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The application of phase-change materials (PCMs) has received significant interest for use in thermal energy storage (TES) systems that can adjust the mismatch between the energy availability and demand. In the building sector, for example, PCMs can be used to reduce airconditioning energy consumption by increasing the thermal capacity of the walls. However, as promising this technology may be, the poor thermal conductivity of PCMs has acted as a barrier to its commercialization, with many heat-transfer enhancement solutions proposed in the literature, such as microencapsulation or metal foam inserts, being either too costly and/or complex. The present study focuses on a low-cost and highly practical solution, in which natural-convective heat transfer is enhanced by placing the PCM in an eccentric annulus within a horizontal double-pipe TES heat exchanger. This paper presents an annulus-eccentricity optimisation study, whereby the optimal radial and tangential eccentricities are determined to minimize the charging time of a PCM thermal energy store. The storage performance of several geometrical configurations is predicted using a computational fluid dynamics (CFD) model based on the enthalpy-porosity formulation. The optimal geometrical configuration is then determined with response surface methods. The horizontal double-pipe heat exchanger studied considered here is an annulus filled with N-eicosane as the PCM for initial studies. In presence of N-eicosane, for the concentric configuration (which is the baseline case), the charging is completed at Fo = 0.64, while the charging of optimum eccentric geometries with the quickest and slowest charging is completed at Fo = 0.09 and Fo = 2.31, respectively. In addition, an investigation on the discharging performance of the studied configurations with N-eicosane shows the quickest discharge occurs with the concentric annulus case at Fo = 0.99, while the discharge time of the proposed optimum annuli is about three times this value. In other words, the proposed optimum geometry with the quickest charging time charges~7.1 times faster but also discharges~3 times slower, which is ideal for a TES, especially when used as passive thermal storage systems in nearly zero-emission buildings. Complementary studies demonstrate that the proposed optimum configuration improves the TES performance also when employing other PCM types as well as various shell-to-tube diameter ratios.

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This study investigates laminar convective heat transfer of water flowing in a mini-channel with a rough surface fabricated by Laser-based Powder Bed Fusion (L-PBF) technology. A Gaussian model was used for generating random roughness, and then the three-dimensional numerical simulation was performed in ANSYS-Fluent 19.1. The numerical results indicated a more than double increase in the Nusselt number of rough channels than that of smooth ones with a marginal pressure drop penalty compared to smooth channels, showing the potential benefits of using rough channels fabricated by L-PBF for heat transfer applications.

K Thermal conductivity (W/m K) L Length of tube (m) m Mass flow rate (kg/s) N Revolution per minute of the rotating valve spindle (rpm) Pe Peclet number Pr Prandtl number Q Heat transfer rate (W) r Inner radius of tube (m) R Radius of spiral coil (m) Re Reynolds number T Temperature (K) U Average overall heat transfer coefficient (W/m 2 K) V Average velocity of mean flow (m/s) Wo Womersly number, Wo = D i 2 υ ω Greek letters α Thermal diffusivity (m 2 /s) µ Dynamic viscosity (kg/m s) ρ Density (kg/m 3 ) υ Kinematic viscosity (m 2 /s) ω Angular pulsation frequency (1/s) ∞ Ambient medium ϕ Nanoparticle volumetric fraction Superscript -Average Subscripts ave Average i Inlet m Mean o Outlet pu Pulsated st SteadyAbstract In the past two decades, enhancement of heat transfer characteristics of original fluid using nanofluids has been proposed by a large number of researchers. In this paper, an experimental study was carried out to investigate effect of pulsation on heat transfer of fluid flow inside a spiral-coil tube. In order to perform the experiments, a hot water reservoir tank was prepared and the spiral-coil was immersed horizontally inside the tank. Average temperature of the hot water bath was kept constant at 60 °C to establish a quiescent region of uniform temperature. The experiments were conducted in turbulent flow regime using distilled water and Al 2 O 3 /water nanofluid at 0.5, 1, and 1.5 % particle volume concentration. Results showed that overall heat transfer coefficient of the base fluid flow increases by using nanofluid or pulsation into the base fluid flow up to 14 %. Heat transfer results also indicated that combination of the nanofluid and the pulsation into the fluid flow can increase significantly the overall heat transfer coefficient up to 23 %. List of symbolsA Inside heat transfer area (m 2 ) C p Specific heat capacity (J/kg K) D i Inner diameter of tube (m) f Frequency (Hz)

Cooling channels are critical in injection mould tooling as cooling performance influences component quality, cycle time, and overall process efficiency. Additively Manufactured moulds allow the incorporation of cooling channels conforming to the shape of the cavity and core to improve heat removal. These conformal channels can reduce the cycle time, reduce mould temperature, and enhance the temperature uniformity on the mould's surface, leading to improved quality of the moulded components and reduced wastage in the production. The design of such channels is more challenging than conventional channels; thus, Computer-Aided Engineering (CAE) has a significant role within the design process. In this paper, a novel design for conformal cooling channels for the production of a commercial component from an industrial partner is investigated. This component had issues of high cycle time and a high defect rate due to residual stresses, resulting in component shrinkage. First, the existing conventional drilled cooling channels in the mould were simulated in Autodesk Moldflow Insight to evaluate temperature distribution and cycle time. Based on the temperature distribution, conformal cooling channels were designed in Solidworks, addressing the problem areas. Next, a simulation of fluid flow in the conformal channels was conducted in ANSYS-Fluent to ensure equal flow distribution in the entire circuit, iteratively arriving at an optimal configuration. Finally, the results of the new conformal channels, including mould temperature and cycle time, were compared with conventional cooling channels in simulation. The results showed a significant reduction in cycle time and improvement in the temperature distribution, thereby minimising residual stresses and shrinkage.

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