# Why Microtubes?

Mezzo has the unique capability to design and manufacture a microtube heat exchanger for a wide range of applications.

When performance matters, engineers trust Mezzo Technologies.

## INNOVATING MICROTUBES

Mezzo has spent the past decade innovating and improving manufacturing methods for heat exchangers using microtubes as small as 0.01" diameter. The use of microtubes allows Mezzo to offer highly competitive performance on many types of heat exchangers, including radiators, intercoolers, oil coolers, and even industrial shell and tube heat exchangers.

Mezzo's microtubes
0.1" and smaller

0.5" and larger

In many cases, microtube heat exchangers provide significantly improved performance over traditional heat exchanger architectures, like tube and fin radiators. In addition to achieving high performance, Mezzo microtube heat exchangers provide practical benefits including:

• The ability to hold very high pressures within tubes
• Flexible tubes which are naturally resistant to damage from debris
• Highly configurable tube patterns which allow Mezzo to achieve precise performance metrics
• Ease of maintenance and cleaning when compared to tube and fin designs

MICROTUBES IMPROVE HEAT TRANSFER

A basic scaling analysis shows how decreasing tube size improves heat transfer for a given core volume. The overall heat transfer coefficient (UA) is a function of both the heat transfer coefficient (U) and the heat exchanger’s surface area (A).

The heat transfer coefficient (HTC) is derived from an experimental correlation for Nusselt Number (NuD), typically in the form:

$$Nu_D = C_1Re^mPr^n$$

where values of m are positive and less than 1. The heat transfer coefficient is then computed as

$$HTC = \frac{Nu_D * k}{D}$$

This can be set up such that the heat transfer coefficient scales with diameter as
$$HTC \propto D^{m-1}$$

Similarly, the surface area scales with number of tubes and single surface tube area:
$$A = N_{tubes}\pi DL$$ $$\propto \frac{1}{D^2}D$$ $$\propto D^{-1}$$

The overall heat transfer coefficient (UA) scales as follows:
$$UA = HTC * A \propto D^{m-2}$$

The plot below shows the relative increase in UA of smaller tube sizes, compared to a same-volume core with 1" tubes. Depending on the tube pattern (value of m), a 0.020" tube could represent a 100-200x increase in UA from a 1" tube.

One of Mezzo's main microtube applications is the automotive racing radiator. Starting in 2014, Mezzo’s IndyCar radiator was approved for use in the IndyCar racing series on Dallara’s DW12 race cars. Teams could elect to use the Mezzo microtube radiator as a drop-in replacement which helped to remedy overheating and debris-fouling issues that plagued the existing tube and fin radiators. In fact, when fitted with a Mezzo microtube radiator on a hot track day, teams saw up to 8°C lower engine temperatures compared to the stock radiator.

For a comparison between the Mezzo IndyCar microtube radiator and the competing tube and fin radiator, see the plots below. The first plot shows that the Mezzo radiator will provide between 4-6% more heat transfer for a given face velocity, but this is not the whole story...
Because the flow through the radiator is driven by the pressure differential around the car, a less restrictive radiator will cause a higher flow of air through the duct. When heat transfer is plotted versus air pressure drop, the improvement in cooling becomes much clearer.
Not only does the Mezzo radiator allows for higher air flows in ducts, but it also provides higher heat transfer at each air velocity. Additionally, race engineers have commented that on tracks with lots of debris, the competing stock radiator would become covered by track debris; meanwhile, the Mezzo microtube radiator was significantly less likely to foul and much easier to clean.

CASE STUDY #2: INTERCOOLER SYSTEM
Mezzo also designs and manufactures water-to-air intercooler systems for high-performance turbocharged engines. Normally, Mezzo designs the air-to-water intercooler and water-to-air intercooler radiator as an optimized package. The benefits of using a setup like this include packaging benefits (i.e. flexible placement of components and less restriction of charge air flow), as well as direct performance benefits.

The following comparison shows performance of a Mezzo water/air intercooler system used to replace an air/air intercooler for a winning team in a top-tier racing series. The Mezzo intercooler system matches total wet weight and charge-air pressure drop of the original air/air intercooler, and gives greatly improved performance at the design condition of 1.5 bar gauge of boost (bringing charge air temperatures up to 150°C) and 35°C ambient air temperatures.

For a comparison between the Mezzo microtube intercooler system and the competing air/air intercooler, see the plots below. The first plot shows the difference between intake air temperature (IAT) and ambient temperature, for several cooling air flow rates.
Clearly, if the cooling air flow rates are unchanged between the air/air intercooler and Mezzo intercooler system, the IAT can be lowered to 8.8°C above ambient instead of the original 15.5°C. That said, if the cooling air ducting is relatively unobstructed, the actual air flow rates will be notably greater, even further decreasing IAT as shown in the plot below.
The second plot shows that because the Mezzo intercooler solution has a very low cooling air pressure drop, it is theoretically possible, in an unobstructed duct, to achieve increased flow such that the charge air is dropped to merely 4°C above ambient. In Mezzo's experience with high-performance racing, it is typical to see increases on the order of 1 horsepower/°C lower of IAT. This means that the drop in IAT here could represent a power increase on the order of 5-10 HP.

Our customers require very high performance. We take great pride in designing, fabricating, and delivering products that meet your specifications on schedule and on budget. We are motivated by new, challenging projects and have both the engineering and manufacturing capabilities needed to complete the entire engineering process from concept to finished product.