PRODUCT SERIES - XF SERIES

Dec 06, 2022by Natasha Sufi

A heat exchanger transfers heat between heat transfer fluid from a primary cooling circuit and fluid from the application to regulate process temperatures, without the fluids ever mixing together. The design of heat exchangers exposes fluids to a considerably larger surface area than other designs of heat exchanger, maximising the area available for thermal exchange to take place whilst keeping pressure drop to a minimum.

Where can a water-to-water heat exchanger be used?

Heat exchangers are usually a good option in situations where there is already a primary cooling circuit in place. Examples of primary cooling circuits include:

Centralised chiller
Centralised flatbed/dry cooler
Centralised adiabatic cooler
Cooling tower
Tap water - Whilst almost infinite levels of cooling can be achieved by using tap water, it is terrible for the environment and for the billpayer.

How does a heat exchanger work?

Applied Thermal Control use plate heat exchangers in the design of the XF series. For more information on the construction of a plate heat exchanger, please refer to Appendix 1 at the end of this document.

How a plate heat exchanger works

By stacking multiple plates together and rotating the gasket to block either the left or right side, a channel is formed. This allows fluid to flow through alternating plates without mixing.

Fluid from the primary circuit will flow through channels 2, 4 and 6, and leave the heat exchanger at a higher temperature. Hot fluid from the application will flow through channels 1, 3 and 5, and exit the heat exchange at a cooler temperature. The hotter fluid is able to transfer some of its thermal energy across the plate into the cooler fluid.

The plates are pressed together, allowing the gaskets to form a seal. The corrugations of the adjacent plates create a tortuous path in which fluid is driven.

Heat exchangers from Applied Thermal Control are arranged in a single-pass configuration. Fluids are then able to then flow around the heat exchanger as shown below:

Fluid passes through the plates in counter-flow. This means that the heat transfer fluid from the primary circuit and hot fluid from the application flow in opposite directions. Counter-flow offers a higher thermal efficiency than parallel-flow.

What are the benefits of a heat exchanger?

Plate heat exchangers are quick and easy to clean

Periodic, onsite cleaning can be performed to flush out any contaminants to prevent fouling, and eventual reduction in heat transfer efficiency over time. Further information on fluid quality can be found below.

It is simple to adjust the cooling capacity of a heat exchanger.

Should the requirements of an application increase or decrease, it is possible to change the cooling capacity of the heat exchanger by exchanging the plate heat exchanger component for one with more or fewer plates. Reducing the number of plates will reduce the cooling capacity.

Plate heat exchangers are responsive.

Because the channel within which fluids flow is so narrow, only a small volume of fluid is contained in the heat exchanger at any one time. This allows temperatures to be readily controlled with a short lag time.

Plate heat exchangers are efficient

Due to the corrugations of the plates, and the narrow channels between them, a plate heat exchanger is able to recover up to 90% of the heat from process fluids.
Because of the absence of a refrigeration circuit or fans, heat exchangers have very low energy consumption.

Heat exchangers are not noisy

A fan is usually the noisiest component in process cooling equipment. The requirement for fans is removed from heat exchangers by transferring unwanted heat into the primary cooling circuit, rather than the environment. This means that heat exchangers operate quietly.

It is not necessary to upgrade air conditioning/ventilation in the building.

As heat exchangers do not eject heat into the surrounding environment, it is not necessary to upgrade the air conditioning and ventilation systems of the building in order to manage heat removed from applications.

Heat exchangers have a small footprint

The compact design of a plate heat exchanger, and redundancy of fans, means that heat exchangers are able to take up less space. The removal of a fan from the design of this process cooling equipment also allows space for additional controls to be added.

Heat Transfer Fluids

The XF Series from Applied Thermal Control is compatible for use with water, deionised water, oil and glycol.

Water

Water is readily available but can be dirty. Some applications are sensitive to particulates or may have small channel sizes making them prone to blockages. The closed circuits within a heat exchanger can help to protect the application.

Water has the potential for microbial contamination, the non-intended introduction of unwanted bacteria. Microbial contamination can lead to accelerated corrosion of the system, blockages, and reduced heat transfer. It is possible to introduce additives to eliminate microbial contamination. In the absence of such additives, Applied Thermal Control offer in-line UV decontamination as an optional control. The use of an in-line UV decontamination pack can prevent growth in the system by passing fluid through steel tubes containing a UV lamp.

Most house water systems run at sub-ambient temperatures. Some applications will require water to be delivered above dew point (the atmospheric temperature below which water droplets begin to condense), such as laser systems. In such cases, Applied Thermal Control offer an additional heater pack. Addition of a heater pack makes it possible to raise the operating range by 35ºC by mounting a heating element into the reservoir.

Generally, house water systems tend to be at lower pressures. To achieve cooling, higher-pressure applications require high back pressure. Heat exchangers allow higher pressure pumps to be installed, raising the pressure of the process circuit. Inversely, some applications are sensitive to higher pressures. In such cases, a bypass on the water circuit allows you to regulate pressure, ensuring protection of the application whilst still achieving the required flow rate and cooling. This is the case for all heat transfer fluids.

As demands on the primary cooling circuit change, variations in the pressure and flow of the circuit occur. An increase or decrease in demand by other systems on the primary cooling circuit can also cause spikes in temperature. Heat exchangers can help to manage this.

Deionised Water

Some applications are sensitive to electrical discharge or may require deionised water for other reasons.

A primary cooling circuit using deionised water is possible, but may be expensive, and there is a risk of microbial contamination within dead legs (pipework isolated from regular flow) of the system as additives cannot be used with deionised water.
It is important to note that when using deionised water, galvanic corrosion may occur if there are mixed materials in the circuit. Use of a heat exchanger allows a circuit of deionised water to be run to the application.

To ensure the quality of deionised water, it is possible to install in-line UV decontamination, as previously discussed. Applied Thermal Control also offer an inline deionising cartridge, which will polish water within the system. Addition of a conductivity sensor makes it possible to measure the purity of deionised water within the system by measuring resistivity and conductivity. It is possible to have this information relayed via volt-free contact or RS485.

Oil

Oil can offer an alternative to deionised water, offering electrical insulation at high operating temperatures. They are non-reactive, and do not mix with water.

Oil is a more viscous fluid and is able to operate at higher temperatures and pressures than water. This viscosity, however, means that oils are more challenging to work with.

When using oil as a heat transfer fluid, a positive displacement pump is required due to issues with viscosity. However, positive displacement pumps do not generally have enough flow for the requirements of a heat exchanger. Gear pumps can be used in replacement but are expensive and noisy.

Glycol

Glycol/water combinations are usually used for their antifreeze properties. Heat exchangers of this type rarely operate at temperatures where this would be of benefit.

However, glycol can be used in situations where microbial contamination is a concern as when prepared at the correct concentrations with water, both ethylene glycol and Hexid fluid (which is propylene glycol based) will help to inhibit the growth of most microbes.

The XF-Series from Applied Thermal Control

This range of floor-standing heat exchangers is designed for use with primary cooling circuits, providing cooling to applications for which the facilities water may be unsuitable for. Closed loop water to water heat exchangers from Applied Thermal Control utilise chilled house water to remove heat from the process coolant via a heat exchanger, providing an efficient way to cool without the need for an additional refrigeration circuit.

Heat exchangers in the XF series provide a barrier, protecting process coolants from potentially harmful cooling water that may contain contaminants. Units from Applied Thermal Control also overcome problems associated with insufficient pressure, fluctuating flow, or very cold water, by providing a stable supply of coolant to the process, regardless of house water condition, thus ensuring that the process remains at optimum performance.

Units in the XF range are self-contained systems with modulated primary supply, a water-to-water plate heat exchanger, coolant storage tank, and pump. A wide range of non-ferrous/stainless steel pumps with varying flows and pressures are available to suit requirement. Pumps are of positive displacement or centrifugal construction with fan-cooled electric motors, supplied in 304 & 316 stainless steel as standard.

Other features of the XF range include:

Supplied complete with circuit breakers and on/off switches
Coolant pump starting contactors
Pump motor protection
IP54 protection
Temperature gauge
Pressure gauge
Coolant safety bypass
Visual tank level indicator
24 V control circuit available

XF004

The XF004 is built into the K1 chiller enclosure, making it easily portable and small enough to fit under a laboratory bench. Designed to provide 4kW of cooling at 10ºC above the temperature of the primary water circuit the XF004 is ideally suited for most laboratory equipment, vacuum pumps and smaller laser systems.