Publisher Summary This chapter discusses the heat transfer and the hydraulic resistance of single tubes, and the banks of tubes of various arrangements in flows of gases and viscous liquids. The focus is on the important problems of the heat transfer and the hydraulic resistance of tubes, in particular with the heat transfer of single tubes, banks of tubes, and systems of tubes in crossflow. The chapter also highlights the influence of the physical properties of fluids on heat transfer. Extensive experimental data will be analyzed and will include investigations of banks of tubes of various arrangements, and a single tube in crossflow in the range of Prandtl number from 0.7 to 500 and that of Reynolds number from 1 to 2xl0 6 .

Heat Transfer from Tubes in Crossflow

The scientific understanding of the molecular size and shape of humic substances (HS) is critically reviewed. The traditional view that HS are polymers in soil is not substantiated by any direct evidence but is assumed only on the basis of laboratory experiments with model molecules and unwarranted

The supramolecular structure of humic substances

Publisher Summary Accurate knowledge of the overall convective heat transfer from circular cylinders is of importance in a number of fields, such as boiler design, hotwire anemometry, and the rating of electrical conductors. The wide dispersion in the published experimental data for the heat transfer from smooth circular cylinders by natural and forced convection is attributed to various factors associated with the experiments. The error due to heat conduction to the supports is particularly important with natural convection, especially where the heat loss and the temperature rise of the cylinder are calculated from the voltage drop across it. A common cause of error is the use of too small a space ratio, so that the temperature and velocity fields are distorted. To reduce this error to less than l%, the space ratio D c /D for natural convection or D T /D for forced convection should exceed 100. The error caused by blockage with wind tunnel measurements can be calculated depending on the type of tunnel. One of the greatest sources of error with forced convection is the failure to allow for the effect of stream turbulence.

The Overall Convective Heat Transfer from Smooth Circular Cylinders

Kinetic data are needed to develop basic understanding of fermentation processes and to permit rational design of continuous fermentation processes.

The kinetics of the fermentation of glucose to lactic acid have been studied at six constant pH levels between 4·5 and 6·0 by measuring the instantaneous rates of bacterial growth and of lactic acid formation throughout each fermentation.

It was found that the instantaneous rate of acid formation dP/dt, could be related to the instantaneous rate of bacterial growth dN/dt, and to the bacterial density N, throughout a fermentation at a given pH, by the expression 



where the constants α and β are determined by the pH of the fermentation.

A kinetic study of the lactic acid fermentation. Batch process at controlled pH

The scientific understanding of the molecular structure of humic substances is critically reviewed here. The traditional view that humic substances are polymers in soil is not substantiated by any direct evidence but only assumed on the basis of laboratory experiments with model molecules and unwarranted results by incorrectly applying either analytical procedures or mathematical treatments developed for purified and undisputed biopolymers. A large body of evidence instead shows an alternative understanding of the conformational nature of humic substances which should be regarded as supramolecular associations of self-assembling heterogeneous and relatively small molecules deriving from the degradation and decomposition of dead biological material. A major aspect of the humic supramolecular structure is that it is predominantly stabilized by weak dispersive forces instead of covalent linkages. Hydrophobic (van der Waals, π-π, CH-π) and hydrogen bonds are responsible for the apparent large molecular size of humic substances, the former becoming more important with the increase of pH. Such novel description of humic substances structure better accounts for their essential role in providing and maintaining soil physical and chemical quality and their reactivity towards pesticides and other environmental soil contaminants. This innovative understanding of the nature of humic substances implies a further development of the science and technology for the control of the chemistry and dynamics of natural organic matter in the soil and the environment.

Edgar L. Piret

Papers

Simultaneous Heat and Mass Transfer in Free Convection

Continuous Flow Stirred Tank Reactor Systems

Crushing of Single Particles of Crystalline Quartz - Application of Slow Compression

Heat Transmission from Fine Wires to Water - Low Velocity Data and Correlation

Effect of Continuously Controlled pH on Lactic Acid Fermentation