Elmar Baumhögger

Bio: Elmar Baumhögger is an academic researcher from University of Paderborn. The author has contributed to research in topics: Speed of sound & Helmholtz free energy. The author has an hindex of 10, co-authored 30 publications receiving 264 citations.

Reducing the power consumption of household refrigerators through the integration of latent heat storage elements in wire-and-tube condensers

Abstract: This study evaluates the influence of latent heat storage elements on the condenser temperature of a commercial household refrigerator. In order to determine the power consumption and the temperature distribution, a standard wire-and-tube condenser is equipped with different heat storage elements (containing water, paraffin or copolymer compound). The results indicate that particularly the application of phase change materials (PCM) lowers the condenser temperature, which leads to a significantly reduced power consumption.

Prediction methods for pool boiling heat transfer: A state-of-the-art review☆

Abstract: Prediction of heat transfer in the evaporator of a refrigeration unit should be as accurate as possible for the successful operation of the whole appliance. The predictive methods used at present are empirical or semi-empirical, particularly for the heat transfer conditions relevant in practice, because theoretically consistent calculation of the heat transfer coefficient in nucleate boiling is not yet possible. One of these which is included in the VDI Heat Atlas and has been updated recently, is presented in the first main part below and is compared with experimental data for 55 fluids. In the second part, eight more prediction methods from the literature are tested using the same experimental database, and the deviations between measurement and calculation are discussed in detail together with the different results calculated with the various methods.

Speed of Sound Measurements and Fundamental Equations of State for Octamethyltrisiloxane and Decamethyltetrasiloxane

Abstract: Equations of state in terms of the Helmholtz energy are presented for octamethyltrisiloxane and decamethyltetrasiloxane. The restricted databases in the literature are augmented by speed of sound measurements, which are carried out by a pulse-echo method. The equations of state are valid in the fluid region up to approximately 600 K and 130 MPa and can be used to calculate all thermodynamic properties by combining the Helmholtz energy and its derivatives with respect to the natural variables. The accuracy of the equation is validated by comparison to experimental data and correct extrapolation behavior is ensured.

Nucleate pool boiling, film boiling and single-phase free convection at pressures up to the critical state. Part I: Integral heat transfer for horizontal copper cylinders

Abstract: Transcritical working cycles for refrigerants have led to increased interest in heat transfer near the Critical State. In general, experimental results for this region differ significantly from those far from it because some fluid properties vary much more there than at a greater distance. In this paper, measurements for two-phase and single-phase free convective heat transfer from an electrically heated copper tube with 25 mm O.D. to refrigerant R125 are discussed for fluid states very close to the Critical Point and far from it. It is shown that heat transfer for film boiling slightly below and for free convection slightly above the critical pressure is very similar. The new – and also previous – experimental data for nucleate boiling, film boiling, and single-phase free convection are compared with calculated results between atmospheric and critical pressure. It can be concluded that the Principle of Corresponding States in its simplest form is very well suited to transfer the results to other refrigerants. In Part II, particular attention will be given to a minimum superheat for nucleate boiling and a maximum superheat for film boiling and single-phase free convection within the circumferential variation of the isobaric wall superheat on the lower parts of the tube.

A review for phase change materials (PCMs) in solar absorption refrigeration systems

Abstract: Energy storage has become an important part in renewable energy technology systems. Solar thermal systems, unlike photovoltaic systems with striving efficiencies, are industrially matured, and utilize major part of sun's thermal energy during the day. Yet, it does not have enough (thermal) backup to keep operating during the low or no solar radiation hours. New materials are selected, characterized, and enhanced in their thermo-physical properties to serve the purpose of a 24 h operation in an efficient thermal energy storage system (TESS). Solar absorption refrigeration system requires a continuous operation in many of its applications (food storage, space cooling etc), which in turn requires an efficient TES system utilizing material with high heat of fusion, eg. phase change materials (PCMs). This review is a comprehensive evaluation of suitable PCM selection, methodologies of integration, enhancements and challenges for operating temperatures of each component in a single-effect solar absorption system affecting its performance. Observations and lessons from previous studies are discussed in detail. Recommendations based on investigation results, advantages and drawback of PCMs, PCM enhancement options, energy, exergy and cost analysis are made for the future research direction.