Evaluation of R448A and R450A as Low-GWP alternatives for R404A and R134a using a micro-fin tubes evaporator model

[EN] When retrofitting new refrigerants in an existing vapour compression system, their adaptation to the heat exchangers is a major concern. R450A and R448A are commercial non-flammable mixtures with low GWP developed to replace the HFCs R134a and R404A, fluids with high GWP values. In this work the evaporator performance is evaluated through a shell-and-microfin tube evaporator model using R450A, R448A, R134a and R404A. The accuracy of the model is first studied considering different recently developed micro-fin tube correlations for flow boiling phenomena. The model is validated using experimental data from tests carried out in a fully monitored vapour compression plant at different refrigeration operating conditions. The main predicted operational parameters such as evaporating pressure, UArp, and cooling capacity, when compared with experimental data, fit within 10% using the Akhavan-Behabadi et al. correlation for flow boiling. Results show that R450A and R404A are the refrigerants in which the model fits better, even though R448A and R134a predictions are also accurate. (C) 2015 Elsevier Ltd. All rights reserved.The authors thankfully acknowledge "Ministerio de Educacion, Cultura y Deporte" (Grant number FPU12/02841) for supporting this work through "Becas y Contratos de Formacion de Profesorado Universitario del Programa Nacional de Formacion de Recursos Humanos de Investigacion del ejercicio 2012". Finally the linguistic support of Irene I. Elias-Miranda is appreciated.Mendoza Miranda, JM.; Mota-Babiloni, A.; Navarro Esbri, J. (2016). Evaluation of R448A and R450A as Low-GWP alternatives for R404A and R134a using a micro-fin tubes evaporator model. Applied Thermal Engineering. 98:330-339. https://doi.org/10.1016/j.applthermaleng.2015.12.064S3303399

Human Factors Aspects of the Transfer of Control from the Driver to the Automated Highway System

DTFH-61-92-C-00100The third in a series of experiments exploring human factors issues related to the Automated Highway System (AHS) investigated the transfer of control from the driver of a vehicle entering an automated lane to the AHS. Twenty-four drivers aged between 25 and 34 years drove in the Iowa Driving Simulator--a moving base hexapod platform containing a mid-sized sedan with a 3.35-rad (180 deg) projection screen to the front and a 1.13-rad (60 deg) screen to the rear. The experiment focused on a generic AHS configuration in which the left lane was reserved for automated vehicles, the center and right lanes were reserved for unautomated vehicles, and in which there was no transition lane and no barrier. The driver took the simulator vehicle onto a freeway, moved to the center lane, and then, after receiving an "Enter" command, drove into an automated lane and transferred control to the AHS. Then, the AHS moved the vehicle into the lead position of the string of vehicles approaching it from behind. RESULTS: The entering response time, lane-change time, entering exposure time, and string-joining time data were used to determine the minimum inter-string gap required to enable the driver's vehicle to enter the automated lane without causing a delay to the string it joins. The required minimum inter-string gap varied with the design velocity and the method of transferring control. With the partially automated transfer method, the required minimum inter-string gap time increased from 1.14 s for the 104.7-km/h (65-mi/h) design velocity, through 3.38 s for the 128.8-km/h (80-mi/h) design velocity, to 7.33 s for the 153.0-km/h (95-mi/h) design velocity. The hourly capacity when the design velocity is 104.7 km/h (65 mi/h) is likely to be four times greater than when the design velocity is 153.0 km/h (95 mi/h) (the hourly capacity for the latter would be only slightly more than the traffic flow that could be achieved without an AHS). It is not the design velocity of 104.7 km/h (65 mi/h) per se that produces the higher capacity--it is the relatively low velocity differential between the design velocity and the speed limit in the unautomated lanes. If the transfer of control from the driver to the AHS were to occur before the driver moved into the automated lane, the required minimum inter-string gap times should be reduced--a possibility that is being investigated in the next in the experimental series. No collisions occurred, suggesting that the drivers were able to join the automated lane safely--a suggestion reinforced by the responses to a questionnaire indicating that the drivers felt safe and believed they controlled the vehicle well during the entry maneuver

Drivers' Activities and Information Needs in an Automated Highway System

DTFH61-92-C-00100These experiments investigated what drivers do when traveling under automated control, and what information they would like to have available during that time. Eighteen drivers ages 25 through 34 and 18 drivers age 65 or older participated in the first two experiments; 6 drivers participated in the third experiment. All experiments were conducted in the Iowa Driving Simulator. The driver drove the simulator vehicle onto a freeway and then moved to the center lane; following a period of manual driving, control was transferred to the AHS, and the driver traveled under automated control for at least 34 min. In the first two experiments, which were run together and consisted of a single trial for each driver, driver activities were videotaped for later analysis. In addition, a laptop computer was mounted near the driver that offered several types of information. Drivers were given a questionnaire after the experiment to allow ratings of and comments on the various information types. In the third experiment, each driver participated in eight trials, once each in the morning and afternoon on 4 days, simulating a commuter experience. Driver activities were again videotaped for later analysis, but there was no laptop computer available. RESULTS: In the two noncommuter experiments, drivers undertook a variety of activities, though despite pre-experiment encouragement to do so, almost no one brought any materials with them. Thus, the activities included such things as reading the strip map that was in the car, talking to the experimenter, adjusting the radio, and so on. The most frequent activity was using the laptop computer. A third of the drivers closed their eyes at least once for 5 or more consecutive seconds, with averages of 5.7 and 7.1 times for males and females, respectively. Regarding the information available on the laptop computer, drivers found information about the next exit to be least useful. Information about the driver's current location and the traffic ahead were more useful than next exit information. And information about time to the destination was selected significantly more frequently than the other three types of information. Drivers offered several suggestions for additional information they would like to have available during a trip on the AHS. In the commuter experiment, it was noted, however, that only two drivers brought something to do on the next-to-last trial, a somewhat surprising result in light of the fact that the drivers clearly knew by then that they would have almost half an hour during which they did not have any driving-related responsibilities

A review of refrigerant R1234ze(E) recent investigations

[EN] Climate change is demonstrated through global surface temperatures increase in the last century. To stop this phenomenon, new regulations that ban or tax greenhouse gas fluids (HFC among them) have been approved. In the medium term, only low-GWP refrigerants will be permitted in developed countries. HFO fluids and most used HFCs as refrigerants in HVACR systems possess similar thermophysical properties. Among them, one of the most promising is R1234ze(E). This refrigerant presents good environmental properties and can be used in most of HVACR applications, pure or mixed with HFC or natural refrigerants (mainly CO2). This paper collects the most relevant research about R1234ze(E) thermophysical and compatibility properties, heat transfer and pressure drop characteristics, and vapor compression system performance; separating those works that consider R1234ze(E) pure or blended. Once the available literature is analyzed, it can be concluded that pure R1234ze(E) is a good option only in new HVACR systems. Nevertheless, if it is combined with other refrigerants, the final GWP value is also considerably reduced, maintaining efficiency parameters at levels that allow them to replace R134a, R404A or R410A in existing systems with minor modifications.The authors thankfully acknowledge the “Ministerio de Educación, Cultura y Deporte” (Grant Number FPU12/02841) for supporting this work through “Becas y Contratos de Formación de Profesorado Universitario del Programa Nacional de Formación de Recursos Humanos de Investigación del ejercicio 2012”.Mota-Babiloni, A.; Navarro-Esbrí, J.; Molés, F.; Barragán Cervera, Á.; Peris, B.; Verdú Martín, GJ. (2016). A review of refrigerant R1234ze(E) recent investigations. Applied Thermal Engineering. 95:211-222. https://doi.org/10.1016/j.applthermaleng.2015.09.055S2112229

Human Factors Aspects of the Transfer of Control from the Automated Highway System to the Driver

DTFH61-92-C-00100The first two experiments in a series exploring human factors issues related to the Automated Highway System (AHS) used a generic AHS configuration--the left lane reserved for automated vehicles, the center and right lanes containing unautomated vehicles, no transition lane, and no barriers between the automated and unautomated lanes--that was simulated in the Iowa Driving Simulator (IDS). The IDS has a moving base hexapod platform containing a mid-sized sedan. Imagery was projected onto a 3.35-rad (180 deg) screen in front of the driver, and onto a 1.13-rad (60 deg) screen to the rear. Thirty-six drivers between the ages of 25 and 34 years participated in the first experiment; 24 drivers who were age 65 or older took part in the second. Both experiments explored the transfer of control from the AHS to the driver when the driver's task was to leave the automated lane. The driver, who was traveling under automated control in a string of vehicles in the automated lane, had to take control, drive from the automated lane into the center lane, then leave the freeway. Results were as follows: (1) The mean time to respond to an "Exit" advisory decreased from 13.41 s to 10.16 s as the design velocity increased from 104.7 km/h (65 mi/h) to 153.0 km/h (95 mi/h). (2) After the transfer of control, the driver remained in the automated lane, decelerating until the velocity was slow enough to allow a safe transition into the slower traffic in the unautomated lanes. It took longer to decelerate (13.19 s vs. 10.26 s) and the exit velocity dropped [105.30 km/h (65.40 mi/h) vs. 99.54 km/h (61.83 mi/h)] as the unautomated traffic density decreased from 12.42 v/km/ln (20 v/mi/ln) to 6.21 v/km/ln (10 v/mi/ln). It also took longer to decelerate (15.23 s vs. 8.62 s) and the extent of the deceleration decreased [42.7 km/h (26.49 mi/h) vs. 13.18 km/h (8.16 mi/h)] as the design velocity decreased from 153.0 km/h (95 mi/h) to 104.7 km/h (65 mi/h). (3) Once in the unautomated lanes, the younger drivers were in the center lane 70% longer than the older drivers. (4) The vehicle immediately behind the driver's vehicle in the automated lane was delayed after control was transferred--the delay increased from 1.36 s to 6.70 s as the design velocity increased from 104.7 km/h (65 mi/h) to 153 km/h (95 mi/h). (5) Allowing for the delay times obtained in these experiments, it was determined that the potential capacity of an automated lane should increase from 634.6 v/h to 2087.8 v/h as the design velocity decreases from 153.0 km/h (95 mi/h) to 104.7 km/h (65 mi/h). (6) Collisions and incursions occurred at unacceptably high rates. (7) The responses to the questionnaire suggest that the drivers were receptive to the AHS concept

Pulse shaping effects on weld porosity in laser beam spot welds : contrast of long- & short- pulse welds.

Weld porosity is being investigated for long-pulse spot welds produced by high power continuous output lasers. Short-pulse spot welds (made with a pulsed laser system) are also being studied but to a much small extent. Given that weld area of a spot weld is commensurate with weld strength, the loss of weld area due to an undefined or unexpected pore results in undefined or unexpected loss in strength. For this reason, a better understanding of spot weld porosity is sought. Long-pulse spot welds are defined and limited by the slow shutter speed of most high output power continuous lasers. Continuous lasers typically ramp up to a simmer power before reaching the high power needed to produce the desired weld. A post-pulse ramp down time is usually present as well. The result is a pulse length tenths of a second long as oppose to the typical millisecond regime of the short-pulse pulsed laser. This study will employ a Lumonics JK802 Nd:YAG laser with Super Modulation pulse shaping capability and a Lasag SLS C16 40 W pulsed Nd:YAG laser. Pulse shaping will include square wave modulation of various peak powers for long-pulse welds and square (or top hat) and constant ramp down pulses for short-pulse welds. Characterization of weld porosity will be performed for both pulse welding methods

Trajectory Based Operations and the Legacy Flight Deck: Envisioning Design Enhancements for the Flight Crew

DTFAWA-10-A-80031This study addresses the gap in scientific information at the intersection of Trajectory-Based Operations (TBO), realistic flight deck \u2013 pilot tasking environments, and human performance assessment. The study explored pilot performance, pain points, and system improvements in a human-in-the-loop heuristic evaluation of prototype displays for selected Next Generation Air Transportation System (NextGen) TBO scenarios. Legacy flight deck systems represent the baseline for innovation of TBO concepts. Because \u201cclean sheet\u201d design of both the NAS and the flight deck is seldom possible, designing human-centered \u201cNowGen\u201d interventions for existing systems is a prudent way to evolve toward NextGen. Study Approach: Three legacy and current generation interfaces were adapted using human-centered design heuristics to support Four-dimensional (4D) RTA-TBO, including a Multifunction Control Display Unit (MCDU), an Electronic Flight Bag (EFB), and an integrated Graphical Flight Planning (GFP) system. Seven airline, corporate, and technical pilots evaluated the interfaces in scenarios using different flight phases, weather, and NAS/Air Traffic Control (ATC) conditions. We obtained feedback from pilots on how well the prototyped interfaces supported pilot decision making, how easy they were to learn, their effect on self-reported workload, and the way in which the information was presented. Results: Evaluation participants responded favorably to the MCDU and integrated GFP RTA-prototypes, while the EFB prototype received less favorable feedback. However, the data collected in this study must be considered preliminary, until we have completed more rigorous human factors evaluation and objective pilot performance measurements. The report concludes with our recommendations for further work to develop and refine recommendations for TBO flight deck design requirements and guidance, including refinement and evaluation of EFB design that could support legacy aircraft participation in TBO