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Development of a thermofluid model for Axial field permanent-magnet Machines

A thermofluid model combining a lumped parameter heat transfer model and an air-flow model of a typical axial-field permanent-magnet (AFPM) machine is developed. The accuracy and consistency of the derived model are assessed by comparing the calculated flow rate and temperature values of a prototype machine with the measured ones. The developed thermofluid model is shown to perform thermal calculations with reasonable accuracy.

Thermal modelling of a night sky radiation cooling system

The thermal modelling of a night sky radiation cooling system suitable for a room is considered in this paper. The system considered consists of radiator panels, a single water storage tank, room air-to-water natural convection heat exchangers or convectors, circulating pump(s), interconnecting pipe work and temperature sensors and controls. The mathematical equations describing the thermal behaviour of the various system components are given. The results obtained compared favourably with values reported in the literature. It is thus concluded that the thermal model presented can be used with confidence as a design tool for the sizing of a night sky radiation cooling system. heat load and weather pattern as shown in figure 2. The optimum sizes for the main components of the system to meet the given requirements may be determined and the system cooling/heat removal capacity calculated. Make-up water Ls ks mt Air relief pressure relief and vacuum breaker Charge/ circulating pump Circulating pump w2 m& Room convector Lt, kt, At Lr, kr, Ar Water storage tank Diameter, Dt Vr = LLLWLH

Simulation of the two-phase flow in a thermosyphon using an inclined transparent tube with the lower-end closed and the upper-end open

Abstract The initial liquid charge of a vertically orientated two-phase closed thermosyphon for adequate thermal performance as determined theoretically by assuming that the condensate is in the form of a relatively thin film underestimates the amount determined by using experimental correlations. Knowing the physical details of the two-phase flow within the thermosyphon could explain this discrepancy. Because, however, of the difficulty of directly observing two-phase flow in an actual metal thermosyphon it was decided to investigate the two-phase flow by using air and water in a transparent tube. The tube that was used is closed at the lower end and open at the top end, was partially charged with water, and air was introduced into the closed end at increasing air flow rates until water droplets were just about to be expelled from the open end. The flow patterns occurring as a function of air flow rate were identified. The average liquid fraction in four sections of the tube was determined for different initial charge fractions and inclinations. It was observed that even at low air flow rates significant quantities of liquid were propelled up into the tube and that the flow is oscillatory. It was concluded that care would have to be taken in assuming a relatively thin and uniform liquid film in theoretically modelling a thermosyphon.

Determining Vacuum-Arc Thruster Performance Using a Cathode-Spot Model

A simple model of the vacuum-arc cathode-spot and plasma region was developed to predict the performance of vacuum-arc thrusters operating roughly in the arc current range 80–300 A with thrust pulses 250 s. The conventional-based cathode-spot model predicts ion current, average ion velocity, and erosion rate to establish thruster performance. Vacuum-arc properties for a range of materials (Al, Ti, Cr, Fe, Ni, Cu, Ag, Pb, Bi) were determined as well as maximum arc spot currents for Ti, Cr, Fe, Ni, and Bi. Model results generally show good agreement with published data and predicted thruster performance is comparable to literature. Most values of ion-to-arc current ratio were within 10% of published experimental data, ion velocities within about 30%, and erosion rates were within roughly 50%, provided macroparticle ejection was low. The crucial role of the ion-to-arc current ratio on thruster performance is assessed.

Parabolic solar cooker: Cooking with heat pipe vs direct spiral copper tubes

Cooking with solar energy has been seen by many researchers as a solution to the challenges of poverty and hunger in the world. This is no exception in Africa, as solar coking is viewed as an avenue to eliminate the problem of food insecurity, insufficient energy supply for household and industrial cooking. There are several types of solar cookers that have been manufactured and highlighted in literature. The parabolic types of solar cookers are known to reach higher temperatures and therefore cook faster. These cookers are currently being developed for indoor cooking. This technology has however suffered low cooking efficiency and thus leads to underutilization of the high heat energy captured from the sun in the cooking. This has made parabolic solar cookers unable to compete with other conventional types of cookers. Several methods to maximize heat from the sun for indirect cooking has been developed, and the need to improve on them of utmost urgency. This paper investigates how to optimize the heat co...

Performance Measurements of a Medium-Current Short-Pulsed Vacuum Arc Thruster

A vacuum arc thruster, powered by a pulsed capacitive circuit, was built and its thrust measured using direct and indirect thrust techniques. Experimental values of ion velocity, ion arc current, and erosion rate were measured. Knowledge of the ion current density distribution was used to consider interference and plume distribution effects on thrust. Both methods measured thrust levels within the expected thrust range (20–60 mN per pulse). Impulse bits as small as 10 nNs could be measured by the direct thrust setup. It was also found that at arc currents >500 A, ion flow was reduced, which resulted in lower thrust.

A Novel Indirect Parabolic Solar Cooker

CITATION: Craig, O O., Dobson, R. T. & Van Niekerk, W. 2017. A Novel Indirect Parabolic Solar Cooker. Journal of Electrical Engineering, 4:137-142, doi:10.17265/2328-2223/2017.03.003.

PBMR Technology Development Projects at Stellenbosch University, South Africa

PBMR has initiated a research and development program wherein a network of expertise relating to PBMR-specific technology is to be established. As a result of this initiative four specific PBMR sponsored technology development projects have been initiated at Stellenbosch University. The work done and still to be done towards these projects will be presented. The first project relates to the characterization of the flow dynamics of particles (ions, atoms and clusters) in a high pressure and velocity (9 MPa and 120 m/s) stream of helium due to various body-force fields (magnetic, electric and centrifugal); the ultimate objective of this project is to develop a graphite dust and particle scrubbing system. The second project relates to an entirely passive reactor cooling system (RCCS) using thermosyphon-type heat pipes with no pumps and active controls. The third project relates to the fuel temperature measurement under normal and loss of coolant pressure conditions using a fibre-optic Bragg-grating method. A fourth project relates to energy efficiency improvement by the conversion of waste, decay, after and residual heat into electrical power. This project makes use of two-phase closed loop thermosyphon-type heat pipes to transport the heat to an external heat engine, such as free piston type Stirling engine or organic Rankine cycle system. The research activities needed to meet the objectives of the above projects will be presented and discussed in this paper.© 2008 ASME

An Open Oscillatory Heat Pipe Steam-Powered Boat

An open oscillatory heat pipe is a very simple device that is capable of doing work. Although as an engine its thermal efficiency is relatively poor, as a heat transfer device it can transfer a relatively large quantity of heat against gravity, without a wicking material or any moving parts. The thermal and fluid dynamic equations are given whereby the device may be mathematically modelled. Computer-generated results for thrust, pressure and temperature as a function of time are given and discussed. Comparing the theoretical with experimentally obtained thrust curves, it is concluded that the mathematical model reflects the physical behaviour of the device reasonably well. Limitations of the present model are discussed and it is recommended that the device should find application in heat transfer rather than as an engine.

Modelling and control synthesis of a micro-combined heat and power interface for a concentrating solar power system in off-grid rural power applications

Concentrating solar power co-generation systems have been identified as potential stand-alone solar energy supply solutions in remote rural energy applications. This study describes the modelling and synthesis of a combined heat and power Stirling CSP system in order to evaluate its potential performance in small off-grid rural village applications in Africa. This Stirling micro-Combined Heat and Power (micro-CHP) system has a 1 kW electric capacity, with 3 kW of thermal generation capacity which is produced as waste heat recovered from the solar power generation process. As part of the development of an intelligent microgrid control and distribution solution, the Trinum micro-CHP system and other co-generation systems are systematically being modelled on the TRNSYS simulation platform. This paper describes the modelling and simulation of the Trinum micro-CHP configuration on TRNSYS as part of the process to develop the control automation solution for the smart rural microgrid in which the Trinum will ser...