1. 08/16/16 1
Experimental Analysis of a
Thermal Energy Storage
with a Coiled-Type heat
source/sink
Vamsi Ram Athuluri
Supervisor: Kamran Siddiqui

2. Contents
 Introduction
 Types of thermal energy storage
 Phase change materials
 Motivation
 Objectives
 Experimental Set up
 Results and Discussion
 Conclusion
 Future Recommendations

3. Introduction
 There is rise in energy demand due to increase in human
population and standard of living.
 Since most of the energy produced in next few decades is
expected to come from fossil fuels , wastage of energy
produced from these should be reduced.
 Thermal energy from industrial flue gases can also be
extracted and stored for future use.
 Renewable sources of energy like sun, wind etc., are
unpredictable, available in small densities and time-dependent
in nature.
 Excess thermal energy from renewable sources can be stored
and used during its unavailability.

4.  Sensible thermal energy storage: Energy is stored in the
from of sensible heat, i.e. the temperature rises with increasing
pressure keeping volume constant.
 Thermo-Chemical energy storage: Energy is stored in a
recombination-dissociation chemical reaction. This has more
energy density and involves almost no energy loss during the
storage process.
 Latent thermal energy storage: Energy is stored in the
form of latent heat, where, phase change of the material takes
place with minimal change in temperature.
Types of thermal energy
storage

5. Phase change materials (PCM)
 Phase change materials
are used for Latent heat
thermal energy storage.
 PCMs can be classified
into three types based on
phase change state as:
• Solid-Liquid PCMs
• Liquid gas-PCMs
• Solid-gas PCMs
Types of Solid-Liquid PCMs
Y. Zhang, G. Zhou, K. Lin, K. Zhang and H. Di, "Application of latent heat thermal energy storage in buildings," Building and
Environment, pp. 2197-2209, 2007

6. Motivation
 Latent thermal energy storage has high energy density and energy
can be stored at constant temperature.
 In latent thermal energy storage, heat transfer process is transient and
complex due to change in phase.
 Most of the geometrical configurations were simple spheres, cylinders,
U-tubes etc., arranged at different positions in PCM storage tanks.
 Coiled-type heat source/sink increases heat transfer area and reduces
the size of the equipment.
 Convective heat transfer studies on coiled-type heat source/sink are
focused on single phase fluids.
 This project is focused on the study of heat exchange between the
PCM around the coiled-type heat source/sink.

7. Objectives
 To build a thermal energy storage system with coiled-type
heat source/sink.
 Conduct thorough testing during charging and discharging of
Phase change material using two different configurations.

8. Experimental Set up
 Helical coils: Four helical coils
of different mean diameters (‘d’)
were made of ¼ inch copper pipes.
 These coils were nested
concentrically and connected by a
couple of three- way valves and T-
joints.
 Coils 4 and 3 will be used as heat
transfer fluid inlets and coils 1 and
2 will be used as out lets.
Coil 1
d= 64 mm
Coil 3
d=172 mm
Coil 4
d=243mm
Coil 2
d=98 mm

9. Photographs of nested helical
coils

10. Flow arrangement
Valve A
Valve B
4
3
1
1a1b
2b
2
2a
Coil 1
Coil 3 Coil 4
Coil 2
T-Joint
T-Joint

11. Storage chamber
 Storage chamber is a conical shaped
can made of 7mm thick aluminum
sheet. It has dimensions as follows:
• Diameter of top end: 410mm
• Diameter of bottom end: 350mm
• Total height: 750 mm
 It is insulated with 30mm thick R13
fiber glass insulation and 8 mm thick
AYR reflective foil insulation to
prevent loss of heat to surroundings.
 Coils are inserted in storage chamber
and 50KG of PCM is filled around the
coils.

12. Heat source
 Water is used as a heat source which transfers heat to PCM.
PID Controller
Supply line
Pump
Needle valve
Return line
Insulated Water
tank Insulated storage container with coils
and PCM
Heater

13. Heat sink
 Cold water is used to absorb heat from salt during discharging.
Sump
Supply linePump
Needle valve
Return line
Water tank
Insulated storage container
with coils and PCM

14. Temperature data acquisition
 Temperatures at various positions in the experimental set up are
measured using 12 T-type thermocouples. All thermocouples were
calibrated.
 Two thermocouples are inserted in the copper tubes in the supply
line just before the needle valves to measure the inlet temperature
of water.
 Two more thermocouple are inserted in the copper tubes in return
line right after the external wall of the container.
 Eight thermocouples were inserted in salt to measure salt
temperatures.

15. Positioning of Thermocouples
Coil 2
Coil 4
Storage
Chamber
TN
TW
TS
T1-2 T2-3 T3-4 TET0-1
Coil 1
Coil 3

16. Complete experimental set up

17. Phase Change Material
 Rochelle salt is used as a phase change material. It is a salt hydrate
with chemical name Sodium potassium tartrate and chemical formula
KNaC4H4O6·4H2O .
 It is a food grade material used for production of pectines and meat
preservatives in food industry and also manufacture of cigarette
paper.
 Thermal properties of Rochelle salt are not widely available. It has a
melting temperature of 70-80o
C.
 It is non explosive, non-oxidizing and chemically stable under
standard environmental conditions.

18. Results and Discussion
 Configuration 1: In this configuration, coils 4 is connected to
coil 1. So, Water entering from coil 4 exits from coil 1.
 Similarly, and coil 3 is connected to 2. So, water entering from coil 3
exits from coil 2.
 Configuration 2: In this configuration, coils 4 is connected to
coil 2. So, Water entering from coil 4 exits from coil 2.
 Similarly, and coil 3 is connected to 1. So, water entering from coil 3
exits from coil 1.

19. Configuration 1
Charging:
 ΔT is temperature drop of heat transfer fluid

20. Configuration 1
Charging:

21. Configuration 1
Discharging:
 ΔT is temperature drop of heat transfer fluid

22. Configuration 1
Discharging:

23. Configuration 2
Charging:
 ΔT is temperature drop of heat transfer fluid

24. Configuration 2
Charging:

25. Configuration 2
Discharging:

26. Configuration 2 with equal water
flow rate
Charging:
 ΔT is temperature drop of heat transfer fluid

27. Configuration 2 with equal water
flow rate
Charging:

28. Configuration 2 with equal water
flow rate
Discharging:
 ΔT is temperature drop of heat transfer fluid

29. Configuration 2 with equal water
flow rate
Discharging:

30. Comparison of configurations
Charging:
 Solid lines represent configuration 1 and dotted lines represent configuration 2
 ΔT is temperature drop of heat transfer fluid

31. Comparison of configurations
Discharging:
 Solid lines represent configuration 1 and dotted lines represent configuration 2
 ΔT is temperature drop of heat transfer fluid

32. Comparison of flow rates
Charging:
 Solid lines represent case with unequal flow rates and dotted lines represent case with
equal flow rates.

33. Comparison of flow rates
Discharging:
 Solid lines represent case with unequal flow rates and dotted lines represent case with
equal flow rates.

34. Comparison of flow rates
 In case 1, different flow rates were used in different pipes and in case
2, same flow rates were used.
 Similar trend is seen in charging and discharging. With the decrease
in flow rate from 4.83 ml/s to 4.234 ml/s, heat flow rate increased.
Case 1 Case 2
4-2 3-1 4-2 3-1
Water flow
rate(ml/sec)
4.234 4.83 4.615 4.615
Charging Rate of heat
transfer (kJ/s)
0.2584 0.1767 0.199 0.1811
Discharging Rate of heat
transfer (kJ/s)
0.253 0.1647 0.2042 0.2053

35. Conclusion
 This thermal energy storage system with coiled-type heat
source/sink provides higher surface area for heat transfer.
 With constant water inlet temperature during charging, heat
absorbed by PCM decreases rapidly with time.
 During discharging, heat released by salt is very high during
phase transition when compared to that when it solidified.
 Second configuration provided more effective heat transfer than
first configuration. It provides uniform and high drop in
temperature of water than first configuration.
 When inlet water has same flow rate, there was little difference
between heat lost in both the coils (4-2 and 3-1).
 Lower water flow rates provided higher rate of heat transfer.

36. Future Recommendations
 Gap between coils should increase from coil 1 to coil 4 since coils 3
and 4 have more surface area.
 Amount of salt between coil 4 and wall of storage chamber should
be reduced.
 Conical storage chamber can be advantageous since it
accommodates more amount of salt at top than bottom and heat
flows in upward direction.
 Water inlet from coils 1 and 2 should be investigated on since higher
water temperature through coils of less surface area may provide
more uniform heat transfer.

37. Thank you