Home - Team 06

UCSD Medical School - Variable Temperature Skin Testing

Sponsored by Dr. Hal Hoffman

Jacob Ayala, Joshua Hsu, Zinan Hu, and Khang Nguyen

Background

     Cold Urticaria is a skin condition that appears after minutes of exposure to cold temperatures. People that suffer from cold urticaria suffer from different symptoms. Typical symptoms of cold urticaria include red itchy welts or swollen skin. For those that have severe cold urticaria, when exposed to the cold, could lead to shock or fainting. For someone who suffers from cold urticaria task like swimming or surfboarding could lead to irritable skin rashes. It's important that people are properly diagnosed for cold urticaria, so they can properly prepare for cold temperatures to avoid irritation, or in the worst cases shock. Typically people are tested for cold urticaria by the ice cube test. This test is done by placing an ice cube on a person's arm for 10 minutes and seeing if that person's skin starts to swell up or develop hives. 

Figure 1: Ice Cube Test with Cold Urticaria Response

    While the ice cube test is used to tell whether or not a person has cold urticaria, it's a poor indicator of severity. It's critical to people with the condition to know what temperatures are safe to go outside and how to prepare for them. A device that could sit on a person's body that could test for the condition at different temperatures would be useful in determining the severity of the condition.

    A previous MAE 156B team worked on this device. They were successful in building the a device that could test for different temperatures, however there were some glaring issues with the design. For example, the device had a hard time reaching the desired temperatures of 0°C, the overall device was difficult to transfer for one person, the contact with the skin was sub-optimal, and after 6 months, the device stopped working. The device was repaired, but after four months it stopped working again. The sponsor would like another device to work just as the previous MAE 156B team's with added requirements which can be found below in the objectives section. 

Statement of Requirements 

• • Be small enough to be comfortably worn on a child’s forearm

  • Improved robustness for higher reliability

  • Able to be put on other body parts

  • Be able to maintenance within 0.5 degree difference for at least 10 minutes

  • Wide temperature variability, from 0°C-20°C

  • Preset programs for quick application of common configurations 

  • Compact enough to be carried by a single person from room to room

Description of final design

    The final design has eight temperature stages with range from 0 - 20°C. Every temperature stage consists of one Peltier device controlled independently. A water block is designed to cool down the hot side of the Peltier by the water pumped from reservoirs. A skin applicator connects to the cold side of the Peltier device to contact the skin closely. The applicator contains a thermistor which returns the current temperature to temperature controller. The temperature controller consists of 3 Arduino board, LCD screen showing the temperature and timing, and buttons to adjust the setting. Peltier devices can heat and cool based on the polarity of the current. Moreover, an IOS app is included to help doctors adjust the temperature easily through their phones.

Figure 2: Final Assembly 

Key Component: Peltier Device

    One of the most important components for this device is the Peltier device as it is responsible for cooling the skin down to low temperatures. A Peltier device is a solid-state heat pump that transfers heat from one side to the other utilizing electrical current. The direction of the current applied to the device determines which side pumps heat. The reason Peltier devices were chosen for this application was due to the simplicity of temperature control as the amount of current dictates how much heat will be pumped and how compact Peltier devices are. The specific Peltier devices that were used in this project were the CUI Devices CP30239H. In order to have eight different testing regions, eight Peltier devices were in conjunction with a temperature controller in order to provide independent temperature control for each of the eight testing regions.

Figure 3: Peltier Device

Key Component: Water Cooling Loop

    In order to ensure performance of the Peltier devices, the heat from the hot side must be rejected effectively. In the previous MAE 156B team's design, air cooling was utilized which was not sufficient in cooling to allow the Peltier devices to reach 0°C. Because of this, liquid cooling was chosen due to its higher effectiveness compared to air cooling. The water cooling loop in the final design utilizes a water block, pump, and reservoir. The job of the water block is to act as the interface between the hot side of the Peltier devices and the cold water. In the case of this liquid cooling system, there is no active cooling as the tests that will be administered with this device will be quite short, usually lasting only 10 minutes. Instead of active cooling, the reservoir will be large enough to accommodate 4.73 liters which will be more than enough to keep the Peltier devices cool enough to function for the duration of a test as the amount of water needed in a worst case scenario was calculated to be around 1.064 liters. The water block was milled out of aluminum and features a single U-channel for the water to flow through which is then sealed by a O-ring gasket. 

Figure 4: Water Cooling Loop

Key Component: PID Temperature Controller

    The role of the temperature controller is to control the temperature of each of the eight Peltier devices independently. For the final design of this device, two Arduino devices were utilized in order to control the Peltier devices through the PWM output and the use of PID control. PID control, or proportional-integral-derivative control, utilizes three constants: proportional, integral, and derivative in order to apply a correction to the error based on the difference between the set point and the measured values. Utilizing this control method, temperatures were able to reach and stay within ±2°C of the set temperatures for each of the eight Peltier devices.