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Liquid Cooling Systems for Efficient Temperature Control of Medical Diagnostics

Figure courtesy of Laird Thermal Systems Recirculating-Chillers.jpg
An illustration of how recirculating chillers operate.
Medical diagnostics manufacturers have several options for thermal management control.

As medical diagnostics labs accelerate automation to increase workflow, systems are becoming more complex as they continue shrink in size, perform multiple tasks, and comprise evermore temperature-sensitive electronic components.

One critical element of today’s diagnostic equipment is its cooling system. The cooling system prevents overheating, which can cause equipment to malfunction. Additionally, cooling solutions help maintain thermal stability of lab instrumentation, which is necessary for high-quality results. For instance, in x-ray and imaging applications, temperature stabilization directly impacts image resolution. Considering the importance of medical imaging and diagnostic tests to monitor and maintain patients’ health, the equipment and the lab must be thermally maintained to ensure equipment consistently meets stated performance expectations.

Cooling Requirements for Medical Diagnostics Equipment

Many types of laboratory equipment require precise cooling for thermally sensitive electronics. In addition to electronics cooling, lab equipment testing chambers may also require temperature control. Chemical reactions release or absorb heat, and precise temperature control is required to keep the reaction stable.

Reagent Storage

Reagents are essential for laboratory and medical testing. Reagent materials are used to detect the presence or absence of a substance, or to test if a specific reaction occurs. Thermal control is vital to preserve reagent materials, which can degrade over time when stored at improper temperatures. When they are kept at room temperature, reagents may become contaminated by microbial growth, which affects test integrity. Reagents can also be negatively affected at low temperatures if they undergo multiple freeze-thaw cycles. Given the high cost of many reagents, thermal control of reagent storage systems should be given a great deal of consideration.

PET and SPECT Scanners

PET and SPECT are gamma-based imaging techniques that allow doctors to check for diseases in the body. Scanners use a specific particle accelerator, known as a cyclotron, to create a radiotracer. Typically made from glucose, the radioactive substance has a very short half-life (i.e., a rapid decay time). The cyclotron typically accelerates an H-ion using alternating electric fields and uses a magnet to bend the path of the charged particle until it hits the target, making the substance radioactive. Both the cyclotron equipment and the detector banks must be cooled. Temperature control within the cyclotron system is critical for operational integrity, performance accuracy, and system reliability. PET and SPECT systems typically have a heat load range of 3~5K W, and liquid cooling systems such as recirculating chillers are often the preferred choice to control the temperature of the imaging system.

Medical X-ray Imaging Equipment

Giving physicians a look inside a patient’s body, medical X-rays are vital for detecting and diagnosing a wide range of injuries or diseases. In X-ray-based imaging techniques, an X-ray beam is projected through a patient to a recording medium. The generation and projection of an X-ray beam is highly inefficient and can produce as much as 5 kW of waste heat. Temperature stability within medical imaging systems is required to enhance imaging performance, increase system reliability, and maximize equipment uptime. Because medical X-ray equipment features many unique cooling challenges, a custom liquid cooling system configuration is often required.

Common Thermal Management Considerations for Medical Diagnostics

 

Space Constraints

The trend toward miniaturization typically increases the heat flux density and heightens thermal challenges. When heat-generating electronics are packaged into smaller housings, natural airflow and heat dispersion are impeded. Waste heat must be dissipated efficiently to ensure proper performance of laboratory equipment.

Environmental Regulations

Another important consideration for diagnostic lab environments is environmental regulation. It is estimated that laboratories can use up to five times the amount of energy per square foot compared with the prototypical office space. Laboratories that qualify for Leadership in Energy and Environmental Design (LEED) certifications must prove efforts to go green. In addition, labs in most countries are now required by law to use cooling equipment with refrigerants that are environmentally safe. Europe’s ROHS (Reduction of Hazardous Substance) regulation requires all equipment be free of lead, mercury, cadmium, and other heavy metals. Cooling systems also need to meet certain safety standards such as UL61010-1 or IEC 61010-1 lab environments. These standards ensure the safety of the operators and include specifications for electromagnetic compatibility and electromagnetic emissions to ensure all laboratory equipment can operate in the same room without interference. When designing laboratory equipment, OEMs will either ask for a certification from the chiller manufacturer, or certify it themselves as part of the installed system.

Cooling Solutions for Medical Diagnostics

Diagnostic laboratories require a compact, energy-efficient cooling solution to support the cooling needs of their entire equipment installation. It should also utilize environmentally friendly refrigerants to meet government regulations and reduce the systems’ overall impact on the environment.

There are two types of liquid cooling solutions: liquid heat exchanger systems and liquid chillers.

Liquid Heat Exchanger Systems

This system uses a liquid-to-liquid or liquid-to-air heat exchanger to cool the coolant in a liquid circuit. While liquid-to-liquid is often used for cooling below ambient temperatures, an air-cooled system cools the coolant near ambient temperature.

Liquid Chillers

Liquid or recirculating chillers utilize a compressor-based system instead of a liquid heat exchanger. It is used for dissipating heat to the outside environment and cooling well below ambient temperatures.

Image courtesy of Laird Thermal Systems Chiller_FAMILY_GROUP.jpg

Laird Thermal Systems offers a series of standard and custom liquid cooling systems designed to maximize temperature stabilization above, below, or equal to ambient temperature.

 

Advantages of Liquid Cooling Systems

Thermal management systems that feature liquid cooling offer higher efficiencies than air-based heat-transfer mechanisms. This translates into higher reliability, reduced field maintenance, greater system uptime, and a lower total cost-of-ownership.

High Heat Pumping Capacity

A liquid cooling system offers higher efficiency than air-based heat exchangers and provides more rapid cooling, quieter operation, higher reliability, and increased system uptime.

High Heat Flux Density

Liquid cooling systems can remove up to five times the amount of heat per square area over conventional air cooling systems. This becomes advantageous in densely packed electronics with limited space to accommodate an air cooling mechanism.

High Coefficient of Performance (COP)

If a piece of laboratory equipment has a heat load of 3 kW, it can require 1 kW or less of energy to properly cool the equipment, which is more efficient compared to other technologies. This efficiency optimizes heat transfer dissipation away from thermally sensitive components to the ambient environment.

High Reliability

Today’s recirculating chillers can be programmed to alert technicians of potential operational issues, such as when low- or high-pressure and temperature limits have been exceeded or when the fluid level drops below recommended levels. Chillers with an optical fluid level sensor (no moving parts) instead of mechanical fluid switches is a great example of providing increased reliability and uptime.

Heat Routing

Liquid cooling allows the integration of a small heat exchanger to be located at the heat source, which then routes heat away through a liquid circuit. This is beneficial in equipment with densely packed electronics where a conventional air-cooling system pushes air through the system using a large duct and increasing system noise.

Rapid Cool Down

Cool-down time is a function of cooling capacity and overall system mass. Liquid cooling systems have relatively larger cooling capacities than conventional heat sink fan mechanisms, which will reduce the time it takes to reach the set point temperature.

Low Noise

Air-based cooling systems with high heat removal requirements will need much larger fans to dissipate heat to the surrounding environment. This makes the air cooling system noisier and exposes the system to a higher vibration compared to liquid-based solutions.

Eco-Friendly

The phase down on environmentally harmful refrigerants, like HFC refrigerants, has led to the development of safe systems utilizing alternative refrigerants. These liquid cooling systems utilize natural, HFO, or HC refrigerants that have a greatly reduced global warming potential (GWP).

Conclusion

Many diagnostic instruments require precise thermal management control to ensure proper performance and accurate results. Today’s liquid cooling systems offer a high COP while delivering efficient and reliable operation to maximize uptime and optimize performance in a wide range of medical diagnostics applications.

 

 

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