Effect of boundry layer control, through surface holes, on the film coefficient of convective heat transfer

This thesis has as its objective, the effect of some boundary layer control on the convective heat transfer film coefficient, metal to liquid. The boundary layer control was produced by drilling 1/16 inch diameter holes on the tube surface. In this modern world of atoms and the current development of large quantities of its energy at low cost, the subject of designing heat exchange devices of higher efficiency is receiving considerable attention. In a reactor, or any type of heat exchange device, there are limits for the temperatures of a heat exchange surface because of corrosion, strength of metals etc. The high heat release rates of 5X105 Btu/hour sq. foot that are common in nuclear reactors have made obsolete the design practices of the boiler industry which considers a heat flux of 1X105 Btu/hour sq. ft. as a maximum rate. Forced convection is extensively used to-day in existing reactors as a means to transfer heat energy generated within the reactor. Some fluid flows through the reactor in passages arranged to provide heat extraction distributed throughout the reactor. In order to get the maximum power from the system, it is essential to design the heat extraction system to remove maximum possible energy with a minimum expenditure of energy for pumping the fluid. If less fluid is pumped for the same extraction of energy, the temperature (outlet) of the fluid will be high and so the energy available will be at a higher potential. These objectives can be achieved with a higher efficiency of heat transfer. The higher efficiency of heat transfer means a device to increase the film coefficient of convective heat transfer which is entirely dependent upon the size and nature of the surface film. This particular investigation was chosen by the author because the control of boundary layer by suction through the slots and porous materials is widely used in aircraft industry. It has been noted by several investigators, when mass crosses a boundary layer in a direction perpendicular to the motion of the fluid, the magnitude and direction of the mass transfer effects the properties of the boundary layer. The boundary layer thickness, stability, velocity, temperature, and concentration profiles are altered. At the same time the heat transfer coefficient is changed. In general, mass transfer from the fluid to the wall (“Suction”) increases the magnitude of the heat transfer coefficient, while mass transfer from the wall to the fluid (“Blowing”) decreases the magnitude of the heat transfer coefficient. The exploitation of these effects has also important applications, to the cooling of gas turbine blades, the development of high lift airfoils and in the industrially important techniques of drying, absorption, extraction, distillation, and adsorption --Introduction, pages 5-6