00:01
In this question it is given that water enters in a heat exchanger and the mass flow rate of the water is 10 kilogram per second.
00:11
In the heat exchanger, its temperature increases from 100 degrees centigrade to 500 degrees centigrade and the pressure remains constant that is 2 ,000 kilo -pascal.
00:26
Air is used to heat this water.
00:30
The inlet temperature of the air is 1 ,400 kelvin and the outlet temperature of the air is 460 kelvin.
00:41
We are required to calculate the second law efficiency.
00:45
So let's see how to solve this question.
00:47
First of all, let's draw a rough diagram of the heat exchanger and the heat exchanger is shown below.
00:54
So here we have the heat exchanger.
00:57
Water is entering from this point let's say this is 1 and it is leaving from this point let's say it is 2 air is entering from this point let's say this is 3 and air is leaving from this point let's say this is 4 now let's apply the energy equation to calculate the mass flow rate of air so we can write m .w multiplied by h2 minus h1 this will be equals to m .d.
01:28
Air, this is the mass flow rate of air, multiplied by h3 minus h4.
01:34
So from here we can write, mass flow rate of air is equals to mass flow rate of water multiplied by h2 minus h1 divided by h3 minus h4.
01:47
Now we will substitute all the values from this steam table.
01:51
So we can write m .d .a is equals to m .w, that means, 10, multiplied by 3 ,467 .55 minus 420 .45 divided by 1 ,515 .27 minus 462 .34.
02:17
So when we further calculate we get mass flow rate of air is equal to 28 .9 .9 kilogram per second...