Ozone Layer Photo Courtesy of NASA

There’s an article in Process Cooling magazine’s January/February 2010 issue regarding the phase out of R22 refrigerant. According to the U.S. Environmental Protection Agency’s (EPA’s) website, effective January 1, 2010, “Virgin R-22 may not be used in new equipment.” This regulation is part of the Montreal Protocol, which, as of September 2009, all countries in the United Nations have ratified in an effort to reduce the amount of ozone-depleting chemicals released into the air. If your equipment or process uses R22, you can legally continue to use R22 in that equipment or process until January 1, 2030. However, the production and import of R22 will be banned in the U.S. after January 1, 2020. As people transition away from R22, it will likely become increasingly expensive to buy it and more challenging to find it. One alternative to R22 is R134A refrigerant, an environmentally acceptable hydroflurocarbon (HFC) according to the EPA. Lytron has been using R134A refrigerant in its Kodiak recirculating chillers since Lytron began manufacturing Kodiaks. Therefore, if you purchase or use Lytron Kodiak recirculating chillers, you can rest assured that your chiller is in compliance with the refrigerant use regulations of the U.S. EPA and the Montreal Protocol.

Stainless Steel Tubes

An article recently published on MachineDesign.com, titled “Comparing Stainless Steel and Other Metals,” is an excellent overview of what stainless steel is as well as its types, properties, and manufacturing challenges. The article, written by Norm Ellis, focuses on the use of stainless steel in the aerospace industry. It contains a table that compares austenitic, ferritic, martensitic, precipitation hardening, and duplex type stainless steels, their percentages of chromium and nickel, and their UTS, yield strength, elongation, and hardness properties. Although steel is typically 66% heavier than aluminum, it is because of steel’s specific strength that it is of interest to aircraft engineers. (Specific strength is the ratio of strength to density.)

According to the American Iron and Steel Institute, stainless steel is steel that contains more than 10% chromium, either with or without other alloying elements. Stainless steel resists corrosion, maintains its strength at high temperatures, and is easily maintained or sanitized. For these reasons, stainless steel is often used in the food, medical, transportation, and aerospace industries.

One of the most common grades of stainless steel is Type 316, the type Lytron uses for the tubes of its standard stainless steel heat exchangers and some tubed cold plates. Type 316 is an austenitic (chromium-nickel stainless class) stainless steel containing 2%–3% molybdenum. The inclusion of molybdenum gives 316 greater resistance to various forms of deterioration, while nickel and manganese keep the metal in an austenitic microstructure. Austenitic stainless steels generally have the best corrosion resistance of all stainless steels because they contain at least 16% chromium. These alloys are also weldable, which is important in the manufacturing of heat exchangers and cold plates.   

When selecting metals for liquid cooling components or systems, there are a large number of considerations. Strength and corrosion resistance are just two of the considerations. In most aerospace liquid cooling applications, weight is one of the other major considerations. Vacuum-brazed aluminum heat exchangers are typically the cooling technology selected because they are lightweight as well as strong. In applications where weight is much less of a factor, the strength and cleanliness of stainless steel might make it worth sticking with stainless.

John, Engineer

Worm Drive Hose Clamp

Lytron frequently receives questions through its “Ask an Engineer” website form. A customer recently asked us the following question: “What is the recommended connection mechanism for heat exchanger tubing with the ‘BD’ designation?”

A beaded (BD) fitting is generally specified when a system requires flexible hoses. The bead prevents the hose from slipping off the cold plate’s or heat exchanger’s tubes while a clamp prevents leaks at the joints. Lytron recommends two types of clamps for the BD fitting: the ear/pinch clamp and the worm/gear clamp.

The pinch clamp is a metal band that is crimped with a special tool. This is the best choice since a pinch clamp can withstand vibration and temperature changes over time without loosening up. Pinch clamps as well as other more sophisticated clamps are available from McMaster-Carr in its “Hose and Tube Clamp” catalog section. The worm clamp consists of a notched band with a screw mechanism to loosen or tighten it. Worm clamps are available at a local hardware or automotive parts store. Lytron’s application note “Fitting and Hose Clamp Selection for Cold Plates and Heat Exchangers” provides more details.

 For OEMs, Lytron can provide custom cold plate or heat exchanger assemblies that include hoses and/or fittings.

 John, Engineer

Recirculating Chiller Performance at 50Hz & 60Hz

Lytron frequently receives questions through its “Ask an Engineer” website form. A customer recently asked us the following question: “We are using a Kodiak chiller for cooling a laser. The chiller was designed for 60Hz but we recently moved to another country where it is 50Hz. Can we run the chiller on 50Hz power or can we change the pump motor to work for 50Hz while keeping the equivalent heat capacity and flow rate?”
 
If you have a chiller with a 60Hz compressor running at 50Hz it has to work harder to maintain the set point temperature. This will lead to premature failure of the compressor. Also, if you run the chiller at 50Hz, the pump motor will run at a reduced speed and thus at a reduced flow rate (generally 15%-17% less). This will result in a reduced cooling capacity by the same factor. Buying a new recirculating chiller with the correct components is economically (and logistically) a better option than replacing parts in an existing machine. Lytron offers chillers with both power configurations. 
 
- John, Engineer

Flat Tube Heat Exchanger

Lytron frequently receives questions through its “Ask an Engineer” website form. A customer recently asked us the following question: “Do your standard heat exchangers, specifically your ES505G24 heat exchanger, require any specific filtration?” Filtration of the coolant will depend on how clean it is. On the liquid side, the largest acceptable particle size for the liquid path is around 0.03″ (or 750 um). In addition, you should ensure that your coolant is clean in order to help minimize the risk of corrosion. For example, if you are using an ethylene glycol and water solution you’ll want to ensure that the water meets the minimum requirements for good quality water.

It is also important that dust and dirt do not clog the fins on the airside. If you are in a relatively clean room indoors, you probably won’t need a filter; however, you may need to clean the heat exchanger periodically to remove dust build up. Our application note on recirculating chiller tune ups shows a picture of what a very dusty heat exchanger/condenser looks like and contains information on how to clean a heat exchanger’s fins.

Recirculating Chiller

Lytron frequently receives questions through its “Ask an Engineer” website form. A customer recently asked the following question: “Does the RC022J03BF2C031 include the optional heater?”

The RC022, one of Lytron’s standard recirculating chillers, does have an optional 2,000 Watt electric resistance heater. This heater option allows the chiller to more quickly reach a set point temperature above the ambient temperature. This is useful for applications where a cold start is necessary or where the coolant set point is frequently cycled. The heater option is available on the RC011, RC022, RC030, and RC045 recirculating chillers. Options available on standard chillers can be reviewed under the chiller specifications page. Additional options are available for custom chillers.

Tube-Fin Heat Exchanger

Lytron frequently receives questions through its “Ask an Engineer” website form. A customer recently asked the following question: “While using your heat exchanger selector tool, a warning popped up stating that “Most heat exchangers have a maximum allowable flow rate of 2 GPM.” I was curious as to why 2 GPM is the highest. What are the limiting factors?”

Most standard heat exchangers are designed to operate with a flow rate between 1 gpm and 4 gpm. Increasing the liquid flow rate beyond the optimum range will not necessarily improve the performance of the heat exchanger. What will happen is the heat exchanger will become air-side limited, which means that a much larger fan may be required in order to continue to increase performance. In extreme cases, a commercial off-the-shelf fan will not be adequate to increase the airflow enough to balance the thermal performance. Refer to Lytron’s Integrating a Heat Exchanger into your System: Fan Considerations for more detailed information.

In addition, Lytron’s standard heat exchangers are designed with 3/8″ OD x 0.028″ wall thickness. For many of the smaller heat exchangers, increasing the liquid flow rate much beyond 2 gpm will substantially increase the liquid side pressure drop through the heat exchanger. This means you will need a much larger pump for your cooling system.