Imagine a handheld air conditioner, resembling a hair dryer, which one could carry around in a handbag or back pack to outdoor activities such as ball games, picnics or for walking about town. This design would enable the user to blow chilled air at the face, collar area or into the top of one’s shirt. Peltier thermoelectric (PTE) coolers have become widely used in portable chillers used in cars, computer microprocessor coolers, etc.
In this application, the PTE device is applied in a handheld blower that runs on rechargeable lithium ion batteries similar to those used in power tools. The blower is folded at the middle on a hinge such that it resembles a hair dryer during operation. The vertical section has a removable battery pack that can be recharged by plugging a cord into the mains or replaced with a freshly charged battery pack. A permanent magnet DC motor, similar to those used in power tools or RC cars, is coupled with a blower fan, to provide fast air flow.
The PTE has a hot and a cold side. The battery pack, the control electronics circuits and the motor are all mounted on heat sinks that are thermally connected to the hot side of the PTE. The electronics consist of a pulse width modulated (PWM) temperature controller, battery charging and monitoring circuits and other circuits.
PTEs require a lot of power and present battery technologies are not developed enough to give long service life in between charging. To increase usage time, several key design elements are chosen. The PWM temperature controllers are more energy efficient than on-off thermostats and ensure longer battery life. The whole device has thermal insulation to ensure that heat is channeled to the PTE. The Li batteries get hot during use and the heat sinks keep them cool and prolong their service.
On the top of the horizontal section is a water-tight compartment with a latched lid where a heat absorbing pad is placed. This may be just a bag of crushed ice, a frozen gel pad similar to the ones used for treating sore muscles, or a specially designed bag of paraffin wax. The latter has very high heat capacity, is harmless to humans, cheaply available and is a good heat absorbing substance that undergoes a phase change, solid to liquid, when heated. This wax is formulated to lower the melting point to about 35 to 40 degree Centigrade. The wax bag is frozen prior to use to prolong service.
The user can carry several wax bags or gel pads in a thermally insulated bag along with recharged batteries for hours of cooling.
Also, the controller has a user selectable function that monitors the battery level and, when it reaches a low level, will switch off the PTE and only enable the motor to run. Thus, the device works as a cool blower when low on battery.