View Full Version : Evaporator Design

Narendrak

25-10-2010, 01:43 PM

hi everybody,

am building a chiller for an industrial application. please let me know if the evaporator design i've done (shown below) has any mistakes in it.

Enthalpy at evaporator entry, kJ/kg =370Enthalpy at evaporator exit, kJ/kg =270Refrigerating effect (from p-h diagram), kJ/kg =100Heat to be removed from water, kJ=4187Mass of refrigerant required, kg =41.87Specific volume of refrigerant at Evap. Temp, m3/kg=0.03911Volume of refrigerant, m3=1.637536Inner dia of the evaporator tube,m=5.72E-03Initial pull down time,hr=1Length of the evaporator, m =17.74

Am using R404a.

If there is any other easier(simpler) method please lemme know.

thanks

Narendrak

25-10-2010, 01:46 PM

hi everybody,

am building a chiller for an industrial application. please let me know if the evaporator design i've done (shown below) has any mistakes in it.

Enthalpy at evaporator entry, kJ/kg =370

Enthalpy at evaporator exit, kJ/kg =270

Refrigerating effect (from p-h diagram), kJ/kg =100

Heat to be removed from water, kJ=4187

Mass of refrigerant required, kg =41.87

Specific volume of refrigerant at Evap.Temp,m3/kg=0.03911

Volume of refrigerant, m3=1.637536

Inner dia of the evaporator tube,m=5.72E-03

Initial pull down time,hr=1

Length of the evaporator, m =17.74

Am using R404a.

If there is any other easier(simpler) method please lemme know.

thanks

NoNickName

25-10-2010, 06:23 PM

Plenty of mistakes. It's only valid for 1 liter of water and apparently for 1K of delta T.

Take a look at this link. DXC program will assist you.

http://www.coolit.co.za/coilsim/index.htm

Go here to download a trail version of DXC program. You can then proceed to design the evaporator.

http://www.technisolve.co.za/

Narendrak

26-10-2010, 04:30 PM

Plenty of mistakes. It's only valid for 1 liter of water and apparently for 1K of delta T.

No nickname, thanks for the reply.

I've considered the total heat to be removed as 4187kJ n i think that must convey tthe mass of wathe fact that the mass of water is 100kg.

Regarding your comment on temperature, well, am not sure

NoNickName

26-10-2010, 06:12 PM

Ok, 100Kg, but the specific heat of water is 4.187 kJ/Kg K, so you only heat or cool 100 Kg by 1K of temperature

Narendrak

27-10-2010, 07:32 AM

Ok, 100Kg, but the specific heat of water is 4.187 kJ/Kg K, so you only heat or cool 100 Kg by 1K of temperature

NoNickname,

My chiller needs to remove this amount of heat (4187 kJ) from water.

The calculation above refers to the properties of refrigerant.

While taking the enthalpy values at evaporator entry and exit from p-h chart, it is noted that the values are from the region of latent heat. So, there would no temperature rise of refrigerant during this heat absorption.

But since water looses the same amount of sensible heat to the refrigerant its temperature decreases.

so, that above explanation should clarify the doubts on temperature rise.

Other than these two please let me know if u find any other mistakes.

N regarding the tools available on net - Guys, am working on a project for thesis to obtain masters in thermal engineering. So, basic calculation are appreciated and reliability on tools really handicaps us from the basic knowledge... What do u say?

D.D.KORANNE

27-10-2010, 08:32 AM

In chiller unit , also account for chilled water pump heat ( in kw) to your total load ,heat gain in chilled water piping .

The chilled water heat is the load too on chiller

taz24

27-10-2010, 08:51 AM

No nickname, thanks for the reply.

I've considered the total heat to be removed as 4187kJ n i think that must convey tthe mass of wathe fact that the mass of water is 100kg.

Regarding your comment on temperature, well, am not sure

Narendrak.

You need to know how much water you are cooling

and you need to know how much heat you are removing.

Then as others have said you need to alow for other factors such as pumps.

So how much water?? 100Kg?

water start temp?? In deg C

water finish temp?? in deg C

and flow rate??

Start with the basics and the rest should be simple..

All the best

taz

.

D.D.KORANNE

27-10-2010, 09:40 AM

Evaporator btu/hr

usgpm = ---------------------

500 x chilled water temp difference (in minus out in deg f )

(old british units used)

a very quick way to get the unknown parameter . However add losses as mentioned above in my thread

applicable for water only

NoNickName

27-10-2010, 09:59 AM

My chiller needs to remove this amount of heat (4187 kJ) from water.

Ok, you will remove that amount of heat from water, but generally your target is a temperature, not some heat.

It is therefore undetermined if you are cooling 100Kg of water at what temperature level.

Do you understand the difference between heat and temperature?

Take a look at this link. DXC program will assist you.

http://www.coolit.co.za/coilsim/index.htm

Go here to download a trail version of DXC program. You can then proceed to design the evaporator.

http://www.technisolve.co.za/

Apologies - I'd read the OP incorrectly.

In order to design either a plate evap, or shell-&-tube evap, you should obtain a heat-exchanger design program, then proceed to design the appropriate unit. It is quite simple, really.

NoNickName

08-02-2011, 07:35 AM

This research was published just today

http://www.sciencedirect.com/science?_ob=GatewayURL&_method=citationSearch&_urlVersion=4&_origin=SDVIALERTHTML&_version=1&_uoikey=B6V2S-51VXWG1-2&md5=09f187ff37a600cc2328f9bd48ac0e91&graphAbs=y

Economic optimization of shell and tube heat exchanger based on constructal theory (http://www.sciencedirect.com/science?_ob=GatewayURL&_method=citationSearch&_urlVersion=4&_origin=SDVIALERTHTML&_version=1&_uoikey=B6V2S-51VXWG1-2&md5=09f187ff37a600cc2328f9bd48ac0e91&graphAbs=y) Original Research Article

Pages 1087-1096

Abazar Vahdat Azad, Majid Amidpour

Research highlights

► In this paper, constructal theory has been employed to optimization of shell and tube heat exchangers. ► Heat exchangers optimized by reduction of total cost using Constructal theory. ► The overall heat transfer coefficient of the heat exchanger is increased. ► Genetic algorithm is used to optimize the objective function. ► The results of this research represent more than 50% reduction in cost.

It's not free, though.

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