.40 Purport) You’ve put in your time at the particular job, knowing that you’ve given it your all and that certain goals just will not be achieved no matter how much more effort is expended. The freedom that comes with living in a modern democratic nation, a place where free will is generally not infringed upon by the forces of government, allows the individual to make decisions that will affect their future. Should they be unhappy in a particular scenario, they can change their setting, find a new place to live and work that will hopefully give them the pleasure they are looking for. There is risk at every turn, however. If you leave the one job you have for another, you could potentially end up losing both, and then be left to worry over what might have been. For the spiritualist sincerely trying to gain the Supreme Lord’s favor, however, there is no such risk. “Does a spiritualist think that they are risking something by dedicating more time to spiritual life? Why is there a distinction between spiritual and material anyway? Doesn’t this whole world belong to God? Am I not connecting with the Lord just by living, working to maintain my family? Isn’t service to man sufficient for serving God?” The separation between material and spiritual life exists in the minds of those who don’t understand how to dovetail every single behavior with service to the Supreme Personality of Godhead. That highest discipline is bhakti-yoga, which aims to keep a link to the divine consciousness in a mood of love through every single activity of the day. Whether to the outsider the behavior appears spiritual or material is of no concern, for the consciousness is focused on the glorious attributes of the Supreme Person. That contemplation then results in work being performed to maintain the concentration, completing the circle. Though the activities may vary, the link to the divine consciousness does not break. Someone not on the divine platform will make distinctions. For instance, hearing, chanting   , remembering, serving, and offering prayers specifically to a deity    or divine figure are seen as behaviors bearing no relation to working hard at the jobsite, studying in school, spending time with the wife and kids, going out to watch movies, playing sports, going out to eat at a restaurant, or so many other things. Because there are distinctions made based on the beneficiary of the activity, the proportion between the two behaviors is also monitored. Sort of like how one will manage the portion sizes of their food intake, the person seeing duality in existence will take stock of how much time is dedicated to spiritual life, for there is the feeling that the material and spiritual are mutually exclusive. Are they not correct? If you’re chanting the holy names of the Lord, like those found in the maha-mantra, “Hare Krishna Hare Krishna, Krishna Krishna, Hare Hare, Hare Rama Hare Rama, Rama Rama, Hare Hare   ”, are you not avoiding some other behavior? If you’re sitting in a church or temple, is that not an explicit act of religion    that is devoid of material association? When one knows the proper definition of God and acts off of it there can be no distinction, as the mentality from the spiritual activities seeps into the consciousness of the individual and then carries over into their other activities. As a crude example to see a similar principle in effect, we can take weight training. During the actual period of exercise, the different muscles atrophy; they are stretched to the limit so that they can increase in strength. What results is that during periods of rest the muscles continue to eat, sort of like burning calories without doing anything extra. Thus the short amount of time spent in explicit exercise ends up resulting in calorie burning distributed throughout the day, even during sedentary periods like sleep. The aim of spirituality is similar, except the benefits are all-encompassing. Submissive hearing of the holy names and pastimes of the Supreme Personality are the most effective form of spiritual activity, as they immediately take the mind somewhere else, a place where the dualities of heat and cold, gain and loss, and elation and suffering are absent. This sort of escape is always sought, such as through movies, books and television shows. The tendency for escape is already there, but in bhakti the destination of the travelling mind is pure, thereby making the hearing spiritual. Despite these cogent truths passed on by the acharyas of the Vedic tradition, the tendency is to think that if I devote too much time to spiritual life, I’ll eventually renounce everything and leave my important obligations neglected. The flaw that immediately jumps to mind is that the worthiness of the obligations supposedly missed is not taken account of. The sports gambler has the obligation of having an internet connection, a cell phone, and a television programming package that carries all the games that he needs to see. The fact that gambling    is rooted in the mode of passion and thus leads to a neutral state is not recognized by the gambler feverishly looking to win the next big payout. The mode of passion is one of the three modes of material nature that govern behavior and also the types of body assumed. The human being typically falls into the mode of passion, with mixes of the modes of goodness and ignorance sprinkled in. The complete description of these modes can be found in the Bhagavad-gita, the most concise treatise on Vedic philosophy, which happens to be delivered by the origin of all knowledge, Shri Krishna. In short we can say that the mode of goodness leads to knowledge, passion to a neutral state coupled with misery, and ignorance to a much worse off position. “The mode of passion is born of unlimited desires and longings, O son of Kunti, and because of this one is bound to material fruitive activities.” (Lord Krishna, Bhagavad-gita   , 14.7) The gambler is in the mode of passion because through the difficult work of making the wager and nervously waiting to see the outcome, even success does not provide enough mental satisfaction to stop the gambler from repeating the same activity. Similarly, the business mogul who has made billions of dollars doesn’t stop where they are, for their activity has not proved to be satisfactory at making them happy. Following bhakti-yoga by learning the principles of the Bhagavad-gita from someone who knows how to apply the concepts into everyday life eventually gives one the ability to properly assess whether their specific obligations feared over are worth having. For argument’s sake, let’s say that there is some fear in the beginning. “I don’t want to chant Hare Krishna too often or read too many books about Krishna’s wonderful pastimes in the sacred land of Vrajabhumi because I’m afraid I won’t be able to take care of my other needs, which keep a roof over my head and food on the table.” Though this fear exists, in real yoga there is never a chance at becoming a loser in God’s eyes, a fact confirmed by Krishna Himself in the Bhagavad-gita. “In this endeavor there is no loss or diminution, and a little advancement on this path can protect one from the most dangerous type of fear.” (Lord Krishna   , Bg. 2.40) When contemplating whether or not to take a new job, there is an inherent risk to consider. Say, for instance, that while working at a job that we are comfortably situated in, another offer comes in. This new place is enticing, as it has certain things that we are looking for. One option is to quit the current job and accept the new position. Ah, but there is a risk. What if we fail at the new job? What if we are unable to perform the tasks to the satisfaction of the proprietor? What if we hate the new work environment? What if the people who promised us the job actually go back on their word and give the position to someone else, after we have quit our current job? In these instances we would become total losers, left without any job. This same risk accompanies every kind of material behavior, those activities where God is not the beneficiary. Indeed, loss is concomitant with gain, as there must be death after birth. The journey through life in the human form involves acquiring certain things and losing others. No property is stable; nothing is permanently retained in our name. With devotional service   , the aim is to purify consciousness, which is an aspect of our identity that stays with us from life to life, as it determined the circumstances of our present birth and the type of nature we assumed. It is seen that some children are born quiet and peaceful, while others are clever, naughty and a general pain in the behind. Some people are born with the ability to adapt to new situations and incorporate the information they acquire very quickly, while others are slow learners and take a long time to complete their tasks. These tendencies are inherited from the previous life, where consciousness was shaped through activity. With bhakti-yoga, the gains never diminish. Even if we devote much time to studying the Vedas and hearing about Krishna and then simultaneously renounce our other obligations, there is never any risk of complete destruction. If the plunge into spiritual life should result in failure, if somehow we break out of the divine consciousness, we get to start off from the same point in the next life. This benefit is present only in bhakti-yoga and not any other endeavor. You leave a construction site with the job half-finished and you have essentially failed. You may have occupied your time with constructive behavior, but otherwise there is no lasting benefit to the work you put in. In bhakti, there is at least the seed of devotion to God remaining inside of you, just waiting to be watered again through the association of saints and the submissive hearing of Krishna-katha, or talks about the Supreme Lord in His personal form. With guaranteed progress, there is no reason not to at least give a little time to spiritual life. The saints know that in the current age of Kali conditions in society are not conducive to following spiritual life with any determination. Houses where the names of the Supreme Lord are chanted regularly in earnest are difficult to find, and it seems that even the prominent spiritualists have ulterior motives. Not to fear, though, for the holy name is all we need to connect with God in a mood of love. The recommendation of chanting the holy names in the maha-mantra daily for at least sixteen rounds on a set of japa beads proves to be our best friend, the most effective weapon in our attack against the thick fog of nescience. Just chant the holy names on a regular basis, even if you think it’s an activity that will cause you to lose out on other obligations, and see what effect it has. Changing from one job to another can leave you without any, but making Krishna the beneficiary of your activities instead of material nature will always make you a winner in the mind, for the Supreme Lord will comfortably rest within your thoughts holding His flute and dazzling your consciousness with His sweet vision. In Closing: At your current jobsite you’re comfortable, Smooth sailing, no signs of any trouble. Then comes an offer from the outside, To work at new job, give up old and tried. Now you have a tough decision to make, Stay where you are or new offer to take. Trouble when new offer should go south, A job at either place you are left without. Only in bhakti-yoga is there not any risk, Following Krishna brings success that is brisk.

உங்கள் கணினிக்கு எனது புத்தாண்டுப் பரிசு

எவ்ளோ நாளைக்குத் தான் உங்களுக்கே நான் பரிசு கொடுக்கிறது?  உங்க எல்லாரோட நட்பையும் இணைக்கிற ஒரு பாலமா இருக்கிற உங்க கணினிக்கு எனது புத்தாண்டுப்  பரிசு...  யோசிக்க எல்லாம் வேண்டாம் காசெல்லாம் கேட்க மாட்டேன் இலவசம் தான்.. ஹீ ஹீ ஹீ ... பாராட்டணும்ன்னு நினைக்கிறவங்க பதிலோட நிறுத்திக்கணும்  திரும்ப எனக்கு நீங்க கூரியர்ல பரிசு அனுப்புறது எல்லாம் எனக்கு பிடிக்காது....