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The final design consists of two main components: the Refrigeration System and Water Bladder Vest
Refrigeration System
Refrigeration System
4-stage refrigeration system
Primary Components:
Condenser
Expansion valve
Evaporator
Compressor
Auxiliary Components:
Sight Glass
Filter Dryer
Compressor Control Board
How It Works (Primary Components)
Stage 1-2: Compressor compresses the gas and increases its pressure. The compression process is an isentropic process, and the refrigerant is currently at a superheated gas state.
Stage 2-3: Fan blows air through the condenser, and the forced convection removed heat from the refrigerant inside the coil. Refrigerant is cooled to a saturated liquid.
Stage 3-4: the expansion valve depressurizes the liquid refrigerant and the refrigerant temperature decreases as well. Refrigerant temperature is low enough to cool circulating water down to required temperature.
Stage 4-1: Refrigerant passes through one side of the evaporator, whereas circulating water passes through the other side of the evaporator to be cooled. Refrigerant is heated to a saturated gas (superheated gas for practicality), and is ready to restart the cycle.
Operating Environments
Ambient Temperature TAmb=110℉
Condensing Temperature TCond=130℉
Evaporator Temperature TEvap=60℉ (Approximately 7℉ superheat is added in actual device for reliability and practicality)
Auxiliary Components
Sight glass: Offer engineers and technicians insight to the condition of refrigerant.
Filter dryer: Remove additional moisture and potential foreign objects
Compressor control board: Provide compressor power, speed control, and overheat shutdown protection. Offer current consumption reading
Fan: Create forced convection to remove heat from the condenser.
All electrical systems are connected to fuses for overcurrent protection.
Water Bladder
Water Bladder
Design was inspired by the usage of a water bladder
Increases surface area in contact with body.
Greatly decreases time required to manufacture
Requires access to Radio Frequency (RF) welding machine
Sponsor decided to outsource manufacturing to SealWerks
Optimize design for outsourced manufacturing using SolidWorks Fluid Simulation
Channel Inner diameters are varied to maximize the flow distribution throughout the vest
Water Bladder Proof of Concept
Water Bladder Proof of Concept
Used 0.6mm plastic drop sheets
Channels are welded into the plastic sheets using a hand soldering iron
Proved the viability of having bladders circulate water around the torso
design focuses on replicating the optimized design from SolidWorks fluid simulation
channel sizes vary to increase flow at the bottom
The vest Is comprised of two bladders Identical bladders that cover the front and back of the torso
Summary of Performance
Summary of Performance
Preliminary testing shows the cooling capacity of the refrigeration system is 451W
Inlet and Outlet Water Temperatures: Tw,in=40.5℃, Tw,out=30.5℃, ΔT=Tw,in-Tw,in=10.0℃
Mass Flow Rate: ṁ=10.8g/s
Cooling Capacity: Q̇in=Cp*ṁ*ΔT=4.18*10.8*10.0=451.44W
Power Consumption is approximately 128W
Compressor Voltage & Current: Vcompressor=27.7V Acompressor=4.1A
Fan Voltage & Current: Vfan=9.0V Afan=1.64A
Total Power Consumption: Ptotal=Pcompressor +Pfan =27.7*4.1 +9.0*1.64 =128.33W
Coefficient of Performance is approximately 3.5
COP=Q̇in/Ptotal=451.44/128.33=3.518
Cooling vest performance, User test 1. Subject is at rest in room temperature.
Cooling vest performance, User test 2. Subject is at rest in room temperature in the beginning, then room heater is turned on to 90℉ ambient temperature
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