David J. Kukulka

Thermodynamic and transport properties of pure and saline water

Publisher Summary This chapter presents a complete collection of the thermodynamic and transport properties of seawater. The chapter reviews the available fundamental data and correlations of both the molecular transport and thermodynamic properties of saline water for a wide range of temperature (t), salinity (s), and pressure (p). The purpose is to establish a database that could be used to achieve systemic representations of, as many as possible, the basic properties required in many areas of analysis and in calculations concerning terrestrial surface-water transport processes and circulations. The properties calculated using a density relation are coefficient of thermal expansion, coefficient of saline expansion, change in specific heat, change in enthalpy, and change in entropy. The results for the change in specific heat along with other previously reported data of other properties are used to calculate the Prandtl number. The Schmidt number is compiled solely from previously reported measurements. However, except at low temperatures and pressures, good agreement can be seen in the comparison of thermal expansion results.

Factors Associated With Fouling in the Process Industry

This study is concerned with the sequence and character of the events that take place after the initial exposure of the surface to the product, that is, the buildup and composition of a conditioning film on the surface. Calculations show that for short transient studies, conditioning film measurements can be made to values as small as 3.0 microns. Utilizing higher heating rates (5 W/cm2) and shorter transients allow measurements to 2.0 microns. This type of monitoring system can function as an alarm device to signal when a critical point of biofilm buildup is reached. Maintenance procedures can be initiated at the proper time rather than at arbitrary intervals, thus minimizing down time and ensuring product safety. Conclusions include methods to monitor and control the conditioning film formation and deposit growth for various process industries.

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.

Transient Evaluation of Process Surfaces Used in Fouling Applications

Fouling is an important and complex problem that affects a variety of industries. Surface fouling 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. It is a transient process that begins with a clean process surface and may progress until the surface can no longer 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 this induction period, a conditioning film forms, and the heat transfer efficiencies do not change significantly. Conditioning film appearance may occur in weeks, days, or minutes. This stage 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 is arrived at when accumulation is almost constant. This accumulation causes heat transfer to significantly decrease and a complete cleaning of the surfaces may be required. Included here is a discussion on process surface materials used in applications where fouling may be a concern. Previous work in this area has prompted this study in order to provide better information for designs involving fouling. Conclusions and observations regarding the materials/surfaces that are commonly used in designs where fouling may be a concern are presented here. Photographs are presented of frontal surfaces and edges. Finally, transient surface roughness values are given for several materials.

Development of Vipertex EHT Solar Surfaces for Enhanced Energy Transfer Applications

Solar energy production is an important source of green energy that utilizes various thermal designs. Development and modeling of enhanced photovoltaic–thermal solar surfaces is the subject of this study. Design criteria include maximization of the overall energy transfer; minimization of material; and a minimization of any friction increases that might occur in the flowing fluid; and all of these are required while at the same time a structurally superior surface is necessary. Most current designs involve the transfer of energy across a flat and unenhanced solar surface. Current surfaces utilize old technology, making them prime candidates for redesign and improved process performance. Previously developed Vipertex EHT series solar surfaces were tested and found to provide an enhanced energy exchange surface, increased heat exchange surface area, lighter structure, and structural rigidity that exceeds current surfaces using the same amount of material. Vipertex solar surfaces that meet those requirements are produced through material surface modifications and result in additional heat transfer surface area, increased energy absorption, increased fluid turbulence, generation of secondary fluid flow patterns, and produces a disruption of the thermal boundary layer. These enhanced surfaces provide important changes to solar surface design that allow the advancement of thermal solar devices.

A General Correlation for Condensation Heat Transfer in Micro-Fin for Herringbone and Dimple-Texture Tubes

An experimental investigation was performed to evaluate the condensation characteristics inside smooth, herringbone and dimple-textured (Vipertex 1EHT) tubes; with the same outer diameter (12.7 mm); using R22 and R410a refrigerants; for a mass flux that ranges from 81 to 178.5 kg/m 2 s. The condensation saturation temperature is 47°C; with an inlet quality of 0.8 and an outlet vapor quality of 0.2. Results indicate that the condensation heat transfer coefficient of the herringbone tube was approximately 3 times that of the smooth tube for R22; and has an enhancement heat transfer factor of 2.3 for R410a. The enhancement heat transfer coefficient multiplier for the textured dimple tube is approximately 2 times that of a smooth tube for R22; and 1.8 for R410a. Severalpreviously reported correlations are used to compare the heat transfer coefficient measurements in the plain tube; while a new equation is proposed to predict the heat transfer coefficient in the herringbone tube.Copyright

Condensation Heat Transfer Characteristics on the Outside of Horizontal Smooth, Herringbone and Enhanced Surface 1EHT Tubes

An experiment investigation was performed using R410A in order to determine the single-phase and evaporation heat transfer coefficients on the outside of (i) a smooth tube; (ii) herringbone tube; and (iii) the newly developed Vipertex enhanced surface 1EHT tube; all with the same external diameter (12.7 mm). The nominal evaporation temperature is 279 K, with inlet and outlet qualities of 0.1 and 0.8. Mass fluxes ranged from 10 to 40 kg m−2s−1. Results suggest that the 1EHT tube has excellent heat transfer performance but a higher pressure drop when compared to a smooth tube. Evaporation heat transfer coefficient for the 1EHT is lower than the herringbone tube and the pressure drop is almost the same.Copyright

Analysis of Flow and Heat Transfer Characteristics Around Oval-Shaped Cylinder

Numerical simulation and experimental study were carried out to investigate the flow and heat transfer characteristics of air flowing across different types of oval-shaped cylinders. These cylinders have axis ratios, e, of 1, 1.5, 2, 3, 4, and 5 with the major axis parallel to the free-stream for Reynolds numbers, based on the hydraulic diameter, varying from 4000 to50000. When e = 1 the tube is a circular cylinder and when 1/e = 0 a flat plate is represented. Numerical results show that the wake size decreases as e increases from 1 to 5. The minimum value of Cp takes place at an angular position decrease as e decreases and the maximum value of Cf gradually increases with the increasing e. Simulated results agree very well with those available in the existing literature. Oval-shaped cylinders have a higher favorable pressure gradient at the front of the cylinder and a lower adverse pressure gradient at the back of the cylinder for flows in inhibiting separation. Empirical correlations for each tube have been obtained by numerical simulation relating the dimensionless heat transfer coefficient with the Reynolds Number and Prandtl Number. Field synergy theory and performance evaluation criteria (PEC) were used to analyze the mechanisms of heat transfer enhancement for oval-shaped cylinders. It was found that an oval-shaped tube with e = 2 has the best comprehensive heat transfer performance at Re >11952. In order to verify the effectiveness and correctness of our numerical model, an experiment was carried out for cylinders for values of e equal to 1, 2, 3 and 4.Copyright

Investigation of Precipitation Fouling in Corrugated Plate Heat Exchangers

Experimental and theoretical investigations of precipitation fouling performance have been performed inside four corrugated plate heat exchangers (PHE). They have different geometry parameters, such as plate height, plate spacing, and plate angle. Heat transfer coefficient and friction factor have been obtained in the clean tests with the range of Reynolds number of 600–6000. Three precipitation fouling experiments focused on temperature influences and geometric designs have been performed. PHE with the largest hydraulic diameter and height to pitch ratio shows the best anti-fouling performance. Scanning electron microscope is used to investigate the microscopic structures of precipitation fouling. A type of Teflon coated plate has been used for testing the anti-fouling characteristic of PHEs. The coated plates show well anti-fouling performance comparing with the common SS-304 plates. A semi-empirical fouling model using Prandtl analogy has been established. The model predictions agree well with experimental data.Copyright

Modeling Fluid Flow of Vipertex Enhanced Heat Transfer Tubes

Abstract Conservation of energy plays an important role in the design of today’s process systems. A wide variety of industrial processes involve the transfer of heat energy and many of those processes employ old technology. These processes would be candidates for a redesign that would achieve improved process performance. Utilization of an enhanced heat transfer surface is an effective method to be utilized in order to develop high performance thermal systems. Enhanced heat transfer surfaces can be produced through material surface modifications that result in: an increase in fluid turbulence, generation of secondary fluid flow patterns, disruption of the thermal boundary layer and additional heat transfer surface area. Modeling single phase fluid flow near an enhanced heat transfer surface is the subject of this study. Criteria include the maximization of the overall heat transfer coefficient; minimization of pumping power; and minimization of the rate of surface fouling. Through the use of computational fluid dynamic (CFD) methods, Vipertex™ was able to develop an optimized, three dimensional, enhanced heat transfer surface. This study details the development of an enhanced surface and its effects on the overall heat transfer, fouling and pumping requirements. The Vipertex 2EHT enhanced heat transfer surface was optimized, then manufactured into tubes and evaluated experimentally to validate its design. Original designs of Vipertex enhanced heat transfer surfaces showed average heat transfer performance gains of approximately 30 percent. Optimized Vipertex EHT enhanced surfaces, are able to increase heat transfer for some flow conditions by more than 200%. Designs that incorporate the Vipertex EHT enhanced surfaces are able to increase heat transfer, minimize total costs and conserve energy. These enhanced surfaces provide an important method to advance the design of heat exchange devices.