Human Body Thermal Model of Thermoelectric Device Implant Power

Client

Biophan Technologies, Inc.

Project Objectives

• Numerically simulate the power generated by an implanted thermoelectric device in the human body
• Determine the overall viability of an implanted thermoelectric device as a power source for medical devices
• Optimize the design and placement of the thermoelectric device in the human body

Summary of Project and Results (Non-Confidential)

• The body section model and thermoelectric device was developed using ANSYS finite element multi-physics software
• A body section mesh was created
  1. Parametric geometries of tissue layers in the section model were created. The tissue layers could then be rapidly modified for different locations of the body, and different body types.
  2. The tissue layers were interfaced to make a body section. The tissues included:
     • Core tissues (lung, abdominal, brain, etc.)
     • Bone, Muscle, Fat, and Skin in that order
  3. A clothing layer was added to the torso, arms, and legs sections
• A thermoelectric device was created
  1. A parametric geometry of a thermoelectric device was created
  2. The thermoelectric device was inserted into the tissues of the body section model
• Heat transfer/heat capacity properties were assigned to the tissues and thermoelectric device
• Heat transfer mechanisms were implemented in the model
  1. Conduction
     • Conduction between the tissues and tissues/thermoelectric device was performed by ANSYS
  2. Circulation System
     • Equations that simulate convective heat transfer between the blood in the arteries and veins to the tissue nodes were applied
     • Artery and vein diameters for each tissue were applied
     • Basal blood flowrates for each tissue were applied
     • The cardiac output and tissue blood flowrates were increased during physical activity
  3. Blood Perfusion
     • Equations at each node that simulate blood perfusion heat transfer were applied. This is the heat transfer that occurs when the blood flows from the arteries through the tissues to the veins.
  4. Metabolic Heat Generation
     • The basal heat generation that occurs in each tissue was applied
     • The heat generation that occurs in muscle tissues during physical activity was applied
• Thermoregulatory control equations were implemented
  1. Equations that control the vaso-constriction/dilation of skin tissue blood vessel diameters were applied
     • This modulates the circulation system heat transfer and blood perfusion heat transfer that occurs in the skin tissues when the body temperature rises or falls
  2. Sweat generation on the skin surface nodes was implemented
     • These equations describe the flowrate of sweat that occurs on the skin surface nodes when the body temperature rises
  3. Shivering heat generation in the muscle tissues was implemented
     • These equations describe the generation of heat that occurs via shivering in the muscle tissues when the body temperature drops
• External environment heat transfer mechanisms were implemented
  1. The external environment conditions that control heat loss from the body section model were air velocity, ambient temperature, relative humidity, and incident radiation
  2. Convection heat transfer between the skin surface nodes and external environment
  3. Radiation heat transfer between the skin surface nodes and external environment
  4. Conduction heat transfer between the skin surface nodes and an external solid material, if needed
  5. Sweat evaporation heat transfer between the skin surface nodes and external environment
     • The rate of sweat evaporation was determined by the temperature of the skin, ambient air temperature, and relative humidity
     • The rate of sweat evaporation was always be limited by the rate of generation of sweat at the skin surface nodes
• The body section model was validated
  1. The body section model was run for a few standard metabolic rates and environmental conditions
  2. The model results were compared with published experimental data
  3. Corrections to the model were made
• The thermoelectric device power output was modeled
  1. The thermoelectric performance characteristics of the thermoelectric device was obtained
  2. A model of the power output of the device for a given temperature of the device, and temperature difference across the device was developed
• Simulations and analysis of the thermoelectric device power output were performed
  1. Optimal Tissue Location
     • The power generated by the thermoelectric device at each tissue interface within the body section model was simulated
     • The tissue location of maximum power was determined
  2. Optimal Body Location
     • The body section model was run for three different locations around the body and the power generated by the device was measured
     • The thermoelectric device was placed at the tissue location of maximum power
  3. Activities-Metabolic Rates
     • The model was run for three activity levels
     • Resting
     • Walking
     • Running
  4. Body Types
     • The model was run for four body types
     • Average
     • Overweight (Thick fat layer)
     • Thin (Thin fat layer)
     • Muscular (Thick muscle layer)
  5. External Environment Conditions
     • The model was run with these ambient external environment conditions
     • Hot (Ambient Temperature = 35 °C)
     • Normal (Ambient Temperature = 25 °C)
     • Cool (Ambient Temperature = 15 °C)
     • Cold (Ambient Temperature = 0 °C)
     • High humidity
     • Low humidity
  6. Clothing
     • The model was run with two types of clothing
     • Thin clothing (Ex. shirt, pants)
     • Thick clothing (Ex. coat, sweater)