Rupakula, Venkata Panduranga Praveen (2005-12). Determination of heat (mass) transfer from blockages with round and elongated holes in a wide rectangular channel. Master's Thesis. Thesis uri icon

abstract

  • Mass transfer experiments were conducted to study the thermal performance characteristics of blockages with round and elongated holes, positioned in a 12:1 rectangular channel. Naphthalene sublimation technique was adopted to conduct experiments with four different blockage configurations, flow rates corresponding to Reynolds numbers (based on channel hydraulic diameter) of 7,000 and 17,000, and at three blockage locations. The hole area to channel area ratio for all four blockage configurations was the same at 0.196. The hole width was half the channel height, and the distance between consecutive blockages was twice the channel height. Average heat transfer, local heat (mass) transfer and overall pressure drop results were obtained. The thermal performance for a particular blockage configuration was measured in terms of the heat transfer enhancement and the friction factor ratio. Heat transfer enhancement was measured as a ratio of average Nusselt number on the blockage surface to the Nusselt number for a thermally fully developed turbulent flow in a smooth channel. Results indicate that this ratio ranged between 3.6 and 12.4, while the friction factor ratio varied between 500-1700. The blockage configuration with round holes was found to yield best thermal performance, while the configuration with largest hole elongation was nearly equal in thermal performance. In order to compare different blockage configurations, an average value of upstream and downstream side thermal performances was used. A general downward trend in Nusselt number ratio with elongation of holes was observed on the upstream side and a reverse trend was observed on the downstream side. An upward trend in the Nusselt number ratio with blockage hole elongation on the downstream side of a blockage was primarily due to jet reversal from the downstream blockage and its impingement on the downstream surface of the upstream blockage. Local experiments were performed to compare against the results from average experiments and also to gain insights into the flow behaviour. There was good agreement between the results from local and average mass transfer experiments. The average variation in Nusselt number ratio between local and average mass transfer experiments was about 5.06%.
  • Mass transfer experiments were conducted to study the thermal performance
    characteristics of blockages with round and elongated holes, positioned in a 12:1
    rectangular channel. Naphthalene sublimation technique was adopted to conduct
    experiments with four different blockage configurations, flow rates corresponding to
    Reynolds numbers (based on channel hydraulic diameter) of 7,000 and 17,000, and at
    three blockage locations. The hole area to channel area ratio for all four blockage
    configurations was the same at 0.196. The hole width was half the channel height, and
    the distance between consecutive blockages was twice the channel height. Average heat
    transfer, local heat (mass) transfer and overall pressure drop results were obtained. The
    thermal performance for a particular blockage configuration was measured in terms of
    the heat transfer enhancement and the friction factor ratio. Heat transfer enhancement
    was measured as a ratio of average Nusselt number on the blockage surface to the
    Nusselt number for a thermally fully developed turbulent flow in a smooth channel.
    Results indicate that this ratio ranged between 3.6 and 12.4, while the friction factor ratio
    varied between 500-1700. The blockage configuration with round holes was found to
    yield best thermal performance, while the configuration with largest hole elongation was
    nearly equal in thermal performance. In order to compare different blockage
    configurations, an average value of upstream and downstream side thermal performances
    was used. A general downward trend in Nusselt number ratio with elongation of holes was
    observed on the upstream side and a reverse trend was observed on the downstream side.
    An upward trend in the Nusselt number ratio with blockage hole elongation on the
    downstream side of a blockage was primarily due to jet reversal from the downstream
    blockage and its impingement on the downstream surface of the upstream blockage.
    Local experiments were performed to compare against the results from average
    experiments and also to gain insights into the flow behaviour. There was good
    agreement between the results from local and average mass transfer experiments. The
    average variation in Nusselt number ratio between local and average mass transfer
    experiments was about 5.06%.

publication date

  • December 2005