## 2 Design, Working Fluid, and Experimental Apparatus of the MF-AHPA
### Experimental Apparatus and Processes
#### 2.3.3 Experimental System to Characterise Heat Pipe Thermal Resistance  
The thermal resistance of the MF-AHPA was experimentally evaluated with various inclination angles in the test setup, as shown in Figure 5. The lengths of the evaporation section, adiabatic section, and condensation section are specified in Figure 5. The experiment was operated at an ambient temperature of 28 \({}^{\circ}\)C without forced air convection. The specifications of the instruments used in this system are listed in Table 4.  
The experimental system consisted of three sub-systems:  
1. Heating sub-system  
Figure 4: The test setup to evaluate heat pipe temperature uniformity.  
Figure 3: The test setup to characterise heat pipe start-up performance.  
A constant 220 V voltage was provided by a TND-1500 VA automatic AC voltage stabiliser with an AC voltage regulator. The evaporation section was heated by a pair of copper blocks. Input heat was measured by a TOS120A power meter. To reduce the heat loss, both the evaporation and adiabatic sections were well insulated. The evaporation section was insulated by three-layer fiberglass insulations with aluminium foil as the surface. The insulation had a total thickness of 15 mm and an exposed surface area of 0.07 m\({}^{2}\). With a fiberglass thermal conductivity of 0.03 W/m\(\cdot\)K, the heat loss of the insulation was estimated to be between 2.8 W and 4.6 W in different operating temperatures ranging from 48 \({}^{\circ}\)C to 65 \({}^{\circ}\)C.  
2. Cooling sub-system  
A thermostatic tank provided constant-temperature water of 45 \(\pm\) 0.1 \({}^{\circ}\)C to cool the condensation section. The flow rate of the cooling water was carefully controlled by a float flowmeter to stabilise the condenser section temperature.  
3. Data acquisition sub-system  
As shown in Figure 5, six Pt100 type resistance thermometers were used to measure the evaporator section temperature (T\({}_{\text{E1}}\), T\({}_{\text{E2}}\), T\({}_{\text{E3}}\)) and condenser section temperature (T\({}_{\text{C1}}\), T\({}_{\text{C2}}\), T\({}_{\text{C3}}\)). All of the temperatures were automatically monitored and collected by an Agilent 34970A and a personal computer (PC). Experimental data were recorded for 3 min at a sampling rate of 1 Hz.  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Device** & **Number** & **Error** & **Range** & **Model** \\ \hline Thermostatic tank & 1 & \(\pm\)0.1 \({}^{\circ}\)C & \(-\)10–160 \({}^{\circ}\)C & DC1010-II \\ Power meter & 1 & \(\pm\)0.50\% & 0–600 W & TOS120A \\ Contact AC\({}^{1}\) voltage regulator & 1 & \(\pm\)0.5\% & 0–300 V & TDGC2-2 KVA \\ Automatic AC\({}^{1}\) voltage stabiliser & 1 & \(\pm\)2\% & 220 V & TND-1500 VA \\ Evaporator section temperature sensor & 3 & \(\pm\)0.5 \({}^{\circ}\)C & 0–400 \({}^{\circ}\)C & P100 \\ Condenser section temperature sensor & 3 & \(\pm\)0.5 \({}^{\circ}\)C & 0–400 \({}^{\circ}\)C & P100 \\ Data acquisition & 1 & NA & NA & Agilent 34970 \\ \hline \hline \end{tabular} \({}^{1}\) Alternating current.  
\end{table}
Table 4: Working ranges and errors of key instruments.  
Figure 5: Experimental test setup to characterise the MF-AHPA thermal resistance. 1. PC 2. Agilent 34970A 3. Cooling water jacket 4. Thermostatic tank 5. Constant voltage source 6. Valve 7. Float flowmeter 8. Heating bars 9. MF-AHPA 10. Heat input meter 11. Insulating blanket.