Heat Transfer, Fluid Mechanics and Thermodynamics - HEFAT2012

This editorial provides an overview of a special issue dedicated to the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics – HEFAT2012 – hosted on Malta. All papers for this conference were peer-reviewed and 270 papers were accepted. Of these, 10 of the best papers were selected for this issue and peer-reviewed for a second time according to journal standards. The 10 papers focus on the characteristics of oxyfuel and air-fuel combustion in an industrial water tube boiler, numerical and optical analysis of a weather-adaptable solar reactor, the mitigation of crystallisation fouling using projectiles in tubular heat exchangers, the mitigation of crystallisation fouling in a single heated tube using projectiles of different sizes and hardness, a framework for the analysis of thermal losses in reciprocating compressors and expanders, an annular impinging jet controlled by radial synthetic jets, multi-effect plants and ionic liquids for improved absorption chillers, the effect of climatic parameters on the heat transfer mechanisms in a solar distillation still, empirical correlations for slightly decaying grid turbulence, and pool boiling on modified surfaces using R-123. The current issue of Heat Transfer Engineering is the ninth special journal issue dedicated to selected papers from the HEFAT conferences.http://www.tandfonline.com/loi/uhte20hb201

Constructal law in technology, thermofluid and energy systems, and in design education : comment on "The constructal law and the evolution of design in nature" by Bejan and Lorente

It has been said many times in one form or another that there is nothing more understandable and practical than a simple theory. As engineers and scientists, we are always looking for a simple theory, law or equation in every engineering science to explain behaviours and to use as design tools. Examples of such simple theories are Bernoulli’s law in fluid mechanics [1], the first and second laws in thermodynamics [2], Fourier’s law in conduction heat transfer [3] and Newton’s law for convective heat transfer [4]. Design, on the other hand, has been viewed by many as the subject (I am specifically not using the word “science”) which is an art in which the engineering sciences are creatively synthesised and where industry experience is preferable and in many cases essential. It may involve considerable research, thought, modelling, interactive adjustment and redesign. What it surely is not – is the application of a simple theory. Because of the lack of industry experience, many university professors find it challenging to teach design to engineering students. Optimisation methods [5] have, however, been developed recently with many objective functions, which now make it possible to conduct designs [6–8] that rely on optimisation procedures. The objective functions now include not only “engineering science parameters” such as dimensions, temperatures and heat transfer rates, but also parameters that quantify parameters such as economics, safety, aesthetic, manufacturability, maintainability and impact on the environment. It shows that design is in many cases not an art anymore and that very good designs can be produced by people with very little industry experience and that optimum designs should be driven by a simple law. However, all these designs are not about the time direction of the “movie” of design generation and evolution and it is not about optimally end design, destiny or entropy. The concept that constructal law defines in physics is “design” (configuration) as a phenomenon in time.http://www.elsevier.com/locate/plrevai201

Selected papers from the sixth HEFAT conference

No abstract available.http://www.tandfonline.com/loi/uhte20ai201

Heat Transfer, Fluid Mechanics and Thermodynamics in Industry - HEFAT2011

This editorial provides an overview of a special issue dedicated to the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics—HEFAT2011—hosted in Mauritius. All papers for this conference were peer reviewed and almost 150 papers were accepted. Of these, nine were selected for this issue and peer-reviewed for a second time according to journal standards. The nine articles focus on recent developments regarding heat transfer in industry and include condensation, frost formation, and frost melt-water retention on microgrooved brass surfaces under natural convection; large eddy simulation technique for the modeling of premixed and non-premixed combustion; nanoparticle related heat transfer phenomena and their application in biomedical fields; heat rejection in condensers close to the critical point; industrial heat utilization through water management; influence of the geometry of open-cell aluminum foam on the thermohydraulic behavior in channel flow; effect of mesh grids on the turbulent mixing layer of an axisymmetric jet; use of the LIVE program at the Karlsruhe Institute of Technology to investigate core melt phenomena; and fluid flow characteristics and associated forced convection in curved ducts. The current issue of Heat Transfer Engineering is the eighth special journal issue dedicated to selected papers from the HEFAT conferences.http://www.tandfonline.com/loi/uhte20hb2014ai201

Heat transfer coefficients for laminar to turbulent flow in tubes at constant heat flux

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.Due to constraints and changes in operating conditions, heat exchangers are often forced to operate under conditions of transitional flow. However, the heat transfer and flow behavior in this regime is relatively unknown. By describing the transitional characteristics it would be possible to design heat exchangers to operate under these conditions and improve the efficiency of the system. This study was aimed at obtaining experimental data for water flowing through a smooth tube with an inner diameter of 8 mm under constant heat flux conditions. Four heat flux test cases were considered namely: 1 409, 3 354, 5 009 and 6 881 W/m2. The experiments covered a Reynolds number range of 500 to 8 800, a Prandtl number range of 4 to 7, a Nusselt number range of 6 to 67, and a Grashof number range of 750 to 25 600. Experiments have shown a smooth transition from laminar to turbulent flow.mp201

Heat transfer coefficients for quasi-turbulent and turbulent flow in solar receiver tubes

Several well-known correlations to determine the heat transfer coefficients of quasi-turbulent and turbulent flow in smooth tubes are available in literature. However, when the results of these correlations are compared with each other, the results vary over a considerable range. Therefore, the purpose of this study was to conduct heat transfer and pressure drop experiments in the quasi-turbulent and turbulent flow regimes and to develop an accurate heat transfer correlation. A total of 1 180 experimental data points were collected from careful experiments that were conducted ourselves using two different test section configurations. The first test section configuration consisted of a tube-in-tube test section on which the wall temperatures were obtained either indirectly with the Wilson plot method or by direct surface temperature measurements. The second test section configuration consisted of single tubes being electrically heated at a constant heat flux. Different test sections covering a range of tube diameters from 4 mm to 19 mm and a range of tube lengths from 1 m to 9.5 m, were used. Experiments were conducted from a Reynolds number of 2 445, which corresponded to the start of the quasi-turbulent flow regime, up to 220 800, which was well into the turbulent flow regime. Water, as well as different concentrations of multi-walled carbon nanotubes, were used as the test fluid, which gave a Prandtl number range of 3-10. A new correlation was developed that could estimate 95% of all the experimental data points within 10% and an average deviation of less than 5%.The DST and NRF.https://aip.scitation.org/journal/apc2020-07-26am2020Mechanical and Aeronautical Engineerin

A review of two-phase flow in inclined tubes with specific reference to condensation

Tilting influences the flow patterns and thus the heat transfer and pressure drop during condensation in smooth tubes. However, few studies are available on diabatic two-phase flows in inclined tubes. The purpose of the present paper is to review two-phase flow in inclined tubes, with specific reference to condensation. Firstly, the paper reviews convective condensation in horizontal tubes. Secondly, an overview is given of two-phase flow in inclined tubes. Thirdly, a review is conducted on condensation in inclined tubes. It is shown for convective condensation in inclined tubes that the inclination angle influences the heat transfer coefficient. The heat transfer coefficient can be increased or decreased depending on the experimental conditions, and especially the flow pattern. Under certain conditions, an inclination angle may exist, which leads to an optimum heat transfer coefficient. Furthermore, this paper highlights the lack of experimental studies for the prediction of the inclination angle effect on the flow pattern, the heat transfer coefficient and the pressure drop in two-phase flows during phase change.http://www.elsevier.com/locate/ijmulflowai201

Experimental study of convective condensation of R134a in an inclined tube

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.Few studies are available in the literature on diabatic liquid-vapour flows in inclined tubes. The present paper is dedicated to an experimental study of convective condensation of R134a in an 8.38 mm inner diameter smooth tube in inclined orientations. Flow patterns, heat transfer coefficients and pressure drops are presented as function of the inclination angle for different mass fluxes and vapour qualities. Tilting influences the flow patterns and thus the heat transfer coefficients for low mass fluxes and low vapour qualities. An optimum inclination angle that leads to the highest heat transfer coefficient can be found for downward flow. The study of the pressure drops in inclined orientations requires the distinction between the frictional and the gravitational pressure drops. However, a void fraction sensor is necessary to measure the gravitational pressure drops.mp201