what is the driving potential for heat transfer?

Question

In a roomm with air at 20 deg. celcius, two cups are placed containing equal amounts of coffee but at 85 deg. celcius and 45 deg celius respectively. Coffee in the first cup cools down to 75 deg. celcius in 2 minutes. How long it will take for the coffee in the second cup to cool down to 35 deg. celcius.

Answer 1

q1=m1.c.(85-20)
q1=65*m1*c
q2=25*m2*c
q1=q2*13/5(m1=m2,c=constant)
so, time required for cup 2 is 5/13*2
=10/13 minutes



There is an elementary equation from basic thermodynamics that states that the rate of heat transfer (Q) equals the mass flow rate (M) times a Constant (the specific heat of water) times the Delta T (fluid temp out minus fluid temp in):
Q = M x C x Delta T
In other words, the rate of heat transfer is directly proportional to mass flow rate. If you increase the flow rate, you will then increase the rate of heat transfer. Since you cannot mess with mother nature, it is very naive to think it works any other way.

Answer 2

6 minutes. The driving potential is temperature difference. As an approximation, you can say that the 85 to 75 degree cup of coffee was (80-20) = 60 degrees above room temp. Similarly, the 45 to 35 degree cup was 20 degrees above room temp. Therefore the driving force for heat loss from cup 2 was one-third that of cup 1, so it would take 3 times as long to cool 10 degrees.

Answer 3

The driving force for atmospheric motion is the sun and, in particular, the uneven distribution of solar radiation across the earth. It is the primary job of the atmosphere to redistribute energy in order to achieve a balance from pole to equator. We need to understand methods of heat exchange in the atmosphere to appreciate how the thin atmosphere keeps us alive
Energy is the ability or capacity to do work on some form of matter.
Potential energy is the energy which a body possesses as a consequence of its position in a gravitational field (e.g., water behind a dam).
Kinetic energy is the energy which a body possesses as a consequence of its motion (e.g., wind blowing across a wind generator). It is dependent upon an object's mass and velocity (e.g., moving water versus moving air).
Internal energy is the total energy (potential and kinetic) stored in molecules.
Heat (or thermal) energy is kinetic energy due to motion of atoms and molecules. It is energy that is in the process of being transferred from one object to another because of their temperature difference.
Radiant energy is the energy that propagates through space or through material media in the form of electromagnetic radiation.


The First Law of Thermodynamics states that energy lost during one process must equal the energy gained during another.

Energy is required to change from solid to liquid, liquid to gas (evaporation), or solid to gas (sublimation). Energy will be released to change from liquid to solid (fusion), gas to liquid (condensation), or gas to solid.

Answer 4

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