Fouling behavior of coconut milk at pasteurization temperatures

Fouling by coconut milk at different heating temperatures (50–54.5 °C, 60–64.5 °C, and 70–74.5 °C) and at three volumetric flows (2,4 and 6 LPM) in a test section equipped with four flat plates was studied. Measurement of the overall heat transfer coefficient (U) and the compositions of deposit mass were completed in order to obtain fouling factors (R_f) and an empirical model for the rate of increase of Biot number (?Bi/?t) as a function of the temperature (T) and the flow (F). The results illustrated that the fouling factor increased, when the temperature fell due to a combination of chemical reaction fouling from proteins and precipitation fouling from fat. The fouling factor also increased, when the flow was lowered due to a slow rate of deposit removal introduced by small shear force. Combination of the two effects revealed that the effect of flow was less significant at higher temperatures. All results can be confirmed by an analysis of fouling compositions. At high temperature conditions, more denaturation of proteins resulted in less ability to entrap fat globules onto heating surface. The heat resistance was found decreasing with increasing temperature.     

Quantifying Implications of Deposit Aging from Crude Refinery Preheat Train Data

Abstract

Heat exchanger fouling has been studied for some time in the petroleum industry. As understanding of fouling dynamics and mitigation methods improves, refinery fouling mitigation strategies are changing. The implications of deposit aging in refinery units have not been addressed in detail: aging refers to where the deposit undergoes physical and chemical conversion over time. In the 2009 Heat Exchanger Fouling and Cleaning conference, Wilson et al. [Ageing: Looking back and looking forward] presented a simple framework illustrating how deposit aging impacts heat exchanger thermal and hydraulic performance. This paper presents insights into deposit aging gained from analysis of refinery monitoring data. Two case studies are presented: (i) one from the Preem refinery in Sweden where stream temperature, flow and gauge pressure measurements indicated a higher deposit thermal conductivity in exchangers located in the hotter section of the preheat train. (ii) US refinery stream temperature, flow and plant cleaning log data, showing an increased resistance to cleaning when deposits are exposed to high temperature for a prolonged period. The use of deposit aging analysis to improve exchanger operation is discussed.     

Determination of Weibull parameters for wind energy analysis of İzmir,Turkey

In this study, the two Weibull parameters of the wind speed distribution function, the shape parameter k (dimensionless) and the scale parameter c (ms^?1), were computed from the wind speed data for ?zmir. Wind data, consisting of hourly wind speed records over a 5‐year period, 1995–1999, were measured in the Solar/Wind‐Meteorological Station of the Solar Energy Institute at Ege University. Based on the experimental data, it was found that the numerical values of both Weibull parameters (k and c) for ?zmir vary over a wide range. The yearly values of k range from 1.378 to 1.634 with a mean value of 1.552, while those of c are in the range of 2.956–3.444 with a mean value of 3.222. The average seasonal Weibull distributions for ?zmir are also given. The wind speed distributions are represented by Weibull distribution and also by Rayleigh distribution, with a special case of the Weibull distribution for k=2. As a result, the Weibull distribution is found to be suitable to represent the actual probability of wind speed data for ?zmir (at annual average wind speeds up to 3 ms^?1). Copyright © 2002 John Wiley & Sons, Ltd.     

Ozone friendly binary blends R 32/R 134a and the ternary R 407b

The objective of this paper is to present thermodynamic properties and characteristics of the binary refrigerant mixtures R 32/R 134a in compositions 20/80%, 30/70%, 40/60% by mass and of the ternary mixture R 407b: 10 wt% R 32+70 wt% R 125+20 wt% R 134a. A computer code has been developed and by use of a Peng–Robinson type equation of state, PVT data for all working fluids are determined. Based on the thermodynamics theory, analytical relationships for the enthalpy, entropy, constant pressure and constant volume specific heats as well as for k-type isentropic change exponents are given. Furthermore, comparisons are provided by means of diagrams illustrating the influence of state conditions on the k-type exponents k_p,V, k_T,V, k_p,T, and classical k (k=c_P/c_V). A systematic study has also been carried out and the data obtained are plotted for a better physical feeling related to the sound velocity of real gas for the R 32/R 134a blend in composition 20/80%. The results are compared with corresponding ones of the ternary R 407b.     

The Experiment Investigation of Cooling-Water Fouling Mechanism-Associated Water Quality Parameters in Two Kinds of Heat Exchanger

This paper mainly discusses the relevance of some cooling-water quality parameters and the cooling-water fouling mechanism. By using plate and shell-and-tube heat exchanger experimental systems that are built to simulate the practical operation of heat exchangers, we acquired groups of data of water quality parameters such as Fe³⁺ and Cl^? in the cycle process. Then some interaction analyses were made to study the connection between water quality parameters and fouling deposition, and the results indicate that water quality parameters influence each other in a cycle process and the interconnections of water quality parameters have a direct and obvious impact on cooling-water fouling growth in the early operation stage. Later, fouling growth becomes stable for the reason that each parameter achieves a dynamic balance. Cooling-water fouling growth is a comprehensive result of water quality parameter dynamic changes.     

Effects of particle fouling and magnetic field on porous fin for improved cooling of consumer electronics

The combined effect of particulate fouling and magnetic field on the efficiency of a convective–radiative porous fin heatsink with temperature‐dependent thermal conductivity is presented. The developed thermal models are solved using differential transformation method. The effects of thermal conductivity, porosity, convection, radiation parameter, and thermal fouling number on the fin thermal efficiency are investigated. The presence of thermal fouling on the surface of the fin is shown to increase the temperature distribution. The presence of particle deposition on the fin surface significantly decreases the rate of heat transfer as additional thermal resistance of the fouling layer decreases the thermal performance of porous fin heatsink. Moreover, the fin efficiency decreases as the value of fouled Biot, Darcy, radiation number, and thermogeometric parameter increases. It is established that M_f < M_c, which indicates that the efficiency of the fouled fin is greater than the efficiency of the clean fin. Furthermore, the result of the present study is validated with the established results of Chebyshev spectral collocation method and fourth‐order Runge–Kutta with shooting method and an error margin of 0.000000023 is established.     

Effects of capillary forces on laminar filmwise condensation on horizontal disk in porous medium

This study investigates the problem of steady filmwise condensation on a horizontal disk embedded in a porous medium. The disk surface is cold and faces upwards into the porous medium, which is filled with a dry vapor. Due to the effects of capillary forces in the porous medium, a two-phase zone is formed between the liquid film and the vapor zone. As in the classical filmwise condensation problem, this study assumes that the inertia within the liquid film is negligible and that the properties of the porous medium, dry vapor, and condensate are constant. Darcy’s law is used to analyze the liquid flow in both the liquid film and the two-phase zone. A capillary parameter, Bo_c, is introduced to characterize the liquid flow caused by capillary forces in the porous medium. It is shown that the mean Nusselt number, , increases at higher values of the capillary parameter, Bo_c. Finally, this study derives a simple closed form correlation for the Nusselt number for the case where the capillary forces are neglected.     

曲线重叠法的关键因素分析及改进

曲线重叠法是油气地质评价中较常使用的一项测井评价技术,能够通过电阻率测井和声波时差测井数据计算出总有机碳含量,但是在该方法中,两个计算参数电阻率基线值和时差基线值是通过观察测井曲线图上两条测井曲线的"重叠情况"而估算出来的,带有很大的人为性和随意性,从而影响了有机碳含量计算的准确度。为了解决该问题,分析了3个绘图参数(R f、△tf、k值)对测井曲线的形状和位置的影响:当定位参数(R f、△tf)改变时,电阻率曲线的形状不变,但是在横向上产生一个总体平移量;当轴比参数(k值)改变时,电阻率曲线的形状和位置都发生变化。因此证明了轴比参数k值是关键参数,提出了使用岩心分析化验数据和测井数据通过二元线性回归模型拟合获得轴比参数k值的方法。由于避开了原公式中的基线值,新方法提高了有机碳含量计算的准确度。     

An Evaluation of Heat Transfer Surface Materials Used in Fouling Applications

Fouling is a very important and complex problem that extends into many fields, including natural, chemical, medical, and industrial processes. Fouling of a surface takes place as a result of the complex reactions that cause deposits to form on process surfaces. A number of parameters influence fouling development, including flow velocity, surface temperature, surface material/finish, surface geometry and fluid properties. Fouling is a transient process that begins with a clean process surface and progresses until the surface no longer can be used effectively. The event sequence of the fouling process appears in general to be universal, beginning when fluid comes into contact with a process surface. During the induction period, the conditioning film forms with heat transfer efficiencies not changing significantly. Conditioning film development is followed by a rapid accumulation of deposit growth. It is during this growth phase that the heat transfer across the process surface starts to dramatically change. Finally, a pseudo steady-state period takes place when accumulation is almost constant. Deposit accumulation causes efficiencies to significantly decrease, and a complete surface cleaning may be required. Conclusions and observations regarding the materials/surfaces that are commonly used in designs where fouling may be a concern are presented here. Comparisons of fouling rate and deposit thickness are given for several materials.     

两种柱形涡流发生器CaSO_4析晶污垢特性实验研究

为得到涡流发生器污垢规律,采用质量浓度为2 100mg/L的硫酸钙过饱和溶液进行了传热过程中的污垢生成实验,并通过离线称重法得到了装有涡流发生器试片表面单位面积污垢沉积量生长曲线.结果表明：涡流发生器直径和排列间距对壁面污垢沉积量有显著影响.当涡流发生器直径（4mm）一定时,试片表面单位面积污垢沉积量均随着涡流发生器排列间距的增大而增加;在排列间距（10mm）一定时,污垢沉积量随着涡流发生器尺寸的增大而减少.     

First-principles study the structural,electronic, vibrational and thermodynamic properties of Zr1−xHfxCoH3

The structural, electronic, vibrational and thermodynamic properties of Zr_1?xHf_xCoH₃ (x = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) are investigated using first principles approach based on the virtual crystal approximation (VCA). The results indicate the series Zr_1?xHf_xCoH₃ have the similar physical properties. When Hf concentration increases gradually, the lattice parameter reduces and the thermodynamic stability first decreases and then increases, respectively. The calculated results of charge distributions and electron localization function (ELF) suggest that the interactions of HCo and HZr_1?xHf_x are primarily metallic with a small covalent component. The band structure and the corresponding density of states (DOS) around the Fermi level (E_f) indicate the metallicity enhances and the electrical conductivity is better with increasing Hf content. The phonon density of states imply that with the increase of Hf content, the covalent interactions between H(4c₂) and Zr_1?xHf_x are weakened, while the covalent interactions between H(8f₁) and Zr_1?xHf_x basically remained unchanged (H(4c₂) and H(8f₁) represent the hydrogen atoms occupying 4c₂ and 8f₁ site, respectively), which is consistent with the results of charge density. Finally, the thermodynamic properties are obtained and discussed on the base of the obtained vibrational properties.     

Measuring Local Crystallization Fouling in a Double-Pipe Heat Exchanger

Abstract

Although fouling is a problem varying in space and time, sizing and assessment of a process apparatus is almost always based on one single integral fouling resistance value. Furthermore, the integral fluid dynamic behavior, e.g. the development of time-dependent pressure drop in a heat exchanger, can be influenced by local constrictions. While it is generally possible to determine the time dependency of the integral fouling behavior, local differences are not taken into consideration at present. Therefore, this paper introduces a metrological, an incremental and a segmental approach to study the local development of crystallization fouling by calcium sulfate in a countercurrent double-pipe heat exchanger. The consecutive approaches allow for thermal, volumetric, gravimetric, and optical fouling investigations, aiming to examine the axial distribution of deposit as well as local differences in the deposit morphology. All methods provided congruent results and local fouling could be described properly. An almost clean surface at the colder end of the heat exchanger and an exponential increase of deposit thickness were observed towards the hot end. Hence, the section near to the hot water inlet turned out to be a key area with regards to increasing fouling mass and structural changes of the layer.     

Effect of viscosity variation on natural convection flow of water–alumina nanofluid in an annulus with internal heat generation

Heat transfer enhancement in a horizontal annulus using the variable viscosity property of an Al₂O₃–water nanofluid is investigated. Two different viscosity models are used to evaluate heat transfer enhancement in the annulus. The base case uses the Pak and Cho model and the Brinkman model for viscosity which take into account the dependence of this property on temperature and nanoparticle volume fraction. The inner surface of the annulus is heated uniformly by a constant heat flux q_w and the outer boundary is kept at a constant temperature T_c. The nanofluid generates heat internally. The governing equations are solved numerically subject to appropriate boundary conditions by a penalty finite‐element method. It is observed that for a fixed Prandtl number Pr = 6.2, Rayleigh number Ra = 10⁴ and solid volume fraction ? = 10%, the average Nusselt number is enhanced by diminishing the heat generation parameter, mean diameter of nanoparticles, and diameter of the inner circle. The mean temperature for the fluids (nanofluid and base fluid) corresponding to the above mentioned parameters is plotted as well. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21016     

Mineral scale formation and mitigation on metals and a polymeric heat exchanger surface

An experimental set-up was built to study heat transfer fouling of different pipe materials used in heat exchangers. Fouling mitigation investigations using wood pulp fibres in suspension in the fouling liquid were also performed. The new set-up allows progressive visual observation of fouling with time together with a recorded history under the same solution conditions. On completion, the tube under investigation could be removed to obtain quantitative data on the progressive build up of the deposit as well as the composition of the deposit.The experimental technique involved a pipe test specimen being centrally located in a cylindrical tank concentric with a vertical agitator to give constant and uniform flow conditions near the tube surface. The investigation of calcium sulphate deposition on four different metal surfaces (copper, aluminium, brass and stainless steel SS 316 respectively) and a polycarbonate surface reveals that the fouling increases with time but at a decreasing rate. The deposition on a metal surface can be seen to increase with increasing thermal conductivity and decreasing total surface energy over the range of experiments. Low surface energy material such as polycarbonate causes less attraction to the floating crystals and receives less deposition in comparison to the SS surface.Bleached Kraft softwood fibres at various concentrations were added to the solution to examine their effects on fouling. The results indicate that fouling is reduced as fibre concentration increases. It was also found that the fouling on stainless steel, brass and copper surfaces were all retarded in presence of fibre in the solution.     

Calcium Sulfate Fouling-Precipitation or Particulate: A Proposed Composite Model

Though it is of great importance, the majority of predictive models tend not to incorporate water chemistry in their formulations. The ionic diffusion model which was developed for CaCO₃, is based purely on crystallization, and is one of the few models that incorporates water chemistry. This model does not provide satisfactory predictions for CaSO₄ fouling. In this article, a new model is proposed for CaSO₄ fouling which takes into account the effect of both crystallization and particulate fouling and is capable of predicting the fouling resistance during the cleaning cycle as well as the fouling cycle. A removal term is incorporated into the model, as the occurrence of particulate fouling for CaSO₄ tends to weaken its crystalline structure and makes it more prone than CaCO₃ to removal. Properties of the electrolyte were evaluated using MINTEQA2 computer code, which is approved by the U.S. Environmental Protection Agency. In this model, particulate fouling is estimated using the physical mechanism for particle transport and adherence, crystallization is estimated by ionic diffusion, and the removal term is approximated using hydrodynamics of flow and deposit properties. The inclusion of both crystallization and removal terms incorporates the effects of both water chemistry and hydrodynamics of the flow and provides a relationship which not only can predict fouling but also can predict dissolution, by change of water quality and/or stopping the operation, or removal by shear stress. The proposed model was assessed using published experimental data. The results indicate that this model provides good predictions: the slope of predicted rates as a function of the experimental rates is 1.05. The experimental results, though limited in number, suggest that crystallization is not the main or only mechanism contributing to CaSO₄ fouling. Particulate fouling seems to be a major contributor. Further experimentation is in process to confirm the degree of particulate fouling and to substantiate or to modify the model accordingly.     

Heat Exchanger Fouling in Phosphoric Acid Evaporators

Multistage shell and tube evaporators are frequently used in phosphoric acid plants to increase the concentration of dilute phosphoric acid to 52–55 wt% P₂O_5. The concentrated phosphoric acid solution is supersaturated with respect to calcium sulfate. As a result, part of the calcium sulfate in the liquor deposits on the heat exchanger tube walls. Because the thermal conductivity of these scales is very low, thin deposits can create a significant resistance to heat transfer. Therefore, regular cleaning of heat exchangers is required, frequently at shorter than biweekly intervals. As the major costs in modern phosphoric acid plants are the cost of energy, a thorough understanding of the fouling kinetics and of the effects of various operational parameters on the behavior of calcium sulfate is required to improve operation and design of the shell and tube heat exchangers, which are extensively used. In this investigation, a large set of heat exchanger data was collected from shell and tube heat exchangers of the phosphoric acid plant of the Razi Petrochemical Complex in Iran, and the fouling deposits were analyzed with respect to appearance and composition. The overall heat transfer coefficients and fouling resistances were evaluated at different times, and a kinetic model for the crystallization fouling was developed. It is shown that the crystallization rate constant obeys an Arrhenius relationship with an activation energy of 57 kJ/mol. The average absolute error of 12.4% shows that the predictions of the suggested model are in good agreement with the original plant data.     

Asymptotic approximations for the flow field in a free convective flow of a non-Newtonian fluid past a vertical porous plate

The problem of suction/injection on free convective flow of a non-Newtonian fluid past a vertical porous plate is modeled in this study. Adopting a series expansion technique about a small parameter E_c and making fairly realistic assumptions, the coupled non-linear partial differential equations are decoupled and expressions for the temperature, velocity, skin-friction and rate of heat transfer are obtained. This is based on the fact that for fairly slow motions of all incompressible fluids, the viscous dissipation heat parameter E_c is small. Our results show that the velocity distribution is highly dependent on the visco-elastic parameter L and we also observe that the rate of heat transfer does not depend on the free convection parameter G_r. Other observations are depicted in Fig. 1, Fig. 2, Fig. 3, Fig. 4.     

Nucleate pool boiling heat transfer characteristics of dilute Al2O3–ethyleneglycol nanofluids

Pool boiling heat transfer coefficients of dilute stabilized Al₂O₃–ethyleneglycol nanofluids as possible coolant fluid are experimentally quantified. The influence of different parameters such as heat flux, heating surface nano-roughness, concentration of nanofluids and fouling resistance on the pool boiling heat transfer coefficient of alumina nanofluids has experimentally been investigated and briefly discussed. Results demonstrated that there are two heat transfer regions with different mechanisms namely free convection and nucleate boiling heat transfer. Studies on the influence of parameter demonstrated that with increasing the heat flux, the pool boiling heat transfer coefficient of nanofluids significantly increases. In contrast, with increasing the concentration of nanofluid, due to the deposition of nanoparticles on the surface, the average roughness of the surface and the heat transfer coefficient dramatically deteriorate, while a significant increase in fouling resistance is reported. Also, studies reveal asymptotic and rectilinear behaviors of fouling resistance parameter in nucleate boiling and free convective domains.     

Study on constant stress: Accelerated life tests of fouling thermal resistance

To shorten the time of fouling tests, fouling life was defined. The statistical analysis method for type II‐censored exponential life data under constant‐stress accelerated life testing models and the accelerated coefficients a and b were obtained. By using an accelerated model, the estimators of the fouling life under usual stress could be obtained. A computing example was given. Results indicated that it is credible and feasible to perform accelerated life tests of asymptotic fouling thermal resistance, and will be of important value to experimental research of fouling. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(2): 110–114, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20105