Frequently Asked Questions

Heat transfer technology is a complex subject and here you will find some of the questions that are most frequently asked about heat exchangers and oil coolers, in terms of performance, design and operation.

We hope you find the answer to your question in the list below. However, if it’s not there, you can also click through to our Contact Us page, complete and send the enquiry form and we will respond directly with an answer to your particular question.

A heat exchanger is a device for transferring heat energy from a liquid or gas, to another liquid or gas without the two ever coming into contact with each other. A typical shell and tube heat exchanger will contain a tube bundle inside an outer shell, or body. Cold water flows through these tubes, whilst hot water, or gas flows around the outside of the tubes, enabling the heat from the hot water or gas to be transferred to the colder water inside the tubes.

A good example of how the process works are swimming pools, where most are heated via a boiler, using Gas, LPG or Biomass as the energy source. In theory, the most efficient way to heat the pool would be to circulate the pool water directly through the boiler. But were this to happen, the chemicals used in the pool water to keep it safe for use, would quickly corrode and damage vital parts inside the boiler, leading to premature failure and a costly replacement.

However, by using a heat exchanger to act as an ‘interface’ between the boiler water circuit and the pool water circuit, the boiler is protected from damage and the pool water is quickly heated up to the required temperature; the pool water passing through the central ‘tube core’, whilst the hot boiler water circulates around the outside of the tubes, transferring heat energy to the pool water.

More examples of applications where Bowman heat exchangers are used.

Mechanical equipment, such as internal combustion engines, gearboxes and transmission systems rely on oil to lubricate moving internal components, enabling them to run freely, whilst reducing wear to metallic surfaces.

In addition to lubrication, engine oil also acts as a coolant, to remove surplus heat from mechanical equipment. For example, a hot engine transfers heat to the oil which then circulates through a heat-exchanger (also known as an oil cooler), using either air or water to cool the oil.

All oils have a recommended operating temperature range and if this is exceeded, the viscosity of the oil can be weakened, reducing its lubrication qualities. Should excessive heat continue to build up, the oils ability to lubricate components will be significantly reduced and in extreme cases, the viscosity may break down, creating conditions where the metal components overheat, leading to premature wear. In extreme cases this could even result in a catastrophic component failure.

This situation can occur where equipment is to be operated at high speeds for extended periods, or where climatic conditions dictate higher ambient air temperatures. In such conditions, adding an oil cooler to the lubrication system, will remove the excess heat, reducing the oils temperature so that it remains within the correct range to protect the equipment, prolonging its operating life.

Whether an air or water cooled oil cooler is used depends on application and operating conditions.

Bowman oil coolers are water cooled ‘shell and tube’ designed units that are robust and reliable over a wide range of operating conditions. For more information about Bowman Oil Coolers

An oil cooler is designed to remove excessive heat from the oil used to lubricate vehicles, machinery, and mechanical equipment. These types of coolers can be either a water-to-oil or air to oil type of heat exchanger.

Lubricating oils are developed for differing kinds of temperature ranges and operating conditions. To ensure an oil protects the machinery or equipment for which it was designed, it should always operate within its designated temperature range.

Too cold and it thickens, making it more difficult for the oil to lubricate the moving parts. Too hot and the viscosity of the oil could start to breakdown, resulting in premature component wear and ultimately equipment failure.

The problem is that moving metal parts generate lots of heat, which gets transferred to the lubricating oil. By adding an oil cooler into the lubrication circuit, the oil temperature is controlled and always kept within the correct operating range.

Oil coolers can be either air cooled or water cooled, depending on the nature of the application. Bowman manufacture a wide range of water cooled ‘shell and tube’ design oil coolers for off/on highway vehicles, construction plant and associated equipment, cooling heavy duty applications such as torque converters, automatic transmission and engine oils.

Find out more about Bowman oil coolers

An oil cooler is designed to remove excessive heat from the oil used to lubricate vehicles, machinery and mechanical equipment. For example, a hot engine transfers heat to the oil which then circulates through a heat-exchanger (also known as an oil cooler), using either air or water to cool the oil.

It achieves this by using a cooling medium – usually either air or water – to transfer heat from the oil and to the cooling medium. It does this without either the oil or cooling medium coming into direct contact with each other.

For example, an air cooled oil cooler often looks like a small car radiator and achieves its purpose by running the oil through finned tubes. The incoming air passes over and around the tubes, removing heat as it passes through.

For many applications, air cooling isn’t appropriate and here water cooling is the solution. Shell and tube oil coolers are very popular, the coolant flowing through the central ‘tube core’, whilst the oil flows around and through the tubes, providing extremely efficient heat transfer.

Bowman manufacture a wide range of water cooled shell and tube oil coolers for torque converters, automatic transmission and engine oils. Find out more about Bowman Oil Coolers.

In certain conditions where there is a significant temperature differential between the cooling medium and liquid being cooled, a shell and tube heat exchanger is often the more cost effective cooling solution compared to a plate heat exchanger. This is due to the small flow path within the plate heat exchanger which creates significant amounts of turbulence, leading to high pressure drop within the unit.

As the name suggests, plate heat exchangers are constructed from a series of thin metal plates. Usually made in stainless steel, each plate contains an intricate pressed pattern, and to ensure the unit is water tight, rubber gaskets are ‘sandwiched’ between all the metal plates, which are then compressed together in a rigid frame to form an arrangement of parallel flow channels with alternating hot and cold fluids.

In contrast, shell and tube design heat exchangers consist of two primary components; the outer body (or shell) and tube core (or bundle) inside the shell. Cooling media flows through the tube core, whilst the hot fluid enters the shell via an inlet port, flowing through and around the outside of the tube core through a series of baffle plates, before leaving the shell via outlet port. For maximum heat transfer efficiency the hot and cold fluids travel in a ‘counterflow’ direction through the heat exchanger. For more information on counterflow.

Whilst plate heat exchangers can be quite compact and have the ability to be increased in size, should cooling requirements change, they are be more costly to maintain than the equivalent shell and tube heat exchanger, as typically the rubber gaskets age harden and need replacing every 2 years. This is a time consuming and costly exercise, putting the heat exchanger out of service for longer periods. Additionally, leak detection can be more difficult and require skilled labour to undertake the work. And, due to greater water flow resistance inside the heat exchanger, there is an increased chance of fouling, reducing the efficiency of the unit.

In contrast, shell & tube heat exchangers are extremely easy to maintain; removing the end covers reveals the tube core, which can be withdrawn for cleaning and routine maintenance. Heat transfer efficiency of a quality shell & tube heat exchanger, such as Bowman, is extremely good, whilst the units themselves are tough, providing long life durability. Shell and tube heat exchangers can also be used with the most demanding cooling media, including sea water and mineral rich or contaminated water.

More information on Bowman’s range of shell & tube heat exchangers

If your pool isn’t heating up to the required temperature, there are a few possible causes. Using this check list could help you locate the problem:

1: Do I have enough energy?
Whether heating your pool with a gas boiler, solar panels, a heat pump, or another energy source, it is important you have enough energy to do the job.

2: Do I have the right heat exchanger?
A common misconception is the larger the heat exchanger, the faster it heats the pool! However, this isn’t necessarily the case. There are many types of heat exchanger used to heat swimming pools and they differ dramatically in design, performance and heat transfer efficiency.

3: My heating system is adequate but my pool still fails to heat up!
Flow rates of both the hot and cold fluids are vital for the heat exchanger to transfer thermal energy to the pool. If the hot water flow rate is too low, the available energy will not be passed through the heat exchanger. However, the flow rate of the pool water is equally important.

4: And if you’ve done all that…
Even if all the equipment is adequately sized, there may still be other parts of the system creating issues that will need to be checked.

5: In summary…
This is a summary of a more detailed article designed to help identify problems with pool heating and heat exchangers. Read the complete article here.

More product information on Bowman swimming pool heat exchangers

Most hot tubs are supplied with an integral electric water heater, which are usually around 3kW output, depending on the capacity of the hot tub. This type of heater will usually increase the water temperature by around 1 – 2° C per hour, so it can take up to 24 hours to heat a tub using ambient temperature water.

To overcome this problem, some users fill their tub with pre-heated (25° C) water from an adjacent boiler, but given that hot tubs usually operate at around 38-40° C, it can still take a further 6 to 10 hours to achieve full temperature, depending on the performance of the electric heater.

This long heat up time has created a high level of dissatisfaction for many owners, who want their hot tubs to be available for use much faster than the standard heating system allows.

Consequently, many hot tub users, especially those in the commercial sector, are switching to a new type of heating system, using an external boiler, linked to a Bowman heat exchanger. The benefits include significantly reduced heat up times – typically 3 – 4 hours using ambient temperature water, or 1 hour using pre-heated water), plus significantly reduced energy costs compared to electric heating.

More information on heating hot tubs with Bowman heat exchangers.

Most hot tubs are supplied with an integral electric heater, usually around 3kW output, depending on the water capacity. However, more recently, there has been a growing trend to use gas heating via an external boiler as this is faster at heating up the water compared to electric. This means when you are not using the hot tub, you can keep it at a lower temperature, or even switch the heating off completely, because it won’t take long to bring it up to the n temperature when you are ready to use it.

The main reason is the length of time required to heat a hot tub with an electric heater – typically up to 24 hours, using cold water. To speed things up, some owners ‘pre-fill’ their tub with hot water from a boiler, but even this can require a further 6 to 10 hours of heating to achieve the required 38-40° C temperature.

Whilst many domestic users were prepared to put up with the inconvenience, commercial users, such as holiday parks could not!

The demand for hot tubs when booking holiday accommodation has risen dramatically and is now the second most requested guest facility. To meet this demand, holiday venues had to find a faster way of heating them, due to guest changeover periods. Typically there is only around 4-5 hours available to be drain, clean, re-fill and heat up before new guests arrive.

The solution was relatively simple – use an external heat source such as a gas boiler and simply bye-pass the hot tubs electric heater. To enable this, a heat exchanger is required to transfer heat from the boiler water to the hot tub water. It’s exactly the same principle used for most swimming pools, but just on a smaller scale.

Bowman developed an ultra-compact heat exchanger that could be installed in the hot tubs pipework and the result was hot tubs heated in 3-4 hours using cold water, or in around 1 hour using pre-heated water.

There was also another benefit. Heating hots with electricity can be very expensive. By switching to gas boiler heating, many users reported a significant reduction in the energy costs – some as much as £500.00 per hot tub!

How holiday parks can benefit by switching to gas heating.

More information on Bowmans hot tub heat exchangers.

With counter flow cooling, the incoming cooling medium absorbs heat as the ‘hot’ fluid travels in the opposite direction. The cooling medium heats up as it travels through the heat exchanger, but as colder water enters the heat exchanger, it absorbs more heat, reducing the temperature much lower than could be achieved with parallel flow.

In a shell and tube heat exchanger, coolant usually flows through the central ‘tube core’ to cool hot oil, water or air which passes over and around the tubes. The direction in which the two fluids travel through the heat exchanger can be either ‘parallel flow’ or ‘counter flow’.

Parallel flow is where the fluid to be cooled, flows through the heat exchanger in the same direction as the cooling medium. Whilst this arrangement will provide cooling, it has limitations and can also create thermal stress within the heat exchanger, as one half of the unit will be appreciably warmer than the other.

In counter flow cooling, the incoming cooling medium absorbs more heat as the ‘hot’ fluid travels in the opposite direction. The cooling medium heats up as it travels through the heat exchanger, but as colder water enters the heat exchanger it absorbs more heat, reducing the temperature much lower than could be achieved with parallel flow.

The mean temperature difference between the cooling medium and the fluid being cooled is also more uniform along the length of the heat exchanger, reducing thermal stress.

Depending on flow rate and temperature, the heat transfer performance could be up to 15% more efficient with counterflow, possibly enabling a smaller heat exchanger to be used, saving space and money!

More information on the benefits of counterflow.

During the course of its operating life, a shell and tube heat exchanger will need cleaning many times. Both fresh water and sea water cooling media today contain high levels of minerals and pollutants, which can build up over time, restricting the water flow through the tube core, resulting in a reduced flow rate and significantly lower heat transfer efficiency.

The good news is that Bowman shell and tube heat exchangers are much easier to clean than many other types and the following information is intended as a basic guide:

  1. Removing the end covers gives access to the tube core, which can be removed from the body (or shell).
  2. The tube plates and external tubes can then be washed using a hand held hose or lance. A steam cleaner can also be used if available.
  3. Small diameter rods or tube brushes can be used to clean through each tube to remove any stubborn deposits.
  4. Detergents or chemicals can be used if tube fouling is severe. Allow plenty of time for the cleaning media to work before hosing down with plenty of water. NOTE: it is important to check any cleaners being used are compatible with the tube material.
  5. Thoroughly flush the tube core with clean water to remove all traces of cleaning chemicals/detergents and if necessary, neutralise the cleaning fluid.
  6. Reassemble the tube core into the body, refit the end covers in their original orientation and tighten to the recommended torque figures– NOTE: always use new ‘O’ seals after cleaning to ensure a watertight joint.

For more detailed information on care and maintenance of your Bowman heat exchanger or oil cooler, download a copy of our ‘Installation, Operation & Maintenance guide’

Swimming pool heat exchangers work by transferring heat energy from a hot water circuit, to the cooler pool water circuit, without the two fluids ever coming indirect contact with each other.

Most swimming pools are heated via a boiler, using fuels such as Gas, LPG or Biomass, as the energy source. In theory, the most efficient way to heat the pool water circuit would be to connect it directly to the boiler.

Were this to happen, the chemicals and minerals added to the pool water to keep it safe for use, would quickly erode and damage vital components inside the boiler, leading to premature failure and a costly replacement.

However, by using a heat exchanger to act as an ‘interface’ between the boiler water circuit and the pool water circuit, the boiler is protected from damage and the pool water is quickly heated up to the required temperature for use.

Shell and tube design heat exchangers are extremely popular for swimming pools, due to their efficiency and ease of maintenance. Inside the ‘shell’ there is a bundle of tubes, known as the ‘tube core’, through which the pool water passes in a single direction.

At the same time, hot water from the boiler is circulated around the outside of all the tubes in the tube core. Traveling in the opposite direction to the pool water flow, the boiler water transfers its heat to the pool water, before being recirculated back to the boiler, for re-heating.

Both water circuits operate in a continuous heating cycle, until the total pool water volume has reached the required temperature, which is usually around 28 – 30° C.

Bowman manufacturer a comprehensive range of swimming pool heat exchangers for everything from spa pools and hot tubs, up to Olympic size pools.

More information on Bowman swimming pool heat exchangers

Selecting the correct heat exchanger is very important to ensure the pool heats up quickly to desired temperature. The main issues to consider when sizing a swimming pool heat exchanger are;

  1. Pool size – what is the water capacity? Heat exchangers are sized according to capacity, so a unit designed to heat a 80m³ (18,000 gal) pool would be no use if you have an 180m³ (39,500 gal) pool.
  2. How is it heated? Usually the choice is either a boiler or renewable energy. If it’s renewable energy, select a heat exchanger specially designed for the lower temperature water provided by solar panels or heat pumps, as these units need less energy to heat the pool to the required temperature.
  3. Boiler water temperature – however, most pools will be heated by boilers, so what is the temperature of the boiler water? Usually it’s between 80°C and 85°C – the ideal temperature for pool heating. Some boilers are lower – around 60°C. So, using 82°C water, a heat exchanger providing 110kW should heat your 180m³ pool efficiently. But if the boiler water temperature is only 60°C, the heat available to transfer drops to around 60kW – a reduction of over 40%, so a larger heat exchanger would be required for the pool to achieve full temperature.
  4. What are the water flow rates? Flow rates are vital for the heat exchanger to transfer thermal energy to the pool. If the hot water flow rate is too low, the available energy will not be passed through the heat exchanger. However, the flow rate of the pool water is equally important. People often think it is important to generate a large temperature differential between the pool water entering and leaving the heat exchanger. They are happy if the pipework connected to the outlet of the heat exchanger is noticeably warmer than it is at the inlet.
    In reality, this actually reduces the efficiency of the heat transfer process! This is because the pool water flow is too low – the water remains in the heat exchanger for too long, so a much smaller volume of water is being heated to a slightly higher temperature. However, with higher flow rates, the time taken to turn over the pool water will reduce and even a small increase in the temperature of the pool water through the heat exchanger (1.5° C for example) will have a greater effect on the heating efficiency of the pool.

More information heat exchanger selection, read the article ‘Why doesn’t my pool heat up faster’.