heat pump lab note (1)

8/17/2019 Heat Pump Lab Note (1)

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&. INTRODUCTION

&.&. /im+ of Heat !"mp /pparat"+0

a1 To demonstrate the performance of a heat pump in both heating and cooling modes.

-1 To demonstrate the process of air conditioning.

&.$. O-2ecti3e+0

To achieve an understanding of the Second Law of Thermodynamics as applied to a heat

pump in both heating and cooling modes.

&.(. E#periment+0

a1 Production of heat balance for a heat pump;

In this experiment it will be shown that the total energy transferring into and out of the

system is !ero.

-1 "erification of the Second Law of Thermodynamics;

The actual and ideal system calculations will be compared.

c1 Study of the performance of a heat pump #pparatus;

Performance of ideal and actual systems will be calculated.

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$. THEORETIC/L O!ER/TION

This apparatus uses water as a source and air as a sin% in heating mode and water as a sin%

and air as a source in cooling mode. In cooling mode heat pump can be named as air cooler.

&igure $ shows the theoretical circuit of apparatus in heating mode drawing energy from the

circulating water and delivering it to the air. The compressor delivers refrigerant under

pressure and at high temperature to the refrigerant'to'air heat exchanger where heat is

transferred to the air and the refrigerant condenses in the process. The refrigerant then passes

through a restriction tube to the low pressure side of the circuit and to the refrigerant'to'water

heat exchanger where it evaporates ta%ing up heat from the circulating water. It then returns

to the compressor.

Fi"re &0 Flow diagram in heating mode

Note: (nergy flows in watts.

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&igure ) shows the theoretical circuit in cooling mode. The direction of flow is now reversed.

The refrigerant passes from the compressor to the refrigerant'to'water heat exchanger where

it gives up heat to the cooling water subse*uently passing through the reducing valve to the

refrigerant'to'air heat exchanger where it evaporates and extracting heat from the air. +hen

the apparatus acts in cooling mode the air is sometimes cooled to below the dew point and

condensate is deposited.

Fi"re $0 Flow diagram in cooling mode

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(. C/LCUL/TION

Notation

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TERM SYM4OL UNITS

iameter of ischarge uct D m&low /ate of ischarge #ir V sm ,

&low /ate of 1irculating water L h L

ensity of #ir at ischarge a ρ ,

mkg

Pitot tube "elocity 2eat l H OmmH )3aximum "elocity in ischarge uct U sm

3ean "elocity in ischarge uct U sm !re++"re+

4arometric Pressure a P )

m N

Ma++ Flo5 Rate+

ry #ir l m $

. −

skg

1ondensate at ischarge)

m $

. −

skg

1irculating +ater ,m $

. −

skg

Temperat"re+

#ir at Inlet$T K

#ir at ischarge)

T K 1irculating +ater at Inlet ,T K

1irculating +ater at ischarge-

T K

1ompressor'2eat Pump ischarge1ooler Inlet 5T K

1ompressor'2eat Pump Inlet1ooler ischarge 6T K

/efrigerant to +ater 2eat (xchanger'2eat Pump ischarge 7T K

/efrigerant to +ater 2eat (xchanger'2eat Pump Inlet 8T K

/efrigerant to #ir 2eat (xchanger'2eat Pump Inlet 9T K

/efrigerant to #ir 2eat (xchanger'2eat Pump ischarge $0T K

!o5er Inp"t

/efrigerator 1ompressor C E atts

&an F E atts

Heat 6"antitie+

Specific 2eat of +ater C C kg ! 0

Specific 2eat of #ir at 1onstant Pressure P C C kg !

0

Specific (nthalpy of +ater "apor "h kg !

Specific (nthalpy of 1ondensate h kg !

Enthalp* Flo5 Rate+

ry #ir (ntering 1onditioner $

# s !

+ater "apor (ntering 1onditioner )# s !

ry #ir Leaving 1onditioner ,# s !

+ater "apor Leaving 1onditioner -

# s !

1ondensate 5# s !

1irculating +ater at Inlet 6# s !

1irculating +ater at :utlet 7# s !

/adiation and Stray Losses 8# s !

!+*chometric Data

/elative 2umidity at Inlet φ

ensity of Saturated +ater "apor at Inlet w ρ ,

mkg ensity of ry #ir at Inlet a ρ

,mkg

Specific 2umidity at Inlet γ

I)eal Heat !"mp

Power Input s !

Input &rom 1old Source)$ s !

:utput to 2ot Sin% l $ s !

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In both heating and cooling modes apparatus is operating as a reversed heat engine or heat

pump since the ultimate effect is to transfer heat from one reservoir to another normally at

higher temperature using mechanical energy wor%ects it isothermally

at a higher temperature =). The intervening processes are termed ?adiabatic@ and ?isentropic@.

Fi"re (0 The %ideal& re"ersi'le engine(

The ?coefficient of performance@ of the machine when operating as a heat pump is defined

asA

$CP H )= $<

#nd when operating as a refrigeratorA

$CP )

$

= )<

These e*uations also apply to a real machine operating between the same temperature limits

but the numerical values will be less than those corresponding to the ideal reversible engine

for whichA

( )$)

)

θ θ

θ

−

= *+, H

CP ,<

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Fi"re 70 The energ- diagram o. the a//arat0s(

The machine is shown diagrammatically in figure - which shows the various energy flows

through the system boundary. They are defined as belowA

(nthalpy of dry air entering conditioner

$$$T C m# P = 6<

(nthalpy of water vapor entering conditioner

"hm# $) γ = 7<

(nthalpy of dry air leaving conditioner

)$,T C m# P = 8<

(nthalpy of water vapor leaving conditioner ( ) "hmm# )$- −= γ 9<

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(nthalpy of condensate

whm# )5 = $0<

(nthalpy of circulating water at inlet

C T m# ,,6 = $$<

(nthalpy of circulating water at outlet

C T m# -,7 = $)<

/adiation and stray losses

8#

(lectrical input to fun

F E

The steady flow energy e*uation for the system may then be writtenA

( ) ( ) ( ) ( ) 8)$5-,76 ###### E E ## F C ++−++=++− $,<

The first term represents the heat supplied to the system from the circulating water. The

second term represents the electrical power input. The algebraic sum of these terms is e*uated

with the increase in enthalpy of the air and water vapor passing through the system together

with the stray losses to the surroundings. The steady flow e*uation applies e*ually with

appropriate changes of sign when the machine is operating as a cooler.

+hen operating in heating mode the coefficient of performance may be defined in twodifferent ways.

&. The overall of external coefficient isA

( ) ( ) ( )

( ) F C E H

E E

#####CP

+

+−++=

)$5-,

$-<

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( )$08

$0

T T

T CP

*+, )−

= )$<

In this case the thermal e*uivalent of the power supplied to the fan reduces the overall cooling

effect since it is transferred to the cooled air on its way to the discharge duct.

The air flow through the conditioner is measured by means of a pitot tube mounted in the

centre of the discharge duct. The pressure of the air at this point is effectively e*ual to that of

the atmosphere a P and its density a ρ is given by the gas e*uationA

$ )T

P

a

a=

ρ ))<

The velocityU corresponding to a velocity head $ H in OmmH )


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The corresponding mass rate of flow isA

)

$

$ 00$05.0

T

P H m a= )8<

The specific humidity of the air entering the conditioner is related to the relative humidity C

as measured by the whirling hygrometer by the e*uationA

a

ρ

φρ γ = )9<

where ρ and a ρ are the densities respectively of saturated water vapor and of air at inlet

conditions. The value of the former together with the enthalpies of steam and water may be

read from steam tables.

7. RE!ORT FORM/T

# brief description of what should be included in each of these sections is included below.

IntroductionA Dour introductory paragraphs must includeA

' :b>ectiveA # single concise statement of the ma>or ob>ective of the lab

' ProcedureA Include the information necessary to allow someone to repeat

what we did.

:bservations and /esultsA

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1alculations will be made for heat pump and air cooler modes.

$. 1alculate mass flow rates of air and water in %gs.

). 1alculate enthalpy flow rates =$ =) E. =8<

,. 1alculate the following coefficient of performanceA

o The overall of external coefficient for real and ideal cases.

o The overall of internal coefficient for real and ideal cases.

o +rite your comments on the results.

-. Show the energy balance of the systemA

o (lectrical energy to compressor motor

o (lectrical energy to fan motor

o 2eat from circulating water

o 2eat tofrom air

o 2eat from condensed water vapour

o 2eat tofrom surroundings.

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heat pump lab note (1)

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