Which Silencer Is Right for You?

Today’s article is a guest article submitted to us by Ron Burg of Mahan’s Thermal Products, experts and specialists in heat exchanger and silencer technology. It is a very good general overview of the choices in silencers, and we encourage you to visit their website. We hope you find it interesting:


No matter what industry it is or which application is being used, utilizing heat exchangers and other types of thermal products in your facility can make noise control an issue. Fortunately, there are many ways for you to cut down on sound attenuation in order to create a better work environment.


There are many different types and models of silencers. If you need assistance selecting a silencer, reach out to trusted professionals such as Mahan’s to help guide you through the process. Six main types of silencers are included below.

Absorptive Silencer: With its classic dissipative design, the absorptive silencer absorbs noise energy through its many types of fibrous packing materials. When sound waves travel through the areas between the fitted fibers, the noise is dissipated from the viscous friction. Absorptive silencers work well on high noise frequencies between 500 and 800 Hertz. Anything above or below this amount, and the silencer will not be as effective.

Blower Silencer: These types of silencers are frequently used in wastewater treatment facilities and industrial processing facilities. Blower installations are typically noisy, making blower silencers essential. When choosing a blower silencer, consider the size and proper type for the application. These two aspects are critical for effectively reducing noise. The size of the blower should be based on gas volume alone, while the design of the silencer must be chosen with the blower size and operating speed in mind.

Engine Exhaust Silencer: Exhaust silencers come in a variety of styles and configurations, and have different attenuation grades. While you can create custom engine silencers, there are also standard styles that you can choose from. Puck-style silencers and low-profile silencers are great for places with minimal vertical space. Puck-style silencers are shaped like a hockey puck. Low-profile silencers are shaped in a rectangular fashion and are best for engines with dual exhaust turbos spaced far apart. Because of their rounded side panels, low-profile silencers are excellent for acoustic performance. Puck and low-profile silencers can come in residential, critical, and hospital attenuation grades.

Industrial Fan Silencer: Many process plants and industries require air fans, force draft fans, and induced draft fans, and they usually need some sort of acoustical treatment to fit into OSHA requirements. There are silencers for all fan types, and many are cost-effective, thanks to computer-enhanced technology. The advantages of each type of fan silencer depends largely on the application, pressure drop, and how much space is available.

Vacuum Pump Silencer: These types of silencers are used to eliminate liquid from gas flow vacuum systems by using liquid ring vacuum pumps or rotary positive blowers. Vacuum pumps are usually loud and require a high-performance silencer.

Vent Silencer: Vent silencers are frequently seen in oil and gas facilities and also in chemical processing heat recovery systems. These systems usually require a pressure relief valve (PRV) and need a vent silencer to effectively silence high-velocity air, steam, and gas vents. Vent silencers can be easily customized to fit any system.



Since 1969, Mahan’s Thermal Products has strived to provide quality production and sale of heat transfer equipment. Mahan’s is dedicated to taking care of its customers at all times and values the long-term relationships it has established with dedicated clients. Whether you need cleaning, repair, or building services or are looking to purchase a superior product at a competitive price, Mahan’s can assist you with your thermal product needs.


In the Tropics? Keep your engine running cool

Tropical conditions are challenging to marine engines. Engines require both air and water for cooling, both of which act efficiently in removing heat. However, in the tropics, the warmer air and water temperatures reduce the efficiency of your cooling system. So, what can be done?

Marinediesel takes the first step in rating your engines for the operating climate. This is one of the benefits of using Marinediesel’s VGT Series: our NIRA ECU allows such changes in rating, avoiding the sometimes large loss in horsepower often shown by the engines made by our competitors.

What can you do?

  1. Check the raw water intake and make certain that the seacock is opening / closing properly.
  2. Make certain coolant levels are topped up.
  3. Check your strainers for debris or blockages.
  4. Check your exhaust system to make certain there are no blockages.
  5. Make certain the air filter is clean and there are no blockages.
  6. Keep your fuel tank topped up. Warm weather increases condensation in the tank and thus, the likelihood of introducing water in the fuel.
  7. Make certain that the louvers venting into the engine compartment are not blocked and that there is adequate ventilation. If not, a blower may be required in extreme conditions.

All of this sounds like basic maintenance procedures, and much of it is detailed in your engine manual. It just pays in the long run to pay extra attention to these items if the vessel will be operated in harsh conditions.

How does a heat exchanger work?


Your engine’s cooling system is highly critical; the combustion process produces an enormous amount of heat, and that heat must be removed or dissipated. If heat is not removed, cylinder and engine block damage may quickly result.

Heat exchangers cool the engine, but work a little differently and more efficiently than a simple raw water cooling system. A heat exchanger consists of a series of tubes, or coils, that fluid flows through. This fluid is enclosed (either cooland or distilled water). Additionally, marine heat exchangers are encased by a jacket, through which raw water (fresh water or sea water) flows through, cooling the enclosed fluid, removing the heat, and exiting the system through the exhaust. The minerals in sea water mean that scaling, or build up, can occur, which is why heat exchangers usually require periodic maintenance. Mineral build up drastically reduces the efficiency of the heat exchanger and thus, the cooling capacity.

This is also why a blocked strainer or faulty impeller quickly damages an engine. When blocked by debris (especially plastic bags), without the raw water to cool the enclosed system, the engine quickly overheats, sometimes in a matter of mere seconds.


Bad practice: Engine idling




A common misconception in the marine industry is that you must allow diesel engines to idle before putting them under load. With modern diesel engines, this belief is 100%, completely incorrect.

In fact, allowing an engine to sit at idle for long periods of time has the opposite effect: It increases wear on the engine, increases emissions, and wastes fuel.

How did this belief get started? Quite simply, people observed truckers at truck stops allowing their engines to idle and thought it was “Best Practice.” On older diesel engines, this may have been the case with fuel efficiency, and it is certainly the case with gasoline engines. Yet, a glance at a fuel consumption curve will show that a diesel consumes more fuel at idle, over a greater time period, than at startup. Additionally, in colder climates, it is believed that idling maintains the temperature. However, all modern diesel engines that are used in cold climates have sufficient heating to allow an easy start.

Unlike gasoline engines, modern diesel engines are designed to heat up under load. The fuel is under compression by heat, combusting more efficiently, and idling does not generate that necessary heat. Sitting at idle does not provide this load, and merely increases the friction in the cylinders. The load is generated on a boat under throttle. Idling for a period of time any more than an initial 30 seconds or so after the engine is started does nothing. No extra lubrication. No benefits. All marine engines manufactured by MarineDiesel are sufficiently lubed in this time period.

Finally, add in the fact that many jurisdictions in the world restrict unnecessary idling, due to emissions, this practice is one that should be eliminated. It just creates waste.



Engine Physics 101: Thermal Efficiency


Today’s article continues our short series about the physics behind diesel engines. The word “efficiency” is often mentioned when looking at diesel engines. All internal combustion engines are heat engines; they convert heat energy into mechanical energy. Indeed, a thorough understanding of thermodynamics is critical when it comes to engine design. This topic is far more involved than can be covered in a simple, short blog article. In general terms, the engine’s efficiency is simply the ratio of how much of the heat produced is converted into usable mechanical energy. The formula used to determine the thermal efficiency of an engine is here:



hth = thermal efficiency

Pb = brake power [kW]

FC = fuel consumption [kg/h = (fuel consumption in L/h) x (ρ in kg/L)]

CV = calorific value of kilogram fuel [kJ/kg]

ρ = relative density of fuel [kg/L]

This formula works well, in an ideal world, where there are no limits on efficiency, and no losses. However, forces, such as friction, are always present and there will be some energy loss in any heat engine. This limitation is known as Carnot’s Theorem, named after the physicist who figured it out. It describes these limits with the following formula:

eta_{text{max}} = eta_{text{Carnot}} = 1 - frac{T_C}{T_H}

Where TC is the absolute temperature of the cold reservoir (the engine when it is cool) and TH is the temperature of the heat reservoir (the maximum engine operating temperature).

In diesel engines, the Diesel Cycle is what defines the amount of energy received from combustion. Since diesel fuel ignites after introduction into the combustion chamber as it is needed, the compression ratio of the engine further determines that engine’s efficiency.

eta_{th} = 1-frac{r^{1-gamma}(r_c^gamma - 1)}{gamma(r_c - 1)} ,

Therefore, whenever you see material or data sheets produced by engine manufacturers describing the efficiency of their engines, these terms are not merely marketing spin, but determined by the physics of the engine itself.            






Maintenance Tip of the Week – Heat Exchanger 03/16/2015


Maintenance Tip of the Week – Heat Exchangers

Periodically inspect and clean your heat exchangers as detailed in your MarineDiesel manual. Corrosion and scaling can build up over time, and the heat exchanger is a vital part of your engine’s cooling system.



Intercooler Issues



The cooling system on diesel engines is one of the most critical systems on any engine. Indeed, on turbocharged engines in particular, large amounts of heat are generated by the combustion process and this heat needs to be dissipated in some manner.

Modern engines use an intercooler to dissipate this heat. An intercooler, strictly defined, is a device that serves to remove heat from a gas or fluid.

The intercooler interior on our VGT Series is pictured above (with the cover removed). In fact, since our VGT Series uses the same engine block on all models, one of the primary differences between our VGT 350 and VGT 500 is that the VGT 500, producing much more heat, requires a much larger intercooler than the VGT 350, which produces less heat. The dimensions of the engine are thus impacted (height). However, MarineDiesel has a fix for this situation, especially for installations in vessels with tight engine compartments. On these vessels, we offer a modification with the intercooler mounted forward, and vertically, thus reducing the overall engine height.

The intercooler on our engines is specifically engineered to provide the requisite amount of cooling. For engines in extreme climates, often additional cooling is required and many vessels have extra heat exchangers connected to the system.

Most intercoolers are relatively low-maintenance devices, however scaling can build up on the interior, and they must be periodically cleaned as detailed in the engine’s manual.



How to keep heat from ruining your marine engine



All engines produce heat; A lot of it. This heat, if not dissipated, will quickly ruin your engine, necessitating expensive and time-consuming repairs. In fact, heat-related problems are a common maintenance issue, not only with MarineDiesel engines, but engines from all manufacturers.

How do you control heat?

Well, the first step is at the manufacturer’s end of things. MarineDiesel designed its’ engines with specific cooling systems for the application. The engines were tested in a lab, and in the field, before they were released for sale into the market. In fact, most changes to our engine product line over the years have been related to increases in the heat removal efficiency of our cooling systems. This is not as easy as it might sound. Emissions regulations, weight, power output, and engine size all are impacted by these changes.

If the engine will be used in a tropical environment, the challenges are multiplied significantly. As a general rule, our service department sees more issues in these regions than in cooler climates in the world. This is especially important in small craft with engine compartments, rather than an engine room.

As an engine end-user, the following tips will help you keep your engine cool and running worry-free:

  1. Make absolutely certain that there is cross-ventilation in the engine compartment (See picture below). Louvers and ventilation must be designed properly, and never be blocked.
  2. Always check exhaust temperature. Catching problems when they occur is easier, and cheaper in the long term.
  3. Install a blower in the engine compartment, if necessary.
  4. Always maintain your grid cooler, keeping it clean and replacing it if corroded.
  5. Ditto, the heat exchanger.
  6. Always ensure that the water intakes are not blocked.

eng vent3





Tight spaces and tighter places



MarineDiesel engines are the lightest, and most compact, of any engine on the market in our class. That is indisputable fact.

Why does this matter?

Quite simply, MarineDiesel engines can fit into tight places that simply do not have the space for our larger competitors. On boats, especially RHIBs or small high speed craft, this is a very important product feature. RHIBs, in particular often have tiny engine compartments located immediately under the deck, with little excess room. The vessel pictured above is a recreational vessel with three engines. Engines made by our competitors would not only never fit in the limited space, but their extra weight would shift the LCG of the vessel considerably.

With catamarans or trimarans, a different problem emerges. The beam on each hull. Port or starbord, engine compartments are narrow, with little extra room.

This can be an issue in industrial applications, too. Our MDPT subsidiary is currently involved in a re-powering project involving armored vehicles. These vehicles are designed with precisely zero excess space, and the smaller, lighter MDPT engines make a big difference in vehicle performance and ease of operation.

In fact, the biggest problem we face in these cramped quarters is providing adequate cooling for the engines, whether on land or at sea. Engines produce a lot of heat, and that heat must be dissipated. Through years of experience, MarineDiesel has learned practices and techniques that provide adequate cooling, such as louver design, blowers, and engine placement.

To illustrate, see the ventilation diagram below:

A - Air should exit the engine bay and the upper section B – Air should enter the engine bay at the lower section

A – Air should exit the engine bay and the upper section
B – Air should enter the engine bay at the lower section