bluuebunny/crossref_metadata_2025 huggingface dataset:
Personalized Pricing and Quality Customization
Authors: Ghose Anindya , Huang Ke‐Wei
Published: October 2009

We embed the principal–agent model in a model of spatial differentiation with correlated consumer preferences to investigate the competitive implications of personalized pricing and quality allocation (PPQ), whereby duopoly firms charge different prices and offer different qualities to different consumers, based on their willingness to pay. Our model sheds light on the equilibrium product‐line pricing and quality schedules offered by firms, given that none, one, or both firms implement PPQ. The adoption of PPQ has three effects in our model: it enables firms to extract higher rents from loyal customers, intensifies price competition for nonloyal customers, and eliminates cannibalization from customer self‐selection. Contrary to prior literature on one‐to‐one marketing and price discrimination, we show that even symmetric firms can avoid the well‐known Prisoner's Dilemma problem when they engage in personalized pricing and quality customization. When both firms have PPQ, consumer surplus is nonmonotonic in valuations such that some low‐valuation consumers get higher surplus than high‐valuation consumers. The adoption of PPQ can reduce information asymmetry, and therefore sellers offer higher‐quality products after the adoption of PPQ. Overall, we find that while the simultaneous adoption of PPQ generally improves total social welfare and firm profits, it decreases total consumer surplus.
Functional aspects of treatment with implant‐supported single crowns: a quality control study in subjects with tooth agenesis
Authors: Goshima Kenichi , Lexner Michala O. , Thomsen Carsten Eckhart , Miura Hiroyuki , Gotfredsen Klaus , Bakke Merete
Published: October 2009

Background: No comprehensive patient‐centered and clinical evaluations of the functional effect of treatment with implant‐supported single crowns (ISSC) have been reported previously.

Objective: To investigate whether and how treatment with ISSC affects masticatory function and Oral Health‐Related Quality of Life (OHRQoL) in subjects with tooth agenesis.

Material and methods: In nine females and nine males (32±10 years) with agenesis treated with one to four ISSC (68% in the premolar region), the treatment effect and masticatory function were assessed. The evaluation was performed first after implant placement shortly before crown cementation, and again 1 month after cementation. It consisted of questionnaires [including Oral Health Impact Profile (OHIP‐49)] and functional examination with plastic strips, the Dental Prescale Film and the Occluzer system, Xylitol color‐changeable gum and slices of Granny Smith apple.

Results: The patients' satisfaction with treatment was high and they experienced a significant overall improvement in their OHRQoL (on average 13% reduction in the total OHIP scores). The cementation of the crowns was associated with a significant increase in the number of near occlusal tooth contacts, contact area, bite force, and masticatory ability and performance. Correspondingly, there was a significant, positive correlation between the number of tooth contacts and (1) occlusal contact area, (2) bite force, and (3) masticatory performance.

Conclusion: Treatment with ISSCs in subjects with tooth agenesis significantly increased masticatory function subjectively and clinically as well as OHRQoL. However, as the functional parameters before replacement of the teeth corresponded to values in subjects with complete dentitions, the functional importance of the increase may be questioned.

To cite this article:
 Goshima K, Lexner MO, Thomsen CE, Miura H, Gotfredsen K, Bakke M. Functional aspects of treatment with implant‐supported single crowns: a quality control study in subjects with tooth agenesis. Clin. Oral Impl. Res. 21, 2009; 108–114.
Histomorphometric comparison of maxillary pristine bone and composite bone graft biopsies obtained after sinus augmentation
Authors: Galindo‐Moreno Pablo , Moreno‐Riestra Ildefonso , Ávila Gustavo , Fernández‐Barbero Juan Emilio , Mesa Francisco , Aguilar Mariano , Wang Hom‐Lay , O'Valle Francisco
Published: October 2009

Introduction: Sinus grafting is a technique oriented to facilitate implant placement in posterior atrophic maxillae. Several modifications of the original technique and a wide variety of materials have been proposed; most of them associated with implant survival rates. However, the quality of the bone obtained after the application of certain grafting materials has not been fully elucidated yet. The aims of this multicenter study were to analyse histomorphometrical samples obtained 6 months after sinus grafting using a composite graft consisting of anorganic bovine bone (ABB)+ autologous bone (AB), and to compare these samples with maxillary pristine bone biopsies.

Material and methods: Ninety maxillary sinus augmentations were performed for delayed implant placement (N=90) in 45 consecutive patients (test group). Bone cores were harvested 6 months after grafting for histomorphometric and ultrastructural study. Control pristine bone biopsies were taken from the posterior maxilla of 10 patients (control). Bone radiographic changes were assessed up to 24 months after implant loading.

Results: The total mean values after analysis of test cores revealed a proportion of 46.08±16.6% of vital bone, 42.27±15.1% of non‐mineralized connective tissue, and 37.02±25.1% of the remaining ABB particles. Significant bone remodeling activities were noticed in sinus grafting samples when compared with pristine bone. A statistically significant difference was observed in the number of osteoid lines between two groups, with higher values in the test one (15.1±11.48% vs. 2.5±2.2%, P=0.0005). Ultrastructural study showed that vital trabecular bone was in intimal contact with ABB particles. Radiographic analysis revealed that the higher the proportion of remaining ABB, the lower the total vertical resorption of the graft.

Conclusion: Sinus grafting constitutes an excellent model for the study of de novo bone formation patterns and graft consolidation, when a combination of different bone substitutes is applied. The combination of ABB+AB yields highly satisfactory outcomes from both a clinical and a histologic perspective.

To cite this article:
 Galindo‐Moreno P, Moreno‐Riestra I, Ávila G, Fernández‐Barbero JE, Mesa F, Aguilar M, Wang H‐L, O'Valle F. Histomorphometric comparison of maxillary pristine bone and composite bone graft biopsies obtained after sinus augmentation. Clin. Oral Impl. Res. 21, 2009; 122–128.
Socioeconomic factors in adolescents’ oral health: are they mediated by oral hygiene behaviors or preventive interventions?
Authors: Polk Deborah E. , Weyant Robert J. , Manz Michael C.
Published: October 2009

Polk DE, Weyant RJ, Manz MC. Socioeconomic factors in adolescents’ oral health: are they mediated by oral hygiene behaviors or preventive interventions? Community Dent Oral Epidemiol 2010; 38: 1–9. © 2009 John Wiley & Sons A/S

Abstract –  Objectives:  To determine whether there is a socioeconomic status (SES) disparity in caries experience (i.e., DMFT) in an adolescent sample from Pennsylvania and to determine whether differences in oral hygiene behaviors and preventive interventions account for this disparity.

Methods:  A cross‐sectional clinical assessment was conducted on a representative sample of 9th grade and 11th grade students across Pennsylvania. These students also completed a brief questionnaire regarding their oral hygiene behaviors. From this group of students, a random subsample of 530 parents completed a questionnaire assessing SES, fluoride exposure, and recency of receipt of dental services. DMFT was examined at two thresholds of severity: simple prevalence (DMFT > 0) and severe caries (DMFT > 3).

Results:  Using structural equation modeling, we found that lower SES was associated with higher prevalence of DMFT and higher prevalence of severe caries. Although lower SES was associated with lower rates of brushing, less use of sealants, and less recent receipt of dental services, these oral health behaviors and preventive interventions did not account for the disparities in DMFT defined by SES.

Conclusions:  There is an SES gradient in caries experience in adolescents in Pennsylvania. Disparities in caries experience, however, cannot be accounted for by SES‐associated differences in brushing, flossing, sealant use, fluoride exposure, or recency of use of dental services. To facilitate the design of preventive interventions, future research should determine the pathways through which SES‐associated disparities occur.
Oral health‐related quality of life of 12‐ and 15‐year‐old Thai children: findings from a national survey
Authors: Krisdapong Sudaduang , Sheiham Aubrey , Tsakos Georgios
Published: October 2009

Abstract –  Objective:  To assess the prevalence and characteristics of oral impacts on daily life, and the relationship between certain dental conditions and impacts attributed to them, in a nationally representative population of Thai school children aged 12 and 15 years.

Methods:  A cross‐sectional study on a representative sample of children in Sixth Thailand National Oral Health Survey. Sample included half the children aged 12‐ and 15‐year‐old selected in Bangkok and all participants in 8 of 16 provinces included in national survey. Children were individually interviewed using the Child‐OIDP (12‐year‐old) and OIDP indices (15‐year‐old), and two questions for overall subjective assessments.

Results:  A total of 1066 12‐year‐olds and 815 15‐year‐olds were interviewed. Some 85.2% of 12‐year‐olds reported experiencing oral impacts during the past 3 months. Child‐OIDP scores ranged from 0 to 68.0 (mean = 7.83, SD = 7.8). Eating was the most commonly affected performance (64.4%), followed by cleaning teeth (51.7%) and maintaining emotional state (49.1%). Among 15‐year‐old children, 83.3% had oral impacts during the past 6 months. OIDP scores ranged from 0 to 39.5 (mean = 5.47, SD = 6.0). The three most commonly affected performances were eating (64.0%), cleaning teeth (55.3%) and maintaining emotional state (53.1%). Toothache and oral ulcers were the two most important perceived causes in 12‐year‐olds. Impacts from toothache were the most prevalent (39.2%) and had a condition‐specific (CS) Child‐OIDP score of 7.0, while oral ulcers affected 24.7% of children; mean CS‐score of 8.0. Among 15‐year‐olds, oral ulcers ranked first in terms of both prevalence (36.2%) and CS‐score (6.0), followed by toothache (prevalence 33.9% and CS‐score 5.0). For both age groups, problems with gums were of less concern.

Conclusions:  Oral impacts were common but not severe in Thai children and adolescents. For both age groups, impacts were mostly on eating performance; toothache and oral ulcers were the two important perceived causes reflecting needs for oral health promotion and treatment of dental caries and oral ulcers.
Treatment practices in adults with chronic immune thrombocytopenia – a European perspective
Authors: Rodeghiero Francesco , Besalduch Juan , Michel Marc , Provan Drew , Grotzinger Kelly , Thompson Gwilym
Published: October 2009

Immune thrombocytopenia (ITP) is characterised by platelet destruction and impaired production leading to isolated thrombocytopenia. The aim of this study, comprising a retrospective longitudinal cohort study complemented by a Delphi panel of 35 physicians, was to describe standard treatment practices and treating physician’s perception and preferences for available treatment options in chronic ITP. The medical records of 610 patients were reviewed over 12 months. Mean age at the start of the observational period was 54.6 yr, median platelet count 77 × 109/L with 41% of patients having symptoms of ITP. Treated patients (61%) received an average of 2.7 medications either for ITP or ITP treatment‐related side effects. An array of products was used, but the most frequent were corticosteroids. Delphi panel physicians (45%) indicated the main goals for treatment were to increase platelet levels to at least 30 × 109/L to prevent bleeding or haemorrhage. The majority (89%) indicated that personal experience influenced treatment choice. Most (>80%) rated splenectomy and high‐dose corticosteroids as the most effective but were concerned about side effects, and many (75%) would like access to interventions with improved efficacy and safety. The study highlights the need for updated evidence‐based treatment guidelines to assist physicians in patient treatment decisions and to realise improvements in patient outcomes. It also identified perceived shortcomings of existing therapies and the need to establish an evidence base for newer interventions that could potentially make lasting response to treatment with fewer adverse effects an achievable goal.
Mutagenicity and Safety Evaluation of Ethanolic Extract of Prunus mume
Authors: Lu Baiyi , Wu Xiaoqin , Dong Yuejie , Gong Jinyan , Zhang Ying
Published: October 2009

ABSTRACT:  The ethanolic extract of Prunus mume (EPM) is a novel polyphenol preparation derived from branches (with leaves) of Prunus mume, which could be used as a functional ingredient for antioxidant and antiobesity therapy. The purpose of this study was to evaluate the safety of EPM. An EPM was prepared and evaluated for oral acute and subacute toxicity in Sprague–Dawley rats, while its mutagenic potential was assessed by a reverse mutation test using Salmonella typhimurium, by a bone marrow cell micronucleus test using ICR mice, and by a sperm abnormality test using ICR mice. The results showed no acute lethal effects at the maximal tested EPM dose of 20 g/kg bw in either rats or mice, suggesting that EPM can be regarded as virtually nontoxic. Administration at levels of 0.84, 1.67, and 3.33 g/kg bw to rats for 30 d did not induce any significant hematological, clinical, chemical, or histopathological changes. No mutagenicity evidence was detected in any of the 3 mutagenic tests. The level of “no observed adverse effect” (NOAEL) for EPM was above 3.33 g/kg bw for the subacute toxicity study.
Antioxidant Activities of the Supercritical and Conventional Satureja montana Extracts
Authors: Grosso C. , Oliveira A.C. , Mainar A.M. , Urieta J.S. , Barroso J.G. , Palavra A.M.F.
Published: October 2009

ABSTRACT:  The antioxidant activities of the volatile and the nonvolatile fractions from Satureja montana obtained by supercritical fluid extraction (SFE) and by conventional techniques, hydrodistillation (HD) and soxhlet extraction (SE), were compared. A good agreement between DPPH and rancimat methods was obtained showing that the extracts were able to scavenge free radicals and to inhibit lipid oxidation. The volatile oil (obtained by SFE at 90 bar/40 °C) was the most effective extract, presenting the lowest EC50 (0.06 g/L) and the highest protector factor (PF = 2.03). These results demonstrated the advantages of SFE over conventional techniques by avoiding thermodegradation and hydrolysis reactions. Furthermore, volatile oil is 15 times richer in thymoquinone than the essential oil (HD). This compound is of great importance due to its antioxidant, neuroprotective, and anti‐cancer activities. The combination of carvacrol + thymol + thymoquinone in volatile oil may be responsible for the increase in the antioxidant activity when compared to HD, which demonstrates that, in this case, SFE improves value to the final product.
Assessing poverty, risk and vulnerability: a study on flooded households in rural Bangladesh
Authors: Rayhan M.I.
Published: October 2009

Flood is a common catastrophe in Bangladesh. This study aimed to examine the poverty, risk and vulnerability for flood hazards. A cross‐sectional household survey was carried out after 2 weeks of the flood in four districts in the year 2005. In total, 600 rural households were interviewed through a three‐stage stratified random sampling. A utilitarian approach was used to assess flood vulnerability and its components. A set of households' characteristics and shock (flood) variables were used as explanatory variables. The results showed that poverty and idiosyncratic flood risks are positively correlated and highly significant. Households with higher educated members, headed by a male and owners of a dwelling place have been found to be less vulnerable to idiosyncratic flood risk. Possession of arable land and a small family size can reduce poverty and the aggregate flood risk.
Natural Convection in Horizontal Duct Connecting Two Fluid Reservoirs
Authors: Bejan A. , Rossie A. N.
Published: October 2009

The paper reports an experimental study of natural convection between two water reservoirs connected through a two-dimensional horizontal duct. The flow field was visualized and the velocities were measured using the thymol blue pH indicator method. The temperature field in the duct region and the heat transfer rate through the duct were also measured. It is shown that the duct flow consists of two streams in counterflow, the warmer stream occupying the upper half of the channel. The two streams are insulated from one another by a mid-depth buffer layer. The measurements demonstrate that the heat transfer mechanism differs fundamentally from the mechanism envisioned in the Bejan and Tien theory [6]. It is also suggested that the basic design of the experimental apparatus can be used in future studies of stability of shear flows in stratified fluids.
Nongray Particulate Radiation in an Isothermal Cylindrical Medium
Authors: Felske J. D. , Lee K. M.
Published: October 2009

The radial radiative heat flux and its divergence are determined both exactly and approximately for homogeneous suspensions of small particles. Scattering is assumed to be small compared to absorption and the absorption coefficient is taken to be inversely proportional to wavelength. The exact solution is reduced to an infinite series of single integrals. The optically thin and the next higher order behavior appear in closed form as the first two terms in the series. Two approximate solutions are also developed. One is in good agreement with the exact solution while the other is not. Finally, a closed form approximate relation is derived for the dimensionless heat flux at the surface. This expression, which also gives the emissivity or absorptivity of the medium, is in excellent agreement with the exact result.
The Prediction of Three-Dimensional Discrete-Hole Cooling Processes: Part 2—Turbulent Flow
Authors: Bergeles G. , Gosman A. D. , Launder B. E.
Published: October 2009

Computer simulations are described of the injection of a secondary coolant fluid through a row of downstream-facing holes arranged across a surface exposed to a hot parallel gas stream, as occurs in certain discrete-hole cooling systems for turbine blades. The simulation is performed by solving the governing equations numerically, with the effects of turbulence modelled in a way which allows for the anisotropies existing in the real situation. Comparisons with measurements obtained for injection angles of 30 deg and dimensionless blowing rates in the range 0.2 to 0.5 show good agreement in the majority of cases. Discrepancies are however observed at conditions of small upstream boundary layer thickness or large injection rates and the causes of these are identified and discussed.
Heat Transfer in the Accelerated Fully Rough Turbulent Boundary Layer
Authors: Coleman H. W. , Moffat R. J. , Kays W. M.
Published: October 2009

Heat transfer behavior of a fully rough turbulent boundary layer subjected to favorable pressure gradients was investigated experimentally using a porous test surface composed of densely packed spheres of uniform size. Stanton numbers and profiles of mean temperature, turbulent Prandtl number, and turbulent heat flux are reported. Three equilibrium acceleration cases (one with blowing) and one non-equilibrium acceleration case were studied. For each acceleration case of this study, Stanton number increased over zero pressure gradient values at the same position or enthalpy thickness. Turbulent Prandtl number was found to be approximately constant at 0.7–0.8 across the layer, and profiles of the non-dimensional turbulent heat flux showed close agreement with those previously reported for both smooth and rough wall zero pressure gradient layers.
An Iterative Boundary Integral Numerical Solution for General Steady Heat Conduction Problems
Authors: Khader M. S. , Hanna M. C.
Published: October 2009

An iterative boundary integral numerical method for solving the steady conduction of heat is developed. The method is general for two- and three-dimensional regions with arbitrary boundary shapes. The development is generalized to include the first, second, and third kind of boundary conditions and also radiative boundary and temperature-space dependent convective coefficient cases. With Kirchhoff’s transformation, cases of temperature-dependent thermal conductivity with general boundary conditions are also accounted for by the present method. A variety of problems are analyzed with this method and their solutions are compared to those obtained analytically. A comparison between the present method and the finite difference predictions is also investigated for a case of mixed temperature and convective boundary conditions. Moreover, two-dimensional regions with three kinds of boundary conditions and irregular-shaped boundaries are used to illustrate the versatility of the technique as a computational procedure.
Critical Heat Flux Experiments and Correlation in a Long, Sodium-Heated Tube
Authors: France D. M. , Carlson R. D. , Chiang T. , Minkowycz W. J.
Published: October 2009

Critical heat flux (CHF) experiments were performed in the Steam Generator Test Facility (SGTF) at Argonne National Laboratory for application to liquid metal fast breeder reactor steam generators. The test section consisted of a single, straight, vertical, full-scale LMFBR steam generator tube with force-circulated water boiling upwards inside the tube heated by sodium flowing countercurrent in a surrounding annulus. The test section tube parameters were as follows: 10.1 mm i.d., 15.9 mm o.d., material = 2 1/4 Cr–1 Mo steel, and 13.1 m heated length. Experiments were performed in the water pressure range of 7.0 to 15.3 MPa and the water mass flux range of 720 to 3200 kg/m2˙s. The data exhibited two trends: heat flux independent and heat flux dependent. Empirical correlation equations were developed from over 400 CHF tests performed in the SGTF. The data and correlation equations were compared to the results of other CHF investigations.
Comparisons between Experiments and a Theoretical Model of Heat and Mass Transfer in Rotary Regenerators with Nonsorbing Matrices
Authors: van Leersum J. G. , Ambrose C. W.
Published: October 2009

A mathematical model of condensation, evaporation and heat transfer in a regenerator having a non sorbing matrix is derived. Good agreement between heat and moisture effectivities predicted by a simulation of the model, and corresponding results from an independently derived equilibrium model is shown for a particular case. Details of an experimental facility for testing the performance of a rotary regenerator are given, and a comparison between results obtained from the facility and those produced by the model are given.
Vortex Instability of Mixed Convection Flow over a Horizontal Flat Plate
Authors: Moutsoglou A. , Chen T. S. , Cheng K. C.
Published: October 2009

The vortex instability of laminar, mixed-convection flow over an isothermal, horizontal flat plate is investigated analytically by the linear stability theory. In the analysis, the main flow and thermal fields are treated as non-parallel and the disturbances are assumed to have the form of a stationary longitudinal vortex roll that is periodic in the spanwise direction. Numerical results for the critical Grashof and Reynolds numbers that predict the first occurrence of the vortex rolls are obtained for fluids with Prandtl numbers of 0.7 and 7. It is found that the flow becomes more susceptible to vortex mode of instability as the buoyancy force increases. The present results are compared with available experimental data and also with analytical results from the wave mode of instability.
Effect of Adiabatic Co-Planar Extension Surfaces on Wind-Related Solar-Collector Heat Transfer Coefficients
Authors: Sparrow E. M. , Lau S. C.
Published: October 2009

The heat transfer response to framing the thermally active cover surface of a flat plate solar collector with adiabatic co-planar extension surfaces has been investigated by wind tunnel experiments. Various framing patterns were employed (leading edge and/or trailing edge and/or side edge framing), along with frames of different width. The experiments were performed for various angles of inclination of the plate surface relative to the oncoming airstream and for a range of Reynolds numbers. It was found that the wind-related heat transfer coefficients can be substantially lower when the collector is framed than when it is unframed. An estimate of the possible reduction of the average heat transfer coefficient can be obtained from the equation h/h* = (Lc/Lf)1/2, where h and h* respectively denote the coefficients in the presence and in the absence of the frame. The quantity Lc is a dimension that is characteristic of the thermally active area of the cover surface, while Lf is a characteristic dimension of the outer edges of the frame. With respect to the reduction of the heat transfer coefficient, framing along the side edges appears to be more beneficial than framing along the leading and trailing edges, as is framing along the trailing edge compared with framing along the leading edge.
High Pressure Homogeneous Nucleation of Bubbles within Superheated Binary Liquid Mixtures
Authors: Avedisian C. T. , Glassman I.
Published: October 2009

The limits of superheat of some binary normal paraffin mixtures were measured at pressures up to 2128 kPa using the floating droplet method. The variation of nucleation temperature with liquid phase mole fraction was found to be nearly linear for these n-paraffin solutions over the whole pressure range in which the experiments were performed. Homogeneous nucleation theory was used to predict the limits of superheat of the solutions tested. The vapor pressures of the mixtures were estimated by using the Peng-Robinson equation of state to evaluate the liquid and vapor phase fugacities, and the mixture surface tensions were calculated using an empirical adaptation of the van der Waals expression for the surface tension of a pure liquid near the critical point. The predicted and measured limits of superheat were found to be in good agreement over the entire pressure range for all liquid phase compositions. The results of the present work could be useful for predicting liquid phase temperatures and compositions at which the microexplosive or disruptive burning of droplets of fuel blends which are mixtures of volatile and nonvolatile liquids will be initiated during droplet combustion at high ambient pressures.
Heat Transfer in Two-Component Dispersed Flow
Authors: Mastanaiah K. , Ganic´ E. N.
Published: October 2009

Measurements have been made of heat transfer near atmospheric pressure in the post dryout region of air-water dispersed flow in an electrically heated 12.95 mm i.d. vertical stainless steel tube with a length of 889 mm. The mass velocity ranges from 30 to 83 kg/m2·s, and the average wall heat flux is varied from 6.4 to 36.2 kW/m2 in the experiments. Correlation of a theoretical analysis with the measured wall temperatures suggests that the effectiveness of wall-to-drop heat transfer depends mainly on the wall superheat for surface temperatures below the minimum film boiling temperature. The local two-phase heat transfer coefficient decreases with increasing wall temperature. It is also found that the thermal entrance length for two-phase dispersed flow exceeds that of the single-phase gas flow, and that it decreases with an increase in wall temperature.
Transient Simultaneous Heat and Mass Transfer in Moist, Unsaturated Soils
Authors: Hartley J. G. , Black W. Z.
Published: October 2009

The transient heat and mass transfer in a moist porous medium adjacent to a cylindrical heat source is analyzed in order to characterize the thermal stability of the medium. In the context of this paper, thermal instability occurs in a moist porous medium as a result of significant drying due to excessive thermally induced moisture movement. A dry zone is created which propagates into the medium and thereby inhibits dissipation of heat from the source. The drying of the porous medium adjacent to the heat source is predicted to occur in two distinct stages. During the first stage the rate of moisture movement initially decreases until a “critical moisture content” is reached. Thereafter the drying rate generally increases until complete drying of the material in the vicinity of the heat source has occurred. The value of the critical moisture content is found to be essentially independent of the strength (heat transfer rate per unit length) of the heat source. The parameters which most significantly influence the transport processes are identified and correlated on the basis of numerical solutions of the governing equations. The critical moisture content and critical heat flux are defined and used to quantify thermal stability limits. The correlations are validated through comparison with experimental measurements made on a native soil. The thermal stability model developed in this work establishes the relationship between the thermal stability limits for large-diameter and small-diameter heat sources. From this relationship the thermal stability associated with large-diameter sources can be accurately predicted from experimental measurements using small-diameter sources and small samples.
Analytic Prediction of the Friction Factor for Turbulent Flow in Internally Finned Channels
Authors: Scott M. J. , Webb R. L.
Published: October 2009

This work develops an analytical model for the friction factor with turbulent flow in internally finned channels. Such channels are an important class of enhanced heat transfer surfaces. Until this work, no analytical models for the turbulent friction factor have been proposed. The present model assumes the validity of the Law of the Wall and applies the logarithmic velocity distribution to the interfin and core regions of the flow. Theoretically based friction factor equations are developed for internally finned circular tubes and rectangular channels. The model predicts Carnavos data for 21 internally finned tubes within ± 10 percent. Friction factor data were taken for five internally finned, rectangular channels. The analytical model predicts these data within ± 10 percent, except for the case of a very high fin.
Unsteady Stagnation Point Heat Transfer with Blowing or Suction
Authors: Sano Takao
Published: October 2009

The effects of blowing and suction on unsteady heat transfer at a stagnation point due to a step change in wall temperature are examined. Two asymptotic solutions for the temperature field at large and small Prandtl numbers are presented. It is shown that the asymptotic solution for large Prandtl number gives sufficiently accurate results for the surface heat transfer even for the moderate values of Prandtl number if Euler transformation is applied to the series.
Destabilization of Film Boiling Due to Arrival of a Pressure Shock—Part I: Experimental
Authors: Inoue A. , Bankoff S. G.
Published: October 2009

Transient heat transfer from an electrically-heated 3 mm o.d. horizontal tube, initially in subcooled film boiling, was measured immediately after passage of a shock wave of 1–5 × 105 N/m2 over-pressure. The fluids tested were Freon-113 and 95 percent ethanol-5 percent water at initially 0.5–2 × 105 N/m2 at 22–24° C. Transient heat transfer rates, averaged over 0.5–1 ms after vapor film collapse, ranged up to 20 times the steady-state value. The maximum transient flux occurred at supercritical contact temperatures, with frequently a minimum in the range of contact temperatures between the homogeneous nucleation and the critical temperature. Photography at 5000 frames/s showed apparently complete vapor film collapse within one or two frames, followed by re-establishment of film boiling in ∼1 ms, and eventually nucleate boiling in ∼100 ms. The surface temperature which gave the highest peak transient flux shifted appreciably with increasing shock pressure, which indicates some compressibility even after “contact” was made. Implications for vapor explosions are discussed.
Destabilization of Film Boiling Due to Arrival of a Pressure Shock: Part II—Analytical
Authors: Inoue A. , Ganguli A. , Bankoff S. G.
Published: October 2009

Vapor explosions are believed to be triggered by the rapid collapse of film boiling of coolant in contact with molten fuel, probably due to local pressure waves from an initially small interaction. In Part I of this work the heat transfer during the first two ms after passage of a shock past a hot nickel tube surrounded by subcooled Freon-113 or ethanol was studied. The following important results were obtained: (1) The peak heat flux exhibits a maximum of a heater surface temperature of 280–350° C, depending upon the strength of the shock. This is well above the critical temperature, so that nucleation considerations are irrelevant. (2) The maximum of the peak heat flux envelope depends upon the shock ΔP, indicating that only partial contact is made upon collapse of the vapor film. (3) The collapse is rapid (1–2 frame at 5000 f/s), and is produced by relatively weak shocks (ΔP = 2–3 atm.). In the present work, the vapor film collapse is studied analytically, in order to obtain additional insight into the mechanism. A Lagrangian transformation due to Hamill and Bankoff is introduced to immobilize the moving boundary, and a polynomial temperature distribution in the transformed mass variable is assumed in the vapor region, as well as in the liquid region. This leads to a set of coupled nonlinear ordinary differential equations in the three regions, which are solved numerically. Two models were developed: (1) A detailed model, taking into account the Knudsen layers at the vapor-liquid and vapor-solid interfaces, and (2) a simplified model, in which these layers were neglected, and a linear temperature profile in the Lagrangian vapor phase variable was assumed. It is found that the initial vapor mass is a key variable determining whether collapse is achieved. In practice, this is a stochastic variable due to bubble departure, which explains the observed heat flux data scatter. The analytical results are in general agreement with the experimental data.
A Three-Dimensional Air-Vapor-Droplet Local Interaction Model for Spray Units
Authors: Palaszewski S. J. , Jiji L. M. , Weinbaum S.
Published: October 2009

An approximate fully three-dimensional numerical model for predicting the detailed flow and thermal characteristics of spray units is presented. The new model differs from all previous analyses of spray cooling systems in that it determines the local variation in the dry-bulb temperature, absolute humidity and the air streamlines throughout the flow field encompassing the spray umbrella and the effect of this local variation on drop cooling. The conservation equations to determine the local absolute humidity, velocity and dry-bulb temperature of the air-vapor phase are written in Lagrangian form where the droplets are treated as spatially varying sources of mass, momentum and energy. The analysis takes into consideration stable and unstable meteorological conditions, turbulent mixing in the atmospheric surface layer and nonuniform upwind and local air-velocity profiles. The numerical model is of intrinsic interest because it demonstrates the feasibility of computing a three-dimensional, two-phase flow field without the use of excessive computer time. Model predictions of droplet return temperature along the spray centerline were compared with data for the Spraco 1751 nozzle. Good agreement was observed.
A Horizontal Flow Past a Partially Heated, Infinite Vertical Cylinder
Authors: Yao L. S. , Chen F. F.
Published: October 2009

The free-convection boundary layer along a partially heated infinitely long vertical cylinder disturbed by a steady horizontal flow is studied. The asymptotic solution indicates that the boundary layer is mainly induced by the buoyancy force in the neighborhood of the thermal leading edge. The effect of the horizontal free stream on the boundary layer gradually increases as one moves upward away from the thermal leading edge along the cylinder. The boundary-layer separation does not occur in the neighborhood of the thermal leading edge. However, the asymptotic solution shows that the forced convection tends to separate the boundary layer along the aft body of the cylinder. The importance of the effect of the forced convection is governed by the parameter εz1/2 where ε is the inverse of the square root of the Richardson number. The asympotic solution is valid as long as the value of εz1/2 is small, and is not explicitly restricted by the Richardson number.
The Influences of Property Variations on Natural Convection from Vertical Surfaces
Authors: Clausing A. M. , Kempka S. N.
Published: October 2009

The objective of this paper is to show the influences of property variations in natural convection. Heat transfer from a vertical isothermal, heated surface to gaseous nitrogen is experimentally investigated. The ambient temperature, T∞, is varied in order to cover a large range of the Rayleigh number and also to enable the generation of large values of this parameter. The range 80 K < T∞ < 320 K results in Rayleigh numbers between 107 and 2 × 1010 for the 0.28 m model. By using a cryogenic environment, large ratios of the absolute temperature of the wall to the ambient temperature, Tw/T∞, are generated without the results being masked by radiative heat transfer. The range 1 < Tw/T∞ < 2.6 is investigated. Variable properties cause dramatic increases in heat transfer rates in the turbulent regime, and virtually no influence is seen in the laminar regime. The results obtained correlate extremely well with the addition of a single parameter Tw/T∞.
Thermally Symmetric Nonlinear Heat Transfer in Solids
Authors: Imber M.
Published: October 2009

Material thermal properties are temperature dependent, and this effect cannot be disregarded at elevated design temperatures. Based upon the principle of equivalent linearization, analytical solutions are developed for thermally symmetric planar solids. The solution method is, in turn, extended to a composite wall whose individual thermal conductivities are also temperature dependent. As a demonstration of the method’s accuracy several numerical examples are shown.
Numerical Solution to a Two-Dimensional Conduction Problem Using Rectangular and Cylindrical Body-Fitted Coordinate Systems
Authors: Goldman A. , Kao Y. C.
Published: October 2009

The temperature distribution in a rectangular plate with a circular void at the center was calculated using a body-fitted coordinate system. Three different transformed geometries were considered: rectangular-rectangular, cut-line, and cylindrical. Problems involving insulated outer surfaces could not be solved using the rectangular-rectangular transformation but could be solved with both the cut-line and cylindrical transformations. The cylindrical transformation also appears to have the capability of being extended to three-dimensional problems.
Steady Laminar Flow through Twisted Pipes: Fluid Flow in Square Tubes
Authors: Masliyah J. H. , Nandakumar K.
Published: October 2009

The Navier-Stokes equation in a rotating frame of reference is solved numerically to obtain the flow field for a steady, fully developed laminar flow of a Newtonian fluid in a twisted tube having a square cross-section. The macroscopic force and energy balance equations and the viscous dissipation term are presented in terms of variables in a rotating reference frame. The computed values of friction factor are presented for dimensionless twist ratios, (i.e., length of tube over a rotation of π radians normalized with respect to half the width of tube) of 20, 10, 5 and 2.5 and for Reynolds numbers up to 2000. The qualitative nature of the axial velocity profile was observed to be unaffected by the swirling motion. The secondary motion was found to be most important near the wall.
Natural Convective Boundary-Layer on Two-Dimensional and Axisymmetric Surfaces in High-Pr Fluids or in Fluid-Saturated Porous Media
Authors: Nilson R. H.
Published: October 2009

In natural convective boundary layers on inclined surfaces, the surface-normal component of the buoyancy force induces a pressure gradient across the boundary layer. For the class of flows in which inertial effects are unimportant (including flows at high Prandtl number as well as flow through fluid-saturated porous media), a local nonsimilarity analysis indicates that the effects of the surface-normal pressure gradient on the temperature profile can be characterized by a single local configuration-parameter which depends on the local geometry and on the Rayleigh Number. Under Mangler’s transformation the reported computational results become applicable to axisymmetric as well as two-dimensional geometries of arbitrary contour. In contrast to the single-parameter dependence of the temperature profiles, the velocity profiles depend upon two local geometric parameters, as illustrated for the example of an inclined flat plate.
Unsteady Mixed Convection Near the Stagnation Point in Three-Dimensional Flow
Authors: Kumari M. , Nath G.
Published: October 2009

The combined effect of forced and free convection on the unsteady laminar incompressible boundary-layer flow with mass transfer at the stagnation point of a three-dimensional body with time dependent wall temperature has been studied. Both semisimilar and self-similar solutions have been obtained. The governing equations have been solved numerically using an implicit finite-difference scheme. The results indicate that the buoyancy force strongly affects the skin friction whereas its effect on the heat transfer is comparatively less. However, the heat transfer is significantly changed due to the wall temperature which varies with time, but the skin friction is little affected by it. The mass transfer and Prandtl number affect both the skin friction and heat transfer. The buoyancy force which assists the forced flow causes an overshoot in both the velocity components.
An Experimental Study of Mixed, Forced, and Free Convection Heat Transfer From a Horizontal Flat Plate to Air
Authors: Wang X. A.
Published: October 2009

A heated flat plate is tested in a wind tunnel to study mixed convection in both upward and downward positions. It is found that the local heat transfer coefficient is strongly dependent on the free stream velocity and the temperature difference between the surface and the free stream. The buoyancy effect is more pronounced for the heated plate facing upward. This paper correlates the experimental data in terms of Nusselt, Grashof, and Reynolds numbers. The points of onset of instability caused by the buoyancy effect are also examined and correlated in terms of the dimensionless groups. Experimental data are compared with analysis documented in the literature, and the agreement is found satisfactory.
On the Thermal Instability of Superposed Porous and Fluid Layers
Authors: Somerton C. W. , Catton I.
Published: October 2009

A solution is presented for the problem of predicting the onset of convection for a system consisting of a volumetrically heated porous bed saturated with and overlaid with a fluid, heated or cooled from below. Results are presented in graphical form in terms of the external Rayleigh number based on the fluid layer, which is shown to be the sole stability parameter of the problem. A wide range of independent parameters are investigated and physical justification for the behavior of the instability with respect to them is given. Finally, the results are compared with the two bounding cases of the problem and are found to be in agreement with them.
A Study on Limiting Exit Quality of CHF of Forced Convection Boiling in Uniformly Heated Vertical Channels
Authors: Katto Y.
Published: October 2009

This paper presents the results from a phenomenological analysis of limited exit quality X°ex, that is, the occurrence of critical heat flux at a nearly constant exit quality X°ex independent of the change of inlet quality under mixed inlet condition. The author’s generalized correlation equations of CHF in uniformly heated channels with subcooled inlet condition are employed for this purpose, and the prediction of X°ex is compared with the existing data of X°ex satisfactorily. As a basis of the above-mentioned analysis, the applicability of the author’s correlation equations to the state near the critical length-to-diameter ratio corresponding to the limiting quality condition is also examined.
Transient Heat-Flux Measurements in the Combustion Chamber of a Spark-Ignition Engine
Authors: Alkidas A. C. , Myers J. P.
Published: October 2009

Heat-flux measurements were obtained at several locations on the cylinder head and liner of a four-stroke, single-cylinder, spark-ignition engine. The variations of heat transfer with air-fuel ratio and volumetric efficiency were investigated. The magnitude of the heat flux was found to be highest at near-stoichiometric composition, whereas at either leaner or richer composition the heat flux decreased. An increase in volumetric efficiency from 40 to 60 percent resulted in an increase in peak heat flux of about 30 percent. The largest cycle-to-cycle variation in the measured heat flux occurred at the time of the initial high rate of heat flux. This is related to the cycle-to-cycle variation of flame propagation in the combustion chamber. Finally, the calculated amount of heat transferred to the walls of the combustion chamber during the closed portion of the engine cycle (intake valve closing to exhaust valve opening) agreed with the corresponding values obtained from the heat-flux measurements.
Attenuation of Thermal Radiation by Pulverized Coal and Char
Authors: Grosshandler W. L. , Monteiro S. L. P.
Published: October 2009

The absorption and scattering of thermal radiation within a dilute cloud of pulverized coal and char is investigated. Results are presented of monochromatic absorptivity measurements on particles 50–150 μm in diameter under conditions representative of the early pyrolysis zone of a combustion chamber. No dependence of absorptivity on coal composition could be discerned for the three lignite and bituminous coals selected. A slight increase in monochromatic absorptivity with temperature and extent of char was observed. For the spectral region investigated, 1.2–5.3 μm, an empirical equation of the form αλ = 0.78 + 0.18/λ1/2 was found to represent the data for all coals and chars within 5 percent. A single total hemispherical absorptivity of 0.89 is recommended for heat-transfer calculations in pulverized coal and char clouds if the particles can be assumed to act as Mie scatters, and if the volume fraction of ash and soot particles is small.
Comparison of the Rhine River and the O¨resund Sea Water Fouling and Its Removal by Chlorination
Authors: Novak L.
Published: October 2009

Microbiological fouling is usually the main fouling mechanism occurring on heat transferring surfaces immersed in natural water of temperature between 5–50°C. The fouling rate of two natural waters—the Rhine river and the sea water of O¨resund—has been studied. The dependence of fouling on flow rate and temperature is given. Chlorination is one of the most common biofouling control methods and it may be used for removal of already formed microbiological deposits. Tests performed on the Rhine water deposit are described and a mathematic description of the chlorination kinetics is presented. The dependence of biofilm destruction on flow rate, temperature, concentration, and operation conditions was examined.