Measurements of skin friction and mean-velocity profiles have been made in fully developed flows in pipes and channels in the Reynolds number range 1000 < Re < 10000 These measurements, and observations of hot-wire signals, indicate rather remarkable differences between two-dimensional and axially symmetric flows and also make it difficult to give a precise definition of the term ‘fully developed turbulent flow’

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Some observations on skin friction and velocity profiles in fully developed pipe and channel flows

Pressure probes for fluid measurement

Heat transfer and friction factor characteristics in turbulent flow through a tube fitted with perforated twisted tape inserts

This paper provides a comprehensive set of equations and guidelines to determine the rate of heat release in full-scale fire tests based on the O2 consumption principle. The approach is different from other investigators as the enphasis is on full-scale fire test applications and the use of volumetric flow rates is avoided. Some general equations for flow rate (i.e., applicable irrespective of the configuration of the gas analysis system) are described first. In subsequent sections, distinctions are made between various gas analyzer combinations to derive the equations for rate of heat release. Procedures to calculate net rate of heat release from a specimen exposed to a gas burner or wood crib ignition source are also given. A summary at the end of the paper lists step by step procedures for all cases covered.

Measuring rate of heat release by oxygen consumption

1. The natural internal temperature gradients during flight were reproduced in various medium and large insects by mounting freshly killed specimens in a wind tunnel and heating them with a high-frequency electric current. The heat flow from the flight muscles to other parts of the body and from the body were investigated. 2. Comparison of dead and living insects showed that most of the heat transfer within the body is by conduction; circulation of the haemolymph during flight contributes little to the heat flow. 3. The temperature excess is high throughout the pterothorax in a large insect; where there are no subcutaneous air sacs it is only about 10% less at the surface of the pterothorax than at the centre. 4. Only about 5-15% of the heat generated in the flight muscles is conducted to the prothorax, head, abdomen and appendages, which remain near the temperature of the air". 5. Usually not more than 10-15% of the heat escapes from the pterothorax by long-wave radiation in a large insect flying under a clear sky. Smaller insects lose relatively more of their heat by radiation. 6. Radiation increases with the insect9s temperature but it is never sufficient to give much protection against overheating. 7. Ordinarily 60-80% of the heat is dissipated from the surface of the pterothorax by convection. 8. In convection from a naked insect the relationships between heat loss, the surface temperature excess, size, and wind speed are nearly the same as in convection from a smooth cylinder or sphere, if allowance is made for turbulence in the air flow over the insect. 9. In dragonflies and denuded bees and moths heated in proportion to their pterothoracic volumes in a constant wind, the temperature excess was proportional to the 1 3-1.5 power of the average diameter of the pterothorax. 10. The coats of hair on bumble-bees, hawk moths, and noctuid moths are excellent insulators against convective heat loss. At normal flying speeds they increase the temperature excess by 50-100% or more--in a large hawk moth probably by at least 8 or 9° C. 11. The insulating value of a coat depends mostly on its density and on the size of the insect, and less on the length of the hair. 12. In dragonflies the pterothorax is insulated nearly as effectively by the subcutaneous air sacs.

Heat Loss and the Body Temperatures of Flying Insects: II. Heat Conduction within the Body and Its Loss by Radiation and Convection

The measurement of air flow

This chapter discusses the different methods for the measurement of pulsating flow. The measurement of pulsating flow, mainly in relation to the use of orifice plates, is probably the most extensively employed of all methods of flow measurement in industry. Measurement of pulsating flow with orifice plates makes use of Hodgson-number criterion. It should be noted that the dimensional analysis from which the Hodgson-number criterion was deduced took account only of velocity pulsations through the orifice; it ignored any changes that might occur in the discharge coefficient of the orifice in pulsating flow and any errors resulting from pressure fluctuations in the manometer system. For flows in which the density does not change appreciably, the turbine meter can be regarded as a linear-output meter. Mass flow meters have been eminently suited to the measurement of pulsating flow. There are certain types of mass flowmeters that are basically volume meters incorporating additional metering devices to measure density. If measurements of the local average of a pulsating velocity are required, these are probably best carried out by means of a hot-wire anemometer suitably connected to an oscillograph that records the waveform.

The measurement of pulsating flow

This chapter presents some typical examples for the measurement of air flow and discusses the methods of its calculation. An application of the pitot-traverse methods is also discussed in the chapter. It is assumed that an estimate is required, subject to an error not exceeding about 2 percent, of the quantity of air flowing along a circular pipe of 40 cm diameter. An example of calibration of a small plate orifice is also presented in the chapter. The chapter illustrates an example where the following conditions had to be met: for certain purposes, a stream of air was to be maintained in a pipe of nominally 2–54 cm diameter by means of a small fan, it was required to provide a ready method of measuring the rate of flow and of maintaining it at any steady value between limits of 1–5 and 3 m/sec.

Examples from practice

This chapter discusses the characteristics of the pitot and static tubes for measurement of incompressible flow. In incompressible flow, the velocity pressure can be obtained from the difference between two pressure observations: the total pressure and the static pressure. The measurement of total pressure is relatively simple. On the surface of any solid body immersed in a stream of fluid, there is some point at which the fluid is brought to rest and the pressure acting is the total pressure of the undisturbed flow. This pressure can be determined by providing an orifice at that point and connecting it to a manometer. This is the basis of the pitot tube, which has been universally adopted for the measurement of total pressure. Pitot-static tubes are the only practical standards of reference for the measurement of air speed against which all other designs, and indeed all anemometers, have to be calibrated either directly or indirectly.

The characteristics of pitot and static tubes in incompressible flow

This chapter discusses the theory of the vane anemometer and its usage. To apply the results of the theoretical analysis that follows to predict the behavior of the vane anemometer in various working conditions, some knowledge is required of the aerodynamic forces acting on small flat plates. An anemometer is generally used to measure air speeds appreciably higher than the lowest speed that will just set the vanes in rotation. In these circumstances, the readings of a well-made anemometer, in which the frictional resistance is very small, do not usually require correction for changes in air density corresponding to normal changes in atmospheric pressure and temperature. However, the vane anemometer measures a local velocity which, subject to the limitations, may be taken as the velocity of the filament of air passing through the center of the vane wheel. Therefore, to determine the quantity of air flowing along a pipe by the use of this instrument, readings must be taken with the axis of the vane wheel at the points at which the velocity head would be observed if a pitot-static tube were being employed for the purpose.

R.C. Pankhurst

Papers

The measurement of air flow

The measurement of pulsating flow

Examples from practice

The characteristics of pitot and static tubes in incompressible flow

The vane anemometer