Flow measurements adiabatic

The mass flow rate under adiabatic conditions is always somewhat greater than that under isothermal conditions, but the difference is normally <20%. In fact, for long piping systems (L/D > 1000), the difference is usually less than 5% (see, e.g., Holland, 1973). The flow of compressible (as well as incompressible) fluids through nozzles and orifices will be considered in the following chapter on flow-measuring devices. 

The scope of coverage includes internal flows of Newtonian and non-Newtonian incompressible fluids, adiabatic and isothermal compressible flows (up to sonic or choking conditions), two-phase (gas-liquid, solid-liquid, and gas-solid) flows, external flows (e.g., drag), and flow in porous media. Applications include dimensional analysis and scale-up, piping systems with fittings for Newtonian and non-Newtonian fluids (for unknown driving force, unknown flow rate, unknown diameter, or most economical diameter), compressible pipe flows up to choked flow, flow measurement and control, pumps, compressors, fluid-particle separation methods (e.g.,... 

Parameters of the Bingham Model from Measurements of Pressure Drops in a Line 107 Pressure Drop in Power-Law and Bingham Flow 110 Adiabatic and Isothermal Flow of a Gas in a Pipeline Isothermal Flow of a Nonideal Gas 113 Pressure Drop and Void Fraction in Liquid-Gas Flow Pressure Drop in Flow of Nitrogen and Powdered Coal 120... 

The heat capacity of a gas at constant pressure is nonually detenuined in a flow calorimeter. The temperature rise is detenuined for a known power supplied to a gas flowing at a known rate. For gases at pressures greater than about 5 MPa Magee et al [13] have recently described a twin-bomb adiabatic calorimeter to measure Cy. 

Total pre.ssure is the pressure of the gas brought to rest in a reversible adiabatic manner. It can be measured by a pitot tube placed in the flow... 

The micro-channels utilized in engineering systems are frequently connected with inlet and outlet manifolds. In this case the thermal boundary condition at the inlet and outlet of the tube is not adiabatic. Heat transfer in a micro-tube under these conditions was studied by Hetsroni et al. (2004). They measured heat transfer to water flowing in a pipe of inner diameter 1.07 mm, outer diameter 1.5 mm, and 0.600 m in length, as shown in Fig. 4.2b. The pipe was divided into two sections. The development section of Lj = 0.245 m was used to obtain fully developed flow and thermal fields. The test section proper, of heating length Lh = 0.335 m, was used for collecting the experimental data. 

Qu W, Mudawar I (2002) Prediction and measurement of incipient boiling heat flux in micro-channel heat sinks. Int J Heat Mass Transfer 45 3933-3945 Qu W, Mudawar I (2004) Measurement and correlation of critical heat flux in two-phase micro-channel heat sinks. Int J Heat Mass Transfer 47 2045-2059 Quiben JM, Thome JR (2007a) Flow pattern based two-phase pressure drop model for horizontal tubes. Part I. Diabatic and adiabatic experimental study. Int. J. Heat and Fluid Flow. 28(5) 1049-1059... 

Two-phase flows containing other types of fluids of interest are those of helium and refrigerants. The former fluid is used for cooling different superconductivity devices, while the latter are used in the refrigeration industry. The pressure drop in a two-phase flow of helium in a tube of 1.6 mm (0.06 in.) I.D. under adiabatic conditions and with heat supply were reported by Deev et al. (1978). They indicated that although the actual measured AP (at P = 1.0 to 1.8 X 10s N/m2) differed... 

A survey of the literature shows that although very different calorimeters or microcalorimeters have been used for measuring heats of adsorption, most of them were of the adiabatic type, only a few were isothermal, and until recently (14, 15), none were typical heat-flow calorimeters. This results probably from the fact that heat-flow calorimetry was developed more recently than isothermal or adiabatic calorimetry (16, 17). We believe, however, from our experience, that heat-flow calorimeters present, for the measurement of heats of adsorption, qualities and advantages which are not met by other calorimeters. Without entering, at this point, upon a discussion of the respective merits of different adsorption calorimeters, let us indicate briefly that heat-flow calorimeters are particularly adapted to the investigation (1) of slow adsorption or reaction processes, (2) at moderate or high temperatures, and (3) on solids which present a poor thermal diffusivity. Heat-flow calorimetry appears thus to allow the study of adsorption or reaction processes which cannot be studied conveniently with the usual adiabatic or pseudoadiabatic, adsorption calorimeters. In this respect, heat-flow calorimetry should be considered, actually, as a new tool in adsorption and heterogeneous catalysis research. 

Let us reconsider the critical flame temperature criterion for extinction. Williams [25], in a review of flame extinction, reports the theoretical adiabatic flame temperatures for different fuels in counter-flow diffusion flame experiments. These temperatures decreased with the strain rate (ua0/x), and ranged from 1700 to 2300 K. However, experimental measured temperatures in the literature tended to be much lower (e.g. Williams [25] reports 1650 K for methane, 1880 K for iso-octane and 1500 K for methylmethracrylate and heptane). He concludes that 1500 50 K can represent an approximate extinction temperature for many carbon-hydrogen-oxygen fuels burning in oxygen-nitrogen mixtures without chemical inhibitors . 

The isothermal and isoperibol calorimeters are well suited to measuring heat contents from which heat capacities may be subsequently derived, while the adiabatic and heat-flow calorimeters are best suited to the direct measurement of heat capacities and enthalpies of transformation. 

Measurement of Performance The amount of useful work that any fluid-transport device performs is the product of (1) the mass rate of fluid flow through it and (2) the total pressure differential measured immediately before and after the device, usually expressed in the height of column of fluid equivalent under adiabatic conditions. The first of these quantities is normally referred to as capacity, and the second is known as head. 

Engl transln in Soviet Physics, Doklady 5, 337-40(1960) CA 55, 24013(1961) (Measurement of adiabatic shock waves in cast Trotyl, crystalline Hexogen and Nitromethane) 65) Dunkle s Syllabus (1960-1961) Shock Waves, which includes Mathematical Background (Sessions 1 2) Fluid Flow (Session 3) Initiation of Shock Waves (Session 4) Properties of Shock Waves (Session 5) Shock Relationships and Formulas (Session 6) Shock Wave Interactions (Sessions 7 8) 66) B.D. 

Rapid aerodynamic flow past obstacles involves adiabatic compressions and rarefactions, and is influenced by relaxation of internal degrees of freedom in a way similar to shock phenomena. This effect has been quantitatively treated by Kan-trowitz18, who developed a method for obtaining relaxation times by measuring the pressure developed in a small Pitot tube which forms an obstacle in a rapid gas stream. This impact tube is not a very accurate technique, and requires a very large amount of gas it has been used to obtain a vibrational relaxation time for steam. 

In some respects, adiabatic calorimetry provides information which is complementary to that provided by heat-flow calorimetry. The latter allows a study to be made of the full composition range at constant temperature, whereas the adiabatic calorimetry study is carried out over the prescribed range of temperature with a constant amount of adsorptive in the adsorption cell (of course, this does not mean that a constant amount is adsorbed). Adiabatic calorimetry allows direct measurements of the heat capacities of adsorbed films, although they are difficult to make accurately... 

For an adiabatic reactor, we may be able to control temperature and conversion using the initiator feed flow (Fig. 4.38). Incomplete conversion introduces recycle streams for the monomer. Because of the effect of chain transfer agents, we often must be able to measure the feed compositions to the reactor. Further, we must know what the chain transfer agents do if they are dominant variables to have any chance of controlling the molecular weight. So our control will only be as good as our correlations or models. Hence in polymer reactors we often have to use what is basically steady-state control on the setpoints of the dominant variables to achieve many of the control objectives that de-... 

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