Stationary Air Conditioning System Analysis
C. W. Bullard,* W. E. Dunn,* S. Stott
NSF I/UCRC Air Conditioning and Refrigeration Center

This project is motivated by the emergence of new technologies for stationary (unitary and split) air conditioning systems: (1) making heat exchangers more compact, (2) varying compressor and fan speeds, and (3) modulating refrigerant flow. The goal is to use models and experimental facilities to focus on these objectives: (1) quantify benefits of ultracompact heat exchangers on steady-state and transient performance; (2) explore energy efficiency and design implications of multi- or variable-speed compressor/fan control in combination with fixed and/or electronic throttling devices; (3) examine the effect of evaporator design on system performance and noise; and (4) expedite the capillary-tube/charge optimization process.

Refrigerator Systems Analysis
C. W. Bullard,* S. Kelman
NSF I/UCRC Air Conditioning and Refrigeration Center

This project investigates the potential of several technologies for increasing performance or reducing cost of domestic refrigerator freezers. The objectives are to (1) quantify the performance tradeoffs associated with using dual evaporator systems as an alternative to mixing cabinet airstreams; (2) analyze strategies for minimizing charge inventory to reduce cycling losses without degrading performance over a wide range of ambient temperatures; (3) identify system and component performance implications of designing for variable-speed compressors; and (4) identify the potential improvements obtainable through capillary tube-suction line heat exchanger design.

Optimization of Thermal Processes
J. C. Chato,* S. Crofts
University of Illinois

Thermal processes generate irreversibilities, i.e., entropy. In many processes, the optimum performance on operating limits can be estimated by finding the minimum rate of irreversibility, i.e., entropy production. Such a technique is often considerably simpler than more conventional ones. The method has been successfully applied to cooled shields in insulations, to heat exchangers, and to heat exchanger networks.

A Study of Optimized Condenser Designs
A. M. Clausing,* A. M. Jacobi,* R. Rasmussen
Frigidaire Co.

This project is directed toward the design of a new generation of heat exchangers for residential refrigerators. In particular, research is being conducted to develop new condenser configurations and to exploit new air-side heat transfer enhancements. Heat transfer diagnostics, system simulation, and simple optimization methods are being used to identify promising new directions for heat exchanger development and to estimate the potential benefits of improved component performance in this application.

Thermal Performance of Wire and Tube Condensers
A. M. Clausing,* T. D. Swofford, J. L. Hoke
UIUC Air Conditioning and Refrigeration Center

An investigation of the thermal performance of the wire and tube condensers that are typically used in domestic refrigerators is being conducted. The emphasis of this investigation is on the air-side heat transfer characteristics. Both forced flow and the natural convection limit are being studied experimentally. Several innovative, high-performance designs are being experimentally evaluated. Simultaneously, a computer model for predicting the thermal performance of wire and tube condensers for a variety of configurations is being developed.

Minimizing TEWI of Split and Unitary Air Conditioning Systems through Use of Ultracompact Heat Exchangers
W. E. Dunn,* C. W. Bullard,* S. Stott
NSF I/UCRC Air Conditioning and Refrigeration Center

With the assistance of heat exchanger manufacturers, this project involves fabrication of a breadboard system to explore the energy conservation benefits of an air conditioning system that employs ultracompact heat exchangers. It is also quantifying 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 system efficiency.

Measurements of Sound Power Radiated by Expansion Devices
P. S. Hrnjak,* N. R. Miller,* E. Rodarte Guajardo, G. Singh
NSF I/UCRC Air Conditioning and Refrigeration Center

The overall aim of this project is to investigate noise radiation and flow-induced force excitation in expansion devices, design and build devices to measure sound pressure inside the refrigeration tubes, and explore possibilities for noise reduction by varying orifice tube geometry or other parameters.

An Experimental Analysis of Orifice Tube Performance
P. S. Hrnjak,* G. M. Singh, A. H. Neto
NSF I/UCRC Air Conditioning and Refrigeration Center

Orifice tubes are the most frequently used expansion devices in automotive A/C systems. Further understanding of two-phase choked flow phenomena is acquired in experimental testing as a part of this project. The influence of diameter, length, screens, and other factors is examined and models are developed.

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.

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.

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.

New Secondary Refrigerants Based on Potassium Formate
P. S. Hrnjak,* Y. Mao, W. Terrell
Kemira

The search for systems that would reduce refrigerant leaks in commercial refrigeration focused attention on secondary loops and secondary refrigerants that are environmentally acceptable and technically sound at temperatures up to -40°C. We research properties and experimentally study the effects of potassium format based coolants on performance of commercial refrigeration systems.

Ice Slurry as a Secondary Refrigerant
P. S. Hrnjak,* J. Nowak,* Y. Mao
American Society of Heating, Refrigeration 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.

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.

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, which is the best conventional system available.

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

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

An Evaluation of Heat Exchangers Using System Information and PEC
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 Air Conditioning and Refrigeration 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.

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.

Measurement of the Relationship between Oil Circulation and Compressor Lubrication in a Mobile AC System under 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 and 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. Our goal 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.

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.

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

This is a preliminary investigation of novel refrigeration cycles and processes.

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.

Development of Next-Generation Building Energy Analysis Tools
C. O. Pedersen,* D. E. Fisher,* R. J. Liesen,* R. K. Strand, R. D. Taylor
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, 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, R. K. Strand, 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.

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.

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.

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 toward highly anisotropic etching of advanced materials.

Flow and Temperature Distribution in Stratified Water Storage
S. L. Soo,* C. W. Sohn,* K. O. Homan
U.S. Army Construction Engineering Research Laboratories, AT23-EB-ESO; National Center for Supercomputing Applications

Thermal energy storage for building and process cooling in the form of chilled water has been demonstrated to be an economical system. Diffusers have been used to achieve natural stratification by taking advantage of the buoyancy forces. It was observed that natural stratification involves the formation of a thermocline by introducing chilled water at suitable inlet condition and geometry. A computer model will be developed for the optimization of design to minimize the volume and optimize the storage capacity, mixing and heat transfer between the warm and cold water, as well as the operating procedures.