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 sameer mohrir August 9, 2000 01:44

Entropy

I would like to ask question to all What will happen to the entropy if glowing tubelights / light bulbs in a closed room are switched off ?

 clifford bradford August 10, 2000 17:14

Re: Entropy

if the room is perfectly insulated and no air can get in or out - nothing: it remains constant. otherwise if the room was simply impervious to inflow/outflow then the entropy would decrease (note however that the entropy increase of the environment would be greater than the entropy decrease of the room.

 sameer mohrir August 10, 2000 23:15

Re: Entropy

This means entropy is property of system.

 John C. Chien August 11, 2000 09:48

Re: Entropy

(1). The foundation of the modern heat engines, such as steam engine, internal combustion engines, jet engines and rocket engines are all based on the concept of thermodynamics and entropy. (2). The design and analysis of these engines (cycles) requires the so-called "h-s" diagram, where h is the enthalpy and s is the entropy. In the h-s diagram, you can plot the state of the flow, such as the free stream state, inlet state, exit state, etc... From the diagram, you will be able to determine the heat energy added to the fluid, or the work done by the fluid, and the loss,etc... (3). Without that, you don't have modern heat engines. It is not an abstract concept at all. (courses required in this area is fluid mechanics, thermodynamics (I,II,III), heat transfer, internal combustion engines, steam turbine engines, gas turbine engines, jet and rocket propulsion.

 clifford bradford August 11, 2000 17:27

Re: Entropy

yes entropy (S) is a property. it is an extensive property. in fluimechanics we often use specific entropy (s) which is an intensive property. you can look up these definitions in a thermodynamics book.

 John C. Chien August 13, 2000 14:26

Re: Entropy

(1). Don't feel bad at all. (2). I have seen people carrying this concept even further to define the efficiency distribution in turbomachinery. (3). From the 3-D code, they define the 3-D efficiency. From the 2-D code, there are 2-D efficiency distribution. (from a world leading company) (4). I must say that, 3-D cfd does open up additional possibilities to do simulation. But it also generate new problems because of the inadequate training in the basic understanding of the subject. (5). This is because the world of thermodynamics, 1-D world, 2-D inviscid and viscous world will generate flow field and concepts which is quite different from that of 3-D . Even the result of 3-D inviscid equation will generate concept which is completely different from that of 3-D viscous equation. It is not easy for an average person to get these results and concepts related. (so, the entropy distribution is 3-D, since it is related to the loss, so, they wrote a subroutine in the 3-D cfd code to calculate 3-D efficiency distribution. So, anything is possible in cfd. this is a true story, not a joke)

 sameer mohrir August 13, 2000 23:16

Re: Entropy

Hello John

Can you tell us which institutes provide training in 3D cfd codes

 John C. Chien August 14, 2000 00:20

Re: Entropy

(1). Most schools involved in cfd should have their own cfd codes for research and training. (2). You can find these schools in the resources sections. (3). From my point of view, the commercial cfd codes are commercial products. These are not for training or educational purpose. They are there to make money. (4). If you can use commercial cfd codes to make money, then it is perfectly all right to use it. But what I am saying is that they are there to make money, not to show you the source code and teach you how to write cfd codes. If the particular feature in cfd is not in the commercial code, then it is not there. And if they figured out that by including the feature in the code they can make more money, I think, they will try to include it in the code. (5). The support engineers are there because it was included in the purchase of the license, not because they have to be there to serve the reader. (6). I think, one of the biggest problem in cfd is the quality of the cfd users. Since there is no law to regulate the quality of the users, more harm will be generate before more good is seen by using cfd. What I am saying is that, the application industries will be contaminated first (except a few experienced user compaines)with wrong solutions. But that's life. Something like silicon implant, it will take a while for an average person to feel the risk. There is nothing wrong with the product in this case either. (7). So, to obtain the befinit fo using cfd, the users must be well trained and educated. (unfortunately, that is not the goal of the commercial code vendors) (8). Since, the code does not read this forum, we try to provide some information or guidlines for the users.

 sameer mohrir August 14, 2000 00:51

Re: Entropy

Hello John