ARF 2-Phase Flow Project Looks at Piping Configuration

What difference does the design of vertical piping arrangements have on two-phase ammonia flow? Can pressure drop in the suction riser be minimized or stabilized, leading to a significant decrease in power consumption at the compressor?

Researchers hope to answer these questions and more with a project being conducted by the Ammonia Research Foundation, or ARF, in conjunction with ASHRAE RP-1327.

The goal: To take the configuration of piping systems from an art to a science.

Jeff Welch, chairman of the research committee, says the project will allow designers to “really see behind the numbers, minimizing the guesswork.”

“If you watch the small things, those small things will contribute to much bigger gains in efficiency. That’s what we’re doing here,” he said.

ARF has entered into an agreement with the Danish Technical Institute to test refrigerant flow using a rig that was previously built for a project DTI is conducting for ASHRAE. The ASHRAE project will determine the minimum vapor velocity required to pull liquid up a pipe.

In contrast, the ARF 2-Phase Flow Project is examining the entrance configuration to the riser. Researchers are comparing elbow and Ptrap configurations to measure differences in pressure drop, hoping to more fully understand how different configurations affect fluid flow behavior.

This collaborative effort has allowed AFR to piggy-back on the larger ASHRAE project and to take advantage of an existing rig to conduct research. Without the ASHRAE project, the ARF 2- Phase Flow project could not have happened, said Bruce Nelson, a member of the research committee and the project’s monitoring subcommittee chairman.

“The information produced by this study will further our understanding of two-phase pressure drop and flow in risers, and should lead to better designs with this critical part of ammonia piping systems,” said Nelson.

A key aspect of the ARF project will assess how liquid is collected before being swept up the pipe.

“It’s easy to see that a Ptrap [at the bottom of the suction riser] will create pools of liquid, but it may not happen the same way with an elbow configuration,” Nelson said. “The ASHRAE handbook will always tell you to put a Ptrap at the bottom of the suction riser, but other engineers say that creates the risk of slug or plug liquid traveling up the riser.”

Slug or plug liquid traveling up the riser can lead to hydraulic shock, and, potentially, mechanical failure of pipes, valves and other components in the system, said Nelson.

A more detailed understanding of pressure drop is also significant for maximizing energy efficiency, especially at freezer temperatures. A large pressure drop in the suction riser forces the compressor to operate at a lower suction pressure, and therefore consumes more power. Obviously, the compressor must then work harder. Researchers are hoping to quantify how pressure drop in different configurations tax the compressor.

The project also allows researchers to visually monitor what is happening through a clear section in the pipe that matches the diameter of a steel pipe. Several tests are being conducted at low temperatures, with comparisons being made on pressure drop and fluid flow between the elbow and Ptrap configurations. There is a major risk of hydraulic shock during a defrost, so researchers are observing flow patterns that could result in slug or plug liquid.

The ASHRAE project was first conceptualized nearly a decade ago. It required building a test rig, now located in Denmark, that could transfer a significant amount of ammonia vapor through a riser pipe. Researchers hope to discover the most efficient velocity required in order for ammonia vapor to sweep ammonia liquid up a pipe. This is important because a majority of the evaporators in the ammonia refrigeration industry are mounted below headers, which are mounted on roofs requiring a riser in the piping. By discovering the most efficient velocity in these risers, systems can be designed more effectively.

“The exciting thing is that the gaps in our knowledge that will close [as a result of the ARF 2-Phase Flow project],” Nelson said. “It’s going to make our systems more energy efficient and safer, and that is directly related to our mission, which is to save energy and improve safety.”

ARF Names Scholarship Recipients

Four students will be recognized as ARF scholarship recipients at the upcoming IIAR Annual Conference and Heavy Equipment Show in Nashville, Tenn. The Ammonia Refrigeration Foundation, which supports research and education programs benefiting the industrial refrigeration industry, named Karlie Healy and Cody Eaton from the University of Wisconsin Madison, Bryan Cius from Erie Community College and Mark Siemsen from Kansas State University as its 2014 scholarship recipients.

The goal of the ARF scholarship program is to encourage young engineers to pursue careers in industrial refrigeration and help develop new interests for natural refrigerants. Scholarship awardees complete an independent study on an industrial refrigeration-related project at the selected universities and colleges around the country.

In addition to supporting engineering education, the ARF scholarship aims to attract future graduates to industrial refrigeration engineering.

“The ARF scholarship program has been a key element of our educational efforts, with the goal of attracting talented young individuals to our industry,” said Tim Facius, ARF executive director. “The schools we have worked with have been carefully selected by our Education Committee for their thermal sciences programs, and the students are selected based on their academic performance and interest in the thermal sciences.”

Karlie Healy will graduate in December with a degree in mechanical engineering and is hoping to work for a manufacturing company. She is interested in thermodynamics, fluid mechanics, mechanical systems and power generation. Last summer she interned at Boston Scientific and Caterpillar.

Cody Eaton is enrolled in the Thermal Energy Certificate Program at Wisconsin and has participated in related research in the solar energy lab and the Engine Research Center. He has completed internships as a machinery reliability engineer at Flint Hills Resources and as a project engineer at BE Aerospace.

Although Erie Community College’s program is aimed at residential and commercial applications, Bryan Cius displayed a passion for industrial refrigeration, choosing to take an elective course in that discipline and showing uncommon interest during a class trip to a large ice cream manufacturing facility.

“His interest in the subject material made him stand out,” said Marvin Tryon, project director for industrial technology at ECC. “It was above and beyond. He was not only the best student in the class, but the most interested.”

Mark Siemsen has been active in the mechanical engineering department throughout his four years at Kansas State. He interned at The Coleman Company in Wichita during the summer of 2013, and he has accepted an internship with Cessna Aircraft’s Pneumatic Systems division for the summer of 2014.

He has shown a special interest in the thermal area, and has worked closely with Don Fenton, professor of mechanical and nuclear engineering at Kansas State.

“Students like Mark are perfect for our industry because they can be effective engineers both for food processing companies and also refrigeration designers,” Fenton said. “All of our students have a solid background in controls and using computers to affect those controls. They can bring that to the refrigeration industry.”

All scholarship recipients will have the opportunity to visit an industrial refrigeration site in the vicinity of their school.

The Ammonia Refrigeration Foundation is a non-profi t research and education foundation that was originally organized by members of the International Institute of Ammonia Refrigeration to promote educational and scientific projects related to industrial refrigeration and the use of ammonia and other natural refrigerants.