Published Article / The simulation of an exhaust manifold's thermal behaviour is an important concern for various reasons. Amongst them is the need to minimise catalyst light-offtime as significant exhaust emissions are generated within this period. Modelling such behaviour is not simplistic as it is governed by complex interactions between exhaust gas flow and the manifold itself. Computational fluid dynamics (CFD) is a powerful tool for such simulations. However its applicability for transient simulations is limited by high central processing unit (CPU) demands. The present study proposes an alternative computational method to assess and rank the relative impact of the manifold's thermal properties on its exterior temperature. The results show that stainless steel manifolds potentially minimise heat loss from the exhaust gas when compared with their cast iron counterparts. This may result in an increase in thermal energy being available to heat the catalyst.

Additive Manufacturing (AM) is a group of manufacturing technologies which are capable to produce 3D solid parts by adding successive layers of material. Parts are fabricated in an additive manner, layer by layer; and the geometric data can be taken from a CAD model directly. The main revolutionary aspect of AM is the ability of quickly producing complex geometries without the need of tooling, allowing for greater design freedom. As one of AM methods, Selective Laser Melting (SLM) is a process for producing metal parts with minimal subtractive post-processing required. It relies on the generation and distribution of laser generated heat to raise the temperature of a region of a powder bed to above the melting point. Due to high energy input to enable full melting of the powder bed materials, SLM is able to build fully dense metal parts without post heat treatment and other processing. Successful fabrications of parts by SLM require a comprehensive understanding of the main process controlling parameters such as energy input, powder bed properties and build conditions, as well as the microstructure formation procedure as it can strongly affect the final mechanical properties. It is valuable to control the parts' microstructure through controlling the process parameters to obtain acceptable mechanical properties for end-users. In the SLM process, microstructure characterisation strongly depends on the thermal history of the process. The temperature distribution in the building area can significantly influence the melting pool behaviour, solidification process and thermal mechanical properties of the parts. Therefore, it is important to have an accurate prediction of the temperature distribution history during the process. The aim of this research is to gain a better understanding of process control parameters in SLM process, and to develop a modelling methodology for the prediction of microstructure forming procedure. The research is comprised of an experiment and a finite element modelling part. Experimentation was carried out to understand the effect of each processing control parameters on the final part quality, and characterise the model inputs. Laser energy input, build conditions and powder bed properties were investigated. Samples were built and tested to gain the knowledge of the relationship between samples' density and mechanical properties and each process control factor. Heat transfer model inputs characterisation, such as defining and measuring the material properties, input loads and boundary conditions were also carried out via experiment. For the predictive modelling of microstructure, a methodology for predicting the temperature distribution history and temperature gradient history during the SLM process has been developed. Moving heat source and states variable material properties were studied and applied to the heat transfer model for reliable prediction. Multi-layers model were established to simulate the layer by layer process principles. Microstructure was predicted by simulated melting pool behaviour and the history of three dimensional temperature distribution and temperature gradient distribution. They were validated by relevant experiment examination and measurement.

yes / A computational network heat transfer model was utilised to model the potential of heat energy recovery at multiple locations from a city scale combined sewer network. The uniqueness of this network model lies in its whole system validation and implementation for seasonal scenarios in a large sewer network. The network model was developed, on the basis of a previous single pipe heat transfer model, to make it suitable for application in large sewer networks and its performance was validated in this study by predicting the wastewater temperature variation in a sewer network. Since heat energy recovery in sewers may impact negatively on wastewater treatment processes, the viability of large scale heat recovery across a network was assessed by examining the distribution of the wastewater temperatures throughout the network and the wastewater temperature at the wastewater treatment plant inlet. The network heat transfer model was applied to a sewer network with around 3000 pipes and a population equivalent of 79500. Three scenarios; winter, spring and summer were modelled to reflect seasonal variations. The model was run on an hourly basis during dry weather. The modelling results indicated that potential heat energy recovery of around 116, 160 & 207 MWh/day may be obtained in January, March and May respectively, without causing wastewater temperature either in the network or at the inlet of the wastewater treatment plant to reach a level that was unacceptable to the water utility.

An advanced finite element (FE) model of the electrofusion welding of thermoplastic pipes has been developed using the ABAQUS FE package. The heat transfer analysis is coupled with thermal deformation analysis to include the time-dependent closure of the initial gap between the pipe and fitting. The effect of radial melt movement into the interface is modelled using a new `virtual material movement¿ technique. The predicted results (temperature distribution in the weld region, melt affected zones and gap closure time) are compared with experimental data and good agreement is found

Furnaces that heat metal parts (blooms) prior to hot-working processes such as rolling or forging are called pre-forming reheat furnaces. In these furnaces, the fundamental idea is to heat the blooms to a prescribed temperature without very large temperature gradients in them. This is to ensure correct performance of the metal parts subsequent to reheating. Due to the elevated temperature in the furnace chamber, radiation is the dominant mode of heat transfer from the furnace to the bloom. In addition, there is convection heat transfer from the hot gases to the bloom. The heat transfer within the bloom is by conduction. In order to design a new furnace or to improve the performance of existing ones, the heat transfer analysis has to be done accurately. Given the complex geometry and large number of parameters encountered in the furnace, an analytical solution is difficult, and hence numerical modeling has to be resorted to. In the present work, a numerical technique for modelling the steady-state and transient heat transfer in a reheat furnace is developed. The work mainly involves the development of a radiation heat transfer analysis code for a reheat furnace, since a major part of the heat transfer in the furnace chamber is due to radiation from the roof and combustion gases. The code is modified from an existing finite volume method (FVM) based radiation heat transfer solver, The existing solver is a general purpose radiation heat transfer solver for enclosures and incorporates the following features: surface-to-surface radiation, gray absorbing-emitting medium in the enclosure, multiple reflections off the bounding walls, shadowing effects due to obstructions in the enclosure, diffuse reflection and enclosures with irregular geometry. As a part of the present work, it has now been extended to include the following features that characterise radiation heat transfer in the furnace chamber · Combination of specular and diffuse reflection as is the case with most real surfaces · Participating non-gray media, as the combustion gases in the furnace chamber exhibit highly spectral radiative characteristics Transient 2D conduction heat transfer within the metal part is then modelled using a FVM-based code. Radiation heat flux from the radiation model and convection heat flux calculated using existing correlations act as boundary conditions for the conduction model. A global iteration involving the radiation model and the conduction model is carried out for the overall solution. For the study, two types of reheat furnaces were chosen; the pusher-type furnace and the walking beam furnace. The difference in the heating process of the two furnaces implies that they have to be modelled differently. In the pusher-type furnace, the heating of the blooms is only from the hot roof and the gas. In the walking beam furnace, the heating is also from the hearth and the blooms adjacent to any given bloom. The model can predict the bloom residence time for any particular combination of furnace conditions and load dimensions. The effects of variations of emissivities of the load, thickness of the load and the residence time of billet in the furnaces were studied.

Buildings account for up to 32% of the total energy use in different countries. Directives from the European Union have pointed out the importance of increasing energy efficiency in buildings. New regulation in countries like Sweden establishes that new buildings should fulfill regulations of Nearly Zero Energy Buildings (NZEB), opening an opportunity for new technologies to achieve these goals. Almost 80-90% of the energy in domestic hot water use is wasted from different applications with almost no use and with a lot of potential energy to be recovered. The present work studied the characteristics of greywater heat exchanger as a solution to recuperate heat from greywater to increase efficiency in buildings. This study explored the fluid mechanics involved in the vertical greywater heat exchangers, analyzing the falling film effect present in drain pipes and the effects of the secondary flow generated in the external helical coil. A heat transfer model from a theoretical approach was proposed and validated. In addition, this study explored the different variables influencing the economic feasibility of the technology and an economic analysis was performed. A theoretical comparison between a greywater heat exchanger application and a reference case without it was evaluated highlighting the importance of all the variables involved in the potential of implementation of the technology. The technology shows big potential in households with high water consumptions, especially with electric boilers.

<p dir="ltr">Transportation and energy production industries strongly rely on improvements in gas turbine performance. The quantification of these improvements is dependent on the accuracy of the measurements performed during testing. An increase of 0.5\% in efficiency is sufficient to secure a new development program worth millions of dollars, but in the case of temperature measurements, uncertainties below 0.5 K are required, which presents a challenge. This work selects heat flux estimation and total temperature measurement uncertainties as major contributors for efficiency uncertainty.</p><ul><li>Heat flux measurements are critical to evaluate the impact on the efficiency. Additionally, thermal fatigue in turbine airfoils defines the life cycle of the engine core. This work performs an estimation of the heat transfer via a simplified numerical model that uses infrared (IR) measurements in the surface of the casing to predict the temperature of the passage wall. The model is validated with real cool-down data of the turbine to yield results within a 10\% of the actual temperature.</li><li>Total temperature measurement suffers from errors due to heat transfer effects in the probe. Two dominant sources of errors are convection and conduction between the thermocouple wires, the probe support, and the flow. These effects can be treated in two different categories: the velocity error, created by a non-isentropic reduction of the flow velocity upstream the thermocouple junction, and the thermal equilibrium effects between the junction and the probe support, involving heat transfer through the wire to the shield and the probe stem due to temperature differences between each component (the so-called \emph{conduction error}). An open jet stand is used to evaluate the effects of velocity error at various Mach numbers. The conduction error is addressed with the design and manufacturing of dual-wire thermocouple probes. The readings from two wires with different length-to-diameter ratios are used to correct for the flow total temperature. This probe yielded a recovery factor of 0.99 +/- 0.01 at Mach 0.6.</li></ul><p></p>