Donald R. F. Harleman

Longitudinal and lateral dispersion in an isotropic porous medium

Coefficients of longitudinal and lateral dispersion were measured for steady uniform laminar flow through an isotropic porous medium. A unique experimental method for measuring lateral dispersion is described. It is found that the ratio of the coefficient of longitudinal dispersion D 1 to the coefficient of lateral dispersion D 2 is given by

Stability and mixing of a vertical plane buoyant jet in confined depth

\frac {D_1}{D_2} = \lambda \Re ^n

CuSO4 treatment of nuisance algal blooms in drinking water reservoirs

where λ and n are dimensionless coefficients dependent upon the pore-system geometry, and [real ] is the Reynolds number based on the seepage velocity, the average grain diameter, and the kinematic viscosity.

A wind-mixed layer model for solar ponds

A plane turbulent buoyant jet discharging vertically into a two-dimensional channel of confined depth is considered. The channel opens at both ends into a large outside reservoir, thus defining a steady symmetrical flow field within the channel. The analysis is aimed at two aspects, the stability and the bulk mixing characteristics of the discharge. A stable discharge configuration is defined as one in which a buoyant surface layer is formed which spreads horizontally and does not communicate with the initial buoyant jet region. On the other hand, the discharge configuration is unstable when a recirculating cell exists on both sides of the jet efflux. It is shown that discharge stability is only dependent on the dynamic interaction of three near-field regions, a buoyant jet region, a surface impingement region and an internal hydraulic jump region. The buoyant jet region is analysed with the assumption of a variable entrainment coefficient in a form corresponding to an approximately constant jet-spreading angle as confirmed by different experimental sources. The properties of surface impingement and internal jump regions are determined on the basis of control volume analyses. Under the Boussinesq approximation, only two dimensionless parameters govern the near-field interaction; these are a discharge densimetric Froude number and a relative depth. For certain parameter combinations, namely those implying low buoyancy and shallow depth, there is no solution to the conjugate downstream condition in the hydraulic jump which would satisfy both momentum and energy conservation principles. Arguments are given which interpret this condition as one which leads to the establishment of a near-field recirculation cell and, thus, discharge instability. The far-field boundary conditions, while having no influence on discharge stability, determine the bulk mixing characteristics of the jet discharge. The governing equations for the two-layered counterflow system in the far field are solved. The strength of the convective transport, and hence the related dilution ratio, is governed by another non-dimensional parameter, the product of the relative channel length and the boundary friction coefficient. Experiments in a laboratory flume, covering a range of the governing parameters, are in excellent agreement with the theoretical predictions, both the stability criterion and the bulk mixing characteristics.

Wind-mixing experiments for solar ponds

Since the turn of the century, copper sulfate has been used extensively as an algicide to control nuisance algal blooms in drinking water reservoirs Recent experimental results have shown that the toxicity of copper to algae is determined by the activity of ionic copper, and not the total copper concentration The sensitivity of algae to ionic copper has been found to vary considerably for different algal species Chemical processes such as precipitation, complexation by dissolved organic substances, and adsorption by suspended material can be important in controlling the chemical speciation of copper added to drinking water reservoirs The copper sulfate dosage required for effective treatment of a reservoir is shown to depend on water chemistry and the copper sensitivity of nuisance algal species By evaluating copper chemistry and copper sensitivity of nuisance algal species it may be possible to obtain effective treatment with lower copper sulfate dosages in some reservoirs

A comparison of velocity measurements using a laser anemometer and a hot‐film probe, with application to grid‐stirring entrainment experiments

Abstract A computer model is described which may be used for predicting transient salinity and temperature profiles in a salt gradient solar pond. It is intended for use in modeling large surface area ponds where wind-mixing would be expected to play an important part in the dynamics of the upper layer. The formulation predicts the depth of the upper convecting zone using a mixed-layer model which incorporates the wind-mixing algorithm described by Bloss and Harleman [1,2]. This is in contrast to earlier solar pond models which have generally assumed a constant value for this layer depth. Results have been obtained for a number of 1-yr simulations of a large hypothetical pond in Richmond, Virginia, and these have been used in testing the sensitivity of the model to several of the input parameters, including the radiation term and the form of the wind-mixing algorithm. The model output is also compared with field data from an operating solar pond and good agreement is found. Results have indicated that some measures will have to be taken to counteract the mixing action due to wind stress, if the upper mixed layer depth is to be maintained at an acceptable level. The model is expected to be useful in large-scale pond design.

Retrofitting Conventional Primary Treatment Plants for Chemically Enhanced Primary Treatment in the USA

Abstract Experiments are described in which wind-induced entrainment was measured in a laboratory tank under strongly stratified double-diffusive conditions in order to calibrate a numerical model for application to solar ponds. Results showed that there was no effect of double-diffusive stratification and that the entrainment followed approximately an inverse Richardson number relationship. Shear-induced mixing was found to play a strong role in the entrainment process, and it is suggested that an effort be made to obtain more data on wind-induced currents in operating solar ponds. An additional series of tests is also reported in which a preliminary investigation of the effectiveness of floating wave suppressors was carried out. These tests showed that the wave suppressors, consisting of either plastic netting or PVC pipes, were able to reduce average turbulence levels in the water, though it appears that there may be some enhanced mixing directly beneath the nets or pipes.

[Reply to “Did the Italian Government approve an obsolete project to save Venice?” by P.A. Pirazzoli] Obsolete? No. Necessary! Yes. The gates will save Venice

A laser‐Doppler anemometer has been used to measure the spatial decay of velocity fluctuations generated by a vertically oscillating grid in a laboratory tank. These velocity data were found to be in agreement with earlier studies using hot‐film probes, though a comparison of the length scales of the motions obtained with the two different probes is difficult. Normalized entrainment rates follow similar trends using values obtained either with the laser or with the hot film, though quantitatively some differences are seen. It is concluded that true turbulence does not exist for distances less than about two mesh spacings from the grid.

A comparison between measured wave properties and simple wave hindcasting models in shallow water

Chemically enhanced primary treatment (CEPT) has been in use for more than 100 years. However, it fell into disfavor in the 1930s when compared to biological treatment because the large concentrations of metal salts produced large quantities of sludge. In the USA, most of the emphasis on chemical treatment has been on phosphorus removal after biological treatment. However, Scandinavian and other European countries are focusing on phosphorus removal before biological treatment. Again, large concentrations of metal salts are needed to achieve low phosphorus effluents. With the technological advancements in polymer chemistry, it has become worthwhile to revisit chemically enhanced primary wastewater treatment with total suspended solids (TSS) and biochemical oxygen demand (BOD) removal as the focus. By replacing some of the metal salt with polymers, significant increases in TSS and BOD removals, compared to conventional primary settling, are possible. In addition, these higher removals are obtained at overflow rates twice that of conventional primary settling.

The approximation of nonlinearities in the filtered Navier-Stokes equations

We are confused by Paolo Antonio Pirazzolis argument in these pages that the proposed sea gates to protect Venice from flooding by exceptional tides will not work in the event of sea-level rise. In fact, the two case studies he provides show that they would protect the city. In his examples, Pirazzoli arbitrarily adds a very large, 50-cm sea-level rise to the peak level of the October 1976 flood, which was a week-long event. A 50-cm rise in sea level corresponds to the Intergovernmental Panel on Climate Changes central value within an extraordinary range that he cites as 9-88 cm of sea-level rise at the end of 100 years. Even if one accepts this number, given the range of uncertainty, recall that it is the assumed sea-level rise at the end of 100 years.