# Help with view factors

1. Apr 16, 2015

### princejan7

1. The problem statement, all variables and given/known data
I found the values $F_{3\rightarrow(1+2)}=0.32$ and $F_{1\rightarrow3}=0.25$
I now want to find $F_{2\rightarrow3}$

2. Relevant equations
Reciprocity relation
$A_iF_{i\rightarrow j}=A_jF_{j\rightarrow i}$

3. The attempt at a solution
Using the reciprocity relation to find $F_{(1+2)\rightarrow3}$
$A_3F_{3\rightarrow(1+2)}=A_{(1+2)}F_{(1+2)\rightarrow3}$
$3(0.32)=6F_{(1+2)\rightarrow3}$
$F_{(1+2)\rightarrow3}=0.16$

Using that to find $F_{2->3}$:
$F_{1\rightarrow3}+F_{2\rightarrow3}=0.16$
$0.25+F_{2\rightarrow3}=0.16$
$F_{2\rightarrow3}=-0.09$

But I get a negative value

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2. Apr 16, 2015

### haruspex

I don't think $F_{(1+2)\rightarrow3}=F_{1\rightarrow3}+F_{2\rightarrow3}$