Design optimisation and commissioning of the Delft rotating heat pipe setup

Abstract

The heat pipe assisted annealing project is a project in which Tata Steel, TU Delft and Drever International work together to develop a continuous annealing line with heat pipes. In an annealing line cold rolled steel is heated to 973 K and cooled down again to change the properties of the steel. In the heat pipe assisted annealing project the cooling line is thermally connected to the heating line via heat pipes. A heat pipe is a closed cylinder which is partly filled with a liquid. Heat pipes are very effective heat transfer devices, due to evaporation of the liquid at one side of the heat pipe and condensation of the vapour at the other side of the heat pipe. Due to rotation and a head, liquid will return to the evaporator side of the heat pipe. Applying heat pipes in a continuous annealing line could lead to energy savings up to 70%.
The TU Delft rotating heat pipe setup is in development for testing the performance of organic working fluids in heat pipes and validation of models, for the temperature range from 423 K to 723 K. The goal of this thesis is described as: finishing the development of the TU Delft rotating heat pipe setup and use this test setup to validate the developed model. This goal was divided into several objectives.
An investigation was made of what has to be done before the commissioning of the setup. It was discovered that the heat input calculation is overestimated, because insulation is not taken into account. Therefore, a new calculation was made. It is concluded that in the worst case scenario 1155 W of heat input is needed. Also, the available band heaters could not be used, therefore IR heating with quartz lamps has been considered. A calculation was made to confirm if they will provide enough power to meet the requirements of the setup. It is concluded that six quartz lamps with an effective heating length of 165 mm will provide enough power. In the fill ratio calculation, it is learned that non-annular flow is beneficial for the heat transfer compared to annular flow. Also, it was decided to fill the heat pipe with 35 grams of Dowtherm A as a start. With this amount of fluid, it is possible to operate the heat in both flow patterns over the whole temperature range. Last, it is concluded that bearing cooling is needed.
Another objective was to select the required data acquisition hardware and program the required software for control and data acquisition. A compactRIO from National Instruments is selected together with several modules. This configuration is able to process all the signals and has extra capacity to handle more signals in the future. A LabVIEW program was designed to control the Delft setup. This program meets all the requirements. It has been tested with dummy signals and during a leakage test with the actual heat pipe.
A model which represents the actual Delft rotating heat pipe setup has been made. The same inputs as in the Delft setup can be adjusted. This model has been developed as a network model. These types of models are often used because of their reasonably accurate and practically simple way to model transient heat pipe analysis. This model was validated with two different papers. In the first paper, an experiment is performed with a stainless steel ammonia heat pipe, which operates in non-annular flow. The data of this paper is only useful for steady state. At the steady state part, the maximum deviation is 0.96 K. In the second paper, a copper-water heat pipe is used. This heat pipe is not rotating, but has a wick. This means its behaviour is similar to a rotating heat pipe with annular flow. The data of this paper is very precise and shown in tabular form at three different points at 4 time stamps. The root-mean-square error between the experiment and the model at all data points is 0.36 K.
The commissioning of the heat pipe is in progress now. When all the safety procedures are checked, the experiments can be conducted.