Experimental setup design for pool boiling on horizontal tube and experimental investigation of pool boiling of acetone

Boiling heat transfer has quite wide usage area for industrial applications. Evaporators, steam boilers, heat pipes are some examples where boiling heat transfer can be seen. Because cost is an important parameter for commercial goods, minimum heat transfer area and maximum heat transfer is the main purpose for a new commercial product design. This purpose makes heat transfer coefficient so significant parameter. Therefore, there are too many studies about boiling heat transfer and enhanced surfaces which provide higher boiling heat transfer coefficient. Although, boiling heat transfer and convection heat transfer have some similarities (like both are occurred between a solid surface and a fluid), due to phase change and molecule movements make boiling heat transfer more complicated. Because boiling has quite complex mechanism, it is not easy to obtain a theoretical correlation as connective heat transfer has. Therefore, usually boiling heat transfer correlations are obtained by experimental studies like convection heat transfer correlations for turbulent flows. An experimental setup, to investigate nucleated pool boiling on horizontal tube, has been designed and built as part of this master thesis. It has been aimed to perform pool boiling experiments on a horizontal tube under different pressure, temperature and heat flux values. Although, pool boiling experiments have been performed for only one tube and one fluid as part of this study, experimental setup has been designed as capable to perform boiling experiments for different type of tubes and fluids. It is know that, pressure is one of the significant parameter for pool boiling. Therefore, experimental setup has been designed to be able to perform boiling experiments for different pressures. Therefore, setup has been designed as a closed loop. Basically, setup designed as an evaporator tank and a condenser tank which connected to each other with two pipes, one pipe connection on top of tanks and another pipe connection at the bottom of tanks. Thus, fluid which evaporates in evaporator tank will go up and move to the condenser tank through connection pipe. Fluid in vapor phase at the condenser will lose heat energy and condense. Condensate fluid will accumulated at the bottom of condenser tank and go back to evaporator tank through connection pipe at the bottom of tanks, regarding combined vessels principle. Evaporator has been design basically as a horizontal cylinder which has a demountable cover on one side to be able to perform experiment on different pipes and welded cover on the other side. Test specimen (pipe) has been assembled on the cover by screwed connection. One side of specimen tube has been closed and other side has been left open to allow heater assembly. In addition, a sight glass has been mounted on the evaporator tank to observe boiling during experiments. Electrical energy has been selected as energy source for boiling. Since, it is more reliable to measure electrical energy which will be provided to specimen pipe to obtain boiling, electrical heater has been preferred. Heater has been designed as helically shape to have homogeneous heat flux on the tube. Selected heater is able to provide 2300 W with 220V. That means, it is possible to have 43000 W/m2 heat flux on the specimen tube which has 33,7 mm diameter. Condenser design includes a helical coil which made of copper located inside a cylindrical tank. Two ends of copper coil have been assembled to a chiller to remove heat from condenser. Copper coil located at the upper side of condenser tank to ensure that liquid phase of fluid level is always stay below the coil. Condenser coil does not work properly if it submerge the liquid phase. In addition a pre-heater which has 2,5 kW power has been added to bottom of condenser tank to heat sub cooled fluid in condenser. To ensure whole power supplied from electrical heater is used for boiling, saturated liquid is needed inside evaporator tank. Otherwise, electrical power will be used first to heat obtain saturated liquid, then boiling. The pre-heater is controlled with a PID controller which gets temperature signal from evaporator via a thermo couple. Because, experimental setup has a closed loop, boiling can be obtained for both negative and positive pressure. A vacuum pump has been implemented to setup to achieve negative pressure in the system. If the power provided from electrical heater in evaporator is equal to power removed from condenser, regime condition is obtained for any pressure or temperature. Regime condition is needed to perform pool boiling experiment and calculate a heat transfer coefficient. To perform pool boiling experiments on designed setup, some auxiliary equipments have been implemented to setup such as a voltage regulator for power supply to specimen tube, a data logger to collect temperature and pressure data and a chiller to remove heat from condenser. Pool boiling experiments have performed for acetone as part of this master thesis for both with regime and without regime condition. Experiments with regime have been performed to calculate a boiling heat transfer coefficient, without regime have been performed to visualization of nucleation on the tube surface. Pool boiling heat transfer coefficient have been calculated by dividing heat flux on specimen tube to excess temperature between surface and saturated liquid. Heat flux calculated by electrical power from main heater which is determined by measuring current and voltage value. Saturation temperature has been determined by measuring pressure via pressure transmitter located on evaporator tank. Surface temperature has been determined by average of temperature measurements for different locations of specimen tube. Surface temperatures have been measured via total 14 pieces thermocouples which located on the top, bottom and side points of tube. Visualization of pool boiling experiments have been performed without regime for 3 different heat flux on stainless steel tube. Pool boiling of acetone have been visualized every 10 kPa pressure change between 40 kPa and 100 kPa pressure. Main purpose of visualization of pool boiling study is understand the effect of pressure and heat flux on nucleation. Experimental pool boiling heat transfer coefficients and Nusselt numbers have been determined for 4 different heat flux values with different saturation pressures. Calculated heat transfer coefficients and Nusselt numbers have been compared to some correlations in literature and seen convergence with Cooper and Ribatski & Jabardo correlations. Because pressure values are different on each regime conditions, it is not proper to propose a heat transfer correlation or Nusselt number correlation regarding experimental results of this thesis study. Nucleated pool boiling of acetone on horizontal tube have been investigated visually for 3 different heat fluxes for different pressure values without regime and seen less nucleate quantity, bigger nucleate size for lower pressures, more nucleate quantity, smaller nucleate size for higher pressure values.