• Title/Summary/Keyword: Heat transfer enhancement

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Experimental study on nucleate boiling heat transfer enhancement using an electric field (전기장을 이용한 핵비등 열전달 촉진에 관한 실험적 연구)

  • Gwon, Yeong-Cheol;Kim, Mu-Hwan;Gang, In-Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.12
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    • pp.1563-1575
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    • 1997
  • To understand EHD nucleate boiling heat transfer enhancement, EHD effects on R-113 nucleate boiling heat transfer in a non-uniform electric field were investigated. The pool boiling heat transfer and the dynamic behavior of bubbles in d.c./a.c. electric fields under a saturated or subcooled boiling were studied by using a plate-wire electrode and a high speed camera. From the pool boiling heat transfer study, the shift of the pool boiling curve, the increase of the heat transfer and the delay of ONB and CHF points to higher heat fluxes were observed. From the dynamic behavior of bubbles, it was observed that bubbles departed away from the whole surface of the heated wire in radial direction due to EHD effects by a nonuniform electric field. With increasing applied voltages, the bubble size decreased and the active nucleation site and the departure number of bubbles showed the different trend. The present study indicates that the EHD nucleate boiling heat transfer is closely connection with the dynamic behavior of bubbles and the secondary flow induced near the heated surface. Therefore, the basic studies on the bubble behavior such as bubble frequency, bubble diameter, bubble velocity and flow characteristics are necessary for complete understanding of the enhancement mechanism of the boiling heat transfer using an electric field.

Heat Transfer Enhancement for Fin-Tube Heat Exchanger Using Vortex Generators

  • Yoo, Seong-Yeon;Park, Dong-Seong;Chung, Min-Ho
    • Journal of Mechanical Science and Technology
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    • v.16 no.1
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    • pp.109-115
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    • 2002
  • Vortex generators are fabricated on the fin surface of a fin-tube heat exchanger to augment the convective heat transfer. In addition to horseshoe vortices formed naturally around the tube of the fin-tube heat exchanger, longitudinal vortices are artificially created on the fin surface by vortex generators. The purpose of this study is to investigate the local heat transfer phenomena in the fin-tube heat exchangers with and without vortex generators, and to evaluate the effect of vortices on the heat transfer enhancement. Naphthalene sublimation technique is employed to measure local mass transfer coefficients, then analogy equation between heat and mass transfer is used to calculate heat transfer coefficients. Experiments are performed for the model of fin -circular tube heat exchangers with and without vortex generators, and of fin-flat tube heat exchangers with and without vortex generators. Average heat transfer coefficients of finn-flat tube heat exchanger without vertex generator are much lower than those of fin-circular tube heat exchanger. On the other hand, fin-flat tube heat exchanger with vortex generators has much higher heat transfer value than conventional fin-circular tube heat exchanger At the same time, pressure losses for four types of heat exchanger is measured and compared.

Pressure drop and heat transfer characteristics of a flat-plate solar collector with heat transfer enhancement device (열전달 향상 장치에 따른 평판형 태양열 집열기의 압력강하 및 열전달 특성)

  • Ahn, Sung-Hoo;Shin, Jee-Young;Son, Young-Seok
    • Journal of Advanced Marine Engineering and Technology
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    • v.37 no.5
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    • pp.453-460
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    • 2013
  • The surface roughness and heat transfer enhancement devices are known to increase the performance of a flat plate soar collector. This study includes the experiments on the effect of the several heat transfer enhancement devices inserted in duct to simulate the flat-plate solar collector. Experiment was basically at a constant heat flux on the upper duct wall. Inserted heat transfer enhancement devices are Chamfered rib $10^{\circ}$, Chamfered rib $20^{\circ}$, Rib & Groove and Rib & Dimple. Reynolds number is in the range of 2,300 to 22,000 which corresponds to turbulent regime. With the heat transfer enhancement devices, heat transfer would increase by the secondary flow and the increase of the heat transfer area. Pressure drop also increases with the insertion of the enhancement devices. Rib & Dimple model is the best in heat transfer enhancement, however, Chamfered rib $10^{\circ}$ model is the lowest in the pressure drop. Considering the heat transfer enhancement simultaneously with low pressure drop increase, performance factor was the best for the Chamfered rib $10^{\circ}$.

Experimental investigation of heat transfer enhancement in horizontal bundle tubes on absorber (수평관군 흡수기의 전열촉진에 관한 실험적 연구)

  • Moon, Choon-Geun;Seol, Won-Sil;Kim, Jae-Dol;Yoon, Jung-In
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.328-334
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    • 2000
  • This research was concerned with the enhancement of heat transfer by surfactant added to the aqueous solution of LiBr. Different horizontal tubes were tested with and without an additive of normal octyl alcohol. The test tubes were a bare tube, floral tube, hydrophilic tube. The additive concentration was about $0.05{\sim}5.5mass%$. The heat transfer coefficient was measured as a function of solution flow rate in the range of $0.01{\sim}0.034 kg/ms$. The experimental result were compared with cases without surfactant. The enhancement of heat transfer by Marangoni convection effect which was generated by addition of the surfactant is observed in each test tube.

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Heat transfer enhancement in electronic modules using a turbulence promoter (난류촉진체에 의한 전자칩의 열전달촉진에 관한 연구)

  • 박시우;정인기
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.6
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    • pp.861-870
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    • 1999
  • An experimental study was carried out to investigate the effects of using various shapes of turbulence promoter on the heat-transfer enhancement of 2-D and 3-D arrays of rectangular modules in a rectangular channel for design of noiseless and low-powered cooling fan in the electronic systems. Measurements of heat/mass transfer coefficients were made using a naphthalene sublimation technique, and the friction factors were measured for Reynolds numbers in the range$3.3{\time}10^3$~$1.6{\time}10^4$. Flow visualization was peformed by oil-film method. It was found that heat transfer and pressure drop increased remarkably due to the existence of the promoter. The results of the performance evaluation based on equal pumping power were showed that substantial heat-transfer enhancement was obtained at low Reynolds number range by use of a turbulence promoter.

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A Study on Heat Transfer Enhancement from Flat Plate Using Multiple Tripping Wires (복수 트리핑 와이어를 사용한 평판에서의 열전달 촉진에 관한 연구)

  • Yoo, Seong-Yeon;Cho, Woong-Sun;Ahn, Jong-Kyu
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.24 no.12
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    • pp.837-845
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    • 2012
  • The purpose of this research is to investigate the heat transfer enhancement by the multiple tripping wires installed on a flat plate. Naphthalene sublimation technique is used to measure the local mass transfer coefficients, and then heat transfer coefficients are calculated using heat/mass transfer analogy. Experiments are performed for the developed and developing flow conditions. Local and average heat transfer coefficients from the flat plate with three tripping wires are compared with those of no and one tripping wire. Remarkable heat transfer enhancements are found resulting from the boundary layer separation by the tripping wires, especially in the laminar boundary layer.

The effect of the shear-rate dependent thermal conductivity of non-Newtonian fluids on the heat transfer enhancement (전단율에 의존적인 비뉴턴 유체의 열전도율이 열전달 향상에 미치는 영향)

  • Sin, Se-Hyeon;Lee, Seong-Hyeok;Son, Chang-hyeon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.5
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    • pp.1717-1724
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    • 1996
  • The present study investigates the effect of the shear rate-dependent thermal conductivity of non-Newtonian fluids on the heat transfer enhancement in a pipe flow. An axially-constant heat flux boundary condition was adopted in the thermal fully developed region. The present analytical results of Nusselt numbers for various non-Newtonian fluids show heat transfer enhancement over those of a shear rate-independent thermal conductivity fluids. The present analytical results showed good agreement with the previous experiments which excluded the temperature-dependent viscosity effect on heat transfer. This study also proposes the use of a shear rate-dependent thermal conductivity fluids in the design of a heat exchanger for heat transfer enhancement as well as reduction of fouling.

Flow and Heat Transfer Characteristics due to Staggered Arrangement of Heat Pipes in Channels with Heat Pipes and Fins (휜-히트파이프로 구성된 채널에서 히트파이프의 엇갈림배열에 따른 유동 및 열전달 특성)

  • 김성훈;진윤근;김철주
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.11
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    • pp.871-879
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    • 2002
  • The characteristics of flow and heat transfer in the heat exchanger of heat pipes with fins have been studied numerically for cooling enhancement of electronic components of KTX (Korea Train eXpress). Numerical analysis and methodology have been conformed by comparing the experimental results for inlined array of heat pipes. The staggered arrangement of heat pipes has been proposed in order to achieve heat transfer enhancement. As results, the geometry change to the staggered array is conformed to increase the heat transfer of the system accompanied by an increase of pressure drop. The current results of friction factor and Colburn j factor are presented in terms of Reynolds number and staggered distance, and are expected to use for design and manufacture of such a system.

A Study on the Drag Reduction Effect and Heat Transfer Enhancement of Non ionized Surfactant and Water Mixture in a Circular Pipe Flow (비이온계 계면활성제 첨가수에 대한 관내 유동저항 감소 및 열전달 촉진에 관한 연구)

  • Kim, Myoung-Jun
    • Journal of Advanced Marine Engineering and Technology
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    • v.31 no.5
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    • pp.552-557
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    • 2007
  • This paper has dealt with the effect of non ionized surfactant and water mixture on drag reduction and heat transfer enhancement in a circular pipe flow with experimentally. The test section was consisted of stainless steel pipe with inside diameter of 16mm. The wire coil was used to increase heat transfer in a pipe and the on ionized surfactant(Oleyl Dihydroxyethyl Amino Oxide, ODEAO) was used to reduce the drag force of water mixture with surfactant. The main parameters of this experiment were diameter and pitch of wire coil and the ratio of test section length and horizontal wire coil length. In this experiment, the acquired results were 1) Drag reduction effect existed in this ODEAO-water mixture, 2) Friction factor and heat transfer were increased with insertion the heat transfer enhancement coil, 3) With increasing of pitch ratio, heat transfer was decreased, and 4) Heat transfer was decreased by the decreasing of inserting coil diameter.

A study of Heat Transfer Enhancement by Temperature Driven Marangoni Convection (온도차 마랑고니 대류에 의한 열전달 촉진에 관한 연구)

  • 김종윤;이동호;박종화;최국광
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.15 no.10
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    • pp.795-801
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    • 2003
  • The primary object of this study is to obtain a basic knowledge of heat transfer enhancement mechanism as affected by temperature driven Marangoni convection. Experiments is achieved to visualize the enhanced heat transfer phenomena by the effect of Marangoni convection through the laser holographic interferometry. Also Nusselt Number is introduced for the relation of Marangoni Number.