Design of heat exchanger step :2 : which type?

5 CommentsTechnical
The next step is to decide which type of exchanger to be used?
The industrial heat exchanger are varies depending upon
1. Transfer process.
2. Number of fluids
3. Compactness.
4. Constriction.
5. Flow arrangement.
6. Type of heat transfer.
See attached figure for more details.

Heat exchanger: step 1: application

1 CommentTechnical

<p>The first step dorm designing a heat exchanger is to understand where it will be used for.</p>
<p>Application is most important criteria and mostly its input from client.</p>
<p>Application demands understanding of functionaries expected, duty needed, properties of both side fluids, system information e.g presuredrop expected, cleaning method of the equipment, hazard category, local laws pertaining to pressure vessel and hazard handling.

Some time the application demand ‘soft’ heat transfer due to the media e.g yeast cooler due to delicate yeast cells are always co-current type which lead to higher surface area and are more costly than counter current heat exchangers; but due to application those are designed that way.

Cooling – Thermal Calculation

Technical

Lets Start with Diffrent Loading Calculation
Step : 1
1. Heat Loss to Atmosphere : Surface Area m² X Delta (Tavg – Troom)ºC x 0.32 = Q1 kcal/ hr
2. Cooling Load : Volume of liquid (lits) x Delta (Tstart-Tend)ºC/Time (hr) = Q2 kcal/hr
3. Heat evolved during Chemical process/ Fermentation : Q3 kcal/hr

Total Heat to be Removed = Cooling Load = Q = (Q1 + Q2 + Q3) X factor of safety

Please note Unit of Measurement carefully

for Q3, what process do you follow in your vessel, you need to find out the Load.

Step : 2
Calculate LMTD {Log Mean Temperature}
DT1 = TmediaStart – TcoolenEnd
DT2 = TmediaEnd – TcoolentStart
LMTD = (DT1-DT2)/ ln(DT1-DT2)

Step : 3
Calculate Overall heat Transfer co-efficient &amp; Surface Area Required
Q = U A LMTD
Hence, A = Q / (U x LMTD)

U, Over all heat transfer co-efficient : 100-250 Kcal/ hr ºC m², this is mainly depends uppon what type of jacket do you use, limped coil or limped jacket or profile sheets or laser welded jacket etc. you need to have some co-relation to evaluate this if the construction of jacket is non-standard. for standard type of jacket, you can get more info on following link
http://www.cheresources.com/jacketed_vessel_design.shtml

and if nothing works, ask me 🙂

Step : 4
Calculate amount of Cooling media needed for cooling
Now here is a trick, their are two type of coolent, one, they cool by their latent heat (e.g Ammonia) or two, they cool by dropping their temperature (e.g glycol water)

for First option, we need to consider Enthalpy of latent heat, devide Q by this, and you will get mass flow, for Second type follow following equation
Q = m . cp. DT (Tstartcoolent – TendCoolent)

Make sure you get these enthalpies at the working temperature, refer Perry’s handbook, or ask your cooling supplier for detail physical properties, as these properties changes with pressure &amp; temperature, for water mix coolent like glycol, the properties changes with concentation of media

I hope this is sufficient in-sight, in case of help, let me know

Cooling Performance – Overview

Technical

Ok, So you want to design cooling for a vessel.. how to?

Step : 1 : What you should know, and what you should ask
What you should know
a) You should know what type of Vessel Construction your are offering
b) You should know what Jacket for cooling you have
c) You should know your Jacket, Heat transfer co-eff co-releation very well
What you should ask
a) Media to be cooled
b) Media for cooling
c) with agitation or w/o agitation
d) Location (in-house or out-side)
e) Cooling performance needed
Step : 2 : Calculated heat Duty/ Cooling Duty
a) Duty due to Surface Loss
b) Duty due to Fermentation/ Process, i.e to remove heat arising from the process
c) Duty due to Cooling withing given time frame
d) Factor of safety : 10 to 20% depending upon your confidence (prooven history will help to reduce this factor of safety)

Step : 3 : Calculate Amount of cooling media needed

Step : 4 : Calculate Area for Cooling jacket

Step : 5 : Calculate Pressure Drop

Step : 6 : Summary

Next post : How to!

Milk Property fact!

1 CommentTechnical,

Just, I got this info & sharing with you
Density of Milk
Whole milk : ρ = 1035.0 − 0.358 T + 0.0049 T^2 − 0.00010 T^3
Skim milk : ρ = 1036.6 − 0.146 T + 0.0023 T^2 − 0.00016 T^3
Buffalo milk : ρ = 923.84 − 0.44 T
Cows’s milk : ρ = 923.51 − 0.43 T

Good, know you know what will be wait of 1 Liter Pouch 🙂

Cooling of Big tanks

Technical

Dear All,

Recently i was working on designing tanks with cooling jacket.
In brewery in particular, there is lots of need of cooling of tank, to take care of heating load generated out of fermentation, surface losses & to get temperature profile.

and as a motive to open this blog, is to share what i learn, in my next post I’ll discuss this in very detail.

See you all soon

PS : if you need any more info ask me, i can add that too in my post!

Earth quake Factors – Why & How

Technical,

Whats is Earth quake factor? and how they affect the calculation?

Their are numerous papers on this, and they are equally qualified to tell you what is earthquake factor all about… but what mater to me is.. how do they do it!

As far as India is concern..The earthquake of 26 January 2001 in Gujarat was unprecedented not only for the state of Gujarat but for the entire country in terms of the damages and the casualties. As the state came out of the shock, literally and otherwise, the public learnt for the first time that the scale of disaster could have been far lower had the constructions in the region complied with the codes of practice for earthquake prone regions. Naturally, as Gujarat began to rebuild the houses, infrastructure and the lives of the affected people, it gave due priority to the issues of code compliance for new constructions.

Seismic activity prone countries across the world rely on “codes of practice” to mandate that all constructions fulfill at least a minimum level of safety requirements against future earthquakes. As the subject of earthquake engineering has evolved over the years, the codes have continued to grow more sophisticated.

Liquid storage tanks are commonly used in industries for storing chemicals, petroleum products, etc. and for storing water in public water distribution systems. Importance of ensuring safety of such tanks against seismic loads cannot be overemphasized.

Earthquake loading – Brief

2 CommentsTechnical,

All designers are accustomed to evaluating moments due to eccentric and wind loads, but there are a few who may not be familiar with the method used for estimating moments due to earthquake. Therefore, the following brief outline is presented because this method is recommended as a design procedure for vessels where dynamic considerations are required. The weight of each vessel element (shell, head, tray, or internal part) is calculated. and then multiplied by the vertical distance from the circumferential seam (or horizontal plane) under
consideration to the center of gravity of the element. The summation of the moments so found ismultiplied by the seismic factor for the area where the vessel is to operate, thereby yielding a moment due to earthquake or seismic disturbance. For vessels, the seismic factor will usually have a value of 0.03 to 0.12, depending upon the geographical location. Expressed mathematically,

Thickness Calculation for Combined loading

Technical,

It is customary for most vessel designers to establish the minimum vessel shell and trend thickness according to the pressure temperature conditions and then calculate the thickness required at the bottom head seam due to bending moments imposed by wind or earthquake forces. Stresses in the longitudinal direction are involved nod the following notation may
be used to summarize the thickness required :

Here, The terms within the absolute value signs are positive for tensile stresses and negative for compressive stresses. The first term gives the thickness required for the longitudinal stress resulting from internal pressure and is positive for pressures above atmospheric and negative for pressures below atmospheric. The second term is the thickness required to resist the longitudinal bending stress and both positive and negative values exist at the same time. The third term is the thickness required for the weight of the vessel above the seam being investigated and, since this is a compressive stress, it has a negative value. The combination giving the highest value establishes the thickness required to resist the longitudinal stresses.

This formula hold good when the units are in Psi, ft & lb, if the units are in MPA, mm, N then remove the ’48’ from the formula.

Design : 2 : Shell (External Pressure)

3 CommentsTechnical,

External pressure can be due to internal negative Pressure, or external loading like wind, earthquake etc. or live load, snow load etc.

One can design Pressure vessel for either sever combination of various load or for most possible occurrence of load combination.

Load combinations are given in respective ‘Building Code’ like API, UBC, IS etc.

Yes, If you noticed I’ve said ‘Building Code’, why? as most of these loading decides how the pressure vessel, and if it fails, it can harm the occupants. hence design of such loading will be governed by building codes.

These Building code will give su way to calculate loading on tank/vessel, and then our design code like ASME, BS,EN will tell us how to derive the thickness from them.

one should note that, nearly all the design code talks about +ve Internal pressure & -Ve internal pressure & its design rules, but none of the code talk about how to do thickness calculation for the loads specified above.

In latest edition of ASME it does talk about these loading, and ask user to use Engineering practices to calculate loadings (UG-22), loading listed in this sections are
(a) internal or external design pressure (as defined in UG-21);
(b) weight of the vessel and normal contents under operating or test conditions;
(c) superimposed static reactions from weight of attached equipment, such as motors, machinery, other vessels, piping, linings, and insulation;
(d) the attachment of:
(1) internals (see Appendix D);
(2) vessel supports, such as lugs, rings, skirts, saddles, and legs (see Appendix G);
(e) cyclic and dynamic reactions due to pressure or thermal variations, or from equipment mounted on a vessel, and mechanical loadings;
(f) wind, snow, and seismic reactions, where required;
(g) impact reactions such as those due to fluid shock;
(h) temperature gradients and differential thermal expansion;
(i) abnormal pressures, such as those caused by deflagration;
(j) test pressure and coincident static head acting during the test (see UG-99).

In next section, we will discuss how to calculate final thickness of a vessel considering all loadings