High-performance Loop Research Articles

High Performance Loop Heat Pipe With Flat Evaporator for Energy-Saving Cooling Systems of Supercomputers

Abstract Two high performance loop heat pipes (LHPs) are developed for direct cooling of the chips in supercomputer. The two LHPs using flat evaporator are: one called water-cooling LHP and another one called air-cooling LHP. The working fluid of LHP is ammonia. The water-cooling LHP can work well at a heat load up to 663 W and air-cooling LHP can work well at a heat load up to 513 W. The two LHPs applying to the real computer servers are realized and tested. The server test results with water-cooling LHP have shown that the operating temperature of central processing units (CPUs) can be controlled to about 67 °C to ensure the reliable operating and acceptable level for electronic chips, even at condenser-cooling water temperature of 40 °C with low water flowrate of 0.055 m3/h. The server test results with air-cooling LHP have shown that the operating temperature of CPUs can be controlled to about 51 °C even at condenser-cooling wind temperature of 30 °C with wind flowrate of 41.88 m3/h.

Two-phase flow characteristics of a high performance loop heat pipe with flat evaporator under gravity

Aiming to fully investigate the two-phase flow characteristics inside a loop heat pipe (LHP), a visualization study for a compact copper-water loop heat pipe with flat evaporator was carried out under gravity favorable mode in this work. Under forced water cooling condition with the cooling water temperature of 25 °C, the results indicated that the compact LHP could efficiently dissipate a maximum heat load of 550 W with the evaporator temperature of 91.2 °C. A minimum LHP thermal resistance was 0.068 °C/W, which was obtained at 500 W. In addition, the evaporator temperatures at boiling incipience under different heat loads were evaluated, which showed slight dependence on the input heat load. Finally, the flow patterns during the startup stage and the steady stage associating with different heating loads were recorded and analyzed to investigate the internal operation mechanism of the LHP. As a result, various two-phase flow patterns were found to be related to the heat load, and the occurrence of partial dry-out was observed in the evaporator at the maximum heat load of 550 W, corresponding to a heat flux of 88 W/cm2.

High performance loop closure detection using bag of word pairs

In this paper, we look into the problem of loop closure detection in topological mapping. The bag of words (BoW) is a popular approach which is fast and easy to implement, but suffers from perceptual aliasing, primarily due to vector quantization. We propose to overcome this limitation by incorporating the spatial co-occurrence information directly into the dictionary itself. This is done by creating an additional dictionary comprising of word pairs, which are formed by using a spatial neighborhood defined based on the scale size of each point feature. Since the word pairs are defined relative to the spatial location of each point feature, they exhibit a directional attribute which is a new finding made in this paper. The proposed approach, called bag of word pairs (BoWP), uses relative spatial co-occurrence of words to overcome the limitations of the conventional BoW methods. Unlike previous methods that use spatial arrangement only as a verification step, the proposed method incorporates spatial information directly into the detection level and thus, influences all stages of decision making. The proposed BoWP method is implemented in an on-line fashion by incorporating some of the popular concepts such as, K-D tree for storing and searching features, Bayesian probabilistic framework for making decisions on loop closures, incremental creation of dictionary and using RANSAC for confirming loop closure for the top candidate. Unlike previous methods, an incremental version of K-D tree implementation is used which prevents rebuilding of tree for every incoming image, thereby reducing the per image computation time considerably. Through experiments on standard datasets it is shown that the proposed methods provide better recall performance than most of the existing methods. This improvement is achieved without making use any geometric information obtained from range sensors or robot odometry. The computational requirements for the algorithm is comparable to that of BoW methods and is shown to be less than the latest state-of-the-art method in this category.

Passivity and robust PI control of the air supply system of a PEM fuel cell model

Fuel cells are electrochemical devices that convert the chemical energy of a gaseous fuel directly into electricity. They are widely regarded as potential future stationary and mobile power sources. The response of a fuel cell system depends on the air and hydrogen feed, flow and pressure regulation, and heat and water management. In this paper, the study is concentrated on the control of the air subsystem that feeds the fuel cell cathode with oxygen—whose dynamics is described with a widely accepted nonlinear model. Due to the complexity of this model, the model-based controllers that have been proposed for this application are designed using its linear approximation at a given equilibrium point, which might lead to conservative stability margin estimates for the usually wide operating ranges of the system. On the other hand, practitioners propose the use of simple proportional or proportional–integral controllers around the compressor flow, which ensures good performance in most applications. In this paper we provide the theoretical justification to this scheme, proving that this output variable has the remarkable property that the linearization (around any admissible equilibrium) of the input–output map is strictly passive. Hence, the controllers used in applications yield (locally) asymptotically stable loops—for any desired equilibrium point and all values of the controller gains. Ensuring stability for all tuning gains overcomes the inherent conservativeness of linearized dynamics analysis, and assures the designer on the current use of robust, high performance loops. Instrumental to prove the passivity property is the exploitation of some monotonicity characteristics of the system that stem from physical laws.

The impinging—stream reactor: A high performance loop reactor for mass transfer controlled chemical reactions

Experimental results related to the performance of the impinging—stream loop reactor and showing the influence of the specific power input in the liquid phase, the gas flow rate and the nozzle diameter on the volumetric mass transfer coefficient are presented and discussed.