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Solar power plant: steam quality questions

by CUaero12
Tags: plant, power, quality, solar, steam
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CUaero12
#1
Jul5-11, 03:06 PM
P: 1
Hey guys, I'm an engineer working on the design of a small start up solar power plant. The solar power plant will operate using "solar troughs" instead of the traditional photovoltaic cells. In these systems water is the working fluid and sunlight is focused from a solar reflector onto a pipe containing the water. Here is an image of a typical solar trough:



The water is pumped through a large field of these parabolic solar troughs until it is superheated steam that is suitable to run through a turbine.

Right now I'm working on the basic heat transfer problem regarding the solar collector field and have run into a bit of a roadblock.

The water will be entering the field at 110 degrees Fahrenheit and needs to exit the field at 550 degrees Fahrenheit. I'm trying to compute how long the pipe in the field needs to be to achieve this temperature. I've got most of it down except the transitional part between liquid and steam. When the water starts to boil, the temperature will remain constant until all of the fluid is vaporized. During this time the quality of the steam will change and the volume of the fluid will be composed of liquid and vapor. I'm trying to iterate through and see how much length of field it will take before the water is completely vaporized (the quality is 100%) but am having trouble figuring out how to compute this. I want to iterate through using a while loop (while the quality of the fluid is less than 100%, keep adding one meter length of pipe to the field until this is achieved) but am stuck on figuring out exactly how.

Does anyone have any ideas or insight into the problem? Let me know if more information about the problem is needed, I can provide more details and numbers if necessary (the mass flow rate through the field is known as well as the heat of vaporization, etc.)
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edgepflow
#2
Jul5-11, 08:02 PM
P: 688
Have you been able to figure out your heat transfer rate per unit length: Q / L ? If not, I can make some suggestions.

If so, the energy required to vaporize the water is: Qvap = mdot * hfg

where,

Qvap = heat required for vaporization
mdot = mass flow rate of water / steam
hfg = latent heat of vaporization (look up in steam tables)

Qvap = heat required for vaporization

and you can solve for length of pipe to transfer Qvap.


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