Flow, adiabatic diabatic

Total Pressure is the pressure that would occur if the fluid were brought to rest in a reversible adiabatic process. Many texts and engineers use the words total and stagnation to describe the flow characteristics interchangeably. To be accurate, the stagnation pressure is the pressure that would occur if the fluid were brought to rest adia-baticaUy or diabatically. 

The plot of the pressure drop depending on the bulk velocity in adiabatic and diabatic flows is shown in Fig. 3.6a,b. The data related to the adiabatic flow correspond to constant temperature of the fluids Tjn = 25 °C, whereas in the diabatic flow the fluid temperature increased along micro-channel approximately from 40 to 60 °C. It is seen that in both cases the pressure drop for Habon G increases compared to clear water. The difference between pressure drop corresponding to flows of a surfactant solution and solvent increases with increasing bulk velocity. 

Fig. 3.6a,b Dependence of pressure drop on fluid bulk velocity in (a) adiabatic flow, and (b) diabatic flow. Reprinted from Hetsroni et al. (2004) with permission... 

For flow of some kind of surfactant solutions (Habon G solutions at concentration 530 and 1,060 ppm) in the tube of d = 1.07 mm in the range of Reynolds number based on solvent viscosity Re = 10-450, the increase of pressure drop in adiabatic and diabatic conditions was observed compared to that of pure water. 

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... 

The absence of heat flow may be a result of the walls not permitting the transfer of thermal energy. Boundaries of this kind are called adiabatic. (Adiabatic walls are infinitely good thermal insulators.) If the walls are non-adiabatic (sometimes called diabatic or diathermal) and do permit heat transfer, but it does not occur, we say that the system is at thermal equilibrium with its surroundings. 

Figure 7 The vapour flow (mol s) and heat exchanger load (kW) in an optimised diabatic column and an adiabatic column. Both columns separate an equirrwlar mixture of toluene and benzene...

Here two different airfoils are Investigated, the circular arc CA-0.1 (thickness ratio of 10 %) and the NACA-0012, Due to the approximately constant cooling rate at local Mach numbers close to one the circular arc airfoil allows some simplifications. The value at Mach number one, denoted by the star, represents the time scale at the entire transonic airfoil section, whereas the cooling rate at the NACA-0012 changes considerably. Condensation onset Mach numbers very close to one are correlated with higher cooling rates and vice versa (Table 1). Usually it is assumed that the temperature gradients in adiabatic flow and with heat addition are identical up to the condensation onset for free stream Mach numbers M < 1, too. However, the numerical results of diabatic flows show a more or less pronounced precompression... 

Fig.7. Condensing flow around a NACA-0012 - static pressure distribution - right, from top Mach number contours adiabatic (M > 1, AM = 0.015), diabatic, condensate mass fraction contours (Ag = 2 g/kg)...

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