Interactions between spherical nanoparticles optically trapped in Laguerre-Gaussian modes

When a Laguerre-Gaussian (LG) laser mode is used to trap nanoparticles, the spatial disposition of the particles about the beam axis is determined by a secondary mechanism that engages the input radiation with the interparticle potential. This analysis, based on the identification of a range-dependent laser-induced energy shift, elicits and details features that arise for spherical nanoparticles irradiated by a LG mode. Calculations of the absolute minima are performed for LG beams of variable topological charge, and the results are displayed graphically. It is shown that more complex ordered structures emerge on extension to three- and four-particle systems and that similar principles will apply to other kinds of radially structured optical mode. © 2005 Optical Society of America

Optically tailored access to metastable electronic states

On irradiating a molecular system with a laser beam of ultraviolet or visible frequency, photon absorption occurs when an electronic state is at a suitable energy level relative to an initial state. Despite meeting this criterion, interesting metastable states can remain inaccessible because of symmetry constraints. In this Letter a mechanism, based on the input of an off-resonant beam, is shown to enable the population of such states. This is achievable because the laser-modified process involves different selection rules compared to conventional photon absorption. The effects of applying the stimulus beam to either a one- or two-photon process are examined

Development of a Mechanistic Chamber Model of a Novel Peristaltic Compressor for Air-conditioning and Refrigeration Applications

The air-conditioning and refrigeration industry are constantly searching for efficiency improvements to vapor compression refrigeration systems. A valve-less compressor with variable volume ratios can significantly increase efficiency and add flexibility to these systems. The novel peristaltic compressor is introduced, which has the ability to operate at variable volume ratios and without valves. This compressor operates by means of a progressively actuated diaphragm that compresses vapor and stimulates flow through a cylindrical chamber. In this study, we will present a discretized thermodynamic model of a peristaltic compressor by splitting the mechanism into a series of conjoined segments. Mass and energy balance equations for each compression segment analyzed to create a mechanistic chamber model of the compressor with the segments interacting through flow of mass between them. This model includes a geometric model of the compression chamber created by the interface between the flexible diaphragm and the cylinder. The geometric model is coupled with the mass and energy balance to predict the compressor performance metrics. The preliminary model results show that the peristaltic compressor presents unique attributes that will be explored in future work

The Thermodynamic Behavior Of Low-GWP Zeotropic Mixtures On Water-Source Heat Pump Equipment

Regulatory changes, aimed at mitigating climate change, are forcing air-conditioning and heat pump manufacturers to change refrigerants in their products, including all Water-Source Heat Pumps (WSHPs). These changes require substantive changes to WSHP equipment design in order to continue to deliver heat pumps that meet product specifications and energy efficiency regulations. Some of the proposed low-GWP refrigerants to replace R410A, such as R452B and R454A, are zeotropic mixtures of refrigerants. Zeotropes with a significant glide may be taken advantage of in the refrigerant-to-water heat exchanger in a WSHP to improve overall system efficiency. However, there is a potential to also reduce system efficiency if not designed appropriately. This work presents a four-component heat pump model which includes a moving boundary condenser model, lumped element evaporator model, and fixed efficiency compressor model. This model was validated against the data of a R410A water-to-water heat pump operated in heating mode with an average 9.7% MAE in prediction of COP. This model was exercised using R452B and R454A and discovered that the latter provided an opportunity to increase the system COP as a result of the increased enthalpy of vaporization of the fluid. Additionally, the moderate glide that these two refrigerants produce is not significant enough to warrant significant consideration for a water-to-water heat pump

Quantitative and Qualitative Evaluation of Various Positive-Displacement Compressor Modeling Platforms

Several regulatory measures aimed to mitigate climate change are forcing compressor manufacturers to replace current refrigerants to those with low Global Warming Potential (GWP). New refrigerants need to be evaluated to ensure adequate efficiency for use in modern products. Evaluation can be done heuristically, which is expensive and timeconsuming, while a carefully designed simulation model can provide similar outcomes for a significantly reduced cost. This paper presents a comparison between various userdeveloped and existing reciprocating compressor models to assist in the selection of a suitable modeling platform for a wideranging study. The reciprocating compressor is selected because of the simplicity of the model to ensure consistency across different platforms. The userdeveloped models are developed in MATLAB™ and Modelica™ for the reciprocating compressor. The same compressor is also modeled using existing compressor modeling platforms, PDSim and GTSuite™. The compressor model includes three main components; geometry, compression process and frictional losses. Other submodels, like valve model and heat transfer model, are also part of the compression process. These platforms are evaluated based on both quantitative and qualitative criteria. Modelica™ is found to be computationally efficient while GTSuite™ took maximum time for simulation among the compared platforms. On a qualitative basis, PDSim is potentially a better platform for compressor optimization; which is also readily available to end user due to its opensource nature and prospects for future model development