Consider the mixing of a steam flow with an oxygen flow in Problem 12.71 . Find the rate of tota

Consider the mixing of a steam flow with an oxygen flow in...

Key Concepts

Exergy

Exergy represents the maximum useful work obtainable from a system as it comes into equilibrium with its environment. It serves as a measure of the quality or usefulness of energy and plays a critical role in assessing the performance of thermodynamic processes.

Availability

Availability is the portion of a system’s energy that can be converted into useful work. It quantifies the potential of an energy stream to perform work when compared to a reference environment and is a fundamental concept when determining the inflow of usable energy in a process.

Exergy Destruction

Exergy destruction quantifies the loss of potential to do work as a result of irreversibilities within a process. It is directly associated with entropy generation and indicates inefficiencies in the system, helping engineers to identify and minimize energy losses.

Mixing Process

A mixing process involves combining two or more different streams, where the mixing is typically irreversible due to spontaneous homogenization. Analysis of mixing processes is essential in exergy assessments because the inherent irreversibility leads to destruction of exergy.

Second Law Analysis

Second law analysis involves applying the principles of entropy and irreversibility to evaluate energy systems. It provides the framework for determining the actual performance compared to the ideal scenario, thus allowing for quantification of exergy inflows and the corresponding losses through exergy destruction.

Transcript

0:00 Hi, everybody.

00:01 So we need to consider a mixing of steam flow with an auction flow and problem 12 .71 and find the rate total flow availability of rate energy destruction in the process.

00:13 Okay.

00:13 So for this, we have your phi equal, your phi n equals m capital phi n equals m, capital, phi, n, equals mh2o, capital phi, h2o plus m -o -2 for oxygen and capital phi o2.

00:40 So your phi -o -h -o -2, i put h -h2, i mean h2, my bad.

00:48 H -1 equals h -o minus t -o minus t -o for initial.

00:55 This equals c .p .h .2.

01:00 T1 minus t initial minus t initial times c .p.

01:07 Log.

01:07 T .1 over t initial minus r log.

01:11 P1 over p initial.

01:14 And if we plug into the numbers, we have 1 .872 times 400 minus 25 minus 29.

01:26 815 times 1 .872 log of 673298 .25 minus 0 .4615 log of 400 divided by 100.

01:48 Okay.

01:50 And so this is going to equal to 438 .3 .438 .3 .435.

01:57 Kilojoules per kilogram and just pause on this video and you know put that into your calculator and you know check if i'm right around okay and now and that's for the h2 so now we're going to do the capital 5 of o2 okay which is going to follow this same equation except for for this we're going to swap out the, you know, h2o, we're just going to swap out where there's h2.

02:28 We're going to swap out.

02:29 Swap that for our o2, okay? so in that case, where i'm just going to write it out, 922, 126 .85 minus 25, minus 298 .15, 0 .922.

02:56 Log and this one is 400298 .15 minus 0 .298 0 .98 log of 400 over 100.

03:17 Okay.

03:19 And so this equals to 120 .494 .9 kilojoules per kilogram.

03:26 Now we can do the phi -in and we're just going to go all.

03:29 The way back up here and use this equation here.

03:33 Okay.

03:38 So we have that.

03:40 1 .8 and now we have this number 138 .34 from the 5h2 plus 3 .2 from 120 .49 and this equals 1174 .5 kilowatts.

04:05 Now, what we can do is mix the temperature, and we find the number of moles and then mixed temperature.

04:14 So we get mh2, capital mh20, and it's 1 .8 divided by 18 .015.

04:23 And we get 0 .1 kilomoles per second.

04:28 And now i'm going to have moles in 02, and it's going to be 3 .2 divided by 3 .1 .3 .1 .3...

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