EXPERIMENTAL STUDY OF LATENT THERMAL ENERGY HEAT EXCHANGERS

1. Experimental Study of Latent Thermal
Energy Heat Exchangers
Pavankumar T, Abhinav Bhaskar, Som Mondal
Department of Energy and Environment, TERI University, New Delhi
Email: pavankumart.dvg@gmail.com
ACKNOWLEDGMENT This work has been carried out at Centre of Excellence in Thermal Energy Storage, TERI University, funded by the Ministry of Human Resource Development, Govt. of India.
 The motivation of the study was to develop understanding and design of latent energy storage heat exchanger for low temperature thermal energy storage
applications.
 Design selection based on the thermo-physical limits of the desired phase change material (PCM) and heat transfer fluid(HTF). In this set of experiment
commercial paraffin wax used as storage material and air is used as HTF.
 Cylindrical geometry used in tubular heat exchanger and commercially available automobile air cooled radiator has been used as heat exchanger in compact
heat exchanger model.
SEM-EBIC
CENTER OF EXCELLENCE IN
THERMAL ENERGY STORAGE
TERI UNIVERSITY
Test tube
Density (kg/m3) 850
Thermal conductivity (W/m.K) 0.19
Specific heat (kJ/kg.K) 2.1
Melting point (°C) 51.3-63.5
Latent heat (kJ/kg) 145
Thermo physical properties of phase
change material
PCM tube diameter, d (cm) 2.1
Air flow tube diameter, D (cm) 9
D/d ratio 0.2
Length of the heat storage tube (cm) 90
Storage capacity (kJ) 38.6
Storage volume(Vs)/heat transfer area(A); [V/AS ratio] 0.44
PCM tube diameter, d (m) 1.8
Air flow tube diameter, D (m) 9
Number of tubes 4
Effective PCM tube diameter, de (cm) 2.38
D/de ratio 0.26
Length of the heat storage tube (cm) 86
Storage capacity (kJ) 91.4
Storage volume(Vs)/heat transfer area(A); [V/AS ratio (m)] 0.88
(a) With single tube (b) With multiple tube
(ii) Compact heat exchanger
Storage unit dimension (cm) 42 cm × 40 cm × 9 cm
Diameter air flow channel, dc (cm) 0.1 cm
Number air flow tubes 37
Length of the tube (cm) 37.3
Storage volume(Vs)/heat transfer area(A); [V/AS r
atio (m)]
1.52
Storage capacity (kJ) 1595
Temperature
of inlet air (°C)
(≤ 110 °C)
Voltage (V) Current (A)
0 - 220 0 – 1.5
Air flow rate (m3/hr) 0 – 14 kg/hr
Operation control parameters in
the experiment setup
Fig. Experimental setup for storage observation.
Fig. Heat flow versus temperature results for commercial
paraffin wax tested on DSC
Fig. Diagrammatic view low temperature
storage application
-5
0
5
10
15
20
25
0
8
16
24
32
40
48
56
64
72
80
88
96
104
112
120
Temperature(°C)
Time (min)
Charging Discharging
0
20
40
60
80
100
0 10 20 30 40 50 60 70 80 90
Temperature(°C)
Time (minute)
T air in
T air out
0
10
20
30
40
50
60
70
80
0 8 16 24 32 40 48 56 64 72 80
Temperature(°C)
Time (min)
Tout T in
0
10
20
30
40
50
60
70
80
81 85 89 93 97 101 105 109 113 117
Temperature(°C)
Time (min)
T in Tout
0
10
20
30
40
50
60
70
0 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120
Temperature(oC)
Time (min)
T PCM tube
surface
Charging Discharging
0
10
20
30
40
50
60
100110120130140150160170180190200210
Temperature(°C)
Time (minute)
T air out
T air in
Ambient temperature (°C) 26
Incoming air velocity (m/s) 1.5
Reynolds number in duct 5606
Charging duration (min) 80
Discharging duration (min) 47
Ambient temperature (°C) 31
Incoming air velocity (m/s) 2
Reynolds number in channel 81.5
Charging duration (min) 97
Discharging duration (min) 117
(i) Tubular heat exchanger
Operating parameter of Single
tube PCM heat exchanger
Operating parameter of compact
PCM heat exchanger
Fig. Heat exchange characteristics of the tubular heat exchanger storage unit during (a) charging
and (b) discharging process
Fig. Heat exchange characteristics of the compact heat exchanger storage unit during (a)
charging and (b) discharging process
Fig. Air inlet and outlet temperatures
difference’s during the process
Fig. Air inlet and outlet temperatures
difference’s during the process
 In tubular heat exchanger it is observed that operating parameters and storage distribution along the flow is major factors influence the performance of storage unit.
 The commercial compact heat exchanger is a good option for high heat transfer from and to air due to the presence of the micro-channels and the fins. It also helps in
compaction of the complete storage unit. However, due to low thermal conductivity, the complete material within the storage unit could not melt. Therefore, there is a need of
extended surfaces or other novel techniques like adding metallic rings, matrices etc. to enhance the effective storage. Further experiments are thus required to improve these
problems and use of extended surfaces with the storage unit will be experimented in future to address this problem.
Fig. PCM temperature in storage unit
during and discharging
Fig. PCM temperature in storage unit
during and discharging