The production of steel is an energy intensive process, using 20GJ/tonne of steel. The energy use needs to be declined by 10% in 2030 in order to be on track of the Sustainable Development Scenario(SDS). About 1GJ/tonne is required today by the annealing process, a heat treatment in which the steel strip is heated to a temperature of about 600-700^oC and cooled afterwards. Tata Steel came up with a way of connecting the cooling and heating section in an innovative way, which can potentially reduce the energy requirements of an annealing line by up to 70%. Horizontal rotating heat pipes are proposed to transfer heat efficiently over its axial length from the strip in the cooling section to the strip in the heating section. Dowtherm A has been selected as the working fluid between 150 and 350^oC. No research is available on rotating heat pipes with Dowtherm A. The aim of this study is to research the relevant internal heat transfer characteristics of a
rotating heat pipe and gain insight into the performance of Dowtherm A as the working fluid in terms of heat transfer efficiency. Furthermore, the aim is to gain knowledge on the effect of non-condensable gas inside a heat pipe and on the way the effects can be modelled in a computationally efficient way. Non-condensable gas is likely to be of influence on heat transfer homogeneity outwards to the relatively cool steel strip. Understanding this influence is another goal of this study. To fulfil the aims of this study, experiments are conducted and a computational model is devised. An experimental setup with working fluid Dowtherm A is used to acquire data at different rotational speeds, operating temperatures and at different thermal inputs and outputs. The rotating heat pipe used is of smaller scale than one in a heat pipe assisted annealing line, but with comparable heat fluxes. Secondly, the devised model is used to both qualitatively and quantitatively study the effect of non-condensable gas for different operating
parameters and non-condensable gas amounts, which is done for conditions as in the experimental setup and as in a heat pipe assisted annealing line. The rotating heat pipe worked successfully during conducted experiments and Dowtherm A has shown to be able to transport at least 280W axially through the inner geometry in the non-annular flow regime, which is 192,000W/m² and corresponds to a vapor flow of 0.001kg/s, at an axial temperature difference of only a few degrees Celsius. Nucleate boiling was considered the dominant heat transfer mechanism through the film in the evaporator, with a typical heat transfer coefficient observed of 4200W/m²K. The condenser has shown a lower film heat transfer coefficient; 1750W/m²K. The effect of rotational speed, power and temperature is minor in the evaporator at conditions tested. The 1D model for determining non-condensable gas distribution showed good agreement with reported experimental data, which show a major axial temperature drop at the condenser end. It was shown that wall conduction influences non-condensable gas distribution for heat pipes with a relatively thick wall, which is modelled by the addition of wall temperature calculations to the 1D model. The effect of non-condensable gas on heat pipe performance showed to be strongly dependent on
operating temperature. Axial convective transport showed to be between two and three orders of magnitude more efficient than pure conduction. Homogeneous heat outflow is achieved when non-condensable gas is not present in the condenser, which can be achieved by extending the heat pipe at the condenser end. The devised model is suitable to predict the effect of operating conditions and design adjustments in an efficient way. Results have shown that Dowtherm A is a suitable working fluid for a heat pipe assisted annealing line, due to the low internal resistances to heat and mass transfer.

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.