Heat Exchanger

Hello chandu krishnamurthi,

You do not advise the mirror size, nor the area in which your stated temperatures exist.

If you can advise those things, along with your location, and the number of sunshine hours annually, then calculations may commence.

It is possible, that you have a high temperature area which is quite small, thus not much quantity of useful heat may be extracted.

Reply please with........

Data is incomplete to tell details but idea of having hot air does not seem good it is better to have a pipeline at the focal line carrying fluid with good specific heat eg.water, therm. oil etc and use it for some other purpose.

But air for drying wud reqire a huge system and wont b economical.

Chandu if you recall heat rises, therefore, if you allow about 25% to rise via a copper tube you can roast above it ,as long as the roasting oven is built to recyle its heat, as in a multiple chicken roasting ovens,that can cook up to 20 chickens at one time.As for the fan assist, if you build next to it a solar powered electric generator or buy one and place it next to it,then you can generate enough electricity to power a convection fan of about 30 cfm capacity, which also recirculate the heat several times around the chickens or other meats,that need roasting such as lamb roasts.Be careful not to burn your fingers, when you are placing the copper tube in the solar heater, because,others before you have lost all their fingers trying to hold onto it, when they were locate the best place to get the heat from.

The heat will be used for roasting varities of vegetable edible seeds used in food industries like ground nut and a number of spice seeds like chillies etc. I am not aware of multiple chicken roasting oven you have referred to. More information on this will be useful for what we have on our mind.

with regards and thanks

chandu

Instal a copper pipe coil at the focas point and blow air through it, the air that comes out of the other end will be very hot indeed!

Spencer.

Copper pipe is a good idea, but black anodized aluminium might be better. Also, you need a large surface area on the inside of the heating enclosure to allow heat transfer to the air. I'm not sure what the best way to construct this will be. The idea of recirculating the air using convection is a good one. Beyond that I don't know.

Hi ca1icOcat.

Here is one way to increase the heating surface with a minimal of volume.

The heater should be a flat rectangular box, this box should have an array of internal and external vanes in line with the airflow, the space between the vanes should not excede 1mm. As I used to work in Stirling engine design this was always a solution to impart more heat to the working gas or air inside the engine.

Too much volume within the heating element will mean less heat to be transfered to the moving air, too small a volume will result in excesive fluid friction!

Spencer.

Dear Scapolie

Your suggestion of using vanes opens very interesting possibilities. I have begun working on it with my team.

With regards and thanks

chandu

hello spencer, right on idea! i tied using the idea of liquid inside a old refigeration unit coil as a heated liquid, that didn twork to well my next step was to take the idea of using the reverse of the heat coil fins used to wrap around the ouside of a stove pipe as heat exchangers , a strip of aluminum flex cable was pop rivetted on to the INSIDE of the stove pipe, problem arose when the air inside the aluminum became superheated much as a doubled over steam jacket will, the pipe got too hot to handle i didn't think of that happening until the finger tips and palms got a bit of a burn. i like the idea you put out, but why wouldnt a 4' long 3 sided garden plant starting reflector with a inward bulge to its centre not work as well? it took a bit of work but i made the dent using a flatter and a plywood swaging pattern to dish in the reflectors centre. the air wasn't too hot but it sure as hell made a batch of sodabread a as fast as the house oven did and with no electric fire heating the kitchen up.

someone one who speaks work - WOW!

Dear Scapolie

You are right it works quite well and the next move is to improve on this basic idea to design a proto type with improved performance. any suggestions?

chandu

Show its sketch w/ dimensions.

Hi Chandu

Go to www.otherpower.com, a demonstration of a dish is there. The temp. is higher, ignites wood in 5 sec.. I would use stainless black piping, we did a heat exchanger for gray waste wates for recup. heat from bath, dish washer and cloth washer. (dryer not yet) , we used copper, but it was gone after a year, many factors to consider, especially chemicals, but if you have heat and water (for your dryer, which i use for drying my hockey and other swety smelly equipment ...) , you will likely have long term problems with copper.

For roasting, i have to think about it, for my boat, i was considering this but shoot the sun rays on stone or metal plate.

One may even make ice with this heat, look for propane refrigerators (do it yourself) and with amonia, it is amazing, silent too.

Kepp us informed !

Dear Yellow Cat

Thanks for your tips and information. Will keep you informed.

With regards and thanks

Chandu

Dear Chandu,

You can explore cooking oil (oils) and the focal point will be quite small so hotter, but beware of fire with oil. Heavy water could be of use ... na, forget that. Cooking oil was my (still is) first choice for heat transferts from the parab. . The parab. even works on a hazy day. My design is evolving toward a half pipe shape , i need to double use the area also for rain water collector and roof structure. Wood 1/8" and epoxies are perfect for creating that monster. So far i find that foil air bubbles insulation is the light easy to use material for heat storage reservoir. I hear someone from Vancouver discovered a credit card thin insulation R20. For space applications.

Later

YC

Dear Chandu Krishnamurthi, I am not sure of the correct spelling but "Namasta and good fortune." One possibility that I have not seen in this discussion is the use of ceramic tile as a "near focal point" heat source. Almost focusing the light onto the tile will give a large output and the tile's melting point (some nearly 5000C) will allow its use for some time before replacement is necessary.

Cordially yours Dragon

Dear Dragonsfarm

Your suggestions opens up very interesting possibilities. We have begun some planning experiments on your suggestion with the team,

with regards and thanks

chandu

i wudnt like to spoil party but air as u know is not at all good for heat transfer so if u want to use maximum heat conc at focal area either u use some thing in tubes which makes good coeff of heat tran. making complexity by increasing area is costly but as i see u r reluctant to dry things so it is better to have a chamber similar to solar cooker where u directly concentrate heat on the subject.

ceramic or firestove bricks are good. although, on tiles, watch for heat contrasts fractures, ie rain water, snow, hail, bricks will be a better choice. what if the focal point was a high performance mirror and the dish would be a sort of fat donut, alowing the light beam LB, to go in the same direction as the sun light SL. that would create more possibilities and added safety. remember, if it is illegal to target a plane with a laser, one would not like to have a LB directed accidently into a plane corridor, so the accidental LB has to be very weak. that's not mentionning birds and children. then i would shoot the LB onto a metal plate (not only aluminum) could be an old large cooking pan bottom s up that will spread the heat to cover for instance a large chicken turning for delicious bbq.

As for the mirror type LBM (light beam mirror) in metal ? , the outer (upper) surface has to be treated for rain water (including hail, snow etc) with an air space and a cover. for abovementionned reasons. sun traking system is easy to do, but can fail ... wind will not affect much the LB as long as the parab. is built properly. you might want to call james bond from an early movie , the vilain had a powerfull parabolica ... i dont remember the name of the movie. hmhmhm

In the plastic industry, I use copper-beryllium as heat transfer medium. It has been the best material I have found that is not precious metal.

Hi David,

Would copper-ber. resist in a salty enviro ? Mylar mirror could be used in the light beam mirror ? i use Rehau's Raupex o2 for my floor heating tubing. It resists heat and cold even freeze. The o2 barrier is good for pumps etc. So far , in plastics, it is the most interesting product i found for heat and cold transfer. It comes in 1000 ft length so minimal joints. 10 yrs and pleased even at 160 °f . Thanks for the info. perhaps C-B could be of use. Besides SSteel.

YC

hi yellowcat.

I have no apparent problems using a water softener to prevent lime built up on my CuBe heat exchangers. Which mean that a great deal of salt goes trough the piping 24/6 years after years. However there are several grades of CuBe! I believe that the lower the hardness on the Rockwell scale C.is the most conductive of all. If my memory does not fail me, on a scale of 200, steel was rated 7 and CuBe was rated 160. That fact should be seriously considered. However I have actually a problem with a CuBe mold where the cavity side surface became rough but not on the core side surface, so I discard salt has the cause.The same water runs also in my molds cooling circuits and without a water softener, lime would built up very fast and clog them.

issa David

hi Issa David

Thanks for the info, in another project, a gray water heat recup system, we had to use SS because copper went in one year only. For this later heat exchanger project, it will be either sea water or fresh water or a mix of both.

I will design and come back later on this.

thanks

YC

hello yellowcat

I understand, your copper heat exchanger went in one year wen exposed to salt.

I am surprised, because most if not all heat exchanger in the plastic industry are made out of copper tubing, and are subject to water softener salty water and from time to time to muriatic acid to dissolve the limestone built up. Also batches of wine before it turns into acetic acid is heated in copper tank, to produce rhum.Furthermore bronze which was recommended to me once to weld a CuBe part is widely used in the marine industry,such as propellers etc..,( I did not pursue the experiment)

So I strongly recommend you to contact a copper-beryllium supplier and expose your problem. They are the best and most reliable sources for the properties of their products. I know though that they sell their products in tubes form. You will also gain knowledge about their standard products before starting the design.