• Title/Summary/Keyword: Nu수

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Experimental Study on Heat Transfer Characteristics of Jet A-1 Fuel (Jet A-1 연료의 열전달 특성에 관한 실험적 연구)

  • Lee, Junseo;Lee, Bom;Ahn, Kyubok
    • Journal of the Korean Society of Propulsion Engineers
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    • v.24 no.5
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    • pp.1-12
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    • 2020
  • In this paper, the heat transfer characteristics of Jet A-1, which is used as a coolant and fuel in a regeneratively cooled thrust chamber, were experimentally studied. By varying the applied current for heating the cooling channel, the simulated specimen diameter, the specimen outlet pressure and the coolant flow rate, the wall temperatures of the specimen and the Jet A-1 temperatures at the specimen inlet/outlet were measured. It was found that the specimen diameter and the flow rate were important factors for the characteristics of heat transfer and the outlet pressure did not affect the performance of heat transfer. The results of the heat transfer experiments were compared with the previous Nusselt number empirical equations and novel Nusselt number empirical equations were finally derived.

Numerical Analysis on Flow and Heat Transfer Characteristics in Louver Fin Heat Exchanger (루버휜형 열교환기내 유동 및 열전달 특성에 관한 해석적 연구)

  • 한진호;박상록;김일겸;임장순
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.12 no.4
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    • pp.398-403
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    • 2000
  • Numerical analysis was conducted to investigate flow and heat transfer characteristics in louver fin exchanger, which were influenced by louver pitch, fin pitch, louver angle and inlet velocity. Standard $k-\varepsilon$ turbulent modelling was used in this study, and compared with laminar modelling. As a result of this study, Nusselt number became smaller as louver pitch or fin pitch was greater. Drag coefficient became smaller as louver pitch or fin pitch was greater, but it was little affected by inlet velocity.

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An Investigation on Heat transfer Characteristics of Inclined Wall Attaching Offest jet (경사진 벽부착 제트의 열전달 특성에 대한 연구)

  • 심재경
    • Journal of Advanced Marine Engineering and Technology
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    • v.22 no.2
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    • pp.200-209
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    • 1998
  • Experiments have been conducted to determine heat transfer characteristics for a two-dimen-sional turbulent wall attaching offset jet at different oblique angles to a flat surface. The local Nusselt number distributions were measured using liquid crystal as a temperature sensor. Wall static pressure coefficient profiles were measured at the Reynolds number Re 53200(based on the nozzle width, D) the offset ratio H/D from 2.5 to 10 and the oblique angle a from $0^{\circ}$, to $40^{\circ}$ It is observed that the maximum Nusselt number point occurs slightly upstream of time-averaged reattachment point for all oblique angles. The correlations between the maximum Nusselt number and Reynolds number offset ration and oblique angle are presented.

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Numerical Study on the Characteristics of Natural Convection Flows in a Cubical Cavity (3차원 정육면체 캐비티내 자연대류 유동 특성에 관한 수치해석적 연구)

  • Myong Hyon-Kook
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.4 s.247
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    • pp.337-342
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    • 2006
  • Natural convection flows in a cubical air-filled cavity that has one pair of opposing faces isothermal at different temperatures, $T_h\;and\;T_c$, respectively, the remaining four faces having a linear variation from $T_c\;to\;T_h$ are numerically simulated by a solution code(PowerCFD) using unstructured cell-centered method. Special attention is paid to three-dimensional flow and thermal characteristics according to the variation of inclination angle $\theta$ of the isothermal faces from horizontal: namely $\theta=0^{\circ},\;15^{\circ},\;30^{\circ},\;45^{\circ},\;50^{\circ},\;60^{\circ},\;75^{\circ}\;and\;90^{\circ}$. Comparisons of the average Nusselt number at the cold face are made with experimental benchmark results found in the literature. It is demonstrated that the average Nusselt number at the cold face has a maximum value around the inclination angle of $50^{\circ}$. It is also found that the code is capable of producing accurately the nature of the laminar convection in a cubical air-filled cavity with differentially heated walls.

Experimental Study of Heat Transfer Characteristics in the Louvered-Fin Type Heat Exchanger (루우버휜형 열교환기의 열전달특성에 관한 실험적 연구)

  • 전창덕;홍주태;이진호
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.8 no.1
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    • pp.120-139
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    • 1996
  • Experiment was performed to study the heat transfer characteristics in 27 kinds of 15 : 1 scale models of multi-louverred fin heat exchangers with a wide range of variables(R $e_{Lp}$ =100~1, 800, $L_p$/F$p$=0.3~0.9, $\theta$=20$^{\circ}$~40$^{\circ}$). Thermofoil heaters were used to heat the louver fins and the local average Nusselt number for each louver in the louver array was obtained at constant wall temperature conditions. Correlations are developed to predict the heat transfer characteristics and drag coefficients. Generally, the heat transfer characteristics in the multi-louvered fins is shown to be similar to those of the laminar heat transfer on a flat plate. As the Reynolds number, the louver pitch to fin pitch ratio$L_p$/F$p$and the louver angle($\theta$) increase respectively, the average Nusselt number increases, but the variation of average Nusselt number as a function of the louver angle is smaller than that as a function of the louver pitch to fin pitch ratio. In case of$L_p$/F$p$ <0.5, the average Nusselt number of the 3rd louver is especially lower than the others, it is expected that it is due to the flow structure such as a recirculation flow and a flow separation.

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Comparison of Performance Characteristics in the Chevron Type Plate Heat Exchanger with Performance Correlation (성능 예측 상관식에 따른 쉐브론 형태 판형 열교환기 성능 특성 비교)

  • Bae, Kyung-Jin;An, Sung-Kuk;Cho, Hyun-Uk;Nam, Sang-Chul;Cho, Hong-Hyun
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.23 no.8
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    • pp.535-542
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    • 2011
  • The performance of a plate heat exchanger for using liquid solution in the absorption chiller-heater was analyzed. The model was developed by using the various performance prediction correlations. The performance characteristics of the plate heat exchanger with the mass flow rate ratio was verified by using experimental data. To investigate performance of plate heat exchanger with geometry variables, the chevron angle, corrugated wave length, and corrugation depth were changed. As a result, the capacity of Kim and Martin correlation models was similar with the experimental data, and the capacity difference was less than 2%. Besides, the pressure drop of Marin correlation model showed a similar variation with experimental data, and the difference of pressure drop was less than 1.5 kPa.

An investigation on heat transfer effects of two dimensional plane jet attaching offseted obliqued wall (단이 진 경사벽면에 부착되는 2차원 평면제트의 열전달 효과에 관한 연구)

  • Yun, Sun-Hyeon;Lee, Dae-Hui;Sim, Jae-Gyeong;Song, Heung-Bok
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.10
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    • pp.1314-1325
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    • 1997
  • Experiments have been conducted to determine the flow and heat transfer characteristics for a two-dimensional turbulent wall attaching offset jet at different oblique angles to a flat surface. The distributions of the wall static pressure coefficient and time-averaged reattachment position for various offset ratios and oblique angles have been measured. The local Nusselt number distributions on the plate surface were also measured using liquid crystal as a temperature indicator. The new hue-capturing technique utilizing a true color image processing system was used to accurately determine the temperature of the liquid crystal. The experiments were carried out at Reynolds number, Re (based on D) of from 7300 to 21,300 with offset ratio, H/D from 2.5 to 10, and oblique angle, .alpha. from 0 deg. to 400 deg..

An experimental study on heat transfer augmentation in fluidized bed heat exchanger (유동층형(流動層形) 열교환기(熱交換器)에서 전열증진(傳熱增進)에 관(關)한 실험적(實驗的) 연구(硏究))

  • Yoo, Ji-Oh;Seo, Jeong-Yun
    • Solar Energy
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    • v.13 no.2_3
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    • pp.91-106
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    • 1993
  • The purpose of this study was to investigate the enhancement of heat transfer coefficient in double pipe fluidized bed heat exchangers. The inner tube used a smooth tube and a finned tube equipped with longitudinal fins. The heat transfer coefficients between the heated tube and fluidized bed of alumina beads were calculated as a function of fluidized velocity in various particle sizes($d_p$=0.41, 0.54, 0.65, 0.77mm) and static bed heights($H_o$=50, 100, 150, 200, 250mm). The coefficient for finned tube is higher than for smooth tube. And the maximum increasing rate is 7.8 times in smooth tube and 12.9 times in finned tube.

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HIGH Ra NUMBER NATURAL CONVECTION IN A TRIANGULAR POOL WITH A HEAT GENERATION (열원이 있는 삼각형 풀의 높은 Ra수 자연대류)

  • Kim, Jong-Tae;Park, Rae-Joon;Kim, Hwan-Yeol;Hong, Seong-Wan;Song, Jin-Ho;Kim, Sang-Baik
    • Journal of computational fluids engineering
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    • v.16 no.3
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    • pp.66-74
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    • 2011
  • A fluid in an enclosure can be heated by electric heating, chemical reaction, or fission heat. In order to remove the volumetric heat of the fluid, the walls surrounding the enclosure must be cooled. In this case, a natural convection occurs in the pool of the fluid, and it has a dominant role in heat transfer to the surrounding walls. It can augment the heat transfer rates tens to hundreds times larger than conductive heat transfer. The heat transfer by a natural convection in a regular shape such as a square cavity or semi-circular pool has been studied experimentally and numerically for many years. A pool of an inverted triangular shape with 10 degree inclined bottom walls has a good cooling performance because of enhanced boiling critical heat flux (CHF) compared to horizontal downward surface. The coolability of the pool is determined by comparing the thermal load from the pool and the maximum heat flux removable by cooling mechanism such as radiative or boiling heat transfer on the pool boundaries. In order to evaluate the pool coolability, it is important to correctly expect the thermal load by a natural convection heat transfer of the pool. In this study, turbulence models with modifications for buoyancy effect were validated for unsteady natural convections by volumetric heating. And natural convection in the triangular pool was evaluated by using the models.

An Experimental Study on the Promotion of the Waste-Heat Recovery in the Fluidized Beds used in Reclamation of Foundry Sand (주물사 재생 유동층내 폐열회수 증진에 관한 실험적 연구)

  • Baek, Ko-Kil;Park, Jong-Suen;Lee, Eun-Pyo;Choi, Sung-Ill;Choi, Guk-Gwang;Jeon, Sung-Taek
    • Solar Energy
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    • v.18 no.2
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    • pp.145-152
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    • 1998
  • In this experimental study, for obtaining the data to be used in the increased recover rate of waste heat from the recirculated sand, the furan foundry sand were used as the fluidized particle in the fluidized bed in which the smooth, spiral and finned tubes($Do={\varphi}12.7$) were horizontally installed and used as the heat-transfer tubes. The heat transfer experiments were performed in the conditions of water Reynolds number of inside tubes in the range of 4,000 to 18,000 and particle Reynolds number of outside tube in the range of 0.8 to 7.5. The heat-transfer coefficients(ho) increase as the higher inside temperature of the fluidized bed and the maximum heat-transfer coefficients can be obtained in the range of 3.5 to 5.5 of particle Reynolds number in the all tubes. The maximum Nu numbers of smooth, spiral and finned tubes are figured as about 1:1.5:3 in order even if the ratios show little different as the temperatures of bed.

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