Bøger af Hans Georg Schrey

Scientific Study from the year 2024 in the subject Physics - Thermodynamics, language: English, abstract: The objective of this report is to make up for the following deficiencies at least on a general level - while still using first principles. Air-cooled condensers are widely used at the cold end of thermal power cycles. With this equipment cooling water required in wet cooled power plants may be saved on a large scale. To operate fans which convey dry cooling air to the condenser modules electric power is required which reduces overall power plant effectiveness. Consequently, pumping power consumption should be as small as possible. During operation it is therefore common to reduce fan power consumption by switching down or off fans of individual modules or, in some case complete ACC streets if ambient conditions and operation parameters are promising. Performance guarantees are normally specified with all equipment in full action. Only primary variable variations such as ambient temperature, ambient air pressure or total steam flow rate for a reduced range at fan full speed are part of the performance guarantee. Therefore, effects of fan switch or high cross-wind levels remain open issues.

Polemic Paper from the year 2023 in the subject Mathematics - Miscellaneous, , language: English, abstract: The purpose of the following report is to demonstrate that with the mathematical tools of the 17th century, a proof to Fermat¿s conjecture may have been possible. The whole procedure is based on planar geometry, which was perfectly known at the time. Moreover, the procedure does not exceed contemporary school mathematics.Fermat¿s last theorem has been a hot topic for mathematicians since it was originally published in Fermat¿s "Arithmetica". Although Pierre de Fermat had claimed to have found an easy proof for his conjecture, he failed to disclose it. Over the past 350 years, mathematicians were unable to find this simple proof. So, over time, it was concluded that Fermat had made an error with his claim. Finally, in 1994 the British mathematician Andrew Wiles found a complex mathematical proof for Fermat¿s conjecture.

Polemic Paper from the year 2018 in the subject Engineering - System Science, , language: English, abstract: Condensing the capacity of air-cooled condensers is critical for proper functionality of steam cycles in power plants. Condensers operate in the low vacuum regime to promote the efficiency of power generation. Leakages enable ingress of ambient air into the steam cycle and thus impede condensation and power generation capacity. Therefore, vacuum tightness is essential for effective plant operation and must be verified by means of an acceptance test.The latest revision of the VGB acceptance test code for the air-cooled condenser (VGB-S-131) proposes a simple procedure to verify ample vacuum tightness and evacuation capacity. However, the following report will demonstrate that the informational value of test results in connection with the proposed procedure are to some extent questionable. They cannot stand for themselves but need to be accompanied by further information gathered from other tests, as for example thermal performance tests. This puts the usefulness of the test itself into question.

Scientific Essay from the year 2018 in the subject Physics - Thermodynamics, , language: English, abstract: This work is concerned with the effects of fouling on different fin tubes and exchangers cooled by air.During operation of heat exchangers layers of deposits or corrosive products may be formed and accumulated on heat exchanger surfaces over time. This leads to additional heat transfer resistance and constriction of fluid flow area. In consequence, the exchanged heat duty is badly affected. The loss of heat duty is extreme if local heat transfer coefficients are high at clean conditions. However, maintaining cooling effectiveness is paramount in most applications. As a remedy, surfaces must be regularly cleaned. Fin tubes are core elements in air cooled exchangers or condensers to transfer heat. Fin tube exchangers are characterized by a multitude of circular, elliptical or channel type core tubes with air-side finning. Generally, the process medium flows on the tube internal side with air as coolant on the external fin side. The report deals with air cooled heat exchangers and condensers under forced or natural draft in dry cooling applications with the focus on the effect of fin side fouling. Water spray injection into the cooling air flow is excluded.Consequently, the effect of fin side fouling layers will be assessed as well as the consequence for air flowrate and heat duty at different convection types. Special attention is given to the effect of fouling on the performance of dry air cooled condensers. Also, differences of forced, induced or natural draft dry cooling applications will be covered.

Scientific Essay from the year 2018 in the subject Engineering - Power Engineering, , language: English, abstract: Tube bundles are standard equipment in heat exchanger design. Typically, when passing the bundle the process flow is subject to several flow re-directions which in consequence, lead to an uneven process side flow profile in parallel tubes. This may be harmless if speed differences are on a low scale. If, however a certain level of maldistribution is exceeded the operator may be confronted with severe consequences.Orifice design to ensure even flow rates in pre-heater applications are well-known in boiler design. Specific equations to assess maldistribution and to design orifices in different flow arrangements have been developed for that purpose. Less attention so far, has been paid to the field of air-cooled steam condensers (¿ACCs¿) although, occasionally some plants encounter problems of steam side maldistribution. This is visible by excessive sub-cooling of border areas (¿cold spot¿ formation) at some condenser bundles caused by premature termination of steam condensation. As a result, the plant performance is badly affected. Moreover, in cold climates these cold spots are a potential risk of frost formation which must be definitely prevented. Well-known calculation procedures of maldistribution will be summarized in PART ONE of this report by creating a unified theory applicable to all types of flow arrangement (single-phase) based on matrix algebra. It is shown how this method can be successfully applied to geometry variations.In PART TWO, the procedure is extended to flow maldistribution of condensing steam in a typical ACC street (two-phase). The basics physics are diligently explained. The procedure enables proper design of ducting geometry. Conclusions for safe everyday operation ¿ especially at variation of ambient conditions - are drawn.

Scientific Essay from the year 2018 in the subject Physics - Thermodynamics, , language: English, abstract: Vacuum tightness is critical for air-cooled condensers operating at low absolute pressure. Low vacuum is aimed for because vacuum dominates the power plant efficiency. To verify vacuum tightness usually a vacuum drop test is made with the system empty at normal atmospheric temperature and free of any liquids. This test is done before commissioning of the power unit and generally follows the recommendations of the Heat Exchanger Institute (HEI) as outlined in §6.1.1 of ¿Standards for Steam Jet Vacuum Systems¿.However, over time of operation the power plant may develop leakages, which were not present at the time of the original drop test. This calls for a tightness test at operating conditions where pre-conditions for the standard vacuum drop test are not fulfilled. The report describes a vacuum drop test without interfering too much into normal power plant operation. The test is suitable for stationary operating conditions using standard operation readings. The assessment of leakage flow is based on the measured vacuum decay rate. It is shown that vacuum decay rates taken from tests before and after commissioning are different. Contractual fixing of acceptable vacuum decay rates should therefore be treated with care. Example graphs for easy evaluation are given.

Scientific Essay from the year 2017 in the subject Physics - Thermodynamics, , course: Heat transfer engineering, language: English, abstract: Air-cooled condensers (¿ACC¿) operating in vacuum are widely used at the cold end of contemporary thermal power plants. Proper functioning of the condenser is paramount for power plant efficiency. To adapt to changing process conditions because of changed ambient air temperature or power station load ACC streets are either taken out of or into service or, module fan speed settings are selected appropriately. Even if all fans are running at same speed local variations of cooling air flow may arise as a consequence of e.g. fan location or local wind impact. The designer must ensure that no negative effect (i.e. no cold spot) may evolve at the steam side of the ACC caused by uneven air side cooling or fan control. The following note describes a theoretical method to assess the effect of air flow variations on ACC performance and provides simple rules to avoid potentially risky situations. An important role for safe operation plays the size of the secondary condenser. The procedure may be used as a guideline for proper sizing of the secondary condenser with respect to airflow maldistribution.

Scientific Essay from the year 2017 in the subject Physics - Thermodynamics, , language: English, abstract: The following report attempts to make up for the deficiencies of theoretical Reynolds comparison by using an approach based on redefined parameter groups ¿ specifically meant for cross-flow air coolers and/or air-cooled condensers. It will allow to directly evaluate different fin tube systems based on their performance characteristics alone. Fin tubes are core elements of air cooled heat exchangers in industrial cooling applications. Thermohydraulic performance of the cooling system defines the overall size of the equipment. Fin tube characteristics vary over a large range resulting from geometry, material or manufacturing process. As a general rule - the better the performance the smaller and more competitive the design will be. Consequently, manufacturers strive for thermohydraulic optimization of their product line. A key factor is the ability to properly compare different cooling devices.Comparison methods have been a topic in the academic field over a long period of time. Methods proposed so far have been based on classical dimensionless parameters, especially Reynolds number. Apart from transport properties Reynolds numbers include a geometric parameter pertinent to the individual heat exchanger system. If geometry is varied Reynolds changes as well. This is one of the reasons why Reynolds based comparison methods - although theoretically sound ¿ lack practical applicability.