The effect of wall heating on the stability of low Reynolds number flows in a horizontal tube is investigated in the present study. Experiments were conducted for the flow of water in a tube with length to diameter ratio of 300. Wide ranges of mass flow rate and heating power were examined under constant wall heat flux. Stability was detected by examining signals of a thermocouple probe and a hot-film annemometer probe placed in the flow at the test section outlet. The onset of a turbulent flow was also marked by significant increases in the value of pressure drop measured across the test section. Results revealed regions of laminar flows, turbulent flows, and flows intermediate in behavior between laminar and fully turbulent. A stability map is presented showing regions of different flows on nondimensional co-ordinates representing forced and natural convection effects.

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