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

Selected papers from the sixth HEFAT conference

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

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

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

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

Relationship between pressure drop and heat transfer of developing and fully developed flow in smooth horizontal circular tubes in the laminar, transitional, quasi-turbulent and turbulent flow regimes

Limited work has been done specifically focussing on the relationship between pressure drop and heat transfer in the transitional flow regime. The purpose of this study was therefore to experimentally investigate and compare the pressure drop and heat transfer characteristics of developing and fully developed flow in smooth horizontal circular tubes in the laminar, transitional, quasi-turbulent and turbulent flow regimes. An experimental set-up was designed, built and validated against data from literature. A smooth circular test section with an inner diameter of 11.5 mm, and maximum length-to-diameter ratio of 872, was used. Pressure drop and heat transfer measurements were taken at Reynolds numbers between 500 and 10,000 at different heat fluxes. Water was used as the test fluid and the Prandtl number ranged between 3 and 7. A total of 317 mass flow rate measurements, 34,553 temperature measurements and 2536 pressure drop measurements were taken. Pressure drop and heat transfer measurements were taken simultaneously and the relationship between pressure drop and heat transfer was investigated. It was found that the Reynolds numbers at which transition started and ended was the same for the pressure drop and heat transfer results. Correlations were developed to determine the relationship between heat transfer and pressure drop, as well as the average Nusselt numbers, in the laminar, transitional, quasi-turbulent and turbulent flow regimes, for both developing and fully developed flow in mixed convection conditions. It was found that the relationship between heat transfer and pressure drop can be used as an additional criterion to distinguish the different flow regimes.This work was produced as part of a PhD in the Department of Mechanical and Aeronautical Engineering at the University of Pretoria by the first author, under the supervision of the second author. (http://hdl.handle.net/2263/44245)The NRF, Stellenbosch University/University of Pretoria Solar Hub, CSIR, EEDSM Hub, RDP and NAC.http://www.elsevier.com/locate/ijhmt2019-02-20hj2017Mechanical and Aeronautical Engineerin

Heat transfer characteristics of developing flow in the transitional flow regime of a solar receiver tube

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.The transitional flow regime has been mostly avoided by designers due to uncertainty and perceived chaotic behaviour. However, changes in operating conditions, design constraints or additional equipment can cause that the flow to move into the transitional flow regime. Previous work done in the transitional flow regime focused on fully developed flow or average measurements of developing and fully developed flow across a tube length and developing flow in the transitional flow regime have not been investigated yet. Therefore, the purpose of this study is to investigate the heat transfer characteristics of developing flow in the transitional flow regime of a solar receiver tube and is work in progress. An experimental set-up was designed, built and validated and heat transfer measurements were taken at a heat flux of 6.5 kW/m2 between Reynolds numbers of 500 and 10 000. It was found that the width of the transition region decreased along the tube length and the heat transfer coefficients decreased as the flow approached fully developed flow.dc201

Experimental study of convective condensation in an inclined smooth tube. Part I : inclination effect on flow pattern and heat transfer coefficient

An experimental study of convective condensation of R134a in an 8.38 mm inner diameter smooth tube in inclined orientations is presented. This article, being the first of a two-part paper (the second part concentrates on the pressure drops and void fractions), presents flow patterns and heat transfer coefficients during condensation for different mass fluxes and vapour qualities for the whole range of inclination angles (from vertical downwards to vertical upwards). The results were compared with three flow pattern maps available in literature. It was found that for low mass fluxes and/or low vapour qualities, the flow pattern is strongly dependent on the inclination angle whereas it remains annular for high mass fluxes and high vapour qualities, whatever the tube orientation. The models of flow pattern maps available in the literature did not predict the experimental data well. In the inclination-dependent zone, experiments showed that there is an optimum inclination angle that leads to the highest heat transfer coefficient for downward flow. The heat transfer coefficient is strongly affected by the liquid and vapour distributions and especially by the liquid thickness at the bottom of the tube for stratified flows. Thus developing a mechanistic model of flow pattern maps is the first step in achieving a predictive tool for the heat transfer coefficient in convective condensation in inclined tubes.The NRF, TESP, University of Stellenbosch/University of Pretoria, SANERI/SANEDI, CSIR, EEDSM Hub and NAC.http://www.elsevier.com/locate/ijhm