Portable Body Temperature Regulator

Inspiration

Around the world, public servants and laborers spend hours in extreme environments to fulfill their daily responsibilities. With very few ways to effectively regulate body temperature under unwieldy clothing, it became a goal of our senior design team to develop a minimally invasive temperature regulation system that can keep users cool in the summer, warm in the winter, and focused on the task at hand.

To help facilitate the concept generation process, different heat transfer methods were researched to explore potential solutions. While passive designs were initially considered due to their simplicity, it was determined that an active design featuring a 6-channel liquid heat exchanger, 4 thermoelectric plates, and controls system would be the best at meeting desired performance targets.

Design

As one of the design leads for the team, I was tasked with creating CAD models and engineering drawings for each subassembly. An overview of the design process is provided in the following section.

Heat Exchanger Subassembly

The heat exchanger subassembly features a C-shaped channel that routes air through a set of 17 fin heat sinks via a 27 CFM fan. To make the product as portable as possible, this design was chosen due to its compact nature, fully insulated enclosure, and strategically placed air passages.

Controls Subassembly

The controls subassembly consists of two components. The first is an electronics box that houses a microcontroller, relay, buck converter, and recessed toggle switch. The second is a hand held controller that features a pair of power switches and a temperature dial.

Heat Exchanger

To arrive at the optimized design layout, the heat exchanger underwent a couple design revisions during initial testing and analysis. To maximize the rate of heat transfer between the thermoelectric plates and the water, the surface area to mass ratio of the heat exchanger was increased by removing unnecessary material around the fasteners, increasing the number of channels from four to six, and reducing the wall thickness of the channels.

Original Design

Iterated Design

Engineering Drawings

Analysis

In order maximize the overall performance of the heat exchanger, a CFD analysis was conducted to improve the flow characteristics of the water. As shown in the image below, the original heat exchanger suffers from non-uniform water flow through the channels. To alleviate this issue, the cross sectional area of the channel was reduced and the geometry of the fin array was modified to increase the velocity of water flowing through the heat exchanger. Although this did not increase the Reynolds number enough to improve heat transfer via turbulent flow, it did increase the total heat transfer area from 18.3 in^2 to 29.3 in^2. For future design iterations, turbulent flow can be induced a number of ways. One way to accomplish this is by increasing the roughness of the channels via trip strips. Another way to accomplish this is by reducing frictional losses present in the tubing system.

[in/s]

Original Design

Re = 362

SA = 18.3 in^2

Iterated Design

Re = 427

SA = 29.3 in^2

Manufacturing

In addition to creating many of the CAD models and engineering drawings for the project, I was responsible for manufacturing a number of custom components for the final prototype. An overview of these contributions is provided in the following section.

Heat Exchanger

To manufacture the heat exchanger, a 3-axis CNC machine was used to cut each plate out of 6061 aluminum. In an effort to maximize surface area and remove excess material, 0.205" wide channels and 0.05" thick walls were created by using a 1/8" carbide endmill.

Fully Assembled Prototype

Outcome

Results

To gauge the effectiveness of the cooling mode, a test was conducted with ice water and compared to a control test conducted with the thermoelectric plates turned off. As shown by the graph, the ice water was maintained at a lower temperature with additional cooling supplied by the heat exchanger.

Heating

Cooling

Page updated

Google Sites

Report abuse