CaptainPanic

My hair caught fire. Why do you ask?

That's because the water flow can be minimal. No need to recirculate it to induce turbulence. Anyway, at 0.011 liter/s, or 0.000011 m3/s, and a diameter of 2.5 inch (0.0635 cm diameter, area perpendicular to flow = 0.0031 m2), your linear velocity will be 0.0035 m/s. Your Reynolds number (to see if it is turbulent or not) is: [math]\mathrm{Re} = {{\rho {\bold \mathrm v} L} \over {\mu}} = {{1000 \cdot {0.0035} \cdot 0.0635} \over {0.001}} = 220[/math] ... which to make a long story short means it will be laminar flow. There will probably be some turbulence around inlets and outlets though. But the lack of turbulence will be no problem. You have all kinds of other problems I already mentioned.

As I explained briefly in my previous post: the heat transfer resistance is in the air around the copper pipe, not the water inside it. So, the answer to your question: it doesn't really matter. Just make the water flow a little with a fan ("forced convection" is your scientific term of the day). Balance the water flow to the heat you need to absorb with the water (i.e. the computer's power). Make sure the water flows so much that it has heated up noticeably, but not too much. 10 degrees Celsius or so... this is a designer's decision. I'll leave it to you. How much power is your computer? Peak power of computers can be in the order of magnitude of 500 W (= 500 J/s). That's probably the CPU and also the video card all running at max. power. If you allow the water to heat by 10 degrees, and you assume that you remove ALL the heat with the water (which is not true), and you assume your computer is always running at max. power (again not true), your total water flow should be: P = F*Cp*dT or: F = P/(Cp*dT)=500/(4180*10) = 0.011 liter/s, or 0.7 liter/minute (about 0.19 gallon/minute). In reality, you will probably need less water, or heat up your water less. Again, doing fancy stuff to the water of the heat exchanger will not make it noticeably more efficient. A fan on the outside will though. I'm sorry not to give you your answer... but I cannot change heat transfer phenomena.

From your other thread, I understand that you want to cool the computer processor (and in fact, the whole computer case) with a cooling element. I.e. put something cold into the computer, so it will absorb the heat from the air inside the computer. Correct? Dedicated systems for computers You're about to spend some money anyway, so my primary advice would be to go to a computer store, and ask them how you can improve cooling. There are dedicated systems for computers! That's better than tinkering with ammonia (toxic, smelly!) inside your living room. Google for [Liquid Cooling Processor], and you will instantly find solutions. My google tells me it can be as cheap as $57, which is probably the same as what you're looking at with your plans. Shop well, and find it even cheaper. Water condensation Secondly, you risk condensation of water (moisture from air) on the copper cooling tube you are about to make. That can drip onto your computer hardware. Water close to electronic hardware is a bad idea. Also, leakage is a risk, but you may be a good plumber so I will not comment on that any more than this. Cool most where it's needed. I am assuming that the air in the computer case can easily get to 50 degrees Celsius, otherwise you wouldn't be worried. But the processors get a LOT warmer - they have their own small fans and radiators. Apply your cooling directly to the processor, and solve your problem at the root. There exist dedicated liquid coolers for processors. Delta T (temperature difference) You are proposing to have a second heat exchanger to cool the coolant, like any refrigerator. But why not simply bubble some air through the hot water? Then you can leave out the ammonia. Some water will evaporate, and that will give cooling. Ok, your coolant will be around 20-30 degrees Celsius, instead of 10 or lower. That only means you need to increase your water flow by 50% or so (just an order of magnitude estimate - no calculation). If you're building it yourself, and you don't really know what you're doing: simple is best. Btw, you probably want to calculate how much air you need. The heat exchange bottleneck The heat will travel the following path: The bulk of the air --> a thin stagnant layer of air around the cooler a thin stagnant layer of air around the cooler --> the copper wall of the cooler the copper wall of the cooler --> a thin stagnant layer of water inside the cooler a thin stagnant layer of water inside the cooler --> the bulk of the water Without even calculating, I can guess that the bottleneck of your heat exchanger is the thin stagnant layer of AIR around the heat exchanger. And that will get worse as the copper pipe gets dusty/dirty. Making the water turbulent will reduce the thickness of the thin stagnant layer of water inside the heat exchanger, but that's not the bottleneck. To make this thing more efficient, you need a fan on the outside, blowing hot air against your heat exchanger. Concluding If this is just a hobby project on an old PC, then go for it. It's fun to play with heat transfer, although it can be difficult. If you're actually trying to improve a good (expensive?) PC, then don't. Go for the professional solutions at your local computer-hardware store. I'm not a computer expert, but 3.4 GHz sounds like it's not a really old crappy PC. I wouldn't play with water near such a PC.

I totally agree with hypervalent_iodine that the Khan Academy is excellent. It's good for almost all ages and levels. I think that 8-year-olds will be able to learn something from it, as well as 80-year-olds. They have maths, physics and chemistry (and possibly more). It has helped me to refresh some topics that I should have learned at university but that I never use and mostly forgot. They have 10-20 minute lectures in the format of a Youtube movie. Somehow, watching a movie is so much more relaxing than reading a book. You actually absorb the same amount of information, but with less effort. Totally worth anyone's time.

If you don't like the speculations forum, don't go there. Simple.

I did not leave it out. I mentioned religion in my post. In the Netherlands, you marry before the state in one ceremony at town hall, and before God in another ceremony in a church. It's a different guy doing the ceremony, at a different moment and possibly even a different group of people attending. And many people don't even marry in a church anymore. And as I wrote, we're talking about law (the plans of a presidential candidate). And although Santorum is more religious than the pope, he is not a religious clergyman, and he is not being elected to say anything about religion. He's trying to get into office to influence federal law. I know that Santorum would like nothing more than turning the USA into a religious country... but even in the US, religion is somewhat separated from the state, isn't it? At least, it still is. Do the Americans employ priests to marry people before the state and god at the same time??? I don't think so. I bet you also have 2 different ceremonies. So, how relevant is a religion when you discuss the state version of marriage? What, you're surprised that politicians try to focus our attention on irrelevant matters, while passing laws on important matters without much debate?

If I follow the thread, then you propose a multi-story greenhouse in Eritrea? The idea of a multi-story greenhouse assumes an abundantly available cheap sustainable form of energy. That assumption is false in modern day Eritrea, which is one of the poorest countries in the world.

Lacking any better way to express my surprise, I will say: Holy crap That was a long, and very educational post. Thanks, Ophiolite. I didn't know there was that much information available. Pardon me for being so ignorant in this field, but I really thought that the majority of paleontologists were digging for dino bones. I knew that microorganisms had formed rocks, and I knew that this happened and happens (it still goes on) on a global scale. But I didn't know this was still visible to us in those rocks. I thought those rocks were, well, rocky at a molecular level. When you take some piece of rock, what can you see? You said that the fossils are mostly complete... And what about my other comment in the later post? In the last 400,000 years, we have had quite severe fluctuations in the earth's temperature, which may have moved entire ecosystems by thousands of kilometers north/south and probably kicked numerous animals into extinction? Is there evidence of that in the past too? (I'm not in a rush, even though my 1st sentence of this last paragraph might sound impatient).

It could be done, but as you correctly say, it would take hundreds to thousands of years. Not a good business plan then. Answer to the other question: yes, some sea weeds are edible. And that's a plant which is already suited for living and growing in the sea.

I'm gonna share my opinion too. I stress that it's an opinion rant. I think gay marriages are ok. A marriage is formal paperwork to say two people belong to each other, and share all kinds of burdens of life. Sex is no argument. Child adoption is no argument. Equal rights is an argument. I'll explain: Sex is allowed before marriage anyway. When the bride and groom kiss, that's certainly not their first kiss, unless it's an arranged marriage and the couple have never met before. The idea of no-sex-before-marriage in Western society was dropped 2 generations ago, although history long before that is full of bastard sons and daughters, and even the bible has a story about a woman who supposedly had no sex before becoming pregnant (it was a miracle). And Greeks (those guys who invented democracy and science) had gay sex too. So, not being married isn't gonna stop gays having sex. We have more than 2 millenia of history to prove that. And therefore I dismiss sex as an argument in the discussion... which doesn't mean I like to have sex with another guy. I think it's disgusting. But I do enjoy watching certain websites on the interwebs where 2 girls... you get the picture. Not very relevant, I think. So, what is a marriage? A marriage is a personal deal between two people, that they belong to each other. They share some burdens in life, and the society acknowledges that and lets them marry to make it official. I see it simply as a bit of paperwork. Bureaucracy. And given the amount of divorces and mistakes made in marriages, so do most people people. So, I do not object the gay people having the same paperwork. All people are equal for the law, so why not all couples too. I read in this thread that gay marriage could be a slippery slope, allowing it to be extended to more than two people. And indeed, I see no reason why it shouldn't. Who cares? For many people, a relation indicates who you live your life with, and who you have sex with. And in both cases, the act of living together, and sharing a bed together with more than two people is ok by many standards. Most people will shrug, and say "not my cuppa tea, but I don't care". Then why do we care when people sign a piece of paper to make it official? As far as I can see, that leaves the tricky bit. Child adoption. And it is vitally important to note that gay marriage does not equate to automatic child adoption. The adoption centres apparently have their own criteria too. Marriage is only 1 checkbox in a really long list of the adoption centres. Adopting a kid takes years, and several metric tons of paperwork. Because gays will never have kids by themselves (nature prevents that), they will always be the most screened parents in the world. Straight couples can make a baby on a drunk night, but you just don't end up at an adoption centre on a drunk night. So, I am assuming that adoption centres screen a couple thoroughly, and that they will filter out all imbalanced couples. They will filter out a couple who together produce more testosteron than a platoon of soldiers on a night out. And they will filter out a couple who will encourage any adopted sons to play only with My Little Pony ( )... Assuming basically that the adoption centres do their job, they will ensure that a child is brought up in a healthy environment. So, the gay marriage is rather irrelevant. In fact, given the amount of douchbags in this world, I think straight couples should be screened before being allowed to have kids too. But from what I read in the news, Santorum is more religious than the pope himself, so religion cannot be ignored. But all I have to say about religion is: you can marry before the church in a separate ceremony. The church can make its own rules, and I couldn't care less. So, they can ban gays from marrying before god just like they can excommunicate someone who is in favor of planned parenthood. I can summarize my point on religion in a few words: it should be separate from the state. And with that, it's irrelevant to the discussion of gay marriages. So, I cannot find a reasonable argument against gay marriage. So, let them marry. Finally, I want to add a comment about the gays: When I look at a gay couple, I see either two guys or two girls, and I expect that they will have sex... And it's expecially the sex that is a good one to joke about. And that is just different than a straigth couple, no matter which way you turn it. And I will make jokes behind their backs, and possibly in their face. It's all in good humour, although it might hurt them. I think some gays can be really sensitive, but that is not my problem. If you're gonna do it in someone else's behind, I will laugh at that. I respect you as a human being, but I laugh at your hobby.

Hey! Congratulations! What's B. Tech.? And how is it relevant in this discussion? (And am I talking to a human, or a spam bot)?

You're confusing me with what you want. In the 1st post, you give the impression you want to talk about realistic and practical things. Things we can build right now if we had enough money and motivation. But in another post (#19), you talk about future tech that we might develop some day. The difference between "practical, right now", and "future tech, some day", is that right now we have limited energy, and some day, we might have almost infinite energy. And that makes a huge difference when you talk about getting stuff into orbit! If you want to get a lot of stuff into orbit, you need a LOT of energy. Low Earch Orbit is about 7.8 km/s, so the kinetic energy for 1 kg is about 30 MJ/kg (excluding all practical issues - in current rocket technology you need to spend a lot more energy). So, what's the topic of the thread? Practical orbital city with real technology (but unlimited financial means)? Or future technology, bound only by the laws of physics (in other words: sci-fi)?

I did not even notice any link? What's the point of spamming in such a way? Or did you guys remove a link before I even replied?

But there may be catastropes that will not show in fossil records. Diseases, changes in predator behavior, climate changes (see below) can all cause an accelerated evolution. And one change might trigger another change too. For example, a certain behavior can cause big changes in a prey animal. Dolphins and orcas are known to invent new hunting methods. That will affect the prey soon enough as the most successful prey animals will have offspring. Of course, I wasn't talking about the global warming of this modern time. I talked about the ice ages and interglacial periods though. (I'll try to be more specific next time, to avoid confusion). We have evidence that the temperature on earth fluctuated over the last 400,000 years with a maximum peak-to-peak amplitude of 10 degrees Celsius. The differences in temperature happened in as little as 5000 years, and caused mass migrations, and possibly extinctions, population booms. For example, we might think a certain animal lived in a vast area, but it actually might have migrated due to a changing climate while it lived in a much more narrow climate band.

Sure we can improve our technology. And yes, we must always do more research. And yes, the tides and waves are a sustainable form of energy, and we would do well to use it. But we cannot expect more energy from the tides than the theoretical maximum. The calculation I showed is the theoretical max. There is nothing more to be expected. All we can do is: 1. Make sure we convert nearly 100% of that energy into a useful form (electricity). 2. Make that as cheap as possible.

Hello! I thought that I would be pointing you in the right direction (or, rather, point you all away from wrong directions). If you think it is better to spend months building a dream (which won't work), then don't come to a science forum. If you want to build something that does work, then please take some advice from engineers who know what they are talking about. When people plan to build something which is obviously not going to work, why should I keep quiet? When someone is hungry, you can either give him a fish, or teach him to fish... but you are asking me to let him starve, and find out how to fish by himself. I do not agree with that kind of thinking. You can follow classes and do research - that's always a good idea. But maybe there are some people around who can save you a lot of time by giving some advice. So far, the majority of the people in this thread have shown no idea of the power that is needed, or how to control the power output (making it only on or off will not work). I'm sorry if I only pointy out problems, without solving them. But I just do not have any interest in building such rollerskates myself. That doesn't mean I cannot reply to this thread.

What's the difference between the two that my questions make sense to one but not to the other? And aren't the majority of paleontologists also vetebrate paleontologists? (Wiki tells me that vetebrate means backbone, which includes fish, reptiles, amphibians and mammals). I know they aren't the largest group of animals in terms of number of species, but they included for a long time the largest animals alive. Anyway, I don't really get your point (which says more about my knowledge about the topic than about your point, probably). What? Did I do something wrong? The majority of people interested in engineering (which is my field of work) like fast cars, jet fighters or sci-fi. I don't complain, even through the majority of engineers do far more relevant things for our society. Dinosaurs are cool because they are the jet fighters of paleontology. In pop culture they are 15 meter tall chickens with teeth and a morning temper (which is probably wrong). They were just an example. Let's forget about the dinosaurs. If I understand the meaning of a diachronous horizon (google doesn't give a simple definition), then it is related to the geograpical location? I am not talking about the geographical vicinity of fossil findings. I am talking about how experts can learn about factors that would severely change a population and eco-system (if any). The examples of triceratops and t-rex were just an example. I should have written "random animal A" and "random animal B", both of which fossils have been found in the same period of several million years. I already said: we forget about the dinos. But one of my points was that you cannot distinguish between different millenia that occurred several million years ago (or can we?). How many clearly distinguishable layers are there? So, how do we know that the ecology in the past did not go through severe changes of eco systems, which would mean that two species found at one site, in the same layer of soil did not live in the same ecosystem? I know that without a good reason to assume that such drastic changes in an ecosystem occurred, there is no reason to assume it did... except that as we look at increasingly recent periods (which also become shorter in duration) we can also distinguish more details and changes. Isn't it reasonable to assume that there have always been a lot of changes? I will refrain from giving any specific examples of such changes or how it might be affecting an ecosystem because I do not want to be attacked on my choice of example, but on the general idea. Is it not supported by the evidence because there's evidence against it, or because there is nothing to support it? p.s. Thanks for having the patience to go through this.

Waves and the tides just do not contain much energy. Every wave and tidal generator will take up a lot of room. I also don't like it, but it seems mother nature ignores our opinions on the matter. If you reserve 1 square kilometer (1,000,000 m2) of space for your tidal generator, and the difference between high tide and low tide is 2 meters, your energy output would be: Mass of water: 1,000,000 (m2) * 2 (m) * 1000 (kg/m3) = 2 * 10^9 kg Average height difference: 1 m Gravity: 9.81 m/s2 -------------------------------------------------------- x Energy = m*g*h = 19.6 GJ And you have that much energy twice per day: 39.4 GJ/day. Expressed in Watts (Watt = J/s), that is 454 kW, which is the same as about 100 households. And that's assuming 100% conversion of the potential energy of the water into electricity. It's a very small amount of energy. Same for waves.

I dunno actually. I guess I have the name CaptainPanic because I typed it into the box where you enter a nickname when you sign up, and it was still free? p.s. Tres Juicy, I think you have an English accent in your French even when you type it. Here's a link to "très". Of course, your name will always sound like you say it sounds, so I'll read it with the English accent from now on

Current technology to live high in the sky is called a skyscraper. The highest is over 800 m tall. If you really want to float, I would propose to use zeppelin/airship technology. At least you're not constantly spending energy to stay up, because that is done by buoyancy. Anything else is ridiculously impractical. Still, becoming airborne is not gonna solve any of the problems you mention. Overpopulation If you want to solve "overpopulation", becoming airborne solves nothing unless you get into orbit. If you want to create housing by thinking upwards, regular apartment buildings do the job quite well. If you want to create more land to grow food, you might as well build a bridge (still stationary). With both a flying thing or a bridge, someone will be in your shadow. Launch spacecraft Altitude is not the bottleneck for launching spacecraft. It's velocity. Launching from high up in the sky will save a spacecraft a miniscule amount of fuel - so little that it's totally not worth it. The reason that some companies and NASA want to launch from an airplane is that they give it some initial velocity. Those 900 km/h make a difference. But I wouldn't want to live in a city with flies at 900 km/hm because it would make it quite impractical to go outside for some fresh air. Weather stations and observatories Why bring the whole city up with them? Why not build dedicated weather stations and observatories without the city? Coincidentally, that is exactly what is done already. Weather balloons report what's going on high up in the atmosphere, and Hubble/Kepler, as well as many observatories on mountains use the thinner atmosphere or complete lack of atmosphere to get a good picture. Making a city fly is pointless. Sorry that I do not share you enthusiasm about it.

It tells me "You need to log in to read this article". I hate that. Why do they want my email? The answer: So, I dismiss your reference because it's going to spam me. Sorry.

This. Totally agree. Scientists shouldn't be so arrogant to think that what they do is really complicated only because they are not able to explain it to someone else. I think it is quite common to be very good at science, and very bad at communicating. (I'm not saying it's a majority among scientists, but it's a significant group). Getting to the point is something most people (including scientists) cannot do. I know scientists who aren't able to tell a stranger the quickest way to the local shopping center. They know the way themselves, but will not be able to transfer that knowledge to a stranger in a limited amount of time.

Maybe... maybe not. But YOU are in a position to vote for who makes the decisions in Washington. Figure out who's making this law, and do not vote for them. SOPA is moronic. I'm not living in the USA, so I just have to hope that America doesn't destroy the internet. I have no democratic power, but I might well be a victim if some publishing company with a commercial encyclopedia decides to gain back some market shares by shutting down wikipedia. From an economic standpoint, any publishing company with encyclopedias is stupid not to at least try. And SOPA pretty much guarantees success.

In order to make a change, you fist need to describe the problem. Reading your opening post, I think we can check that box. Then next, I guess you need a plan what to do next? A goal? And if you want our advice (I guess you do, since you came to a forum) we need some boundary conditions. Are you gonna stay with your wife, or not? Do you want to meet all your other relatives on a regular basis or not? In other words: how drastic can the changes in your life be? Personally, I would recommend to get out of there for a while. Alone. Move to a different country if you can, or at least to a new town. A place where people do not know you, and don't expect a certain behavior from you. It gives you a completely fresh start. Start searching for a job relatively far away from home. Living somewhere else will make you comfortable with the person you think you really are (yes, that sounds funny). You actually should get used to you. Build some self-confidence. If you've been away for long enough, you hopefully built up enough self-confidence so that even moving back to the old place should not make you fall back to your old role. You do not have to completely break with your past, but make sure you have plenty of time away from it. If your facebook or whatever social internet terror you might use is cluttered with stuff you'd rather forget, then make an effort to clean it up before moving to a new place. Make sure you're not constantly reminded of the loser you used to be. I've moved a couple of times in my life, and once you get past the bureaucratic issues (can be horrible), it's a good feeling to make a fresh start. Everybody develops, but also everybody seems to expect the same behavior from other people - and that can cause conflicts when people outgrow their current environment. It takes a little time to get used to changes in friends/relatives, and for some it's completely impossible to accept changes in others. So, moving away removes these expectations, and removes some boundaries for you to change. I admit it can be daunting to live in a place where you don't know anyone, and it takes quite a bit of initiative to get a group of friends... and I'm not even talking about the trouble to get a job. It's a big step, but it can be totally worth it. I recommend to search for a relatively dynamic environment, because it's easier to become friends with other newcomers than with people who have already established a group of friends or a family.