PhD Theses

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Browsing PhD Theses by Author "Kadete, Henry"

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    Enhancement of heat tranfer by corona wind
    (University of Dar es Salaam, 1987) Kadete, Henry
    The mechanism of heat transfer enhancement across solid gaseous interfaces by corona wind directed towards the heat transfer surface is investigated. Basic principles of heat transfer, negative dc corona and the nature of corona wind are studied. Voltage-current characteristics of negative dc corona in geometries which create corona wind are measured. The velocity distribution and velocity characteristics of corona wind are measured by Pitot-tube and by hot-wire constant-temperature anemometer. Corona wind is visualized by Toeplers children measurements. Corona wind is also visualized by the injection of carbon dioxide generated mist into the flow. Heat transfer measurements with and without corona wind reaching an upward facing heat transfer surface are made. Voltage-current characteristics of a corona triode are measured. The corona triode is used to generate corona wind and to control the magnitude of current which reaches the heat transfer surface. Heat transfer measurements in this corona triode geometry are made. Conclusions are that corona wind may adequately be described by the Navier-Stokes equations of motion. The Coulombion drag forces transferred to the neutral gas background create corona wind. The corona current is a function of the applied voltage and the electrode gap geometry. The average corona wind turns out to be proportional to the square root of the corona current. The corona wind velocity distribution is bell shaped with a maximum of about 5 m/s.The electro kinetic conversion efficiency is of the order of one percent. The enhancement of heat transfer by corona wind insignificant. Heat convection enhancement by up to 90 percent is measured. The enhancement of convective heat transfer by corona wind blowing on a heat transfer surface turns out to be proportional to the 0,3Power of the corona current. It turns out that the enhancement of convective heat transfer is only due to the augmentation of the hydrodynamic flow of the air. The corona wind is laminar, less turbulent than a mechanically created jet, has a small spread with a cross-section area of about 2x4 on-1i and has a long reach of up to 25cm which makes it superior to mechanically created jets for enhancement of heat convection by blowing towards heat transfer surfaces. The Langmuir-Child equation for space charge limited Current [SCLC] in vacuum is expressed in a general form in a gaseous media.