Heat pipes are devices used to transfer heat over a certain distance. A typical heat pipe looks like a metal rod, but modern versions, which are used for example to cool the hottest part of a phone, have a flat geometry. The principe of heat pipes is also considered in aerospace research [66]. Here, we will examine a simple model to understand the principle of a heat pipe (Fig. 6.17). The pressure difference Δp is modelled in a linear approximation, with Δp = R_p Ω, where Ω is the rate of substance flowing down the pipe. The system is considered in a stationary state, so that the heat transfer P_Q is the same (in absolute value) on both sides. The heat of evaporation ℓ_ℓg is given and assumed independent of temperature. The temperature difference ΔT = T₊ − T₋ is assumed small in order to simplify the calculations. Neglect the molar volume of the liquid v_ℓ compared to that of the vapour v_g and treat it as an ideal gas. Express the heat transfer P_Q as a function of the temperature difference ΔT.

Figure 6.17

Transcribed Image Text:

Pa P T T+ Pa p+Ap