Herbert Zondag - Academia.edu (original) (raw)

Papers by Herbert Zondag

Proceedings of the 15th International Heat Transfer Conference, 2014

A phenomena-based method is presented to study the kinetics of the dehydration reaction of Li2SO4... more A phenomena-based method is presented to study the kinetics of the dehydration reaction of Li2SO4.H2O single crystals. The reaction proceeds by nucleation and growth processes, which are recorded photographically using a camera system. Based on a series of pictures of surface observations under isothermal conditions, an areic nucleation rate and growth rate were estimated. Since only surface information was obtained so far, an experimental study about the speed of growth into the crystal was carried out to quantify the growth rate in-depth. Together with the surface information, a nucleation and growth model was developed and employed to predict the reaction kinetics. The fractional conversion of the dehydration reaction was calculated and compared with experimental results from TGA (thermogravimetric analysis) measurements. A satisfactory prediction was achieved as a function of sample medium and experimental environment.

Solar Energy, Mar 1, 2003

Various concepts of combined PV-thermal collectors are possible. These concepts differ in their a... more Various concepts of combined PV-thermal collectors are possible. These concepts differ in their approach to obtain the maximum yield and it is not easy to say whether the yield of a complicated design will be substantially higher than the yield of a simpler one. In order to obtain a clearer view on the expected yield of the various concepts, nine different designs were evaluated. The channel-below-transparent-PV design gives the best efficiency, but since the annual efficiency of the PV-on-sheet-and-tube design in a solar heating system was only 2% worse while it is easier to manufacture, this design was considered to be a good alternative.

Shrinking core model for the reaction-diffusion problem in thermo-chemical heat storage. In

DOI to the publisher's website. • The final author version and the galley proof are versions of t... more DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

In this study the dehydration reaction of Li2SO4.H2O crystals is investigated at different temper... more In this study the dehydration reaction of Li2SO4.H2O crystals is investigated at different temperatures with the help of optical microscopy. The nucleation and nuclei growth processes during the reaction were recorded photographically using a camera system. Based on a series of pictures the propagation of the reaction front on the crystal surface was captured and an effective speed of growth (in μm/min) was estimated. It is demonstrated, using this in situ measurement technique, that the effective speed at certain temperature and water vapor pressure is a constant for different nuclei. From the surface observations it appeared that the mode of growth of nuclei is non-isotropic with a preferential direction along the [010] axis. In order to measure the growth rate in-depth, measurements on encapsulated crystals were also carried out. It is observed that the propagation of the interface in the crystal is linear and cracks have a remarkable influence on this propagation speed because of a higher mass diffusivity in the cracks.

Applied Thermal Engineering, Jun 1, 2016

Journal of Solar Energy Engineering-transactions of The Asme, Oct 16, 2009

Water vapor sorption in salt hydrates is one of the most promising means for compact, low loss, a... more Water vapor sorption in salt hydrates is one of the most promising means for compact, low loss, and long-term storage of solar heat in the built environment. One of the most interesting salt hydrates for compact seasonal heat storage is magnesium sulfate heptahydrate ͑MgSO 4 •7H 2 O͒. This paper describes the characterization of MgSO 4 •7H 2 O to examine its suitability for application in a seasonal heat storage system for the built environment. Both charging (dehydration) and discharging (hydration) behaviors of the material were studied using thermogravimetric differential scanning calorimetry, X-ray diffraction, particle distribution measurements, and scanning electron microscope. The experimental results show that MgSO 4 •7H 2 O can be dehydrated at temperatures below 150°C, which can be reached by a medium temperature (vacuum tube) collector. Additionally, the material was able to store 2.2 GJ/ m 3 , almost nine times more energy than can be stored in water as sensible heat. On the other hand, the experimental results indicate that the release of the stored heat is more difficult. The amount of water taken up and the energy released by the material turned out to be strongly dependent on the water vapor pressure, temperature, and the total system pressure. The results of this study indicate that the application of MgSO 4 •7H 2 O at atmospheric pressure is problematic for a heat storage system where heat is released above 40°C using a water vapor pressure of 1.3 kPa. However, first experiments performed in a closed system at low pressure indicate that a small amount of heat can be released at 50°C and a water vapor pressure of 1.3 kPa. If a heat storage system has to operate at atmospheric pressure, then the application of MgSO 4 •7H 2 O for seasonal heat storage is possible for space heating operating at 25°C and a water vapor pressure of 2.1 kPa.

Energy Procedia, Oct 1, 2017

Solar Energy, Feb 1, 2002

Four numerical models have been built for the simulation of the thermal yield of a combined PV-th... more Four numerical models have been built for the simulation of the thermal yield of a combined PV-thermal collector: a 3D dynamical model and three steady state models that are 3D, 2D and 1D. The models are explained and the results are compared to experimental results. It is found that all models follow the experiments within 5% accuracy. In addition, for the calculation of the daily yield, the simple 1D steady state model performs almost as good as the much more time-consuming 3D dynamical model. On the other hand, the 2D and 3D models are more easily adapted to other configurations and provide more detailed information, as required for a further optimization of the collector. The time-dependent model is required for an accurate prediction of the collector yield if the collector temperature at the end of a measurement differs from its starting temperature.

Journal of Thermal Analysis and Calorimetry, Jan 5, 2016

Interface advance plays an essential role in understanding the kinetics and mechanisms of thermal... more Interface advance plays an essential role in understanding the kinetics and mechanisms of thermal decomposition reactions such as the dehydration reaction of lithium sulfate monocrystals. However, many fundamental processes including mass transfer during interface advance are still not clear. In this work, the dynamics of interface advance, involving interaction between interfacial reaction and mass diffusion, is investigated numerically together with microscopy observations. A mathematical model is developed for interface advance with a moving boundary and then solved by using a conservative scheme. To examine the significance between the intrinsic chemical reaction and mass diffusion, a Damköhler number is defined as Da ¼ k r L=ðD e c 0 Þ. Numerical results at various Da values are discussed to distinguish the limiting step of the dehydration reaction of lithium sulfate monocrystals. Moreover, experiments are carried out with a hot-stage microscopy system where the propagation of the reaction interface into the crystal bulk is followed in situ. By fitting the experimental results with the numerical results, the effective diffusivity of water through the dehydrated crystal is estimated to be in the order of 10 À8 m 2 s À1. According to the corresponding Da values, it is found that, within the reaction temperature ranging from 110 to 130°C and a partial water vapor pressure of 13 mbar, the rate of dehydration interface advance in the bulk of large crystals (typically in the order of millimeters) is not constant, but shows a small decrease over time due to the influence of mass diffusion.

International Journal of Heat and Mass Transfer, Oct 1, 2017

Development of a validated 2D model for flow, moisture and heat transport in a packed bed reactor... more Development of a validated 2D model for flow, moisture and heat transport in a packed bed reactor using MRI experiment and a lab-scale reactor setup.

Water vapor sorption in salt hydrates is a promisi ng method to realize seasonal solar heat stora... more Water vapor sorption in salt hydrates is a promisi ng method to realize seasonal solar heat storage in the residential sector. Several materials already showed promising performance for this application. However, the stab ility of these materials needs to be improved for long term (30 ye ar) application in seasonal solar heat storages. Th e purpose of this article is to identify the influence of the materia l properties of the salt hydrates on the performanc e and the reaction kinetics of the sorption process. The experimental investiga tion presented in this article shows that the two s alt hydrates Li 2SO 4·H 2O and CuSO 4·5H 2O can store and release heat under the operating co nditions of a seasonal solar heat storage in a full y reversible way. However, these two materials show differences in terms of energy density and reaction kinetics. Li 2SO 4·H 2O can release heat with an energy density of around 0.80 GJ/m 3 within 4 hours of rehydration at 25°C, while CuSO 4· 5H 2O needs a...

In chapter 2 the materials and methods used will be discussed. The thermo-chemical material and t... more In chapter 2 the materials and methods used will be discussed. The thermo-chemical material and the reactor modeling are briefly described and the system layout is presented. In the result chapter 3, first the required system dimensions are determined. Afterwards the performance of the reactor model is analyzed. The chapter ends with an investigation of the annual performance of the combined storage system under consideration. Finally in chapter 4 some conclusions are presented.

Journal of Energy Storage, 2018