Coil Heating Element Shielding for Accurate Thermostat Sensing
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Solution Overview
Problem
Existing electric coil heating elements face issues with imperfect temperature correlation due to poor contact between the cookware and the coil, leading to premature tripping of bimetallic thermostats, which results in reduced performance and conservative calibrations.
Innovation Solution
The electric resistance heating coil assembly incorporates a spiral wound sheathed heating element with a bimetallic thermostat mounted on a shroud cover, featuring thermal breaks and a heat transfer disk to limit radiative heat transfer and enhance conductive heat transfer, allowing for more accurate temperature measurement and reduced thermostat cycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the thermostat contacts the cookware bottom to improve temperature correlation, then measurement precision improves, but the thermostat is exposed to radiative heat from the coil causing premature tripping
Solution Approach 1:
A heat transfer disk is introduced as an intermediary component between the coil and the thermostat. The disk is positioned to receive conductive heat from the coil while its larger surface area and thermal mass prevent direct radiative heat exposure to the thermostat, allowing accurate temperature sensing without premature tripping
Solution Approach 2:
The shroud cover is designed with differentiated thermal properties: the portion near the coil allows conductive heat transfer to the thermostat, while the portion exposing the thermostat to radiative heat is modified with thermal breaks or insulation to create localized thermal zones that protect the thermostat
2Reliability
If the thermostat is remotely positioned from the cookware, then radiative heat exposure is reduced, but temperature correlation becomes imperfect reducing performance
Solution Approach 1:
The heat transfer disk serves as a mediator that extends the thermal coupling between the coil and thermostat. It conducts heat from the coil surface to the thermostat while physically separating the thermostat from direct radiative exposure, achieving both accurate temperature correlation and reduced radiative heat impact
Solution Approach 2:
The solution moves the thermostat interaction from a direct one-dimensional contact to a two-dimensional heat transfer path through the disk, allowing thermal energy to reach the thermostat through conduction across the disk surface while blocking the direct radiative path
3Use of energy by moving object
If poor contact exists between cookware and coil, then radiative heat transfer increases causing coil sections to glow red hot, but this exposes the thermostat to excessive radiative heat
Solution Approach 1:
The thermal breaks in the shroud cover, which initially seem to reduce heat transfer, actually convert harmful direct radiative heat into beneficial indirect conductive heat transfer through the heat transfer disk, protecting the thermostat while maintaining heating function
Solution Approach 2:
The heat transfer disk acts as a mediator that intercepts radiative heat from the coil and converts it to conductive heat transfer, preventing direct radiative exposure to the thermostat while maintaining thermal coupling for accurate temperature sensing
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design improves the accuracy of temperature measurement and reduces the maximum temperature of internal electrical contacts, enabling the use of lower-cost materials and faster thermostat response times, while maintaining continuous operation even under conditions that would trip other heating elements.
Implementation Method 1
a bimetallic thermostat mounted to a shroud cover and connected in series between a first and second coil section of the spiral wound sheathed heating element
Implementation Method 2
The bimetallic thermostat is spring loaded such that a distal end of the bimetallic thermostat is urged away from a top surface of the spiral wound sheathed heating element
Implementation Method 3
A heat transfer disk is positioned on the bimetallic thermostat at the distal end of the bimetallic thermostat
Implementation Method 4
The shroud cover defines a plurality of thermal breaks around the bimetallic thermostat. The plurality of thermal breaks limits thermal conduction between the shroud cover and the bimetallic thermostat
Implementation Method 5
a spiral wound sheathed heating element having a first coil section and a second coil section
Data Source
AI summary
An electric resistance heating coil assembly includes a spiral wound sheathed heating element having a first coil section and a second coil section. A bimetallic thermostat is connected in series between the first and second coil sections of the spiral wound sheathed heating element. The bimetallic thermostat is spring loaded such that a distal end of the bimetallic thermostat is urged away from a top surface of the spiral wound sheathed heating element. The electric resistance heating coil assembly also includes a shroud cover and a heat transfer disk.