4 replies to this topic

[imtinan]

I am doing calculation for the change in air temperature due to the radiation intensity of 1000 Btu/hr.ft2. The reason for doing this calculation is that get the maximum ambient temperature around a Shelter for PLC of FFG (Flame Front Generator) in order to finalize the HVAC requirements for this shelter. Any suggestion regarding this matter will be highly appreciated. Regards, IM

[imtinan]

Ankur,Art, Fallah & Breizh, Please help me regarding this matter. Regards, IM

[gegio1960]

in the meantime you can do two things:

- search in the forum

- google "conduction of heat in solids calculation excel"

good luck 

[thorium90]

Does it really need anything more than a sun shield?

 

Not sure if the following is useful since its not really exactly what you want...

Attached Files

•  flare height.pdf   608.51KB   47 downloads

Edited by thorium90, 10 February 2013 - 07:59 AM.

[kkala]

The topic has been stagnant for a month. Below are some notes, subject to criticism and additions, for want of something better.

1. Radiation is practically transparent to ambient dry air, at least for distances like flare-ground. No heating of air is assumed to occur by travel of radiation through it (absorptivity=0, transmissivity=1).

2. Total radiation intensity Ko=1000 Btu/ft2/h = 3.15 kW/m2 on ground, composed of flame radiation Ko'=2.15 kW/m2 on ground just below flame center, plus solar radiation K''=1 kW/m2 at same time, as indicated on the attached "flareR.xls".

Flare flame at max length, corresponding to max flare discharge; solar radiation at maximum

Note: In case that mentioned 1000 Btu/ft2/hr do not include solar radiation, above has to be revised accordingly.

3. Radiation intensity K falling on the FFG shelter (flareR.xls).

3.1 Solar K" = 1 kW/m2

3.2 From flame K' =Ko'(h²/(h²+L²) per equation (20), para 4.4.2.3.3 (Radiation) of API RP 521 (4th ed, 1997). This can be also written as K' = Ko'cos²θ; see "flareR.xls" for meaning of h, L, θ.

3.3 Total K = K" + Ko'cos²θ; e.g. for θ=30° Κ= 1+2.15cos²30° = 2.61 kW/m2

4. Shelter should be a closed room due to HVAC. Suppose a roof wide enough not to let radiation fall on peripheral walls. Help on estimating roof temperature profile (see post no 3 by geggio 1960) is welcomed. At present roof is assumed grey, of absorptivity say 0.4 (e.g. covered with thin aluminum sheet for protection), having uniform surface temperature and receiving heat 0.4*2.61~ 1.0 kW/m2. Unsteady heat conduction will rise temperature along roof thickness with time, on the other hand max flare discharge will be for some limited time. Surface temperature cannot be higher than (2610/5.672E-8)^-1/4 = 463 oK = 190 oC, if I rightly understand Stefan - Boltzmann's low .

5.1 R Reed, "Furnace Operations" (Gulf 1976), Chapter 2 - Flaring and disposal, says for Ko=1000 Btu/f2/h onto grade of emissivity=0.80: max grade temperature is approximately 190 oC after 20 min exposure, but it can be as high as 90 oC at the end of 1 min.

5.2 Attached  "flare001.pdf" (from web) mentions 31 oC temperature above ambient for radiation level = 1000 Btu/ft2/h, without explanations.

Attached Files

•  flareR.xls   22.5KB   73 downloads
•  flare001.pdf   524.64KB   74 downloads

Edited by kkala, 12 March 2013 - 08:23 AM.