Custom Transmission
Oil Cooler

Lytron has added a new transmission oil cooler to its plate-fin heat exchanger custom solution gallery. The oil cooler was designed and manufactured by Lytron for cooling oil in a ground based vehicle. It features vacuum-brazed aluminum plate-fin technology and has two liquid loops – one for the hot oil and one for a Propylene Glycol (PGW) based coolant. The heat exchanger is also chromate coated for corrosion protection.

Lytron designs and manufactures oil coolers using various technologies, including tube-fin, flat tube, and plate-fin construction. For more information on how we select the best technology for OEM applications, please review our blog article, “Oil Coolers: Flat Tube or Plate-Fin,” as well as our Engineering Design webpage.

Heat Exchanger ES Series

Lytron frequently receives questions through its “Ask an Engineer” website form. A customer recently asked us the following question: “We’re planning on using one of your flat tube heat exchangers for radar cooling. What is the MTBF for your ES Series heat exchangers?” 

Corn Can Become Propanediol

With liquid cooling, one of the most important decisions is what heat transfer fluid to use in your application. Ethylene glycol (EG) and water solutions and propylene glycol (PG) and water solutions are often used as the coolant in cold plates, cooling systems, chillers, and heat exchangers. Although straight water provides better thermal performance than EG and PG solutions, EG and PG solutions provide corrosion protection and freeze point suppression needed in many applications. In addition to EG and PG, there is now another glycol option for heat transfer applications that many people might not yet be aware of – a 1,3 propanediol (PDO) product derived from corn sugar.

PDO, also known as trimethylene glycol, actually has the same chemical formula as propylene glycol but is different in molecular structure. PDO can be manufactured from petroleum by conventional chemical processing, or can be produced from corn sugar by a bio-processing route that involves fermentation.[i] Since 2006, DuPont Tate & Lyle has been producing Bio-PDO™ for heat transfer applications under the brand name Susterra™. According to the company’s website, “From ‘cradle-to-gate,’ the production of Bio-PDO consumes up to 40% less energy and reduces greenhouse gas emissions by more than 40% versus petroleum-based 1,3-PDO and PG.”[ii] Bio-PDO is also non-flammable, non-toxic, and biodegradable.

There are tradeoffs between EG and PG, which is one reason that some engineers and equipment operators may want to consider Bio-PDO based glycols. EG has desirable chemical properties, including a high boiling point, low freezing point, stability over a wide range of temperatures, and relatively high specific heat and thermal conductivity. If toxicity is a concern, however, engineers and equipment operators may opt for PG instead of EG. PG is generally considered safe for the environment and for food processing applications. PG has a lower thermal conductivity than EG though, resulting in a reduction in thermal performance. In addition, PG has a higher viscosity than EG[iii], which translates to higher power consumption for recirculation pumps and a higher minimum operating temperature if you use PG instead of EG. Bio-PDO solutions offer comparable or better performance than PG solutions while also being non-toxic and renewable.

Dynalene is one of the companies that is using Susterra to manufacture ready-to-use heat transfer fluids. The company’s BioGlycol® product includes Susterra and a proprietary corrosion inhibitor package called PE-1. Dynalene recommends a concentration of 20% or greater of BioGlycol in water solutions for inhibiting corrosion and suppressing the freezing point. According to Dynalene[iv], BioGlycol offers greater thermal stability at high temperatures while possessing similar or better physical properties compared to EG and PG fluids. BioGlycol’s thermal conductivity, for example, is approximately 10% better than PG’s. (See Table 1: Glycol Thermal Performance Comparison.)

Table 1: Glycol Thermal Performance Comparison in 50% Water Solution[v]

In addition, BioGlycol provides 30% lower viscosity at low temperatures as compared to traditional petroleum derived propylene glycol. (See Table 2: Viscosity Comparison for Glycols in 50% Water Solution.)

Table 2: Viscosity (μ) Comparison for Glycols in 50% Water Solution[vi]

There are many coolant options available for your liquid cooling loop. Whichever coolant you choose, it’s critical that your coolant be chemically compatible with all of the materials within your loop. Check with your coolant supplier for information on compatibility or test your coolant in a non-mission critical version of your application. In addition to chemical compatibility, you should review the thermal conductivity, temperature stability, freeze point, viscosity, toxicity, environmental impact, cost, availability, and other chemical properties of your heat transfer fluid.  

For more information on BioGlycol or Dynalene’s heat transfer fluids, please visit http://www.dynalene.com/products/bioglycol.asp or call +1-610-262-9686. For more information on cold plates, chillers, cooling systems, or heat exchangers for liquid cooling or air cooling, please contact Lytron at +1-781-933-7300.

[ii] http://www.duponttateandlyle.com/life_cycle.html.

[iii] According to http://physics.info/viscosity/, EGW’s viscosity is approximately 16 η (μPa s) versus PGW’s viscosity, which is approximately 40 η (μPa s) at 25°C.

[iv] http://www.dynalene.com/products/bioglycol.asp.

[v] and [vi] Data provide by Patrick McMullen, Dynalene, http://www.dynalene.com/.

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.

EGW Wordle

Many customers ask us what concentration of ethylene glycol we recommend they use in their chillers, cooling systems, and/or liquid cooling loops. It depends quite a bit on your thermal and mechanical requirements, such as required thermal performance, how often you replace your fluids, if you are concerned about corrosion, etc. For most applications, however, we recommend using a solution consisting of 30% ethylene glycol and 70% water (EGW). Water has the best thermal performance, while the inhibited glycol provides freezing point suppression and corrosion protection.

When higher concentrations of glycol are used, it can cause problems within your cooling loop. Over time, the concentration of glycol will increase due to evaporation of water from the system. When the glycol concentration is too high, glycol will collect in pump seals forcing them apart and creating a leak path.

What concentration of glycol are you using? Have you experienced any problems in the past because of your glycol concentration? Please share your experiences.