An experimental investigation is presented in this paper on the vapor compression refrigeration cycle used in an ice-making machine with a multi-channel evaporator. To study the operation performance of the refrigeration system in the ice-making machine, the fluid temperature distribution in multi-channel evaporating coils are tested and the dynamic variations in each cooling loop are investigated during the ice-generating phase. The results show that the external cooling loops have the largest temperature fluctuations caused by the large initial refrigerant injecting mass flow and the external environmental disturbances. For the inner cooling loops, the related temperature profiles of different test points have relative stable variations. To reduce the temperature fluctuations of the outside loops, it is suggested to reduce the initial refrigerant mass flow and adjust the initial opening of the thermal expansion valve. Moreover, it is the normal phenomenon for the slight temperature variations for the temperature curves of different test points, caused by the adjustment of thermal expansion valve. During the ice-making process, both the sensible heat removal phase and latent heat removal phase are experienced successively. To remove the sensible heat of water, the refrigerant system is operating in high efficiency with test points having a rapid linear temperature reduction. While for eliminating the latent heat of ice, it requires much more power supply, the relating test points have a temperature decrease with fluctuations. To improve the operation performance of ice machine, some suggestions and improvements are proposed. 相似文献
IntroductionSafety management in construction is complicated due to the complex “nature” of the construction industry. The aim of this research was to identify safety management factors (e.g., risk management and site management), contextual factors (e.g., organisational complexity) and combinations of such factors connected to safety performance. Method: Twelve construction projects were selected to compare their safety management and safety performance. An analytical framework was developed based on previous research, regulations, and standards where each management factor was defined. We employed qualitative comparative analysis (QCA) to produce case knowledge, compare the cases, and identify connections between the factors and safety performance. The material collected and analyzed included, for example, construction planning documents, reports from OHS-inspections, safety indicators, and interviews with project leaders and OHS experts. Results and conclusions: The research showed that: (a) the average score on 12 safety management factors was higher among projects with high safety performance compared to projects with low safety performance; (b) high safety performance can be achieved with both high and low construction complexity and organizational complexity, but these factors complicate coordination of actors and operations; (c) it is possible to achieve high safety performance despite relatively poor performance on many safety management factors; (d) eight safety management factors were found to be “necessary” for high safety performance, namely roles and responsibilities, project management, OHS management and integration, safety climate, learning, site management, staff management, and operative risk management. Site management, operative risk management, and staff management were the three factors most strongly connected to safety performance. Practical implications: Construction stakeholders should understand that the ability to achieve high safety performance in construction projects is connected to key safety management factors, contextual factors, and combinations of such factors. 相似文献
Previous research suggests that performance‐prove goal orientation is positively related to knowledge hiding. However, we argue that this effect depends on the focus of performance feedback (i.e., individual‐ and group‐focused feedback), which shapes the nature of the competitive expression of performance‐prove goal orientation (i.e., intragroup and intergroup oriented). We conducted three studies to test our theoretical model. The results of Study 1 with time‐lagged data from 128 part‐time MBA students showed that performance‐prove goal orientation was positively related to knowledge hiding when performance feedback focused more (vs. less) on individual performance but was negatively related to knowledge hiding when performance feedback focused more (vs. less) on group performance. Study 2 replicated these moderation findings in an experimental study of 210 undergraduate students. Study 3 again replicated the moderation effects using multisource data from 317 employees and their supervisors. It also included creativity as an outcome of knowledge hiding and illustrated the distal consequence of the moderation effects of individual‐ and group‐focused performance feedback. We then discussed the implications for the theory and practice of performance‐prove goal orientation and knowledge hiding. 相似文献
Objective: This article aims to evaluate the safety performance of cable median barriers on freeways in Florida.
Method: The safety performance evaluation was based on the percentages of barrier and median crossovers by vehicle type, crash severity, and cable median barrier type (Trinity Cable Safety System [CASS] and Gibraltar system). Twenty-three locations with cable median barriers totaling about 101 miles were identified. Police reports of 6,524 crashes from years 2005–2010 at these locations were reviewed to verify and obtain detailed crash information. A total of 549 crashes were determined to be barrier related (i.e., crashes involving vehicles hitting the cable median barrier) and were reviewed in further detail to identify crossover crashes and the manner in which the vehicles crossed the barriers; that is, by either overriding, underriding, or penetrating the barriers.
Results: Overall, 2.6% of vehicles that hit the cable median barrier crossed the median and traversed into the opposite travel lane. Overall, 98.1% of cars and 95.5% of light trucks that hit the barrier were prevented from crossing the median. In other words, 1.9% of cars and 4.5% of light trucks that hit the barrier had crossed the median and encroached on the opposite travel lanes. There is no significant difference in the performance of cable median barrier for cars versus light trucks in terms of crossover crashes. In terms of severity, overrides were more severe compared to underrides and penetrations. The statistics showed that the CASS and Gibraltar systems performed similarly in terms of crossover crashes. However, the Gibraltar system experienced a higher proportion of penetrations compared to the CASS system. The CASS system resulted in a slightly higher percentage of moderate and minor injury crashes compared to the Gibraltar system.
Conclusions: Cable median barriers are successful in preventing median crossover crashes; 97.4% of the cable median barrier crashes were prevented from crossing over the median. Of all of the vehicles that hit the barrier, 83.6% were either redirected or contained by the cable barrier system. Barrier crossover crashes were found to be more severe compared to barrier noncrossover crashes. In addition, overrides were found to be more severe compared to underrides and penetrations. 相似文献