Heat transfer continues to play a major role in new emerging areas such as sustainable development and reduction of greenhouse gases as well as for micro- and nano-scale structures and bio-engineering and in traditional areas like heat exchangers, gas turbine cooling, turbulent combustion and fires, electronics cooling, melting, solidification and many others. Tremendous advancements have been achieved during recent years.

The Wessex Institute of Technology (WIT) Heat Transfer Conference Series aims to provide a forum for presentation and discussion of new approaches and applications of computational methods and experimental measurements to heat and mass transfer and related phenomena.

Many relevant research topics were discussed during the Fourteenth International Conference on Simulation and Experiments in Heat Transfer and its Applications held in Ancona, Italy during September 2016. This special issue of the International Journal of Computational Methods and Experimental Measurements contains the edited versions of some selected papers presented at the Conference. The contributions reflect the quality and width of the topics covered in the conference.

The guest editors would like to thank all the distinguished and well-known scientists who supported the Conference by serving on the International Scientific Advisory Committee, reviewing the submitted abstracts and papers. The excellent administrative work of the conference secretariat at WIT is greatly appreciated and the efficient co-operation and encouragement by the staff at WIT Press were essential in producing this special issue.|

Hundreds of young people have had limbs amputated after being wounded by civil wars, explosions or gunshots. Heat and perspiration within a prosthetic socket are the most common side effects of reduced quality life for prosthesis. Besides, the environment between liner and skin is an ideal host of residual limb skin problems such as contact dermatitis and bacterial infections. It is important to minimize the limiting heat transfer to improve amputee safety and comfort. Usually, when there is a skin problem, the treatment requires the amputee not to wear his/her prosthesis for an extended period of time. This functional loss can adversely affect the amputee’s physical, mental and emotional well-being. This work aims to highlight a number of important issues concerning the effect of thermal conditions on prosthetics to shed light on new design methods for prosthetics.

The number of disposable molecular diagnostics tests in the IVD market has been growing rapidly and is bound to continue to grow in the near future. The internal complexity of these rapid tests increases with the complexity of the diagnostic assay implemented by them. Some assays require precise tem- perature control (±1°C –5°C) for an extended time (i.e. 15–60 minutes) for the reactions involved to run properly. Microheating components in them must meet strict criteria with respect to power con- sumption, physical size and cost. The proposed finite element model is intended to provide tools for in silico validation of device designs (geometries, structural materials), as well as to help in the interpre- tation of heat transfer processes inside the thermal system present in a molecular diagnostics device. The proposed model was developed for and validated with polyimide etched foil heating elements actively controlled via a mini-thermostat. The thermostat was designed for battery-based operation and implemented with open-source hardware (Arduino-compatible). Plastic test structures were created that emulated disposable Lab-on-a-Chip devices with microfluidic channels to hold liquid volumes on the scale of 0.1 mL. The experimental setup was demonstrated to maintain target temperatures over at least 30 minutes with at least ±1°C around the set point operated from batteries. Physical parameters of the resistive heating element used were fed into the finite element model and simulation results compared to the performance of the aforementioned experimental setup.

This paper focuses on thermal transport processes and systems and discusses their modeling, simulation, design and optimization to reduce the effect on the environment, reduce energy consumption and enhance product quality and productivity. These processes are generally quite complex and several challenges are encountered to obtain accurate and reliable results that can be used as the basis for design and optimization. Some major challenges are material properties, model validation, uncertain- ties in the governing parameters and operating conditions, complex combined transport mechanisms, and multiscale effects. Once accurate simulation results are obtained, these can be used to optimize the process to enhance the output. Reduction in energy and material consumption, as well as the effect on the environment, are of particular concern today. The paper discusses these aspects and presents a few practical systems by way of illustration. For example, working with the changing environment, the energy consumed by the thermal system for the cooling of data centers can be minimized. Similarly, other concerns and approaches are outlined.

We report on the development of measurement system for characterizing physico-chemical properties of colloidal liquids used in heat transfer applications. In future thermal management, colloids consisting of micro- and nano-sized particles will play major roles in heat transfer for thermal storage and heat- transfer enhancement. In these applications, an important issue is the dispersion stability of colloidal particles. The functionality of the colloidal liquids becomes deteriorated when the particles aggregate and turn into sedimentation. The dispersion of colloidal liquid is maintained by the interaction of electrokinetic forces acting on the particles. The electrostatic state of the surface of a particle is represented by zeta potential, which represents the electrical potential difference between the particle surface and the surrounding. The zeta potential can be measured from the mobility of colloidal particles under electrophoresis. We use a pair of evanescent waves for measuring the zeta potential of colloidal particles. An evanescent wave propagates along an interface and exponentially attenuates away from it. The use of evanescent waves can achieve a spatial resolution smaller than a micrometer, which is not feasible with a conventional optical system whose resolution is bounded by diffraction limit. We describe the principle and design of the measurement system. A prototype measurement system was developed in the laboratory. We report on the development and performance of the system for characterizing col- loidal particles for heat transfer applications.

To evaluate the wall heat losses in combustion vessel, an alternative to existing macroscopic models of heat transfer is suggested. This study aims to provide a physical approach for wall heat transfer based on kinetic theory of gases to describe the conduction phenomena between gas particles and the cold wall in short scales. The model mentioned is implemented in a code simulating combustion in a constant volume spherical chamber.

In the last twenty years the modeling of heat transfer on gas turbine cascades has been based on computational fluid dynamic and turbulence modeling at sonic transition. The method is called Conjugate Flow and Heat Transfer (CHT). The quest for higher Turbine Inlet Temperature (TIT) to increase electrical efficiency makes radiative transfer the more and more effective in the leading edge and suction/pressure sides. Calculation of its amount and transfer towards surface are therefore needed. In this paper we decouple convection and radiation load, the first assumed from convective heat transfer data and the second by means of emissivity charts and analytical fits of heteropolar species as CO₂ and H₂O. Then we propose to solve the temperature profile in the blade through a quasi-two-dimensional power balance in the form of a second order partial differential equation which includes radiation and convection. Real cascades are cooled internally trough cool compressed air, so that we include in the power balance the effect of a heat sink or law of cooling that is up to the designer to test in order to reduce the thermal gradients and material temperature. The problem is numerically solved by means of the Finite Element Method (FEM) and, subsequently, some numerical simulations are also presented.

This study reports the results of a numerical investigation and optimization of the hydrodynamic and thermal performance of two new types of pin-fin and plate-fin heat sinks. The first type consists of inclined cones and is inspired by the larger heat transfer extents in impinging flow conditions, whilst the second type concerns wavy form plate-fins chosen such as to combine the effects of thermal boundary layer re-initialization, flow separation and large heat transfer area of classical plate fins. Fairly complex features are considered, which cannot be manufactured easily using traditional approaches. However, in this study we exploit the manufacturing flexibility offered by a new surface-structuring technology, which allows to produce more complex geometries than possible with the current state-of-the-art techniques. A simplified numerical methodology has been proposed to decrease the computational cost, which was then validated with respect to the literature and the laboratory tests. Baseline versions of the two proposed geometries were compared to more common geometries found in the literature in order to make a first choice. The results show that the inclined cone features can increase the heat transfer coefficient, especially in inverse configuration, whereas the wave structures require very large pressure losses to achieve similar levels of thermal performance. Subsequently, only inclined cones have been optimized using an Evolutionary Algorithm optimization platform. The optimized geometries increase the overall performance, especially reducing the pressure drop, in comparison to the geometries found in the literature.

Steam cycles are a mature technology that has been used for many decades to produce power from heat. Novel expanders that can expand in the two-phase region have been developed for years but only recently have achieved a level of maturity that makes them commercially interesting.

In this study wet and dry steam cycles recovering heat from gas turbines in offshore industry are compared in a thermodynamic basis. Three different cycle configurations are studied in three scenarios with different combinations of power and heat demand. Every case is optimized with and without restrictions for two-phase steam expansion.

It is shown that wet expansion cycles can achieve higher steam pressures which increase steam cycle efficiency. Steam cycle power increase has been found to be large for single expansion cases (20%) due to the low pressures that can be achieved by the dry cycles.

Optimization of two-stage wet expansion does not produce significant improvements and in some cases results are equivalent to single stage wet expansion cycles.

Energy savings and CO2 emissions reduction when comparing with the reference cases without steam cycle installation are found to be in the range of 17%–26%.

Flame spread along the energized polyethylene (PE) insulated copper wire under low pressure was investigated experimentally to gain a better understanding of electrical wire fire in aircraft and space habitats. Three types of sample wires, with the same insulation thickness and different core diameters, were used in this research study. First, a simplified model was developed to quantitatively explain the impact of lower pressure on the flame propagation over the energized wires. As with the pressure decreased, both of Grashof number (Gr) and Reynolds number (Re) were decreased and the air-flow diffusion played a gradual and dominant role in the combustion process. Mainly caused by the decrease of natural convention, the heat loss turned to be reduced, resulting in the reduction of oxygen flow and the formation of carbon black was inhibited. Second, several experiments were conducted to investigate the flame spread along the energized wires in a walk-in hypobaric chamber. The experimental results showed that, with the decrease of pressure, the flame height was reduced, the flame shape turned to be spherical, and the blue area showed increased. But the flame shape was reduced gradually along the wire, till extinguished when the pressure set out below a critical value. The accumulation of melt insulation increased and the dripping behavior occurred easily under lower pressure. Moreover, the influence of overload current on the flame spreading velocity was also presented. This work was useful for a further study on the fire risk of electrical wires under low pressure.