Cant do it....

[Simo@work]

This friggin assignment.... I just cant finish it?? I cant seem to re-arrange the friggin equation properly.. been thinking about it too much. <img src= "smileys/confused.gif">



Arse!



Simo'

[GreenSaxo]

let us have a go??

[Dannysp8]

Thats why i dont think too much, it hurts <img src= "smileys/silly.gif">

[Andysaxo.]

lol having a few proplems fella!?



im glad i dont have to do assignments anymore, them days r long gone! lol



simo ive put them other pics of my car up for ya under the post "more pics of my VTS" they are a lot better and u can use them for ya main site! <img src= "smileys/grin.gif">



chers andy

[Scott]

you thicko!! <img src= "smileys/smiley2.gif"><img src= "smileys/silly.gif">

[Simo@work]

<img src= "smileys/confused.gif">



I've started to type what I've completed, as I thin kI need a break from the question im stuck on... it cant be that hard?? Think i've just blinded my mind to it.. <img src= "smileys/silly.gif">



I'll post a condensed version here..



Simo'

[GreenSaxo]

cool..

[Simo@work]

No doubt, now i've condensed 25 sheets of scrawl into 5 lines, it will be easy.. <img src= "smileys/silly.gif">



Q = (M x 900) =[80 x 4.18 x (T-20)]=(U x 116.82 x L)



L =[70 ”“ (90 ”“ T) ] / [ln (70 /(90-T))]



I need to express L in terms of T… cancel a few factors out of the top equation. Once simplified, I will have to calculate U from the data above…



Once I’ve found U, I will be able to calculate Q and T…. and ultimately I will be able to calculate M



The bit i’m having trouble really is expressing L in terms of T, and simplifying the top equation…



Once I’ve done this bit, I know how to do the rest of the question….. this is just a snippet froma big mother of a calculation! <img src= "smileys/smiley3.gif">

[Dannysp8]

Get that to fuck.....

[Andysaxo.]

im with danny on this one!!! lol



cheers andy

[XPT_Furio]

Hmmmmm, fucked if i know! <img src= "smileys/grin.gif">

[Hanny_lou]

erm... wats the question-- is it econmics?

[GreenSaxo]

ok.. im off to bed now... if ur still stuck by 2morrow lunchtime.. i will have a go at it!!

[Simo@work]

LMAO... it was supposed to be handed in last Thursday.. so it'll be leaving via email in the morning, completed or not... I think? <img src= "smileys/smiley9.gif">

[Simo]

I've just completed the fucker... time for a beer!! <img src= "smileys/cool.gif">





Data :-



Do = 0.0254mDI = 0.0210mMCW = 80kgs-1NT = 400 tubes

6 tube-side passesLatent heat of condensing vapour = 900kJ/kg

ho = 2500 W-2K-1Inlet temp of cooling water = 20”žaCThermal conductivity (steel) = 50 W/mK

1/hfI = 0.0004 (Wm-2K)-11/hfo = 0.0002 (Wm-2K)-1



Firstly, a value of hI must be calculated¡K using :-



(hI DI / k) = 0.023 x [(ƒÃ¢ v DI) / ƒÃ�]0.8 x [(Cp x ƒÃ�) / k]0.33



Number of tubes = 400¡K number of passes = 6. ƒÃŒ No of tubes / pass = 66.667



The cross sectional flow area / pass= 66.667 x (ƒÃ*/4) x 0.0212 m2

= 0.02309 m2



The volumetric flow rate is calculated as follows¡K mass flow / density

ƒÃŒ volumetric flow rate = 80 kgs-1 / 1000m3kg-1=0.08m3s-1



Hence the velocity = 0.08 m3s-1 / 0.02309m2



ƒÃŒ velocity = 3.46ms-1



Next, the values of Re and Pr must be calculated¡K









Re = ƒÃ¢ v DI / ƒÃ�



ƒÃŒ Re = (1000 x 3.46 x 0.021 ) / 900 x 10-6



And so, the value of Re = 80733.33 and hence the Re number should be recorded¡K



Re = 8.07 x 104¡K. ƒÃŒ The flow is turbulent!



The value of Pr must now be calculated¡K



Pr = (c x ƒÃ�) / kPr =(4.18 x 900x10-6) / 610 x10-6



Therefore, Pr = 4.18 x 900 x 10-6



Pr = 6.17



Then¡K using, hI = 0.023 x (k / DI) x Re 0.8 x Pr0.33)



ƒÃŒ hI = 0.023 x (610 x 10-6 / 0.021) x (8.07 x 104)0.8 x (6.17)0.33



and Hence, hI = 10.26 kW/m2K



From the data tables¡K hO = 2.5 kW m-2K-1



Then¡K



1 / UO = [(1 / hI) x (DO / DI)] + [(DO ln (DO / DI)) / 2k] + (1 / hO) + [(1 / hfI) x (DO / DI)] + (1 / hfO)



where¡K (1 / hfI) = 0.0004 (W/m2K)-1and(1 / hfO) = 0.0002 (W/m2K)-1





Therefore¡K



1 / UO = [(1 / 10260) x (0.0254 / 0.0210)] + [(0.0254 ln (0.0254 / 0.0210)) / 2 x 50] + (1 / 2500) + [(0.0004) x (0.0254 / 0.0210)] + (0.0002)



ƒÃŒ 1 / UO = 1.25 x 10-3 m2K / W



ƒÃŒ UO = 799.98 W/m2KƒÃŒ UO = 800 W/m2K





The area of the heat exchanger can now be calculated¡K using.



AO = NT ƒÃ* DO LƒÃŒ AO = 400 x ƒÃ* x 0.0254m x 3.66m



Hence, AO = 116.82m2



Overall Heat Balance equation¡K



Q = (MV x L) = (MCW CPcw ƒÂ´T)CW = (UO AO ƒÂ´Tlm)



Where, L = 900kJ/kgAO = 116.82m2UO = 0.8 kWm-2K-1CPcw = 4.18 kJ kg-1K-1

MCW = 80kgs-1



ƒÃŒ Q = (900 MV) = (80 x 4.18 x ƒÂ´Tcw) = (0.8 x 116.82 x ƒÂ´Tlm)



ƒÃŒ Q = (900 MV) = (334.4 x ƒÂ´Tcw) = (93.46 x ƒÂ´Tlm)





Then¡K ƒÂ´Tcw = (T ¡V 20)



And so¡KQ = (900 MV) = (334.4 (T-20)) = (93.46 x ƒÂ´Tlm)





AndƒÂ´Tlm = ƒÂ´T1 - ƒÂ´T2 / ln(ƒÂ´T1 / ƒÂ´T2)ƒÂ´T2 = (90 ¡V T)





ƒÃŒ ƒÂ´Tlm = 70 ¡V (90 ¡V T) / ln [70 / (90-T)]



ƒÃŒ ƒÂ´Tlm = (-20

[Dannysp8]

Yer thats what i was gona say <img src= "smileys/silly.gif">

[tgazvtr]

Same here <img src= "smileys/smiley4.gif"> I think that would just peck my head!<img src= "smileys/smiley5.gif">

[Simo]

Great stuff aint it!! <img src= "smileys/silly.gif">



Just doing the last question, then gonna email it in about 40 mins...



Thank fuck!! I can then enjoy my days off... for a change.



Simo'

[tgazvtr]

Is right!

[Areke]

I hate school, im glad im not going to school anymore!!!