Mathematical Methods for Solar Chimney Analysis

Solar Chimney Power Plants (SCPP) – also known as Solar Updraft Power Plants – consists in a structure composed by a glass collector, placed in a few meters from the ground, with a chimney in its center, in order to promote a pressure differential and consequently a heated air flow. On the bottom of the chimney, a turbine convert the kinetic energy from the heated airflow in electric power. Many mathematical and numerical methods for predict the performance of this kind of renewable energy plant have been conducted, but always with a divergence among them. The main objective of this work is to compare the mathematical methods of evaluation the overall performance, as well to propose a more accurate mathematical method, comparing all results with Manzanares Plant and other methods in the literature. Two approaches were studied and then modified: one based on continuity and momentum equation and the other based on the sum of all pressure drops along the system. The main reasons of the difference between the models analyzed are highlighted. The results shows that one of the proposed methods leads to a divergence of only 1.3% when compared to Manzanares pilot plant, i.e., with an excellent agreement with experimental data

Risk factors for unfavourable postoperative outcome in patients with Crohn's disease undergoing right hemicolectomy or ileocaecal resection An international audit by ESCP and S-ECCO

Background Patient and disease-related factors, as well as operation technique all have the potential to impact on postoperative outcome in Crohn's disease. The available evidence is based on small series and often displays conflicting results. Aim To investigate the effect of pre- and intra-operative risk factors on 30-day postoperative outcome in patients undergoing surgery for Crohn's disease. Method International prospective snapshot audit including consecutive patients undergoing right hemicolectomy or ileocaecal resection. This study analysed a subset of patients who underwent surgery for Crohn's disease. The primary outcome measure was the overall Clavien-Dindo postoperative complication rate. The key secondary outcomes were anastomotic leak, re-operation, surgical site infection and length of stay at hospital. Multivariable binary logistic regression analyses were used to produce odds ratios (OR) and 95% confidence intervals (CI). Results Three hundred and seventy five resections in 375 patients were included. The median age was 37 and 57.1% were female. In multivariate analyses, postoperative complications were associated with preoperative parenteral nutrition (OR 2.36 95% CI 1.10-4.97)], urgent/expedited surgical intervention (OR 2.00, 95% CI 1.13-3.55) and unplanned intraoperative adverse events (OR 2.30, 95% CI 1.20-4.45). The postoperative length of stay in hospital was prolonged in patients who received preoperative parenteral nutrition (OR 31, CI [1.08-1.61]) and those who had urgent/expedited operations (OR 1.21, CI [1.07-1.37]). Conclusion Preoperative parenteral nutritional support, urgent/expedited operation and unplanned intraoperative adverse events were associated with unfavourable postoperative outcome. Enhanced preoperative optimization and improved planning of operation pathways and timings may improve outcomes for patients

Mathematical Methods for Solar Chimney Analysis

Solar Chimney Power Plants (SCPP) – also known as Solar Updraft Power Plants – consists in a structure composed by a glass collector, placed in a few meters from the ground, with a chimney in its center, in order to promote a pressure differential and consequently a heated air flow. On the bottom of the chimney, a turbine convert the kinetic energy from the heated airflow in electric power. Many mathematical and numerical methods for predict the performance of this kind of renewable energy plant have been conducted, but always with a divergence among them. The main objective of this work is to compare the mathematical methods of evaluation the overall performance, as well to propose a more accurate mathematical method, comparing all results with Manzanares Plant and other methods in the literature. Two approaches were studied and then modified: one based on continuity and momentum equation and the other based on the sum of all pressure drops along the system. The main reasons of the difference between the models analyzed are highlighted. The results shows that one of the proposed methods leads to a divergence of only 1.3% when compared to Manzanares pilot plant, i.e., with an excellent agreement with experimental data

Magnetizer design based on a quasi-oppositional gravitational search algorithm

The gravitational search algorithm (GSA) is a novel metaheuristics approach inspired by the laws of gravitation and motion. In GSA, a set of agents, called masses, searches the design space to find the optimal solution by simulation of Newtonian laws of gravity and motion. In this paper, a standard and an improved GSA (IGSA) approach based on a quasi-oppositional approach are presented and tested on a magnetic pole design benchmark. Results indicate that the performance of proposed IGSA on the magnetic pole design is better than that of classical GSA. © 1965-2012 IEEE

Application of cuckoo search for design optimization of heat exchangers

A wide variety of evolutionary optimization algorithms have been used by researcher for optimal design of shell and tube heat exchangers (STHX). The purpose of optimization is to minimize capital and operational costs subject to efficiency constraints. This paper comprehensively examines performance of genetic algorithm (GA) and cuckoo search (CS) for solving STHX design optimization. While GA has been widely adopted in the last decade for STHX optimal design, there is no report on application of CS method for this purpose. Simulation results in this paper demonstrate that CS greatly outperforms GA in terms of finding admissible and optimal configurations for STHX. It is also found that CS method not only has a lower computational requirement, but also generates the most consistent results