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>

300MW급 Shell형 1단 분류층 가스화기 성능에 대한 전산수치해석 : 석탄・바이오매스 혼합비에 따른 CO2 가스화 반응

홍정우,박상신,송지훈,황정호 한국수소및신에너지학회 2012 한국수소 및 신에너지학회논문집 Vol.23 No.3

Recently, gasification technology for coal blended with biomass has been an issue. Especially, An advantages of coal blended with biomass are 1) obtaining high cold gas efficiency, 2) obtaining syn-gas of high-high heating value (HHV), and 3) controlling occurrence of CO2. In this study, the efficiency and characteristic of 300MW Shell type gasifier were predicted using CFD simulation. The CFD simulation was performed for biomass・coal blending ratios of 0∼0.2, 0.5, 1 and O2/fuel ratios of 0.5~0.84. Kinetic parameters (A, Ea) obtained by CO2gasification experiment were used as inputs for the simulation. In results of CFD simulation, residence times of particle in 300MW Shell type gasifer presented as 7.39 sec ~ 13.65 sec. Temperature of exit increased with O2/fuel ratio as 1400 K ~ 2800 K, while there is not an effects of biomass・coal blending ratios. Considering both aspects of temperature for causing wall slagging and high cold gas efficiency, the optimal O2/fuel ratio and blending ratio were found to be 0.585 and 0.05, respectively.

Computational investigation on the performance and parameter matching of ejectors in bi-ejector refrigeration system

Shengqiang Shen 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11

A design of bi-ejector refrigeration system was presented by the authors. In the system there are two ejectors: one is to suck refrigerant steam from evaporator and discharge to condenser, the other is a jet pump which pumps liquid refrigerant from condenser to generator. With numerical computation, the two aspects are investigated: (1) the flow characteristics of flow field in ejector. (2) the matching characteristics of the two ejectors. The simulation shows that the discharge pressure of jet-pump could be higher than that of motive steam with proper entrainment ratio. On the given refrigeration condition, the higher the generator pressure, the lower the entrainment ratio of steam-liquid ejector, but the entrainment ratio of steam-steam ejector is higher. With suitable matching parameters of two ejectors, the optimal COP of the system could be achieved.

다중효용증발식 해수담수화 설비의 운전 강건성 보장을 위한 열증기압축기 연구

박일석(Park Il Seouk) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5

Efficiency of a multi-effect desalination (MED) system with a thermal vapor compressor (TVC) is highly affected by the entraining performance of TVC. TVC's high entraining ability makes it possible to reduce the heat transfer area in evaporators or keep the top brine temperature (1<SUP>st</SUP> effect cell-side temperature) lower. Therefore, to achieve a higher entrainment ratio of TVC, we investigate the cases in which the motive steam flows into the primary nozzle with a swirl component. The compressible, axi-symmetric, and swirled flow is numerically solved for various swirl-to-axial component ratios. The Mach number, isobars, radial velocities, and shock patterns are compared to evaluate the effect of the swirled motive steam inflow on the entrainment ratio. This numerical study revealed that there exists an optimum swirl angle that maximizes the entrainment ratio.

전산해석을 통한 고압열증기압축기 형상변수에 관한 강건 설계

박일석(Park Il Seouk) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.12

A high motive pressure thermal vapor compressor(TVC) for a commercial multi-effect desalination(MED) plant is designed to have a high entraining performance and its robustness is also considered in the respect of operating stability at the abrupt change of the operating pressures like the motive and suction steam pressure which can be easily fluctuated by the external disturbance. The TVC having a good entraining performance of more than entrainment ratio 6.0 is designed through the iterative CFD analysis for the various primary nozzle diameter, mixing tube diameter and mixing tube length. And then for a couple of TVC having a similar entrainment ratio, the changes of the entrainment ratio are checked along the motive and suction pressure change. The system stability is diagnosed through the analyzing the changing pattern of the entrainment ratio.

Length effect on entrainment limitation of vertical wickless heat pipe

Seo, J.,Lee, J.Y. Pergamon Press ; Elsevier Science Ltd 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.101 No.-

Heat pipes, which are heat transfer devices with high thermal conductance, have been studied extensively 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 entrainment limit-an important design parameter-is examined to determine its sensitivity to the length-to-inner-diameter (L/D) ratio. Experiments are performed to measure the entrainment limits of heat pipes with various length scales. It is found that the entrainment limit points are affected by the L/D value of the heat pipe; this effect has not been considered in former correlations. Thus, a new modifying factor that includes the effect of L/D is formulated from experimental results. The correlation with the modifying factor showed good agreement with experimental results obtained in both former researches and the present study.

Study on the Conceptual Design of a Solar Ejector Refrigeration System

Md Khairul Bashar Shovon,RAMAN SENTHILKUMAR,Tae Ho Kim,Heuy Dong Kim 대한설비공학회 2020 International Journal Of Air-Conditioning and Refr Vol.28 No.1

The refrigeration system based on the conventional compression cycle consumes an enormous amount of high-grade energy. Using fossil fuels as the energy sources results in the addition of CO2 into the atmosphere and consequently stimulating higher greenhouse effect. The ejector refrigeration systems powered by renewable energy sources would be an effective alternative without increasing global CO2 footprint. In this study, the performance characteristics of a solar ejector refrigeration system working with R718 are analytically calculated by using a one-dimensional flow model. At the critical mode, the solar ejector-refrigeration system is analyzed at various working conditions such as condenser temperature, evaporator temperature, generator temperature, and ejector area ratio. The critical system performance is analyzed to meet any designated working conditions with a wide range of condenser temperatures. It is found that during the critical mode of operation, higher area ratio, higher evaporator temperature and lower generator temperature enhance the performance of the system. The minimum evaporator temperature, and the maximum generator temperature designed to acquire the required coefficient of performance value are also calculated.

Exergy analysis of two-stage steam-water jet injector

Qin Cai,Mingwei Tong,Xiujuan Bai 한국화학공학회 2012 Korean Journal of Chemical Engineering Vol.29 No.4

Exergy analysis is used as a tool to evaluate exergy losses in the steam-water jet injector so as to improve its overall performance. What this article addresses here is mainly about a parametric study on the injector under various operating conditions, such as different inlet water temperature, inlet steam pressure, pressure ratio, entrainment ratio and flowrate ratio. In addition, the irreversible losses in the component parts of the two-stage injector were analyzed in detail. The results show that the operating parameters have great effects on exergy efficiency of the injector. The average exergy efficiency of the two-stage injector is 21% more than that of the single-stage one. Moreover, calculations based on experimental data indicate that the highest exergy losses due to irreversibility occur in the first-stage mixing chamber. In light of this comparison, the exergy losses occurring in the system are proportional to the exergy efficiency obtained by applying the system.

분류층 석탄 가스화기 반응 유동장 변수 전산해석 연구

송우영(W.Y. Song),김혜숙(H.S. Kim),신미수(M.S. Shin),장동순(D.S. Jang),이재구(Jae-Goo Lee) 한국전산유체공학회 2014 한국전산유체공학회지 Vol.19 No.3

Considering the importance of the detailed resolution of the reacting flow field inside a gasifier, the objective of this study lies on to investigate the effect of important variables to influence on the reacting flow and thereby to clarify the physical feature occurring inside the gasifier using a comprehensive gasifier computer program. Thus, in this study the gasification process of a 1.0 ton/day gasifier are numerically modeled using the Fluent code. And parametric investigation has been made in terms of swirl intensity and aspect ratio of the gasifier. Doing this, special attention is given on the detailed change of the reacting flow field inside a gasifier especially with the change of this kind of design and operation parameters. Based on this study, a number of useful conclusions can be drawn in the view of flow pattern inside gasifier together with the consequence of the gasification process caused by the change of the flow pattern. Especially, swirl effect gives rise to a feature of a central delayed recirculation zone, which is different from the typical strong central recirculation appeared near the inlet nozzle. The delayed feature of central recirculation appearance could be explained by the increased axial momentum due to the substantial amount of the presence of the coal slurry occupying over the entire gasifier in gasification process. Further, the changes of flow pattern are explained in detail with the gasifier aspect ratio. In general, the results obtained are physically acceptable in parametric study.

The Effect of Round Flow Path Discharger and Back Panel Open Ratio on a Performance of Open Refrigerating Showcase

Myung Keun Gong,Gun Woo Kim,오명도 대한설비공학회 2019 International Journal of Air-Conditioning and Refr Vol.27 No.3

Numerical study is conducted to confirm the effect of round flow path control and back panel open ratio on a performance of open refrigerating showcase in this study. The rounding control is applied to flow path of air discharger in various radii and the punched panel with various open ratios is applied to back panel of showcase. These structural changes have a significant impact on its aircurtain performance because both changes can affect flow pattern of showcase. To prove it, the two-dimensional steady simulation is performed using k k –ε ε turbulent model. The performance of showcase is assessed using entrainment factor which is a ratio between cooled air and ambient air at the suction of refrigerating part. As a result of simulation, the curved path at air discharger reduces the entrainment factor by a maximum 9% less than typical design. The curved flow path removes the dead zone at the honeycomb structure of discharger. In addition, it is found that there is an optimal back panel open ratio at the storage space of the showcase. When the back panel open ratio is 0%, the cooled air from the discharge is attached to the cold storage area because of the Cowanda effect. However, the Cowanda effect is eliminated when back panel open ratio increases. Results address that the entrainment factor remains almost the same at back panel open ratio 3.93% or more. Lastly, the simulation of showcase with product in cold storage area is conducted to confirm the structure changes effect on performance of real use showcase according to KS Standard.