experimental study of thermal energy storage system...

381 Ankit Bansal, Dr. Vijay Kumar Bajpai

International Journal of Engineering Technology Science and Research

IJETSR

www.ijetsr.com

ISSN 2394 – 3386

Volume 4, Issue 4

April 2017

Experimental Study of Thermal Energy Storage System using

Rock Pebble Bed and Refractory Brick

Ankit Bansal1, Dr. Vijay Kumar Bajpai

2

1M.Tech Scholar, School of renewable energy and efficiency,

2Professor, Department of mechanical engineering,

National Institute of Technology Kurukshetra, INDIA

ABSTRACT:

Energy storage is critically important for success of any intermittent energy source in meeting demand. As solar energy

is of irregular nature, some medium are required for the storage of solar energy to meet the demands. These medium

may include water, rock beds, bricks, sand and soil. Sensible heat thermal energy storage devices helps to compensate

the increasing demand of conventional energy source by preventing the mismatch between energy supply and energy

demand and also by utilization of waste heat used for space heating. In this paper an experimental analysis has been

carried out to study the thermal energy storage system using thermal energy storage materials such as rock pebble bed

and refractory brick. As rock and refractory bricks are less costly, abundantly available and can be served as viable

media for thermal energy storage.

Keyword: Rock pebble bed; Refractory brick; Thermal energy storage;

I. INTRODUCTION:

Solar energy is intermittent in nature. Due to irregular nature of solar energy, an energy storage unit is

required to attach with solar energy collectors to store energy for its effective utilization when sunshine is not

available. For a variety of application the thermal energy might be required when there is no sun radiation.

The need of storage of sun energy is therefore desirable for various applications during off sun shine hours

and cloudy season. ES (Energy Storage) system can contribute remarkably in meeting society’s needs for

more efficient, environment friendly energy in, building cooling and heating and utility applications. The use

of ES systems has significant benefits such as [Dincer et al. 2002] –

• Reduced energy costs,

• Reduced energy consumptions,

• Reducing initial and maintenance cost.

A major advantage of solar thermal power generation is the availability of thermal storage, thus enabling

dispatchable power generation during cloudy periods or after dark (Harmeet et al. 2010). There are three types

of thermal energy storage (TES) systems, sensible heat storage (SHS), latent heat storage (LHS) and the

thermochemical energy storage. The choice of storage media depends upon the nature of the process.

Sensible heat storage can be achieved using solid or liquid media and involves storing energy in a material

without phase change of material in the temperature range of the storage process. Latent heat storage involves

storing energy in phase change materials and heat is stored when material changes phase from solid to liquid.

There are some advantages for Sensible heat storage as compared to Latent heat storage at high temperatures

including simplicity of design and construction, ease of control and hence lower cost. Thermochemical

storage involves chemical reaction for storing thermal energy. In this paper packed bed storage system using

different energy storage material and performance of the system with respect to time has been calculated.



IJETSR

www.ijetsr.com

ISSN 2394 – 3386

Volume 4, Issue 4

April 2017

II. SENSIBLE THERMAL ENERGY STORAGE:

Sensible heat storage is achieved by increasing the temperature of the storage medium. Thus, it is advisable

for the storage medium to have high specific heat capacity, compatibility with its containment and, most

importantly, low cost(Anderson et al. 2015). Basically specific heat, density, thermal conductivity are the

main properties of sensible thermal energy storage. Sensible heat storage may be grouped on the basis of the

heat storage media as liquid media storage (like water, oil based fluids, molten salts etc.) and solid media

storage (like rocks, metals and others).

a) STORAGE IN ROCK PEBBLE BED:

The packed bed consists of a bed of loosely packed rock material through which the heat transport fluid can

flow. The thermal energy is stored in the packed bed by forcing hot air into the bed and utilized again by

recirculating ambient air into the heated bed. The energy stored in a packed bed storage system depends on

several parameters, including rock size and shape, packing density, heat transfer fluid, storage heat losses etc.

Solar energy can also be stored in rocks or pebbles (packed in insulated vessels), and it is convenient for use

in buildings for space heating. This type of storage is used very often for temperatures up to 100°C in

conjunction with solar air heaters (Dincer et al. 2002).

Fig1: Rock pebbles used as thermal energy storage

material

Fig2 : Refractory bricks used as thermal energy

storage material

b) STORAGE IN REFRACTORY BRICKS:

Refractory brick consist of aluminium oxide(37%), magnesium oxide(61%), ferrric oxide(1.6%) and other

materials. Magnesium oxide (magnesia), aluminum oxide (alumina) and silicone oxide are refractory

materials, and they are also suitable for high-temperature sensible heat storage (Sukhatme et al. 1996). Bricks

made of magnesia have been used in many countries for many years for storing heat. The heat is stored at

night (when electricity rates are low) by switching on the electric heaters and is supplied during the day for

space-heating purposes by allowing air to pass through the devices.

III. EXPERIMENTAL SETUP:

The experiment setup consist of following three sections:

i. Inlet section

ii. Thermal energy storage section

iii. Outlet section

The experiment has been performed to study the performance of the thermal energy storage system using

energy storage materials such as rock pebble bed, refractory bricks.



IJETSR

www.ijetsr.com

ISSN 2394 – 3386

Volume 4, Issue 4

April 2017

Fig3: Photographic view of experimental setup

IV. MEASURING DEVICE AND INSTRUMENTS:

Inlet and outlet temperature of air was measured with J-type thermocouple connected with a digital

temperature indicator that shows the temperature reading.

Multi stem thermometer is used to measure the temperature of thermal energy storage section.

The air velocity is measured by Anemometer.

In experiment, hot air blower is used to heat the thermal energy storage section instead of solar energy.

V. EXPERIMENTAL RESULTS AND GRAPHS:

a) Variation of thermal energy storage section(TESS) temperature with time for refractory bricks during

charging:

In starting, the temperature of thermal energy storage section for refractory bricks increases in fast manner but

after sometime the temperature of thermal energy storage section become constant and that time steady state

reached. After that the temperature of TESS does not increase because at this time steady state is reached.

020406080

100

TEM

PER

ATU

RE

( ⁰C

)

TIME (HOUR)

VARIATION OF TESS TEMPERATURE FOR REFRACTORY BRICKS



IJETSR

www.ijetsr.com

ISSN 2394 – 3386

Volume 4, Issue 4

April 2017

Fig4: Variation of thermal energy storage section (TESS) temperature with time for refractory brick during

charging.

b) Variation of thermal energy storage section (TESS) temperature with time for rock pebble bed during

charging:

In starting, the temperature of thermal energy storage section for rock pebble bed increases in fast manner but

after sometime the temperature of thermal energy storage section become constant and that time steady state

reached. After that the temperature of TESS does not increase because at this time steady state is reached.

Fig5: Variation of thermal energy storage section (TESS) temperature with time during charging for rock

pebble bed.

c) Variation of thermal energy storage section (TESS) temperature with time for both rock pebble bed

and refractory bricks during charging:

0

20

40

60

80

100

TEM

PER

ATU

RE

( ⁰C

)

TIME (HOUR)

VARIATION OF TESS TEMPERATURE FOR ROCK PEBBLE BED

0

10

20

30

40

50

60

70

80

90

TEM

PER

ATU

RE

( ⁰C

)

TIME (HOUR)

VARIATION OF TESS TEMPERATURE WITH TIME DURING CHARGING

Refractory brick

Rock pebble bed



IJETSR

www.ijetsr.com

ISSN 2394 – 3386

Volume 4, Issue 4

April 2017

Fig6: Comparison of thermal energy storage section (TESS) temperature with time for both refractory brick

and rock pebble bed during charging.

During charging process, hot air blower is used to heat the thermal energy storage section to store thermal

energy. In between 09:45 and 10:20 temperature of rock pebble bed is more than refractory brick and after

10:20 temperature of refractory brick is more than rock pebble bed. As value of ρCp value of refractory brick

is more than rock pebble bed, so refractory brick store more thermal energy than rock pebble bed and also

final temperature of refractory brick is more than rock pebble bed as shown in fig.

d) Variation of thermal energy storage section (TESS) temperature with time for both rock pebble bed and

refractory bricks during discharging:

During discharging, inlet and outlet section closes. And temperature of thermal energy storage section start

decreases during discharging. Although k(thermal conductivity) and ρCp (storage capacity) values of

refractory brick is more than rock pebble bed but due to less value of k of rock pebble bed it act as insulating

material as compare to refractory brick and loss less energy as compare to refractory brick as shown in fig

7.So rock pebble bed act as better thermal storage material as compare to refractory brick. During discharging

at 14.40 temperature of rock pebble bed thermal storage is more than refractory brick thermal storage.

Fig7: Comparison of thermal energy storage section (TESS) temperature with time for both refractory brick

and rock pebble bed during discharging.

CONCLUSIONS:

The heat storage model has been developed in this paper for finding performance of thermal energy storage

system using rock pebble bed and refractory bricks. In this system the heat is stored at quite higher

temperature (average temperature being 530C ). Although K (thermal conductivity) and ρCp (storage capacity)

values of refractory brick is more than rock pebble bed but due to less value of K of rock pebble bed it act as

insulating material and lose less energy as compare to refractory brick. So rock pebble bed can act as better

storage material. However the efficiency of energy storage system may be improved by combining two

mediums such as rock pebble bed and refractory brick.

0

10

20

30

40

50

60

70

80

90

11

:10

11

:20

11

:30

11

:40

11

:50

12

:00

12

:10

12

:20

12

:30

12

:40

12

:50

13

:00

13

:10

13

:20

13

:30

13

:40

13

:50

14

:00

14

:10

14

:20

14

:30

14

:40

TEM

PER

ATU

RE

( ⁰C

)

TIME (HOUR)

VARIATION OF TESS TEMPERATURE WITH TIME DURING DISCHARGING

REFRACTORY BRICK

ROCK PEBBLE BED



IJETSR

www.ijetsr.com

ISSN 2394 – 3386

Volume 4, Issue 4

April 2017

REFERNCES: [1] Sukhatme, S.P., “ Thermal Energy Storage System”, in Solar Energy- Principles of Thermal Collection and Storage,

2nd

ed. Tata McGraw-Hill Education, pp. 258-284,1996.

[2] Dincer, Ibrahim, Rosen, Marc A., “Thermal Energy Storage- Systems and Applications”.1st ed. John Wiley & Sons,

Ltd., pp. 123-141,2002.

[3] Singh, Harmeet, Saini, R.P., Saini, J.S., “Performance of a packed bed solar energy storage system having large sized

elements with low void fraction”. Solar Energy Materials and solar cells, vol.14, pp.22-34, 2010.

[4] Anderson, Ryan, Bates, Liana, Johnson, Erick, Morris, Jeffrey F., “ Packed bed thermal energy storage: A simplified

experimentally validated model”.Journal of Energy Storage,vol.4, pp. 14-23,2015.

experimental study of thermal energy storage system...

Documents