EXPERIMENTAL STUDY OF HFC-134a GAS HYDRATE FORMATION PROCESS

第54卷增刊化工学报Vol 54 Suppl2003年12月Journal of Chemical Industry and Engineering (ChinaDecember 200EXPERIMENTAL STUDY OF HFC-134GAS HYDRATE FORMATION PROCESSLI Jinping, 2, LIANG Deqing, GUO Kaihua?, FAN Shuanshi and WANG Ruzhu'Institute of Refrigeration and Cryogenics, Shanghai Jiaotong University, Shanghai 200030, China;gzhou Institute of Energy Conversion,Chinese Academy of Sciences, Guangzhou 510070, Guangdong, China)Abstract Refrigerant gas hydrates have brilliant prospects as cool storage material of air-conditioningsystem. In this paper, when the ratio of the weight of HFC-134a to that of water is 2. 17%, systematicexperiments have been carried out on the formation process of the HFC-134a gas hydrate including of thephase equilibrium, the influence of supercooling degree, and the influence of agitation. The results indicatethat the critical decomposition temperature and the critical decomposition pressure of R134a hydrate is283 4K and 414K respectively, the formation of gas hydrate was promoted with increasing thesupercooling degree and the agitation. However, it is desired that the supercooling degreTherefore, it is important problem that the study of optimum of supercooling degree for cool storage systemKeywords refrigerant gas hydrate, formation process, phase equilibrium, agitation, supercooling degree1 INTRODUCTIONagitation.2 EXPERIMENTAL APPARATUSGas hydrate are ice-like clathrates compoundswhich are comprised of guest molecules gasExperimental apparatus used in this study wasmolecules)and host molecules ( water molecules). shown in fig. 1. The apparatus consists of aRefrigerant gas hydrates, which are usually called cylindrical quartz glass with a magnetic stirrer. Thewarm ice", can be formed at temperature 5-12 maximum effective volume of the cell(includingwith a reaction heat 320--430 kJ/kg, which the volume of blades and platinum resistance )isenables refrigerant gas hydrates one of the most 1.84 X 10-4m. The magnetic stirrer with threepromising cool storage material of air-conditioning blades (P4X10-m)was placed in the center of thesystem [1,2]flanges, and the speed of the stirrer can beIn this paper, when the ratio of the weight of controlled in the range of 0-1000 r.min-1.TheHFC-134a to that of water is 2.17%temperature in the cell was measured by a platinumexperimental study has been carried out on the resistance thermometer with the accuracy of tformation process of the HFC-134a gas hydrate 0.1K, and pressure by a strain gauge type pressurencluding of the phase equilibrium, the influence of transducer with the accuracy of 0.06%.Thesupercooling degree (S D), and the influence ofemployed water (100g )was deionized. Thecertified purity of refrigerant R134a used was moreFirst author: LI Jinping, male, born in 1977, Ph. D Candidate.than 99. 9%. So, refrigerant were used withoutCorresponding author: Prof. FAN Shuanshi, Eanyhydrate @ms giec accn中国煤化工Foundation item: supported by the National Natural ScienceCNMHGwere as follows. AtFoundation of China(No 50176051)and the State Key Development the temperature of 293K, the weighed deionizedProgram for Basic Research of China (No. 2000026306)water was charged into the glass cell, the glass cellVol 54 Suppl.Journal of Chemical Industry and Engineering ( China)differences of the critical decompositiontemperature and the critical decomposition pressureof R134a hydrate between this experiment [e.g.point B(283 4K, 414kPa) in fig. 2] and theliterature [4](283. 49K, 417kPa)are 0. 09K and0. 003 MPa respectively. These differences areestimated to be technical deviations in thismeasurement methodln(P/P)=T[a1(1-T)+a2(1-T,)2+Fig 1 Schematic plan of experimental apparatusas(1-T)2+a4(1-T,)3]1-to refrigerant cylinder: 2-to vacuumWhere T8.074883--pressure transducer: 4-magnetic stirrer5-platinum resistance; 6--flange: 7-quartz glass cell;1.39779,a3=0.613357,a4=-3.60021.AndT8-water bath: 9 data collection unit; 10--computerand P are critical pressure and critical temperaturewas evacuated and flushed with the gaseous R134a respectively, T-=374 30K, P(=4.0640MPa.and re-evacuated. Then desired amount ofIn(P)=a/T-+b(2)refrigerant (2. 17g) was fed into the cell. AnWhere P is the equilibrium pressure in MPaelectronic balance, with the accuracy of 0.01g, T is the equilibrium temperature in K, and a and bweighed the deionized water (100g) and the are constants, a=-16893 0, b=58.714.charged pressure was 560kPa, which is lower than 3. 2 Influence of supercooling degree tothe pressure of saturated HFC-134a at 293K.formation of R134a hydrateThe cell was immersethe temperaturesupercooling degree to thecontrolled bath with the fluctuation of +0. 05Kformation of R134a hydrate at 475 rotation perThe R134a refrigerant-water mixture was agitated minute rpm. is shown in fig 3. Theby the stirrer, and was cooled down with the supercooling degree (S D) is the differencetemperature controlled bath until the gas hydrate between temperature at quadruple point Le g. Bformed. Then the temperature of the bath was set (283. 4K, 414kPa) in fig. 2] and the temperatureup to desired temperature with agitation. When set by the temperature of the temperaturethe temperature and the pressure in the cell became controlled bath. The larger the supercoolingconstant, the temperature and the pressure data degree is, the faster the hydrate formation processwere recorded as equilibrium data.finishes. However, it is desired that thesupercooling degree is smaller. Therefore, it is3 RESULTS AND DISCUSSIONimportant problem that the study of optimum of3.1 Quadruple point of R134a hydratesupercooling degree for cool storage system.The R134a hydrate dissociation curve and the 3. 3 Influence of agitation to formation ofsaturatd P-t curve are shown in fig. 2. TheR134a hydratesaturated P-t curve and hydrate of r134a/waterThe influence of agitation to the formation ofdrawn by the eq. (1)[3] and eq. (2)(43 respectively R134a hydrate is shown in fig 4. At the samewere used to check the credence of thsuperc中国煤化工ressure vs, timeexperimental method. At the same temperature,curveTHCNMHGhills in the curvethe maximum difference of saturated pressure of Ocan ue concluded that R134aR134a between the data calculated by the eg. (1) hydrate with 960 rpm nearly finishes formation in 8and the experimental data is 0. 002 MPa. And the hours, while with 320 rpm doesn't. Large quantity of100化工学报December 2003600a saturated vapor pressure of eq (1)experimental saturated vapor pressureA RI34a hydrate dissociation curve of eq (2)x experimental dissociation curve of R134a hydrate265T/KFig 2 Phase graph of R134a2940=475rmin1300time/hFig. 3 Influence of supercooling degree to formation of R134a hydrate① P ys, time with5.4KSD;①1-TAK S D② P vs, time with6.4KSD.;②1-T中国煤化工③Pws. time with7.4KSD.;③I-TCNMHG④ P vs, time with8.4KSD.;④l- T ys. time with8.4KSDVoL 54 Suppl.Journal of Chemical Industry and Engineering (China)294600subcooling degree is 6.4 K300284274time/hFig 4 Influence of agitation to formation of r134a hydrate①一Pws. time with960r·min-1;①l- T vs time with960r·min-1② P ys, time with320r·min-1;②l-Tws. time with320rmin-1;3-P vs, time without agitation I-T. time without agitationthe R134a hydrate forms earlier with 960 rpm than hydrate is 28. 4K and 414K respectively.with 320 rpm, while the R134a hydrate formsThe formation of gas hydrate was promotedmore concentrated with 960rpm than with 320 with increasing the supercooling degree and therpm. Without agitation, there is not apparenttrack of R134a hydrate formation in the curve supercooling degree is smaller. Therefore, it isand 3, maybe because of an observed hydrate important problem that the study of optimum offilm forming at the interface of R134a gas andsupercooling degree for cool storage system.liquid water that prevents the R134a gas and liquid referenceswater from diffusing mutually.Thus, the agitation promotes the formation of I Tomlinson J J. Hea Pump Cool Storage in a Clathrate of Freon.In: Proc. of the 17th IECEC. April, 1982. 2060--2064R134a hydrate. However, if it is to control 2 Carbajo J J. A Comparative Study of Water, Ice, and Clathratesquantity and time of the R134a formation,anfor Cool Storage Application. In: Proc. of the 20th IECEC.Apil,1985.2307-2312appropriate agitation should be considered3 Kamei A, Piao C-C, Sato H. Thermodynamic Charts and CyclePerformance of r134a. ASHRAE Trans., 1991, 97(Part 1)4 CONCLUSIONS141中国煤化工 Matsuo M, YoshidaThe phase-diagram of R134a hydrate wasCNMHHFC Alternativedetermined and the quadruple point of hydrate wasbtained. The critical decomposition temperatureThermophysics,1999,20(6):269274and the critical decomposition pressure of R134a