Direct contact heat transfer between an evaporating fluid and an immiscible liquid

  • Martyn Lench

    Student thesis: Doctoral Thesis


    An investigation has been conducted into the process of cooling water by the evaporation of droplets of isopentane in direct contact. The research has potential industrial application to a pickling acid recovery crystalliser. In order to minimise industrial equipment size a counter current flowing apparatus was developed and studied. Studies of optimum column height were carried out over a wide range of flow and drop size values.

    Several computer-based models have been developed to predict optimum column height. The results of initial models were used to modify experimental work and gave rise to the measurement of initial drop size using a high speed video camera technique.

    A more sophisticated version of the computer based model has been developed and is the major product of this research. This included the development of a dimensionless correlation for instantaneous heat transfer to an evaporating droplet. This is based on existing correlations which are compared and modified empirically. The correlation produced is:

    Nu= 2 + 0.76 Re 1/3 Pr 1/2

    The computer model with this correlation is accurate to within 22%. The model assumes an average vapour half opening angle (β) of 135° based on published work. Drop velocities are based on terminal values and rigid sphere behaviour of 2-phase droplets is assumed. The final model assumes that the vapour and liquid dispersed phase remain attached as they rise through the column.
    Reynolds number of the continuous phase is found to have no independent effect on minimum evaporative height.

    The pinch temperature difference in the temperature profiles through the evaporative column is found to be significant in determination of minimum evaporative height. An approximate relationship of the form:

    Minimum evaporative height α ΔTpinch-0.5 is proposed.
    Date of AwardAug 1991
    Original languageEnglish
    Awarding Institution
    • Polytechnic of Wales

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