Counterflow Process Research Articles

A low-order dynamic model of counterflow heat exchangers for the purpose of monitoring transient and steady-state operating phases

We present a model-based real-time method to monitor a counterflow heat exchanger’s thermal performance for all operating conditions. A first principle reference model that describes the reference counterflow process in an accurate manner is derived first. Real gas behavior is taken into account. Without simplifications, the respective equations must be solved in an iterative, computationally expensive manner, which prohibits their use for real-time monitoring purposes. Therefore, we propose one-step-solvable model equations, resulting in an approximate but quick model, which is able to track an important thermal property reliably. The monitoring, i.e., the online estimation of the thermal properties, is achieved via a nonlinear Kalman-Filter. Due to the low-order dynamic model formulation, the overall monitoring scheme is accompanied by an acceptable computational burden. Moreover, it is easy to deploy and to adapt in industrial practice. Monitoring results, where the reference model replaces a real process with supercritical carbon dioxide, are given and discussed herein.

Osmo-dehydration of Plums and Berries - A Review

The influence of different osmotic dehydration methods on morphological and nutritional attributes of plums and berries has been reviewed and presented in this review. Several researches have been done for retention of bioactive compounds varying osmotic conventionally drying solution, brix, critical moisture content, drying temperature, drying time and methodology of osmotic dehydration process. Osmotic dehydration is a counter flow process which results in solids gain or impregnation, enhancing the textural and rheological properties of plum and related fruits. Osmotically dehydrated plums require less drying time than which results into improved overall quality. Reviews suggested that various osmotic agents with low molecular weight lead to higher water loss. Osmotic dehydration improves the overall quality of plums and berries as compared to the conventional drying methods.

蒸发式冷凝器传热传质数值模拟研究

采用VOF法，建立二维水蒸气传热传质顺流和逆流的计算模型，计算所得的平均液膜厚度模拟值比实验测量值大3.03%~6.90%，比Nusselt理论的预测值大8.33%~10.34%，在合理的误差范围，说明该模型切实可行。运用该模型计算并分析水与空气顺流和逆流过程中，液态水的流动分布、空气与水流速度分布以及空气中水蒸气的质量含量分布情况，结果表明：在气–液两相逆流过程的气–液界面的总传热量中，潜热传热量所占比值在90%以上，比气–液两相顺流时高，在气–液相界面处是以水蒸发传质引起的潜热换热为主、温差引起的显热传热为辅的换热形式，逆流比顺流更有利于传热。 The VOF (volume of fluid) method is used to establish a two-dimensional water vapor heat and mass transfer parallel flow and counter flow model. The deviation of calculated film thickness, which is changed with Re values, is greater than the experimental measurement’s value by 3.03% - 6.90%, and the predicted value of the Nusselt theory by 8.33% - 10.34%; it indicates that the model is feasible. The model is used to calculate and analyze liquid water flow distribution, air and water quality and velocity distribution, water vapor quality content distribution in the air, in water and air’s parallel flow and counter flow processes. The results show that: in gas-liquid two- phase counter flow process, the ratio of latent heat transfer rate in total heat transfer rate is above 90% at gas-liquid interface, higher than that of gas-liquid two-phase parallel flow; at air-liquid interface, the main heat transfer is latent heat transfer caused by water’s evaporation and mass transfer, and the supplemented heat transfer is sensible heat transfer caused by temperature difference; counter flow is more conducive to heat transfer than parallel flow.

ANALYSIS ON MEMBRANE HEAT EXCHANGER APPLIED TO ABSORPTION CHILLER

A novel membrane heat exchanger was proposed and analyzed. It was expected that the novel heat exchanger could be applied to the lithium bromide absorption chiller. Polyvinylidene fluoride hollow fiber module was adopted as the solution heat exchanger. The hot feed solution from the generator flowed into the lumen side of the membranes while the cold feed solution from the absorber flowed away from the shell side. Heat transfer and mass transfer occurred simultaneously in the membrane module, and only water vapor could diffuse across the membrane pore due to the water vapor pressure difference between the inside and outside of the membrane. Mathematical equations of the heat and mass transfer processes in the membrane heat exchanger were built, and the parallel flow process and the counter flow process were compared by numerical simulation. The simulation results show that the counter flow process was the better flow mode because the mean temperature difference was larger and the mass transfer was more steadily from the lumen side to the shell side. The heat caused by water vapor mass transfer may account for one-third of the total heat transfer. As a result, the membrane heat exchanger not only reinforced the heat recovery but also enlarged the deflation range and reduced the circulation rate and the heat loads of the generator and absorber. Eventually, the coefficient of performance of the heat exchanger was increased.

Evaluation of the correlation of the drift coefficients of random nterdiffusion processes

Random processes, specifically diffusion and wave processes, as well as the random process of crossing of two counterflows are studied. A relation is obtained for the probability distribution for the crossing process for discrete and continuous distributions of the random quantities. Examples of the density distribution of a crossing process are examined. The crossing properties of Gaussian processes are studied. A great deal of attention is devoted to wave corrections to the diffusion equation. The wave equation for the evolution of the probability density function is examined, and the wave coefficient is obtained for the particular case of random counterflow processes. A method of evaluating the drift correlation coefficients for random counterflow processes is developed. Algorithms are proposed for statistical modeling of the distribution function for the crossing process: Monte Carlo numerical modeling and an analytical-statistical method. A comparative characteristic is given for both methods.

Co-firing used engine lubrication oil with LPG in furnaces

Abstract Combustion and heat transfer characteristics obtained based co-firing LPG with used engine oils (UEO) in a furnace, are investigated experimentally. In an attempt to assess UEO as a fuel, the UEO-based results are compared with results obtained using two other fuels, namely diesel, and a used cooking oil (UCkO). To ease its admission to the furnace and its subsequent vaporization and combustion, UEO is preheated by allowing it to flow upwardly in a vertical pipe surrounded by hot gases generated from LPG combustion. UEO that reaches the tip of the pipe un-vaporized, spills and hence has the chance to further heatup and vaporize as it exchanges heat with the upwardly flowing LPG combustion gases, in a counter flow process. Runs are divided into three groups based on the mass ratio of the liquid-fuel/LPG and the mass flow rate of the LPG supplied to the furnace. Ranges of these quantities over which UEO qualify as a good fuel and/or good promoter to radiation have been identified.

Process design for the removal of residual monomer from latex products using supercritical carbon dioxide

One of the most important environmental incentives for the polymer industry is to reduce the residual monomer in polymer products. Although several techniques are available for the removal of residual monomer, most methods are rather energy intensive and time consuming. Since supercritical carbon dioxide (scCO 2) is known to have a plasticizing effect on many polymers and is a good solvent for most commonly used monomers, a scCO 2-based process forms an interesting alternative. This paper focuses on the development of a post-emulsion polymerization process, which decreases the amount of methylmethacrylate (MMA) in polyMMA lattices using scCO 2. Typically, the method comprises a counterflow process, in which part of the residual monomer is converted by the increased diffusion inside the polymer particles due to the swelling by scCO 2. In addition, the amount of residual monomer is further reduced by the extraction capacity of scCO 2. Experimental studies have shown that the scCO 2 extraction of MMA is the predominant effect as compared to the enhanced polymerization due to plasticization. From a mass transfer model, the largest resistance in the extraction process appears to be situated in the water phase near the scCO 2 interface due to a relatively small surface area as compared to the overall polymer–water interfacial area. A viability study, including equipment sizing and economic evaluation, has shown that the removal of residual monomer from latex products using scCO 2 in principle yields a process which is both technically and economically feasible, capable to meet the future requirements.

Saturation of the thermoacoustic separation of a binary gas mixture

Spoor and Swift have previously shown [Phys. Rev. Lett. 85, 1645–1649 (2000)] that sound waves can produce the separation of a binary mixture of gases in a duct. This phenomenon is caused by the conspiracy of two effects at the thermoviscous boundary layer: (i) oscillating temperature gradients drive thermal diffusion perpendicular to the direction of sound propagation; and (ii) viscosity sets up a time-averaged counterflow process. In order to assess the relevance and potential uses of this mechanism, it is important to determine the concentration gradient at which the separation process saturates. Here, it is shown that the saturation is determined primarily by ordinary diffusion and by a remixing flux due to the oscillatory motion. Both of these remixing processes are proportional to the concentration gradient, but only the latter process depends on the acoustics, being proportional to the squared volume flow rate and inversely proportional to the frequency. For He–Ar mixtures, saturation concentration gradients near 10%/m have been achieved, in agreement with detailed calculations of these processes. Evidence to date supports the possibility of more challenging separations, e.g., of isotopes. [Work supported by the DOE Office of Basic Energy Sciences.]

Heat and mass transfer processes in connected saturated He II baths

We report on a preliminary experiment designed to study combined heat and mass transfer processes associated with two-phase vapour/He II flow systems. The experiment consists of two separate baths connected by two channels, the upper one being for vapour flow and the lower one containing He II. Thus, the experiment simulates a two-phase flow with constant and known void fraction. Heat transfer between the two baths is governed by the counterflow process in the lower tube and vapour mass flow in the upper tube. Steady state and dynamic models, based on the energy and momentum equations, agree well with experimental results. We also explore the use of a porous plug in the lower channel to compensate for the level changes in the two baths.

Counter-flow liquid injection plasma synthesis of spinel powders

A novel counter-flow liquid injection plasma synthesis (CF-LIPS) reactor has been developed to produce ceramic powders. By using a counter-flow plasma configuration, entrainment of reactant particles into the plasma is improved compared to conventional injection methods. The counter-flow process also creates large recirculation zones which increase the residence time to more than 100 ms as predicted by modeling results [1]. The long residence time ensures complete evaporation and decomposition of precursor particles and complete reactions to the desirable products. Also, the process employs liquid precursors rather than solids, resulting in less contamination of products from unevaporated reactants. Results show that CF LIPS is an excellent method for producing single-phase and spherical spinel powders with a narrow particle size distribution. Particle size increases with increasing precursor concentration based on the synthesis of magnesium aluminate powders. Characterization techniques include X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), X-ray mapping, centrifugal sedimentation particle size distribution analysis, and vibrating sample magnetometer (VSM) measurements. In addition, crystallographic studies are conducted to determine the bond lengths, bond angles, and stoichiometries of the as-produced spinels.

A Comparison of High-Pressure and Low-Pressure Processing of RIM-PUR Systems in Shoe Manufacturing: Factors Influencing Material Properties

In the technical production of moulded parts, the technique of mixing the PUR components by the counterflow process under high pressure is widely used. This process has been the subject of intensive study in respect of both pro cess control and the quality of the resultant mixture. With the aid of model substances, investigations were carried out at the IKV in Aachen on the in fluence of the mixing head geometry, flow controllers and different runner geometries.

Nonlinear modelling of counterflow processes using weighted residual methods

This paper discusses the applicability of the weighted residual technique in obtaining low-order nonlinear models for counterflow processes. Two forms of model, namely hyperbolic and parabolic types, are derived and their performance contrasted. Legendre polynomials are used as the basis functions in the modelling. It is found that parabolic models based on a Taylor diffusion approximation appear to give the better transient behaviour.

Pointwise control of a counterflow process

A linear dynamics-quadratic cost control problem is considered for a counterflow process with pointwise inflows, The process is modelled by a hyperbolic system in which the inflows act both as distributed nod as boundary controls. Riccati equation characterizing the optimal control is reduced to a system of X—Y equations.

Questions and replies: renal mechanisms for urinary concentrating and diluting processes

Mechanisms for urinary concentration or dilution depend on counterflow processes, both tubular and vascular, within the renal medulla. Recently, there have emerged differing hypotheses about the renal tubular processes responsible for maintaining a hypertonic medullary interstitium. In this Editorial Review, R.W. Berliner frames three questions germane to this issue, and J.P. Kokko and D.J. Marsh provide their responses to these queries. The major issues addressed are: 1) What are the major unresolved question(s) concerning the mechanism by which concentrated urine is formed? 2) Current evidence suggests that the urea concentration in thin ascending limbs is slightly lower in the lumen than in interstitial fluid. Is the transepithelial concentration gradient between thin ascending limb and renal medullary interstitium sufficient to permit an entirely passive mechanism for diluting tubular fluid in the thin ascending limb? 3) A simple three-compartment model for the renal medullary concentrating process would include the tubular lumen, peritubular capillary, and the interstitium. Is it possible to generate a model that, by juxtaposing medullary structures, might explain renal medullary counterflow processes more adequately than the simple three-compartment model?

Thermodynamic approach to qualitative properties of trajectories of heat and mass transfer in gas-solid flow systems—I. Nonreacting systems

Study is made of qualitative properties and stability of trajectories of simultaneous heat- and mass-transfer processes in gas-solid flow systems. Liapunov functions based on the thermodynamic principle are constructed, and instability of trajectories of counter flow processes is thermodynamically grounded. Emphasis is made on a general character of the above thermodynamic approach to the stability and qualitative properties of trajectories.

Thermal Performance Models and Drift Loss Predictions for a Spray Cooling System

The relation between the Spray Energy Release (SER) and the spray nozzle efficiency (η) is considered with the view toward increasing the utility of previous spray thermal performance information. Through the approximate analysis of an assumed counter-flow process, the relevant parameters that η depends upon have been identified as the total heat transfer factor c′/cw, the sensible heat factor φ, and the SER. In general η cannot be correlated with wind speed alone. Similarities and differences between the NTU and SER methods are also considered. Values of SER are established from data obtained from a prototype spray system and a laboratory scale single column spray system. A simplified drift loss prediction model which is in good agreement with experimental data is proposed for an open atmosphere spray system.

Classical and Quantum-Mechanical Turbulence in He II Heat Flow

The theory of the He II thermal counterflow process in wide ($dg{10}^{\ensuremath{-}3}$ cm) channels is investigated on the assumption that both the normal and superfluid components make a transition from a laminar to a turbulent type of flow. A critical heat current ${W}_{0}$ is identified with the superfluid transition. The superfluid turbulent state is taken to be essentially that described by Vinen in terms of quantized vortex line and has an associated mutual friction. A second critical heat current ${W}_{c}$ is identified with the normal-fluid transition. It is argued that this transition is essentially of a classical turbulent type, with the added condition that the critical value of the Reynolds number must depend on the extent of mutual-friction coupling. This interpretation is shown to be consistent with experimentally observed critical heat currents, as well as with critical-velocity effects found in other types of flow. The assumption of two critical heat currents defines three distinct flow regions. It is shown that these three regions are essentially the same as those found experimentally by Allen, Griffiths, and Osborne. On the basis of some simplifying assumptions regarding the normal-fluid turbulent state, the temperature and pressure gradients accompanying thermal counterflow are calculated. Comparison with experiment shows good qualitative and often quantitative agreement. It is also shown that the model developed can be successfully used to interpret experiments involving flows of a nonthermal counterflow type.

Bellamy Field Tests: Oil From Tar by Counterflow Underground Burning

Abstract From 1955 to 1958 the Phillips Petroleum Co. conducted a series of small scale counterflow combustion field tests in a tar sand about 60-ft deep and 6 to 12-ft thick near Bellamy, Mo. A total of seven different well patterns, including conventional five-spots and seven spots plus a 15-well line drive pattern and a 10-well radial pattern, were employed. Electric heaters, gas burners and wellbore fuel packs were tested as counterflow ignition devices. Direct drive ignition followed by reversal to counterflow operation was not possible in this case because of formation plugging by the semi-solid tar during the direct drive phase. Sustained counterflow burning was achieved with wellbore fuel packs under controlled conditions which permitted close correlation of fire front velocity, air velocity, air-oil ratios and yields for a wide variation in process parameters. The tar in place was about 100 API with a reservoir viscosity greater than 500,000 cp. The composite oil product was 260 API with a viscosity in the range of 5 to 15 cp. Vertical sweep efficiency in the line drive pattern was essentially 100 per cent, with no evidence of gravity segregation. Original tar in place ranged between 800 and 1,000 bbl/acre-ft, specific rock permeability averaged about 800 md before burning and elective air permeability with residual oil and water in place (at the time of ignition) averaged 250 md. The volume of oil recovered during stabilized line drive counterflow burning represented about 67 per cent of the volume of tar originally in place in the burned out zones. A minimum was found when air-oil ratios were plotted against formation air velocities, and a limiting air velocity existed below which the counterflow fire front reversed and burned back over its own trajectory, using the residual coke left behind. Introduction Early in 1955 the Phillips Petroleum Co. began preparations to field test counterflow underground combustion as a method for producing oil from high viscosity hydrocarbon deposits, such as bituminous (tar) sands. At that time all published information on the use of underground burning to increase oil recovery was based on the direct drive process, in which the fire front moved through the formation in the same direction as the injected air stream. Such direct burning is not applicable to many heavy oil sands or to most tar sands because the heat-thinned native hydrocarbon congeals in the cold rock ahead of the fire front forming a gas permeability block which smothers the combustion. Laboratory experiments first demonstrated that this permeability blocking would not occur if the fire front and the air stream moved in opposite directions. In this counterflow (reverse) burning process the heated heavy oil or tar is driven back through the combustion zone. Here thermal cracking produces relatively light hydrocarbon products which pass through the heated rock behind the fire front (largely in the vapor phase) and are incapable of causing a gas permeability block. Exploratory coring revealed that consolidated bituminous sandstones with a combination of tar saturation, permeability, thickness and depth favorable for experimental field testing existed at several points in western Missouri. By the fall of 1955, a test site for determining technical feasibility of the counterflow process under field conditions had been selected near Bellamy, Vernon County, Mo. about fifty miles north of Joplin. The pay zone was too thin and too shallow to constitute a commercial prospect, but these same factors permitted controlled experimental operation with a small compressor installation and with a large number of monitor wells. These were needed for adequate observation of the underground phenomena at reasonable cost. RESERVOIR CHARACTERISTICS The reservoir chosen for the experimental field tests was a 12-ft thick section of tar sand extending from 49 to 61 ft subsurface, with shale and siltstone laminations sealing the top and bottom. This section was part of a larger 30-ft thick tar sand deposit which extended both above and below the test zone. Core analyses showed that the 12-ft sand was effectively subdivided into two approximately equal sections, with the lower zone being consistently more permeable than the upper zone. The most significant laboratory core data are summarized in Table 1. The line drive test which is the principal subject of this report utilized only the lower 6-ft thick zone, with the upper zone regarded as part of the 55-ft overburden. WELL PATTERNS The over-all field test program involved a total of seven different well patterns, including conventional five-spots and seven-spots plus a 15-well line drive pattern and a 10-well radial pattern. JPT P. 109ˆ

Critical Velocities of Ions in Liquid Helium II Detected by Heat Flush

The discontinuity in the drift velocity of ions in liquid helium, previously detected by the time-of-flight method, is confirmed by the heat-flush method in a wide channel. The critical velocity is found to be $〈{v}_{c}〉=4.96\ifmmode\pm\else\textpm\fi{}0.35$ m/sec independent of beam geometry and of ionic density. The detailed analysis of the beam displacement in the two-fluid counterflow process allows one to conclude that the new dissipation suffered by the beam at $〈{v}_{c}〉$ is essentially due to its interaction with the normal fluid.