2000 IIAR Technical Papers
   Nashville, TN
  22nd Annual Meeting

Ammonia/Carbon Dioxide Hybrid Systems: Advantages and Disadvantages   
Author: Will Stoecker

Occasionally, ammonia is not selected for an industrial refrigeration system either because of personal preference of the end user or because of code restrictions. This paper explores the possibility of hybrid systems which use ammonia confined to the machine room as the high side, while carbon dioxide serves the refrigeration loads either as a secondary coolant or as the refrigerant of the low- temperature circuit in a cascade system.
Carbon dioxide has some advantages and disadvantages, and its advantages can be exploited when combined with highly-efficient ammonia high side. Carbon dioxide is virtually non-toxic, maintains a convenient pressure in low- temperature evaporators, and possesses some of the same superior heat-transfer properties of ammonia. A disadvantage of CO2 as a secondary coolant compared to its use as the low- temperature in a cascade system. For ultra-low temperature evaporation, for example for evaporating temperatures -50 degrees Fahrenheit (-45 degrees Celsius), the size and volumetric capacity of a CO2 compressor is less than that of an ammonia compressor operating at the same saturated suction temperature. As a secondary coolant where the liquid CO2 changes phase in the low- temperature heat exchanger, the cost of pumping CO2 would be modest, compared to pumping a fluid that remains liquid throughout its circuit. IF CO2 is pressurized so that it remains in the liquid state during its cycle, research in commercial refrigeration is showing that frost forms uniformly on the coil and loner periods of operation between defrost is possible.      
Applications of Inverters for Capacity Control
Author: David Miller   

In recent years there has been great pressure to reduce energy consumption or increase control efficiencies in the refrigeration industry. as a result, many have applied variable frequency drives (inverters) to condenser fan motors to accomplish this end. AC-style drive systems have been used for years in other applications and only recently have been applied to condenser and evaporator fan applications due to recent advances in electronic technologies. These advances have reduced the cost of inverters enough to allow their use in areas not typically seen before. This paper will discuss the problems related to the application of inverters for purpose of controlling capacity and reducing energy consumption in air-cooled condensers and non DX-style evaporators.   
The Use of Carbon Dioxide/ Ammonia Cascade Systems For Low Temperature Food Refrigeration  
Author: Andrew B. Pearson   

This paper describes a system providing air temperatures in the range -30 degrees Celsius (-22 degrees Fahrenheit) to -50 degrees Celsius (-58 degrees Fahrenheit) for large freezing duties without pumping ammonia through production areas. Carbon dioxide is compressed to a saturation temperature of about -20 degrees Celsius (-4 degrees Fahrenheit) from evaporation temperatures as low as -55 degrees Celsius (-67 degrees Fahrenheit), and a packaged ammonia plant is used to condense the carbon dioxide before re-expansion. The key benefits are a more compact and efficient installation, particularly with much smaller compressors and with small pipes in the production area, and more efficient operation at the low temperatures. the ammonia system, and consequently the regulatory requirements for a large facility are simplified. The paper includes a technical evaluation of a current project, and the operational and financial benefits provided by the cascade systems.
Liquid Carryover: Prevention and Mitigation of Its Damaging Effects 
Author: Wayne Wehber,  Mike Fisher, & Charlie Klockner     

Separation of a liquid mass fraction form vapor flow has been a topic of many articles and discussions. We wish to present some of the history behind the devolvement of the current methodology utilized today as well as additional insight into the separation mechanisms involved. A greater understanding of the physics involved, the application operational parameters, and the effects of vessel orientation can prevent the phenomenon of liquid carryover. Liquid carryover can exist as a mist or a liquid when escaping the separation mechanisms.
Single Stage vs. Two Stage Ammonia Refrigeration Systems 
Author: Mike Zion

Mechanical refrigeration systems were first introduced in the late 1800s using reciprocating steam engines modified for this purpose. They were limited in single stage applications to suction temperatures of about -10 degrees Fahrenheit to -20 degrees Fahrenheit due to high compression ratios. Lower temperature operation was both uneconomical due to poor volumetric efficiency and impractical due to high discharge temperatures. Compounding, or multi-stage operations with intercooling, was introduced to overcome these problems. this was done with individual low stage (booster) and high stage compressors, or in some cases with a single machine having both low stage and high stage cylinders driven by a single motor on a common shaft.
Pipe Stress of Flexibility Analysis in Refrigeration Piping
Author: Thomas Riley

Refrigeration piping design is a function of: 1) the refrigerant material properties; 2) the fluid flow characteristics within the piping, as defined using Bernoulli's theorem for the total energy balance; 3) the mechanical characteristics of the pipe, as defined using mechanics of materials; and, 4) the installed systems cost. The third area is discussed in the paper. Within mechanics of materials, flexibility analysis is used to predict the piping system behavior under specified loading conditions.
Proper Application of and Good Practice with Ammonia Pumps  
Author: Henry Bonar II

The application and use of the pumps for high efficiency liquid refrigerants recirculating systems requires knowledge in several areas of liquid flow. In particular, knowledge is needed to understand applications that involve pumping fluid at or near saturated conditions. (i.e., fluids on the verge of boiling). The advent of PSM (Process Safety Management-OSHA) and the process Hazard Analysis requirements have made everyone aware of safety in operating systems.    
History of Process Freezing, and Application of Blast and Contact Freezers in the Food Industry 
Author: John D. Piho, P.E.

The food Industry has used various methods to freeze food products over the course of history. The purpose of this paper is to review these methods and the various improvements made in food freezing technology. The paper is not intended one type of technology over another nor is it our intent to provide detailed design information in the selection of that freezer or the technology used. Our main emphasis is how the various technologies used for Blast and Contact Freezers have evolved over history and how they are applied to the food products we use in our every day lives.
A Review of Lubricant Chemistry for Use in Ammonia Refrigeration Systems  
Author: Thomas E. Rajewski & Kenneth C. Lilje, Ph.D.

Ammonia is one of the oldest, continuous technologies for vapor compression refrigeration. Historically, solvent refined naphthenic mineral oils have been applied to traditional systems. Advances in lubricant technology have lead to several improvements in lubricant durability, cleanliness and life. These advances have allowed system engineers for further advance system design, producing lower temperatures through the use of direct expansion evaporators. The physical properties and resulting behavior of each lubricant type can be attributed to specific chemical characteristics of the lubricant. This paper will outline how the chemistry of each lubricant base stock influences the system behavior. Specifically, it will outline how contaminants, functional groups, branching and additives play a role in the behavior of a lubricant in an ammonia system.
Design Consideration for a Low-Charge, Central Ammonia Refrigeration System Retrofit of an Existing Cold Storage Warehouse 
Author: Michael Browning  

As we enter the twenty-first century, the food storage and distribution industry is witnessing a return to the refrigerant of its roots: ammonia. The ban on the manufacture of CFCs, utilized as an alternative to ammonia for the industry from the 1940s through the 1980's forced corporations and business owners to either construct new plants or retrofit old plants with either ammonia or an alternative refrigerant. For the Superfresh grocery chain, converting existing cold storage warehouse from R-12 to ammonia at their Baltimore, Maryland, distribution center meant making decisions to meet the challenge of renovating a 1950s warehouse complex refrigeration system. IN the end, the modernizing of this facility and the designing and installing of a state-of-the-art ammonia refrigeration system was an unqualified success.  
Two-Phase Flow Behavior Pipes, Valves and Fittings
Author: Bent Wiencke  

The prediction of two-phase flow pressure drop during the design of piping systems for industrial plants (e.g., refrigeration, power, and petrochemical plants), can be associated with a high degree of uncertainty. The simplifications that lead to a solution in single-phase flow, such as averaging the velocity over pipe diameter, are generally not applicable to two-phase flow. Attempts to obtain purely analytical correlations, (e.g., deriving them from the conservation equations), for the calculation of pressure drops have failed so far. Most of the correlations are thus purely empirical, and their agreement, if any, is strictly limited to the range of data from which they were derived. the selection of an appropriate correlation for a specific design problem cannot be done by means of design charts; the ranges of the major parameters that characterize the flow must be identified. The difficulties associated with the design of two-phase flow piping are not limited to identifying a correlation for the calculation of pressure losses, but also includes understanding the unique physical behavior of the two-phases as they interact.  
Cutting and Boning Room Design: Fabrication Room Challenges 
Author: Walter Gameiro 

As we began to write this paper another E-Coli outbreak hit the Northeast United States. As part of my research, I obtained the 1998 report form the Texas Restaurant Association Education Foundation, which provided several significant statistics... some people have the perception that many of these cases can be blamed on bad, or even lock of refrigeration. While in some cases this may be true, in most cases this is not the cause. Food processing plants themselves can contribute in various ways the combination of food products being processed.