Development of a Liquid-Trap Heat Pipe Thermal Diode

Abstract

An all-aluminum axial-groove liquid-trap heat pipe diode, 470 mm long and 10 mm o.d., has been developed with a forward-mode performance of nearly 90 Wm, when ammonia is used as the working fluid at 20°C. The diode is bendable, of simple design, and of reliable performance. A mathematical model, based on an energy balance for evaporator and trap, has been developed for predicting the transient shutdown of the diode. Theroretical predictions and experimental results are in good agreement. The time for complete shutdown of the diode is on the order of 20 min. The respective shutdown energy is about 4 Wh. A reverse-mode heat flow of about 1.5 W has been measured. Thereby, a turndown ratio of about 300 has been established.

Thermal diodes, regulators, and switches: Physical mechanisms and potential applications

“…Many different heat pipe thermal diode designs with asymmetric shapes have been demonstrated (including the liquid trap diode, the liquid blockage diode, and the gas blockage diode), and these designs have been discussed in textbooks. 175,178 One example that provides a sense of heat pipe thermal diode performance is the liquid trap diode developed by Groll et al 179 This diode has an asymmetric shape, with a liquid trap appended on one end of a traditional heat pipe. In the forward mode, the end of the heat pipe with the liquid trap is heated, the liquid in the liquid trap evaporates, and the thermal diode functions as a typical heat pipe.…”

Bridging‐Droplet Thermal Diodes

“…[40] While a self-assembled thiol monolayer may not have the exact same properties as the bulk liquid, this is nonetheless extremely close to a typical value of k c ≈ 0.2 W m −1 K −1 used to model hydrophobic monolayers in general. [38] The expression for h i is equivalent to h e from Equation (5), except that now the temperature corresponds to T steam . Using Equations (4)- (8), theoretical values for h f were obtained corresponding to each experimental value for T H and T C (Figure 4a).…”

“…The term “diode” is derived from the greek roots “di,” meaning “two,” and “ode,” meaning “path.” A thermal diode is therefore a device that conducts heat more efficiently along one path (forward mode) compared to the opposite path (reverse mode). [ 1 ] Thermal diodes are desirable for the smart thermal management of electronics packaging [ 2–4 ] or spacecraft, [ 5,6 ] as they can effectively dump onboard heat while also shielding from external heat sources. The effectiveness of a thermal diode is quantified by its diodicity (also known as the rectification coefficient), which compares the effective thermal conductivity in the forward mode ( k f ) to that in the reverse mode ( k r ) [ 7 ] : …”

Thermal diode in gas-filled nanogap with heterogeneous surfaces using nonequilibrium molecular dynamics simulation

“…15 The recent emergence of nanotechnology has led to experiments involving the use of asymmetric carbon nanotube, R max $ 0.07; 6 asymmetric graphene oxide, R max $ 0.25; 16 electrochemically tuned thermal diode material, R max $ 0.5; 17 and asymmetric radiative thermal transport, R max $ 0.11. 9 To improve the relatively low R, liquid-based systems have been employed using nonlinear convection in heat pipes, R max $ 200 18 and 1000 19 or heterogeneous water wettings, R max $ 100 20 and 0.46. 21 However, liquid-based systems result in a relatively slow transient response $10 min, which may limit their performance in some applications.…”