Heat Transfer between 3 plates of different materials
Heat Transfer between 3 plates of different materials
(OP)
Hi!
I have a problem and it is the following:
There are 3 plates of 20cm x 20 cm x 10cm (for refractory) , 5cm (for insulation), and 1.9cm (for Shell)...as per attached image. In one face, the hotter face, there is a temperature (ti) of 1000°C. Taking into account the following thicknesses of each material...I want to know the final temperature of the coldest face considering that in the coldest face has a initial temperature of 25°C and the air is flowing through that coldest face.
The thermal conductivity of each material is as follows:
(refractory = 0.52 W/m*K, insulation = 0.46 W/m*K, and Shell = 52 W/m*K)
I used SOLIDWORKS SIMULATION to solve this problem. When I give the THERMAL LOADS to each face, I begin with the known temperature and it is the hotter face (1000°C = ti) but for the coldest face I give a CONVECTION ISSUE as thermal load but SOLIDWORKS asks me for two parameters:
-Convection Coefficient and Bulk Ambient Temperature.
I consider that air is flowing through coldest face so I put 25°C in BULK AMBIENT TEMPERATURE but for convection coefficient...I had problems with that part.
I found on engineering toolbox web site of a empirical formula to know the convection coefficient or convective heat transfer coefficient of air when air velocity is from 2 to 20 m/s and it is the following:
- hc = 10.45 - v + 10 v ^1/2. (V = m/s speed)
I used 20 considering standard value and the value was 35.1 W/m2*K.
The software solved the solution and tf (final temperature) was like 90-100°C. I want to know if what I did was correct or what steps I did wrong.....hope you can help me how can I be sure that I am in the correct path
Thankyou
Roland
I have a problem and it is the following:
There are 3 plates of 20cm x 20 cm x 10cm (for refractory) , 5cm (for insulation), and 1.9cm (for Shell)...as per attached image. In one face, the hotter face, there is a temperature (ti) of 1000°C. Taking into account the following thicknesses of each material...I want to know the final temperature of the coldest face considering that in the coldest face has a initial temperature of 25°C and the air is flowing through that coldest face.
The thermal conductivity of each material is as follows:
(refractory = 0.52 W/m*K, insulation = 0.46 W/m*K, and Shell = 52 W/m*K)
I used SOLIDWORKS SIMULATION to solve this problem. When I give the THERMAL LOADS to each face, I begin with the known temperature and it is the hotter face (1000°C = ti) but for the coldest face I give a CONVECTION ISSUE as thermal load but SOLIDWORKS asks me for two parameters:
-Convection Coefficient and Bulk Ambient Temperature.
I consider that air is flowing through coldest face so I put 25°C in BULK AMBIENT TEMPERATURE but for convection coefficient...I had problems with that part.
I found on engineering toolbox web site of a empirical formula to know the convection coefficient or convective heat transfer coefficient of air when air velocity is from 2 to 20 m/s and it is the following:
- hc = 10.45 - v + 10 v ^1/2. (V = m/s speed)
I used 20 considering standard value and the value was 35.1 W/m2*K.
The software solved the solution and tf (final temperature) was like 90-100°C. I want to know if what I did was correct or what steps I did wrong.....hope you can help me how can I be sure that I am in the correct path
Thankyou
Roland





RE: Heat Transfer between 3 plates of different materials
In any case, the surface temperature seems high; I get more like 36ºC
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RE: Heat Transfer between 3 plates of different materials
But...how did you do it?
Roland
RE: Heat Transfer between 3 plates of different materials
TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Heat Transfer between 3 plates of different materials
@ IRstuff
It is not supposed that R by conduction = (e1/k1 + e2/k2 + e3/k3)1/A = 1/R = A / (e1/k1 + e2/k2 + e3/k3) and it is more like = 0.13 W/K so adding the R by convection it would be like 0.11 W/K. So the Q of the system ´d be 116 W and the temperatura of the cold face its more like 108°C So...there is something that I dont get...and also how do I choose a correct convective heat coefficient for air taking into account air speed
Hope you can help me
Roland
RE: Heat Transfer between 3 plates of different materials
The convection coefficient is dependent on air speed and geometry. There are tables and graphs on the web: http://www.engineeringtoolbox.com/convective-heat-... so 35 W/m^2-K was pretty much the value for 20 m/s, but that, I think, is specifically for a flat plate.
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RE: Heat Transfer between 3 plates of different materials
RE: Heat Transfer between 3 plates of different materials
@dvd
The main idea is to check SOLIDWORKS SIMULATION (THERMAL ANALYSIS) is a good software to solve these kind of problems taking into account you feed the input data correctly. I made an analysis using SOLIDWORKS FLOW SIMULATION considering HEAT CONDUCTION IN SOLID. I made an external analysis where air speed is 20 m/s and adding over the hot face a CS plate in order to represent the temperature of 1000°C. (Volume source and a temperatura of 1000°C) This was to indicate to the program that the hot face of the initial 3 plates is 1000°C. Realizing this I checked that the temperatura in the cold face is between 23 to 26°C. The convection coefficient is the matter actually.
@ IRstuff
I found on engineering toolbox (the website you already wrote) web site of a empirical formula to know the convection coefficient or convective heat transfer coefficient of air when air velocity is from 2 to 20 m/s and it is the following:
- hc = 10.45 - v + 10 v ^1/2. (V = m/s speed)
I used 20 considering standard value and the value was 35.1 W/m2*K.
The table is made using above formula but it says is empirical. I think there should be another good way to find out the correct value of HEAT TRANSFER COEFFICIENT OF AIR CONSIDERING SPEED.
Roland
RE: Heat Transfer between 3 plates of different materials
http://www.cheresources.com/content/articles/heat-... but there are other correlations that have been developed: http://www.pathways.cu.edu.eg/ec/text-pdf/part%20b...
For the length of your plate, the equation from the first citation results in 40W/m^2-K
TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers
RE: Heat Transfer between 3 plates of different materials
TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers