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Transcribers Name: xxx

Applied Thermodynamics for Marine Systems

Prof. P.K.Das.

Dept. of Mechanical Engineering

Indian Institute of Technology

Lecture # 20

Psychometrics (Contd.)

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ah ((seen))((00:57:54.20 min)) what is your hm ah what is your humidity ratio or specific

humidity.

now hm this keeps some sort of a measure of some sort of a measure of water vapor present

water vapor actually present in a sample of moist air.

but it has been seen that this does not give us much information regarding the comfort feeling in

a particular sample of air okay. for that we need to define certain other quantities.

first we would like to define due point temperature and then we will go to the other quantities.

due point temperature, it is related to the process of condensation and we are familiar with this

process that mean ((02:05:54.20 min)) that ah.

when the temperature is lowered, then in a particular sample of moist air at certain temperature

we will find ah the presence of liquid water.

now this liquid water there generally formed in the {form in}((02:27:54.20 min)) in the form of a

small droplets and cold surfaces and they are most commonly known as due.

so thats why the temperature at which these liquid droplets appear, that temperature is known

as due point temperature.

thermodynamically the process is something like this

(Refer Slide Time: 02:47:54.20 min)

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if we have the TS diagram and this the true phase zone. so, hm a constant pressure line is

something like this.

this is the constant pressure line.

let, this is the critical point k and condition of the water vapor in a particular sample of in a

particular sample of ah hm ah hm air. that is given by this particular point.

now hm

this is {e}((03:53:54.20)) is equal to constant. this is a constant pressure line. okey.

now keeping the pressure same, if we cool the sample, then we are following this path. if we

come to this point then what will happen. then we will have saturated vapor and after this point

we will have we will enter the true phase zone.

so here we are having superlative vapor and we are cooling it along this constant pressure path.

so here we will come to the saturated vapor line so now it is saturated and after this

((04:45:54.20)) small amount of its rejection or its destruction from the sample then we will have

condensation.

so here we will have formation of water droplet or due. so this temperature is called [noise] due

point temperature.

let us denote it by d. so this is the due point temperature. so you can see that,[noise] for a

particular sample, a particular sample means it will be at a particular temperature and at a

particular pressure.

it will have a due point temperature. if keeping the pressure same if we want to i mean if we

start on extracting heat from the sample, then at one temperature its temperature is falling at

one temperature, it will it will start condensation will start in the sample and that temperature is

known as due point temperature. so this is about due point temperature.

now hm

then we like to let us call a due point temperature.