Investigations into single-slug dense-phase pneumatic conveying

After reviewing existing theories in detail, the author has found a serious error in a popular model for the prediction of pressure drop in single-slug dense-phase pneumatic flow. The purpose of this study is to analyse the mechanism of slug flow and develop a new method for determining pressure drop accurately, so that commercially used densephase pneumatic conveying systems can be designed by theory. The present study lays the foundation for modem dense-phase pneumatic conveying design. Subsequent investigators and prospective users of the system will benefit from this work mainly in three aspects: (1) a better knowledge about the conveying mechanism; (2) a more accurate estimation of the operating factors; (3) a design based more on theory than empiricism

Evaluation of the impacts of emergency vehicle signal preemption

Emergency vehicle signal preemptions are designed to give green light to responding emergency vehicles by preempting signals as they proceed through signalized intersections. A direct objective of signal preemption is to reduce response time for emergency vehicle while enhancing safety. However, signal preemptions interrupt regular signal operations and thus cause extra traffic delay to general traffic. Studies have been conducted on evaluating the effectiveness of signal preemption from the perspective of improving emergency vehicle response time. It has been found that these studies have been using traffic simulation models which cannot reflect the real traffic conditions, particularly associated with preemption. With the observational data (GPS data from paratransit vehicles) available, this study evaluates the impact of emergency vehicle on regular traffic and analyzes signal transition for preemption; The impact of emergency vehicles on regular traffic is based on hypothesis tests on the variance and mean of speeds for the general traffic under the preemption conditions versus those under normal conditions. The results from the test on variance indicate that significantly larger variance can be produced by emergency preemption than that in normal conditions which implies that general traffic in preemption would experience greater safety risk when emergency vehicles preempt signals at intersections. The results from the test on the mean of speed show that the speed of traffic running in the same direction as emergency vehicle is lower than that in normal conditions; that in the opposite direction is statistically the same as in normal conditions; while the traffic on crossing streets seems running slower than in normal conditions. To derive the conditions under which preemption can disrupt traffic less, regression analysis is conducted by which the speed in preemption is related to the factors such as average speed and standard deviation of general traffic in normal conditions, duration and time period of preemption, and roadway classification where traffic is traveling on. It is found that vehicles tend to travel at relative high speeds in preemption conditions if vehicles also run fast in normal conditions. This observation leads to the recommendation that preemptions be provided on relative high speed roadways. It is also found that preemption in peak periods slow down traffic which implies that it is better to reduce the use of preemption during peak periods. Long preemption is also found having negative impact on the speed of general traffic. Thus, the duration of preemption should be kept to a minimum; Signal transition is analyzed based on its characteristics including the length of transition, number of signal cycles during transition, average cycle length in transition, and number of short/long cycles in transition. Regression analysis is performed to relate the speed in preemption/transition and some of these characteristics of transition. However, none of these characteristics are found significant in impacting the speeds in preemption conditions; Keywords. Emergency Vehicle Signal Preemption, Signal Transition, Impact Analysis