Potential of heat pipe technology in nuclear seawater desalination

The official published version of this article can be found at the link below.Heat pipe technology may play a decisive role in improving the overall economics, and public perception on nuclear desalination, specifically on seawater desalination. When coupled to the Low-Temperature Multi-Effect Distillation process, heat pipes could effectively harness most of the waste heat generated in various types of nuclear power reactors. Indeed, the potential application of heat pipes could be seen as a viable option to nuclear seawater desalination where the efficiency to harness waste heat might not only be enhanced to produce larger quantities of potable water, but also to reduce the environmental impact of nuclear desalination process. Furthermore, the use of heat pipe-based heat recovery systems in desalination plant may improve the overall thermodynamics of the desalination process, as well as help to ensure that the product water is free from any contamination which occur under normal process, thus preventing operational failure occurrences as this would add an extra loop preventing direct contact between radiation and the produced water. In this paper, a new concept for nuclear desalination system based on heat pipe technology is introduced and the anticipated reduction in the tritium level resulting from the use of heat pipe systems is discussed

CFD modelling of a two-phase closed thermosyphon charged with R134a and R404a

This paper examines the application of CFD modelling to simulate the two-phase heat transfer mechanisms in a wickless heat pipe, also called a thermosyphon. Two refrigerants, R134a and R404a, were selected as the working fluids of the investigated thermosyphon. A CFD model was built to simulate the details of the two-phase flow and heat transfer phenomena during the start-up and steady-state operation of the thermosyphon. The CFD simulation results were compared with experimental measurements, with good agreement obtained between predicted temperature profiles and experimental temperature data, thus confirming that the CFD model was successful in reproducing the heat and mass transfer processes in the R134a and R404a charged thermosyphon, including the pool boiling in the evaporator section and the liquid film in the condenser section

Modelling and simulation techniques for forced convection heat transfer in heat sinks with rectangular fins

The official published version of this article can be found at the link below.This paper provides a comprehensive description of the thermal conditions within a heat sink with rectangular fins under conditions of cooling by laminar forced convection. The analysis, in which increasing complexity is progressively introduced, uses both classical heat transfer theory and a computational approach to model the increase in air temperature through the channels formed by adjacent fins and the results agree well with published experimental data. The calculations show how key heat transfer parameters vary with axial distance, in particular the rapid changes in heat transfer coefficient and fin efficiency near the leading edges of the cooling fins. Despite these rapid changes and the somewhat ill-defined flow conditions which would exist in practice at the entry to the heat sink, the results clearly show that, compared with the most complex case of a full numerical simulation, accurate predictions of heat sink performance are attainable using analytical methods which incorporate average values of heat transfer coefficient and fin efficiency. The mathematical modelling and solution techniques for each method are described in detail.This work was part of a project funded by Solas Technology Limited, Ireland

Removal of copper ions from aqueous solution using low temperature biochar derived from the pyrolysis of municipal solid waste

Includes graphical abstract.Sustainable methods to produce filter materials are needed to remove a variety of pollutants found in water including organic compounds, heavy metals, and other harmful inorganic and biological contaminants. This study focuses on the removal of Cu(II) from copper aqueous solutions using non-activated char derived from the pyrolysis of mixed municipal discarded materials (MMDM) using a new heat pipe-based pyrolysis reactor. Adsorption experiments were conducted by adding the char to copper solutions of varying concentration (50–250 mg/L) at a constant temperature of 30 °C. The effect of pH on copper adsorption onto the char was also investigated in the range of pH 3 to 6. Copper removal using the char was found to be heavily dependent on pH, adsorption was observed to decrease below a pH of 4.5. However, the initial copper concentration had a little effect on the sorption of copper at high concentration solutions (above 100 mg/L). Overall, the biochar showed an effective copper adsorption capacity (4–5 mg/g) when using copper solutions with a concentration below100 mg/L and pH >4.5. Copper removal using the char tended to follow the pseudo second order kinetic model. Langmuir isothermal model was shown to be the closest fitting isotherm using the linearized Langmuir equation. However, the variety of feedstock used to produce the char led to a variation in results compared to other studies of more specific feedstocks.The reported work was funded by EPSRC under Grant 1956470

An Investigation into the use of Water as a Working Fluid in Wraparound Loop Heat Pipe Heat Exchanger for Applications in Energy Efficient HVAC Systems Energy

Wraparound heat pipes have been used for many years and have found a niche application in outside air handling units in hot and humid climates. They are used in conjunction with primary, chilled water cooling coils to enhance the efficiency of moisture removal and ensure that the process consumes minimal energy. The type of heat pipe employed is a gravity assisted thermosyphon which is formed into a loop and ‘wrapped’ around the main cooling coil. The traditional working fluid for HVAC heat pipes has been a refrigerant and a replacement fluid is desirable as a short and long-term option. From an environmental standpoint, water is an ideal candidate and many of its thermal transport properties suggest that it should be viable. There are manufacturing issues associated with using water which are not the concern of this paper; the paper’s intention is to prove the viability of water and compare its performance with that of traditional refrigerants. At the conditions used for the experimentation, the results suggest that the use of water in a loop heat pipe can enhance the effectiveness of the arrangement by up to 18% when compared with a conventional refrigerant filled pipe. The type of thermosyphon, or gravity-assisted heat pipe, that is under consideration has a performance which can be quantified using an effectiveness model. This model has been used in the investigation to compare the performance of identical pipes filled with different working fluids. The effectiveness of the heat pipe is determined by many variables and a good proportion of these are related simply to tube orientation, size and flow path. The application of wraparound heat pipes that is under consideration relies upon specific sizes and orientations of tubes and the conclusions of the report give pointers towards further research which needs to be undertaken, or is currently underway, in order to determine the extents of applicability of water as a working fluid

Film boiling heat transfer and vapour film collapse on spheres, cylinders and plane surfaces

Copyright @ 2009 Elsevier B.V. The final version of this article may be viewed at the link below.An experimental study of transient film boiling was conducted, with different coolant velocities, on two spheres with different diameters, two cylindrical specimens of different lengths in parallel flow, a cylinder in cross flow and two flat plates with different lengths. A frame by frame photographic study on the nature of the vapour/liquid interface and the collapse modes has revealed a new mode for film collapse, in which an explosive liquid–solid contact is followed by film re-formation and the motion of a quench front over the hot surface. Steady state tests were carried out on a plate similar to the short plate used in the transient experiments and the heat transfer, film stability and collapse results are compared with those of the transient investigation. Heat transfer coefficients and heat fluxes during film boiling were found essentially to depend on specimen temperature and water subcooling. In contrast, the influences on heat transfer of specimen size and water velocity were relatively small for the ranges studied. A theoretical model predicted heat transfer coefficients to within 10% of experimental values for water subcoolings above 10 K and within 30% in all cases

Numerical modelling of a two-phase twin-screw expander for Trilateral Flash Cycle applications

This paper presents numerical investigations of a twin-screw expander for low grade (≤100°C) heat to power conversion applications based on the bottoming Trilateral Flash Cycle. After a thorough description of the modeling procedure, a first set of simulations shows the effect of different inlet qualities of the R245fa working fluid and of the revolution speed on the expander performance. In particular, at 3750 RPM and an inlet absolute pressure of 5 bar, the volumetric and adiabatic efficiencies will increase from 24.8% and 37.6% to 61.2% and 83.1% if the inlet quality in the intake duct of the expander increased from 0 to 0.1. To further assess the effects of inlet quality, inlet pressure and revolution speed on the expander performance, parametric analyses were carried out in the ranges 0-1 inlet quality, 5-10 bar pressure and 1500-6000RPM speed respectively. © 2018 The Author(s).European Union’s Horizon 2020 Research and Innovation Programme under grant agreement no. 680599, (ii) Innovate UK (project no. 61995-431253, (iii) Engineering and Physical Sciences Research Council UK (EPSRC), grant no. EP/P510294/1 and (iv) Research Councils UK (RCUK), grant no. EP/K011820/1

Advanced Heat Exchangers for Waste Heat Recovery Applications

The incentive for industrial waste heat recovery, which has attracted much research interest in recent years, has been twofold: the obligation to reduce greenhouse gas emissions in line with climate change targets and the need for processes to reduce overall energy consumption in order to remain commercially competitive [...