6 replies to this topic

[djack77494]

sara,
It is true that all of the three heat transfer mechanisms can be important contributors to a heat transfer design. Such is the case in the design of most fired heaters and boilers. Typically you would have Radiant and Convection Sections of the furnace. They are named due to the dominant mode of heat transfer from the combustion side of the equipment. Generally the process or utility side of the boiler/heater gains heat by Conduction through the tube wall followed by (mainly) Convection into the process/utility fluid. Radiation dominates only at relatively high temperatures, and as the combustion gases cool, you would typically have a transition to the "Convection Section" of the boiler/heater. In fact, whenever you move heat through a solid you will have conduction; through a fluid you will have convection; in a vacuum or at high temperatures you will have Radiation.

A recent post mentioned the excellent website developed by Mr. V Ganapathy on boilers. Though it's been a while since I visited that site, I seem to remember it having an excellent tutorial section on fundamentals. You might want to try it or the WinHeat site for more information. There are others as well. Try Google.
Doug

[Art Montemayor]

Sara:

Whoever told you that a boiler represents a good example of simultaneous conduction, convection, and radiation heat flow is steering you in the correct direction.

How heat is transfer by all three methods is your responsibility to know, and this knowledge is obtained by studying any convenient, good heat transfer text book. In fact, you don't even have to go to the library anymore to find out this information. You can use the Google Search Engine and you will find probably hundreds of thousands of "hits" on the subjects. It is of little importance for you to know how to write the words conduction, convection, and radiation if you don't know what they are and how heat is transferred in each of these methods.

I sincerely hope you take this task seriously and study the 3 basic forms of heat transfer. All of Process Heat transfer in engineering is based on these principles. If you don't know them and dominate them also, you will never succeed as an engineer.

Good Luck.

[trilok_sontakke]

Sara:

I will give you example of real world which will help you to interpriate conduction, convection and radiation easily.

Imagine that your class has examination and one student is seated on each bench.Teacher enters with question papers. she can distribute the papers among the students by three ways.

1.she will count the students in each row and handover all the papers to student seated on first bench, he will then take one paper for himself and passes the remaining to student seated behind him.each student does the same thing.
2. she will individually go to each and every student and give him paper.
3. she simply throws papers to each student without moving from her position.

way no. 1 is similar to conduction process. think that teacher is source, students are molecules and paper is energy. thus energy is transferred from molecule to molecule.

way no.2 is similar to convection.energy is tranferred from source to molecule.

way no 3 is similar to radiation where enegy is transferred by means of thermal radiations for which medium is not required.

hope you can interpriate the logic.

[kumaqal.engr]

Sara:
The best way to find the mode of heat transfer in boiler is that first you understand all the mode of heat transfer.

http://www.spiraxsar...ules/2_5_01.asp


just check out this site to get more information
certainly it will help you

[Art Montemayor]

A good example of radiation is obtained by going out to the beach on a bright, clear day at about mid-day and taking all your clothes off - except your bathing suit. Wait around about 4 hours, exposed to the direct radiation of the sun's rays and you will have first hand knowledge and experience of what radiation is and what it can do the next morning when you try to get out of bed.

If you don't have a beach handy, then find an industrial flare - like those used in oil refineries. While the flare is burning exhaust gases, try walking towards it - you don't have to take your clothes off for this one. I can assure you that the effects of radiation will be felt as you get closer and closer to the flare pipe.