Advanced Thermal Solutions, Inc.
Case Study: Thermal Management in Medical Diagnostic Equipment
DRAFT – August 2016

ATS Case Study: Thermal Management in Medical Diagnostic Equipment

Medical diagnostic equipment, including MRI scanners or EKG machines, poses similar thermal challenges as other electronics, including telecommunications, retail, and consumer. But medical diagnostic equipment also presents unique design issues that must be considered.

From isothermal and cyclic temperature demands to the necessity of repeatability, which ensures accuracy, to patient safety and comfort, a number of factors have to be accounted for in a design.

Experts from Advanced Thermal Solutions (ATS), a leading-edge engineering and manufacturing company focused on the thermal management of electronics, were faced with those issues when tasked by Harvard Medical School to design a cooling system for the analysis and observation of tissue samples in a laboratory setting.

ATS engineers were tasked with solving the following problem and design goals in the Harvard Medical School project:

• Provide long-term temperature control for an embedded tissue sample.
  • The tissue is embedded in an optimum cutting temperature (OCT) fluid
    • The OCT would hold the tissue stationary.
    • OCT allows sample to be cored for analysis.
  • Constant temperature must be maintained through the work day.
  • Repeatable temperature.
  • Allows the sample to be used in a milling machine.

The design goals from Harvard also included:

• Create a cooling system to maintain tissue samples below minus 70 degrees Celsius for six hours.
• Ensure operator visibility of the samples.
• Eliminate humidity and frost within the system to prevent sample contamination.

Overview of ATS Solution to Meet Design Goals

The solution ATS engineered consisted of both convection and conduction cooling.  A reservoir holds the cooling medium, tissues are loaded in the medium through an opening in the top and a duct cycles cool air over the top of the samples to maintain temperature and humidity requirements.

As seen in the following photo, the system consisted of:

• Coring machine
• Tissue sample loading area
• Duct to circulate cool air
• Reservoir for cooling medium

Figure 1. Prototype sample created by ATS engineers for Harvard Medical School laboratory.

Conduction Cooling Design

The tissue sample is loaded into a removable aluminum cassette that is tightly fit into a cassette receiver, which contacts the cassette on five sides to allow for conduction cooling. The receiver is then lowered into a reservoir containing a slurry of dry ice and ethyl alcohol that maintains a constant temperature until the dry ice evaporates. The reservoir is double-walled and insulation is used to extend the evaporation time of the dry ice.

The receiver has fins drawing heat down from the base of the cassettes, based on ATS heat sink architecture that it has used to create industry-leading products such as the maxiFLOW™ heat sink, and ensuring contact with the slurry for a longer period of time.

Through CFD analysis and laboratory testing, it was determined that the fins extending into the fluid maintained the critical temperature below the minus 70 degrees Celsius threshold for 9.75 hours.

Using analytical modeling, part of the ATS 3-Core Design Process, ATS determined that the optimal number of fins in the cassette receiver would be 10. Further testing using thermal couples demonstrated that there was a 2.5-degree difference between the coldest points at the bottom of the fins and the tissue samples in the cassette. This showed that the design managed the conduction resistance successfully.

Figure 2. Testing with thermal couples demonstrated that the temperature difference between the bottom of the fins and the top of the cassette was 2.5 degrees, which was a successful design.

Figure 3. Using analytical modeling [a heat sink calculation similar to that used in other electronics industries] ATS determined that the optimal number of fins was 10.

Convection Cooling Design

Conduction cooling was only part of the solution. There was also the issue of maintaining the temperature on the top of the samples and ridding the environment of humidity from the ambient air in the lab. ATS engineers designed a convection cooling system to fulfill this requirement.

A heat exchanger was placed with one side in the dry ice and alcohol slurry and the other side extending into a duct to cool the air passing over it. This utilizes the same cooling medium for both convection and conduction to ensure there is no temperature differential throughout the sample and that the sample is as isothermal as possible.

Air is pushed by a Sanyo Denki twin blade fan, which was tested at a lower temperature of minus 80 degrees Celsius, through a duct and into the heat exchanger. The heat exchanger forms a thermal link between the air in the duct and the slurry mixture and its double-sided fins give it optimal pressure drop and thermal resistance characteristics. Through CFB and analytical testing, it was determined that 10 fins was the correct balance between surface area and pressure drop for the exchanger.

From the heat exchanger the air moves through the ducts and into a diffuser at the top of the system that spreads it over the sample creating a barrier between the tissue and the ambient environment of the lab so moisture and heat are not transferred in.

Testing the initial design with an array of thermocouples and ATS Candlestick Sensors with the ATVS-2020, ATS engineers determined there was too much mixing between the air flowing over the samples and ambient air. The diffuser was redesigned with a new connection to the duct and an optimized outlet radius.

In the ducts, a molecular sieve desiccant in a monolith honeycomb structure was used to reduce the dew point of the air to minus 84.4 degrees Celsius – well below the minus 72 degrees of the air in the duct.

Figure 4. Initial testing led to a redesign of the diffuser to prevent ambient humidity mixing with the air over the tissue samples.

Final Conclusions

In the final testing of the Frozen Tissue Microarrayer System, using thermocouples and ATS Candlestick Sensors with the ATVS-2020, the tissue temperature stayed constant over the six-hour period required and well below the minus 70 degrees Celsius threshold. In fact, testing determined that the tissue temperature remained below the threshold for nearly eight hours before it warmed beyond a usable temperature.

The system was a success and met the original design objectives of the customer and would work for the length of time that was required.

Figure 5. The final testing showed that the ATS design kept tissue temperature (shown in blue in the graph above) below the minus 70 degrees Celsius threshold for more than the required six hours.

The process of designing the Frozen Tissue Microarrayer demonstrated that the classic laws of thermodynamics utilized in electronics cooling can be applied when designing thermal solutions for the medical industry. Fin efficiencies, heat sink optimizations, and pressure drop calculations are standard regardless of the application.

Although unique challenges are presented in the medical industry (such as tighter temperature goals, isothermal surfaces, and repeatability), it demonstrates that thermal solutions should be considered earlier in the design process to incorporate them into overall system as much as possible.

The experts at ATS incorporated traditional thermal calculations, including its leading-edge heat sink technology, and successfully adapted them for a medical application, providing Harvard Medical School with a new apparatus that meets the strict requirements for testing tissue samples.

Visit www.qats.com, call 781-769-2800 or email us at [email protected] to learn more about ATS and its Thermal Management Analysis and Design Services.

Advanced Thermal Solutions, Inc.
Case Study: Thermal Management in Medical Diagnostic Equipment
DRAFT – August 2016

ATS Case Study: Thermal Management in Medical Diagnostic Equipment

Medical diagnostic equipment, including MRI scanners or EKG machines, poses similar thermal challenges as other electronics, including telecommunications, retail, and consumer. But medical diagnostic equipment also presents unique design issues that must be considered.

From isothermal and cyclic temperature demands to the necessity of repeatability, which ensures accuracy, to patient safety and comfort, a number of factors have to be accounted for in a design.

Experts from Advanced Thermal Solutions (ATS), a leading-edge engineering and manufacturing company focused on the thermal management of electronics, were faced with those issues when tasked by Harvard Medical School to design a cooling system for the analysis and observation of tissue samples in a laboratory setting.

ATS engineers were tasked with solving the following problem and design goals in the Harvard Medical School project:

• Provide long-term temperature control for an embedded tissue sample.
  • The tissue is embedded in an optimum cutting temperature (OCT) fluid
    • The OCT would hold the tissue stationary.
    • OCT allows sample to be cored for analysis.
  • Constant temperature must be maintained through the work day.
  • Repeatable temperature.
  • Allows the sample to be used in a milling machine.

The design goals from Harvard also included:

• Create a cooling system to maintain tissue samples below minus 70 degrees Celsius for six hours.
• Ensure operator visibility of the samples.
• Eliminate humidity and frost within the system to prevent sample contamination.

Overview of ATS Solution to Meet Design Goals

The solution ATS engineered consisted of both convection and conduction cooling.  A reservoir holds the cooling medium, tissues are loaded in the medium through an opening in the top and a duct cycles cool air over the top of the samples to maintain temperature and humidity requirements.

As seen in the following photo, the system consisted of:

• Coring machine
• Tissue sample loading area
• Duct to circulate cool air
• Reservoir for cooling medium

Figure 1. Prototype sample created by ATS engineers for Harvard Medical School laboratory.

Conduction Cooling Design

The tissue sample is loaded into a removable aluminum cassette that is tightly fit into a cassette receiver, which contacts the cassette on five sides to allow for conduction cooling. The receiver is then lowered into a reservoir containing a slurry of dry ice and ethyl alcohol that maintains a constant temperature until the dry ice evaporates. The reservoir is double-walled and insulation is used to extend the evaporation time of the dry ice.

The receiver has fins drawing heat down from the base of the cassettes, based on ATS heat sink architecture that it has used to create industry-leading products such as the maxiFLOW™ heat sink, and ensuring contact with the slurry for a longer period of time.

Through CFD analysis and laboratory testing, it was determined that the fins extending into the fluid maintained the critical temperature below the minus 70 degrees Celsius threshold for 9.75 hours.

Using analytical modeling, part of the ATS 3-Core Design Process, ATS determined that the optimal number of fins in the cassette receiver would be 10. Further testing using thermal couples demonstrated that there was a 2.5-degree difference between the coldest points at the bottom of the fins and the tissue samples in the cassette. This showed that the design managed the conduction resistance successfully.

Figure 2. Testing with thermal couples demonstrated that the temperature difference between the bottom of the fins and the top of the cassette was 2.5 degrees, which was a successful design.

Figure 3. Using analytical modeling [a heat sink calculation similar to that used in other electronics industries] ATS determined that the optimal number of fins was 10.

Convection Cooling Design

Conduction cooling was only part of the solution. There was also the issue of maintaining the temperature on the top of the samples and ridding the environment of humidity from the ambient air in the lab. ATS engineers designed a convection cooling system to fulfill this requirement.

A heat exchanger was placed with one side in the dry ice and alcohol slurry and the other side extending into a duct to cool the air passing over it. This utilizes the same cooling medium for both convection and conduction to ensure there is no temperature differential throughout the sample and that the sample is as isothermal as possible.

Air is pushed by a Sanyo Denki twin blade fan, which was tested at a lower temperature of minus 80 degrees Celsius, through a duct and into the heat exchanger. The heat exchanger forms a thermal link between the air in the duct and the slurry mixture and its double-sided fins give it optimal pressure drop and thermal resistance characteristics. Through CFB and analytical testing, it was determined that 10 fins was the correct balance between surface area and pressure drop for the exchanger.

From the heat exchanger the air moves through the ducts and into a diffuser at the top of the system that spreads it over the sample creating a barrier between the tissue and the ambient environment of the lab so moisture and heat are not transferred in.

Testing the initial design with an array of thermocouples and ATS Candlestick Sensors with the ATVS-2020, ATS engineers determined there was too much mixing between the air flowing over the samples and ambient air. The diffuser was redesigned with a new connection to the duct and an optimized outlet radius.

In the ducts, a molecular sieve desiccant in a monolith honeycomb structure was used to reduce the dew point of the air to minus 84.4 degrees Celsius – well below the minus 72 degrees of the air in the duct.

Figure 4. Initial testing led to a redesign of the diffuser to prevent ambient humidity mixing with the air over the tissue samples.

Final Conclusions

In the final testing of the Frozen Tissue Microarrayer System, using thermocouples and ATS Candlestick Sensors with the ATVS-2020, the tissue temperature stayed constant over the six-hour period required and well below the minus 70 degrees Celsius threshold. In fact, testing determined that the tissue temperature remained below the threshold for nearly eight hours before it warmed beyond a usable temperature.

The system was a success and met the original design objectives of the customer and would work for the length of time that was required.

Figure 5. The final testing showed that the ATS design kept tissue temperature (shown in blue in the graph above) below the minus 70 degrees Celsius threshold for more than the required six hours.

The process of designing the Frozen Tissue Microarrayer demonstrated that the classic laws of thermodynamics utilized in electronics cooling can be applied when designing thermal solutions for the medical industry. Fin efficiencies, heat sink optimizations, and pressure drop calculations are standard regardless of the application.

Although unique challenges are presented in the medical industry (such as tighter temperature goals, isothermal surfaces, and repeatability), it demonstrates that thermal solutions should be considered earlier in the design process to incorporate them into overall system as much as possible.

The experts at ATS incorporated traditional thermal calculations, including its leading-edge heat sink technology, and successfully adapted them for a medical application, providing Harvard Medical School with a new apparatus that meets the strict requirements for testing tissue samples.

Advanced Thermal Solutions, Inc.
Case Study: Thermal Management in Medical Diagnostic Equipment
DRAFT – August 2016

ATS Case Study: Thermal Management in Medical Diagnostic Equipment

Medical diagnostic equipment, including MRI scanners or EKG machines, poses similar thermal challenges as other electronics, including telecommunications, retail, and consumer. But medical diagnostic equipment also presents unique design issues that must be considered.

From isothermal and cyclic temperature demands to the necessity of repeatability, which ensures accuracy, to patient safety and comfort, a number of factors have to be accounted for in a design.

Experts from Advanced Thermal Solutions (ATS), a leading-edge engineering and manufacturing company focused on the thermal management of electronics, were faced with those issues when tasked by Harvard Medical School to design a cooling system for the analysis and observation of tissue samples in a laboratory setting.

ATS engineers were tasked with solving the following problem and design goals in the Harvard Medical School project:

• Provide long-term temperature control for an embedded tissue sample.
  • The tissue is embedded in an optimum cutting temperature (OCT) fluid
    • The OCT would hold the tissue stationary.
    • OCT allows sample to be cored for analysis.
  • Constant temperature must be maintained through the work day.
  • Repeatable temperature.
  • Allows the sample to be used in a milling machine.

The design goals from Harvard also included:

• Create a cooling system to maintain tissue samples below minus 70 degrees Celsius for six hours.
• Ensure operator visibility of the samples.
• Eliminate humidity and frost within the system to prevent sample contamination.

Overview of ATS Solution to Meet Design Goals

The solution ATS engineered consisted of both convection and conduction cooling.  A reservoir holds the cooling medium, tissues are loaded in the medium through an opening in the top and a duct cycles cool air over the top of the samples to maintain temperature and humidity requirements.

As seen in the following photo, the system consisted of:

• Coring machine
• Tissue sample loading area
• Duct to circulate cool air
• Reservoir for cooling medium

Figure 1. Prototype sample created by ATS engineers for Harvard Medical School laboratory.

Conduction Cooling Design

The tissue sample is loaded into a removable aluminum cassette that is tightly fit into a cassette receiver, which contacts the cassette on five sides to allow for conduction cooling. The receiver is then lowered into a reservoir containing a slurry of dry ice and ethyl alcohol that maintains a constant temperature until the dry ice evaporates. The reservoir is double-walled and insulation is used to extend the evaporation time of the dry ice.

The receiver has fins drawing heat down from the base of the cassettes, based on ATS heat sink architecture that it has used to create industry-leading products such as the maxiFLOW™ heat sink, and ensuring contact with the slurry for a longer period of time.

Through CFD analysis and laboratory testing, it was determined that the fins extending into the fluid maintained the critical temperature below the minus 70 degrees Celsius threshold for 9.75 hours.

Using analytical modeling, part of the ATS 3-Core Design Process, ATS determined that the optimal number of fins in the cassette receiver would be 10. Further testing using thermal couples demonstrated that there was a 2.5-degree difference between the coldest points at the bottom of the fins and the tissue samples in the cassette. This showed that the design managed the conduction resistance successfully.

Figure 2. Testing with thermal couples demonstrated that the temperature difference between the bottom of the fins and the top of the cassette was 2.5 degrees, which was a successful design.

Figure 3. Using analytical modeling [a heat sink calculation similar to that used in other electronics industries] ATS determined that the optimal number of fins was 10.

Convection Cooling Design

Conduction cooling was only part of the solution. There was also the issue of maintaining the temperature on the top of the samples and ridding the environment of humidity from the ambient air in the lab. ATS engineers designed a convection cooling system to fulfill this requirement.

A heat exchanger was placed with one side in the dry ice and alcohol slurry and the other side extending into a duct to cool the air passing over it. This utilizes the same cooling medium for both convection and conduction to ensure there is no temperature differential throughout the sample and that the sample is as isothermal as possible.

Air is pushed by a Sanyo Denki twin blade fan, which was tested at a lower temperature of minus 80 degrees Celsius, through a duct and into the heat exchanger. The heat exchanger forms a thermal link between the air in the duct and the slurry mixture and its double-sided fins give it optimal pressure drop and thermal resistance characteristics. Through CFB and analytical testing, it was determined that 10 fins was the correct balance between surface area and pressure drop for the exchanger.

From the heat exchanger the air moves through the ducts and into a diffuser at the top of the system that spreads it over the sample creating a barrier between the tissue and the ambient environment of the lab so moisture and heat are not transferred in.

Testing the initial design with an array of thermocouples and ATS Candlestick Sensors with the ATVS-2020, ATS engineers determined there was too much mixing between the air flowing over the samples and ambient air. The diffuser was redesigned with a new connection to the duct and an optimized outlet radius.

In the ducts, a molecular sieve desiccant in a monolith honeycomb structure was used to reduce the dew point of the air to minus 84.4 degrees Celsius – well below the minus 72 degrees of the air in the duct.

Figure 4. Initial testing led to a redesign of the diffuser to prevent ambient humidity mixing with the air over the tissue samples.

Final Conclusions

In the final testing of the Frozen Tissue Microarrayer System, using thermocouples and ATS Candlestick Sensors with the ATVS-2020, the tissue temperature stayed constant over the six-hour period required and well below the minus 70 degrees Celsius threshold. In fact, testing determined that the tissue temperature remained below the threshold for nearly eight hours before it warmed beyond a usable temperature.

The system was a success and met the original design objectives of the customer and would work for the length of time that was required.

Figure 5. The final testing showed that the ATS design kept tissue temperature (shown in blue in the graph above) below the minus 70 degrees Celsius threshold for more than the required six hours.

The process of designing the Frozen Tissue Microarrayer demonstrated that the classic laws of thermodynamics utilized in electronics cooling can be applied when designing thermal solutions for the medical industry. Fin efficiencies, heat sink optimizations, and pressure drop calculations are standard regardless of the application.

Although unique challenges are presented in the medical industry (such as tighter temperature goals, isothermal surfaces, and repeatability), it demonstrates that thermal solutions should be considered earlier in the design process to incorporate them into overall system as much as possible.

The experts at ATS incorporated traditional thermal calculations, including its leading-edge heat sink technology, and successfully adapted them for a medical application, providing Harvard Medical School with a new apparatus that meets the strict requirements for testing tissue samples.

Visit www.qats.com, call 781-769-2800 or email us at [email protected] to learn more about ATS and its Thermal Management Analysis and Design Services.