Turbine Blade De-Icing with Microwaves - Test

Benefits

Increased blade life & efficiency, safer operation of cold weather turbines; decrease turbine down‐time

Purpose

Investigate the use of microwave de‐icing technology to enhance the performance of wind turbine blades operating in cold environments

Background and Objectives

Spring 2015 Feasible Study

• Deicing requires: surface heat flux of 1.4kW/m2 ,20‐25 minutes of test period and microwave interactive material
• Options: horn antenna and slotted waveguide antenna at 2.45 or 5.8 GHz

Semester Objectives

• Design and test blade‐compatible microwave susceptor coating layer
• Demonstrate effective microwave delivery at 2.45GHz
• Build a microwave laboratory test facility and collect deicing data

Microwave Absorbing Materials

Problem

• G10/FR4 and Ice are transparent to incident microwave radiation

Solution

• Susceptor coating on blade surface

Requirements

• Maximize conversion of absorbed microwave radiation to heat
• Withstand cyclic thermal stress
• Resistant to UV degradation

Comparison of Coating Methods

	Uniform Surface?	Easy to apply to blade?	Resistant to degradaton?	%Absorption?	Rate of heating	Max temp
Sputtered AI Film	Yes	No	No	Up to 50%	< 3 min	200 °C
Absorptive Paint	Yes	Yes	Yes	Up to 40%	N/A	900 °C
Dielectric Coating	Yes	Yes	Yes	Up to 99%	< 1 min	800-950 °C

Microwave System

Microwave generation:

• Operates at 2.45 GHz
• Microwave Power – ~ 1 kW : 60% efficient
• Cheap – around $50
• Easy to drive – circuits already exist
• Air cooled

Microwave delivery options:

Type	SWA	Horn Antenna
Profile	Low (planar form)	High
Manufacturing	Good	OK
Bandwidth	Narrow	Broad
Gain	15dBi - 20dBi	15dBi - 30dBi
Pattern	Highly directional	Moderately directional

Practical Application

Tower Configuration

• Arrays of SWAs
  • 42 SWAs needed for gain of 9 dBi
• Arrays of horns
  • 110 horns needed for gain of 10 dBi
  • 40 horns needed for gain of15 dBi

Blade Configuration

• SWA incorporated inside the blade

Microwave Deicing Test Results

Results:

• Ice melted within 30 mins
• Test bed ambient temperature remained below freezing