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$: COURSE INFORMATION COURSE TITLE: …author.uthm.edu.my/uthm/www/content/lessons/173/labsheetseparating...Separating and throttling calorimeter are used to determine the dryness fraction$
UNIVERSITI TUN HUSSEIN ONN MALAYSIA Faculty of Mechanical and Manufacturing Engineering

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BDA 27201 - Edition III/2011 1

COURSE INFORMATION

COURSE TITLE: ENGINEERING LABORATORY IV (BDA 27201) TOPIC : SEPARATING AND THROTTLING CALORIMETER 1. INTRODUCTION Separating and throttling calorimeter are used to determine the dryness fraction of steam. In this experiment, the combination of these two calorimeters is used to determine the dryness fraction of the steam supplied to the system. The separating calorimeter is a mechanical process in which the incoming wet steam is made to change direction through a series of obtuse angle. As the steam travels through this angle, the inertia of the water droplets prevents them from following the changes in direction of the steam and causes them to drop out of the steam into the collection chamber. In the throttling calorimeter, the incoming steam is fed into the throttling calorimeter body via a fixed orifice, the pressure inside the calorimeter body being slightly above atmospheric. This causes the steam to become superheated and by measuring the final temperature and pressure this steam, the dryness fraction of the steam can be calculated. However, both these types of calorimeters have shortcoming. The separating calorimeter cannot separate out all of the water and some is carried over with the dry steam. The throttling calorimeter relies on the steam being throttled into the superheat region, which is not possible if the steam is too wet before throttling. The solution to these problems is to combine the two types of calorimeter by connecting them in series; the separating calorimeter being nearest to the incoming main. The schematic of the separating and throttling calorimeter is shown in Figure 1 and they are mounted physically on a freestanding unit with integral instrumentation.


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Figure 1: Schematic of system

The unit is provided with a pressure gauge for measuring the steam main pressure and a mercury manometer for measuring the pressure inside the throttling calorimeter. Temperatures of the steam main and the throttling calorimeter interior are measured by a multipoint pyrometer, the readout of which is mounted at the top of the unit. Figure 2 shows the equipment panel mounted on a freestanding framework.

Figure 2: The equipment panel mounted on a freestanding framework

P1

X

Xs

T1 T2

M anometer

P2

Titisan Air Yang Diasingkan W s

Kalorimeter Pemisah

Air Penyejuk Masuk Air Penyejuk

Keluar

Kalorimeter Pendikit

Pemeluwap

Air Yang Tersejat Wt

Steam Inlet V alve

A nalogue S electo r sw itchTem perature Selector Sw itch

Throttling Calorim eterM anom eter Isolating V alve (V 2)Separating Calorim eter

Slight G lass

C ondenser

C ooling W ater In

D rain V alveCo oling W ater O ut

C ondensate C ollection V essel


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2. OBJECTIVES To determine the dryness fraction of steam 3. LEARNING OUTCOMES At the end of this experiment, students should be able to:

a. Understand the concepts of dryness fraction b. Implement and analyze the required data collectively within

member of group. c. Produce good technical report according to the required

standard 4. THEORY The following are the relevant theories pertaining to the experiment

Dryness Fraction The dryness fraction is defined as the quantity of dry vapour present in any wet vapour mixture.

water steamdry ofQuantity

steamdry ofQuantity fraction Dryness

Separating Calorimeter

This is a mechanical process where the incoming steam to the calorimeter is made through a series of obtuse angle where the inertia of the water droplets causes them to separate from steam flow. If

tW = quantity of dry steam discharged from calorimeter

sW = quantity of water separated in the calorimeter in the same time interval;

then the dryness fraction as measured by the separating calorimeter (Xs)

sts WW

tWX

(1)


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Throttling Calorimeter

Consider a fluid flowing through a throttling orifice from higher pressure P1 to a lower pressure P2. From the steady flow energy equation, it can be shown that adiabatic throttling is a constant enthalpy process. The wet steam before the throttling will become superheated steam at the lower pressure after throttling. Enthalpy of wet steam at P1 before throttling;

111 fgtf h XhH

where

1fh = specific enthalpy of saturated liquid (sensible heat) corresponding to pressure P1

tX = dryness fraction of steam measured by throttling calorimeter

1fgh = specific enthalpy of vaporisation (latent heat) corresponding to

pressure P1 Enthalpy of superheated steam at P2 after throttling

2222 spg tt ChH

where

2gh = specific enthalpy at saturated vapour corresponding to pressure P2

pC = specific heat at constant pressure

2t = steam temperature at throttling calorimeter

2st = saturated steam temperature corresponding to pressure P2

Since 21 HH ,

22211 spgfgtf tt Chh Xh

1

1222 )(

fg

fspg

hhttch

Xt

(2)


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Combined Separating and Throttling

If w = quantity of water in steam leaving the separating calorimeter and entering the throttling calorimeter, then by definition of dryness fraction

t

tt W

wWX and )1( tt XWw

But the separating calorimeter has already removed Ws water, therefore total quantity of water is (Ws + w) in wet steam ts WW Applying this to the definition of dryness fraction

ts

sts

WWwWWWX

ts

t

WWwW

but )1( tt XWw

ts

ttt

WWXWW

)1(

tts

t XWW

W x

From equation (1) st

s WWtW

X

Therefore: True dryness fraction,

ts XXX x (3)


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5. EQUIPMENT Cusson P7660 Separating and throttling calorimeter (as shown in Figure 3).

6. PROCEDURES

a. Start cooling water flow through condenser. b. Place condensate collecting vessel under the condenser outlet. c. Close small valve on throttling calorimeter to isolate the manometer. d. Open the steam valve and allow the steam to flow through the calorimeters

to warm up the system. Ensure that the water flow through the condenser is sufficient to condense all the steam.

e. When condition have stabilised, open the valve to the manometer. f. Allow the separated condensate level to build up in the separating

calorimeter until liquid can be seen in the calorimeter condensate level tube.

g. Drain the condensate-collecting vessel. h. Refit the main condensate-collecting vessel under the condenser outlet.

Figure 3: Cusson P7660 Separating and throttling calorimeter


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i. Measure and record:

a. Initial value of fluid level in the separating calorimeter. b. Initial value of condense level in the main condensate-

collecting vessel. c. The steam pressure in the steam main. d. The steam pressure after throttling. e. Steam main steam temperature. f. Temperature in the throttling calorimeter. g. Barometric pressure.

The value from (c) to (f) parameter values should be checked about six times during the course of measurement.

j. Allow the apparatus to cool and turn off the condenser cooling water. k. Drain the separating calorimeter. l. Empty the condensate-collecting vessel.

7. EXPERIMENT DATA

Refer to the data sheet provided in Appendix A.

8. RESULT AND DISCUSSION

a. Complete the data sheet provided in Appendix A. b. Calculate the dryness fraction for the steam after flow through the

separator, Xs and throttle, Xt. c. Give suggestion on the overall performance of steam line based on the true

dryness fraction, X obtained.

9. QUESTIONS

a. Explain the importance of the dryness fraction value for a steam power

plant in terms of safety and economic. b. Define the overall processes of steam power plant in obtaining the

practical and effective dryness fraction.

10. CONCLUSION

Deduce conclusions from the experiment. Please comment on your experimental work in terms of achievement, problems faced throughout the experiment and suggest recommendation for improvements.


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APPENDIX A

SEPARATING AND THROTTLING CALORIMETER

DATA SHEET: Observed Readings

Parameters 1 2 3 4 5 6 Ave.

Barometric pressure, bar.abs

Separator: Steam pressure, bar.abs

Throttle: Steam pressure, mm.Hg

Throttle: Difference in mercury level due to water, mm.Hg

Separator: Steam temperature, oC

Throttle: Steam temperature, oC

Separator : Amount of collected water, ml

Throttle: Amount of condensed water, ml

Derived Results

Parameters Average

Throttle: Specific heat at constant pressure, kJ/kgK

Separator: Steam pressure, bar.abs

Throttle: Steam pressure, bar.abs

Separator: Saturated liquid enthalpy, kJ/kgK

Separator: Latent heat, kJ/kgK

Throttle: Vapour Enthalpy, kJ/kgK

Throttle: Saturated steam temperature, oC

Separator: Dryness fraction of steam, Xs

Throttle: Dryness Fraction of steam, Xf

Steam Line: Dryness fraction, X

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