This paper presents an analysis which happens to be an extension of the previous study (1999) of the authors on subcooled inverted annular flow film boiling. A physical model for constant heat flux condition at the wall of a vertical tube with vapour film at the periphery and liquid in the core region is considered in the analysis. Employing Levy's (1960) postulation a relationship between the system parameters and the dryness fraction is obtained and subsequently utilized in the development of the theory for inverted flow film boiling. Further, using Van Driest (1956) mixing length theory velocity and temperature profiles are evaluated to establish the local heat transfer coefficients. A correlation is proposed to predict the mean heat transfer coefficient for constant heat flux conditions of the tube wall.

While a large number of correlations have been proposed for the pressure drop encountered in gas-liquid two-phase flow in pipes, insufficient attention has been paid to the flow regimes associated with specific datasets used in developing these correlations. This may reduce the extrapolative accuracy of these correlations, and limit their utility in the design of future steam generation plants, air-conditioners with new alternative refrigerants, and other emerging applications of two-phase flow. In this study, five commonly used correlations for the frictional pressure drop component in gas-liquid two-phase flow in a horizontal smooth tube were examined for the experimental dataset sorted by the predicted flow regime using the Taitel et al method in order to explore the potential for using flow regime information to improve the predictive accuracy. The simple homogeneous model correlation was found to work very well for all of the entire annular data, with an average accuracy of ±27%, and the Chisholm correlation worked best for intermittent data, with agreement within ±24%, where the simple homogeneous correlation offers ±36%. These results may support the premise that consideration of some flow pattern indicator may prove effective in establishing better two-phase flow correlations.

This paper considers the many techniques that have been developed to enhance convective heat transfer. They are presented according to the mode of heat transfer. The current advanced enhancement represents 3rd generation heat transfer technology. The many contributions of Prof. Ralph Webb are integral to this development. It is felt that this field has a bright future.

An experimental investigation, coupled with theoretical modeling of CaCO3 fouling in plate-and-frame type heat exchangers (PHEs) have been conducted. Four different plates, made of SS-304, are used in two different surface patterns (chevron and zig-zag) of varying corrugation severity (waviness depth and pitch) and area enhancement. They were further characterized in clean, non-fouled convection by their measured heat transfer coefficients and friction factors in the Reynolds number range of 600–6000. The flow-fouling experiments delineate the effects of temperature and plate-surface geometry on growth rates and stabilization of fouling resistance, along with the anti-fouling behavior of plates coated with a hydrophobic PTFE (Teflon) film. Moreover, the microscopic structure of fouling deposits is mapped in a scanning-electron microscope. Corrugated plates with the largest height-to-pitch ratio and hydraulic diameter are found to have the lowest fouling growth rate and resistance; Teflon-film coating of plate surface is also found to mitigate fouling relative to the performance of bare stainless steel plates. Finally, a semi-empirical fouling model, based on the Prandtl–Taylor analogy, has been devised to describe the experimental data and provide a predictive tool.

While the majority of studies examining the relationship between flow regime and thermofluid performance rely on subjective flow regime determination, objective techniques are needed to more firmly establish the nature and repeatability of these phenomena. This study describes a nonintrusive optical flow regime characterization methodology used to study horizontal, adiabatic, two-phase flow of water-water vapor and water-nitrogen gas in small (8.84mm) diameter tubes. The method relies on shining a fiber-optic light source through the top of a borosilicate glass tube at the outlet of a smooth copper tube, using a CMOS camera to capture light rings resulting from total internal reflection at the liquid-vapor interface, and extracting a film thickness profile from successive images. Using these unique temporally varying film profiles, quantitative identification measures were developed for the primary flow regimes, including the ability to explain and quantify the more subtle transitions that exist between dominant regimes as the two-phase flows progress from saturated liquid to qualities of 0.32. Application of this methodology has shown the Taitel-Dukler, Ullmann-Brauner, and Wojtan etal. phenomenological flow regime maps to capture the salient features and transition boundaries, with varying accuracy, for small-diameter two-phase flow in a mass flux range of 15 to 230kg/m(2)-s.

A non-intrusive optical method for two-phase flow pattern identification was developed to validate flow regime maps for two-phase adiabatic flow in a small diameter tube. Empirical measurements of film thickness have been shown to provide objective identification of the dominant two-phase flow regimes, representing a significant improvement over the traditional use of exclusively visual and verbal descriptions. Use of this technique has shown the Taitel-Dukler, Ullmann-Brauner, and Wojtan et al. phenomenological flow regime mapping methodologies to be applicable, with varying accuracy, to small diameter two-phase flow.

Extended performance evaluation criteria (ExPEC) have been used to assess the performance characteristics of single-phase fully developed laminar flow through bundle of ducts with non-circular shape rectangular, isosceles triangular, elliptical, trapezoidal and hexagonal. The bundle of circular tubes has been used as a reference heat transfer unit. Constant wall temperature has been selected as the thermal boundary condition. The performance characteristics of the bundles with non-circular ducts have been evaluated and compared to those of the reference unit for different objectives and constraints imposed. As a common constraint, the hydraulic diameter of the duct has been specified.The results clearly show that the rectangular, trapezoidal or hexagonal duct configuration can compete, in some cases, with the circular tube configuration. The choice of the tube shape and geometrical details depends on the constraints imposed and the objectives pursued. The results obtained from the present study revealed that they differed from those obtained with a common constraint of specified cross sectional area. (C) 2014 Elsevier Masson SAS. All rights reserved.

This paper presents correlations developed for predicting critical heat flux (CHF) and pressure drop in tubes containing multiple short-length twisted tapes (MSLTT) at operating conditions applicable to pressurised water reactors (PWRs). The specific design application motivating these developments was the Inverted Pressurised Water Reactor (IPWR) for which MSLTTs were chosen for the tubular flow channels in order to reduce the excessive pressure drop caused by full-length twisted tapes (FLTTs). Available correlations were examined, but they either had applicability ranges that for some parameters did not cover the IPWR operating conditions, or did not exhibit acceptable accuracy. Accordingly, a new correlation was developed for MSLTTs that is accurate for IPWR conditions. The MSLTT correlation is bounded by the performance of a FM for fully developed swirl, and the empty tube value where the swirl intensity is negligible. The development of the thermal-hydraulic analysis methodology for the tubular flow channels was completed by modifying existing correlations for pressure drop with multiple short-length twisted tapes and the attendant swirl decay between the individually spaced tapes. The methodology described herein can be used for the overall design of an IPWR as well as any heat transfer apparatus using MSLTTs in circular tubes at the operating conditions specified in this paper. (c) 2012 Elsevier B.V. All rights reserved.

By generating helical swirling motion inside a tube with a twisted-tape insert, forced convective heat transfer is significantly enhanced. The primary mechanism entails imparting a centrifugal force component to the longitudinal fluid motion, which superimposes secondary circulation over the main axial flow to promote cross-stream mixing. Based on experimental flow visualization and computational modeling of single-phase laminar flows, a fundamental scaling of the cross-sectional vortex structure and a parametric analysis of the primary enhancement mechanisms in single-phase flows are delineated. Heat transfer coefficient and friction factor correlations for both laminar and turbulent regimes are presented, and the damping effect of swirl on the transition region is highlighted. In flow boiling with net vapor generation, tape-twist-induced helical swirl pushes liquid droplets from the core to the wall to enhance heat transfer and delay dryout. In subcooled boiling, the radial pressure gradient due to the swirl promotes vapor removal from the heated surface to retard vapor blanketing and accommodate higher heat fluxes. The scaling and phenomenological descriptions of the underlying vapor-liquid transport in these different boiling modes and regimes are presented along with any available predictive correlations.

The science and art of heat and mass transfer enhancement, or augmentation, or intensification, has evolved into an important component of varied aspects of thermal science and engineering. The accumulated literature in enhanced heat and mass transfer includes thousands of references, and it continues to grow. This poses a challenge for the dissemination of appropriate design and application information. To give an overview of the current state of this important technology, representative developments over the past several years in each category of enhancement techniques are cited and commented on. The discussion is divided into the literature dealing with passive enhancement techniques, active enhancement techniques, and compound enhancement techniques.

Heat transfer enhancement, which is often also referred to as augmentation or intensification, has evolved into an important component of thermal science and engineering. The accumulated literature in enhanced heat and mass transfer includes thousands of references, and it continues to grow. To give an overview of the current state of this important technology, representative developments over the past ten years in each category of enhancement techniques are cited and commented on. The discussion is divided into the literature, passive enhancement techniques, active enhancement techniques, and compound enhancement techniques.

Extended performance evaluation criteria (ExPEC) have been used to assess the performance characteristics of single-phase fully developed laminar flow through heat exchangers with rectangular, isosceles triangular, elliptical and hexagonal ducts. The heat exchanger with circular tubes has been used as a reference heat transfer unit. The constant wall temperature has been selected as thermal boundary condition. The performance characteristics of the heat exchangers with non-circular tubes have been evaluated and compared to those of the reference unit for different objectives and constraints imposed. As a common constraint, the cross sectional area of the non-circular duct has been specified. The results from this study have clearly showed that, in some cases, the rectangular and elliptical duct configuration can compete the circular tube unit. The choice of the duct shape depends on the constraints imposed and the objectives pursued. The results obtained from the present study have confirmed again the importance of the use of ExPEC (two objectives to be pursued simultaneously) to assess the benefits and select the optimal heat exchanger design. Copyright © 2012 Praise Worthy Prize S.r.l. All rights reserved.

Recent investigation of the performance characteristics of some passive compound heat transfer enhancement techniques revealed that the combination of corrugated tubes with twisted-tape inserts seems to be a very attractive enhancement technique for single-phase turbulent flow. This holds in the range of height-to-diameter ratios e/D-i > 0.04 and small relative pitches of the twisted tape, H/D-i. This paper presents the latest results of an experimental investigation of the friction factors and heat transfer coefficients (inside with water as working fluid and outside with condensing steam) of eight single-start, spirally corrugated tubes with geometrical parameters: 0.053 < e/D-i <0.089 and ridge pitch-to-height ratio 6.8 < p/e < 11.0 combined with twisted tapes with H/D-i = 4.7, 5.7, and 7.6, in the range of Reynolds number, 3.5 x 10(3) < Re < 5.0 x 10(4). The increase of outside heat transfer coefficient E-0 is presented as a function of geometrical parameters of the depth of the corrugated tube through the Weber number, We, and the relative pitch of the twisted tape H/D-i. The effect of Reynolds number on E-0 is discussed.

For the past 40 years considerable attention has been devoted to the innovation, characterization, and implementation of polymer heat exchanger technology, driven by the corrosion resistance, low density, low cost, and ease of manufacture of many polymeric materials. Moreover, new polymer composites, with higher impact and yield strengths, higher temperature limits, and higher thermal conductivities, promise to bridge the performance gap that exists between polymers and corrosion-resistant metals. This paper begins by reviewing the history of polymer heat exchangers and the technical limitations that have motivated much of the research on this technology. The notable developments that have taken place in the last decade and primary potential applications for polymer heat exchangers are then discussed, including solar water heaters, heat recovery systems, and seawater heat exchangers, in particular, for the desalination industry. The paper closes with a review of compact polymer heat exchangers, with millimeter-sized passages, and thoughts on future applications of this most promising technology.

Isothermal pressure drop tests were performed on horizontal round tubes each containing identical, physically separated, equally spaced, short-length twisted tapes (TTs). The tests investigated the dependence of the Darcy friction factor, f, on the empty tube Reynolds number Re, TT twist ratio y, and TT spacing s. The variation of f across TTs belonging to the same test section was also examined. Ranges of the experimental variables examined were: 10,000⩽Re⩽90,000, 1.5⩽y⩽6, and s=30, 40 and 50. The number of 360° revolutions was held constant for all the tapes and equal to 1.5. Tap water at room temperature and nearly atmospheric pressure was used as the working fluid. A correlation for the Darcy friction factor, in the form f=f (Re, y, s), was developed from the collected experimental data, with excellent accuracy.

Enhanced heat transfer has evolved into an important component of heat transfer experimentation and theory. The accumulated literature includes thousands of references. To give an overview of the current state of this important technology—for the past ten years, representative developments in each category of enhancement techniques are cited and commented on. The discussion is divided into the literature, passive enhancement techniques, active enhancement techniques, and compound enhancement techniques.

Probes (sampling, temperature, pressure) for high-temperature environments, such as gas turbine combustors, can survive only if they are cooled. To keep probe size small, the cooling passages must be microchannels, [O] 100 micrometer internal diameter. For logistical reasons, the length-to-diameter ratio is considerable. Heat fluxes are high, so that boiling occurs even with high velocities. The limiting factor for probe survivability, then, is the critical heat flux (CHF). This paper summarizes an experimental study of CHF in cooling channels that might be used for probes. A CHF correlation for water coolant is developed for design. An orifice at the channel inlet, originally conceived for enhancement, was found to dramatically improve the flow stability and increase the CHF. Pumping power requirements for plain tubes and orificed tubes are also documented.

Phase-change processes, such as pool and flow boiling, are generally very effective modes of heat transfer. However, the demands of modern thermal systems have required the development of methods to enhance boiling systems. While heat fluxes above 108W/m2 have been accommodated in carefully controlled situations, the required fluid and the convective conditions usually dictate maximum heat fluxes several orders of magnitude lower. Two major contemporary areas, enhanced surfaces for pool boiling and enhanced surfaces and inserts for forced convection boiling/vaporization, are discussed, as they facilitate the attainment of high heat fluxes. In addition to these passive techniques, active techniques and compound techniques are mentioned. The taxonomy of enhanced heat transfer is covered, and recommendations are given for future work.