Numerical investigation of the energy performance of a guideless irregular heat and mass exchanger with corrugated heat transfer surface for dew point cooling

© 2016 The Author(s) The paper presents an investigation into the energy performance of a novel irregular heat and mass exchanger for dew point cooling which, compared to the existing flat-plate heat exchangers, removed the use of the channel supporting guides and implemented the corrugated heat transfer surface, thus expecting to achieve the reduced air flow resistance, increased heat transfer area, and improved energy efficiency (i.e. Coefficient of Performance (COP)) of the air cooling process. CFD simulation was carried out to determine the flow resistance (K) factors of various elements within the dry and wet channels of the exchanger, while the ‘finite-element’ based ‘Newton-iteration’ numerical simulation was undertaken to investigate its cooling capacity, cooling effectiveness and COP at various geometrical and operational conditions. Compared to the existing flat-plate heat and mass exchangers with the same geometrical dimensions and operational conditions, the new irregular exchanger could achieve 32.9%–37% higher cooling capacity, dew-point and wet-bulb effectiveness, 29.7%–33.3% higher COP, and 55.8%–56.2% lower pressure drop. While undertaking dew point air cooling, the irregular heat and mass exchanger had the optimum air velocity of 1 m/s within the flow channels and working-to-intake air ratio of 0.3, which allowed the highest cooling capacity and COP to be achieved. In terms of the exchanger dimensions, the optimum height of the channel was 5 mm while its length was in the range 1–2 m. Overall, the proposed irregular heat and mass exchanger could lead to significant enhanced energy performance compared to the existing flat-plate dew point cooling heat exchanger of the same geometrical dimensions. To achieve the same amount cooling output, the irregular heat and mass exchanger had the reduced size and cost against the flat-plate ones

Development of an Electromagnetic Sensor for in Pipeline Inspection and Asset Management for the Water Industry

In the UK, the Water Services Regulation Authority (OFWAT), estimates that for all the water and sewage companies there was over 3,365 Ml/d (megalitres per day) of water leakage in the reported period 2010 and 2011, which was still at 3094.21 Ml/day in the 2013 review. Leakage estimates do not include water siphoned illegally through unaccounted connections worsened as asset management of buried utility services has been overlooked for years. With the asset management programme framework (AMP6) due to come into effect in April 2015, water companies are expected to get more out of their existing infrastructure and making considerable investment while keeping bills reasonable for customers. Improving the management of these assets is therefore a priority, as effective asset management enables companies to reduce cost, through leakage management, to plan investments and repairs, and to evaluate operational risks by better fault prediction rather than the current reactive approach.This research focuses on the water distribution network as an asset that include leaks and pipe infrastructure with different materials and diameters. A novel method for leak detection and asset management using an electromagnetic sensor has been developed. Trials in the laboratory showed the sensor is capable of detecting pipe types and conditions thus improving leak detection and asset management in the water industry without extensive digs and modification to existing access valves within the network for system deployment. Furthermore, the sensor would potentially benefit the gas industry by modifying the frequency of operation to match gas filled cylindrical metal structures

Simulation and experiment on thermal performance of a micro-channel heat pipe under different evaporator temperatures and tilt angles

© 2019 Elsevier Ltd For a solar collector with a heat pipe, the tilt angle is an important factor which has a direct impact on the orientation (surface azimuth angle) and affects the amount of solar radiation reaching the surface of the collector. The performance of the microchannel heat pipe (MCHP), as a highly efficient heat transfer device, can be influenced by gravity and two-phase flow pattern. The relationship between the performance of the MCHP and the tilt angles is nonlinear. In this paper, the effect of the evaporator temperature and tilt angle on the thermal performance of the MCHP, especially the temperature distribution along the heat pipe wall and the effective thermal conductivity, will be investigated. An experimental study with different evaporator temperatures and tilt angles is carried out. Additionally, thermal characteristics of the MCHP have been simulated and verified by the experimental results. In addition, the temperature distribution along the MCHP and the effective thermal conductivity for different working conditions have been performed. These results would provide many references for the solar collector with MCHP system design, optimization, and installation

Magnetic Excitations of Undoped Iron Oxypnictides

We study the magnetic excitations of undoped iron oxypnictides using a three-dimensional Heisenberg model with single-ion anisotropy. Analytic forms of the spin wave dispersion, velocities, and structure factor are given. Aside from quantitative comparisons which can be made to inelastic neutron scattering experiments, we also give qualitative criteria which can distinguish various regimes of coupling strength. The magnetization reduction due to quantum zero point fluctuations shows clear dependence on the c-axis coupling.Comment: 4 pages, 5 figures, to appear in Frontiers of Physics in China: a special issue on Iron-based superconductor

Pooled Analysis of Meningioma Risk Following Treatment for Childhood Cancer.

IMPORTANCE: Meningioma is the most common subsequent neoplasm following cranial irradiation among survivors of childhood cancer, but there are still uncertainties regarding the magnitude of the radiation dose-response association, potential modifiers of radiation risks, and the role of chemotherapy. OBJECTIVE: To evaluate meningioma risk in survivors of childhood cancer following radiotherapy and chemotherapy and identify possible modifying factors of radiation-associated risk. DESIGN, SETTING, AND PARTICIPANTS: This international case-control study pooled data from 4 nested case-control studies of survivors of childhood cancer diagnosed between 1942 and 2000, followed through 2016. Cases were defined as participants diagnosed with a subsequent meningioma. Controls were matched to cases based on sex, age at first cancer diagnosis, and duration of follow-up. Data were analyzed from July 2019 to June 2022. EXPOSURES: Radiation dose (Gy) to the meningioma site and cumulative chemotherapy doses, including intrathecal and systemic methotrexate doses. MAIN OUTCOMES AND MEASURES: The main outcome was subsequent meningioma, assessed using odds ratios (ORs) and excess odds ratios per gray (EOR/Gy). RESULTS: The analysis included 273 survivors of childhood cancer who developed meningioma (cases) and 738 survivors who did not (controls), with a total of 1011 individuals (median [IQR] age at first cancer diagnosis 5.0 [3.0-9.2] years; 599 [59.2%] female). Median (IQR) time since first cancer was 21.5 (15.0-27.0) years. Increasing radiation dose was associated with increased risk of meningioma (EOR/Gy, 1.44; 95% CI, 0.62-3.61), and there was no evidence of departure from linearity (P = .90). Compared with survivors who were not exposed to radiation therapy, those who received doses of 24 Gy or more had more than 30-fold higher odds of meningioma (OR, 33.66; 95% CI, 14.10-80.31). The radiation dose-response association was significantly lower among patients treated at age 10 years or older compared with those treated before age 10 years (EOR/Gy, 0.57; 95% CI, 0.18-1.91 vs 2.20; 95% CI, 0.87-6.31; P for heterogeneity = .03). Risk associated with radiation remained significantly elevated 30 years after exposure (EOR/Gy, 3.76; 95% CI, 0.77-29.15). We found an increased risk of meningioma among children who had received methotrexate (OR, 3.43; 95% CI, 1.56-7.57), but no evidence of a dose-response association or interaction with radiation dose. CONCLUSIONS AND RELEVANCE: These findings suggest that the meninges are highly radiosensitive, especially for children treated before age 10 years. These results support the reduction in whole-brain irradiation over recent decades and the prioritization of approaches that limit radiation exposure in healthy tissue for children. The persistence of elevated risks of meningiomas for 30 years after cranial radiotherapy could help inform surveillance guidelines

Window screening, ceilings and closed eaves as sustainable ways to control malaria in Dar es Salaam, Tanzania.

BACKGROUND\ud \ud Malaria transmission in Africa occurs predominantly inside houses where the primary vectors prefer to feed. Human preference and investment in blocking of specific entry points for mosquitoes into houses was evaluated and compared with known entry point preferences of the mosquitoes themselves.\ud \ud METHODS\ud \ud Cross-sectional household surveys were conducted in urban Dar es Salaam, Tanzania to estimate usage levels of available options for house proofing against mosquito entry, namely window screens, ceilings and blocking of eaves. These surveys also enabled evaluation of household expenditure on screens and ceilings and the motivation behind their installation.\ud \ud RESULTS\ud \ud Over three quarters (82.8%) of the 579 houses surveyed in Dar es Salaam had window screens, while almost half (48.9%) had ceilings. Prevention of mosquito entry was cited as a reason for installation of window screens and ceilings by 91.4% (394/431) and 55.7% (127/228) of respondents, respectively, but prevention of malaria was rarely cited (4.3%, 22/508). The median cost of window screens was between US $21-30 while that of ceilings was between US$301-400. The market value of insecticide-treated nets, window screening and ceilings currently in use in the city was estimated as 2, 5 and 42 million US$. More than three quarters of the respondents that lacked them said it was too expensive to install ceilings (82.2%) or window screens (75.5%).\ud \ud CONCLUSION\ud \ud High coverage and spending on screens and ceilings implies that these techniques are highly acceptable and excellent uptake can be achieved in urban settings like Dar es Salaam. Effective models for promotion and subsidization should be developed and evaluated, particularly for installation of ceilings that prevent entry via the eaves, which are the most important entry point for mosquitoes that cause malaria, a variety of neglected tropical diseases and the nuisance which motivates uptake

On the multi-orbital band structure and itinerant magnetism of iron-based superconductors

This paper explains the multi-orbital band structures and itinerant magnetism of the iron-pnictide and chalcogenides. We first describe the generic band structure of an isolated FeAs layer. Use of its Abelian glide-mirror group allows us to reduce the primitive cell to one FeAs unit. From density-functional theory, we generate the set of eight Fe $d$ and As $p$ localized Wannier functions for LaOFeAs and their tight-binding (TB) Hamiltonian, $h(k)$. We discuss the topology of the bands, i.e. allowed and avoided crossings, the origin of the d6 pseudogap, as well as the role of the As $p$ orbitals and the elongation of the FeAs$_{4}$ tetrahedron. We then couple the layers, mainly via interlayer hopping between As $p_{z}$ orbitals, and give the formalism for simple and body-centered tetragonal stackings. This allows us to explain the material-specific 3D band structures. Due to the high symmetry, several level inversions take place as functions of $k_{z}$ or pressure, resulting in linear band dispersions (Dirac cones). The underlying symmetry elements are, however, easily broken, so that the Dirac points are not protected, nor pinned to the Fermi level. From the paramagnetic TB Hamiltonian, we form the band structures for spin spirals with wavevector $q$ by coupling $h(k)$ and $h (k+q)$. The band structure for stripe order is studied as a function of the exchange potential, $\Delta$, using Stoner theory. Gapping of the Fermi surface (FS) for small $\Delta$ requires matching of FS dimensions (nesting) and $d$-orbital characters. The origin of the propeller-shaped FS is explained. Finally, we express the magnetic energy as the sum over band-structure energies, which enables us to understand to what extent the magnetic energies might be described by a Heisenberg Hamiltonian, and the interplay between the magnetic moment and the elongation of the FeAs4 tetrahedron

Consistent model of magnetism in ferropnictides

The discovery of superconductivity in LaFeAsO introduced the ferropnictides as a major new class of superconducting compounds with critical temperatures second only to cuprates. The presence of magnetic iron makes ferropnictides radically different from cuprates. Antiferromagnetism of the parent compounds strongly suggests that superconductivity and magnetism are closely related. However, the character of magnetic interactions and spin fluctuations in ferropnictides, in spite of vigorous efforts, has until now resisted understanding within any conventional model of magnetism. Here we show that the most puzzling features can be naturally reconciled within a rather simple effective spin model with biquadratic interactions, which is consistent with electronic structure calculations. By going beyond the Heisenberg model, this description explains numerous experimentally observed properties, including the peculiarities of the spin wave spectrum, thin domain walls, crossover from first to second order phase transition under doping in some compounds, and offers new insight in the occurrence of the nematic phase above the antiferromagnetic phase transition.Comment: 5 pages, 3 figures, revtex