Drying Dynamics of Ulva Prolifera with the Heat Pump Microwave Method

Transcription

1 Drying Dynaics of Ulva Prolifera with the Heat Pup Microwave Method Dan Su, Shujun Li *, Fengin Zhao, Youfu Cao Chinese Acadey of Agricultural Mechanization Sciences Beijing, China Abstract The drying dynaic characteristics and odels of aterials were respectively studied in the process of Ulva Prolifera drying with heat pup and icrowave. Through the coparative regression analysis on the coon diffusion drying odel and the drying test data, Page equation was chosen to siulate heat pup and icrowave drying curves, and the heat pupicrowave drying atheatical odel was set up in stages, which was close to the actual. Thus, the drying dynaic characteristics of Ulva Prolifera with the heat pup-icrowave ethod can be predicted well. Keywords - heat pup; icrowave; drying; Ulva Prolifera; dynaics I. INTRODUCTION Nowadays, hybrid drying techniques are being developed to axiize the benefits of different drying techniques, i.e. produce better quality of foodstuffs, reduce drying tie and increase drying rate[1].materials drying is a coplicated process of unsteady heat and ass transfer, the water loss process during the drying is not only influenced by the drying ethods and conditions, but also has obvious differences with the different aterial types, teperature, huidity, internal structure, physical and cheical properties, and external shapes. Especially during the icrowave drying, the quality of aterials (such as color, texture, flavor and nutrients) will be seriously ipacted, and even its coercial value lost if the drying process is not controlled properly due to extreely fast drying rate[]. Therefore, the drying dynaic regulation should be astered in order to better design the drying equipent, effectively control the key paraeters of drying process and iprove the quality of products. The drying dynaics is to study the average water content changes of aterials with tie during the drying process, and indirectly reflect the transission rate of heat and quality fro acro and icro. The drying dynaics research is the basis of equipent aplification design. For soe aterials with unknown drying characteristics, if the drying dynaics research is ade on the equipent in the laboratory scale, the less aterials are used, which will be the theoretical basis for the aplification design of industrial dryer through the changes in different drying paraeters[3]. This study is to ake the research on dynaic characteristics of Ulva Prolifera by the use of heat pup, icrowave and heat pup-icrowave drying ethods on the basis of the raw aterial of Ulva Prolifera, set up the relevant dynaic equation of thin layer drying and conduct the experiental drying curve fitting, which offers the theoretical basis for the subsequent process optiization test, akes iproveent on energy transfer, drying tie, drying unifority and product quality and provides the theoretical basis for the aplification design of industrial dryer. II. MATERIALS AND METHODS A. Materials Fresh Ulva Prolifera, which were collected fro Xiangshangang Bay, Ningbo.The heat pup-icrowave drying equipent (hoeade), beater (hoeade), TB- 14 electronic balance (Sartorius Intec Instruent Beijing Co., Ltd.), MB45 oisture eter (OHAUS International Trade (Shanghai) Co., Ltd.).All cheicals and reagents were of analytical grade. B. Method The fresh raw saples were washed several ties with natural seawater to reove epiphytes, slie and sall grazers, and flushed with fresh water 3 5 ties to reove salt. Following the cleaning process, the saples were scattered evenly by beater. The process flow path chart of experients was shown in Fig.1. Figure 1. The process flow path chart of experients 1) Heat pup drying The heat pup drying should be conducted under the condition of teperature respectively in 40, 50 and 60 and wind speed respectively at 0.5, 1.0 and 1.5/s, until the oisture of saples was reduced to around 7% (W.b.) fro 80%, and sapling shall be ade every 0 inutes. The average value shall be as the test value after repeat three ties. ) Microwave drying DOI /IJSSST.a ISSN: x online, print

2 The icrowave drying should be conducted under the condition of icrowave intensity respectively at w/g,.5w/g and 3w/g and PR respectively at, 3 and 4, until the oisture of saples was reduced to around 7% (w.b.) fro 80%, and sapling shall be ade every 5 inutes. Each experient repeatd for three ties and the average value as the results. 3) Heat pup-icrowave drying After saples were dried to the breaking point and has the water content of 8% (w.b) through the heat pup at the teperature of 46, the heat pup-icrowave drying should be conducted under the condition of icrowave intensity at.1w/gand interittent ratio at PR=until the oisture of saples was reduced to around 7% (w.b.) fro 80%. The sapling ethod is respectively siilar to and Each experient repeat for two ties and the average value as the results. 4) Packaging After treatents, the saples were placed into Aluinu foil bag and exhaust air then seal for further analysis. C. Test Index and Measureent Method The dry basis oisture content of aterials is usually adopted in the theoretical calculation of aterials drying because the absolute dry substance is unchanged with the oisture quality of aterials, which is convenient to calculate[4]. The oisture eter shall first be used to easure the water content of saples, and then the corresponding heating schedule shall be chosen to easure the oisture content of wet basis in the different drying tie through the tiing sapling and according to the rough scope of aterial water content. The average value fro three parallel saples shall be regarded as the easureent result of the wet basis water content of saples, and the dry basis oisture content of saples during the different periods shall be obtained according to the following conversion equation. w M 100% (1) 1 w Where, w the wet basis oisture content of saple, %, M the dry basis oisture content of saple, kg/kg The drying rate is defined as the oisture quality of web aterial vaporization per unit area (contact area of aterial and drying ediu) in unit tie. If the contact areas of drying ediu and aterial are difficult to confir, the drying strength is usually used as the drying rate, which eans the change in huidity ratio of aterial with tie, usually shown in N [5]. d dm M M d, i 1 d, i N () d dt t t i 1 i Where, N -the drying rate, kg/(kg in), M - t d d, i 1 i drying 1 basis oisture content, kg/kg, M d, i content, kg/kg. - t i drying basis oisture The oisture ratio (MR) refers to the oisture not reoved due to the undried aterial under the drying condition, usually MR used in the equation [6] as follows: M M i e MR (3) M M 0 e Where, M -drying basis oisture content of aterial, kg/kg, i M e -drying basis oisture content during the aterial balance, kg/kg, M -initial drying basis oisture content of 0 aterial, kg/kg In general, above equation can be siplified as Equation (4) because the equilibriu oisture content of aterial M e is so sall copared with M i and M 0, which is difficult to easure. M i MR (4) M D. Drying Matheatical Model Soe coon atheatical odels of thin layer drying which are suarized by the scholars through the drying test on different aterial characteristics, have been widely used. Generally, there are the following 3 atheatical odels to describe the aterial drying equation (shown in Table I). TABLE I COMMON THIN LAYER DRYING MODELS Ite Nae Equation 1 Newton odel[7] MR=exp(-kt) Page odel[8] MR=exp(-ktn) 3 Henderson and Pabis[9] MR=aexp(-kt) Notes: k, n and a are the undeterined coefficients of drying odels. The reasonable drying odel should be selected for the drying curve in the process of drying description, and the paraeters of aterial oisture ratio and drying tie obtained by the test under different drying condition, should be conducted the data analysis and treatent by the use of SPSS19.0 analysis software. III. 0 RESULTS AND DISCUSSION A. Analysis on Characteristics of Ulva prolifera Thin Layer with Heat Pup Drying Method Dry basis oisture content (kg/kg) Figure. The drying rate curves of Ulva prolifera at different teperature (1/s) DOI /IJSSST.a ISSN: x online, print

3 Dry basis oisture content (kg/kg) Figure 3. The drying rate curves of Ulva prolifera at different velocity (40 ) The drying rate curves of saples at different teperature and velocity were shown in Fig. and Fig.3. It can be observed fro Fig that saples in the process of heat pup drying ost was in the falling rate drying stage. The drying rate increased with the gradual increase in the teperature. The drying rate curves at the different teperature generally had siilar trend. It can be seen fro Fig.3 that the drying rate increased with the velocity increasing. This is because the increase of velocity can take the oisture on the surface of the aterial away faster, and reduce the fil thickness of boundary layer of ass transfer and heat transfer on the surface of aterial. Then, the drying rate shall gradually increase after the increased in the ass transfer gradient between aterial surface and the external. At the beginning of drying stage, the ipact of velocity on the drying rate was obvious, but the influence was weaken when the drying rate reduces. At this oent, the drying process was subject to the internal diffusion coefficient, and the ipact of velocity was less copared to that of teperature. Therefore, it showed that teperature and velocity were the ore iportant factors for the characteristics of Ulva Prolifera drying. B. Analysis on Characteristics of Ulva prolifera Thin Layer with Microwave Drying Method Dry basis oisture content (kg/kg) Figure 5. The drying rate curves of Ulva prolifera at different PR (.5w/g) The drying rate curves of saples at icrowave intensity and PR were shown in Fig.4 and Fig.5. It can be observed fro Fig.4 that the drying rate increased and the drying tie decreased with the icrowave intensity increasing. It can be seen that the acceleration drying stage was very short, the constant speed stage was longer relative to the heat pup drying, and the rest tie was in the falling rate stage during the process of icrowave drying. When the electric field intensity and frequency are constant, the conversion of icrowave energy to heat energy depends on the dielectric properties of aterials, and the dielectric property of aterial is ainly subject to the oisture content. At the beginning of drying, saples had ore oisture content, absorbed ore icrowave energy and had fast drying rate. With the reduction of water content of saples, the icrowave energy absorbed reduced and the falling rate drying period cae. With the increased of the icrowave intensity, the constant speed stage is gradually shorten. Fro Fig.5, we can see that the drying rate reduced with the increase of PR, the constant speed stage increased with the increase of PR, but the drying tie was gradually extended. C. Matheatical Model of Drying Curve 1) Model selection Matheatical odel were shown in Table II. It can be seen that, three odels are respectively regarded as the functional relationship between ln(mr) t and ln(- ln MR) lnt. The relational diagra of ln(mr) t and ln(- ln MR) lnt can be respectively drawn after above data substituted into each relational equation. TABLE II MATHEMATICAL MODELS AFTER LINEARIZATION Dry basis oisture content (kg/kg) Figure 4. The drying curves of Ulva prolifera at different icrowave intensity (PR=) Ite Model Nae Model 1 Newton Model ln MR kt Page Model ln(-ln(mr)) ln k nln t 3 Henderson and Pabis Model -ln(mr) lna kt DOI /IJSSST.a ISSN: x online, print

4 The relationship between[-ln(mr)]-t and ln[-ln(mr)]-lnt at different teperature and velocity is shown in Fig. 6 and Fig.7. (b) Different velocity (a) Different Teperature Figure 7. Relationship between ln(-lnmr) and lnt at different teperature and velocity Fro Fig.6 and Fig.7, we can see that the deterination coefficient R of ln(- ln MR) lnt is above 0.95, which was larger than that of ln( MR) t after the curve linear fitting respectively. Thus, ln(- ln MR) lnt curve has better linear relation than ln(mr)-t fitting. Therefore, Page odel was suitable for setup of the atheatical odel of heat pup drying of thin layer for Ulva Prolifera. (b) Different velocity Figure 6. Relationship between (-lnmr) and t at different teperature and velocity (a) Different Microwave Intensity (a) Different Teperature (b) Different PR Figure 8. Relationship between lnmr and t at different icrowave intensity and PR DOI /IJSSST.a ISSN: x online, print

5 Fro Fig.8 and Fig.9, we can see that the deterination coefficient Rof ln(- lnmr) ln t was above 0.98, which was larger than that of ln(mr) t after the curve linear fitting respectively. Thus, ln(- lnmr) ln t curve has better linear relation than ln(mr) t fitting. Therefore, Page odel was suitable for setup of the atheatical odel of icrowave drying of thin layer for Ulva prolifera. TABLE III THE DRYING CONSTANT VALUE AND THE CORRELATION COEFFICIENT OF PAGE MODEL UNDER THE HEAT PUMP DRYING CONDITION Teperature Wind Drying Deterination Speed Constant Coefficient T/ u/(/s) lnk n R lnk 0.0T 0.411u 3.701, R (5) n T u R , (6) (a) Different Microwave Intensity (b) Different PR Figure 9. Relationship between ln(-lnmr) and lnt at different icrowave intensity and PR ) Fitting of Model After the test results that obtained at different teperature and velocity, are conducted the change in ln(- ln MR) and ln t, the linear regression analysis shall be ade by the use of SPSS 19.0 software, and the undeterined coefficient ln k, n and the deterination coefficient R of linear regression were gained as shown in Table III. It can be obtained fro Table 3 that ln k and n reduced with the increased of teperature and velocity. The correlation coefficient was above 0.997, which showed that the equation eet the actual operation paraeter. Thus, the regression equation was obtained after the ultiple linear regression analysis was ade for the drying constant lnk and n in Table III. The test values of the correspondence coefficient of teperature (T) and velocity (u) independent variables in Equation (5) and Equation (6) respectively was 0.00 and 0.034, which were all saller than 0.05, and ean that there was the significant eanings. Thus, the linear relationship existed between the drying constant ln k and n respectively with variable teperature and velocity. ln(-ln(mr)) ( 0.0T 0.411u 3.701) (7) (0.009T 0.91u 0.578) ln t The values of drying constant k and N of Page equation at different icrowave intensity and PR shall be analyzed by the use of SPSS 19.0 software, and the regression analysis results on Page drying equation are shown in Table IV. TABLE IV VALUES OF DRYING CONSTANTS AND CORRELATION COEFFICIENTS OF THE PAGE MODEL FOR MICROWAVE DRYING Microwave Intensity Inter ittence Drying Constant Deterination Coefficient P/(w/g) PR lnk n R It can be seen fro Table 4 that ln k and n values increased with the increased of icrowave intensity, and reduced with the increased of PR. For the values of drying constant k and n under the drying condition, the ultiple regression analysis should be ade by SPSS 19.0, and the relationships between the obtained drying constant respectively with icrowave intensity and interittence ratio were shown in the following equations. lnk 0.45P 0.99PR 5.085, R (8) n 0.081P 0.006PR 1.183, R (9) DOI /IJSSST.a ISSN: x online, print

6 The test value P of the correspondence coefficient of P and PR in above two odel equations was below 0.05, which ean that there was the significant eanings and the linear relationship existed between the drying constant k and N respectively with icrowave intensity and interittence ratio. Thus, the thin layer drying odels of the icrowave under different operation condition shown in Page Equation (8) and (9) were finally obtained. ln(-ln(mr)) (0.45P 0.99PR 5.085) (10) (0.081P 0.006PR 1.183) ln t 3) Deterination of Thin Layer Model of Heat Pup- Microwave Drying According to the optiization result of heat pupicrowave drying in Chapter (4), the water content of Ulva Prolifera at the breaking point was reduced to around 8%(w.b), with the dry basis of 36.99% (d.b) and the oisture ratio M= Therefore, the thin layer drying odel of cobined drying can be obtained as follows after the integration of heat pup and icrowave drying odels described in above two sections. ln(-ln(mr)) ( 0.0T 0.411u 3.701) (0.009T 0.91u 0.578)ln t, MR (11) ln(-ln(mr)) (0.45P 0.99PR 5.085) (0.081P 0.006PR 1.183) ln tmr, ) Drying Model Verification In order to verify the accuracy of the regression odel, the data of heat pup-icrowave drying shall be verified. The forecast should be ade by the use of Page equation under the sae condition, and the coparison of the predicted value and the actual value is shown in Fig.10. The organization of the lecture is as follows. After a general introduction of the effect of fault on the power syste, the usefulness and requireent of a fault current liiter is presented to the students which has been discussed in section II. The traditional ways of fixing fault currents in power syste has been discussed in section III. In section IV, operating principle, design details, and experiental results of agnetic current liiter has been presented. The analysis and siulation results of high teperature superconducting fault current liiter has been discussed in section V. The lecture has been concluded in section VI. IV. CONCLUSION This study was to ake the research on Ulva Prolifera, and conduct heat pup-icrowave drying test on Ulva Prolifera. In which, the change rule of the drying rate subject to teperature, velocity, icrowave intensity and PR were analyzed, and the drying dynaic characteristics and odels of aterials in the drying process were studied. The results showed that the whole heat pup drying process was the falling rate drying, the drying rate increased with the increased of teperature. The velocity was the iportant factor on the thin layer drying rate. At the beginning of drying stage, the wind speed had obvious ipact on the drying rate. With the continuation of tie, the influence of the velocity on the drying rate was weaken. Thus, teperature and velocity were the key factors to ipact the drying rate of Ulva Prolifera. With the icrowave intensity increasing, the drying rate increased and the drying tie decreased. The acceleration and constant speed drying stages were shorter, and the drying process was ostly in the stage of speed reduction. Moreover, the drying rate reduced with the increased in PR of icrowave, and the drying tie gradually extended. Through the regression analysis and coparison of three diffusion drying odels and test data, Page equation was selected to siulate heat pup and icrowave drying curves, and the heat pup-icrowave drying atheatical odel was set up in stages, which was close to the actual. Figure 10. Coparison between experiental data and predicted data Fro Fig.10, It can be finded that the actual value and the predicted value were basically fitting, which shows that Page equation accurately reflects the rule of heat pupicrowave drying, and has soe predictive functions in Ulva Prolifera during the heat pup-icrowave drying process.under the sae condition. REFERENCES [1] Huang, L., Zhang, M, Trends in developent of dried vegetable products as snacks, Drying Technology: An International Journal, VOL. 30, No. 5, pp , 01. [] Wu Yanyan, Ren Zhongyang, Yang Xianqing, et al., Research progresses in aquatic product drying kinetics, Science and Technology of Food Industry, vol. 33, No. 4, pp , 01. [3] Shi Qilong, Zhao Ya, Li Zhaojie, et al, Matheatical Modeling on Heat Pup Drying of Horse Mackerel, Agricultural Transactions of the Chinese Society for Agricultural Machinery, vol. 40, No. 05, pp , 009. [4] Liu C, Wang F, et al., Robust H Control for Satellite Attitude Control Syste with Uncertainties and Additive Perturbation, International Journal of Science, vol. 01, No. 0, pp. 1-9, 014. [5] Midilli A, Deterination of pistachio drying behavior and conditions in a solar drying syste, International Journal Energy Research, vol.5, No. 08, pp , 001. [6] O Callaghan J R, enzies D J, Bailey P H, Digital siulation of agricultural dryer perforance, Agric Eng Res, vol. 16, No. 03, pp. 3-4, DOI /IJSSST.a ISSN: x online, print

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