Showing papers by "Josua P. Meyer published in 2017"

Characterisation of a grooved heat pipe with an anodised surface

Abstract: A grooved heat pipe (GHP) is an important device for managing heat in space applications such as satellites and space stations, as it works efficiently in the absence of gravity. Apart from the above application, axial GHPs are used in many applications, such as electronic cooling units for temperature control and permafrost cooling. Improving the performance of GHPs is essential for better cooling and thermal management. In the present study, the effect of anodization on the heat transfer characteristics of a GHP is studied with R600a as a working fluid. In addition, the effects of fill ratio, inclination angle and heat inputs on the heat transfer performance of a GHP are studied. Furthermore, the effect of heat flux on dimensional numbers, such as the Webber, Bond, Kutateladze and condensation numbers, are studied. The inclination angle, heat input and fill ratio of GHPs are varied in the range of 0°–90°, 25–250 W and 10–70 % respectively. It is found that the above parameters have a significant effect on the performance of a GHP. Due to the anodisation, the maximum enhancement in heat transfer coefficient at the evaporator is 39 % for a 90° inclination at a heat flux of 11 kW/m2. The reported performance enhancement of a GHP may be due to the large numbers of nucleation sites created by the anodisation process and enhancement in the capillary force due to the coating.

The constructal size of a heat exchanger

Abstract: The architecture of heat exchangers is a classical subject that has been studied extensively in the past. In this paper, we address the fundamental question of what the size of the heat exchanger should be, in addition to what architectural features it should have. The answer to the size question follows from the tradeoff between (1) the useful power lost because of heat transfer and fluid flow and (2) the power destroyed during transportation, manufacturing, and maintenance. Changes in heat exchanger size induce changes in the opposite sign in the power requirements (1) and (2). This fundamental tradeoff regarding size is illustrated by considering one side of a heat exchanger (one flow passage) in laminar flow and in fully rough turbulent flow, with several duct cross sectional shapes and arrays of channels in parallel. The size tradeoff is present in heat exchanger applications across the board, from vehicles to stationary power plants.

Numerical Investigation into the Thermal Performance of Single Microchannels with Varying Axial Length and Different Shapes of Micro Pin-Fin Inserts

Abstract: This study investigates numerically the thermal performance of combined microchannel heat sink with micro pin-fins with different cross-sectional shapes. The objective of this study is to investigate the best geometric configuration that maximizes the heat transfer from the heated base when the combined heat sink is subjected to a steady, laminar, incompressible convective fluid flow and heat transfer. The axial length of the solid substrate and microchannel is varied from 1 to 10 mm with fixed total volume of 0.9 mm3 while the number of rows of the different shapes of micro pin-fins was varied between three and seven. It was observed that best performance is obtained with a sixth row of circular-shaped micro pin-fins for the optimized combination of the microchannel and micro pin-fin heat sink. Results of the optimal axial length for fixed pressure drop range are also presented.

A novel combined model of discrete and mixture phases for nanoparticles in convective turbulent flow

Abstract: In this study, a new combined model is presented to study the flow and discrete phase features of nano-size particles for turbulent convection in a horizontal tube. Due to the complexity and many phenomena involved in particle-liquid turbulent flows, the conventional models are not able to properly predict some hidden aspects of the flow. Therefore, a new form of Brownian force is implemented in the discrete phase model to predict the migration of the particles as well as energy equation has modified for particles. Then, the final results are exported to the mixture equations of the flow. The effects of the mass diffusion due to thermophoresis, Brownian motion, and turbulent dispersion are implemented as source terms in equations. The results are compared with the experimental measurements from the literature and are adequately validated. The accuracy of predicted heat transfer and friction coefficients is also discussed versus measurements. The migration of the particles toward the centre of the tube is ...

Thermal conductivity and viscosity of mango bark/water nanofluids

Abstract: A novel heat transfer fluid with bio-nanomaterial, which is environmentally safe, is prepared and its thermo-physical properties such as thermal conductivity and viscosity are measured. The bio-nanomaterial considered in this study is mango bark. A two-step process is employed to prepare a stable nanofluid. The average particle size was measured using scanning electron microscope and is found to be 100nm. The stability of the nanofluid is checked by measuring the absorbance and viscosity at a constant temperature. The concentration of nanofluid and temperature are varied between 0.1 to 1 vol% and 10 to 60 o C, respectively for the measurement of viscosity and thermal conductivity. The measurement shows that the measured thermal conductivity of the water is comparable with the standard data presented by American Institute of Physics and American Chemical Society. Also, the measured thermal conductivity of the nanofluids showed a slight enhancement compared to the thermal conductivity of water. The measured viscosity of the nanofluids shows exponentially decreasing trend.

Small-Scale Dish-Mounted Solar Thermal Brayton Cycle

Abstract: The small-scale dish-mounted solar thermal Brayton cycle in the 1- to 20-kW range has several advantages such as mobility, bulk manufacturing, cogeneration, and hybridization. Another advantage is that an off-the-shelf turbocharger from the motor industry can be applied as the microturbine in the cycle. The main disadvantages are low turbine and compressor efficiencies as well as heat and pressure losses. The chapter shows that the method of total entropy generation minimization can be used to maximize the net power output of the cycle by optimizing an open-cavity tubular solar receiver and counterflow plate-type recuperator. Results show that, with the use of an off-the-shelf turbocharger and low-cost optics, the cycle could generate solar-to-mechanical efficiencies of up to 12% with much room for improvement. Remaining challenges and future possibilities are discussed. It is recommended that the cycle should be further developed and investigated as a clean energy technology.