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# Solar Heat

08/05/2011 7:48 PM

When an object with flat surface is exposed to direct sun light, assume the object surface is black:

1. what is the steady state temperature of the object?

2. If this object in put inside a glass box, what is the steady state temperature of the object ?

CAn any one show the theory , better still calculation ?

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#1

### Re: Solar Heat

08/05/2011 8:01 PM

Are you really an engineer?

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#2

### Re: Solar Heat

08/05/2011 8:05 PM

why the question? Is there anything wrong with my question?

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#59

### Re: Solar Heat

08/08/2011 6:31 PM

Isn't the engineer the guy that wrecks train?

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#62

### Re: Solar Heat

08/09/2011 8:50 AM

Are you one, or did you graduate from Wiki, Google and a garage?

I am sure you do not know the answer but to show your omniscience you make these disparaging comments. It shows only your ignorance and contempt to all other opinions and queries. I also notice that you are generally the first to come up with your puerile diatribes.

To learn one needs humility first.

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#63

### Re: Solar Heat

08/09/2011 9:21 AM

I see you haven't met lyn then?

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#3

### Re: Solar Heat

08/05/2011 9:43 PM

1. It would depend on the latitude, altitude, time of day, ambient temperature, angle of incidence, and how black "black" is....

2. It would further depend on how thick and what type the glass is, and if it is say a Fresnel lens.

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#5

### Re: Solar Heat

08/05/2011 9:57 PM

1. It will be good of you if you could show the formula and method, use variable for sun irradiation power , ambient tempt,etc.

2. I meant normal glass,assume the most normal condition, eg 5~6 mm glass

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#6

### Re: Solar Heat

08/05/2011 10:45 PM

I don't think there is any such thing as "the formula" for this. Maybe a bunch of formulas, each with limiting conditions that may be hard to decide which are important. As Mikerho suggests, this is probably better measured than calculated.

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#7

### Re: Solar Heat

08/05/2011 11:42 PM

It is always better to have a first cut rough estimation/calculation first before you fab a real set up.

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#8

### Re: Solar Heat

08/05/2011 11:54 PM

It is always better to have a first cut rough estimation/calculation first before you fab a real set up.

However, if you don't know where to start, it can be a real time-waster.

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#10

### Re: Solar Heat

08/06/2011 12:54 AM

However, if you don't know where to start, it can be a real time-waster.

You don't where to start, that's why you ask.

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#41

### Re: Solar Heat

08/07/2011 8:58 AM

Sometimes, it's better and quicker to do a quick test...

90 degrees C if you want a figure, but there are so many variables which will be cooling it, distance between the glass and the surface, wind etc.
Maybe if you tell us the real application we can point you in the right direction.
No calculations were harmed in the process of making these... solar hot water panels
Del

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#15

### Re: Solar Heat

08/06/2011 8:23 AM

As a start, power from the sun, above atmosphere, = 1.4kW/m2.

Using 1.0kW/m2 to allow for atmospheric absorption, and assuming your object is in a vacuum, it reaches equilibrium temp when radiated heat = incoming heat. Radiated heat calculated using Stefan-Boltzmann constant 5.673*10-8 watt*m-2*degK-4, I get temp 364Â°K = 91Â°C.

This seems surprisingly low as even in UK in the open air, metal objects left in the sun can easily get too hot to touch. Anybody comment?

If the object is in the air, it also loses heat by convection so reaches lower temp. For natural convection, heat loss varies as ΔT 1.25, at a guess something like 3 watt*m-2*ΔT 1.25. That's 500 watt*m-2 for a domestic radiator with water temp 80Â°C, room temp 20Â°C, ΔT 60Â°C. You can use that to get an estimate.

Cheers.....Codey

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#16

### Re: Solar Heat

08/06/2011 10:31 AM

Hi Codey,

Your answer provides the closest I was hoping. GA for you. Thanks !

My experience of leaving a metal object under direct sun will be too hot to touch, so, your estimation of 91 Deg C is not too far.

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#17

### Re: Solar Heat

08/06/2011 11:06 AM

Thanks bravo88.

I should have written 3 watt*m-2*ΔT -1.25, but I'm sure you know what I meant.

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#33

### Re: Solar Heat

08/07/2011 3:37 AM

When it comes to a closed box, assume the air inside and inner glass surface temps are the same as the plate (close enough). Heat leaves the box by conduction through the glass. Heat loss rate is

U *ΔT *A /h , where:

U = conductivity of glass, Watts/ meter of thickness /sq meters of glass area /deg C

ΔT = temperature difference thru glass, deg C

A = area of glass, sq meters

h = thickness of glass, meters

Apply Stefan-Boltzmann & convection formulae to radiate heat off outside glass surface.

This is one of those problems where you use an iteration technique:

1) Assume what the temperature of the plate will be

2) Do a glass conduction calculation using this temperature, assuming outside glass surface temp is ambient (for starters) to determine heat loss by glass conduction

3) Do a Stefan-Boltzmann calc etc, (assuming outside glass surface temp = plate temp (for starters)) to determine heat loss from glass to ambient air

4)Compare 2) and 3) to see if a) outside glass surface temp is same in both cases b) heat output is the same in both cases. Also check that c) sun heat in = heat out

5) Recalculate with new values of plate temperature and outside glass surface temperature, until you home in on the solution.

This is an easy problem using a spreadsheet.

You could also use Nusselt/Grashof/Prandtl convection loss formulae for convection. My reference, Eastop & McConkey, Applied Thermodynamics for Engineering Technologists, Longman 3rd ed 1978, pp 681-684 (natural convection). Sorry, I don't have a reference for the tables needed.

I was surprised there was significant loss by radiation, but until you do the calc ...

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#55

### Re: Solar Heat

08/08/2011 9:50 AM

91 C is just a few of your centigrade celsius Fancy degrees below boiling point of water, so I say your estimate is congruent with your experience- one can be scalded in a second at temps of approximately 68 C; see graph in primitive US Fahrenheit degrees here: http://www.accuratebuilding.com/services/legal/charts/hot_water_burn_scalding_graph.html

Yours and Dels were good answers, Though I would add to the original poster that the idea of steady state is a false notion as the insolation changes in cloudy conditions as well as over the diurnal cycle.

Finally, Insulation in the collector and conductivity of materials used for enclosure (metal vs Glass) play a major role in minimizing losses of heat from the system.

Here is an article I wrote back in 1977 about my first efforts at constructing a solar collector:

http://www.motherearthnews.com/Do-It-Yourself/1977-11-01/Recycle-a-Refrigerator-into-a-Solar-Water-Heater.aspx

No where near as sexy as Del's, but it was a "hands on them thats doin" project back in the 1970's.

Unless you put in a means to stop it, (check valve) or covers over plates, these will reverse and thermosiphon overnight, reradiating all that heat back into space.

Milo

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#56

### Re: Solar Heat

08/08/2011 1:38 PM

I can imagine a comedy sketch involving check valves, along the lines of 'whos on first'.
Have you got the valves?
Check, valves.
Have you got the check valves?
...heck you can make it up yourself from here on in.
Del

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#57

### Re: Solar Heat

08/08/2011 1:46 PM

Czech

Tee hee.

I think on your side of the pond these are called "valves?"

Milo

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#58

### Re: Solar Heat

08/08/2011 3:35 PM

Yup...
Double check...valve.

Del

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#4

### Re: Solar Heat

08/05/2011 9:53 PM

You are going to have to make more assumptions to reasonably manage the math and model the problem.

Do you know that there are three primary mechanisms of heat transfer? What are they? What is the main mechanism in your scenario?

The easiest way by far, would to obtain the data empirically by setting up a series of experiments.

The answers to both 1. and 2. are: "It depends." (on a lot of things)

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#9

### Re: Solar Heat

08/06/2011 12:03 AM

As I recall, dark green absorbed more heat than black.

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#11

### Re: Solar Heat

08/06/2011 1:05 AM

It depends on what the temperature is.

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#12

### Re: Solar Heat

08/06/2011 1:07 AM

So far, this thread is a self-fulfilling prophecy.

Just get a blackboard, a window pane, a thermometer, and a sunny day--and measure.

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#13

### Re: Solar Heat

08/06/2011 2:08 AM

A global experiment! Have certain subscribed persons from all over the globe submit data to a dedicated server.

Data to be recorded:

• Latitude
• Longitude
• Time of day
• Ambient temperature
• Local atmospheric pressure
• Ambient relative humidity
• Current local wind speed.
• Degree of Atmospheric Clarity (OK, I made that one up, but I think it's important).
• Make and model of recording instruments.
• Name and ID number of the technician(s) in charge of instruments and data recording.

We can then analyze the data and get plots that look like target practice silhouettes having been shot with a 12-gauge shotgun using ellipsoid pure lead shot from 30 feet away.

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#14

### Re: Solar Heat

08/06/2011 2:59 AM

1. Minimum temperature of the object is equal to the ambient temperature at steady state in case of only conduction heat transfer. But here more heat transfer is due to absorption of solar radiation, so temperature of the object will be be higher than ambient. Objects at any temperature emit heat in the form of infrared radiation and its more for more hot bodies. So the steady state temperature of the object is the point of equilibrium where rate of heat absorption and radiation back to atomosphere is equal.

2. Steady state temperature inside a glass box is higher than the previous one because in this case emmediate contact is air inside the glass wich is at much higher temprature than ambient. Here, steady state temperature will depend on two equilibriums, (i) object and air inside the glass & (ii) glass and ambient.

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#18

### Re: Solar Heat

08/06/2011 10:32 PM

You will need to supply variables in order to get a solution. I thought of at least 15 in the last 60 seconds. So, although I don't want to further disrespect you, your question does not seem to be very well engineered.

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#21

### Re: Solar Heat

08/06/2011 10:59 PM

To suggest your solution, you need not have the fixed values for the variables, just use variables in your method or formulae, and also you can always make real world assumptions. What is important is the method , not the exact numerical answer.

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#19

### Re: Solar Heat

08/06/2011 10:34 PM

try here www.seris.nus.edu.sg

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#23

### Re: Solar Heat

08/06/2011 11:16 PM

Thanks, good link, right at my home ground ! And do you believe it, it is just about 1 km away from my previous office last year !

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#20

### Re: Solar Heat

08/06/2011 10:45 PM

Solar collectors use a vacuum, a special absorbent but not reradiating coating on the heat pipe tube, which looks black. I have personally seen more than 270 F in a synthetic oil system used to drive an ammonia refrigerating system for an off the grid house.

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#22

### Re: Solar Heat

08/06/2011 11:05 PM

If you can get 270 F in solar collector, that's is very impressive and useful. Does it use a concentrating mirror or focus lens or Fresnel lens ?

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#24

### Re: Solar Heat

08/06/2011 11:24 PM

We frequently achieve 350 degrees F in solar collectors, if we fail to provide coolant flow. What is the steady state temperature of the black surface of the collector? It is only steady state when there are no variables.

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#25

### Re: Solar Heat

08/06/2011 11:42 PM

Hi PFR,

The solar collector you used, does it use parabolic mirror or concentrating lens, or is it just plain black surface.

By the way, in my earlier thread , by the word variable, I meant mathematical symbols.

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#42

### Re: Solar Heat

08/07/2011 9:25 AM

We measured 130ÂºC at Bangalore, India (13Âº Latitude) during summer, mid day on a matte black painted aluminium surface inside glass covered box. This was without any active collection of energy. Just an equilibrium value measured by a thermometer.

We also could get about 800W/ square meter area into water passing through pipes welded under this. Through the day the total wattage averaged about 2.5 to 3 KWHr/Sq.Mtr.

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#44

### Re: Solar Heat

08/07/2011 11:34 AM

Hi bioramani,

Double GA for you!

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#51

### Re: Solar Heat

08/07/2011 7:30 PM

It uses heat pipe technology, with mechanical heat transfer from copper to coolant. We use evacuated tube collectors, not because they achieve higher efficiency at converting solar insolation to high temperatures, versus some other technologies, but because the usefulness of the heat energy is the primary design goal. As was very accurately pointed out in the magnifying glass example, energy density, in addition to energy utilization, are much more important factors in designing a useful solar collector. Here is a key. Removing energy from a collector impacts all of the functions inherent in it's usefulness as an energy plant.

I point this out, because the it appears that the answers to your question about the basic solar properties of an absorbent material are being interpreted as criteria for solar design. The replies have been very good, and I thank all of you who contributed.

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#26

### Re: Solar Heat

08/07/2011 12:13 AM

Hi Bravo,

The calculations are all here in other posts, but as a theoretical exercise, if your object is completely thermally insulated (i.e. radiation can get in, no energy can get out) then exposed to solar radiation it can reach the surface temperature of the sun (about 5700K). This is your theoretical maximum.

Obviously it won't get there - you will radiate heat more and more quickly away from the plate as the plate itself heats up. The steady state is simply the point where what goes in balances what comes out - and this depends on all sorts of things - what the object is made of, whether it's in a vacuum, what conduction / convection channels are available to it etc.

Concentrating thermal technolocgy works by concentrating the sun's radiation onto a small area collector to minimise heat loss (i.e. there is not much area to shed the heat away) - so lots goes in compared to the amount that leaves. They don't get to the theoretical maximum, but a few thousand degrees is not unheard of.

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#28

### Re: Solar Heat

08/07/2011 12:57 AM

Hi RobertOz,

My question 2, if I use a glass box to house the solar collector, how much more effective it is.

If a method can be found to collect more sun energy without using parabolic mirror or lens, it will be very useful.

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#31

### Re: Solar Heat

08/07/2011 2:37 AM

The glass box is used to limit convection (not conduction or radiation - these will still occur with the glass box in place). To limit conduction you must isolate the plate from other solids/liquids using insulation. Presumably you want to heat some water or something so you would want to maximise the conduction of heat leaving the plate and entering the water, but prevent conduction to everything else. (note that convection is really a special case of conduction - it's just that the substance being conducted to is a fluid, so it drifts off, made bouyant with the heat).

A vacuum-filled glass box will stop all convection - an air-filled glass box will prevent some convection as the air next to the plate will be warmer, and heat flow is governed by temperature difference - in warm air the plate will lose less of its energy to the air than it will to cold air.

But as the air heats up, the glass box heats up and the glass box itself begins to radiate / convect / conduct more heat out of the system, so without a vacuum in the box, you will still have in-box convection and then heat loss through the hot glass.

However without doing any calculations, I'd expect putting the glass box in place will make an enormous difference to the heat of the plate. A double glazed box even more so. An evacuated glass box even more still. (Don't use a radiation-blocking glass though - the sunlight won't get in!).

Essentially the purpose of the glass box is to put a pocket of warmer air around the plate, limiting its ability to shed heat to the air.

As the temperature of the plate goes up, the radiation-loss increases to the fourth power ... so at high temperatures your glass box will play a much smaller role, since radiation will take over as the dominant transfer mode.

This link might help - look under "Gray Bodies and Emissivity Coefficients" to get a sense of what radiation losses you'll see at various temperatures. You won't know the emissivity coefficient for your plate though - so you'll have to guess - everything else in the formula you will be able to just plug in (google the value for the Stefan Boltzmann constant). Make sure you do everything in Kelvin (temp in Kelvin = temp in Celsius + 273).

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#32

### Re: Solar Heat

08/07/2011 3:12 AM

GA. RabertzOz. But I feel glass box with air may be better compared to vacuum because glass box is acting like a green house, trapping & reflecting back the infrared radiation from plate which will be converted back to heat. Air inside the glass box will hold the heat and transfer to plate by conduction and convection. Please clarify, if I am wrong.

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#34

### Re: Solar Heat

08/07/2011 4:48 AM

and GA to your post (above)!

Hmmm... it's going to come down to the calculations... but I tend to fall on the side of wanting to remove the convection currents by making a vacuum. I'd also tend to worry that heating the air heats the glass - then the glass begins losing large amounts of heat to the atmosphere on the other side (hence the double glazing argument).

It might be a case where there is a limiting temperature - below Tlim the radiation transfer is low and the convection is the main problem, but above Tlim and the greenhouse effect kicks in and limits the effects of radiation and you're better off with the air... I'm not sure - but nice logic!

By the way - these things are often non-intuitive - for instance as you add lagging (insulation) to a pipe you effectively increase the surface area. In certain (very specific) cases the increase in radiation and convection heat loss caused by adding the insulation can more than offset the thermal resistance of the insulation... so a pipe losing 100W per metre length uninsulated may lose 110W per metre length once insulated. Wouldn't that leave you scratching your head??

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#35

### Re: Solar Heat

08/07/2011 5:05 AM

An interesting point. This may be theoretically possible, but I suspect only if the insulating material is a poor insulator. (I haven't tried any sample numbers yet.)

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#38

### Re: Solar Heat

08/07/2011 5:35 AM

I remember running the numbers once... can't remember the exact results, but it turned out to only come into play for quite small diameters... so in microfluidics or chemistry-lab stuff, or heat loss along electric cables the effect was quite real - even for good insulators... if you plotted heat loss against insulation thickness it went up for a while before dropping back down after some critical thickness was reached. Very non-intuitive...

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#36

### Re: Solar Heat

08/07/2011 5:29 AM

Hi Bravo,

Just re-reading your question 2... imagine you have a magnifying glass. You focus the sun onto a piece of paper and in one second it starts to burn (i.e. you have temperature in excess of Farenheit 451). Now imagine the magnifying glass has a 50x magnification - i.e. it concentrates some area of sunlight onto an area 50 times smaller. This smaller bit is the bit that burns - let's say that is one square millimetre.

If you leave the piece of wood in the sun, that same square millimetre will absorb exactly the same amount of energy in 50 seconds as it did in 1 second under the magnifier. The only reason it doesn't burn without the magnifying glass is because the energy has had longer to dissipate back out of the wood (or deeper into it).

So you're not gaining anything by concentrating except higher temperatures - you don't get more energy, you just put it into a smaller area. This is very useful if you want to boil the water to create steam, but if you just want to use the water to heat your domestic hot water, you a far better off with a good flat plate, because the lower temperatures allow you to put more of the available energy into your water rather than risk radiating it back into space, which you do as soon as you move to extreme temperatures.

So for your black plate example, if you want to collect the energy for domestic purposes, you actually want lower temperatures not higher.

If you want to boil water to make electricity, you really have to use a concentrator in order to reach the temperatures you need... but in doing so you will have almost certainly reduced your efficiency while increasing your temperature, by vastly increasing the outward radiation.

So for pure efficiency, go for a glass-covered matte black plate (or a thermo-siphon) and keep your temperatures near to the required end-user temperature (say 60C for domestic hot water).

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#37

### Re: Solar Heat

08/07/2011 5:34 AM

a

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#39

### Re: Solar Heat

08/07/2011 5:56 AM

ok - then my bet would be you want to find a surface that is well-designed for accepting solar radiation but well-designed to not radiate it out again, mount it on a very good insulator and stick it in a glass box, surrounded by a second glass box. Evacuate the space between the two glass boxes (i.e. put your plate in a double-glazed glass box). I reckon that is about the highest temperature you could get with low-tech apparatus... let us know when you get some measurements!

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#40

### Re: Solar Heat

08/07/2011 7:19 AM

Yes, that is also my conclusion , much appreciate your input !

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#60

### Re: Solar Heat

08/08/2011 11:44 PM

Problem with glass cover: About 4% of incident energy is reflected back before it gets to the solar array. Add another sheet of glass and there is a further loss of 4% of 96%.

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#61

### Re: Solar Heat

08/08/2011 11:49 PM

good point, but it is worth it if it prevent more loss from conduction.

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#29

### Re: Solar Heat

08/07/2011 1:45 AM

Exactly my point, though I didn't elaborate as you have done in more detail.

GA!

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#27

### Re: Solar Heat

08/07/2011 12:29 AM
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#30

### Re: Solar Heat

08/07/2011 1:52 AM

In addition to the amount of incoming radiation from the sun (which varies) the steady state temperature will depend on the properties of the object as well as its surroundings. You have not provided sufficient information allow a definitive answer. However there have already been given answers that represent practical situations that may resemble yours.

In the branch of physics referred to as thermodynamics. In the basic university courses on that subject there is introduced the concept of the control volume, whose utility for calculation purposes derives from the fundamental idea of conservation of energy. This forms the foundation theory for solution of your problem. The idea is that your 3 dimensional object with its black flat surface comprises a body whose average temperature at the black surface exposed to solar energy constitutes a control volume.

I think we can presume your interest is in the maximum temperature that volume of material will reach under conditions of solar energy input. And we'll assume that condition is reached when the heat radiated out of the body is the same as the solar energy absorbed. And steady state means that the body has a constant temperature and therefore a zero change in heat content

So we are looking at a "control volume" holding a constant amount thermal energy at some temperature which permits the solar heat into the volume (total solar heat radiation exposure minus amount of radiation reflected back into space.) to equal the sum of all heat that leaves the volume by radiation, conduction and convection. This so called "heat transfer" is usually dealt with as rates of heat flow of which there are numerous calculation methodologies available from simple to complex.

You have methods of determining the solar energy flux. What you don't know yet is how much of that will be reflected back from the black surface. It may be more than you think.

Also what you don't know is how much heat is radiated from the total surface including the black part that faces the sun. In addition there will be some heat conducted to the body's mounting points and to any air in contact or heat transfer media. If there is air flowing over the body a third path of heat transfer will be by convection. At steady state the sum of these three will equal the net amount of solar flux absorbed by the black surface.

If your application is some kind of solar panel then you'll find plenty of info both here and on the rest of the internet as well as the many books on DIY solar power. If it is something new and creative you may have to get into some basic texts on heat transfer for the simple equations covering conduction and radiation and data on related properties of various materials. If you have to get into convection the math gets more complicated due to the complexity of fluid flow but there are lots of simple approximations as well as practical test methods once you get hardware together.

You can learn a lot from folks who have experimented with and built solar devices and a little bit of basic engineering will help you filter and adapt the info you receive to fit your own purposes.

Some here in this forum may want to suggest specific links or books to aid you. Not that heat transfer calculations though generally simple can be a real swamp when it comes to converting units, metric to English and orders of magnitude. You'll need to spend a lot of time rechecking your calculations to make sure you've got them right until you get real familiar with the drill. The nice thing about working in this area of engineering is that most of the time you are dealing with temperature measurement and the hardware for that is cheap and easy to get especially with the advent of DVM's with thermocouple readers and inexpensive noncontact IR thermometers.

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#43

### Re: Solar Heat

08/07/2011 11:12 AM

When I am faced with an intractable problem like this, I find it helpful to just make a simple model and take measurments. All variables of construction and material and initial and ambient conditions will resolve themselves into the measurement I make of my model. Then, I change a material or add one etc. and measure again.
Sometimes a working model is better than a theory or a formula. It may even be faster and sometimes a whole lot more accurate because all of the variables are present, including the ones you couldn't know or account for. Also, the materials and conditions are easily changed and remeasured.
My own tests have shown that an aluminum plate with High-temp flat-black paint, in a box with Argon or Nitrogen or both will get pretty hot. But the same plate in a box with saline at saturation under glass will get even hotter, but take longer to heat up. Both tests assume insulation of the box and the plate is suspended within the space of the box.
A multi-layer saline pond will accumulate an enormous amount of heat, and is one of the better ideas for solar collecting.

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#45

### Re: Solar Heat

08/07/2011 11:44 AM

Ref your test, do you mean the plate is immersed in saline solution contained in the box ? Or do you mean there is a sandwitched layer of saline solution within the glass?

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#48

### Re: Solar Heat

08/07/2011 1:13 PM

The plate and the glass have saline in between. Got to coat the aluminum very well or anodize it to do this though...

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#46

### Re: Solar Heat

08/07/2011 11:56 AM

I would set up an experiment using some different types of models ,one glass box one plastic box different shades of black flat surfaces etc. and at each one place a garden thermometer.and as far as getting the math right how about using Prism Math Maybe GM or some one of the big auto makers has some data on this hot box question.ds.

I was convinced collecting energy was about reflecting sun and black,the color Absorbs heat and makes a glass and metal enclosed auto hotter, but not sure heat is always energy.I wonder if you could use glass that is a partial mirror/ reflective and then using a black background behind it and maybe more mirror behind that like a prism or wall of mirrors . Some antique mirrors look as though they have a lead backing.
Maybe while youre gathering the data you could find out what panels send out cooling shade cover,wouldnt that would be great for this heat wave or solar storm or whatever it is.Nothing is impossible.

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#49

### Re: Solar Heat

08/07/2011 1:17 PM

The saline does something like that with the mirrors. It has a very high refractive index that prevents the waveform from coming back out at the same angle it went in, so it becomes trapped! Heat builds up considerably, and from the right angle, the saline looks black to the eye because there is so little return/reflection from that direction. Layers of different saturated salines deposited one on top of the other create a very dark bottom...

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#47

### Re: Solar Heat

08/07/2011 12:17 PM

Have a look at some of Gaiatech's threads, he covers much of this ground

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#50

### Re: Solar Heat

08/07/2011 2:44 PM

I've run into a situation similar to the saline immersion design with double glazed insulated windows where the outer glass was impact glass with the lexan sandwiched/bonded to two layers of clear glass and the inside glass being Low-E clear glazing with the space being Argon filled.

The outer impact glass let the full spectrum in minus UV which the lexan layer filtered out and the Low-E inner glass reflected the heat but it became trapped between the layers and heated up the whole window to about double outside ambient temperature even though the HVAC inside the house was set at 70F.

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#52

### Re: Solar Heat

08/07/2011 7:49 PM

Please stand by. I am trying to get my black cat flat enough to fit in between the storm windows.It was tough enough getting the thermometer to stay where I placed it.

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#53

### Re: Solar Heat

08/07/2011 8:42 PM

ooohhh

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#54

### Re: Solar Heat

08/08/2011 1:13 AM

Yes Dear,

You are lucky to get very good and accurate reply to your first question, specially by Code master GURU.

Your second question: If the object is put in a glass box, definitely the heat loses are reduced and steady temperature is ~120 degree cels. All the boundary conditions remains the same as for your first question.

Again if you put 2 glass covers on top and insulate the object on the sides and bottom, in this case steady temperature is ~140 degree cels. Further if you keep on increasing the no of glass covers on top, it will result in lowering the temp because the input radiation will be reduced.

LUV-nps

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