Alexander S. Rattner

Dynamic model for small-capacity ammonia-water absorption chiller

Optimization of the performance of absorption systems during such transient operations as start-up and shut-down to minimize lifetime costs is particularly important for small-capacity chillers and heat pumps. Dynamic models in the literature have been used to study responses to step changes in single parameters, but more complex transient processes, such as system start-up, have not been studied in detail. A robust system-level model for simulating the transient behavior of an absorption chiller was developed here. Individual heat and mass exchangers were modeled using detailed segmental models. System parameters used in the model were representative of a 1-RT (3.5-kW cooling) absorption chiller currently under development. Representative simulations were performed for the full “cold start-up” process and for system responses to step changes in the desorber coupling-fluid temperature and valve settings. Results from this analysis can be used to optimize start-up and steady-state performances.

Coupling-fluid heated bubble pump generators: Experiments and model development

Single-pressure absorption heat pumps operate using solely thermal input and are ideal candidates for distributed cooling applications. Liquid circulation in such systems has conventionally been achieved with spot-heated bubble-pump generators, vertical tubes in which intense localized heat desorbs refrigerant. Rising refrigerant bubbles lift solutions to an upper reservoir, which feeds other system components. While this method of refrigerant separation and fluid circulation is simple, it necessitates a source of high-grade energy and thus cannot be employed in many settings. In this investigation, a full-length coupling-fluid heated bubble-pump generator is investigated. In this implementation, heating fluid is circulated through an annular jacket around the bubble-pump tube. Because the heat transfer area is much larger than in conventional spot-heated bubble-pump generators, relatively low-temperature thermal sources can be employed. Results are presented from an experimental study of a 7.8-mm-internal-diameter bubble-pump generator with water-steam working fluid over a range of operating conditions. This bubble-pump generator can operate with thermal input as low as 11 K above the fluid saturation temperature. A mechanistic fluid flow and heat transfer model is developed and validated. This investigation demonstrates that coupling-fluid heated bubble-pump generators are a promising alternative to conventional spot-heated implementations and can enable refrigeration using low-grade thermal energy.

Model-based feedback control of an ammonia-water absorption chiller

In this study, potential control strategies for a small-scale, 3.5-kW ammonia–water absorption chiller are developed and investigated numerically using a dynamic simulation model. The dynamic model is employed to study the response of the system under varying ambient temperatures and cooling load demands. Two strategies are investigated for feedback control of the system. The first control loop maintains the evaporator temperature glide set-point (Tevap,out – Tevap,in), while the second control loop regulates desorption temperature to provide the desired cooling duty and maintain the delivered coolant temperature at a set-point. At design operating conditions, the proposed control for evaporator temperature glide requires ∼250 s to reach the set-point of 3°C, starting from ambient conditions. With the proposed implementation of desorption temperature control, the system can respond to changes in ambient temperature and cooling load demand, and maintain the delivered coolant temperature within ±0.75°C of the set-point. At part-load operation, the proposed techniques can increase the system coefficient of performance by 8% or greater.

Temperature-Weighted Assessment of Waste Heat Availability With Matched End-Use Applications for Optimal Primary Energy Usage in the USA

Approximately two-thirds of all input energy used for power and electricity generation in the USA is lost as heat during conversion processes. Additionally, 12.5% of primary fuel and 20.3% of the electricity generated through these processes are employed for space heating, water heating, and refrigeration where low-grade heat could suffice. The potential for harnessing waste heat from power generation and thermal processes to perform these low-grade tasks is assessed here. By matching power plant outlet streams with applications at corresponding temperature ranges, this study identifies sufficient waste heat to satisfy all residential, building, and manufacturing space and water heating needs. Sufficient high temperature exhaust from power plants is identified to satisfy 27% of residential air conditioning demand with thermally activated refrigeration or all industrial low temperature (100–150°C) process heating and refrigeration needs. Exhaust from vehicle engines is sufficient to satisfy all in-vehicle air conditioning and 68% of electricity generation demand. Energy usage and waste heat availability and application information collected for this study is compiled in a thermodynamically informed database. By providing SQL queries, this database can answer detailed questions about energy sources and demands delineated by temperature, energy scale, process, and location. This capability can inform future infrastructure and development to effectively capture waste heat that would be lost today, substantially reducing the USA national energy intensity across all end uses.© 2010 ASME

Framework and algorithms for illustrative visualizations of time-varying flows on unstructured meshes

A framework for illustrative visualization of fluid simulation datasets is presented.New algorithms are developed for feature identification and matching in field data.Novel implementations are described for multiple illustrative visualization effects. Photo- and physically realistic techniques are often insufficient for visualization of fluid flow simulations, especially for 3D and time-varying studies. Substantial research effort has been dedicated to the development of non-photorealistic and illustration-inspired visualization techniques for compact and intuitive presentation of such complex datasets. However, a great deal of work has been reproduced in this field, as many research groups have developed specialized visualization software. Additionally, interoperability between illustrative visualization software is limited due to diverse processing and rendering architectures employed in different studies. In this investigation, a framework for illustrative visualization is proposed, and implemented in MarmotViz, a ParaView plug-in, enabling its use on a variety of computing platforms with various data file formats and mesh geometries. Region-of-interest identification and feature-tracking algorithms incorporated into this tool are described. Implementations of multiple illustrative effect algorithms are also presented to demonstrate the use and flexibility of this framework. By providing an integrated framework for illustrative visualization of CFD data, MarmotViz can serve as a valuable asset for the interpretation of simulations of ever-growing scale.

Generalized Framework and Algorithms for Illustrative Visualization of Time-Varying Data on Unstructured Meshes

Photo- and physically-realistic techniques are often insufficient for visualization of simulation results, especially for 3D and time-varying datasets. Substantial research efforts have been dedicated to the development of non-photorealistic and illustration-inspired visualization techniques for compact and intuitive presentation of such complex datasets. While these efforts have yielded valuable visualization results, a great deal of work has been reproduced in studies as individual research groups often develop purpose-built platforms. Additionally, interoperability between illustrative visualization software is limited due to specialized processing and rendering architectures employed in different studies. In this investigation, a generalized framework for illustrative visualization is proposed, and implemented in marmotViz, a ParaView plugin, enabling its use on variety of computing platforms with various data file formats and mesh geometries. Detailed descriptions of the region-of-interest identification and feature-tracking algorithms incorporated into this tool are provided. Additionally, implementations of multiple illustrative effect algorithms are presented to demonstrate the use and flexibility of this framework. By providing a framework and useful underlying functionality, the marmotViz tool can act as a springboard for future research in the field of illustrative visualization.

Design and Analysis of the Absorber Component in Waste-Heat-Driven Diffusion Absorption Refrigeration Systems

The diffusion absorption refrigeration (DAR) cycle can provide refrigeration in remote locations using waste-heat or other low-grade-thermal input. Unlike conventional absorption systems, the DAR cycle receives no mechanical input, so all flows must be driven by passive mechanisms. Further, a third inert gas is employed to allow refrigerant expansion since conventional throttling devices impart large pressure drops. Thus, DAR absorber design is challenging due to increased mass transfer resistance from the inert gas, multiple outlet flow paths for the inert gas and solution, and limited (passive) external cooling. In the present study, a detailed, coupled heat and mass transfer model is developed for a counter-flow serpentine-tube DAR absorber. The model is applied to the analysis of an absorber for a small-scale refrigeration system with a 36 W cooling capacity. Studies are conducted to investigate the effect of key configuration and operational parameters on absorber performance, and guidelines are provided for component and system design.Copyright

Simple Mechanistically Consistent Formulation for Volume-of-Fluid Based Computations of Condensing Flows

Numerous investigations have been conducted to extend adiabatic liquid-gas VOF flow solvers to include condensation phenomena by adding an energy equation and phase-change source terms. Some proposed phase-change models employ empirical rate parameters, or adapt heat transfer correlations, and thus must be tuned for specific applications. Generally applicable models have also been developed that rigorously resolve the phase-change process, but require interface reconstruction, significantly increasing computational cost and software complexity. In the present work, a simplified first-principles-based condensation model is developed, which forces interface-containing mesh cells to the equilibrium state. The operation on cells instead of complex interface surfaces enables the use of fast graph algorithms without reconstruction. The model is validated for horizontal film condensation, and converges to exact solutions with increasing mesh resolution. Agreement with established results is demonstrated for smooth and wavy falling-film condensation.Copyright

MarmotViz User Guide

MarmotViz is an illustrative visualization plug-in for ParaView. It is intended for generating enhanced visualizations of time-varying datasets on unstructured connected meshes. A detailed description of the implemented algorithms and program structure can be found in the related document: Generalized framework and algorithms for illustrative visualization of time-varying data on unstructured meshes . This document provides details for compiling/building MarmotViz, using the MarmotViz plug-in in ParaView, and extending the MarmotViz plug-in.