Design of a Reliable and Feasible Low-Cost Refrigeration Device

for Vaccine and Drug Storage in Developing Countries

Figure 1: 2D Drawing of our Design of a Cooling Cylinder

                                                                                                                               The Chillers

Ryan Immel, Corey Pichler, Christy Poole, Ben Kealy, Eric Balboni

  Executive Summary

The ‘Cold Chain’ is a term describing the method of supplying vaccines and drugs at a constant low temperature to remote locations with out a power infrastructure.  The problem that interests Air Products and Chemicals Inc. is finding a method of a low-cost, reliable, and portable refrigeration device to store the medicines. It is our goal to design and build a simple device that meets Air Products’ needs as well as being able to provide 5 kg of ice per day or equivalent cooling without the aid of a power source.

The idea for the design came from two patents (1,740,737 and 1,811,523) that describe an absorption refrigeration system called the Crosley Icy Ball that uses heat as the power source.  The device is a closed system that uses two fluids; ammonia as the refrigerant and distilled water as the absorbing fluid. 

The design consists of an ammonia water mixture that sits at the bottom of a stainless steal pipe that is 6 inches in diameter.  In the first step, the pipe is heated at the bottom to separate the ammonia and the water.  A medium such as water can be used so the pipe is not exposed to open flame. 

In the second step the ammonia vapor will travel up the column, separating by use of a heat exchanger and cooling coil. The cooling coil will be approximately a foot in length such that enough surface area is added for a more efficient separation. The greater concentration of ammonia will cause a greater cooling effect.

In the third step ammonia vapor will rise up to the top where a combination of the pressure and the cool water on the outside of the pipe will cause the ammonia to condense.  Once the allotted time lapses the heat source and the cool water will be removed causing a drop in pressure and a rise in temperature that will cause the ammonia to evaporate.  Ammonia boils at -33 degrees C and thus heat will be absorbed from the surroundings and cause the pipe to become extremely cold at the top chamber.

The device is required to produce the equivalent cooling of 5 kg of ice every day. Ice has a heat of fusion of 334.7 kJ/kg so the device must produce 1673.6 kJ of cooling. With a constant heat of 400W applied to 1 liter of mixture in the bottom of the device for approximately 20 minutes a minimum of 88 grams of ammonia condenses into liquid (9% of mixture). The heat of vaporization of ammonia is 1371.2 kJ/kg so the cooling produced by one run of the device is 120.7 kJ. With this setup the device will need to be run 14 times a day to meet the same cooling as 5 kg of ice.

 Once the process is completed, a valve will be opened letting any excess ammonia and water drain back to the mixture at the bottom.  Once the ammonia is reabsorbed and the system reaches ambient conditions, the process can be repeated again. 

                                                                                                                                  Design Details

Our device is an absorption refrigeration system run on an ammonia-water mixture. The bottom of the device is heated causing the absorbent fluid to heat up and boil off some of the ammonia. A gas which is rich in ammonia rises up the device and is forced to flow along the walls where it losses heat to a counter-flow water jacket.  This causes the temperature of the gas to drop slightly allowing most of the water to condense and drop off, leaving a more pure ammonia gas. This gas then flows through a check valve into the top portion of the device where it is not allowed to escape.

This top portion of the device is submerged in a much larger water jacket that is fed by a hose providing 1 liter every 5 seconds. This large jacket cools the top portion and the gas collected inside. As more gas boils off of the heated absorbent fluid the pressure in the system increases to a point where the ammonia begins to condense in the top portion. The heat is removed before the temperature of the absorption fluid reaches the boiling temperature of water, and the whole system is allowed to return to ambient temperature. When the temperature of the whole system returns to ambient conditions it creates a pressure difference between the collected ammonia at the top and the cooled mixture at the bottom.

            The water is drained from the water jackets and a Styrofoam insert is placed inside the top water jacket to form an insulated cooling box. Ice packs are laid on the top part of the device inside the cooler box and a Styrofoam lid is placed on top to prevent unnecessary losses to the air. A valve connecting the top collection section to the rest of the device is opened allowing the pressure to drop in the collection section. The lower pressure allows the liquid ammonia to vaporize, this process requires energy that is absorbed from the surroundings and causes below freezing temperatures (down to -28 C). The heat is removed from the surrounding ice packs and once frozen and the packs can then be removed and used in cooler boxes.

            Once the system has finished cooling, a second valve is opened to remove any water that has condensed in the top portion of the device, leaving a completely empty cooling section for the next run. At this point all the initial mixture should be back in the absorbent fluid exactly the same way it was before heated. Once both of the valves have been closed, the Styrofoam insert has been removed, and the water jackets have been refilled the system is ready to be run again.

            The device is required to produce the equivalent cooling of 5 kg of ice every day. Ice has a heat of fusion of 334.7 kJ/kg so the device must produce 1673.6 kJ of cooling. With a constant heat of 400W applied to 1 liter of mixture in the bottom of the device for approximately 20 minutes a minimum of 88 grams of ammonia condenses into liquid (9% of mixture). The heat of vaporization of ammonia is 1371.2 kJ/kg so the cooling produced by one run of the device is 120.7 kJ. With this setup the device will need to be run 14 times a day to meet the same cooling as 5 kg of ice.

Sponsored by: Air Products and Chemicals, Inc.

John Cirucci

Air Products and Chemicals, Inc.

7201 Hamilton Blvd

Allentown, PA 18195-1501

The company who is graciously sponsoring this project is Air Products and Chemicals, Inc. Air Products was founded more than 60 years ago, and today, Air Products ranks 281st in sales and 276th in total assets among FORTUNE magazine's April 2005 list of the 500 largest corporations in the U.S. The companies’ main consumers are in healthcare, technology, energy, and industrial markets worldwide. Air Products provides services and solutions, atmospheric gases, process and specialty gases, performance materials and chemical intermediates. The company has built leading positions in key growth markets, such as semiconductor materials, refinery hydrogen, home healthcare services, natural gas liquefaction, and advanced coatings and adhesives.

Please visit their website via: www.airproducts.com

April 24th, 2006

A special thanks to our faculty advisors: Professor Nedwick and Professor Savas Yavuzkurt.