Solar Radiation/Heat Transfer Effect on Water Filled Steel Pipe

[Ecorp]

Could anyone please help me find a source/aid in solving this problem?

I have to meet the CA water quality standard that will not allow treated effluent to exceed 5F of the average stream temp. which will receive treated water.

I will have a 36" o.d. steel duct. pipe that is approx. 3 miles long transport treated water, above the ground surface, assuming influent water temp. of 68F. The flow will be approx. 9600gpm (assume pipe is always full) and the ambient air temp (I will assume worse case scenario) will be 110F. The pipe will be subject to direct solar radiation on top half of pipe and my version of the computer program "qpipe" forces me into a subterrainian condition. How can I figure the heat losses/increases either over the 3 mile pipe length or per mile?

What if I use HDPE pipe of same o.d? (Would use of HDPE be way too costly compared to steel?)

Regards,

 

[KernOily]

You could start with a VERY basic heat transfer analysis. The max mean solar incident radiation is around 940 W/m2 at the equator, if memory serves. You could use that as a conservative starting point. A text on solar engineering will give you the derating factors for your actual altitude. You might find that info in the ASHRAE handbook also.

You can use the 3E insulation program (get it off the web from

http://www.naima.com)

to get the emissivity value of the pipe.

For the pipe heat transfer calcs you can look in a process engineering text or a heat transfer text. You will also need the wind speed in your area to allow for convective losses. If the wind speed is high enough, convection is significant.

Can't tell about HDPE vs. steel just off-the-cuff without doing the arithmetic. Black is as good an emitter as it is an absorber. Need the emissivity values first.

My stuff is all packed away right now since I just moved my office or I woul dget it for you. This should get you started. Thanks!
Pete

 

[BobPE]

Ecorp:

74Elsinor is right on in his response. A simple heat transfer calc will give you a good understanding of what you face. Pipe material will only mildly increase or decrease heat loss and will be the last choice I think you would make in your decision. I worked on a project that involved transfer of river water from one basin to another. I used a pipe and an existing stream as the conveyance conduit. This was in the NE USA and the seasonal conditions caused all sorts of problems, more so than pipe material selection would correct for. The design ultimately had large chillers on the effleuent to remove heat to meet stream discharge conditions. This project involved a big flow (100,000 gpm) and you can imagine the size of the chillers. You will really have to focus on ambient seasonal conditions for the period your permits require you to meet the temp discharge requirements. Your negotations in advance of design and final permitting will also be very important as any gain you make in getting the limit more flexible will result in great cost savings for you. Focus on that stream you are discharging too and question all the data that any permitting agency gives you on it, that worked for me in my case as we negotiated the temps after the design was done and all could see the magnitude of investment of capital equipment for just a fraction of a degree in temp reduction.

I know this is a cop out, but I do not have my Heat and Mass Transfer book with me either. If 74Elsinor dosn't get it, I will be near my book next week.

Take care...

BobPE

 

[25362]

When doing solar radiation heat up estimates, it is convenient to have white paints or pigments, since their absorptivity for solar radiation is 0.14 on the average, while the low temperature radiation to the cooler surroundings are 0.92 on the average.

 

[JKEngineer]

Ecorp -
You do not cite the expected stream temperature. You give an anticipated 68F inlet to the pipe and a worst case air T of 110F. The stream T will fix the amount of heat you can afford to gain.

I agree with the previous commenters. A relatively straight forward hand calc will tell you something about how bad things are and what factors need to be addressed. I expect that both solar loading and convective loading will be factors. You could address them by: emissivity adjustment of the pipe surface -- could even consider low emissive top for solar rejection and high emissive bottom for re-radiation to the ground (if you think the ground is cool - but at 110F air T I doubt it); aluminum cladding of the pipe; insulation and aluminum cladding; exterior shading to cut solar loading.

If you seriously want some aid in solving this, I would be glad to discuss it with you. Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com

 

[denniskb]

I have developed software for this application and will try to run your case in the next few days and post the result.

Be careful with using reflective surfaces as they will work the day you put them on and a few days later will have a slight layer of dust on them and will loose almost all of the benefit.

Insulation will work very well and that can include an air gap. Even a simple light colored plastic film loosely tied to the pipe can provide a significant reduction in heat load. Dennis Kirk Engineering

http://www.ozemail.com.au/~denniskb

 

[KernOily]

Dennis - you raise some interesting, timely, and immediately applicable points. Do you have any data that details the effect/change on emissivity of dust layers or oxidation layers of various thicknesses? I am up against this problem all the time - not necessarily from the solar viewpoint, but from radiative heat loss from high-temperature piping systems and equipment. I am constantly trying to find better data for emissivity to sharpen my pencil in my heat transfer calcs. As you probably know the handbooks are pretty iffy when it comes to emissivity, at least the ones I've seen are. I'd love to discuss this further or see what data you have. Thanks!
Pete

 

[Ecorp]

I have more information on this ever challenging problem.

Two Pipe sizes
A.(20" Schedule 40 Steel Pipe); Q20 = 0.38 m3/s
Outside Diameter 0.5080 m
Inside Diameter 0.4778 m
Wall Thickness 0.01509 m

B. (36" Scedule 40 Steel Pipe); Q36 = 0.61 m3/s
Outside Diameter 0.9144 m
Inside Diameter 0.8763 m
Wall Thickness 0.01905 m

Assumptions:
1. Air Temp. will effect water inside the pipe through convective heat transfer. But this would not be the same as heating the pipe with an electric blanket at 43C. I am still trying to compensate for the heat source from the sun transmitted through the air(an insulator)and then being applied around the outside surface of the pipe through the steel and into the water assuming Laminar Flow.

Tmax,air=43C(Summer)
August: Tave,air=34C(high); Tave,air=14C(low); Twater,influent=19.5C
December:Tave,air=12C(high); Tave,air=3C(low); Twater,influent=14.7C
*It can be safely assumed that August will control and I still don't know the stream temps for August or Dec. but I will simply come up with a temp. increase for per meter of pipe.

2. I will have to calculate the effects of solar radiation and the emissivity properties of the outside of the pipe itself as well as the ground located underneath. As you all pointed out this is a difficult one to pin down but I will have to do the best with the charts that are provided online. I will assume new steel pipe that has not been coated or painted. I will also have to assume ground without vegetation and go with the higher values on steel and soil to be conservative.

Solar Radiation
August 296.5 W/m2(612.2ly)
December 78.2 W/m2 (161.6 ly)

3. I will assume no heat input due to friction of the water travelling through the pipe and pressure in equals pressure out (even though it wont) since flow work effects make a small contribution to heating water.

4. I am assuming that all other possible heat sources in this system, that I haven't listed, will be negligable (maybe this is a bad assumption).

I hope this helps and thanks alot.
Nathan

 

[denniskb]

74Elsinore - yes I do have some limited information which I gained second hand from some research done here a few years ago and I can pass it on so long as it becomes a two way exchange to add value to the information available to those interested. Contact me at denniskb@ozemail.com.au

First a brief introduction to the application I developed and will use to try and help Ecorp with his situation. In Australia we have some quite extreme temperatures (up to 55degC)and levels of solar radiation (up to 1100 W/m2) and these occur in areas with significant mining and processing facilities. Within these are many emergency safety showers because of fired equipment, hot fluids and chemical useage. The water delivered to the showers can get very hot (up to 88degC recorded) and can cause more harm to personnel than the original injury (at 60degC third degree burns with 5 sec exposure).

My software was developed to determine the heat load in the pipes and the max equilibrium temperature achievable so that we could design cooling circuits to keep the shower temperatures acceptable. It includes internal conduction (incl film coeff) and convection (forced), external conduction (incl flim coeff), convection (natural) and radiation (both solar and ambient) and conduction through up to three layes of pipe or insulation. It deals with pipe in the sun, shade or buried. I deals with CS, SS, HDPE and UPVC pipe and many types of insulation (including air gap).

Many miners use HDPE pipe from borehole to the minesite and within the minesite and there was lots of concern about the impact on water temp. One of the manufacturers did lots of field tests to try and dispell concerns and in fact developed an excellent and cheap way to significantly reduce the heat load using a reflective plastic film simply tied to the pipe. It works very well, reducing water temperature from 65 to 35 degC. Many other options were tried, including a two layer HDPE with a white outer. This product worked even better when it was new but after only a few weeks returned to the same heat load as plain black HDPE. The change was due to a layer of red dust on the outer surface. Cleaning improved it for a while but was impratical and eventually the white layer became stained.

My application was able to duplicate the result from these test with quite reasonable accuracy.

Anyway enough of this I need to see if I can apply my solution to Ecorp's problem. Dennis Kirk Engineering

http://www.ozemail.com.au/~denniskb

 

[JKEngineer]

Dennis -

Sounds like you have had some interesting work.

If I read your last post correctly, many of your applications deal with stagnant water in the pipes. This does not sound like the situation that Ecorp is facing. His system, I think, will have a steady flow and therefore much lower net temperature rise. Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com

 

[denniskb]

JKEngineer - No the situation we dealt with was for both water flowing and static. One of the primary outputs of the calculation is water temperature rise per metre for the input flow rate. To reduce the temperature of the water it is continually circulated and passed through a cooling tower or heat exchanger. Alternatives of dumping to grade and evaporative cooling are also used where necessary. Dennis Kirk Engineering

http://www.ozemail.com.au/~denniskb

 

[denniskb]

I have run case B outlined above by Ecorp with the following details.

Water, 20 C, 606 l/sec
Air, 43.3 C, Sky 12 C
Ambient Surfaces 43.3 C
Solar 296.5 W/m2
Pipe 914.4 mm OD, 19.05 mm WT
Surface Carbon Steel Clean, Absorp (solar) 0.45, Absorb (amb) 0.20, Emmis 0.55
Internal Conv Coeff 1952 W/m2.K
External Conv Coeff 3.03 W/m2.K
Radiative Coeff -0.93 W/m2.K

Heat Gain 140.3 W/m, 48.9 W/m2 (Outside), 50.9 W/m2 (Inside)
Temp Rise 0.023 C/100 m, 0.014 C/min

The temperature rise over 4.8 km will be only around 1.1 C

Contact me at denniskb@ozemail.com.au and I will forward you a pdf of the calc so you can check the inputs are correct.

If the pipe is lightly rusted (or dusty) the temperature rise could be 7.5 C.

If the pipe is HDPE (clean) the temperature rise could be 5 C

Let me know if you want to see other outputs. Dennis Kirk Engineering

http://www.ozemail.com.au/~denniskb