Design of Heat Pipe for Reduction of Heat Accumulated in Paddy Bulk Storage

Name: ณัฐวุฒิ ดุษฎี

Name: Natthawut Dussadee

Organization : มหาวิทยาลัยเทคโนโลยีพระจอมเกล้าธนบุรี

keyword: Thermosyphon heat pipe

; Heat exchangers

Abstract: In this research, performance analysis and economic evaluation of thermosyphon paddy bulk storage for self-heat rejecting have been investigated. The study can be divided into three parts: firstly, to study the thermal performance of a small scale thermosyphon paddy bulk storage, secondly, to develop the mathematical model with lump analysis for predicting paddy bed temperature, and finally to design and test a storage unit with optimal size of heat pipe. In the first part, thermal performance of a small scale thermosyphon paddy bulk storage having methanol as working fluid and the affecting parameters such as initial moisture content, cooling air temperature, heat transfer area, and paddy qualities have been studied. The storage is a double-wall steel cylinder with 636 mm outside diameter and 1500 mm length. The evaporator section consists of a set of 70 copper tubes with 3.0 m2 heat transfer area. The condenser section is the upper body of the storage tank and is ventilated with controlled air. The paddy of 115 kg with 26.9 and 13.5% wet basis are placed in the evaporator section of the thermosyphon. The paddy of 1 15 kg with 26.9 and 13.5% wet basis were placed in the evaporator section of the thermosyphon. From the experiments, it is found that the thermosyphon can maintain the paddy bed temperature at 31-32 OC and 28-29 OC, respectively compared with 45 OC and 31-32 OC in case of the unit without any control. In addition, it is observed that temperature difference in the paddy bed depth in the unit with thermosyphon is very small compared with the latter one. The actual overall heat transfer coefficient between the bed and working fluid is 4.3 w/m2~. The paddy qualities such as the head rice yield and the whiteness are in good condition. In the second part, The mathematical model with lump analysis is developed to predict paddy bed temperature and it is found that the model developed could be used to predict the paddy bed temperature accurately. The simulated results agree very well with those of the experiments. This means that the lump analysis is a good approach for predicting the bed temperature and is a tool to find out the suitable heat transfer area at evaporator section. From the simulated results, the heat transfer area should be over 16 m2 for the climate of Chiang Ma., Thailand in case of 1000 kg paddy storage. Most of the bed temperature is lower than 28 OC at this condition and the paddy deterioration is very low. In the third part, the thermal performance, and the economic analysis of a prototype paddy bulk storage with R22 as working fluid have been considered. The unit consisted of a steel cylindrical bin with diameter of 1250 mm and length of 1500 mm that contains 1000 kg of paddy. The evaporation section of the thermosyphon embedded in the paddy bulk is a set of copper tubes with the total heat transfer area of 8.5 m2. The condenser section with the total area of 12.2 m2 is exposed to the ambient air. From the experiments, it is found that for the paddy with moisture content of 26.9% and 13.5% wet basis, the thermosyphon can maintain the paddy bed temperature to 37-38 OC and 28-29 OC, respectively, compared with 65 OC and 31-32 0C for the unit without any control. Moreover, a very small temperature difference in the bed depth is also observed in the unit with thermosyphon. The paddy qualities in terms of head rice yield, percentage of brown and white rice for the unit with thermosyphon is very close to those of the unit with aeration. Furthermore, the optimal size thermosyphon paddy storage having 16 m2 evaporator section area is constructed in order to investigate the mathematical model accuracy and its performance. From these results, the developed mathematical model has been found to be able to satisfactorily predict the paddy bed temperature for paddy moisture content of 12.3% wet basis and agrees very well with those of experiment values. The experiment shows that the average monthly (January 16- February 16, 2002) paddy bed temperature is about 22.0 "C and the temperatures among the top, the middle, and the bottom are slightly different. From the economic analysis, the payback period and the IRR of the thermosyphon paddy bulk storage having 16 m2 surfsoe area compared with the unit with aeration technique are 3.83 years and 22.83%, respectively. Therefore, it is concluded that the thennosyphon paddy bulk storage has a high potential to be replaced the aeration paddy bulk storage.

มหาวิทยาลัยเทคโนโลยีพระจอมเกล้าธนบุรี

Address: Bangkok

Email: info.lib@mail.kmutt.ac.th

Name: Tanongkiat Kiatsiriroat

Role: Advisor

Created: 2544

Issued: 2006-12-26

Modified: 2017-09-20

วิทยานิพนธ์/Thesis

ISBN: 9742260834

CallNumber: JGSEE23

eng

DegreeName: Master of Engineering

Level: Master's Degree

Descipline: Mechanical Engineering

Grantor: King Mongkut's University of Technology Thonburi

©copyrights King Mongkut's University of Technology Thonburi

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