Experimental Research of the Heat Transfer Characteristics using a ...

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ScienceDirect Energy Procedia 69 (2015) 1059 – 1067

International Conference on Concentrating Solar Power and Chemical Energy Systems, SolarPACES 2014

Experimental research of the heat transfer characteristics using a packed-bed of honeycomb ceramic for high temperature thermal storage system Y. Wanga *, F.W. Baia, Z. F. Wanga, Hiroaki Kirikib, M.X Hanb, Shuichi Kubob a

The Key Laboratory of Solar Thermal Energy and Photovoltaic System, IEE-CAS, No.6 Beiertiao, Zhongguancun, Bejing, 100190,China b Ceramics Structure Development Project, IBIDEN CO.,LTD.,1-1,Kitagata,Ibigawa-cho,Ibi-gun,Gifu Pref.,501-0695,Japan

Abstract Due to intermittent nature of solar energy, the thermal energy storage (TES)is vital for the concentrated solar power (CSP) technologies. This paper reports on an experimental investigation of the heat transfer characteristic of a packed-bed using honeycomb ceramic for high temperature thermal storage system. The experimental results showed that the honeycomb ceramic material can be used as the thermal storage material for high temperature packed-bed thermal storage system. After 8 hours of charging, the temperatures of the thermal storage module were 600°C, 500°C and 400°C. And the air outlet temperature is above 483°C after two hours of discharging when the air flow rate is 150m3/h. © Published by by Elsevier Ltd.Ltd. This is an open access article under the CC BY-NC-ND license © 2015 2015The TheAuthors. Authors.Published Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer review by the scientific conference committee of SolarPACES 2014 under responsibility of PSE AG. Peer review by the scientific conference committee of SolarPACES 2014 under responsibility of PSE AG Keywords:packed-bed thermal storage, honeycomb ceramic, heat transfer performance;

1. Introduction Conversion of solar energy into thermal energy is the easiest and the most widely accept method. Due to intermittent nature of solar energy, the thermal energystorage (TES) is vital for the concentratedsolar power (CSP) technologies. Sensible heat storage is the most simply and inexpensive way of energy storage system although there

* Corresponding author. Tel.: +010-82671373; fax: +010-62587946. E-mail address:[email protected]

1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer review by the scientific conference committee of SolarPACES 2014 under responsibility of PSE AG doi:10.1016/j.egypro.2015.03.209

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are few advantage of phase change energy storage over sensible heat storage, but the technological and economical aspects make sensible heat storage superior[1]. The form of sensible heat storage in packed-bed of solid material is especially suitable when air is used as the heat transfer fluid in the solar receiver because of the significantly lower fabrication costs and conventional materials [2, 3]. Materials such as rocks, metals, concrete, sand, and bricks can beused depending on the application [4]. The heat transfer to and from of a flowing fluid to a packed bed has been investigated since Schumann’s original work [5]. The numerical results show that the porous structure which maximize heat transfer between fluid and storage media and minimize heat transport inside the storage media [6-8]. The experimental results show that the heat transfer coefficient increases along a straight line with an increase in air flow rate and decreases along a straight line with an increase in the particle diameter (size or element) [9,10]. Ryan [11] develops an experimental heat system and equivalent model. The model agreed with the experimental data, and the model shows thatan increasing Stanton number at the exterior wall leadto greater heat losses from the systems. In this paper, we describe the design and fabrication of a packed bed thermal storage system. In order to analyze the heat transfer performance between air and honeycomb ceramic, the temperature of air and honeycomb ceramic, the air flow rate and the pressure drop were measured by experimentally. 2. A packed-bed thermal storage system 2.1. A packed-bed thermal storage apparatus Fig.1 shows the schematic of the packed-bed thermal storage module. The packed-bed thermal storage module is a box which is consisted of inlet pipe, outlet pipe, cover plates and the thermal storage materials. The size of the thermal storage module is 1512h1412h1584mm. The air was used as the heat transfer fluid during the charging and discharging. Honeycomb ceramics were used as the thermal storage materials, and 4000 pieces of honeycomb ceramic were inserted into the thermal storage module. Fig.2 is the picture of honeycomb ceramic material. The size of the honeycomb ceramic is 34.3h34.3h100mm. The property of honeycomb ceramic was showed in Table1.

Fig.1 The schematic of packed-bed thermal storage


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(a)

(b) Cross section Fig.2 The structure of honeycomb ceramic Table 1 Property of honeycomb ceramic material Aperture ratio Porosity Cell density Heat storage capacity Conductivity (%) (%) (cell/cm2) (MJ/m3) (W/m.k) 74 42 45 197 10.7 Note: Aperture ratio is ratio of the open area to the total area of the honeycomb ceramic

2.2. A packed-bed thermal storage system In order to analyze the heat transfer performance of the packed-bed thermal storage, an experimental system of thermal storage was built-up. Fig.3 is the layout of the packed-bed thermal storage system using honeycomb ceramic as the thermal storage material. The thermal storage system is consisted of fan, high temperature air furnace, packed-bed thermal storage module, pressure drop sensor, thermocouple and flow meter. In the system, the fan transported airfrom the environmentto the furnace or pipes. The high temperature furnace is the heating apparatus to heat the air. The pressure drop when air flows through the thermal storage module were measured by the pressure drop sensor. The air temperature, honeycombceramic temperature and the surface temperature of the thermal storage were measured by several thermocouples. Fig.4 is the figure of the packed-bed thermal storage system using honeycomb ceramic for high temperature thermal storage. In order to analyze the performance of the thermal storage module and the heat transfer between air and honeycomb ceramic, air volumetric flux, temperatures of air, honeycomb ceramic and the surface of the thermal storage module, the pressure drop of the thermal storage module which air flows from the inlet to outlet were measured. The inlet air flow rate was measured by a volumetric flow meter with the range from 15 to 300m3/h and the error is ±0.5%. The outlet air flow rate was measured by a vortex flow meter with the range from 80 to 800m3/h

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and the error is ±0.5%. The pressure drop of the thermal storage was measured by the pressure drop sensor which the error is ±0.5%.

Fig.3 Schematic of packed-bed thermal storage system

Fig.4 The photo of the thermal storage system

The temperatures of air, honeycomb ceramic and the surface of the thermal storage module were measured by thirty-eight K-type or S-type thermocouples, which all error is ±0.1ć. The positions of the thermocouple inserted into the thermal storage module are shown in Fig.5.

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Fig.5 The position of the thermocouple in the packed bed thermal storage module

The thermocouples of 1-10 and 1-11 were measured the air inlet temperature and the air outlet temperature. In order to measure the temperatures of honeycomb ceramic, 27 thermocouples were inserted into the thermal storage module and attached to the honeycomb ceramic surface. The thermal storage module is divided into three blocksalong the length by thermocouples. The thermocouples of 1-1 to 1-9, 2-1 to 2-9 and 3-1 to 3-9 which were measured the honeycomb ceramic temperatures of the first block, the second block and the third block.The thermocouples of 2-10 to 2-14 were measured the surface temperature of the thermal storage module. 3. Results and discussion In order to analysis the charging/discharging performance of the packed-bed thermal storage,the temperature of air and honeycomb ceramic, the air flow rate, the pressure drop between the inlet and outlet of the TES were tested. The average temperature of honeycomb ceramic on every block of the packed–bed thermal storage along length is defined as Eqs.(1). ೕసవ

ܶ௜,௔௥௘௔ =

σೕసభ ்೔,ೕ ଽ

(i=1,2,3)

(1)

Where, i=1,2,3 means the first block, the second block and the third block. The rate of charging/discharging is defined as the ratio of temperature difference and time. ܴ=

ο் ௧

(2)

Where, ܴ is the rate of charging/discharging, K/Min; οܶis the temperature difference, K ‫ݐ‬isthe time, Min. 3.1. The charging heat transfer performance Fig.6 shows the temperature of air and the honeycomb ceramic variation with time.During the charging, the range of air flow rate is 70Nm3/h~120Nm3/h.The high temperature air furnace was used to heat the air which was transported by the fan from the environment, so the air inlet temperature was increasing with time at first. Fig.6 is shown that when the inlet temperature is tend to be a constant, the speed rate of temperature in the first block became slowly, but the speed rate of temperature in the second and the third blocks were quickly. That is because the temperature difference between air and honeycomb ceramic at the first blockis smaller, and heat which air exchange to the thermal storage material reduced, somore heat can be exchanged from air to the solid material at the next blocks. The average temperatures of three blocks were 600ćǃ500ć and 400ć after 520 minutes when the charging process was completely.

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Fig.6 The temperature variation with time

As we know the heat transfer rate is related to air flow rate, temperatures of the heat transfer fluid and storage material. The air flow rate and the rate of charging at the first block with the time were shown in Fig.7. It can be seen that the rate of charging increased with air flow rate increased. But when the air flow rate is relatively steady, the rate of charging decreased with the time except for the early stage of charging.That is because the difference between the air and thermal storage material was become smaller with the charging process. So enlarged the volume of thermal storage module, produced thermocline in thermal storage can enhance the efficiency of heat transfer.

Fig.7 The rate of charging and air flow rate with time

Fig.8 shows the honeycomb ceramic temperature variation and rate of charging variation with time. The results from Fig.8 show that when the temperature of honeycomb ceramic reached 150ćˈthe rate of charging between the air and the honeycomb ceramic decreased for the whole thermal storage module. The figure also indicated the rate of charging decreased along the length of the thermal storage module which means the rate of charging was related to air inlet temperature and the thermal storage material temperature.

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(a)

The first block (inlet)

(b)

The second block

(c) The third block (outlet) Fig.8 The variations of temperature and rata of charging with time

3.2. The discharging heat transfer performance Ensuring more heat can be exchanged to air, the air flow direction is inverse comparingto the charging, which means that the air inlet while charging is the air outlet while discharging. Fig.9 shows the air temperature variation with time. The numbering of the thermocouples 111 according to Fig.3means air inlet temperature and the numbering of the thermocouples 110 means air outlet temperature. When charging process is completed, the discharging is beginning, and the temperature of the pipes and the thermocouples are very higher, so the air inlet temperature is higher than the actual inlet temperature at the first discharging period. The air outlet temperature is 438ć after two hours discharging when the air flow rate is 150Nm3/h. The result also suggested that the heat can be exchange from solid to gas when using the air as the heat transfer fluid and honeycomb ceramic as the thermal storage material.

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Fig.9 The temperature variation with time

Fig.10 is the variation of honeycomb ceramic temperature and rate of discharging variation with time. At first, the rate of discharging increases with the time at first block and second block. About two hours later,the rate of discharging decreased with the temperature of ceramic decreased. But at the third block, the inlet air temperature was higher, so the difference temperature was lower than the former blocks, the rate of discharging decreased with time.But the rate of discharging is larger at third block than the former blocks, which means that theheat transfer performance is related to the temperature of honeycomb ceramic, the high temperature of thermal storage material, the higher rate of discharging. The results indicated that in order to enhance the heat transfer efficiency, the temperature of thermal storage material must be higher in thermal storage system using solid as the thermal storage material. 4. Conclusion In this paper, the heat transfer characteristic of charging and discharging were researched by experimentally. (1) The honeycomb ceramic material can be used as the thermal storage material for high temperature packedbed thermal storage system. After 8 hours of charging, the temperatures of the thermal storage module were 600°C, 500°C and 400°C. And the air outlet temperature is above 483°C after two hours of discharging when the air flow rate is 150Nm3/h. (2) The heat transfer rate wherever charging or discharging between the air and the honeycomb ceramic is higher at high temperature difference stage. The heat transfer rate is related to the temperature and air flow rate.

(a)

The first block (outlet)

(b)

The second block


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(c) The third block (inlet) Fig.10 The variations of temperature and rata of charging with time

Acknowledgements This work was supported by a research grant from the Key Laboratory of Solar Thermal Energy and Photovoltaic Systems, China (Project No: National Natural Science Foundation of China (51306170). This work was done by INSTITUTE OF ELECTRICAL ENGINEERING, CHINESE ACADEMY OF SCIENCES, and IBIDEN Co., Ltd., Japan cooperation. Finally, the authors thank the reviewers for their helpful comments and suggestions. References [1] Harmeet Singh, R.P. Saini, J.S. Saini. A review on packed bed solar energy storage systems. Renewable and Sustainable Energy Reviews, 2010, 14:1059-1069. [2] Markus Hanchen, Sarah Bruchneer, Aldo Steinfeld. High-temperature thermal storage using a packed-bed of rocks-Heat transfer analysis and experimental validation. Applied Thermal Engineering, 2011, 31:1798-1806. [3] Coutier JP, Faber EA. Two applications of a numerical approach of heat transfer process within rock beds. Solar Energy, 1982, 29(6):451– 462. [4] Hasnain SM. Review on sustainable thermal energy storage technologies, Part I: heat storage materials and techniques. Energy Convers Manag, 1998, 39:1127–1138. [5] Schumann TEW. Heat transfer: a liquid flowing through a porous prism. Heat Transfer 1929;405–416. [6] Chao Xu, Xin Li, Zhifeng Wang, Yaling He, Fengwu Bai. Effects of solid particle properties on the thermal performance of a packed-bed molten-salt thermocline thermal storage system.Applied Thermal Engineering, 2013, 57:69-80. [7] S.A. Zavattoni, M.C. Barbato, A. Pedretti, G. Zanganeh, A. Steinfeld. High temperature rocked-bed TES system suitable for industrial-scale CSP plant-CFD analysis under charger/discharge cyclic conditions. Energy Proccedia, 2014, 46:124-133. [8] G. Zanganeh, A. Pedretti, S. Zavattoni, M.Barbato, A. Steinfeld. Packed-bed thermal storage for concentrated solar power Pilot-scale demonstration and industrial-scale design. Solar Energy, 2012,86:3084-3098. [9] Furnas CC. Heat transfer from a gas stream to a bed of broken solids. IndEngChem J, 1930,721–731. [10] Lof GOC, Hawley RW. Unsteady state Heat transfer between air and loose solids. IndEngChem J, 1948, 40(6):1061–1071. [11] Ryan Anderson, Samira Shiri, Hitesh Bindr, Jeffrey F. Morris. Experimental results and modeling of energy storage and recovery in a packed bed of alumina particles.Applied Energy, 2014, 119:521-529.