Reducing the amount of required propane refrigerant in the condenser of a commercial air-conditioner by increasing the inlet temperature

The use of synthetic refrigerants in the refrigeration and air conditioning sector is now obsolete due to the fact that they are not environmental friendly. They damage ozone layer and cause global warming which have both direct and indirect adverse effects on humans and environment. Today, the use of alternative refrigerants is well accepted. Hydrocarbon refrigerants are natural compounds, which do not damage the ozone layer, and have very little impact on global warming. The use of a simple hydrocarbon, propane, as a refrigerant is becoming increasingly popular these days due to its high heat capacity and its short lifetime in the atmosphere. However, since propane is extremely flammable, it is prudent to minimize the amount of propane in the system in order to reduce the risks associated with leakage of the explosive gas. In this research, the possibility of reducing the mass of propane in the condenser without sacrificing the heat transfer capacity of the system has been investigated. In an air-conditioner or refrigeration system, condenser accommodates the most mass of the refrigerant compared with those in the other parts of the system. A MATLAB script has been developed which model the performance of a commercial portable air-conditioner. The results show that by increasing the working temperature of condenser from 30oC to 46oC at the ambient temperature of 27oC, about forty percent propane mass saving is achievable. These temperatures are still far below the critical (370oC) and auto-ignition (540oC) temperatures of propane

A novel ember shower simulator for assessing performance of low porosity screens at high wind speeds against firebrand attacks

Previous studies have shown the effectiveness of low porosity and double-layer screens against radiant heat flux from fires. The performance of screens against firebrand attack is also required to be assessed prior to making a decision on their possible application in wildland fire prone areas. The available laboratory-scale devices simulate firebrands at wind speeds less than those of severe firebrand attacks. A relatively low cost, laboratory-scale fire ember shower simulator has been designed and manufactured in-house. The simulator is able to assess the performance of low porosity screens at high wind speeds without any reverse flow and possible consequent safety hazards and offers reasonable control over the size and mass of the generated firebrands

Flow field and performance study of vertical axis Savonius type SST wind turbine

It has been suggested that waste heats or naturally available heat sources can be utilized to produce swirling flow by a design similar to that of split channels which is currently used to initiate fire whirls in laboratories. A new hybrid power system has been proposed combining the conventional Savonius wind turbine and split channel mechanisms. Previous computational and experimental works indicate a performance improvement in the new hybrid design (named as swirling Savonius turbine, SST) compared to the conventional Savonius turbine. However, the lack of detailed descriptions of the flow field around the swirling Savonius turbine inhibits complete understanding of performance of the hybrid power system. The aim of this study is to numerically explore the three-dimensional unsteady flow around the rotor, and develop a simulation method for predicting their aerodynamic performance using control volume based CFD package of ANSYS CFX. Sliding mesh feature of CFX allowed to solve the motion of the moving blades. Numerical simulations results of SST were compared with the experimental results. A discussion on the detailed flow field characteristics, including velocity vector, velocity streamlines, pressure distribution, vorticity analysis, and examination of power and torque coefficients behavior are presented

Geometrical optimization of a swirling Savonius wind turbine using an open jet wind tunnel

It has been suggested that waste heats or naturally available heat sources can be utilized to produce swirling flow by a design similar to that of split channels which is currently used to initiate fire whirls in laboratories. The new design combines the conventional Savonius wind turbine and split channel mechanisms. Previous computational and preliminary experimental works indicate a performance improvement in the new design (named as swirling Savonius turbine) compared to the conventional Savonius design. In this study, wind tunnel experiments have been carried out to optimize the swirling Savonius turbine geometry in terms of maximum power coefficient by considering several design parameters. The results indicate that the blade overlap ratio, hot air inlet diameter and the condition of the top end plate have significant influence on power and torque coefficients, while a larger aspect ratio and closed top end plate have some favourable effects on the performance. The optimum configuration has been tested in four different wind velocities to determine its influence on the performance, and power coefficients were found to be higher in high wind velocities. The performance comparison of optimum configuration with conventional Savonius rotor showed an increase of 24.12% in the coefficient of power

Impacts of room temperature on the performance of a portable propane air conditioner

The performance of a portable propane air conditioner system, in which the temperatures of the air passing over the condenser and evaporator are equal, has been experimentally investigated under different room temperatures and refrigerant charge levels. The research has been carried out in a range of room temperatures from 20°C to 35°C and in undercharge, standard charge and overcharge conditions. The results show that, at higher room temperatures, the refrigerant temperature in all parts of the system, the density of the refrigerant at the inlet and outlet of the condenser, mass of the refrigerant in the compressor, the mass flow rate of the refrigerant and the cooling capacity of the system in either the undercharge or full charge condition, the specific cooling capacity of the undercharge system, the useful work of the compressor, and the maximum pressure of the refrigerant increase. The increase in room temperature decreases the density of the refrigerant at the inlet and outlet of the capillary tube, the mass of the refrigerant in the capillary tube, the refrigerant subcooling at the inlet of the capillary tube, the maximum velocity of the refrigerant and the coefficient of performance. In addition, the increase in room temperature at overcharge condition causes an increase in the mass flow rate, cooling capacity and specific cooling capacity to a maximum value followed by their decrease. The most important difference between a portable air-conditioner and a non-portable system is the increase in cooling capacity with an increase in room temperature in full charge condition

Comparing the Conventional with Low Dose of Bupivacaine Plus Fentanyl in Spinal Anesthesia on the Neonate Apgar Score in Yazd City

Introduction: Spinal anesthesia is the preferred method of anesthesia in cesarean section, due to less complications. The augmentation of opioids to spinal anesthetics can improve the quality and increase the duration of analgesia. This study aimed to compare the conventional with low dose of bupivacaine plus fentanyl in spinal anesthesia on the neonate Apgar score in elective cesarean section. Methods: The present double-blind randomized clinical trial was conducted on 150 pregnant mothers undergoing cesarean section with the spinal anesthesia during 2017-2018. The mothers were randomly assigned to two groups of 75. The spinal anesthesia was performed in the first group with the injection of 15 mg of 0.5% hyperbaric bupivacaine plus 1 ml of normal saline, and in the second group with the injection of 12.5 mg of 0.5% hyperbaric bupivacaine plus 25 μg of fentanyl. For both groups, 1- and 5-minute neonatal Apgar scores were assessed. Finally, the data were analyzed by SPSS17 software using statistical tests. Results: The mean age of the samples was 30.1±5.19 years with a range of 18-42 years (P-value=0.246). The mean gestational age was 38 weeks, the mean 1-minute Apgar score was 8.88 and the mean 5-minute Apgar score was 9.89. Conclusion: With the augmentation of fentanyl to bupivacaine for spinal anesthesia, the conventional dose can be reduced, which not only reduces the common side effects of Marcainee, but also provides an appropriate level of anesthesia and does not affect the neonatal Apgar score

Bushfire traps: the application of mesh screens to contain bushfires

Bushfires have become an all too frequent natural disaster in Australia. The severe impact of the incidents, especially in recent years, indicates the relative ineffectiveness of available techniques to contain them. The options to eliminate or reduce their impact include the application of wire meshes, which appears to be an effective technique. As filters and flame arrestors the benefits of meshes are well-established, and Australian standard for construction in bushfire prone areas (AS3959) recommends their use. However, the effectiveness of wire meshes in controlling bushfire propagation requires further investigation. In recent research carried out by the authors, it has been revealed that the screens are able to reduce the radiant heat flux, as well as effectively to weaken ember attack. The effects of screen parameters such as cell size, porosity, cell shape, weaving type and the screen orientation with respect to wind direction have been investigated experimentally and the results are presented in this paper

A review of the water desalination systems integrated with renewable energy

Water and energy are indispensable entities for any flourishing life and civilization. The water and energy scarcities have emerged due to the dramatic growth in the population, standards of living, and the rapid development of the agricultural and industrial sectors. Desalination seems to be one of the most promising solutions to the water problem; however, it is an intensive energy process. The integration of the renewable energy into water desalination systems has become increasingly attractive due to the growing demand for the water and energy, and the reduction of the contributions to the carbon footprint. The intensive investigations on the conventional desalination systems, especially in the oil-rich countries have somewhat overshadowed the progress and implementation of the renewable energy desalination (RED) systems. The economic performance evaluation of the RED systems and its comparison with conventional systems is not conclusive due to many varying factors related to the level of technology, the source of energy availability, and the government subsidy. The small RED plants have a high capital cost, low efficiency and productivity which make RED systems uncompetitive with the conventional ones. However, the selection of the small RED plants for the remote arid areas with small water demands is viable due to the elimination of the high cost of the water transportation, and the connection to the electricity grid. The purpose of this paper is to review the technology, energy, and cost of the recent available desalination systems and their potential to be integrated with the renewable energy resources. This review suggests that the solar still distillation (SD) system, which is simply a natural evaporation-condensation process, is the most practical renewable desalination technique to be used in the remote arid areas; however, a further research is required to enhance their performance and to increase the productivities of these systems

Effective factors on the performance of woven wire screens against leaf firebrand attacks

Firebrand spotting is the dominant wildfire propagation mechanism. The use of wire screens to prevent firebrand entry into structures is recommended or mandated by many standards. The existing standards address only one feature of screens which is opening size. This experimental study aims to explore several other factors that may influence the performance of wire screens and may need to be incorporated in codes and standards development process for structures located in wildfire prone areas. The results demonstrate a previously unreported shattering mechanism in the case of Eucalyptus populnea (from the Myrtle family) leaf firebrands under a moderate wind speed of 14.5 m/s. The results also show that screen porosity, screen type and wind speed would be appropriate to be addressed in developing standards, but there is no need for concern about screen orientation as long as the screen is placed perpendicular to the wind direction during the experiment

The Quantitative and Qualitative Study of the Effectiveness of the Problem-based Learning Approach in Teaching Research Methods

Research methods is an essential ingredient of postgraduate programs across a wide range of social science disciplines. The purpose of this study was to compare the effectiveness of problem-based learning (PBL) and lecture-based learning (LBL) approaches to teaching research methods through a mixed-methods approach in an explanatory sequential design. The quantitative data were collected following a quasi-experimental design whereby two classes of research methods in a postgraduate program randomly received either an LBL or a PBL treatment. To assess students’ academic achievement, a final exam on the course was used. The results indicated a higher academic achievement of students in the PBL class compared to LBL class. The qualitative data were gathered through a semi-structured interview to gain deeper insight into the quantitative results. The thematic analysis of the interviews showed that PBL led to deeper and more meaningful learning, increased students’ knowledge in their field of specialty, provided more enjoyable and active learning, increased the students\u27 skills in doing their thesis projects, enhanced their autonomy and independence, and also promoted their dignity and status