Heat-transfer studies

Chen, J. C., and S. Kalish, 1970, An Experimental Investigation of Two-Phase Pressure Drop for Potassium with and without Net Vaporization, 4th Int. Heat Transfer Conf., Paris-Versailles. (3) Chen, J. C., et al., 1966, Heat Transfer Studies with Boiling Potassium, Nuclear Eng. Dept., Brookhaven Natl. Lab. Annual Report, BNL-50023 (S-69), pp. 52-54, Brookhaven, NY. (4)... 

Heat-Transfer Studies Fitting General Form I... 

The concept of a fluidized bed consisting of electrically conducting particles as a statistically continuous electrode was first discussed by Le Goff et al. (Lie). Interesting similarities with heat-transfer studies in fluidized beds may be exploited to advantage by use of the limiting current method. 

From this discussion of parameter evaluation, it can be seen that more research must be done on the prediction of the flow patterns in liquid-liquid systems and on the development of methods for calculating the resulting holdups, pressure drop, interfacial area, and drop size. Future heat-transfer studies must be based on an understanding of the fluid mechanics so that more accurate correlations can be formulated for evaluating the interfacial and wall heat-transfer coefficients and the Peclet numbers. Equations (30) should provide a basis for analyzing the heat-transfer processes in Regime IV. 

Mochizuki, T. Mori, Y.H. (2006). Clathrate-hydrate film growth along water/hydrate-former phase boundaries - numerical heat-transfer study. J. Crystal Growth, 290 (2), 642-652. 

In summary it may be stated that all available data of known reliability support the Orr-DallaValle conclusion that thermal conductivities of suspensions may be calculated by means of Eq. (35). This does not prove that the other effects (such as particle size) do not in actuality influence the thermal conductivity of suspensions, but rather that within the ranges of particle sizes (2 to 260 v) and Reynolds numbers (3,000 to 3 X 106) investigated, the effects were too small to be measurable. In view of the over-all conclusions (at the end of this section) in regard to the utility of further heat transfer studies in this field, it is not recommended that a more detailed investigation of the thermal conductivity of suspensions be undertaken at this time. 

D7. Dunn, L. G., Powell, W. B., and Seifert, H. S., Heat Transfer Studies Relating to Power Plant Development, Roy. Aeronaut. Soc. 3rd Anglo-American Aeronaut. Con., 1951. 

Morice, L., Bourbigot, S., and Leroy, J.M. 1997. Heat transfer study of polypropylene-based intumescent systems during combustion. J. Fire Sci., 15 358-374. 

Heat transfer studies on fixed beds have almost invariably been made on tubes of large diameter by measuring radial temperature profiles (1). The correlations so obtained involve large extrapolations of tube diameter and are of questionable validity in the design of many industrial reactors, involving the use of narrow tubes. In such beds it is only possible to measure an axial temperature profile, usually that along the central axis (2), from which an overall heat transfer coefficient (U) can be determined. The overall heat transfer coefficient (U) can be then used in one--dimensional reactor models to obtain a preliminary impression of longitudinal product and temperature distributions. 

In the last section, convection in a two-dimensional porous medium is presented as a physical problem. Porous media is important in environmental heat transfer studies, transpiration cooling, and fuel cells, as some examples. Using the slug flow assumption, the energy equation is solved using an alternating implicit method to show its effectiveness. 

Sunkoori, N. R., and Kaparthi, R., Heat Transfer Studies between Particles and Liquid Medium in a Fluidized Bed, Chem. Eng. Sci. 12,166-174 (1960). 

Most heat transfer studies were carried out under ambient conditions and with fine particles in small experimental sets. Though exhaustive reviews have been presented (e.g., Grace, 1986 Glicksman, 1988 Leckner, 1990), the data obtained at Tsing Hua University (Bi and Jin, 1989, 1990 Bai and Jin, 1992) will be the focus of this discussion and will be compared to the results of other researchers. 

Now that we have introduced the heat convection coefficient, we will define our first dimensionless number, the Nusselt number, which is used in heat transfer studies. We represent the size of a particular plant part by a characteristic dimension d, which for a flat plate is the quantity / in Equation 7.10 and for a cylinder or sphere is the diameter. This leads to... 

EXPERIMENTAL DETAILS OF HEAT TRANSFER STUDIES IN BUBBLE COLUMNS... 

The earliest heat-transfer studies neglected the effective axial conduction term as this was expected to be negligible by comparison with the bulk-flow term in the long beds typically used in industry. Axial dispersion was also neglected in mixing studies, and experiments by Hiby (1 ) confirmed the absence of axial... 

In heat transfer studies we are interested in thermal radiation, which is the fonn of radiation emitted by bodies because of their temperature. It differs from other foniis of electromagnetic radiation such as x-rays, gamma rays, microwaves, radio waves, and television waves that are not related to temperature, All bodies at a temperature above absolute zero emit thermal radiation. 

In fluid flow and heat transfer studies, the ratio of dynamic viscosity to density appears frequently. For convenience, this ratio is given the name kinematic viscosity v and is expressed as v = filp. Two common units of kinematic viscosity are m /s and stoke (1 stoke = 1 cm /s = 0.0001 mVs). 

The friction coefficient is an important parameter in heat transfer studies since it is directly related to the heat transfer coefficient and the power requirements of the pump or fan. 

In heat transfer studies, the primary variable is temperature, and it is desirable to express the net buoyancy force (Eq. 9-2) in terms of temperature differences. But this requires expressing the density difference in terms of a temperature difference, which requires a knowledge of a property that represents the variation of the density of a fluid with temperature atconstant pressure. The property that provides that information is the volume expansion coefficient /3, defined as (Fig. 9-4)... 

Discussion Because of the convenience it offers, naphthalene has been used in numerous heat transfer studies to determine convection heat transfer coefficients. 

Mahulikar, S.P., PhD Thesis, Heat Transfer Studies in Microchannels, School of Mechanical and Production Engineering, Nanyang Technological University, Singapore, 1999. 

For an extended review of experimental work on mini and microchannels, the reader is refered to the Thome (2004) and Kandlikar (2002) papers. This brief review covers a representative selection of heat transfer studies in minichannels and its aim is to illustrate the tendencies observed in the presented data. Recently Kandlikar (2004) developed a new general correlation adapted to minichannels which gives very good results for low qualities but fails to take dry-out into account, as noted by the author in question. Lately Thome et al. (2004) and Dupont et al. (2004) proposed a semi-empirical three zone model which is the only published work to predict the unique trends observed in minichannels. In this model the dominant boiling mechanism is the evaporation of the liquid film pressed under confined bubbles. 

Figure 14. Experimental apparatus for boiling heat transfer study and sehematie diagram of test section.

Nusselt number. A value used in heat-transfer studies and calculations to compare heat losses by conduction from various shaped objects under various conditions. It is combined into a single number that is the function of the actual heat loss (g), the temperature difference (AT) between the body and its surroundings, the size (d) and shape of the body, and the thermal conductivity (k) of the fluid surrounding the object, in the equation Nu = Qd/NTk. 

It is noted that Sideman and Pinczewski [135], among others, have examined this hypothesis in further details and concluded that there are numerous requirements that need to be fulfilled to achieve similarity between the momentum, heat and mass transfer fluxes. On the other hand, there are apparently fewer restrictions necessary to obtain similarity between heat and low-flux mass transfer. This observation has lead to the suggestion that empirical parameterizations developed for mass transfer could be applied to heat transfer studies simply by replacing the Schmidt number Sct = ) by the Prandtl number Prt = and visa versa. 

Dimensional analysis. In the absence of an analytical solution or analogy between heat and momentum transfer, the (dimensionless) heat transfer coefficient may be obtained from the correlation of experimental data in terms of appropriate dimensionless numbers obtained from a dimensional analysis. In Section 5.3 we shall review the foundations of dimensional analysis in a manner particularly suited to heat transfer studies. 

So far, we have learned the evaluation of heat transfer by analytical means and by the analogy between heat and momentum transfer. When an analytical solution is beyond our reach, or when there exists no analogy between momentum and heat, we rely on experimental measurements. Dimensional analysis provides an effective way of organizing experimental data. The next section is devoted to a review of the methods of dimensional analysis, arranged in a manner particularly suitable to heat transfer studies. 

Local heat transfer measurements were carried out in the once-through system for the same aqueous polyacrylamide solutions used in the friction factor and viscosity measurements shown in Figs. 10.22 and 10.23 [37, 93]. These heat transfer studies involving a constant heat flux boundary condition required the measurement of the fluid inlet and outlet temperatures and the local wall temperature along the tube. These wall temperatures are presented in terms of a dimensionless wall temperature 0 in Fig. 10.27 for four selected concentrations. Here 0 is defined as... 

The solid line in the figure represents the general trend of the experimental observations of Refs. 35 and 85, confirming the fact that the heat transfer reduction always exceeds the friction factor reduction. This contradicts the common assumption of the validity of the Reynolds or Colburn analogy made in a number of heat transfer studies of viscoelastic fluids [101-106],... 

Enhancement of Pool Nucleate Boiling Heat Transfer. Study of the enhancement of boiling heat transfer has been one of the fastest-growing areas of research in recent years. The annual publication rate in this area has grown to around 300 papers per year (Bergles [135]). 

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