thermal conductivity

[superduper12]

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Q/t = kA[(Th-Tc)/L]

Situation 1 - comparing lengths slab 1> slab 2

so pretend you have two slabs between the heat source and heat sink. slab 1 and slab 2....slab 1 is longer than slab 2....does this mean that the temperature gradient across slab 1 will be greater than the tempeature gradient across slab 2. I understand that they conduct heat at the same rate

Situation 2 - comparing thermal conductivity slab 1 > slab 2

Now the slabs are the same length but slab 1 has a higher thermal conductivity (k)than slab 2. so heat will flow faster in slab 1. because it flows faster, t increases and...and Q/t remains the same for both slabs

Situation 3 - comparing area slab 1> slab 2

slab 1 has a larger crosssectional area than slab 2. since slab 1 has a greater area, it takes a less time...so in the end Q/t...stays the same for both slabs.

am I thinking of this correctly?...or is time not a factor and I should think about temp gradients.

 

[superduper12]

i think i got it wrong. if t changes than Q/t will change and doesn't change because the heat source will continue to supply same Q, under any conditions.

so I should probably think in terms of temp gradient.

So in situation 2,.... since slab 1 has a higher k, the temp different will be lower across slab 1, thus keeping the heat flow rate (Q/t) the same.