Can heating 2 sets of 1L water or 1 set of 2L water have a variation in terms of fuel efficiency? Can one be more fuel-efficient than the other?
(migrated from chemistry site)
$\begingroup$
$\endgroup$
5
-
4$\begingroup$ All else being equal, probably yes. 2 sets by 1L will have a larger surface area for heat loss. $\endgroup$– LLlAMnYPOct 23, 2015 at 10:19
-
2$\begingroup$ Can you give a bit more detail about what heating regime you're using? At the moment your question is too vague to be usefully answered. $\endgroup$– John RennieOct 23, 2015 at 10:32
-
$\begingroup$ @JohnRennie To vague? See comment 1. One 2L container will have less surface area for heat loss and will be more efficient in any regime. $\endgroup$– paparazzoOct 23, 2015 at 12:52
-
$\begingroup$ Too many unknowns. Are the volumes of water in exactly the same size and shape container, e.g., both are in a 15 cm diameter, 3 L sauce pan? What about the area of the heat source? Identical or different? This is an ill-defined question. $\endgroup$– Bill NOct 23, 2015 at 16:41
-
$\begingroup$ @BillN The question is CAN and that is answerable. One container will equal or better every time. $\endgroup$– paparazzoOct 24, 2015 at 3:44
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
6
Heat that has to go into the water is the same. What you have to worry about is heat loss to the surroundings.
As stated in the comment you will have less surface area for heat loss with a single container. Assume a simple sphere. Volume is proportional to the cube of the radius and area is proportional to the square of the radius. If you do the math one container has 2 to the power -2/3 area compared to two. Or one has 63% of the area or two. Surface heat loss of one is 1/3 less than with two.
After heated one container will also cool more slowly than two smaller containers.
-
$\begingroup$ JohnRennie is right: the question is too vague. How about if both containers are adequately insulated and heated by an immersion heating element, for instance? $\endgroup$– GertOct 23, 2015 at 15:16
-
$\begingroup$ @Gert So insulated? More surface area is more surface area. More surface area is more heat loss. Immersion as in a bath? It will still take a bigger bath for two 1L and the bath will have more surface area, more heat loss, and less fuel efficiency. $\endgroup$ Oct 23, 2015 at 15:37
-
$\begingroup$ You also have to consider the surface area for delivery of heat to the water. The shape of the containers is critical. $\endgroup$– Bill NOct 24, 2015 at 23:22
-
$\begingroup$ @BillN Would a smaller area be better or worse? Really, shape effects heat delivery? Heat is shape aware? Please post an answer and enlighten me. $\endgroup$ Oct 25, 2015 at 1:10
-
$\begingroup$ Fourier's Law says that the rate of heat transfer depends on the area across which the heat flows. How you construct the source/recipient interfaces and the recipient/non-source regions will affect the efficiency of the system. For a total immersion bath, one could design a way to heat two 1L containers simultaneously faster than one 2L container because a larger area increases the heat transfer rate. Can there be a difference in efficiencies? Yes. Is it always one 2L is better? No. $\endgroup$– Bill NOct 26, 2015 at 17:22