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[技术] 廉价滴太阳能热空气集热器制作

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发表于 2013-11-20 08:19:02 | 显示全部楼层 |阅读模式
找到的这分资料:廉价滴太阳能热空气集热器制作,非常好做,用一些废易拉罐就可以,转来与大家分享.

太阳能热空气集热器
DIY solar air heating collectors are one of the better solar projects. They are easy to build, cheap to build, and offer a very quick payback on the cost of the materials to build them. They also offer a huge saving over equivalent commercially made collectors.
Two of the more popular designs are the pop can collector and screen absorber collector. The pop can collector uses columns of ordinary aluminum soda pop cans with the ends cut out. The sun shines on the black painted pop cans heating them, and air flowing through the inside of the can columns picks up the heat and delivers it to the room. The screen collector uses 2 or 3 layers of ordinary black window insect screen as the absorber. The sun shines on the screen and heats it, and the air flowing through the screen picks up the heat and delivers it to the room.

太阳能热空气集热器制作

太阳能热空气集热器制作

This page gives a rundown on building each of the two collectors, and also compares the heat output of the two collectors in a side by side test of the two. The two collectors were built specifically for this side by side test and are identical in size, box construction and glazing -- only the absorbers are different.
Note that for ease of testing these collectors were built small (2 ft by 3 ft), but for real heating you want to go much larger. A 4ft by 8 ft collector is about the minimum to contribute some real heat, and larger is better


 楼主| 发表于 2013-11-20 08:19:46 | 显示全部楼层

太阳能热空气集热器制作

太阳能热空气集热器制作

The test collectors: Pop can collector on left and screen collector on right
Collector Basics
There is a lot of not so good information out there on what makes a good solar air heating collector design, so I thought I would include a little info on solar air collector physics, what makes for a good design, and how one can measure and compare collectors accurately. If you are an old hand at this stuff, just skip this section.
How do collectors work, and what makes a good design?
On just about all solar thermal collectors, the sun shines through the glazing, and hits the collector absorber heating it. The air flows through the inlet and over or inside or through the absorber picking up heat as it goes. This heated air then flows out the collector outlet and into the room being heated. The main differences between air heating collector designs have to do with how the air flows over the absorber.
In full sun, the incoming solar energy is about 1000 watts per square meter of collector area. Of this 1000 watts/sm, about 10% is absorbed or reflected by the glazing and never gets to the absorber. Of the remaining solar energy, about 95% is absorbed by the absorber. So, for the 1000 watts/sm that arrive at the collector face, about 850 watts/sm end up actually heating up the absorber.
Most of this 850 w/sm that made it into the absorber end up going down one of two paths:: one part is picked up by the air flowing through the collector and ends up heating the room, and the other part ends up being lost out the glazing. The job of the collector designer is to maximize the first part and minimize the 2nd part.
 楼主| 发表于 2013-11-20 08:20:32 | 显示全部楼层

The heat output the collector can be calculated as:
Heat Output = (Temperature Rise)(Airflow)(air density)(specific heat of air)
Temperature rise is the increase in air temperature from the inlet to the outlet of the collector -- often around 50 to 60F for well designed collectors. For example, air might enter at 65F and exit at 120F.
Airflow is the volume of air flowing through the collector expressed in cubic ft per minute (cfm) -- often around 3 cfm/sqft of collector area for well designed collectors.
Air density and Specific Heat are physical properties of air that you don't really have any control over -- air density is 0.075 lbs per cubic foot under standard conditions, and the Specific Heat of air is about 0.24 BTU per lb per degree F.
Its very important to note that the heat output depends on BOTH the Temperature Rise and the Airflow. Many of the videos out there talk only about temperature rise as though that is all that mattered, when it fact its only half the story. It is quite common for a collector to have a very high temperature rise and have a low heat output because the airflow is much to low.
There is a tendency to think that things that increase the collector temperature rise will improve the efficiency of the collector, but, in general, the most efficient collectors will have a temperature rise that is just enough to be used for space heating and an airflow that is relatively large. The reason for this goes back to that portion of the heat that the absorber takes in that ends of being lost out the collector glazing. You want to minimize those glazing losses, and an important way to do that is to keep the absorber temperature as low as possible -- the cooler the absorber runs, the less heat will be lost out the glazing. A way to keep the absorber cooler while extracting the same amount of energy from it is more airflow.
On solar air heating collectors, it is relatively easy to get most of the suns energy into the collector absorber. The difficult part of air collector design is getting the heat transferred from the absorber into the air. Air is a low density material with a low specific heat, and that makes the heat transfer from absorber to air difficult. The things that tend to help in the transfer of heat from the absorber to the air stream are a high volume of airflow, a lot of absorber area, and good and even airflow of high velocity air over the full surface of the absorber. All of these things help to efficiently pick up heat from the absorber, and to keep the absorber at a cooler temperature so that losses out the glazing are minimized.
The good characteristics of the pop can collector from an efficiency point of view are that it has a lot of absorber area (about Pi times what a flat plate would have), and it has a mixed flow of relatively high velocity air through he can columns. The good characteristics of the screen collector are that the thousands of strands of screen wire provide a lot of screen to air heat transfer area, and that the inlet and exit vents are arranged such that the airflow is required to pass through the screen to get from the inlet to the outlet.
While there are no hard and fast rules, a temperature rise through the collector of about 50 to 60F works well in that is is warm enough to feel warm coming out of a heater vent. If the room temperature is 65F, than the collector outlet temperature will be about 120F. Moving air that is much cooler than this will not feel warm. Going for a temperature rise greater than 60F usually means a hotter collector absorber and increased heat loss out the glazing.
Airflow through the collector of around 3 cfm per sqft of collector area for a collector with a well designed absorber is about right. More airflow would make the collector more efficient, but it also increases noise and fan power, and may lower the temperature rise to the point where the air does not feel warm to people for space heating. The about 3 cfm per sqft of absorbers seems to be a good compromise between efficiency and the other factors.
Measuring Performance
Even though solar air heating collectors have been around a long time, it seems there are still significant design improvements that can be made to both performance and cost/labor of construction. This seems like a very interesting and worthwhile area to work on.
If you do want to work on an improved air collector design you must have a way to measure performance so you know if the changes you are making actually improve efficiency or not. Its fine to speculate on what might help, but if you don't measure the actual performance carefully, you really don't know if a change helps or hurts performance. Right now, when you look across Youtube etc., it seems like we have a lot of speculation and not a lot of careful measurement going on. Its not that difficult or expensive to do side by side tests of collector designs and to measure the performance.
Measuring the absolute performance of a collector is difficult. A collectors performance depends on its design, but is also influenced by solar intensity, ambient temperature, wind and collector orientation -- all things that vary quite a bit from day to day and even minute to minute. One way to get around most of the variations is to test a baseline or reference collector side by side with the collector you are making changes to. If the two collectors are side by side, then they see the same ambient temperature, the same solar intensity and the same wind. If you make a change to your test collector and it performs better relative to the reference collector, than you can be sure the change you made was a good one.
 楼主| 发表于 2013-11-20 08:20:55 | 显示全部楼层
With side by side collectors, you need only measure the inlet and outlet temperatures of each collector and the airflow through each collector. Changes that increase the product of the airflow times the temperature rise improve the heat output of the collector -- its as simple as that. The test setup section below shows a more detailed example of a side by side test. If you set up the two collectors so that you can adjust the airflow such that both collectors receive the same airflow, then the collector with the greatest temperature rise is the winner.
The details on testing below show one set of insturments that allow accurate testing on a fairly small budget. For other low cost instrumentation ideas... But, just buying the cheapest instruments on eaby or at the local store and not doing anything to check their calibration is unlikely to give accurate results.
Building the Pop Can Collector
I'm just going to cover building the pop can and screen absorbers and not say much about the collector box and glazing, as these are the same for both, and are well covered elsewhere. There are some links at the end that also cover building both types of collectors.
The steps in building the pop can absorber -- I've tried to use techniques that don't require much in the way of special tools:
1. Collect the cans.
If you drink pop or beer, this is not really a problem, but if you don't, you need to find a source of intact cans. Recycling places are a place to start. Some civic organizations collect pop cans for recycling and may be happy to let you sort through for the intact ones and sell them to you. You may have friends who will save cans for you.
2. Clean the cans.
The cans typically have some residue and need to be cleaned. Most people just use soapy water for this. Be sure to rinse the soap off.
3. Cut the ends out of the cans.
This requires more skill and effort than it might seem at first. Various ways have been worked out to do this -- I'll show the way I did it, but the links at the end provide other methods.
Cutting out the bottom of the cans:
I tried several methods, and ended up using a spade style wood drilling bit. The bit is 1 1/2 inch diameter. I mounted an electric drill in a woodworking vice, chucked the spade bit, and clamped the trigger on. Then with gloves and safety glasses on take a can in both hands, center it on the space bit, and slowly advance the can into the turning spade bit. This take a little practice, but is not that difficult. But, it is not something for kids to try. There are sharp edges and if the bit catches the can, it can rip it out of your hands easily.
The spade bit I bought (an Irwin) had little spurs out at the edges of the bit. These tended to catch the can suddenly and make the cutting process hard to control, so I ground down the spurs. This makes the process more controllable. A lot of spur bits do not have these spurs at all.

 楼主| 发表于 2013-11-20 08:22:47 | 显示全部楼层

太阳能热空气集热器制作

太阳能热空气集热器制作


1.5 inch spade bit.

太阳能热空气集热器制作

太阳能热空气集热器制作


Drilling can bottom out with spade bit.

太阳能热空气集热器制作

太阳能热空气集热器制作


The finished hole.
 楼主| 发表于 2013-11-20 08:23:50 | 显示全部楼层
Another method I tried that worked quite well was to use a belt sander to basically sand off the bottom of the can. The can is not flat on the bottom, but has a ridge around it a little ways in from the outer diameter of the can. The idea is to just sand through this ridge, at which time the bottom of the can falls out. Its very fast and controllable. The down side is that it actually takes off a bit of the surface where you will later be gluing the cans together. I decided to go with the spur bit as its almost as fast and leaves a good gluing surface, and does not require any special tools.

太阳能热空气集热器制作

太阳能热空气集热器制作


Using gloves, push the can down on the the belt
using the guard to keep the can steady and vertical.
Very fast.

太阳能热空气集热器制作

太阳能热空气集热器制作

 楼主| 发表于 2013-11-20 08:24:18 | 显示全部楼层
4. Cutting out the top of the cans:
First, break the tabs off.
To open the top up, I just used tin snips to make radial cuts in the top of the pop can. Each cut starts at the drinking hole and extends outward toward the can rim. I then bent the resulting pieces out toward can walls by first pushing the can down on a pipe, and then bending the pieces out with a gloved hand.

太阳能热空气集热器制作

太阳能热空气集热器制作


Snap the pull tabs off.

太阳能热空气集热器制作

太阳能热空气集热器制作


Make radial cuts with tin snips.
 楼主| 发表于 2013-11-20 08:27:11 | 显示全部楼层

太阳能热空气集热器制作

太阳能热空气集热器制作


Push the can down onto a pipe to start
bending the cut pieces in.

太阳能热空气集热器制作

太阳能热空气集热器制作


Finish bending the pieces in with
a gloved hand. Be careful of
sharp edges.

太阳能热空气集热器制作

太阳能热空气集热器制作

Again, there are several ways to do this, and the links at the end show some of them. Greg worked out a way to use 55 mm hole saw to cut the lids out.
There may be some advantage to trying to bend the radial pieces remaining after the tin snip cuts in such a way as to cause more mixing of the air, but this would increase the pressure drop through he collector.
 楼主| 发表于 2013-11-20 08:27:49 | 显示全部楼层

5. Gluing the can columns.
To glue the cans into straight columns you need some kind of form to place the cans in while the glue sets. I used a couple of boards nailed together to form a "V". Greg used a length of PVC pipe that was sawed in half.

太阳能热空气集热器制作

太阳能热空气集热器制作


A form for stacking cans while the glue cures.

太阳能热空气集热器制作

太阳能热空气集热器制作



 楼主| 发表于 2013-11-20 08:28:38 | 显示全部楼层
Two cans glued together using silicone caulk
Put the first can in the form with the top pointing up, apply a bead of glue around the bottom of the 2nd can and press it down onto the first can. Repeat this process until all the cans for one can column have been glued. Place a weight on the top of the column to maintain a little pressure while the glue sets.
For glue, I used silicone caulk. Its a good high temperature material that remains a bit flexible and does not stink or outgas after its initial cure.
Keep in mind that the cans must not only be glued together but also sealed so that air does not leak out between the can joints and into the collector box.
6. Preparing the cans columns for painting:
The can surfaces should be prepared for painting. I just wiped them down with acetone, but a more careful preparation may be in order to insure the paint stays well attached over the long haul. Some of the links at the end may have better preparation methods.

太阳能热空气集热器制作

太阳能热空气集热器制作

7. Build the manifolds:
There are manifolds along the top and bottom of the collector that distribute the air evenly to each can column. The manifold wall also holds the can columns securely in position.
I used thin plywood for the manifold wall. A 2 3/8 inch hole saw turned out to be a good fit for the cans to nest into at both the top and bottom. Its important to take some care in laying out the holes that accept the cans to get an even spacing. I taped the two manifold boards together and drilled both at the same time -- this only works because the 2 3/8th hole size fits both the top and the bottom of the cans snugly.

太阳能热空气集热器制作

太阳能热空气集热器制作

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