Hsu, Chia-Hsiang (2014-05). Enhancement of Pool Boiling Heat Transfer in Confined Space. Master's Thesis. Thesis uri icon

abstract

  • Pool boiling is an effective method used in many technical applications for a long time. Its highly efficient heat transfer performance results from not only the convection effect but also the phase change process in pool boiling. Pool boiling enhancement has been studied in the past decade. However, the mechanisms of pool boiling has not yet been fully understood because of the many parameters that affect its behavior including the latent heat of vaporization, nucleation density, bubble and fluid motion, interaction at the interface, and the physical properties of surface. Among the current studies, bubble departure rate is viewed as one of the dominant factors that affect heat transfer. This research considers the effect of bubble confinement on pool boiling. In the study, confinement was achieved by placing a flat plate over heated surface. The flat plate has a hole in the middle, and there is a gap between the flat plate and the heater. The diameters of hole are 2 mm, 3 mm, and 4 mm; the gap distances are 2.3 mm, 3.6 mm, and 5 mm. The heater consists of an indium-tin-oxide layer deposited on a silicon wafer. An IR camera and high speed cameras are used to acquire the surface temperature distribution and bubble image. By controlling the plate hole size and the gap distance, the effect of confinement on heat transfer performance can be evaluated. Moreover, heat transfer performance of pool boiling with three-2mm-holes plate was investigated and compared with that of single-2mm-hole plate with the smallest gap size. At the lower heat flux values, heat transfer enhancement in confined space was experimentally observed. Surface temperature can be reduced by 4 ?C at most. Results indicate that higher bubble departure rate and coalescence effect might be the dominant factor for improving heat transfer performance in a confined space caused by induced shear flow.
  • Pool boiling is an effective method used in many technical applications for a long
    time. Its highly efficient heat transfer performance results from not only the convection
    effect but also the phase change process in pool boiling. Pool boiling enhancement has
    been studied in the past decade. However, the mechanisms of pool boiling has not yet
    been fully understood because of the many parameters that affect its behavior including
    the latent heat of vaporization, nucleation density, bubble and fluid motion, interaction at
    the interface, and the physical properties of surface. Among the current studies, bubble
    departure rate is viewed as one of the dominant factors that affect heat transfer.

    This research considers the effect of bubble confinement on pool boiling. In the
    study, confinement was achieved by placing a flat plate over heated surface. The flat
    plate has a hole in the middle, and there is a gap between the flat plate and the heater.
    The diameters of hole are 2 mm, 3 mm, and 4 mm; the gap distances are 2.3 mm, 3.6 mm,
    and 5 mm. The heater consists of an indium-tin-oxide layer deposited on a silicon wafer. An IR
    camera and high speed cameras are used to acquire the surface temperature distribution
    and bubble image. By controlling the plate hole size and the gap distance, the effect of
    confinement on heat transfer performance can be evaluated. Moreover, heat transfer
    performance of pool boiling with three-2mm-holes plate was investigated and compared
    with that of single-2mm-hole plate with the smallest gap size.

    At the lower heat flux values, heat transfer enhancement in confined space was
    experimentally observed. Surface temperature can be reduced by 4 ?C at most. Results
    indicate that higher bubble departure rate and coalescence effect might be the dominant factor for improving heat transfer performance in a confined space caused by induced shear flow.

publication date

  • May 2014