14 Questions
Which of the following modes of heat transfer does not require a material medium?
Radiation
What is the working equation for conduction?
$Q = dR_{th} \frac{T_1 - T_2}{\kappa A}$
What material has the highest thermal conductivity?
Copper
What is the qualitative behavior of a hot arm actuator based on the simplified lumped element model?
Energy conversion from thermal to mechanical mode
What is the equation for convection heat transfer between a moving fluid and a surface at temperature T1 and T2?
$Q = hA(T1 - T2)$
For radiation, what is the equation for heat transfer from a perfect blackbody surface area at Ts to the surroundings at temperature T?
$Q = \epsilon\sigma A(T^4 - T_s^4)$
What is the equation for heat transfer due to convection from a surface at temperature Th to the surroundings at temperature T∞?
$Q_{conv} = hA(Th - T_\infty)$
What is the formula for the voltage drop across the hot arm (eh) in terms of input voltage (e), resistivity of the actuator material (ρ), and its geometry?
$eh = \frac{e \rho}{L / Ah + \rho (L / Ac)}$
What is the equation for thermal strain (ε) in the hot arm of a thermal actuator when heated from temperature T∞ to Th?
$\epsilon_h = \alpha T(Th - T_\infty)$
What is the additional piece of strain (ε extra) experienced by the hot arm due to being hooked to the cold arm?
$\epsilon_h = \alpha T(Th - T_\infty) + \epsilon_extra$
What is the formula for finding the temperature Th of the hot arm in terms of input voltage (e), resistivity of the actuator material (ρ), its geometry, and heat transfer coefficient (h)?
$Th = \frac{2hpAh}{e} + T_\infty$
In what mode does a small object completely surrounded by a large surface experience heat transfer?
Radiation
What phenomenon induces bending moment in the cold arm of a thermal actuator?
Differential thermal expansion
What physical concept does the equation $Q = hA(T1 - T2)$ represent?
Fourier's law of heat conduction
Test your knowledge on thermal actuators and heat transfer modes. Understand the qualitative and quantitative descriptions of the three modes of heat transfer and the behavior of a hot arm actuator based on a simplified lumped element model.
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