30120140505009

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30120140505009

  1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 91-98 © IAEME 91 STUDY ON WATER MODEL OF SOLAR ENERGY AND VACUUM GLASS GRAIN DRYING EQUIPMENT Hui Shen, Ji-Ping Zhou, Ya Sun, Sheng-yong Ye, Hai-meng Ju, Jian Sun (Mechanical Engineering College Yangzhou University, Yangzhou County 225009, China) ABSTRACT The paper introduces the water model of solar energy and vacuum glass grain drying equipment.We have established the water flow model of moisture content and calculated moisture content of each drying cycle.The result shows that moisture content of grain decreases to 14.0368 % after nine drying loops,and decreases to 12.9741% after twelve drying loops. It is hard to continue to reducing the moisture in grain. After calculating,we know the best drying time is 2.57 hours. Keywords: Grain drying; Solar Energy Equipment; Quality control. 1. INTRODUCTION Existing dryers mostly use heater installation as drying energy, but energy consumption is large. The existing dry technology also creates the grain internal stress and increases the grain crack rates, so that it can not guarantee a good quality dried grain, which reduces the economic efficiency of grain production greatly. Due to existing dry technical have some technical barriers. It is vital to develop solar energy and vacuum glass dry technology applications in our country. In particular, some small, simple solar drying chamber development should appears imminently. Grain usually requires low drying temperature, just matching the low temperature heat utilization in the field of solar energy. Therefore, it is necessary to apply solar energy into dry agricultural and subsidiary products. It has broad prospects for development. [1] 2. DESIGN OF SOLAR ENERGY AND VACUUM GLASS GRAIN DRYING EQUIPMENT Solar Energy and Vacuum Glass Grain Drying Equipment is shown in figure 1. The equipment was consisted of six parts: solar collector, grain drying warehouse, circulating water pump, control system, hot water tank and connection water pipes. Hot water flows from solar INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 5, Issue 5, May (2014), pp. 91-98 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2014): 7.5377 (Calculated by GISI) www.jifactor.com IJMET © I A E M E
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 91-98 © IAEME 92 collector into heat exchanger under the section of water pump. Then hot water flows back into the tank after exchanging heat with the cold water in heat exchanger. Figure 1: Solar Energy and Vacuum Glass Grain Drying Equipment Figure 2: Grain Drying Warehouse Model Grain drying warehouse model shown in figure 2. Grain flows from grain bucket into drying warehouse under the action of gravity, and flows along the surface of heat exchanger slowly, then flows out from grain outlet at the bottom of drying warehouse. A ventilation installation is at the bottom of drying warehouse. The cold wind passes through heat exchanger under the action of
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 91-98 © IAEME 93 installation and then exchanges heat with hot water in heat exchanger. The heated hot air takes away moisture inside grain through grain layer. The hot air was exhausted from air outlet at the top of the drying warehouse after passing through three layers of heat exchanger. 3. CALCULATION OF GRAIN MOISTURE The grain drying time relates to the evaporation efficiency of grain moisture content. Researching grain drying model is also studying grain moisture content flowing model[2] . We establish a model about the degree of grain drying along with time to calculate grain moisture content.Therefore we use relative moisture content to characterize the degree of drying, namely[3] : ( ) eMM MtM MR − = 0 e- ……………..………………….1 • In the formula: MR is the relative moisture content; ( )tM is moisture content of grain at t time, %; 0M is grain moisture content at the initial time, %; eM is grain moisture content in drying balance moment, %. MR changing along with drying time.The calculation errors of the thin layer drying formula proposed by Page is smaller.The formula of Page’s model is as follows: ( )c kt-exp=MR …….…….…………...…….…2 In the above formula k, c are the drying constants. They were decided by temperature of drying hot air, relative humidity and the types of grain. The expressions of k, c are as follows: RHTc RHTk 078867.0002425.06545.0 01413.00001746.001579.0 ++= −+= ………..…...….3 In the formula:T isthe temperature of drying hot air, o C; RH is the relative humidity of hot air. We can solve MR of t time by formula 2 and 3.We need to know 0M and eM ,so that we can get ( )tM by formula 1. For the balance of grain drying moisture, we use the modified Henderson equation to calculate the variation of grain moisture. Specific expressions are as follows[3] : ( ) ( ) 31 21 1ln a e aTa RH M       + −− = ……...………......…..…..….4 In the formula: eM is equilibrium moisture content of grain, %; RH is relative humidity of hot air; T is the temperature of dry hot air, o C; 321 aaa 、、 are the Coefficients of equation coefficients. For rice, they were respectively chose 1.9187×10-5 、51.16、2.4451. Three pieces of heat exchange beds divide grain layer into three layers in the drying warehouse. We regard grain which on the low level of heat exchange bed as 1st, grain which on the middle level of heat change bed as 2nd, and grain which on the top level heat exchange bed as 3rd. Because the cold air has been heated by three layers of heat exchange beds, so the air temperature is different in each layer. Moreover, the air humidity through the first layer is the same as the air
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 91-98 © IAEME 94 humidity entering the second layer. The air humidity through the second layer is the same as the air humidity entering the third layer. So the air humidity through each layer is different, we need to calculate equilibrium moisture content of each layer. The 1st, 2nd, the 3rd grain equilibrium moisture respectively is ' enM , '' enM , ''' enM .The air relative humidity through the layer 1 and layer 2 and layer 3 respectively is ' nRH , '' nRH , ''' nRH .The air relative humidity increment through the layer 1 and layer 2 and layer 3 respectively is ' nRH∆ , '' nRH∆ , ''' nRH∆ .Namely: ''''''' '''' nnnn nnn RHRHRHRH RHRHRH ∆+∆+= ∆+= …….……..……...…5 Grain moisture evaporates into the air and then forms air relative humidity increment. We can get it by calculating the reduced amount of MR .The drying temperature and air relative humidity is different, so the MR of each layer is different. And when the grain drying cycles in the same layer are different, the MR is also different. The 1st, 2nd, the 3rd grain relative moisture content respectively are ' nMR , '' nMR , ''' nMR .After drying t time, the moisture content respectively is ( )' ntM , ( )'' ntM , ( )''' ntM . Air relative humidity refers to the ratio of vapor pressure in the air to the saturated vapor pressure. It also refers to the ratio of the quality of water vapor in the air to the quality of water vapors in the saturated air under the same temperature[5] ,that is: ( ) ( ) ' ''' ' s nn n R tMtM HR − =∆ ( ) ( ) '' ''''' '' s nn n R tMtM HR − =∆ ………………………...…6 ( ) ( ) ''' '''' 1''' s nn n R tMtM HR − =∆ − In the above formula '''''' ,, sss RRR respectively is quality of water vapor in saturated air, which passed through 1st, 2nd, 3rd layer. Its unit is g/kg. Due to the air temperature in each layer is different, the quality of water vapor in saturated air is also different. The air temperature in the first layer is 45.5o C, g/kg67' =sR .The air temperature in the second layer is 55.9 o C, g/kg122'' =sR . The air temperature in the third layer is 60.6o C, g/kg155''' =sR . We can get that expression of moisture content in each layer by equation 1. ( ) ( )( ) '''''' eennn MMtMMRtM +−= ( ) ( )( ) ''''''''''' eennn MMtMMRtM +−= ………..……..…..…..7 ( ) ( )( ) ''''''' 1 '''''' eennn MMtMMRtM +−= −
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 91-98 © IAEME 95 Then we bring equation 3 into equation 2 to calculate ' nMR , '' nMR , ''' nMR after N times of drying cycles. In the formula, t is the time of a single-layer drying cycle. Its unit is min. ( )[ ]' 078867.07648375.0'' 01413.00237343.0exp nRH nn tRHMR + +−= ( )[ ] ( ){ }'' 078867.079.0'''' 01413.002555.0exp nn RHRH nnn tRHRHMR ∆+− ∆++−= ……...….8 ( )[ ] ( ){ }'''' 078867.08.0''''''' 01413.0026.0exp nnn RHRHRH nnnn tRHRHRHMR ∆+∆+− ∆+∆++−= We bring air temperature and humidity of each layer into equation 4, then we can get ' enM , '' enM , ''' enM . ( ) ( ) 4451.2 1 5 ' ' 16.515.45109187.1 1ln       +× −− = − n en RH M ( ) ( ) 4451.2 1 5 '' '' 16.519.55109187.1 1ln       +× ∆−−− = − nn en RHRH M ……….……….9 ( ) ( ) 4451.2 1 5 '''' ''' 16.516.60109187.1 1ln       +× ∆−∆−−− = − nnn en RHRHRH M In the equation 7, ( )' 1−ntM is the moisture content that grain flow through the lowest heat exchange bed in the N-1th drying cycle. ' 0MR of the first drying cycle is the initial relative moisture content of grain, 1.23' 0 =MR [6] . ' nRH in equation 5 and equation 8 is ventilation initial relative humidity. No matter how many times of the drying cycle, its value is the air relative humidity, %55' =nRH . Accordingly, for the Nth cycle at t time, in equation 6 to equation 9 there are ' nRH∆ 、 '' nRH∆ 、 ''' nRH∆ 、 ' nMR 、 '' nMR 、 ''' nMR 、 ' enM 、 '' enM 、 ''' enM 、 ( )' ntM 、 ( )'' ntM 、 ( )''' ntM .There are 12 unknown quantities totally. We can solved it through 12 equations. 4. CALCULATION OF DRYING CYCLES The moisture in dried grain affects the security of grain storage. Our country has the unification stipulation in the moisture content of safe storage. Various types of rice have different stipulations about highest moisture content according to the environmental temperature. All kinds of the moisture content should not exceed 14.5%[7] .In this paper, the rice drying device that we researched is recirculating drying. Each drying cycle time is 4.3min. We can calculate the moisture content of each drying cycle by equation 6 to equation 9. As shown in table 5-2:
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 91-98 © IAEME 96 Table 1: Drying Parameters n ' nRH∆ '' nRH∆ ''' nRH∆ ' nMR '' nMR ''' nMR 1 0.0073 0.0051 0.0049 0.9494 0.9421 0.9342 2 0.0061 0.0043 0.0041 0.9494 0.9420 0.9345 3 0.0051 0.0036 0.0035 0.9494 0.9420 0.9347 4 0.0042 0.0030 0.0029 0.9494 0.9420 0.9349 5 0.0035 0.0025 0.0024 0.9494 0.9419 0.9350 6 0.0028 0.0021 0.0021 0.9494 0.9419 0.9351 7 0.0023 0.0018 0.0017 0.9494 0.9419 0.9352 8 0.0019 0.0015 0.0015 0.9494 0.9419 0.9353 9 0.0015 0.0013 0.0013 0.9494 0.9419 0.9354 10 0.0012 0.0011 0.0011 0.9494 0.9419 0.9355 11 0.0010 0.0009 0.0009 0.9494 0.9418 0.9355 12 0.0008 0.0008 0.0008 0.9494 0.9418 0.9356 n ' enM (%) '' enM (%) ''' enM (%) ( )' ntM (%) ( )''' ntM (%) ( )'' ntM (%) 1 12 11.6247 11.5108 21.2258 21.7172 22.3376 2 12 11.6083 11.5220 19.6613 20.0693 20.5899 3 12 11.5945 11.4560 18.3503 18.6885 19.1254 4 12 11.5830 11.4353 17.2535 17.5333 17.8999 5 12 11.5734 11.4179 16.3355 16.5665 16.8742 6 12 11.5653 11.4034 15.5671 15.7571 16.0156 7 12 11.5586 11.3913 14.9237 15.0795 15.2967 8 12 11.5530 11.3811 14.3850 14.5120 14.6946 9 12 11.5482 11.3726 13.9338 14.0368 14.1904 10 12 11.5443 11.3655 13.5559 13.6387 13.7680 11 12 11.5410 11.3596 13.2393 13.3053 13.4143 12 12 11.5382 11.3546 12.9741 13.0260 13.1178 From table 1 we can analyze the changes of water potential in the drying process. The moisture content of grains after a drying cycle is ( )' ntM . From the table, we also can find that the moisture content of grain is 14.0368% after nine times drying cycle, so it can be satisfied with safe storage. The grain moisture content reduces along with increasing the times of drying cycles. But grain moisture content reduces more gradually with the increasing times of drying cycles. As is shown in figure 3, the curvature of ( )' ntM , ( )'' ntM , ( )''' ntM reduces gradually with the times of drying cycles changes. With the times of drying cycles increases, the drying air humidity increment in each layer reduces gradually. As shown in figure 4 we can also find that under the condition of the same
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 91-98 © IAEME 97 drying cycles the increment of ventilate humidity through the first heat exchange bed is bigger than the second layer and the third layer. Figure 3: Change of Moisture Content Figure 4: Increment Rate of Ventilation Function Through above analysis, we can find that the moisture content of grain is 12.9741% after 12 times of drying cycles.The change in moisture content would be subtle,and energy consuming will increase at the same time if the times of cycles are added continously.Therefore, grain drying device designed in this paper uses 12 times drying cycle. 5. CONCLUSION We have researched water model of grain and calculated moisture content during each drying cycle. Research shows that grain moisture content falls below 14.0368% after nine drying loops,and falls below 12.9741% after 12 times of drying cycles. Hence after that, it is difficult to continue reducing grain moisture content.
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 5, May (2014), pp. 91-98 © IAEME 98 6. REFERENCES [1] Chen K J, Li J L, Zhang R H. Status and prospect of heat pump drying[J]. Transactions of the Chinese Society of Agricultural Machinery, 2000, 31 (3): 109 - 112 (in Chinese). [2] Total output of primary agricultural products. http://www.stats.gov.cn. [3] Cao Chongwen. The principles and technologies of agricultural products drying [M]. Beijing: China Agricultural University Press, 1998, 1~6(in Chinese). [4] Zhao X W, Zhou B. Present situation and development trend of the grain drying technology in China[J]. Cereal and Seed Industry, 2003, 2:15-17(in Chinese). [5] Cao Chongewen. The principles and technologies of agricultural products drying[M]. Beijing: China Agricultural University Press, 1998, 369~386 (in Chinese). [6] Yang Z, Shao Y J, Duan J L. Development of mechanization of grain drying in south China[J]. Agricultural Mechanization of China, 2000, 3:39~40(in Chinese). [7] Cao C W, He J B. Developing trend of drying equipments of grains in oversea [J]. Modernized Agriculture, 2002, 1:40~43 (in Chinese). [8] Li C Y. Development of drying equipment of paddy grains in tropic region of south China[J]. Tropic Agricultural Engineering, 2002, 4:25~29 (in Chinese). [9] Ajeet Kumar Rai, Vivek Sachan and Maheep Kumar, “Experimental Investigation of a Double Slope Solar Still with a Latent Heat Storage Medium”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 1, 2013, pp. 22 - 29, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [10] Mamdoh Al-Busoul, Aiman Al-Alawin and Hamza Al-Tahaineh, “Influence of Air-Fuel Ratio and Particle Size on Fluidized Bed Combustion of the El-Lajjun Oil Shale”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 5, 2013, pp. 130 - 138, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [11] Ajeet Kumar Rai, Nirish Singh and Vivek Sachan, “Experimental Study of a Single Basin Solar Still with Water Cooling of the Glass Cover”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 6, 2013, pp. 1 - 7, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [12] Phairoach Chunkaew, Aree Achariyaviriya, Siva Achariyaviriya, James C. Moran and Sujinda Sriwattana, “Operating Parameters Effects on Drying Kinetics and Salted Sunflower Seed Quality Utilizing a Fluidized Bed”, International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 4, Issue 6, 2013, pp. 256 - 268, ISSN Print: 0976-6480, ISSN Online: 0976-6499.

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