Experimental investigation for the optimization of heat pipe performance in latent heat thermal storage

Chandrakishor Ladekar,S. K. Choudhary,S. S. Khandare 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.6

We investigated the optimum performance of heat pipe in Latent heat thermal energy storage (LHTES), and compared it with copper pipe. Classical plan of experimentation was used to optimize the parameters of heat pipe. Heat pipe fill ratio, evaporator section length to condenser section length ratio i.e., Heat pipe length ratio (HPLR) and heat pipe diameter, was the parameter used for optimization, as result of parametric analysis. Experiment with flow rate of 10 lit./min. was conducted for different fill ratio, HPLR and different diameter. Fill ratio of 80 %, HPLR of 0.9 and heat pipe with diameter of 18 mm showed better trend in charging and discharging. Comparison between the storage tank with optimized heat pipe and copper pipe showed almost 186 % improvement in charging and discharging time compared with the copper pipe embedded thermal storage. Heat transfer between Heat transferring fluid (HTF) and Phase change material (PCM) increased with increase in area of heat transferring media, but storage density of storage tank decreased. Storage tank with heat pipe embedded in place of copper pipe is a better option in terms of charging and discharging time as well heat storage capacity due to less heat lost. This justifies the better efficiency and effectiveness of storage tank with embedded optimized heat pipe.

방열관의 배치와 관내 유속이 온수난방 온실의 온도분포에 미치는 영향

신현호,김영식,남상운 (사) 한국생물환경조절학회 2019 생물환경조절학회지 Vol.28 No.4

본 연구는 난방온실의 온도분포 균일화를 위한 기초자료 제공을 목적으로 온수난방 방식의 토마토 재배 온실에서 난방실험을 통하여 난방배관의 표면온도와 실내기온 사이의 상관관계를 분석하고, 난방배관의 열전달특성분석과 난방배관 배치의 개선을 통하여 난방배관 표면온도의 편차를 줄이고 균일도를 향상시키기 위한 방안을도출하였다. 서로 다른 두 온실의 온도분포를 분석하여최대편차와 균일도를 검토한 결과, 온수의 유량이 많고난방배관의 길이가 짧게 배치된 온실의 온도편차가 작고, 균일도는 높은 것으로 나타났다. 또한 순환팬을 가동한경우에 온도편차는 작아지고 균일도가 개선되는 것을 확인할 수 있었다. 난방배관의 표면온도와 실내기온 사이의 상관관계를 분석한 결과, 두 온실 모두에서 유의적인(p<0.01) 정적 상관관계가 있는 것으로 나타났다. 온수난방 온실에서 실내기온의 분포는 난방배관 표면온도의 분포에 영향을 받는다는 것을 확인할 수 있었고, 온도편차가 최소화 되도록 난방배관을 배치함으로써 실내기온 분포의 균일도를 개선할 수 있는 것으로 판단되었다. 난방배관의 열전달 특성을 분석한 결과 배관의 길이가 길어지면 온도편차는 커지고, 관내의 유속이 빨라지면 온도편차는 작아지는 것으로 나타났다. 따라서 지선배관의길이가 짧아지도록 난방배관을 배치하고, 관내의 유속을제어함으로써 온실의 온도분포와 환경의 균일성을 개선할 수 있을 것으로 판단되었다. 국내 온실에서 가장 많이 사용하고 있는 튜브레일(40A) 방식의 온수난방시스템에서 하나의 지선배관에서의 온도편차를 3o C 이내로조절하기 위해서는 관내의 유속이 0.2, 0.4, 0.6, 0.8, 1.0m·s-1일 때 난방배관의 길이는 각각 40, 80, 120, 160, 200m 이내로 제한해야 하는 것으로 분석되었다 In order to provide basic data for uniformization of temperature distribution in heating greenhouses, heating experiments were performed in two greenhouses with a hot water heating system. By analyzing heat transfer characteristics and improving pipes layout, measures to reduce the variation of pipe surface temperature and to improve the uniformity were derived. As a result of analyzing the temperature distributions of two different greenhouses and examining the maximum deviation and uniformity, it was found that the temperature deviation of greenhouses with a large amount of hot water flow and a short heating pipe was small and the uniformity was high. And it was confirmed that the temperature deviation was reduced and the uniformity was improved when the circulating fan was operated. The correlation between the surface temperature of the heating pipe and the indoor air temperature was a positive correlation and statistically significant(p<0.01) in both greenhouses. It was confirmed that the indoor temperature distribution in a hot water heating greenhouse was influenced by the surface temperature distribution of heating pipe, and the uniformity of indoor temperature distribution could be improved by arranging the heating pipe to minimize the temperature deviation. Analysis of the heat transfer characteristics of heating pipe showed that the temperature deviation increased as the pipe length became longer and the temperature deviation became smaller as the flow rate in pipe increased. Therefore, it was considered that the temperature distribution and the uniformity of environment in a greenhouse could be improved by arranging the heating pipe to shorten the length and controlling the flow velocity in pipe. In order to control the temperature deviation of one branch pipe within 3oC in the tube rail type hot water heating system most used in domestic greenhouses, when the flow velocity in the pipe is 0.2, 0.4, 0.6, 0.8, 1.0m·s-1, the length of a heating pipe should be limited to 40, 80, 120, 160, 200m, respectively. Additional

히트파이프와 루프히트파이프의 성능향상에 관한 최신기술

정의국(Eui Guk Jung),권정훈(Cheong Hoon Kwon),부준홍(Joon Hong Boo) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11

This paper has dealt with the three latest technologies for performance improvement of heat pipe and loop heat pipe. First, a part of the liquid in the condenser is bypassed to the evaporator in order to reduce the interface flow resistance caused by the counter flow of liquid and vapor inside the heat pipe. By applying this technology, the maximum amount of heat transfer caused by dry-out of the heat pipe was increased, and the experimental results were introduced, which improved the heat transfer performance by reducing the thermal resistance. Second, a technique of bypassing a portion of the vapor generated from the evaporator to the liquid reservoir was introduced in order to overcome the operational limit of the loop heat pipe. Through the application of the vapor bypass technology, the temperature overshoot on the evaporator wall of the loop heat pipe could be eliminated, and the heat transfer performance could be improved at high heat load range. Third, a performance prediction model of the micro heat pipe was developed. In this study, a performance prediction model for micro heat pipe to which the augmented Young-Laplace equation is applied is presented. This mathematical model has the advantage of being able to predict the shape of the phase change interface created inside the micro heat pipe more precisely than the previous model. The three latest technologies mentioned above can be studied more popularly in the future and can contribute to the technological expansion of heat pipe and loop heat pipe.

히트파이프와 루프히트파이프의 성능향상에 관한 최신기술

정의국(Eui Guk Jung),권정훈(Cheong Hoon Kwon),부준홍(Joon Hong Boo) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11

This paper has dealt with the three latest technologies for performance improvement of heat pipe and loop heat pipe. First, a part of the liquid in the condenser is bypassed to the evaporator in order to reduce the interface flow resistance caused by the counter flow of liquid and vapor inside the heat pipe. By applying this technology, the maximum amount of heat transfer caused by dry-out of the heat pipe was increased, and the experimental results were introduced, which improved the heat transfer performance by reducing the thermal resistance. Second, a technique of bypassing a portion of the vapor generated from the evaporator to the liquid reservoir was introduced in order to overcome the operational limit of the loop heat pipe. Through the application of the vapor bypass technology, the temperature overshoot on the evaporator wall of the loop heat pipe could be eliminated, and the heat transfer performance could be improved at high heat load range. Third, a performance prediction model of the micro heat pipe was developed. In this study, a performance prediction model for micro heat pipe to which the augmented Young-Laplace equation is applied is presented. This mathematical model has the advantage of being able to predict the shape of the phase change interface created inside the micro heat pipe more precisely than the previous model. The three latest technologies mentioned above can be studied more popularly in the future and can contribute to the technological expansion of heat pipe and loop heat pipe.

Hybrid heat pipe based passive cooling device for spent nuclear fuel dry storage cask

Jeong, Y.S.,Bang, I.C. Pergamon ; Elsevier Science Ltd 2016 Applied thermal engineering Vol.96 No.-

Conventional dry storage facilities for spent nuclear fuel (SNF) were designed to remove decay heat through the natural convection of air, but this method has limited cooling capacity and a possible re-criticality accident in case of flooding. To enhance the safety and capacity of dry storage cask of SNF, hybrid heat pipe-based passive cooling device was suggested. Heat pipe is an excellent passive heat transfer device using the principles of both conduction and phase change of the working fluid. The heat pipe containing neutron absorber material, the so-called hybrid heat pipe, is expected to prevent the re-criticality accidents of SNF and to increase the safety margin during interim and long term storage period. Moreover, a hybrid heat pipe with thermoelectric module, a Stirling engine and a phase change material tank can be used for utilization of the waste heat as heat-transfer medium. Located at the guide tube or instrumentation tube, hybrid heat pipe can remove decay heat from inside the sealed metal cask to outside, decreasing fuel rod temperature. In this paper, a 2-step analysis was performed using computational fluid dynamics code to evaluate the heat and fluid flow inside a cask, which consisted of a single spent fuel assembly simulation and a full-scope dry cask simulation. For a normal dry storage cask, the maximum fuel temperature is 290.0@?<SUP>o</SUP>C. With hybrid heat pipe cooling, the temperature decreased to 261.6@?<SUP>o</SUP>C with application of one hybrid heat pipe per assembly, and to 195.1@?<SUP>o</SUP>C with the application of five hybrid heat pipes per assembly. Therefore, a dry storage cask with hybrid heat pipes produces relatively low temperature inside a cask and reduces the possibility of structural failure due to thermal degradation.

Length effect on entrainment limit of large-<i>L</i>/<i>D</i> vertical heat pipe

Seo, Joseph,Bang, In-Cheol,Lee, Jae-Young Elsevier 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.97 No.-

<P><B>Abstract</B></P> <P>Heat pipes, which are heat-transfer devices of high thermal conductance, have been studied intensively because of their applicability and efficiency. However, only a small number of studies have been conducted on relatively long heat pipes. Here, the thermal hydraulic characteristics of a long heat pipe are studied. In particular, the thermal performance of the heat pipe and the entrainment limit, one of the important design parameters, are examined, so as to determine their sensitivities to the length-to-inner-diameter (<I>L</I>/<I>D</I>) ratio. Experiments are conducted to measure the heat removal performance and limitations of the heat pipe for various length scales. It is found that the heat-pipe performance exhibits a similar trend for various <I>L</I>/<I>D</I>, but with differing values. It is also found that the <I>L</I>/<I>D</I> effect on the entrainment limit for a large-<I>L</I>/<I>D</I> heat pipe differs significantly from the predictions of conventional correlations. Therefore, in order to develop a practical passive heat-pipe-based heat-removal device, an entrainment limit expression incorporating <I>L</I>/<I>D</I> correction is required.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effects of the <I>L</I>/<I>D</I> ratio on the thermal hydraulics of heat pipes are examined. </LI> <LI> The effects of the <I>L</I>/<I>D</I> ratio on the entrainment limit are also considered. </LI> <LI> Various entrainment limit correlations are compared against experimental data. </LI> <LI> Discrepancies between experiment and theory are examined for various <I>L</I>/<I>D</I> values. </LI> <LI> The need for an entrainment limit correlation with <I>L</I>/<I>D</I> correction is confirmed. </LI> </UL> </P>

박판형 히트파이프의 모세관력 향상을 위한 구조 개발

문석환(Seok-Hwan Moon),박윤우(Yoon-Woo Park) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

Considering using the heat pipe in Electronic Telecommunication Fields is in incremental increase. Especially in the electronic packaging application, the thin flat heat pipe has relatively higher applicability compared with the circular heat pipe. The thin flat heat pipe(TFHP) could be realized by pressing the circular heat pipe or welding two plates, however the envelope for the thin flat heat pipe with the total thickness of 2㎜ was obtained by the extrusion process through the present study. The thin flat heat pipe has the simple capillary wick structure consisting of rectangular cross sectional grooves built on the inner wall of that. Although the groove is simple as the capillary wick and many of that are built on the inner wall, it is difficult to realize a relatively high capillary force by the grooves. In the present study, to overcome the poor capillary force in the thin flat heat pipe with grooves, the thin flat heat pipe with wire bundle was fabricated and tested. Through the performance test, the thin flat heat pipe with the wire bundle showed the lower thermal resistance about 3.4 times and higher heat transfer rate about 3.8 times than the thin flat heat pipe with grooves as the capillary wick respectively. The possibility of the wire bundle in the thin flat heat pipe as the capillary wick was validated in the present study and the study for commercializing will be followed in the future.

가스내장 히트파이프의 냉시동특성과 성능에 관한 연구

홍성은,강환국 대한설비공학회 2006 설비공학 논문집 Vol.18 No.11

Considering heat pipe design principles in fabrication and operational performances, water is one of the most recommended working fluids to make mid to low temperature heat pipes. But the conventional water heat pipes might encounter the failure in a cold start-up operation when socked at a chilling temperature lower than the freezing point. If they are subjected to a heat supply for start-up at a temperature around -20℃, the rate of the vapor flow and the corresponding heat transfer from the evaporator to the condenser is so small that the vapor keeps to stick on the surface of the chilling condenser wall, forming an ice layer, resulting in a liquid deficiency in the evaporator. This kind of problems was resolved by Kang et al. in 2004 by adopting a gas loading heat pipe technology to the conventional water heat pipes. This study was conducted to examine a chilling start-up procedure of gas loading heat pipes by investigating the behaviors of heat pipe wall temperatures. And the thermal resistance of the gas loaded heat pipe that depends on the operating temperatures and heat loads was measured and examined.Two water heat pipes were designed and fabricated for the comparison of performances, one conventional and the other loaded with N2 gas. They were put on start-up test at a heat supply of 30W after having been socked at an initial temperature around -20℃. It was observed that the gas loaded one had succeeded in chilling start-up operation.

지역난방 이용 공동주택 통합배관시스템의 효용성 검증

오규성(Gyu Sung Oh),김영일(Young Il Kim),김선혜(Sean Hay Kim) 대한설비공학회 2018 설비공학 논문집 Vol.30 No.10

This study validates effectiveness of a combined piping system for an apartment using district heating. The existing district heating system is composed of four pipes (four-pipe system), but the suggested combined piping system is composed only of two pipes (two-pipe system). Thanks to this simplification, the two-pipe system will reduce heat loss of supplied heating energy. Performance of the four-pipe system and the two-pipe system were analyzed using TRNSYS 17 in the aspect that 1) If it can provide sufficient heating energy for space heating and hot water simultaneously, and 2) How much of the heat loss of the hot water supply pipe may be reduced. Measured energy consumption were compared with simulation results, that revealed good agreement. This study also proposes an optimal operation strategy of the hot water set temperature for the two-pipe system. It is confirmed that the two-pipe system can provide sufficient heating energy and uses less energy compared to the four-pipe system.

히트파이프 배열을 갖는 태양열 축열시스템의 열전달 해석

정의국(Jung Eui-Guk),김종규(Kim Jong-Kyu),강용혁(Kang Yong-Heack),부준홍(Boo Joon-Hong) 한국태양에너지학회 2010 한국태양에너지학회 학술대회논문집 Vol.2010 No.4

Heat transfer analysis results were shown for the solar thermal storage system which used heat pipe array. The thermal storage system was composed of thermal storage tank and charging/discharging heat exchanger by connection with the heat pipes. Heat pipe heat exchanger was attached to system, and could carry out charging and discharging to thermal storage tank at the same time. Height of the thermal storage tank was 600 ㎜, and that of the charging/discharging heat exchanger was 400 ㎜. Length of the heat pipe was the same as the total height of thermal storage system, and outer and inner diameter were 25.4 ㎜(O.D.) and 21.4 ㎜(I.D.) respectively. Diameter of the circular was 43 ㎜(O.D.), and fin geometries were considered as the design parameters. High temperature phase change material(PCM), KNO₃ was charged to storage tank to adjust melting temperature. Energy relations between heat exchanger and thermal storage tank were defined by the thermal resistance and node temperature. Physical transient equations of the heat pipe heat exchanger/thermal storage and PCM was modeled with energy conservation. Furthermore, melting/solidification phase change interface radius were calculated based on latent and sensible heat. Thermal storage system sizes satisfying inlet and outlet conditions of the charging/discharging heat exchanger were predicted according to heat pipe fin pitch variation of the thermal storage. Maximum and minimum heat pipe row was predicted to 899 and 808 respectively.