HEAT TRANSFER - CHILLED WATER SYSTEM

Q=h x A x delta T

h=convective heat transfer coeficient of steel=6.5W/m2-deg

A= area=pi x d x l=3.14 x 0.2 x 1 (considering 1 meter length) = 0.628 m2

so Q=6.5 x 0.628 x (35-30)

Q= 20.41 Watt/meter.

regards

jignesh142

"h" can not be treated as function of steel. as it depends on the fluid, velocity of fluid, flow pattern, mounting arragement, nusselt number, prandlt number and many more parameters..

An alternative to manually calculating the energy loss in BTU/hr is a software called 3E Plus.

Download the 3E Plus software from the following US Department of Energy web site:

http://www1.eere.energy.gov/industry/bestpractices/software.html

This tool will allow you to model energy loss, and determine optimum insulation thickness. It has a huge database of insulation types, so you will find one that is best suited for your application, and will assist you in coming up with an economic justification for adding insulation.

In the USA, there are incentives available (depending on region) to help offset the cost of insulation. Contact your local utilities to see if they offer a similar program.

Good luck!

Forget about energy loss, you need to handle the problem of condensation if there is no insulation.

Hi ,

In cold insulation there is no concept called Heat loss and only heat gain from atmosphere is there . So if ur not providing any insulation in ur chilled water pipe line u 'll have a heat gain of 57.86 w/m . If a minimum thickness of insulation (25 mm ) will increase ur efficiency of the system 89.78 % considering the facts below .

Data is furnished below :

Process temp: 25 deg c

Ave ambient temperature :35 deg c

Relative humidity :44.9%

Dewpoint : 20.2 deg c .

Some of the contributors mentioned already condensation: the heat added to you chilled water line will be consisting of three factors:

• Direct conduction/convection due to contact with warmer air. Depending on the wind speed you will have conduction (wind) or convection (no wind)
• Radiation: the heat from surrounding objects and the sun will be absorbed by you pipe. absorbtion rate depending on surface material (forget colour)
• condensation: humidity in the air will condensate and give it's heat to your fluid. This will be the biggest "loss". Depending on the wind speed and humidity level.

Succes with your cheap solution, nature will be happy with it.

I would like to make a comment with respect to the 1st point:

wind or no wind there is a "convection" since convection means "taken with" and heat transfer in a fluid environment is generated by the heating/cooling of layers which due to different reasons move and take or bring energy with. Conduction is ONLY in solids or in fluid layers which are so relatively thin that a fluid flow cannot occur. There is also what is called free convection which occurs only due to the density differences generated by heating or cooling. It is quite surprising that you affirm that in case of "no wind" there is convection and in case of "wind" there is conduction. I would suggest you have a look to the books since giving an answer is also a responsibility of correctness.

The rest is qualitatively correct it would have been interesting to mention that if conduction or convection is proportional to the temp diff radiation is proportional to a higher power.

I do not completely agree with your statment on conduction: it does happen in gasses to. (Air is known to be an insulator but even insulators do conduct, H₂ is a good conductor)

I agree that I somehow maluse the word to differentiate the wind/no wind situation. In case of wind the thicknes of the insulating air layer is depending on the wind speed. (above 8.7m/sec it is nearly gone)

In a no wind situation the thickness is depending on dT.

The two situations need complete different approaches to arrive at the solution.

In temperature loss calculations we use the word convection for the heat driven effect of air displacement.