Exchanger Sizing 3

[jboy]

Could anybody please point me in the right direction as of where to begin sizing exchangers. The exchanger would have oil on one side ,water on the other (plate type exchanger). I am looking for a general formula with a definition of all terms involved. Please note i have no past experience on this subject.
Thanking you.

 

[svanels]

Can you e-mail me more information about your project ?

Regards Steven van Els
SAvanEls@cq-link.sr

 

[jboy]

svanels
Thankyou for taking interest.In response to my question.
I need to set a temporary cooling water supply to provide cooling water to two gas turbine units. Lube oil will be on one side of the plate exchanger, with fresh water being the cooling medium. I need to keep the oil at 60 oC. I am told the the produced heat will be approx 120 BTU's.
How do i start to size the exchanger and find the required flow of water?

What i really need is a general formula along with definitions to cover the usuall systems on a production platform.

While on the subject can you tell me what the the followings terms mean

Q= UA (dt)
Q = WC (dt)

LMTD
regards
jboy

 

[svanels]

Oke jboy

Q is a rate of energy transfer can be BTU/time,
kcal/sec, kW.
the 120 BTU stated does not make any sense, since there is no time frame

U is a Global(Universal) Heat Transfer coeficient { maybe the terms are not exact because I am translating it from my sources}
if you have two fluids separated by a wall, there will be transfer of heat which involves:
2x convection (interface wall and fluid)
conduction (through the wall)

A combination of these 3 processes generates U

A is the contact Area (wall) between the fluids
dt is the temperature difference

LMTD is the Logaritmic Mean Temperature Differential, which will depend on the type of heatexchanger (current flow, counter current flow, etc)

Heat Transfer is very Empirical stuff, so do not expect to solve all with some simple formulas, youl will need to use graphics, tables etc.

Input variables:


Lube Oil: inlet temp + outlet temp
flow

Water: Inlet temp

Heat to be removed or water outlet temp

Sources:
Heat Transfer J.P Holman, McGraw-Hill
Momentum, Heat and Mass Transfer Bennett & Myers McGraw-Hill



Maybe a tube-shell heat exchanger will do.

Depending on where you are, you could rent or borrow a heat exchanger.

Keep me informed
Steven van Els
SAvanEls@cq-link.sr

 

[prodeng]

A couple of additional comments. In the HVAC world, 1 hour is assumed whenever you see a number like 120 BTU. The term U is the inverse of the resistance to heat flow, and generally can be found in a chart of various physical characteristics of materials. The second equation is referring total heat transferred (BTU) where C = specific heat of the fluid, and generally instead of W (weight), mass flow rate x time is used. For HVAC conditions, time is assumed to be 1 hour, so the equation boils down to Q = mass flow rate x specific heat of fluid x change in temperature. This gives BTU/hr, which you stated was 120. You can set the two Q values equal (heat lost = heat gained), look up the specific heat for each fluid (usually is also temperature dependent - which makes heat exchanger problems more difficult to calculate), find out the efficiency of the heat exchanger and know your starting water temperature. The information you have given is not enough to solve the problem unless you assume a few things (i.e. do both fluids end up at the same temperature?, what is the starting temperature of the oil?, what is the flow rate of the oil?). Without making a few assumptions or getting the facts, you can't determine the flow rate of the water needed. The LMTD is one method of determining how the differing temperatures relate. In other words, the fluid starts out cool and heats up while the other starts hot and cools down. This may affect the specific heat value (depending on the range), and as they approach the same temperature, not as much heat is transferred in the same amount of time. The LMTD factors that in to give you a type of average. This type of problem is not easy to work through by hand, and especially if you have no background in this area.

 

[svanels]

The heat transferred Q = 120 BTU/hr still does not make any sense

assumptions:

specific heat of oil cp = 2.1 kJ/(kg * K)

oil inlet temp = 65 Celsius
oil outlet temp = 60 Celsius

dt = 5 celsius = 5 K (kelvin)

Q = m*cp*dt

where Q = heat transfered {120 BTU/hr or 35 watt}
m = mass flow ?
cp = specific heat {2.1 kJ/(kg * K}
dt = temperature difference { 5 Kelvin}

m = Q / (cp *dt)

which leads to a mass flow m = 12 kg/hr


if we take a density of rho = 860 kg /m3 for the oil
the flow will be:

v = m / rho ---> v = 0.234 liter/min or 0.062 gpm (gallon per minute)


My designers manual (hydraulics) suggest for schedule 40 pipe a velocity of 2 to 4 feet per minute in oil suction lines

Using 1/8 npt pipe I will have at 0.36 gpm, a velocity of 2 feet/min

if I compare 0.36 gpm with 0.062 gpm I com to the conclusion that the 1/8 npt pipe is way to big, probably the oil will degradate in the heatexchanger or the heatexchanger will fit in your pocket.
Steven van Els
SAvanEls@cq-link.sr

 

I am in a search of a generalised design procedure to design a shell and tube type heat exchanger air to air bases generating hot air with the help of diesel firing at its centre. this will be very helpfull to my research project. I am also in search of refering some commercially available software if possible.

 

[nandan]

can anyone assist me with heat exchanger design.shell and tube type.some simple thermodynamic formulae.

 

[DJS1]

Software for various HE designs can be obtained from HTFS or HTRI. Try

http://www.HTFS.com.

Cheers

Douglas

 

[sudhi]

I need some info regarding radiator design.
What is the max tip speed permissible for the rad fan ?
What should be the max gap between the rad shroud and the fan?
What should generally be the pressure drop through the rad and across the rad?

Is there any book that gives step by step description regarding radiator design?

 

[jitin]

hi
i want a complete exhaustive shell and tube design procedure.
i want all the corelations for different conditions. iwas unable to find the complete procedure with all details till now. i hope u will be able to help me.i also want some computational methods for the design. i want to develop a design program myself.
thank u

 

[carrie]

i need to find out how much energy (in BTU's) would be required to cool a room (50x80x26.67 = 106680 cubic feet) from 95 to 80 degrees fahrenheit. please help!

 

[jaypar]

Carrie, a rough calculation to find the energy required to cool the room can be obtained by the basic equation
Q = M (Mass of air in the room) x Cp(air) x delta T (Difference between 95 - 80)
Now mass of air in the room is = Volume of air in the room x density of air
We know the volume of air - 106680 cu.ft


Calculating Mass:
In order to calculate mass we need to first calculate density :
Density = (Pressure x mol wt) /( R X Temperature)
Pressure = 1 atmosphere
Mol wt. of air = (0.79 x 28 + + 0.21 x 32) = 29.0 kg/kg mol
R= UNIVERSAL GAS -LAW CONSTANT = 0.08206
T = Avg temp = (T1+T2) in deg.C/2 +273 = in Deg.K
Density in this case = 1 x 29.0/( (0.08206)x (273+30.8) )= 1.16 kg/ m3/16.018 (conversion factor in lb/ft) = 0.0724 lb/ft3
Thus mass of air in the room = 106680 ft3 x 0.0724 lb/ft3 = 7725.6 lb

Specifc heat of air = Source Perry 5th edtn: pg 3-130
= 0.25 btu/lb deg.F

Thus Q = 7725.6 LBS X 0.25 Btu/lb deg.F X 15 deg.F = 28971 BTU / 3412 = 8.5 kW .

This is quick and rough calculations. Hope you find it useful.

For further reading, may I suggest you go through
Simple Solutions to Energy Calculations - Second Edition
by Richard R. Vaillencourt, 182pp - illus - hardcover, ISBN:
0136750672

http://www.engineeringbookstore.com/smeb/EnergyServices/Simple.htm

THere are websites that offer software and can be found at

http://www.hvac-calc.com/hvac/firstfloor4.asp

http://www.aecalc.com/software.html

For freebies: see below

http://www.hvacmall.com/news/article_00246.htm

Jatin / Sudhi/Nandan,
I suggest you have a look at Heat transfer by Kern for a comprehensive look at heat exchangers.
Also for further reading look at
Engineering Heat Transfer 2nd edition by William Janna
or Compact heat exchangers by Kays and London

For heat exchanger softwares BJAC used to be comprehensive it was brought out, I believe by ASPEN TECHNOLOGIES, HRTI is one place you can look at, Chemcad , AES also have heat exchanger softwares.

 

[TBP]

Unless you're planning on doing a lot of applications like this, it's usually easier just to provide the manufacturers with the required data, and let them run the numbers. It may be 5 years (if ever) until you do another one of these, and you will have likely forgotten even where the info on this one is.

Heat exchanger manufacturers will be happy to perform these calculations for any prospective customer. They just need some basic data.

In the case of the oil cooler, there must be an oil pump. Get the GPM or litres/sec from the manufacturer. The specific heat of the oil (and any other data specific to the fluid that may be required, like viscosity, etc). Inlet oil temp expected, and outlet oil temp required from the cooler. Then all you need is the inlet cooling water temp, and any limitations such as max outlet water temp, max available cooling water flow, etc.

Any heat excanger manufacturer I can think of will provide you with a selection, and a data sheet showing flows, temps, pressure drops, connection sizes, surface area, material of construction, weight of the unit, etc. And, of course, price & delivery.

 

[simulation]

I am working for Hyprotech and HTFS is part of that. We deliver simulation software for e.g. shell & tube heat exchangers and plate exchangers.

Let me know if I can be of any help. mark.vanderaa@hyprotech.com

 

[rusman]

Most widely used software for thermal design of the Heat Exchanger is HTRI and HTFS, although other software is also avail at the market.

HTRI = Heat Transfer Research Inst. - u have to be a member of HTRI to get the HTRI software. ie your company need to be a member, or can be NGO (non-govermen-organisation) or even educational institution. The cost is varies depend on the type of the organisation.

HTFS - Heat Transfer Fluid System - by AEAT technology which is together with HYPROTECH Ltd.

HTFS will give more conservative result (more heat transfer area) compare with HTFS, ie will end up with bigger heat exchanger. Client would prefer to use HTFS as it will give bigger size, but contractor would prefer to use HTRI as it will give smaller area.

HTRI will give better and wider vibration result (fluidelastic resonance etc) compare with HTFS, though HTFS can also predict vibration effect.

Hand calculation will require alots of iterative method, you can try using method by Kern (Process Heat Transfer) or by Chemical Engineers' Handbook.

Alternatively, u can roughly estimate the heat transfer area required by assuming U value (overall heat transfer coefficient, available from Perrys Handbook or from GPSA Databook), and from knowing LMTD and heat duty, Q, u can simply calculate the heat transfer area required.

Thanks

Rusman
Senior Process Engineer
Malaysia
man@rwsb.po.my

 

[habibnezhad]

hi
i want to know about compact heat exchanger that use in textile machines for example, STENTER machines . these exchangers with hot oil (250-270 centigrad)hot the air.
iwant calculate how many exchanger are need,exchanger dim.
how any pipe need in one exchanger(with elipse section pipe)and length of pipes,oil flow speed,witdh of machine is 320 cent. and machine has 4 chamber. the machine was made by VAMATEX company.

tanking you
habibnezhad

 

[tej]

i want nozzel diameter for different flowrate(50 , 120 m3/hr)

 

Hi

To size,design, and price PLATE HEAT EXCHANGERS you should try http:

http://www.phewizard.com

 

[Stephan]

Hi

To size,design, and price PLATE HEAT EXCHANGERS you can find assitance at

http://www.phewizard.com

Regards

Stephan