• Title/Summary/Keyword: Heat Transfer Control

Search Result 550, Processing Time 0.028 seconds

Experimental Study of the Superheat and Control of the Refrigerant Flow-Rate in the Evaporator of a Multi-type Air-Conditioning System (멀티형 공조시스템의 증발기 과열도에 관한 실험적 연구 및 냉매유량 제어)

  • 김태섭;홍금식;손현철
    • 제어로봇시스템학회:학술대회논문집
    • /
    • 2000.10a
    • /
    • pp.221-221
    • /
    • 2000
  • The heat exchange part in a modern multi-type air-conditioning system employs multiple-pass heat exchangers. The heat-transfer performance of an each pass in such an exchanger depends strongly on the length of the two-phase region and the mass flow of the refrigerant. The total length and diameters of the pipes, the exit conditions, and the arrangement of each pass as well as the geometrical shape of the distributor at the branching sections are considered to be major factors affecting the heat-transfer performance. The refrigerant commonly used in these systems is HCFC-22. The two objectives of this paper are to investigate the characteristics of the refrigerant flow rate and the superheat in the evaporator of a multi-type air-conditioning system for a single or simultaneous operating conditions and to control the superheat and the refrigerant flow rate of the evaporator.

  • PDF

An Experimental Study on the Effect of Fluid Flow and Heat Transfer Characteristics by the Longitudinal Vortices (종방향 와동이 유체유동 및 열전달 특성에 미치는 영향에 관한 실험적 연구)

  • 양장식;김은필
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.12 no.9
    • /
    • pp.843-852
    • /
    • 2000
  • The flow characteristics and the heat transfer rate on a surface by interaction of a pair of vortices were studied experimentally. The test facility consisted of a boundary-layer wind tunnel with a vortex introduced into the flow by half-delta winglet protruding from the surface. In order to control the strength of the longitudinal vortices, the angles of attack of the vortex generators were varied from $\pm20\;degree\;to\;\pm45$ degree, but spacings between the vortex generators were fixed to 4 cm. The 3-dimensional mean velocity measurements were made using a five-hole pressure probe. Heat transfer measurements were made using the thermochromatic liquid to provide the local distribution of the heat transfer coefficient. By using the method mentioned above, the following conclusions were obtained from the present experiment. The boundary layer was thinned in the regions where the secondary flow was directed toward the wall and thickened where it was directed away from the wall. The peak augmentation of the local heat transfer coefficient occurred in the downwash region near the point of minimum boundary-layer thickness.

  • PDF

Turbulent natural convective heat transfer charateristics in a square enclosure with control plates attached at the horifontal partition (제어판이 부착된 수평격판에 의해 분리되는 밀폐공간내의 난류 자연대류 열전달 특성)

  • 김점수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.12 no.2
    • /
    • pp.150-160
    • /
    • 2000
  • Turbulent natural convective flow and heat transfer in a square enclosure with horizontal partition are investigated numerically. The enclosure is composed of a lower hot and a upper cold horizontal walls and adiabatic vertical walls. Partitions carried with the upward, downward, and both control plates are attached perpendicularly to the one of the vertical insulated walls, respectively. The low Reynolds number $k-\varepsilon$ model is adopted to calculate the turbulent thermal convection. The governing equations are solved by using the finite element method with Galerkin method. The computations have been carried out by varying the length of partition, the position of control plates, and the Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height for water(Pr=4.95). When the control plates are attached at the edge of partition, the stability of oscillating flow grows wrose with the increase of Rayleigh number and the partition length. The heat transfer rate has been reducer than that of no control plate due to the restraint of control plates with the increase of Rayleigh number.

  • PDF

The Experimental Study of the Heat Flux and Energy Consumption on Variable Flow Rate for Secondary Side of DHS (지역난방 2차측 유량변화가 내부 열유속 및 에너지소비량에 미치는 영향에 관한 실험적 연구)

  • Hong, Seong-Ki;Cho, Sung-Hwan
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.27 no.5
    • /
    • pp.247-253
    • /
    • 2015
  • The presented work demonstrates the effects of flow rate on the secondary side of DHS (District Heating System). Increasing flow rate at the secondary side of DHS decreases energy consumption and time to reach the set-point of the heated room while increasing heat flux on the floor in the heating space. When flow rate increases, the overall heat transfer rate of radiant floor also increases. However, the results also show overall heat transfer rateto not increased linearly and thus the existence of an optimal flow rate for the secondary side of DHS. Control of the radiant floor with hot water may be more effectively accomplished with a combined control strategy that includes heat flux and a temperature set-point. This experimental analysis has been performed using a lab-scaled DHS pilot plant located at Jeonju University in Korea.

Analysis of Heat and Mass Transfer in an Evaporative Cooler with Fully Wetted Channel (채널이 수막으로 완전히 덮여 있는 증발식 냉각기에서의 열 및 물질전달 해석)

  • Song, Chan-Ho;Lee, Dae-Yeong;No, Seung-Tak
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.25 no.12
    • /
    • pp.1766-1775
    • /
    • 2001
  • A theoretical analysis on the heat and mass transfer in an evaporative cooler is presented in this work. The evaporative cooler is modeled as a channel filled with porous media the interstitial surface of which is covered by thin water film. Assuming that the Lewis number is unity and the water vapor saturation curve is linear, exact solutions to the energy and vapor concentration equations are obtained. Based on the exact solutions, the characteristics of the heat and mass transfer in the evaporative cooler are investigated. The comparison of the cooling performance between the evaporative cooler and the usual sensible heat exchanger is also carried out. Obviously, the evaporative heat exchanger shows better cooling performance than the sensible heat exchanger. This is due to the latent heat of water vaporization, which results in apparent increases both in the interstitial heat transfer coefficient and the specific heat of the air stream in the evaporative cooler.

Transient Heat Transfer in Porous Media under Oscillating Flow Condition (왕복유동조건에서 다공성 물질의 비정상 열전달)

  • Byeon, Su-Yeong;Lee, Dae-Yeong;No, Seung-Tak
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.25 no.3
    • /
    • pp.422-432
    • /
    • 2001
  • An analytical characterization is presented on the transient heat transfer by an oscillating flow through a porous slab. Based on a two-equation model, analytic solutions are obtained for both the fluid and solid temperature variations. Two parameters are identified as the Stanton number for the internal heat exchange and the ratio of the thermal capacities between the solid and fluid phases. The heat transfer characteristics are shown to be classified into four regimes according to the two parameters and physical interpretation is presented on the particular heat transfer processes within each regime. In addition, the condition for the local thermal equilibrium between the phases is examined and the relevant criterion is suggested.

Hydration Heat and Strength Properties of Mass Concrete Transfer Girder (고강도 매스 콘크리트-보의 수화열 및 강도특성)

  • Kang, Yeon-Woo;Kim, Gyu-Yong;Kim, Soon-Mook;Kim, Soo-Bong;Han, Jang-Hun;Jung, Jae-Yung
    • Proceedings of the Korean Institute of Building Construction Conference
    • /
    • 2013.11a
    • /
    • pp.28-29
    • /
    • 2013
  • When concrete was hardened, it should had considered a crack to make internal stress by hydration heat. For control of crack, admixture was use to change cement because hydration heat was effect to cement. High strength mass concrete had much hydration heat with high volume of cement. It was necessary to reduce hydration heat in construction method. In this study, it evaluates hydration heat, compressive strength of transfer concrete girder regard to field construction type such as separation, whole etc. Also, we test compressive strength of concrete with core and mold specimen.

  • PDF

Effect of Radiation Heat Transfer on the Control of Temperature Gradient in the Induction Heating Furnace for Growing Single Crystals (전자기 유도가열식 단결정 성장로의 온도 구배제어에 있어 복사열 전달의 효과)

  • Park, Tae-Yong;Shin, Yun-Ji;Ha, Minh-Tan;Bae, Si-Young;Lim, Young-Soo;Jeong, Seong-Min
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
    • /
    • v.32 no.6
    • /
    • pp.522-527
    • /
    • 2019
  • In order to fabricate high-quality SiC substrates for power electronic devices, various single crystal growing methods were prepared. These include the physical vapor transport (PVT) and top seeded solution growth (TSSG) methods. All the suggested SiC growth methods generally use induction-heating furnaces. The temperature distribution in this system can be easily adjusted by changing the hot-zone design. Moreover, precise temperature control in the induction-heating furnace is favorably required to grow a high-quality crystal. Therefore, in this study, we analyzed the heat transfer in these furnaces to grow SiC crystals. As the growth temperature of SiC crystals is very high, we evaluated the effect of radiation heat transfer on the temperature distribution in induction-heating furnaces. Based on our simulation results, a heat transfer strategy that controls the radiation heat transfer was suggested to obtain the optimal temperature distribution in the PVT and TSSG methods.

A Study on Heat Transfer Performances of a Heat Pipe Heat Sink for Power Control Semiconductors (전력제어 반도체용 히트파이프 냉각기의 열전달 성능 연구)

  • 강환국;김재진;김철주
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.13 no.8
    • /
    • pp.701-709
    • /
    • 2001
  • In this days, heat pipe heat sink has been widely applied to power controllers for railway substations to remove heat from power semiconductors(diodes or thyristors). The heat pipe heat sink consists of a aluminum heating block for mounting the thyristor, 2~3 heat pipes and large number of aluminum fins. The present study was to get fundamental informations of the structure, design parameters and heat transfer performances of heat pipe heat sink. Series of operational test for a unit with 3 heat pipes were performed and its heat flow circuit was analysed from the experimentally obtained data on wall temperature distribution. Total resistance was ranged 0.02~$0.03^{\circ}C$/W for a power range from 40W to400W. The time to get the steady state was approximately longer than 20 minutes, and overshooting was not occurred during start up operation.

  • PDF