An Evaluation of Heat Exchangers Using System Information and PEC
A. M. Jacobi,* C. W. Bullard*
NSF I/UCRC Air Conditioning and Refrigeration Center

Air-side heat transfer is the limiting factor in many air conditioning and refrigeration systems. Related work in the Center is developing a fundamental understanding of the way in which various heat transfer enhancement mechanisms work: louvers; vortex generators; wavy fins; pulsed flow; and sawtooth-shaped wire-on-tube configurations. The purpose of this project is to use knowledge of why these approaches work and determine which approaches are best suited to each application: domestic and commercial refrigeration; room, mobile, or split system air conditioners. Such information is needed to provide the basis for customizing each heat transfer enhancement strategy to various components and systems.

An Investigation of Alternative Refrigeration Cycles
T. Newell*
NSF I/UCRC Air Conditioning and Refrigeration Center

Preliminary investigation of novel refrigeration cycles and processes.

Design and Control of Mobile Air Conditioning Systems
N. R. Miller,* J. Solberg
NSF I/UCRC Air Conditioning and Refrigeration Center

This work integrates thermal design principles with modern control techniques to provide the basis for developing optimal systems for transient operation and varying environmental conditions. An experimental facility has been constructed to develop and evaluate alternative control techniques and hardware for mobile air conditioning systems. Alternative control methods that involve the use of advanced electronic devices and novel types of actuators and control inputs are being investigated. The project will determine which combinations of sensors, actuators, and control devices work best.

Design and Testing a Stationary Air Conditioning System with Minimum Total Equivalent Global Warming Impact
C. W. Bullard,* W. E. Dunn,* S. A. Stott
U. S. Department of Energy, NSF EEC 96-12120 DOE

With the assistance of heat exchanger manufacturers, this project involves fabricating a breadboard system to explore the energy conservation benefits of an air conditioning system employing ultracompact heat exchangers. The study also seeks to quantify the benefits of reducing transient losses by reducing charge inventory as a potentially simple alternative to variable-speed fans and compressors as a means of increasing energy efficiency.

Design of Heat Exchangers for Frosting Conditions
P. S. Hrnjak,* C. W. Bullard,* Y. Wu
NSF I/UCRC Air Conditioning and Refrigeration Center

This project involves experimental and analytical investigations of ways to control the spatial and temporal distribution of frost on heat exchangers of various geometries, e.g. those with circular, elliptical, and flat tubes. It also includes investigations of the effect of flow conditions on frost density, and relate this full heat exchanger performance to that which has been observed for single plates and fins. Additional wind tunnel tests will explore the feasibility of eliminating frosting altogether in supermarket and transport applications requiring that food temperatures be maintained at temperatures å?C using high-performance, ultracompact heat exchangers with enhanced air-side heat transfer surfaces.

Development of Next-Generation Building Energy Analysis Tools
C. O. Pedersen,* D. E. Fisher* (Okla. St. Univ.), R. J. Liesen,* M. Turner
U. S. Army Construction Engineering Research Laboratories, DACA88-96-0005-08

This project includes research and development in the areas of building energy analysis and computer simulation of building systems. The context for this research is a new computer program, called EnergyPlus, which is being developed under DOE sponsorship. EnergyPlus will include a detailed thermal zone model and a state of the art HVAC system simulation. The zone model will accurately predict the performance of the building envelope and will calculate the effect of energy saving systems such as passive solar and advanced fenestration. The HVAC system simulation will be integrated with the zone model to allow for the analysis of processes such as moisture adsorption in building elements and hydronic radiant heating.

Development of a Toolkit for Building Thermal Load Calculations
C. O. Pedersen,* D. E. Fisher (Okla. St. Univ.), R. K. Strand (Archit.), J. Asmundsson, M. Turner
American Society of Heating, Refrigerating and Air-Conditioning Engineers

This project will collect and codify state of the art building thermal load calculation algorithms in a modular format. The toolkit, under the sponsorship of the ASHRAE technical committee for thermal load calculations, will provide a repository for building thermal modeling techniques in a readily accessible and usable structure. This research will also complement the existing ASHRAE toolkits for systems and central plant modeling.

Dual Evaporator Refrigerator Research
T. Newell,* C. Bullard,* M. Stein, D. Gerlach, C. Inan
Arcelik

Testing and modeling of dual evaporator refrigerators are the object of this project. The effects of both heat and mass transfer are included. Modeling of refrigerator cabinets during opened and closed door conditions are included in the study.

Evaluation of Secondary Loop Processes for Use in Low-Temperature Refrigeration for Supermarkets
P. S. Hrnjak,* W. Terrell, Y. Mao
U.S. Environmental Protection Agency, CR-824346-01-0

Supermarkets are second only to automotive A/C systems in polluting the atmosphere with refrigerants. A circulating liquid concept should increase energy efficiency, reduce inventory and leakage of expensive and environmentally damaging refrigerant, and utilize centralized units that are more reliable, efficient, and less expensive. The project determines viable fluids, appropriate defrost technique, and will experimentally verify models developed. Additional attention is given to CO2 and ice slurry as secondary fluids that operate with phase changes.

Fractination and Maldistribution of Refrigerant Ternary Mixture when Evaporating in Brazed Plate Heat Exchangers
P. S. Hrnjak,* D. Tallitsch
The Trane Co.

The goal is to investigate maldistribution and fractination in brazed plate heat exchangers, especially when operating with lower mass velocities. Special attention is focused on the stability of the superheat signal. Oil hold-up is investigated along with different distribution options.

Frost-Tolerant, Ultracompact Heat Exchangers for Supermarket Refrigeration
P. S. Hrnjak,* C. W. Bullard,* D. Carlson
U. S. Department of Energy

This project explores design strategies for minimizing performance degradation of microchannel heat exchangers during frosting conditions (e.g., fin and louver design, variable-speed fans) in commercial and transport refrigeration applications. The next step is to quantify the interaction between parameters (e.g., airflow rates) affecting the design of air curtains and evaporators (e.g., face velocities) in refrigerated display cases. The final task is to develop and test ways of integrating ducted evaporators into a display case in a manner compatible with efficient operation of its air curtain.

High-Efficiency Residential Air Conditioning/Heat Pump System Based on Transcritical R744 Cycle
P. S. Hrnjak,* C. W. Bullard,* A. Beaver
Hydro Aluminum

The transcritical CO2 cycle is very promising at low-temperature lifts, particularly for heat pumps. We are comparing the performance of several in-house developed systems to the baseline R410A system that is the best conventional system available.

High-Intensity, Short-Pulse, Laser Beam Interactions with Solid Materials and Plasmas
M. A. Shannon,* C. Li, H. Chung
University of Illinois

The main objective of this research is to investigate energy coupling of high-power, short-pulse lasers with solids and plasmas, and specifically to investigate using lasers for near diffraction-limited micromachining and forming. The ultimate goal is to understand and control laser beams irradiating solids to create high-intensity filaments on the order of microns. Achieving this would increase the spatial resolution and depth of field of current laser-machining and joining processes, but the greatest impact could be on the fabrication of micron-sized structures for 3-D micromachines.

Ice Slurry as a Secondary Refrigerant
P. S. Hrnjak,* J. Nowak,* Y. Mao
American Society of Heating, Refrigerating and Air-Conditioning Engineers

Secondary loops offer great potential for charge reduction in refrigeration systems. Single phase secondary refrigerants are simpler to use but due to sensible heat, require significant flows. Ice slurry has potential in flow reduction and thermal storage. We study experimental flow and heat characteristics of propylene glycol slurry.

Measurement of the Relationship between Oil Circulation and Compressor Lubrication in a Mobile Air Conditioning System under a Variety of Transient and Steady State Operating Conditions
N. R. Miller,* C. Cusano,* P. Hrnjak,* T. Newell,* J. Chappell, J. Drozdek
NSF I/UCRC Air Conditioning and Refrigeration Center

Work within the Air Conditioning and Refrigeration Center as well as work carried out elsewhere shows the lack of understanding of the relationship between oil circulation in mobile air conditioners and the state of compressor lubrication. The nature of compressor lubrication is poorly understood under transient operating conditions. The state of lubrication of swashplate contacts within the compressor ultimately determines the longevity of the compressor. The goal of this project is to develop and demonstrate techniques that permit the simultaneous measurement of circulating oil concentration and the state of lubrication at the shoe/plate contact in a mobile style air conditioning system during various transient and steady state system operating conditions. Once developed, the measuring system can be applied to critical contacts in other refrigerant compressors.

Mobile Air Conditioning System Based on Transcritical CO2 Cycle
P. S. Hrnjak,* C. W. Bullard,* R. McEnaney, D. Boewe
Hydro Aluminum

Thermodynamic analysis indicates that the transcritical CO2 cycle has lower COP than R134a. Better thermophysical properties are the advantage for R744. Our initial results indicate better performance of CO2 system then off-the-shelf R134a systems over most of the operating range. We are exploring the causes and further potential of the system.

Mobile Air Conditioning Systems
P. S. Hrnjak,* C. W. Bullard,* M. Giannavola, R. Murphy
Delphi Thermal Systems, Inc.; U.S. Army CECOM

This project explores the use of transcritical cycles for vehicle air conditioners and heat pumps, using carbon dioxide as the refrigerant. It includes the design, simulation, and wind tunnel experiments on novel heat exchanger designs. Full-scale system tests will systematically explore a variety of options for controlling evaporator exit state; compressor discharge temperature; evaporator pressure; charge distribution; and high-side pressure to trade off capacity vs. COP. In both heating and cooling modes, data will be obtained on performance of control-related components (e.g., valves, high- or low-side receivers, compressor modulation), and used to develop governing equations for system simulation models.

Modular Simulation Model for Air Conditioning Systems
C. W. Bullard,* D. Harshbarger
NSF I/UCRC Air Conditioning and Refrigeration Center

The purpose of this project is to develop a detailed air conditioner simulation model with a modular structure that can accommodate the various types of heat exchangers, expansion devices used in a wide variety of stationary and mobile air conditioning and refrigeration applications. The work builds on an existing model/solver structure that enables the user to exchange input and output variables without rewriting or recompiling the program.

Multidisciplinary Research and Education Program in Laser and Thermal Science with Application to Microfabrication Engineering
M. A. Shannon,* J. Hammonds, J. Selby
National Science Foundation, CTS 9703402

The goal of this project is to advance the state of knowledge of laser and thermal science in both the education of students and in research towards highly anisotropic etching of advanced materials.

Optimization of R134a Air Conditioning Systems
P. S. Hrnjak,* S. Nelson
Ford-Visteon

Mobile air conditioning systems are responsible for significant refrigerant leaks. Recent increased requirements for high efficient systems along with leak issues are driving research in new technologies that will result in more energy efficient systems with minimal TEWI.

Optimization of Wire-on-Tube Condensers
C. W. Bullard,* P. Barnes
American Society of Heating, Refrigerating and Air-Conditioning Engineers

This project builds upon prior experimental work to develop design tools for wire-on-tube condensers such as those used in domestic refrigerator-freezers and some commercial applications. The focus is on development of simulation and optimization models that can be used to quantify tradeoffs between thermal performance and other factors affecting cost-effectiveness consumer acceptance: weight, volume, face velocity.

Pulse-Width Modulation of a Scroll Compressor
C. W. Bullard,* P. S. Hrnjak,* S. Ilic
Copeland Corp.

Mechanical flow modulation is a potentially feasible alternative to variable-speed motors for air conditioning and refrigeration compressors. In this project, experiments are being conducted in a well-instrumented environmental chamber using a pulse-width-modulated scroll compressor. The goal is to develop a fundamental understanding of the effects on the rest of the system and ultimately to identify component design and system control strategies to achieve maximum energy efficiency.

Residential Air Conditioning Systems
P. S. Hrnjak,* C. W. Bullard,* M. Richter
Hydro Aluminum A. S.

The goal of this project is to design and evaluate a prototype transcritical carbon dioxide-based heat pump for residential heating and cooling. Experiments will systematically explore ways of controlling evaporator exit state; compressor discharge temperature; evaporator pressure; charge distribution; and high-side pressure to trade off capacity vs. COP. Data will be used to develop and validate a system simulation model and to suggest design and control strategies for the next-generation prototype system.

Salt Gradient Solar Pond Research
T. A. Newell*
Illinois Department of Energy and Natural Resources, STILENRAE25SLRPND129; International Salt Co.; Gundle Lining Systems

A half-acre solar pond has been constructed in the agriculture section of campus. Continuing research investigates the feasibility of solar ponds for low-temperature heating processes.

Signal at the Evaporator Exit for Improvement of Refrigerant Distribution
P. S. Hrnjak,* M. A. Shannon,* T. Leicht
Electric Power Research Institute

The existance of droplets in the superheated vapor at the evaporator exit is an indication of refrigerant maldistribution. Analysis of frequency content related to liquid mass fraction indicates that it could be a reliable signal for control of ganged MEMS valves used for refrigerant throttling.

Thermal Radiative Emission from Surfaces in the Presence of Electric Fields
M. A. Shannon,* B. Pahl
University of Illinois

During short-pulse, high-power laser irradiation of solids, electrons are ejected from the surface in large numbers and with high energy, which creates very high transient electromagnetic fields near the surface. Radiant thermal emission from the surface may change nonlinearly because of the presence of this induced field. The purpose of this project is to measure the distribution of thermal radiation with wavelength under applied electric fields to determine the relative importance of electromagnetic fields on thermal emission at different temperatures.