Figure 2. Positions of thermocouples along the TMMHP
Five 1.1 mm holes are drilled according to the Figure 2. Five copper constantan (K-type) thermocouples have been inserted to reach the vapor core and brazed with silver to know the internal working fluid’s state. Then another five thermocouples have been attached right beside the holes by quick fixing adhesive to measure the surface temperatures at those locations. The condenser-end of the heat pipe is then plugged into one end of a capillary tube while the other end is attached with a vacuum pump. When pressure within the heat pipe goes well below the atmospheric pressure, then lock for a couple of minutes to reconfirm its air freeness. Then a pinch- clip is used to choke the capillary tube near the junction, and a slim syringe (Dispovan, 1 ml) filled with 0.5 ml of distilled water, which is 100% (Fill Ratio) of the empty space of the evaporator, is injected into the capillary tube. Actually, the water is sucked into the capillary tube spontaneously because of having lower than atmospheric pressure within the tube. After filling, the condenser-end of the TMMHP is now pinched and sealed by brazing.
At the evaporator, a fire and electric shock proof tape has been laid around and then 36SGW nichrome heater wire has been coiled out at a closer pace possible without clinging to each other. To avoid the dispersion of heat produced by the heater in view to keep the heat input value significantly unaltered, the coil was insulated by the asbestos rope by many folds and was extended up to the end of adiabatic section. Finally, another strip of insulating tape was wrapped around to avoid getting soaked by the splash of water. Now the condenser-end of the TMMHP is wrapped up with cotton and inserted into a plastic container which has two outlets. Then the outlets are connected with flexible water tube—upper one is fitted with the valve of the coolant (water) reservoir and the lower one is dipped into an empty bucket to collect the used coolant.
The whole setup is then mounted on a rig which is placed on a wooden table. All the thermocouples have been calibrated and found with ±0.1 degree Celsius variations. Then the thermocouples have been connected with a digital thermometer through a selector switch. The coolant reservoir is filled with the supplied water which is placed above the level of TMMHP. To produce the variable heat input for the heat pipe, a Variac has been introduced, which is then monitored by one ammeter and one precision voltmeter to record the current and voltage simultaneously.