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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Filmwise condensation inside a non-circular tube in the presence of forced convection and a non-condensing gas.

Author: KRISHNASWAMY S

Year: 2004

Supervisor(s): John Williams

For tomorrow’s environment friendly vehicles (fuel cell, hydrogen IC), on-board water management is of major importance and condensers are needed for recovery of water from the exhaust stream, which contains molecular species that do not condense along with the vapour. This thesis describes experimental and modelling studies of the exhaust condenser problem.

Accurate experimental data have been obtained using steam-air mixtures in an exhaust heat exchanger tube of a proposed fuel-cell engine. The data cover the range of practical interest. Steam-air mixtures were passed through a flattened tube having internal hydraulic diameter 2.99 mm and a working length of 1 m. Water flowing under laminar flow conditions through an annular space on the outside of the test condenser tube was used as coolant to simulate the air-side resistance (including the fins) in the actual application. Laminar flow mixing boxes were designed to ensure accurate measurement of the mean coolant inlet and exit temperatures. Surface temperatures at six positions were obtained from thermocouples embedded in the tube wall. Provision for condensate collection at the tube exit was incorporated into the apparatus design. Steam was supplied from an evaporator and the vapour mass flowrate was obtained from the electrical power input to the evaporator, incorporating a correction for the relatively small thermal loss to the environment. The non-condensing gas (air) was injected through a sparge tube at the base of the evaporator and its flowrate metered using a variable aperture float-type flowmeter. The ranges of variables used were: inlet absolute pressure (147 - 165 kPa), inlet temperature (57 - 177°C), inlet steam mole fraction (0.13 - 0.43) and steam-air mixture mass flowrate (0.5 - 0.9 g/s).