Heat Transfer Performance of Pulsating - - PowerPoint PPT Presentation

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Heat Transfer Performance of Pulsating - - PowerPoint PPT Presentation

Aug 27, 2022 31 likes •197 views

Study on the Surfactant Influence on the Heat Transfer Performance of Pulsating Heat Pipe Xuehui Wang 1,2 , Bo Li 1 , Yuying Yan 1 , Xiaohong Han 2 , Guangming Chen 2 1.

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SLIDE 1

以直线发电机为负载的热声斯特林 发动机输出特性研究

Second ThermaSMART Annual Workshop, Kyushu University, Japan

Xuehui Wang1,2, Bo Li1, Yuying Yan1, Xiaohong Han2, Guangming Chen2

Study on the Surfactant Influence on the Heat Transfer Performance of Pulsating Heat Pipe

  • 1. Fluids and Thermal Engineering Research Group, University of Nottingham, UK, NG7 2RD
  • 2. Institute of Refrigeration and Cryogenics, Zhejiang University, Hangzhou, China 310051
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SLIDE 2

Contents

Discussions Results & Conclusions Simulation/Experiment Introduction & Background

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SLIDE 3
  • 1. Introduction & Background
  • Working principle:

Due to the influence of the surface tension, a train of vapor slugs and liquid plugs will be formed once charging a small channel by a fluid The heat will be dissipated by the oscillation of the slugs The input heat in EV section will cause the un-balance of the slugs

The surface tension, unbalanced oscillation motions define the PHP

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SLIDE 4
  • 1. Introduction & Background

Surface tension; Thermal conductivity; Specific heat; Viscosity; … … Inner diameter; Cross-section shape; Channel configuration; Number of turns; Length of section; … ... Charge ratio; Inclination angle; Gravity field; Heat flux; … …

Geometric Parameters Physical Properties Operational parameters

  • The heat transfer performance of the PHP is greatly influenced by many parameters, and they can be

divided into three groups

  • Few studies showed the influence of surface tension on the heat transfer performance of PHP
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SLIDE 5
  • 2. Simulation/Experiment

 Mass conservation  Momentum conservation  Energy conservation  Mass balance

  • Theoretical analysis on heat transfer

For the liquid slug with two adjacent vapor plugs

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SLIDE 6
  • 2. Simulation/Experiment

液塞1 液塞2

d

气塞

q

Qvl m1 Qvl m2

2 1

i j i

v l v tf j fg

Q dm dm dt dt h

 

+

i i i

v v fg v w

Q dm h Q 

2/3 2/3

1.34 1 3.35 Ca r Ca   

2 ( )

i

wi vi v w tf v l tf

T T Q R L       

_equ lv 0.5 0.5 0.5

( ) ˆ 2 '' ( ) ( ) ˆ 2 2

v v lv v

p T p M m R T T      

( ) ''

l w lv fg

k T T m h   

For the vapor plug with two adjacent liquid slugs  Mass conservation  Energy conservation Thin film area

u Ca   

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SLIDE 7
  • 2. Simulation/Experiment
  • Fig. 1 For a vapor plug
  • Fig. 2 For a liquid slug
  • The heat transfer of the liquid plug and vapor plug are analyzed

based on the model presented

For a typical long vapor plug, the heat transfer in the liquid conduction contributes a lot. For a liquid slug, the convection heat transfer ratio is great. However, the contribution of heat transfer in meniscus also play an important role, which is greatly influenced by surface tension of the working fluid.

10, , 10; 100

w l l lv lv v d c

T T T T T T p p Pa       

10, , 10; 100

w l l lv lv v d c

T T T T T T p p Pa       

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SLIDE 8
  • 2. Simulation/Experiment

 Theoretical analysis on the force

The length of slug/plugs are randomly and small compared with the length of pipe. So it is assumed the length distribution functions of the slugs in every single channel are the same

  • Force/Pressure drop caused by U-turn
  • Force/pressure drop by the gravity
  • Force/pressure drop by the flow resistance
  • Force/pressure drop by the capillary force

FC Ff Fpf

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SLIDE 9
  • 2. Simulation/Experiment

 Theoretical analysis on the force

1 2 3 4 5 0.1 0.2 0.3 0.4 0.5 0.6 Ratio Velosity(m/s) L=10d, gravity L=10d, capillary resistance L=5d, gravity L=5d, capillary resistance 1 2 3 4 5 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Ratio of capillary resistance

Velosity(m/s) surface tension=70mN/m surface tension=60mN/m surface tension=50mN/m surface tension=40mN/m

For typical liquid slug, the capillary resistance could be the same level of the gravity of the it. Meanwhile, with the decrease of the surface tension of the working fluid the ratio of the capillary tension sufficiently decrease.

'

g f

F F F F

  

1=

'

g

F F 

2=

' F F

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SLIDE 10
  • 2. Experimental rig

Cooling module Data collecting module Heating module PHP module

  • The rig for the experimental rig is shown below
  • Criteria for the performance

(thermal resistance) (superheat)

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SLIDE 11
  • 3. Results &Discussions

2000 4000 6000 8000 q=1911 q=1592 q=1274 q=955

Time(s)

DI water 10 ppm concentration 20 ppmconcentration 40 ppmconcentration

60 80 40 20 Superheat(K) q=637

Startup

2000 4000 6000 8000 q=1911 q=1592 q=1274 q=955 Superheat(K)

Time(s)

DI water 10 ppm concentration 20 ppm concentration 40 ppm concentration

20 40 60 80 startup q=637 2000 4000 6000 8000 10000 q=1911 q=1274 q=1592 q=955 Superheat(K)

Time(s) DI water 10 ppm concentration 20 ppm concentration 40 ppm concentration

20 40 60 80 q=637

startup

  • The influence of the surfactant on the startup characteristics of the PHP

The surfactant solution decreases the start up power of the pulsating heat pipe

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SLIDE 12
  • 3. Experimental results

4000 8000 12000 16000 20000 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Thermal resistance(K/W) Heat flux(W/m

2)

DI water 10 ppm concentration 20 ppm concentration 40 ppm concentration

4000 8000 12000 16000 20000 0.2 0.4 0.6 0.8 1.0 Thermal resistance(K/W) DI water 10 ppm concnetration 20 ppm concnetration 40 ppm concnetration

heat flux(W/m

2)

4000 8000 12000 16000 20000 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Thermal resistance(K/W) DI water 10 ppm concentration 20 ppm concentration 40 ppm concentration Heat flux(W/m

2)

  • The influence of the surfactant on the heat transfer performance of the

PHP

The existence of the surfactant greatly enhances the heat transfer of the PHP

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SLIDE 13

2000 4000 6000 8000 80 100 120 140 160 180

q=13057 q=14650 q=9873 q=16242

Temperature(℃) Time(s)

DI water 10 ppm concentration 20 ppm concentration 40 ppm concentration

q=11465

dryout

2000 4000 6000 8000 10000 90 120 150 180

q=19427 q=16242 q=17384 q=14650 q=13057

Temperature(℃) Time(s)

DI water 10 ppm concentration 20 ppm concentration 40 ppm concentration q=11465

dryout 2000 4000 6000 8000 10000 100 120 140 160 180

q=21019 q=19427 q=17834 q=16242 q=14650

Temperature(℃)

Time(s)

DI water 10 ppm concentration 20 ppm concentration 40 ppm concentration q=13057

dryout

  • The influence of the surfactant on the dry-out characteristics of the PHP
  • The influence of the surfactant on the dry-out characteristics of the PHP
  • 2. Simulation/Experiment

The existing of surfactant increases the dry-out heat flux of the pulsating heat pipe

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SLIDE 14
  • 3. Conclusions

For the PHP with surfactant solutions, they start at a lower heat flux. Furthermore, the temperature fluctuates at a lower level. The heat transfer performance of the PHP significantly improves by using surfactant solutions as the working fluid The experimental results indicated that the dry-

  • ut heat fluxes are higher when the working

fluids are surfactant solutions

 Decrease the superheat of the bubble  Better wetting of the wall  Decrease the capillary resistance

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SLIDE 15
  • 4. Discussions
  • 1. Is there a ‘best condition’ or ‘dead condition’ for the PHP?

Best: making best use of the heat; Dead: the unbalanced flow is balanced Charging a pipe Plugs and slugs Oscillation motions Heat dissipated Input heat EV positive negative

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SLIDE 16
  • 4. Discussions

length

  • 2. Whether the initial distribution of the vapor plug and liquid slug affect the

performance of the PHP? If so, how to build the analytical model?