Yuki Sakamoto

Sakamoto, Yuki

2030

Naragakuen University Academic Repository

Measurement of Thermophysical Properties of Thermal Storage System  - Measurement of CaCl2?nNH3 system by arbitrary heating method - Yuki Sakamoto Department of Liberal Arts, Nara Bunka Women’s College, 3-15-1, Nakatomigaoka, Nara city,  Nara, 631-8523, Japan SUMMARYIn order to measure thermophysical properties of CaCl2?nNH3 system as one of thermal storage systems, the effective thermal conductivity and the thermal diffusivity of CaCl2?8NH3 system were measured by arbitrary heating method and compared with those of CaCl2?4NH3 system. The values of ?  and ?  of CaCl2?8NH3 system in the measuring temperature range (290 K to 350 K) were 0.1?0.5 W/(m?K) and 0.04?0.17x10-6 m2/s, respectively. It was found that the behavior of thermophysical properties of CaCl2?8NH3 system was different from that of CaCl2?4NH3 system.KEY WORDS: thermal storage system, thermophysical properties, ammine complex, calcium chloride, ammonia,  arbitrary heating method 1. INTRODUCTIONRecently, the possibility of significant global warming resulting from emissions of greenhouse gases by fossil fuel combustion has become an important concern within the international community. In the energy sector, energy utilization technologies in many industries are expected to develop high efficiency and high performance. For thermal energy storage systems utilizing a low heat source as solar energy or hot effluent (approximately 353?373K), the processes using the chemical reaction of anhydrous salt with NH3 have been proposed and discussed for its practicably1?6). For example, some prototypes of energy storage unit using CaCl2?nNH3 system have been designed and measured these performances 3?6).The reaction products from anhydrous salts and ammonia are referred to as ammoniated salts or ammine complexes and the state is either solid or liquid. The reaction is similar to hydration of anhydrous salts. In this study, the chemical reaction of CaCl2?4NH3 with 4NH3 was chosen here for the thermal energy storage system (see the ? 39?? 40?following reversible chemical reaction: Ammoniation/Deammoniation). In this reversible reaction, ?H (enthalpy change) is 43.8 kJ/mol-NH3 at 0.1 MPa, 304 K 1), the value of which is considerably higher than the latent heat of vaporization of liquid NH3, 23.4 kJ/mol-NH3 at 0.1 MPa, 240 K 2).CaCl2?4NH3 + 4NH3 ?  CaCl2?8NH3 +?HIn the author’s previous work10), in order to measure the thermophysical properties (effective thermal conductivity and effective thermal diffusivity) of CaCl2?nNH3 system, the measurement unit has been developed by arbitrary heating method using Laplace transform7?10) and measured effective thermal conductivity and effective thermal diffusivity of CaCl2?4NH3 system.  In this study, in order to develop the thermal energy storage system using CaCl2?nNH3 system, the thermophysical properties (effective thermal conductivity and effective thermal diffusivity) of CaCl2?8NH3 system were measured and compared with those of CaCl2?4NH3 system. 2. PRINCIPLE OF MEASUREMENTIn this study, this principle of measurement is only shown. Regarding the principle of this measurement method in detail, refer to arbitrary heating method by Iida et al.7,8,9) and the author’s previous work10).2.1. Fundamental relation of heat conduction for one dimensional cylindrical coordinate Assuming heat flux is the direction of radius r  only, where t , T  and ?  are , respectively, time, temperature and thermal diffusivity, and ?)0,(rT constant, that is, initial temperature distribution is uniformity. Considering ),( tr?  as temperature difference in equation (1),   )0,(),(),( rTtrTtr ???  (1) The fundamental heat conduction equation is given by ????????rtrrrtrttr?????????? ),(1),(),(22  (2) Equation (2) is transformed by using Laplace transformation and substitution of 0)0,( ?r?  into equation (2), and then is rewritten to the ordinary differential equation, general solution as equation (3) is given by  )/()/( 00 rsDKrsCI ???? ???  (3)  where ?  and s  are Laplace integration of ? ? )(),( ttr rr ?? ??  and Laplace parameter, and 0I and 0K  are modified Bessel functions of the first and the second kind of zero-order, and then C  and D  are constants of integration, respectively. On the other hand, heat flux ),( trq  is given by Fourier's equation. rtrrtrTtrq??????? ),(),(),( ????  (4) where ?  is thermal conductivity. ? 41?Equation (4) is transformed by Laplace transform, and then given by ? ?)/()/( 11 rsDKrsCIsq ????? ????  (5) 2.2. Measurement system Figure 1 shows the principle of measurement. Considering the infinite tubular sample???around the infinite cylindrical sample??? in Fig. 1. In this experiment, the supplied sample is the case of cylindrical sample ???.Hence tubular sample??? is the case of reference sample. Assuming the heat flux is only direction of radius and the contact resistance is negligible, and the symbol × is expressed a measuring point of temperature and the measuring point 2 is defined as the boundary surface. The temperature response ),( tri?  at each measuring point i (i=0,2,R) is rewritten as )(ti? , Laplace integration of each point is expressed by dtte isti )(0?? ?? ??  (6) In this measurement system, the temperature responses of central point in the cylindrical sample as the supplied sample and surface point of the reference sample were measured at the same time in Fig. 1.Assuming ?? , ??  and  ?? ??pc ? pc : specific heat, ? ?density?are, respectively, thermal diffusivity, thermal conductivity and heat capacity of the reference sample, and are well known. In ???, 0),0( ?tq . Hence ? ? 00 ??rq . Thus 0??D  in equation (5), and substitution of ? ? 100 ?I  into equation (5), then given by 0)/( 2200 ??? ??? rsI ?  (7) where ?? is thermal diffusivity of the supplied sample.  Hence, in this case, 02 ??  is calculated. Thermal diffusivity ?? is calculated from Figure 2 immediately.  Then thermal conductivity of the supplied sample ??  is given by the following equation.  Figure 1. Principle of measurement.????? ?????????? ??????????? ????????? ??????????????????????????????????????? ?)/()/(1)/(12121021rsKDrsICrsI????? ????????? ???????? (8) Then ?C  and ?D  are given by )/()/()/()/()/()/(2000202002rsKRsIRsKrsIrsKRsKC R???????????????? ???????? (9) )/()/()/()/()/()/(0202002002RsKrsIrsKRsIrsIRsID R???????????????? ???????? (10) Regarding the range of Laplace integration, its range is expressed as from maxt  to zero, and the relation between maxt  and s  is expressed as the following equation by Iida et al.9). 8? maxst ?12In this experiment, s  was determined to satisfy maxst  = 10.  3. EXPERIMENTAL SECTION 3.1. Materials CaCl2 used in the experiment is produced by Wako Pure Chemical Industries Ltd. Japan. It is guaranteed reagent grade, and it is specified as the pure grade having minimum purity of 95.0 %. CaCl2 is used without further purification. NH3 gas of 99.99 % purity is provided from Seitetsu Kagaku Co. Ltd. Figure 2. Determination of thermal diffusivity for temperature measurement of central point.1.02.03.04.05.06.07.08.09.00.0 1.0 2.0 3.0 4.02/ rs ??)/( 20 rsI ??02 /??? ????? ????????? 42?3.2. Experimental apparatus  Figure 3 schematically shows the experimental apparatus of the measurement system. This system consists of measurement unit (cell)? as the reactor, NH3 glass vessel, pressure regulator valve, pressure gauges, thermocouples and constant temperature water bath. The measurement cell is made of stainless steel and it is covered with water jacket, which can control the temperature in the measurement cell. The NH3 vessel is pressure resistance glass vessel, which volume is 0.3x10-3 m3, (up to 2.0 MPa), and the volume of the liquid NH3 is measured by a microscope with an accuracy of ± 0.05 % of full volume (0.5x10-3 m3).  In order to insulate the measurement unit from the surroundings, the apparatus is wrapped foamed polystyrol. The temperature in this unit is measured by using C-A type thermocouples by the digital thermometer and the temperature data as the digital signal (change of mV) transferred to the micro computer and are analyzed.   The amount of liquid NH3 transferred to the measurement cell from the NH3 vessel can be measured by the microscope. The temperature of the measurement cell, unit and the NH3 vessel are controlled by using constant temperature bath having minimum accuracy within ± 0.1 K separately.  The pressure in the vessels is measured by Bourdon gauge, which accuracy is ± 0.1 % of full scale (up to 2.0 MPa). The pressure control in the measurement cell is carried out using the pressure regulator valve.  This measurement cell consists of two major units, a stainless steel pipe (Length: 230 mm, OD: 76.3 mm, ID: 68.3 mm) and a reinforced pressure proof glass tube as the reference sample (Pyrex 7740: OD: 40.0 mm, ID: 32.0 mm) , and the temperature response is measured by the stainless steel covered C-A thermocouple (? 0.65 mm), which are inserted in the measurement cell. Regarding the measurement cell in detail, refer to the author’s previous work10).   3.3. Experimental Procedure 3.3.1. Preparing for CaCl2?8NH3 system (Ammoniation) CaCl2 of 0.218 mole (approximately 24.2 g) was crushed below size of 200 JIS mesh and was dried at 773 K approximately for 5 hours by an oven. A dried powder sample was placed in the measurement cell. It was sealed, and 1: Measurement cell, 2: Pyrex glass vessel,  3: Pressure gauge, 4: Pressure regulator valve,  5: Constant temperature bath, 6: Pump,  7: Thermocouple, 8: Digital thermometer,  9: Micro Computer, 10: Temperature controller,  11: Water jacket12334567891011Figure 3. Schematic diagram of measurement unit.? 43?worked by the vacuum pump in order to remove air and any water from this measurement cell. The NH3 vessel was also evacuated for 2 hours and NH3gas introduced from the cylinder into the NH3 vessel, which was kept at constant temperature (273 K) by the cooling liquid. After liquid NH3 was charged in it, its volume was measured by the microscope rapidly and recorded. Then this measurement cell was connected with the NH3vessel shown in Fig. 3. NH3 gas moved to the measurement cell through the pressure regulator valve keeping constant pressure (0.5 MPa) during the reaction. The level of liquid NH3 in the NH3 vessel was measured by reading the scale of the NH3 vessel using the microscope, and mole number of NH3 absorbed to pure CaCl2 was calculated from this volume change.  When 8 moles of NH3 was absorbed to the pure CaCl2, the experiment of ammoniation is just finished.  3.3.2 Measurement of thermophysical propertiesAfter temperature of cell is settled with the measurement temperature and the temperature of measuring points arestabilized, and start heating of the measurement cell by charging electricity to Ni-Cr wire, where heating rate and maximum heating temperature are 5 K/min. and 10 K, respectively, in order to avoid the violent reaction in the measurement cell during the measuring time. Temperature changes (change of mV) of C-A type thermocouple are measured by the digital thermo meter and input was recorded to the micro computer system, and the scan rate is every 9 seconds and the measurement time is 30 minutes. 4. RESULTS AND DISCUSSION Figures 4 and 5 show the relation between thermophysical properties of CaCl2?4NH3 system10) and CaCl2?8NH3system and temperature. ?  (effective thermal conductivity) and ? ? (effective thermal diffusivity) of CaCl2?4NH3system were approximately constant (0.2 W/(m?K) and 0.075x10-6 m2/s, respectively) in the measuring temperature range of 290 K to 350 K. However, ?  and ? ? of CaCl2?8NH3 system increased with increasing temperature in the measuring temperature range (290 K to 350 K). It was found that the behavior of thermophysical properties of this system was different from that of CaCl2?4NH3 system. The values of ?  and ?  of CaCl2?8NH3 system were 0.1?0.5 W/(m?K) and 0.04?0.17x10-6 m2/s, respectively.  In order to analyze the behavior of thermophysical properties of CaCl2?4NH3 system and CaCl2?8NH3 system, Figures 6 and 7 show the relation between ?  of CaCl2?4NH3 system and CaCl2?8NH3 system, pressure in the measurement cell and temperature. In Fig. 6, it was seemed that ?  of CaCl2?4NH3 system had no influence in the range of measuring temperature and measuring pressure in the measurement cell. However, in Fig. 7, ?  of CaCl2?8NH3 system increased with increasing temperature in the measuring temperature range. Regarding the reason of the difference of the behavior of both systems, it was seemed that ?  of CaCl2?4NH3 system and CaCl2?8NH3 systems were influenced by the packed density (?bulk: CaCl2?4NH3 system: 0.232 x103kg/m3, CaCl2?8NH3 system: 0.320 x103kg/m3) of those systems .  ? 44?In general, it is well known thermal conductivities of solids depend on many factors and are difficult to measure or predict. In particular, in porous solids, for example, the thermal conductivity is strongly dependent on the void fraction (related to the packed density in this experiment), the pore size and the fluid contained in the pore11).On the other hand, a theoretical equation of thermal conductivity for porous solids has been developed as Kunii-Smith’s equation (equation (11) : excluding the term of radiation) 12).?????????????dcvvc ???????/3/21  (11) where ?  , c?  and d?  are effective thermal conductivity, thermal conductivity of continuous phase (NH3 gas in this experiment) and thermal conductivity of discontinuous phase (CaCl2?4NH3 and CaCl2?8NH3 in this experiment), respectively, and then v?  and ?  are void fraction of discontinuous phase (related to the packed density in this Figure 4. Relation between thermophysical properties of CaCl2?4NH3 system and temperature10).Figure 6. Relation between ?  of CaCl2?4NH3 system,  pressure in the measurement cell and temperature10).0.00.10.20.30.40.50.6280 290 300 310 320 330 340 350 360Temperature [K]? [W/(m?K)], ? [×106  m2 /s] ?, Effective thermal conductivity?, Effetive thermal diffusivity?bulk = 0.320×103 [kg/m3]0.00.10.20.30.40.50.6280 290 300 310 320 330 340 350 360Temperature [K]? [W/(m?K)]0.00.20.40.60.81.0Pressure [MPaG]?, Effective thermal conductivityPressure in cellFigure 5. Relation between thermophysical properties of CaCl2?8NH3 system and temperature. Figure 7. Relation between ?  of CaCl2?8NH3 system,  pressure in the measurement cell and temperature. .0.00.10.20.30.40.50.6280 290 300 310 320 330 340 350 360Temperature [K]? [W/(m?K)], ? [×106  m2 /s] ?, Effective thermal conductivity?, Effective thermal diffusivity?bulk = 0.232×103 [kg/m3]0.00.10.20.30.40.50.6280 290 300 310 320 330 340 350 360Temperature [K]? [W/(m?K)]0.00.20.40.60.81.0Pressure [MpaG]?, Effective thermal conductivity Pressure in cell? 45?experiment) and ratio of fluid film thickness and particle (grain) diameter, respectively. In equation (11), it was found that the values of ?  and c? were influenced by those of v?  and d? . In this experiment, it was seemed that ?of CaCl2?8NH3 system had the influence of c? , d?  and v?  by increasing the packed density. It is necessary to investigate the detailed effect of the void fraction and /or the packed density for the effective thermal conductivity of this system.  5. CONCLUSIONS The thermophysical properties (effective thermal conductivity and effective thermal diffusivity) of CaCl2?8NH3system as a thermal energy storage system were measured by arbitrary heating method using Laplace transform and compared with those of CaCl2?4NH3 system. As a result, the following conclusions were obtained.   ?  and ? ? of CaCl2?8NH3 system increased with increasing temperature in the measuring temperature range.The values of ?  (effective thermal conductivity) and ? (effective thermal diffusivity) of CaCl2?8NH3 system were 0.1?0.5 W/(m?K) and 0.04?0.17x10-6 m2/s, respectively. It was found that the behavior of thermophysical properties of this system was different from that of CaCl2?4NH3 system and seemed that the those of CaCl2?8NH3system had the influence of the thermal conductivity of continuous phase (NH3 gas), the thermal conductivity of discontinuous phase (CaCl2?8NH3) and the void fraction of discontinuous phase by the packed density. ACKNOWLEDGEMENTS The author is grateful to Professor Hideki Yamamoto of Kansai University for the support to this study.  NOMENCLATURE?  = thermal diffusivity and effective thermal diffusivity [m2/s]?  = temperature difference [K] ?  = Laplace integration of ?  [-] : ? ?dtte st?? ?? ??0?  = thermal conductivity and effective thermal conductivity [W/(m?K)]?  = bulk density [kg/m3]pc  = specific heat [kJ/(kg?K)] DC,  = constant of integration [-]  0I  = modified Bessel function of the first kind of zero-order [-] ? 46?0K  = modified Bessel function of the second kind of zero-order [-] q  = heat flux [W/m2]q  = Laplace integration of q [-] r  = radius [mm] R  = outer diameter of sample [mm] s  = Laplace parameter [-] t  = time [s] maxt  = time step of measuring time [s] T  = temperature [K] ? = sample ???? = sample ???i  = measuring point REFERENCES 1) Yoneda, N. and Hagiwara, I. (1979). “Study of Chemical Heat Pump for Thermal Energy Storage”. Solar Energy,5, 4, pp.4-15.  2) Wentworth, W. E. and Jhonston, D. W. (1981). “Chemical Heat Pumps Using a Dispersion of a Metal Salt Ammoniate in an Inert Solvent”. Solar Energy, 26, pp.141-146.  3) Hall, C. A. (1976). “DEVELOPMENT OF AMMONIATED SALTS THERMOCHEMICAL ENERGY STORAGE SYSTEMS Phase?”. U.S. Department of Energy.  4) Jeager, F, A., Haas, W. R. and Anderson, J. E. (1979). “DEVELOPMENT OF AMMONIATED SALTS THERMOCHEMICAL ENERGY STORAGE SYSTEMS Phase?”. U.S. Department of Energy. 5) Sakamoto,Y.and Yamamoto, H. (1990). “Performance of Thermal Storage Unit Using CaCl2-NH3 System Mixed with Ti”. The Canadian Journal of Chem.Eng ., 68, pp.948-951.  6) Sakamoto,Y.and Yamamoto, H. (1995). “Effect of Metal Additive on The Performance of Horizontal Thermal Energy Storage Unit Using CaCl2-NH3 system”. in Proceedings of The 2nd International Conference on New Energy Systems and Conversions, 31.July-4.August, Istanbul, Turkey, pp.419-428.  7) Iida,Y. and Shigeta, H. (1981). “Measurement of Thermal Properties of Solids by Arbitrary Heating: 1st report”. The Japan Society of Mechanical Engineers (JSME) International Journal, 47, pp.470-477. (in Japanese). 8) Iida,Y. and Shigeta, H. (1981). “Measurement of Thermopysical Properties of Solids by Arbitrary Heating: 2nd report”. The Japan Society of Mechanical Engineers (JSME) International Journal, 47, pp.2324-2332. (in Japanese). 9) Iida,Y., Shigeta, H. and Akimoto, H. (1982). “Measurement of Thermopysical Properties of Solids by Arbitrary Heating: 2nd report”. The Japan Society of Mechanical Engineers (JSME) International Journal, 48, pp.142-148. ? 47?(in Japanese). 10) Sakamoto,Y. (2007). “Measurement of Theermophysical Properties by Arbitrary Heating Method - Development of Presuure and Corrosion Resistance Measurement Unit -”. Narabunka Women’s College Study Report, 38, pp.55-66 11) Bird, R., Stewart, W. and Lightfoot, E. (1960). “TRANSPORT PHENOMENA”. John Willy &Sons.  12) Kunii, D. (1976). “Netsuteki tanisousa (Thermal unit operation)”. Vol. 1. Maruzenn. (in Japanese). ? 48?

Measurement of Thermophysical Properties of Thermal Storage System : Measurement of CaCl_2・nNH_3 system by arbitrary heating method

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Measurement of Thermophysical Properties of Thermal Storage System : Measurement of CaCl_2・nNH_3 system by arbitrary heating method

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