2 replies to this topic

[rene1185]

I am given the temp and pressure of the inlet caustic solution, the concentration of caustic coming out of each stage as well as the steam pressure and temp. How do i calculate the overall heat transfer coefficient in each effect system if i can using a triple effect (forward feed) evaporator?

[Art Montemayor]

Rene:

Your question is vague and begging the obvious answer: You calculate the Overall Heat Transfer Coefficient ("U") for each evaporator coil in the manner and methods taught you in your Unit Operation Course. I'm assuming you are in a Unit Ops course, even if you don't state as such. You are probably studying Evaporation and its associated problems and calculations - simple heat and material balances.

You should have already had an introduction to heat transfer; otherwise, you wouldn't know what a "U" means, how it is derived, and how to calculate it. If you have not had this introduction to heat transfer, then you can't be expected to understand anything about what is going on in the Evaporation section of Unit Ops. Additionally, you wouldn't be able to understand the responses you obtain from this Forum.

Please be specific in your query. If you know what a "U" is and what it represents, state so and tell us why you can't calculate it. Also - and very important - what exactly have you been assigned (or are trying to figure out)? Have you been told to calculate the "U" in each of the evaporator coils? Or have you been told to use existing, empirical "Us" to calculate the heat transfer area? Tell us exactly what you are assigned or what you have taken on and what part of it is giving you problems. We cannot teach you Unit Operations on this Forum; nor are we about to do your homework for you. But we can certainly explain any details you don't understand. Tell us the details, please. Then, we start to help.

[rene1185]

Hi there,

thanks for your reply. My project is to design a multiple effect caustic evaporator. All i am given are:
-Feed flowrate
-Feed temp
-Feed Pressure
-Inlet Steam temp
-Inlet steam Pressure

I have chosen to use a vertical falling film evaporator

My questions are:
-without being given any other information, how can i design an evaporator (ie height of evaporator, inside and outside diameters), do i assume the overall transfer coefficients for each evaporator becos all i have been given in literature are a range of values for what U might be. Sorry if i have confused you but i hope this has made things clearer.