Rohsenow equation

Although these two forms of analysis give rise to somewhat similar expressions, the basic terms are evaluated in quite different ways and the final expressions show many differences. Some data fit the Rohsenow equation reasonably well<88), and other data fit Forster s equation. 

The condition of the heater surface greatly affects heat transfer, and the Rohsenow equation given above is applicable to clean and relatively smooth surfaces. The results obtained using the Rohsenow equation can be in error by 100% for the heat tran.sfer rate for a given excess temperature and by d"30% for the excess temperature for a given heat transfer rate. Therefore, care should be exercised in the interpretation of the results. 

Recall from thermodynamics that the enthalpy of vaporization hyg of a pure substance decreases with increasing pressure (or temperature) and reaches zero at the critical point. Noting that hfg appears in the denominator of the Rohsenow equation, wc should see a significant rise in the rate of heat transfer at high pressures during nucleate hniling. 

An equation of the Nusselt type has been suggested by Rohsenow... 

The equations provide reasonable estimates per Rohsenow, who suggests using with caution, only when performance on the system is not available. Ganapathy offers simplified equations and nomographs to solve these relations. 

Sato and Matsumura (1964), and Bergles and Rohsenow (1964) have proposed the equation for the incipient boiling condition in the case that surface cavities of all sizes are available for nucleation. Hino and Ueda (1985) studied incipient boiling of fluorocarbon R-113 in a stainless steel tube of d = 1 mm at mass velocity G = 158—1,600 kg/m s, and inlet subcooling ATsub,m = 7s — Tin ranged from 10-... 

Yoder showed that radiation heat transfer and axial conduction heat transfer in the tube wall have a negligible effect on predicting wall temperatures. The following equations were used by Yoder and Rohsenow (1980) as well as previous investigators such as Bennett et al. (1967b), Hynek (1969), and Groeneveld (1972). 

It is not surprising that the foregoing equation is imperfect and contains a coefficient which is constant for one liquid-solid system only. Rather it is surprising that an equation based on the idea of a controlling macroconvection and on empirical relationships such as Eqs. (2) and (3) should fit any real system. An example of the suitable agreement between Addoms data for water on a platinum wire, Fig. II, and Rohsenow s equation is shown in Fig. 

In one respect Eq. (20) is satisfying. The exponents on the Reynolds and Prandtl numbers are roughly the same as those used for ordinary forced-convection heat transfer. The negative sign on the Prandtl-number exponent in Rohsenow s equation has seemed illogical to many scientists. The logical exponents found by Forster and Zuber... 

In addition to the equations of Rohsenow and of Forster and Zuber, which are the most theoretical equations now available, there exist many equations which are simply empirical correlations. Little pretense is made that these additional equations are defensible on theoretical grounds beyond simple dimensional analysis. A few of these are given below. 

Data from a single laboratory for tubes of different diameters are needed. Tubes are thicker than the bubbles produced, but the reverse is true for wires. The diameter effects may not be the same in the two cases. The equations of Rohsenow and of Forster and Zuber predict that the geometric arrangement is of no consequence. The prediction is not proved at present. 

Rohsenow [32] has improved on the above analysis by performing an integral analysis that drops the assumption of a lirjear temperature protile. Based on this analysis, the following equation for the modified latent heat is recommended ... 

An equation of the Nusselt type has been snggested by Rohsenow [Trans. Am. Soc. Mech. Eng., 74, 969 (f952)]. 

It follows from this that, under the assumptions made, the specific enthalpy hi, of the flowing condensate is independent of the film thickness. The equation further shows that the enthalpy of vaporization Ahv in the equations for Nusselt s film condensation theory has to be replaced by the enthalpy difference Ah. If we additionally consider that the temperature profile in the condensate film is slightly curved, then according to Rohsenow [4.10] in place of (4.27), we obtain for Ah the more exact value... 

D. P. Traviss, W. M. Rohsenow, and A. B. Baron, Forced Convection Condensation inside Tubes A Heat Transfer Equation for Condenser Design, ASHRAE Trans., 79, pp. 157-165,1972. 

Rohsenow and Griffith propose a correlation for peak flux represented by equation (1). Their correlation is based upon considerable experimental data for the boiling of organic liquids and water ... 

For horizontal tube, L is replaced by the tube diameter, D, and constant 0.943 becomes 0.725. An improvement to the Nusselt model was made by Rohsenow (1956) who considered the effects of subcooling within the liquid film and also allowed for a nonlinear distribution of temperature through the film due to energy convection. The latent heat of vaporization, / fg, was replaced by a modified form /zfg = /Zfg + 0.68Cpf(Tsat - Ts ) in the above equation. 

Reif F (1967) Statistical physics. McGraw-HiU Book Company, New York Resibois P, De keener M (1977) Classical kinetic theory of fluids. Wiley, New York Reyes Jr JN (1989) Statistically derived conservation equations for fluid particle flows. Nuclear thermal hydraulics 5th winter meeting. In Proceedings of ANS winter meeting Rohsenow WM, Choi H (1961) Heat, mass, and momentum transfer. Pretice-HaU Inc, Englewood Cliffs... 

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