W. Heidemann

Numerical Investigation of the Effect of Baffle Orientation on Heat Transfer and Pressure Drop in a Shell and Tube Heat Exchanger With Leakage Flows

The commercial CFD code FLUENT is used to investigate the effect of baffle orientation and of viscosity of the working fluid on the heat transfer and pressure drop in a shell-and-tube heat exchanger in the domain of turbulent flow. The shell-and-tube heat exchanger considered follows the TEMA standards and consists of 76 plane tubes with fixed outside diameter, which are arranged in a triangular pitch. Two baffle orientations as well as leakage flows are considered. In order to determine the effect of viscosity on heat transfer and pressure drop, simulations are performed for the working fluids air, water, and engine oil with Prandtl numbers in the range of 0.7 to 206. For each baffle orientation and working fluid, simulations are performed using different flow velocities at the inlet nozzle. Heat transfer and pressure drop are reported in order to describe the performance of vertically and horizontally baffled shell-and-tube heat exchangers. The heat transfer coefficient is described as modified shell-side Nusselt number, which is defined similar to the VDI method.

Steady-state and transient temperature field in the absorber tube of a direct steam generating solar collector

Abstract The temperature field in the absorber tube of a direct steam generating parabolic trough collector is calculated. Steady-state and transient operating conditions are considered. A universal program was developed for solving the two-dimensional transient temperature field using a modular nodal point library. The temperature field is extremely asymmetric due to the variation of the heat transfer coefficient at the inner surface and the solar irradiation at the outer surface of the absorber tube. High temperature peaks are found, especially in stratified flow at higher void fractions. The transient behaviour of the absorber tube has been analysed by stepwise increasing or decreasing the solar irradiation. The response time of the absorber tube is between 70 and 140 s for different void fractions inside.

Performance of Large-Scale Seasonal Thermal Energy Stores

More than 30 international research and pilot seasonal thermal energy stores (TESs) were realized within the past 30 years. Experiences with operation of these systems show that TES are technically feasible and work well. Seasonal storage of solar thermal energy or of waste heat from heat and power cogeneration plants can significantly contribute to substitute fossil fuels in future energy systems. However, performance with respect to thermal losses and lifetime has to be enhanced, while construction costs have to be further reduced. This paper gives an overview about the state-of the-art of seasonal thermal energy storage with the focus on tank and pit TES construction. Aspects of TES modeling are given. Based on modeled and measured data, the influence of construction type, system configuration, and boundary conditions on thermal losses of large-scale TES is identified. The focus is on large-scale applications with tank and pit thermal energy stores and on recent investigations on suitable materials and constructions. Furthermore, experiences with the operation of these systems with respect to storage performance are discussed.

Seasonal Hot Water Heat Store With Self-Supporting Shell Cover

A new self-supporting cover for seasonal hot water stores has been developed. It is installed at the Institute of Thermodynamics and Thermal Engineering (ITW) as shell cover with prefabricated sandwich elements made of high-performance concrete with PUR core. Due to the significantly higher strength of the high-performance concrete very thin units can be produced. In contrast to conventional self-supporting covers for the construction no scaffolding and hence no foundation is required. Reduced material usage and consequently reduced primary energy demand for construction is a further advantage of this concept.

The Effects of Boundary Design on the Efficiency of Large-Scale Hot Water Heat Stores

Boundary design of stratified hot water heat stores is important not only to minimize the thermal losses to the ambient but also to preserve the thermodynamic quality of the stored energy. A new method of characterization, which equivalently accounts for both these concerns, is applied in this paper to investigate into the boundary design of large-scale hot water heat stores. A variety of concepts related to general design of the containments, namely, the effects of the thermal conductivity and thickness of the container wall, are numerically analyzed. The design insights provided by the analysis are in good agreement with the corresponding experimental results for small-scale hot water heat stores found in the literature. Different ways of insulation application, differential application of the external insulation, and insulation of the top walls are further investigated to obtain ideas for the efficient use of the insulation material. The new characterization scheme proves to be an efficient tool to rank the performance of different boundary designs during storing process of large-scale stratified hot water heat stores and to provide valuable design insights.