Practical Automotive Maintenance: Heat Exchangers

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Heat Exchangers

07.03

00:00	As we know, coolant absorbs heat as it passes through or by engine components.
00:04	The problem is, it can only absorb, so much heat before it's no longer effective, which results in an overheating cooling system and inevitable damage to the engine components it's meant to cool.
00:16	So, how do we get all that heat out of the coolant, so it can continue to maintain the correct engine temperature? This is the job of a heat exchanger, most commonly referred to as the radiator.
00:26	It functions by transferring heat from the coolant to the multiple tubes and fins in the core of the radiator that are then cooled by the atmospheric air flowing through it as we drive along or by fans when we're stationary.
00:39	We'll start by learning the general makeup of a radiator.
00:42	The centerpiece of the component is referred to as the core and is constructed of multiple vertical and horizontal hollow tubes which our coolant flows through.
00:52	Between these tubes we find thin metal fins that are bent in a stacked zigzag pattern.
00:57	These provide more surface area for the transfer of heat from the core to the ambient airflow as it passes through.
01:04	These fins have small air gaps in between each bend that allow air to flow over them as we drive along.
01:10	There will also be end tanks on either sides or top or bottom depending on the design.
01:15	Located on these tanks is our inlet and outlet, allowing hot coolant to flow in from the engine and once the fluid passes through the core it exits the other side via the outlet and back into the engine to start the cycle again.
01:28	On top we'll typically see a fill point or radiator cap attached to an overflow tank with an overflow tube.
01:35	However, due to packaging constraints, some vehicles contain a separate header tank with hoses connecting it to the radiator and this acts as a remote fill and bleed point.
01:45	I will just mention that we won't be getting into bleeding cooling systems just yet as we'll be covering this process in detail in an upcoming module.
01:53	On the bottom of our radiator we'll also find a drain plug as well as some mounting points to fit our vehicle.
01:59	These come in all shapes and sizes depending on the end tanks, material, mounting style and packaging constraints.
02:06	These mounts will have rubber isolators on the mounting points to aid in vibration, thermal and electrical isolation, securing the radiator firmly and preventing cracking or frictional wear caused by harsh bumps or repeated movement.
02:19	Rubber isolators also provide a barrier between the hot radiator and surrounding components which helps us prevent heat transfer that could potentially affect nearby parts.
02:29	The first generations of radiators were made from a copper and brass core and end tanks.
02:34	This was done because of the great thermal capacity of copper, being almost double that of aluminium, as well as its ability to dissipate heat and cool down incredibly quickly, making it perfect for radiator construction.
02:47	This did come with some drawbacks though, being much heavier and more costly to manufacture compared to aluminium.
02:54	It's for this reason that around the 1970s the brass copper radiators began to phase out and were replaced with the ones that we know and use today.
03:03	Today's standard of radiator for both OEM and aftermarket manufacturers consists of an aluminium core with end tanks being made either from aluminium or plastic.
03:12	OEMs tend to favour plastic tanks for cheaper manufacturing costs, while aftermarket manufacturers usually favour aluminium.
03:20	Although plastic end tanks do offer cheaper construction for mass production, they do have a few disadvantages.
03:27	It's obvious our radiator is exposed to a vast heat range and this causes the plastic end tanks to expand and contract, which when repeated across a long timeline can cause the plastic to fatigue, eventually leading to breaking down and cracking the end tanks.
03:43	We can generally see when a plastic end tank is deteriorating by identifying discolouring as it turns from a shiny black plastic to a faded black or brown.
03:52	We may also see thin white lines spanning across the tank and this suggests high levels of fatigue and thinning, indicating the radiator's end tanks are becoming extremely brittle.
04:02	Aluminium end tanks are more resistant to breakdown and the negative effects that heat cycling can cause.
04:08	A good quality all-aluminium radiator will typically remain in good working order for a longer period of time, given the appropriate maintenance is done with regard to the fluid to prevent corrosion and breakdown.
04:20	Other parts we may see on the radiator are OEM temperature sensors or extra accessory ports for additional sensors, such as aftermarket temperature and pressure sensors, as well as some mounting tabs or retainers for cooling fans.
04:33	Radiators are the most well-known heat exchangers in cars, but others like the heater core inside the cabin also play important roles.
04:42	Other heat exchangers include oil, fuel, transmission and differential coolers which operate similarly with cores, fins and end tanks and may feature thermostats for temperature control.
04:53	Power adders like turbochargers use intercoolers or charge coolers to cool compressed intake air.
04:58	With air-to-air types being the most common, their efficiency entirely depends on the core design and airflow.
05:05	Maintaining adequate airflow to air-to-air heat exchangers is critical for cooling efficiency.
05:11	Stacking multiple coolers like an oil cooler, power steering cooler and intercooler in front of the radiator can restrict airflow and negatively impact radiator performance, leading to rising coolant temperatures.
05:23	Alternatives to air-to-air cooling include water -to-air intercoolers and interchillers.
05:29	Water-to-air systems popular in high power drag builds and some modern OEMs use coolant circulated through a sealed core to absorb heat from charged air.
05:38	The coolant is stored in a separate tank and cooled via a dedicated radiator or often simply packed with ice for drag racing applications.
05:46	Water-to-air systems benefit from better packaging flexibility and superior efficiency, but they're also considerably more expensive and complex.
05:56	Interchillers function like water-to-air systems, but integrate with the vehicle's AC system.
06:02	Instead, of using ice, they use refrigerant to chill the coolant before circulating it through the intercooler.
06:08	This setup provides continuous cooling as long as the AC is active, offering consistent intake temperature control without the short-term limitations of ice.
06:17	With that covered, let's now run back over the main points found in this module.
06:21	Heat exchangers transfer excess heat from engine coolant, oils or intake air through a core made of small tubes and overlapping fins which dissipate heat via atmospheric air or supercooled fluids.
06:34	While older radiators used copper for its thermal efficiency, modern units primarily use aluminium for its lighter weight and lower cost.
06:42	In tanks found on the sides or top or bottom, direct fluid flow and are made from plastic, pressed aluminium or billet aluminium in high performance applications.
06:51	Charge air coolers come in air-to-air, water-to -air and interchiller types, all designed to cool intake air before combustion.