Experimental study of cryogenic chill-down on coated stainless steel transfer lines

1. ANALYTIC STUDY OF 2-PHASE FLOW
OF LIQUID NITROGEN THROUH
COATED TRANSFER LINES
Guided By,
Prof. JESNA MOHAMMED
Department of Mechanical Engineering
TKMCE
Abhinand C
Ajay Krishnan
Anandakrishnan N
Ananthu Thilak
Arjun V
Geo T Sam

2. CONTENTS
• INTRODUCTION
• MULTIPHASE FLOW
• CHILLDOWN PROCESS
• FLOW REGIMES
• LITERATURE REVIEW
• PROBLEM DEFINITION
• OBJECTIVE
• METHODOLOGY
• EXPERIMENTAL SETUP
• EXPERIMENTAL PROCEDURE
• RESULTS AND DISCUSSION
• CONCLUSION
• REFERENCES

3. INTRODUCTION
• Cryogenic fluids are employed throughout the chemical, aerospace, medical and
food industries.
• Transporting cryogenic liquid through pipe line is an indispensable process for
undertaking cryogenic mission and establishing a normally operated cryogenic
system.
• The transferring process is a complex process involving two phase transfer
phenomena with phase change, pressure surges and flow reversals.
• Chilldown process can be said as the voracious evaporation of the cryogen while
transferring through pipelines which is initially in thermal equilibrium with the
environment.
• The phenomenon is still a mystery to us so are the role of various factors in the
process.

4. MULTIPHASE FLOW
• Multiphase flow is simultaneous flow of:
 Materials with different states or phases (i.e. gas, liquid or solid)
 Materials with different chemical properties but in the same state or phase (i.e. liquid-
liquid systems such as oil droplets in water).
TWO PHASE FLOW
• Heat transfer in a two-phase two-component system are easy to analyze because only the
physical (material) properties of the phases dependent on temperature.
• Two-phase single-component systems require their own very complicated mathematical
modelling and dedicated two-phase single component experiments.
• The complications are due to the fact that inertia, viscosity and buoyancy effects can be
attributed both to the liquid phase and vapor phase, and also due to the impact of surface
tension.

5. CHILLDOWN PROCESS
• Chilldown can be defined as the inverse process of boiling and can be explained by
a reverse boiling curve.
• Chilldown is the process of introducing the cryogenic liquid into the system, and
allowing the hardware to cool down to several hundred degrees below the ambient
temperature.
• Some quantity of the cryogen must be used to chill down the tube before single-
phase liquid can be transferred through the entire line.
• When any cryogenic system is initially started it must go through a transient
chilldown period prior to a steady operation.
• Various regimes of the boiling curve are Film boiling, Transition boiling, Nucleate
boiling and single phase convection.

6. INVERSE BOILING CURVE

7. CHILL DOWN CURVE

8. INVERSE BOILING CURVE
• Quenching process begin in the film boiling regime of the boiling curve (Point F) and move
towards Point E, then to Points D, C, B, and A.
• If the excess temperature (the difference between the inner wall surface temperature and
the fluid saturation temperature) is very large then Film boiling occurs.
• As a result of film boiling the surface is not wetable by the liquid, causing a vapor blanket to
shroud the surface. The cooling of the tube wall causes the transfer of heat from the wall
surface to the fluid..
• A further infusion of cryogen to the wall surface will continue to cool down the surface;
finally allowing the liquid to begin a direct contact with the surface that is known as re-
wetting.
• This moment of the first liquid contact is known as the quenching front, and can be said as
the Leidenfrost point of the boiling curve. The
• Leidenfrost point is the point of the minimum heat flux in the film boiling regime, marking
the onset of the transition boiling regime in a quenching process.

9. • During transition boiling, the heat transfer mode is intermittent as a results of this
alternating liquid wetting and vapor drying on the wall surface takes place.
• Heat transfer is greatly increased by the presence of liquid contact. Due to the
decrease in the wall superheat the heat flux increases due to more liquid-to-wall
contact.
• Further cooling of the surface through the transition boiling regime will result in a
local peak heat flux termed the critical heat flux (CHF).
• The CHF point represent the onset of the nucleate boiling regime and represents
the maximum heat flux for the nucleate boiling regime.
• The chilldown process continues toward point A where boiling (phase change)
eventually ceases and single liquid phase convection begins.
• To chilldown as quickly and efficiently as possible the film boiling regime must be
minimized.

10. FLOW REGIMES

11. • The multiphase flow is characterized by different regimes where the pressure
drop and heat transfer characteristics are significantly different. The various
regimes in two phase flow through a vertical and horizontal pipe is shown in
the figure.
• In tube chilldown, the vapor and liquid flow simultaneously inside the channel
or pipe.
• In addition to the usual inertia, viscous and pressure forces present in single
phase flow, two phase flows are also affected by interfacial tensile forces, the
wetting characteristics of the liquid on the tube wall and the exchange of
momentum between the liquid and vapor phases.
• Condensation inside horizontal tubes is governed by a combination of gravity
forces and interfacial shear stresses, the relative contribution of which change
with geometry and fluid flow conditions.

12. • The various flow regions in two phase flow is shown in figure. The flow profiles can be
summarized as
• Bubbly flow: usually observed at very low vapor quality, with the bubbles residing in
the upper portion of the pipe (as a result of buoyancy forces).
• Plug flow: as the quality is increased, the bubbles tend to coalesce producing larger
plug-type bubbles.
• Stratified flow: observed at low mass flow rates and higher qualities.
• Stratified-wavy flow: as the flow rate and/or quality are increased the liquid-vapor
interface becomes unstable (due to Helmholtz instability).
• Slug flow : At high liquid flow rates the amplitude of the waves may grow until the crest
spans the cross-section of the pipe forming large vapor slugs.
• Churn flow: the slug bubbles grow larger, they start to break up leading to a more
random and unstable flow.
• Annular flow: At higher vapor velocities and moderate liquid flow rates the flow
structure is observed to be annular, with liquid film covering the entire circumference of
the pipe with an inner vapor core. At a high liquid flow rate, the concentration of the
liquid drops in the vapor core increases. The merging of these liquid droplets can lead
to large lumps, Breaks or wisps of liquid in the gas core.

13. LITERATURE REVIEW

15. • Parametric effect of inclination of transfer line and mass flux on cryogenic chill
down process can be refered from Jijo Jhonson and SR Shine (2015).
 They found that higher mass flux causes the transition from film boiling to
nucleate boiling at higher wall temperature (faster flooding of wall by liquid film).
 The peak flux increases with increase in mass flux of the cryogen.
 Lower chilldown time revealed for 10◦ inclination of the test section.

16. • The experiment on effect of flow direction with respect to gravity was conducted
by S.R Darr(2016). He examined 9 different flow directions including horizontal,
30deg inclined and declined,45deg inclined and declined,60deg inclined and
declined , and vertically upward and downward.
 New heat transfer correlations were developed to predict data for film boiling ,
nucleate boiling and transition boiling. There correlations can be used for
numerical simulation of cryogenic chilldown to help predict the chill down time and
propellant consumption for different system variables.

17. • Experimental results of thin walled stainless tube with liq nitrogen under a wide
range of pressure and mass flux in terrestrial gravity conditions are analysed for
veritcally upward flow orientation of test section(against gravity) was obtained by
S.R Darr in 2016.
 The variation of heat transfer coefficient for each boiling regime and critical heat
flux with mass flux , pressure, inlet sub cooling, equilibrium quality and axial
location have been identified and have shown that the major influential variable in
all cases is mass flux.
 The data from the study will enable future works in the development of robust
correlations for the critical heat flux and film boiling , transition boiling and
nucleate boiling heat transfer coefficients.

18. • Coatings of a poor thermal conductor on metallic components may shorten the
lengthy cooldown process prior to operation of cryogenic equipments as first
shown by Cowley, Timson and Sawdye in 1962.
• Operation and response of low temperature system may be improved by coating
fluid exposed to surface of hardware as shown by Allen in 1966.
• In coated section the cool down rate is faster than uncoated pipelines at lower
fluid velocity for constant fow rate by leonard in 1966.
• The importance of multilayer insulation and its various applications in cryogenics
was explained by C.L Tien and G.R Cunnigton in 1972-73.
• Heat transfer enhancement in channel for film boiling by low thermal conductive
coating is done by G.A Drietser in 2004.

19. PROBLEM DEFINITION
• When liquid cryogen flows and comes in contact with the transfer line rigorous
evaporation takes place.
• It is very critical in the design of liquid propellant delivery systems since it
consumes time and usable cryogen.
• So we have to effectively study and design a system in such a way that it consumes
only minimum cryogen and chill down takes place rapidly.
• The present work has been directed towards increasing the heat transfer during
the period immediately after the introduction of a transfer line at room
temperature in to liquid nitrogen.Evidence from earlier literatures suggest decrease
of chill down time using low thermal conductive coating.
• Inspired by this idea the chill down performance is analysed using polyeurethane
coatings on steel tube and compare it with uncoated section Performance.

20. OBJECTIVE
• Experimentally study the transient heat transfer and determine the final
temperature of each insulations and numerically check the effectiveness.
• Conduct the chill down experiment with coated surfaces(polyurethane) for
different mass flow rate.
• Compare the performance of the coatings at different mass flow rate with
uncoated pipeline.

21. METHODOLOGY
• Literature survey has been done and proper knowledge has made.
• Test section is 9.5mm ID and 150 mm length ss pipe.
• test sections are internally coated by a simple method of fill and drain. the prepared
coating was first filled in to the tube with the other end closed. immediately the tube
was inverted and drained off creating a very thin layer(~.1mm).
• thermocouples are attached to the test section at four different sections at
3cm,6cm,9cm and12 cm from the inlet of the test section.
• The test sections are insulated externally by using polyurethane form.
• Leak test was carried out by using nitrogen gas.
• The experiment was conducted for three test sections for three different mass flow
rates. the average of all thermocouple readings were chosen as the chill down time. the
results are depicted in graph.
• The inlet pressure chosen are 7.59psi(.5 bar),10psi(.7 bar) and 12 psi(.82 bar).

22. EXPERIMENTAL SETUP
• The chill down study was conducted in the space technology lab in department of
mechanical engineering.the model of experimental setup is shown in the figure.
The liquid nitrogen in the dewar is forced to flow through the test section
by external pressurization from the gas cylinder.the flow was regulated
with valves until suitable flow rate was achieved.

23. • Various elements in the experimental setup are given below:
1. External pressurization with gaseous nitrogen
2. Dewar vessel 55 liters
3. Bypassing to ensure nitrogen enters as liquid into the test section.
4. Pressure transducers
5. 30 volts dc power supply
6. The test section of stainless steel with ID 9.5mm and 150mm length.
7. Thermocouple connecting the external surface of the test section to the data
acquisition system.
8. Insulating material reducing heat flow into the test section:
 Nitrile rubber
 Polyurethane form

25. Test section with thermocouples connected

26. coated test section with insulated
polyurethane form

27. EXPERIMENTAL PROCEDURE
• The data acquisition program was initiated to record data as soon as triggered.
• The gaseous nitrogen tank was connected to the liquid nitrogen Dewar. The
required supply pressure was obtained by manually regulating the pressure
regulator.
• Pressure transducers are connected to the inlet and exit of the test section. A 30v
dc power supply is used for the pressure transducer. These are connected to the
data acquisition system and the initial readings at the inlet and exit test section is
obtained in volts.
• The lines before the test section were allowed to be chilled prior to the beginning
of the experiment and the vapour generated were vented to atmosphere via
bypass line.

28. • Data acquisition system was triggered and line to test section were opened
simultaneously after the cool down of inlet supply system.
• Liquid nitrogen was allowed to flow through the test section facility until all
thermocouples that are in contact with the pipe wall read a steady value
corresponding to the saturation temperature of the liquid nitrogen; at that point it
can be concluded that the chill down process was complete.
• Temperatures, mass flow , supply pressure and the test section inlet and outlet
pressures are calculated.
• A single phase mass flow meter was employed for measuring the mass flux of the
system. A rota meter was employed for the purpose. In order to ensure that only
gaseous nitrogen enters the mass flow meter the outlet from test section was
heated in a constant temperature water bath of 100°c

29. • Experiments were again repeated based on the above steps with supply pressures
of 7.5 psi, 10 psi and 12.5 psi respectively.
• The above procedure was repeated for the coated test section.

30. REFERENCES
• Hua H., Chung J.N., Amber S.H., An experimental study on flow patterns and
heat transfer characteristics during cryogenic chilldown in a vertical pipe,
Cryogenics Vol.52,pp. 268–277, 2012.
• Johnson J., ShineS.R. Transient cryogenic chill down process in horizontal and
inclined pipes, Cryogenics, Vol.71 pp.7-172015
• Cowley C.W., Timson W.J, Sawdye J.A., A method for improving heat transfer to
a cryogenic fluid , advances in cryogenic engineering Vol.7, pp. 10002-10009,
1962.
• Allan L.D., A method of increasing heat transfer to space chamber cryo panels,
advances in cryogenic engineering Vol 11, p 547-553, 1966.
• Leonard K.E, R.C Getty and D.E Frank, A comparison of cooldown time between
internally coated and uncoated propellant line, Advances in cryogenic
engineering Vol 12 P 331-339, 1967.
• C.L Tien, G.R Cunnington, Cryogenic insulation heat transfer, advances in heat
transfer Vol 9, P 349-417, 1973.
• C.L Tien, G.R Cunnington, Cryogenic insulation heat transfer, advances in heat
transfer Vol 12, P 419-427, 1972.
• G.A DREITSER,heat transfer enhancement in channels for film boiling of
cryogenic liquids,applied thermal engineering vol-25 ,pg -2512-2521 ,2004.