Loop Heat Pipe Operation Using Heat Source Temperature for ... · Loop Heat Pipe Operation Using Heat Source Temperature for Set Point ControlTemperature for Set Point Control JeJe

Loop Heat Pipe Operation Using Heat Source Temperature for Set Point ControlTemperature for Set Point Control

Jentung KuJe tu g uNASA Goddard Space Flight Center

Greenbelt, Maryland301-286-3130

[email protected] tu g u @ asa go

Kleber Paiva, Marcia MantelliFederal University of Santa CatarinaFlorianópolis Santa Catarina BrazilFlorianópolis, Santa Catarina, Brazil

2011 Spacecraft Thermal Control WorkshopEl Segundo, California, March 8-10, 2011

https://ntrs.nasa.gov/search.jsp?R=20110013401 2018-11-08T12:58:04+00:00Z

Introduction

• Loop heat pipes (LHPs) have been used for thermal control of several NASA and commercial orbiting spacecraft.

• The LHP operating temperature is governed by the saturation temperature of its compensation chamber (CC)temperature of its compensation chamber (CC).

• Most LHPs use the CC temperature for feedback control of its operating temperature.

• There exists a thermal resistance between the heat source to be• There exists a thermal resistance between the heat source to be cooled by the LHP and the LHP’s CC. Even if the CC set point temperature is controlled precisely, the heat source temperature will still vary with its heat output.

• For most applications, controlling the heat source temperature is of most interest.

• A logical question to ask is: ”Can the heat source temperature be used f f db k t l f th LHP ti ?”for feedback control of the LHP operation?”

• A test program has been implemented to answer the above question.

2

Test Program• Objective• Objective

– To investigate the LHP performance using the CC temperature and the heat source temperature for feedback control

• Test article• Test article– A miniature LHP built by Thermacore in 2003 under NASA’s Cross

Enterprise Technology Development Program (CETDP)– An aluminum thermal mass is attached to the LHP evaporator toAn aluminum thermal mass is attached to the LHP evaporator to

serve as the instrument simulator.• Test variables

– Location of the temperature sensor used for feedback control ofLocation of the temperature sensor used for feedback control of LHP operation: CC, evaporator, and thermal mass

– Heat load to the thermal mass: 10W to 140W– Aluminum thermal mass: 110g and 350gg g– Thermal control device attached to the CC: thermoelectric

converter (TEC) and electric heater (EH)– Temperature control scheme: PID (proportional–integral–derivative

control) and on/off • Only the results of PID control are presented.

3

CETDP MLHP Design• CETDP MLHP built by Thermacore - 2003CETDP MLHP built by Thermacore 2003

Item Description

EvaporatorSS - 6.35 mm O.D. x 51 mm length

Aluminum Shell

Primary Wick

SS - 5.6 mm O.D. x 2.4 mm I.D

1.2 µm pore size

1.0 x 10-14 m2

Secondary Wick SS - screen, 400 x 400 meshSecondary Wick SS screen, 400 x 400 mesh

CompensationChamber

SS - 9.52 mm O.D. x 25.5 mm length

Vapor Line SS - 1.59 mm O.D. x 610 mm length

Li id Li SS 1 59 O D 795 l thLiquid Line SS - 1.59 mm O.D. x 795 mm length

Condenser SS tubing - 2.39 mm O.D. x 200 mm lengthSaddle: aluminum

Working Fluid Ammonia, 1.5 g

T t l M 79 gTotal Mass 79 g

Condenser

Vapor line

TEC

EvaporatorCC

Condenser

Vapor line

Condenser

Vapor line

TEC

EvaporatorCC

Liquid lineLiquid line

4

TC Locations

Evaporator/CC with

Evaporator/CC with Thermal Mass 2 (110g)

Evaporator/CC with Thermal Mass 1 (350g)

Condenser Section

5

Location of Control Temperature SensorTh l ti f th t l t t f f db k t l i• The location of the control temperature sensor for feedback control is shown below for conditions where 350 gram mass and 110 gram thermal mass were attached to the evaporator.– TC#2 on the CCTC#2 on the CC– TC#5 on the evaporator– TC#33 on the thermal mass.

• Effect of high thermal resistance between thermal mass and LHPEffect of high thermal resistance between thermal mass and LHP– A large thermal resistance was imposed between the thermal mass and the

evaporator in this test (0.23 K/W or 4.4W/K).– High thermal resistance: TC #33 was used for feedback control– Near-zero thermal resistance: TC#5 was used for feedback control

6

Test Variables

THERMAL MASS 110g

or350g

TEC EH

TMEVAPCC EVAPCC TM TMEVAPCC EVAPCC TM

PID On/Off PID On/Off

7

EH versus TEC

• The following charts show the effect of using LHP CC temperature and the heat source temperature for feedback control.

– The CC was not preheated prior to start-up.• Also shown are the effect of using TEC and electrical heater for CC

temperature control.• All tests employed the PID control scheme.• No sophisticated control algorithm was used for transient operation.

8

CC Controlled at 293K – EH/2W/PID/350g

• CC, evaporator and TM temperatures were stable between 20W and 120W.• CC could no longer be controlled at 293K at 140W due to condenser limit (CC

temperature rose to 297K)• The start-up transient is shown in next slide

12/15/2009; 253K sink; 350 g mass;EH set point@293K on the CC - TC2

340

350

140

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310

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330

340

e (K

) 100

120

140

W)

TM (33) Evap. Power

Evap.(5

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310

Tem

pera

ture

40

60

80

Pow

er (W

CC (2)

CC In (27)

Vap. Line (11)

250

260

270

-20

0

20CC In (27)

Liq. Line

EH power

8:45 9:15 9:45 10:15 10:45 11:15 11:45 12:15 12:45 13:15 13:45

Time (HH:MM)

9

CC Controlled at 293K – EH/2W/PID/350g

• Loop started as soon the power was applied to TMLoop started as soon the power was applied to TM. • Right after start-up, CC temperature rose because of the return of warm liquid. • The CC eventually reached its natural operating temperature of 295K, higher than desired

set point.• During the transient from 10W to 20W, EH power (2W) was not enough to raise the CC

temperature quicklytemperature quickly.

12/15/2009; 253K sink; 350 g mass;EH set point@293K on the CC - TC2

320

140

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300

310

e (K

) 100

120

140

W)

TM (33)

Evap.(5)

CC (2)

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280

Tem

pera

ture

40

60

80

Pow

er (W

Evap. Power

CC (2)CC In (27)Cond. In (13)

240

250

260

-20

0

20Power

Cond. Out (23)

EH power

8:45 9:00 9:15 9:30 9:45

Time (HH:MM)

10

Evaporator Controlled at 303K – EH/3W/PID/350g

• Simulated near-zero thermal resistance between heat source and LHPSimulated near-zero thermal resistance between heat source and LHP.• Evaporator temperature was stable at 303K between 10W and 100W. • The CC temperature decreased in steps between 20W and 100W in order to maintain

evaporator at 303K.• At 120W, the condenser limit was reached. The CC did not have enough subcooling to

maintain the evaporator at 303Kmaintain the evaporator at 303K.

12/14/2009; 253K sink; 350 g mass;EH set point@303K on the Evaporator - TC5

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350

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3 0

e (K

)

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W)

TM (33)

Evap. Power

E (5

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pera

ture

40

60

Pow

er (W

Evap.(5

CC In (27)

Vap. Line (11)CC (2)

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20

0

20CC In (27)

Liq. Line

EH power

11/3/10

25013:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00 17:30

Time (HH:MM)

-20

11

Evaporator Controlled at 303K – EH/3W/PID/350g

• Initially, CC/evaporator at 299K. As 10W was applied to evap, EH heated the CC because the evaporator set point was 303K.

• When the evaporator reached 303K, EH was deactivated. However, heat leak raised CC to 312K when the loop started with evaporator at 316K.

• Cold liquid led to CC temperature drop to 298K and evaporator to 300K. EH heated the CC until evaporator reached 303K. This was followed by a few more cycles of temperature oscillation, and loop eventually reached SS. y y p , p yTM sensible heat also contributed to the temperature oscillations.

• The loop was never shut down (vapor line TC 11 was at CC saturation temperature all the time).

12/14/2009; 253K sink; 350 g mass;EH set point@303K on the Evaporator - TC5

300

310

320

100

120

140

TM (33)Evap (5)

CC (2)

270

280

290

empe

ratu

re (K

)

40

60

80

Pow

er (W

)

CC In (27)Vap Line (11)

250

260

270

Te

0

20

40Evap PowerCond Out (23)

EH Power

3/2//10

24013:30 13:45 14:00 14:15 14:30 14:45 15:00

Time (HH:MM)

-20

12

TM Controlled at 313K – EH/4W/PID/350g

• At 10W the loop repeatedly started and shut down (see next slide)At 10W, the loop repeatedly started and shut down (see next slide).• At 40W, TM oscillated between 312K and 314K, less at 60W. No oscillation at 80W.• At 100W, condenser limit and CC at 287K. 120W, condenser limit, CC at 292K.• Temperature oscillations resumed at 30W and 10W (not just a start-up transient effect).

12/16/2009; 253K sink; 350 g mass;EH set point@313K on the TM - TC33

330

340

350

120

140

Evap

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330

ure

(K) 80

100

(W)

TM (33)

Power

Evap (5)

Vap Line (11)

280

290

300

Tem

pera

tu

20

40

60

Pow

er (

CC In (27)

Vap. Line (11)

CC (2)

250

260

270

-20

0

20

EH Power

11/3/10

8:00 9:00 10:00 11:00 12:00 13:00 14:00Time (HH:MM)

13

TM Controlled at 313K – EH/4W/PID/350g• Initially, CC, evaporator, and TM were at 294K.

Wh 10W li d EH h h CC Wh TM h d 313K EH d i d• When 10W was applied to evaporator, EH was on to heat the CC. When TM reached 313K, EH was deactivated. However, CC temperature rose due to heat leak from the evaporator.

• As the loop started, CC temperature dropped to 297K due to cold liquid injection. TM was at 307K.• EH heated the CC. The loop was shut down with 4W to CC and 10W to TM. The loop then repeated startup and

shutdown.• At 20W, the oscillation reduced. Loop did not completely shut down (TC 11 always followed TC 2) although

forward/back flow alternatedforward/back flow alternated.

12/16/2009; 253K sink; 350 g mass;EH set point@313K on the TM - TC33

320

330

120

140

TM CC (2)

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e (K

)

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100

120

W)

Evap.(5

CC (2)

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290

Tem

pera

ture

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60

80

Pow

er (W


240

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260

0

20

40

Evap Power EH Power

11/3/10

2408:30 8:45 9:00 9:15 9:30 9:45 10:00 10:15 10:30 10:45 11:00

Time (HH:MM)

0

14

CC Controlled at 293K – TEC/1W/PID/350g• CC, evaporator, and TM temperatures were stable between 10W and 120W. CC and TM

temperatures increased with increasing power.• CC temperature dropped when the heat load increased from 20W to 40W and from 40W to

60W because 1W to TEC was not enough to heat the CC during the transient.• At 140W, condenser limit was reached - TEC cooled the CC (negative TEC power).• Performance was similar to that demonstrated in 2003 tests.

12/07/2009; 253K sink; 350 g mass;TEC set point@293K on the CC - TC2; PID

340

350

140

160

310

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330

(K) 100

120

140

TM (33)

Evap P

Evap (5)

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310

Tem

pera

ture

40

60

80

Pow

er (W

)Power

CC (2) Vap Line (11)

260

270

280

0

20

40CC In (27)

Liq Line (24)

TEC Power

25013:30 14:30 15:30 16:30 17:30

Time (HH:MM)

-20

15

CC Controlled at 293K – TEC/1W/PID/350g

• When 10W was applied to TM CC temperature rose due to heat leak TEC cooled the CCWhen 10W was applied to TM, CC temperature rose due to heat leak. TEC cooled the CC.• As the loop started, CC temperature dropped due to injection of cold liquid. TEC raised CC

temperature.• The TEC power of less than 1W was not sufficient for CC temperature control during

transients.12/07/2009; 253K sink; 350 g mass;TEC set point@293K on the CC - TC2; PID

305

310

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300

atur

e (K

)

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)

TM (33)Evap (5)

CC (2)

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pera

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40

Pow

e

Evap Power


270

275

13:30 13:45 14:00 14:15 14:30-10

0

10p

TEC Power

Time (HH:MM)

16

Evaporator Controlled at 303K – TEC/1W/PID/350g

• Evaporator at 303K between 10W and 100W CC evaporator and TM temperatures wereEvaporator at 303K between 10W and 100W. CC, evaporator and TM temperatures were stable.

• At 120W, condenser limit – evaporator was above 303K. TEC cooled CC.• Evaporator was controlled at 303K again when the heat load decreased to 30W and 10W.

12/08/2009; 253K sink; 350 g mass;TEC set point@303K on the evaporator - TC5; control off

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re (K

)

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100

W)

TM (33)Evap Power

Evap (5)

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pera

tur

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60

Pow

er (W

CC (2)

CC In (27)

Vap Line (11)

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0

20Liq Line (24)

TEC Power

25013:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30

Time (HH:MM)

20

17

TM Controlled at 313K – TEC/1W/PID/350g• TM at 313K between 40W and 80W. CC and evaporator temperatures dropped at each

power increase.• At 100W condenser limit – TEC cooled CC.• Temperature oscillations between 10W and 20W. No oscillations at 40W and above.

12/09/2009; 253K sink; 350 g mass;TEC set point@313K on the TM - TC33; PID

330

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350

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100

110Evap Power

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atur

e (K

)

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r (W

)

TM (33)

Evap (5)Vap Line (11)

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Tem

pera

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Pow

e

CC (2)

CC In (27)

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20

Liq Line (24)

TEC Power250

13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30

Time (HH:MM)

10

18

TM Controlled at 313K – TEC/1W/PID/350g• Initially with 10W to TM, TEC was turned on to heat CC until TM reached 313K.• When the loop started, CC temperature dropped sharply due to cold liquid injection. TEC was turned on to heat

the CC. With only 10W to the TM, the loop was shut down, followed by repeated start-up/shutdown cycles. • At 20W, temperature oscillations occurred, but no repeated start-up/shutdown cycles.• At 40W, no temperature oscillations.

12/09/2009; 253K sink; 350 g mass;TEC set point@313K on the TM - TC33; PID

310

320

70

80

90

TM (33)CC (2)

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ure

(K)

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60

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(W)

Evap (5)

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Tem

pera

tu

20

30

40

Pow

er

Evap Power

CC ( )

Vap Line (11)

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280

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0

10CC In (27)

TEC Power

13:00 13:15 13:30 13:45 14:00 14:15 14:30 14:45 15:00

Time (HH:MM) 11/3/10

19

Pre-heating the CC prior to Start-up

• In typically LHP applications, the CC was preheated prior to start-up to ensure the evaporator wick is fully wetted.

• The following slides show that pre-heating the CC did not have much g geffect on the temperature control when the control temperature sensor was placed on the heat source.

• Using the TEC resulted in better temperature control than using the l t i l h t i l b th TEC ld l id lielectrical heater, mainly because the TEC could also provide cooling

to the CC.

20

TM Controlled at 313K (CC Preheated to 298K) –EH/4W/PID/350g

• At 10W, the loop repeatedly started and shut down (see next slide).At 40W TM ill t d b t 312K d 314K l t 60W N ill ti t 80W• At 40W, TM oscillated between 312K and 314K, less at 60W. No oscillation at 80W.

• At 100W, condenser limit and CC at 287K, TM at 323K. At 120W, CC at 292K and TM at 335K.• Temperature oscillations resumed at 30W and 10W (not just a start-up transient effect).

12/18/2009; 253K sink; 350 g mass; Pre-heating CC; EH set point@313K on the TM - TC33; PID

330

340

350

110

120

130Evap Power

310

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330

ure

(K)

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80

90

100

(W)

TM (33)

E (5)

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290

300

Tem

pera

tu

30

40

50

60

Pow

er (Evap (5)

CC I (27)

Vap Line (11)CC (2)

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270

10

0

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20

30CC In (27)

EH Power

2508:00 9:00 10:00 11:00 12:00 13:00 14:00

Time (HH:MM)

-10

2/27/10

21

TM Controlled at 313K (CC Preheated to 298K) –EH/4W/PID/350g

• Initially, CC, evaporator, and TM were heated to 298K. • When 10W was applied to evaporator, EH was on to heat the CC. When TM reached 313K, EH was

deactivated. However, CC temperature rose due to heat leak.• As the loop started, CC temperature dropped to 297K due to cold liquid injection. TM was at 306K.• EH heated the CC. the loop was shut down with 4W to CC and 10W to TM. The loop then repeated startup

and shutdown cycles.• At 20W, the oscillation reduced. Loop did not completely shut down (TC 11 always followed TC 2) , p p y ( y )

although forward/back flow alternated.


330 140Evap (5)

TM (33)

310

320

K)

80

100

120

CC (2)

TM (33)

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300

Tem

pera

ture

(K

40

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80

Pow

er (W

)CC (2)

CC In (27)

Vap Line (11)

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280

0

20Evap Power

EH Power

2/27/10

2608:30 8:45 9:00 9:15 9:30 9:45 10:00 10:15 10:30 10:45

Time (HH:MM)

-20

22

TM Controlled 313K (CC pre-heated to 298K) –TEC/2W/PID/350g

• TM controlled at 313K between 10W and 80W little oscillations• TM controlled at 313K between 10W and 80W – little oscillations• At 100W - condenser limit• TM controlled at 313K again as heat load lowered to 30W and 10W

02/03/2010; 253K sink; 350 g mass; Pre-heating CC; TEC set point@313K on the TM - TC33; PID

330

340

350

90

100

110Evap Power

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ture

(K)

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r (W

)

TM (33)

Evap (5)

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pera

t

20

30

40

50

Pow

er

Evap (5)

CC In (27)

CC (2)

Vap Line (11)

250

260

270

13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00-10

0

10TEC Power

13:00 13:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00

Time (HH:MM)

2/26/10

23

TM Controlled 313K (CC pre-heated to 298K) –TEC/2W/PID/350g

• Initially TEC heated CC so that TM would be raised to 313K• When TM reached 313K, CC was at 316K. TEC cooled CC (negative power). • No repeated start-up/shutdown cycles – effect of TEC power 2W vs 1W for 12/9/09• Immediately after start-up, CC temperature dropped due to cold liquid injection, bringing the TM to 312K.• In the next heating cycle, the loop was shut down and re-started. The cold shock was mild and the loop

soon reached SS.


320

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e (K

)

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W)

CC (2) TM (33)

Evap (5)

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pera

ture

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60

Pow

er (W

Evap Power

CC In (27)

Vap Line (11)

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280

0

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TEC Power

26013:00 13:15 13:30 13:45 14:00 14:15

Time (HH:MM)

-20

2/26/10

24

Pre-set CC Temperature Profile to Control TM at 313K (CC Preheated to 298K) – EH/4W/PID/350 g

• The CC temperature was pre-set to previously experimentally determined values (function of power input) in order to keep TM at 313K at all powers.

• The control temperature sensor was located on the CC.• Temperature oscillations at 10W and 20W, stable 40W to 100W• Condenser limit was reached at 100W; EH deactivated, and TM at 317K.

02/04/2010; 253K sink; 350 g mass; Pre-heating CC; EH - adjustable CC temp. to control TM@313K; PID

340

350

100

110

Evap

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e (K

)

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)

TM (33)

Evap Power

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Tem

pera

ture

30

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60

Pow

er (WEvap (5)

Liq Line (24) CC (2)

Vap Line (11)

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0

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20CC In (27)

EH Power

2/26/10

2508:11 9:11 10:11 11:11

Time (HH:MM)

-10

25

Pre-set CC Temperature Profile to Control TM Controlled 313K – TEC/PID/2W/350g

• The CC temperature was pre-set to previously experimentally determined values (function of power input)The CC temperature was pre set to previously experimentally determined values (function of power input) in order to keep TM at 313K at all powers.

• The control temperature sensor was located on the CC.• All temperatures were stable. At each power increase, TM temperature dropped because of a step change

in the pre-determined CC set point.• Condenser limit was reached at 100W. CC could not cooled further to maintain the TM at 313K.

02/04/2010; 253K sink; 350 g mass; Pre-heating CC; TEC - adjustable CC temp. to control TM@313K; PID

340

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90

100

110Evap Power

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e (K

)

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)

TM (33)

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Tem

pera

ture

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Pow

er (WEvap (5)

CC (2)

Vap Line (11)

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20CC In (27)

Liq Line (24)

TEC Power

2/26/10

25012:30 13:30 14:30 15:30 16:30

Time (HH:MM)

-10

26

Effect of Thermal Mass

• The following slides show the test result with 110g thermal mass attached to the evaporator.

• In theory, a smaller thermal mass should reduce the time delay in the y yfeedback control when the control temperature sensor is located on the thermal mass.

• Test results under the current test program did not show much th l ff t th LHP t t t l Thi b dthermal mass effect on the LHP temperature control. This may be due to the proximity of the control temperature sensor and the heater locations on the thermal masses.

27

TM Maintained at 313K (CC Preheated to 298K) -EH/4W/PID/110g

• TM temp was maintained at 313K with oscillations up to 80WTM temp was maintained at 313K with oscillations up to 80W.• At 100W, TM temp at 315K due to condenser limit (EH deactivated, no oscillations).• Temp oscillations resumed at 30W and 10W.

01/21/2010; 253K sink; 110 g mass; Pre-heating CC; EH set point@313K on the TM - TC33; PID01/21/2010; 253K sink; 110 g mass; Pre heating CC; EH set point@313K on the TM TC33; PID

330

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120

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Evap Power

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ture

(K) 80

100

(W)

TM (33)

Evap (5)

Vap Line (11)

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300

Tem

pera

t

40

60

Pow

er

CC In (27) Liq Line (24)

CC (2)

250

260

270

20

0

20( ) Liq Line (24)

EH Power

3/2//10

25013:30 14:00 14:30 15:00 15:30 16:00 16:30 17:00

Time (HH:MM)

-20

28

TM Maintained at 313K (CC Preheated to 298K) -EH/4W/PID/110g

• At 10W, repeated start-up/shutdown cycles even with 110g TM.• At 20W, still large temperature oscillations.


320

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TM (33)

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ure

(K)

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CC (2)

TM (33)

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Tem

pera

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Pow

er (CC (2)

Vap Line (11)

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10

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10Evap Power CC In (27)

EH Power

3/2//10

26013:30 13:45 14:00 14:15 14:30 14:45

Time (HH:MM)

-10

29

TM Controlled at 313K (CC Pre-Heated to 298K) –TEC/2W/PID/110g

TM t ll d t 313K b t 20W d 80W• TM was controlled at 313K between 20W and 80W• Condenser limit was reached at 100W; TM at 323K• TM was controlled at 313K as heat load decreased to 30W• Temperature oscillations at 10W at the beginning and the end of the test.


340

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90

100

110Evap Power

310

320

330

re (K

)

60

70

80

W)

TM (33)

280

290

300

Tem

pera

tur

30

40

50

Pow

er (WEvap (5)

CC I (27)CC (2)Vap Line (11)

260

270

280

0

10

20CC In (27)

Liq Line (24)

TEC Power

2/26/10

2508:30 9:30 10:30 11:30 12:30

Time (HH:MM)

-10

30

TM Controlled at 313K (CC Pre-Heated to 298K) –TEC/2W/PID/110g

TEC 2W CC t t f t th th t f TM• TEC 2W max. CC temperature rose faster than that of TM• TEC cooled CC after TM reached 313K, the loop then started. TM oscillated between 312.3K and 313.7K• Repeated start-up/shutdown at 10W


310

320

50

60

70

Evap (5)

TM (33)

290

300

ture

(K)

30

40

50

r (W

)

CC (2)

CC In (27)

Vap Line (11)

280

290

Tem

pera

t

10

20

Pow

erEvap Powerp ( )

TEC Power

260

270

20

-10

0

Liq Line (24)

2/26/10

2609:00 9:15 9:30 9:45 10:00 10:15

Time (HH:MM)

-20

31

Using Pre-set CC Set Point to Maintain TM at 313K (CC Pre-Heated to 298K) – EH/4W/PID/110g

Th CC t t t t i l i t ll d t i d l (f ti f i t)• The CC temperature was pre-set to previously experimentally determined values (function of power input) in order to keep TM at 313K at all powers.

• The control temperature sensor was located on the CC.• TM temperature was controlled at 313K between 10W and 80W. Condenser limit was reached at 100W. • At each CC set point change, TM could not follow immediately, resulting in TM temperature fluctuations.

02/01/2010; 253K sink; 110 g mass; Pre-heating CC; EH - adjustable CC temp. to control TM@313K; PID

320

330

100

120

Evap Power

300

310

re (K

) 80

W)

TM (33)

Evap (5)

Vap Line (11)

280

290

Tem

pera

tur

40

60

Pow

er (W

CC (2)

Vap Line (11)

270

280

20CC In (27)

Liq Line (24)

EH power

11/3/10

26013:00 14:00 15:00 16:00 17:00

Time (HH:MM)

0

32

Using Pre-set CC Set Point to Maintain TM at 313K (CC Pre-Heated to 298K) – TEC/2W/PID/110g

• The CC temperature was pre-set to previously experimentally determined values (function of power input) in order to keep TM at 313K at all powers.

• The temperature sensor was located on the CC.• TM temperature was controlled at 313K between 10W and 80W. Condenser limit was reached at 100W. • TM temperature oscillated at 10W and 20W.

02/01/2010; 253K sink; 110 g mass; Pre-heating CC; TEC - adjustable CC temp. to control TM@313K; PID

320

330

90

100

110

TM (33)

Evap Power

300

310

re (K

)

60

70

80

90

W)

TM (33)

Evap (5)

CC (2)

280

290

Tem

pera

tu

30

40

50

Pow

er (W

CC In (27)

CC (2)

Vap Line (11)

250

260

270

-10

0

10

20Liq Line (24)

TEC Power250

9:00 9:30 10:00 10:30 11:00 11:30 12:00 12:30

Time (HH:MM)

10

33

Summary of Test Results

• The LHP CC temperature or the heat source temperature can be used for LHP set point control with a control heater attached to the CC.

• The traditional method of using CC temperature for LHP set point gcontrol yields best temperature stability.

– However, the heat source temperature will vary with the heat output from the heat source.

Using the heat source temperature as feedback for LHP set point• Using the heat source temperature as feedback for LHP set point control will maintain the heat source at the desired temperature regardless of the heat output.

– However, temperature oscillations may appear during transients and can , p y pp gbe severe at low heat loads.

• Using a TEC to control the CC temperature yields better temperature stability than using an electric heater.

Th t l h t l ff t th t t t bilit– The control heater power also affects the temperature stability.

34

Concluding Remarks

• There are many factors to be considered in deciding which temperature should be used for LHP feedback control.

• For most applications, using the CC temperature for feedback control gis preferred as long as the heat source can be maintained within the required temperature range.– A simple control algorithm will suffice for SS and transients.– The CC set point can be varied while the LHP is operating in space.

• The heat source temperature can best be used for feedback control for applications where the heat load varies constantly without frequent LHP start ups and shut downsLHP start-ups and shut-downs.

– The heat source can be maintained within a tight temperature range through automatic adjustments of the CC temperature.

• More sophisticated (smart) control algorithms must be employed when p ( ) g p yfrequent start-ups or rapid power changes are involved if the heat source temperature is to be used for feedback control.

35

QUESTIONS?

36

Loop Heat Pipe Operation Using Heat Source Temperature for ... · Loop Heat Pipe Operation Using Heat Source Temperature for Set Point ControlTemperature for Set Point Control JeJe

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