Proceedmqs of the 7th Internatumal Working Conference on Stored-product Protection - Yolume 2

A study on using heat pipetemperature for storing up grain

Zhu Zhi-Ang1

Abstract

This paper deals With the application of heat pipe technologyfor safely stonng up gram and the possibilny of loweringtemperature of grain heap for mnumizmg or elrmmatmgmildew. Some analysis data and detailed demonstrationexamples are given m this paper.

Foreword

In the cold season, because gram's function performance ofheat loss IS no good, the temperature of lower strata gram ISlOoe higher or even more higher than the temperature ofthe upper's Thanks to physical condition of store up gramand gram's breathmg, It often leads to local gram thetemperature elevate of gather. Because heat can not rejectm time, gram goes mouldy. For this reason, the highertemperature of store up gram IS one key factor to interfereWIth safety of stonng up gramIf heat can be rejected, and the temperature difference

can be reduced possibly. It IS very favourable Withpreventmg from gomg and stonng safely up gram.Heat pipe technology had been used sme SIxties. It IS a

new technology of stonng safely up grain

Heat pipe's structure,principles and characteristics

The standard heat pipe IS composed of: the wall of acontainer and core of absorbs hquid and working medium.See figure 1There are three workmg part m the heat pipe, evaporate

part, adiabatic part and condensate part. Its workmgprmciple IS when heatmg evaporate part, the workmgmedium evaporated by heat absorb, the steam and latentheat transported grve condensate part. It IS condensatebecome the liquid returmng evaporate part by capillarity, itthere are closed work order of SIX. see figure 2.In a word, the heat pipe can high-speed transport quantity

1 Institute of Gram and OJ.! Science of Shanxi Province, Chma No33,lst Segment.Jmci Road, Tmyuan 030024 Chma

technology for lowering

of heat, by usmg medium's phase transition under givenstate. It there are not anything mechanical movement m allworking process. And It IS SImple of structure, workreliable, a small volume, lighter weight. Its use hfe-span ISnumber year or number ten year under rational design andbetter technological of assemble.

The main characteristics

1 Higher abihty of heat transfer. The heat pipe's heattransfer speed IS 200m/s or higher. It IS severalhundreds times faster than that of steel pipe at the sametempera ture

2. The better performance of isothermal The longerIsothermal zone's forms, because ItS heat drag IS verylittle m heat pipe, by temperature difference only have 1-sc.

3 It has the performance of one-way only heat condition.4. The direction's reversibility of heat transfer. Either oftwo IS heated, it become evaporate part, and other endbecome condensate part. when heat pipe under zero-gravity state or lay aside of honzontal.

5. The alterability of thermal current density: The heat pipemay be designed straight pipe, annular, bobbin and etcaccordmg to using demand. The area of different heattransfer can change the thermal current density.The scope of heat PIpe'S adaptmg temperature is - 200'C

- 2200oe.Itmay be divided into high-temperature heat pipes rover

3500e ). mesotherm heat pipes (500e - 3500e), lowtemperature heat pipes (under 50'C) etc three scope ofworkIng temperature.

The heat pipestechnology's development

Thanks to heat PIpe'S specific property of heat transfer fastand Isothermal, It is used in many engineermg and SCIencesrealm. For example 1: A warplane runway can not be usedafter accumulated somw in winter, Siberia Russian country.For solvmg the question, There are more than four thousandand four hundred low temperature heat pipes of more than10 meter and L kind, have been installed under thewarplane runway. The quantity of heat m soil have beentransported to over warplane runway, it have been used to

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Proceedings of the 7th International Worktng Conference on Stored-product Protection. - Volume 2

melt snow It had been used loss than 40 year.For example 2: avoiding the spontaneous ignition of coal

heap and to reducing worsen of coal quality They have seentesting and studying by Nanjm college of chemical industryand DongNan unrversity. They used heat pipe of low

temperature to lower swiftly coal heap's temperature, from70°C to 55°C and the region may lower to under than 40°Cafter frve day Expenment has proved that heat pipes forheat loss IS a better measure for coal heap's store of longtime m chma

core of sbsorbs liquid

the wall of a container

,..-- ~::-"1:'(>t---ir---~w~o~rk~·I~ng medium

Fig.I. Heat pipe's composition structure sketch map

I -E- liquid's return +- exothermal +- IHeat absorb c mdeusate

I ..lo. stearn ..lo. steam's tram sport ..lo. IFig.2. The pnnciple of heat pipe's work

The theory and sumg of heat PIpe'S technology aredeepening and developing m Many territory. The heat pipesof Each types and different function are emergmg The heatpipe's expend, Especially at mall-SIzednucromnuaturef 4)10- 500um, L = 10 - 30mm) and large-scale very-large-scale(4)300mm, L = 100M). Thanks to Energy saving aregettmg uruversal followWIth interest and an urgent need mpresent worlds, The heat pipe technology will further getgood graces, and it will facilitate the developing ofcorrelation technology.

The design and application ofthe heat pipe for storing up grain

The practicality of the heat pipe to give off heat forstoring up grain

In our province, grain reserves are largely m the form ofdepot of room deposit, in new building depot, especially thenewly-built ones. We also have other forms to store up grainsuch as the trampet deposit, the deposit of Soviet Umonstyle, the old temples and underground deposit.

The climate of Shanxi vanes greatly. The averagetemperature IS between 4°C to 14°C. The frost season iscomparatively long, usually between 140 to 240 days everyyear and It ISdecreased progressively from the north to thesouth. The average underground temperature from 4to 20meters deep IS around Ire to 16°C. FIgure 3 shows theregulation of the gram temperature change m room deposit.From the analysis we can see that the basic regulation of

the gram temperature change m a year is as follow: Thetemperature m the upper layer of gram vanes greatly inaccordance with the temperature of the day, Its difference ISaround 28°C. The temperature m the middle and bottomlayers vary slightly. The difference ISabout 9°C. The gramtempera ture changes a month later than the air temperaturedoes. During winter and early spnng seasons, the gramtemperature m the bottom layer IS higher than that of theupper layer. The average difference is 10°C. In the summerseason the grain temperature m the bottom layer IS lowerthan that of the upper layer. Its average difference IS10°C,In autumn and early wmter seasons the grain temperature inthe middle layer IS comparatively high The temperaturedifference of the upper layer IS around lOt:, and the

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Proceedmqs of the 7th Intematumai Working Conference on Stored-product Protection - Volume 2

numencal value of the temperature difference for stonng upgram vanes accordingly with the changes of temperature m

different places

°c35

30

25

20 ~-:::::;;;t=~"===~~~15r10

o -4~"';""----------------1"-+----5

-10

o 1 2 3 4 5 6 7 8 9 10 11 12 (month.in 1995)

Fig. 3. The curves of gram temperature changes m four seasonsExplain: 1 Curve A: The temperature of the barn

Curve B: The gram temperature of the upper layerCurve C: The gram temperature of the rruddle layerCurve D: The gram temperature of the bottom layer

2 The map IS based on the No.7 National bam storage m Lmfen, Shanxi The gram temperature was measured fromthe wheat storage (the third class) m 1995

3 The map was drawn m Apnl, 1997 Drawer: Zhu Zhi-ang

Dunng the storage, the local heat of gram can occur mcertam places stonng up gram ownmg to the low conductionof the heat (usually about 0.1 - O. 2kk/m he). When thegrain temperature reaches 35°e to 40oe, The change ofcolors m the gram can be seen accompamed With moldWhen the gram temperature nses to 500e to 55°e, poorquality of gram was to occur thus the gram loss can not beavoided.By adopting the heat pipe With low temperature, the heat

in the gram deposit can be ehmmated through the pipe Withhelp of the utility of the temperature differences betweenchmate and gram in cold season so that the temperature mgrain deposit can be maintained as low as we expect. As forthe heaps of again With higher temperature, It IS necessaryto insert the heat pipe timely to ehmmate the heat,meanwhile the condensate agent IS also adopted WIth the useof temperature differences between the chmate and the gramm summer so as to reduce the loss of gram in storage.

The designing shapes of the heat pipe

The heat pipe of low temperature With gravity IS designedand made With carbon steel and ammonia Its diameter ISbetween 20 to 120 mm. And Its length around 1.5 to 4. 5mThe installation of the heat absorption and the heat loss ISalso necessary m the condensate part of the pipe.

This kind of heat pipe possesses the one-way heatconduction. It IS very useful to store up energy. Throughusing ItS gravrty The clumney effect of condensing agent mevapovatmg part IS greatly enhanced. Owing to the highpressure head, the structure of the inside of the pipe can bemade SImple to simplify the structure of the whole heat pipeand mcrease the heat conduction.

The demands of storing up grain by the heat pipe

Inside the room deposit the best way to lay the heat pipeis vertical mstallation (~= 90, see figure 4), usually theangle should not be less than 50 (see figure 4) The heightabove surface of the gram heap should be around 500 mmThe place and the distance for the mstallation of the heatpipe depend on the local temperature and the regulation oftemperature changes accordinglyOutside the room deposit, the installation of the heat pipe

should be 1.5 m away from the wall and 3 - 10 meters deepm the ground, usually install the pipe 5 meters away fromthe south wall. If necessary put each from both east andwest walls. The forms of the pipe can be made in L form orman umbreulle from. Water proof and leakage should bepaid much attention to. In the area with longer cold weatherthe outside pipes can be put in small numbers or none.

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Proceedings of the 7th Internatwnal Working Conference on Stored-product Protection - Volume 2

Fig. 4. The heat pipe is mstalled angle of mclmanon sketch map

In the underground barn and cave dwelling barn it isnecessary to choose the most suitable to install the heat pipeaccording to the local conditions.If the gram storage IS in summer, we propose to install

heat pipes in the gram timely and take them out when thegrain temperature becomes low.For those with high temperature, msert heat pipes With

different length to elimmate the heat In summer, It ISbetter to use condensate agent to control the rising of thegrain temperature in the condensate part of the heat pipe.

The illustration of primarily correlated factors

In grain storage the number and the distance of the heatpipes installed should depend mamly on different weather inthe areas and different SItuations for storing up the grain.To those with local heat of grain, install the pipes at the

beginning and observe the temperature changes timely toavoid the high temperature difference in very short time.To those with mstalled pipes, It IS better to open the

wmdows and doors of the room in cold and dry season, so asto ehminate the heat through the pipes and from the upperlayer of the gram. The grain temperature is loweredgradually and the dew can be aVOId.To make sure that the gram is stored up in low

temperature, the roofs of the barns should be designedproperly and the matenals used for the walls to keep thetemperature should be SUItable. With proper conditions the

heat pipe can be installed in the ground, for the coldtemperature accumulated in the soil in wmter can be givenoff dunng summer to prolonge the delaying time of graintemperature change so that the grain temperature of storingup the gram can be kept low.

The Analysis Of TheEconomic Accounting

The cost of the materials

raw matenal: 40 steel pipe 114 yuan /per piece.Supplementary material: fillings (replacements), rainsmg

hquid 30 yuan/per piece.cost of production: (making and assembhng) 80 yuan/per

piece.total production cost: 224 yuan/per piece

Economic analysis

For a barn of 2500 thousand kg, ten pieces of pipes areneeded. The total cost will be 3000 yuan (each costs 300yuan). For the barn of 50 million kg, the total cost IS 68thousand yuan, including 8000 yuan for reserve use.This investment IS about 0.002 yuan per kg. of grain on

average The heat pipes can be used at least 10 years orlonger. By usmg heat pipe we can control the rismgtemperature of the grain heap so that there IS no need for us

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Proeeedmqs of the 7 th Internatwnal Working Conference on Stored-product Protectwn - Volume 2

to rotate the gram and turn over the gram in the sun shmeThus we can save the mechamcal fees for ventilating thebarns. By usmg the heat pipe we can also reduce the loss ofgram so as to assure the credibihty of stonng up gramsafely

Conclusion and Discussion

Conclusion

Adoptmg the heat pipe of low temperature WIth gravitycan conduct large quantities of heat so that It IS feasible togive off the heat from the barns and keep the barns m lowtemperature Dunng the whole starage penod there IS noneed to consume any form of energy so as to avoid the atrpollution. So It IS a technological and economical measure tostore up gram safely

Discussion

Design and make still better heat pipes If the conditionsfor stonng up gram allow. Considering the differentmoisture and temperature in the gram, and test the time ofgrvmg off heat by pipes, ItS mfluenced areas and the rate oflowing the temperature in order to decide the proper

distance to mstall the heat pipe in different weather and

conditions

References

C hang Rang, etc 1996, The Techmques of Storing upGram, Gram Bureau of Sharon Provmce, Taiyuan, Chma,490P

Gram Bureau of SIchuan Province, 1984, Savmg andPreservmg of Gram and 011 The Pubhshmg House ofSCience and Technology, Chengdu, SIchuan, Chma,732p.

Huang Wenymg, 1995. Designmg BaSISof the Heat PIpe andIts Exchanger, The Pubhshmg House of Railway, Chma ,149p

Chen Guobang, etc. 1994, the Latest Cryogen Technologyof Low Temperature, The Pubhslung House of MechamcalIndustry, Benmg , Chma , 434p.

Fan Yongheng, 1994, Study of Prevention and Cure ofInsects m Stormg up Gram in the Region of Shanxi, NewsReport of SCIence and Technology m Stonng up Gram andall, National Gram Reserve Bureau, Chma , 2, 27 - 29.

Xm Daommg, 1991, The Study OF Heat PIpe and ItsApplication Progress, The Pubhshmg House of ChongqmgUniversity, Dujianyan, SIchuan, Chma , 311p

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