Calculating Insulation Heat Loss?

[Michael Duncan]

Hi everyone, I'm working on a calculation regarding heat loss due to no insulation on a pipe and wanted to get some feedback on how accurate my logic may be and how to proceed.

My process is superheated steam. I used resistance conduction and convection formulas to get a BTU/hr loss rate of heat for uninsulated pipe. Knowing that the evaporation enthalpy is 777 BTU/lb for saturated steam, I can get a lb/hr value for steam loss. However, this is of course for saturated and not superheated so it won't be entirely accurate.

What's the best way to proceed forward to get an estimated energy loss of superheated steam for noninsulated pipe?

Thanks very much.

 

[pmover]

all you need is steam temperature, pipe size, pipe length, & pipe wall thickness to determine heat loss. personal protection is more important; hence, insulation is applied.

 

[Heaviside1925]

What delta Ts are you using for resistance conduction and convection formulas? I would think you would have a rate depended formula based on delta T that you would integrate across the length to give you your temps on one end and the other.
My go-to on all things steam:

https://www.spiraxsarco.com/resourc...tables/superheated-steam-region?sc_lang=en-GB

Once you know your temp on one end and the other, then look up your enthalpy difference and that's the losses.

 

[Snickster]

Heat loss is based on the equation

Q = U A dT

It does not matter whether the steam is at saturation or superheated as far as dT is concerned but only slightly since if saturated dT is constant where if superheated dT varies.

Also if steam is condensing versus superheated and noncondensing it will change the internal heat tranfer convection coeficient slightly but it will have a neglible change in the overall U value. The insulation thickness governs the value of U such that the resistance of the internal convection film, pipe metal conduction resistance, and external convection film resistance can be neglected without affecting the calculated value of Q significantly.

 

[georgeverghese]

Table 5-2 in Perry Chem Engg Handbook 7th edn saves you all the toil in calculating this bare pipe heat loss.

Q = (hc + hr) x A x dt

Q = btu/hr, A = surface area in ft2 / linear ft of pipe , dt = temperature in the pipe - external temp in degF.

What medium is flowing inside the pipe has little bearing on the value of hc + hr . This is because the poor external natural convection heat transfer coeff on the pipe external surface is the biggest impediment to heat transfer and therefore dominates.

 

[pierreick]

Hi,
Try this calculator :

https://checalc.com/calc/inshoriz.html#google_vignette

Click on reference 1 on this page to get details about the calculation.
Pierre