Turbulent flow with separation and recirculation over a double backward facing step has been investigated experimentally. Time mean stream wise, transverse and cross-stream components of the velocity fluctuations, together with turbulence kinetic energy and Reynolds shear stresses, were measured using a laser Doppler anemometer, operating in the differential Doppler mode with forward scattering. Ordinary tap water was used in a closed loop flow system with a Reynolds number of 30,210 and significant changes of flow patterns, increases in turbulence kinetic energy, velocity fluctuations and shear stresses were observed downstream of the step expansion.

In electro-rheological (ER) devices the control of temperature is often of paramount importance. For a device through which the ER fluid is not able to flow continuously to and from a reservoir, where it may be cooled, this can be a problem. Such a situation occurs in the ER catch. The heat generated there will predominantly be dissipated from the outer surface of the drive/input. The rate of heat transfer is thus principally a function of the speed and area of that surface and the temperatures of the ER fluid and atmosphere. Since these factors reflect on the levels of electro-stress, current requirement and viscosity of the ER fluid, an opportunity exists for optimisation of catch performance. The paper shows the results of an investigation into the effects on the cooling/heating problem of varying the radii of the clutch rotors, their relative rotational speed and inter-electrode spacing. Equilibrium fluid temperatures are confirmed by experimental evidence. The effects of heat generation in run up to speed and clutch locked periods, (through electro viscous drag and dielectric loading respectively) are quantified and compared with the case of a contemporary ER fluid in a cylindrical catch on zero volts idling. At any given operating condition, uniform temperature, viscosity and constant electro stress are assumed throughout the fluid.

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Research is currently being conducted into the construction of high-temperature (>1000°C ) tubular heat exchangers that are to operate with a large pressure differential between low-pressure combustion gas and a process fluid. High operating temperatures preclude the use of metals. Therefore it is necessary to use ceramic heat transfer components and to insulate other components to counteract the direct heat. As the high-temperature ceramic heat transfer tubes exhibit a variable thermal expansion relative to the outer metallic casing and tube sheet, it is necessary for the seals to slide. This prevents excessive axial stress being set up in the ceramic tubes, thus prolonging their life.

An investigation was carried out with the object of determining the physical effects of separation and the associated reattachment and redevelopment, upon the heat transfer characteristics of turbulent flow in pipes and to compare the results of these flow conditions with the fully developed one-dimensional condition and with a recently developed numerical technique for the solution of recirculating flows.Separation of the flow was induced in a 4ft length of 2 in. internal diameter nicrome tube of wall thickness 0.001 in. by means of a sudden enlargement of diameter at the entry of the tube. The tube was electrically heated by the passage of a current along its length. The first 25 in. of the tube was metered by thermocouples which gave the wall temperatures and from these the local heat transfer rates and Reynolds numbers up to 5 X 10 4 using air as the working fluid.