Modeling heat transfer in a jet of hot air to decontaminate meat products

Air pre-heater and economizer are heat transfer surfaces in which air temperature and water temperature are raised by transferring heat from other media such as flue gas. Hot air is necessary for rapid combustion in the furnace and also for drying coal in milling plants. So an essential boiler accessory which serves this purpose is air pre-heater. The air pre-heater is not essential for operation of steam generator, but they are used where a study of cost indicates that money can be saved or efficient combustion can be obtained by their use. The decision for its adoption can be made when the financial advantages is weighed against the capital cost of heater. The efficiency of the boiler increases with the increase in the temperature of the combustion air used in the furnace. This is achieved by the increased temperature of the flue gas in the air preheater and economizer zone. This paper deals with the different ways to obtain the maximum heat from the flue gas travelling through the air preheater and the economizer zone to improve the boiler efficiency.

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Adjoint Optimization of Heat Transfer Within a Stirling Engine

10.1115/power2021-65804 ◽

2021 ◽

Author(s):

Anthony A. DiCarlo ◽

Rickey A. Caldwell

Keyword(s):

Heat Transfer ◽

Heat Sink ◽

Convective Flow ◽

Transfer Rate ◽

External Heat ◽

Stirling Engine ◽

Flow Dynamics ◽

Optimization Approach ◽

Cfd Simulations ◽

Hot Air

Abstract This work aims to determine the optimal heat sink fin shape to promote the efficient rise of hot air away from the heat sink. The heat transfer and convective flow dynamics external to a commercial Stirling engine are investigated. In particular, this study employs an adjoint optimization approach based on CFD simulations to determine the sensitivity of the objective function to the shape of the heat sink and influence on the natural convection heat flow away from the external heat sink. This deterministic optimization approach increases the heat transfer rate of the heat sink by nearly 20% in this study when performing a small number of design iterations.

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Heat transfer characteristics of unexpanded jet impingement in piccolo hot air anti-icing chamber

Applied Thermal Engineering ◽

10.1016/j.applthermaleng.2021.117540 ◽

2021 ◽

pp. 117540

Author(s):

Zhiqiang Guo ◽

XiaoFeng Guo ◽

Qian Yang ◽

Wei Dong

Keyword(s):

Heat Transfer ◽

Jet Impingement ◽

Heat Transfer Characteristics ◽

Transfer Characteristics ◽

Hot Air

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Unsteady Conjugate Heat Transfer Investigation of a Multistage Steam Turbine in Warm-Keeping Operation With Hot Air

Volume 8: Microturbines, Turbochargers, and Small Turbomachines; Steam Turbines ◽

10.1115/gt2018-75926 ◽

2018 ◽

Author(s):

Piotr Łuczyński ◽

Dennis Toebben ◽

Manfred Wirsum ◽

Wolfgang F. D. Mohr ◽

Klaus Helbig

Keyword(s):

Heat Transfer ◽

Conjugate Heat Transfer ◽

Flow Patterns ◽

Operating Conditions ◽

Angle Of Incidence ◽

Time Step ◽

Hot Air ◽

Wide Range ◽

Vortex Systems ◽

Operating Points

In recent decades, the rising share of commonly subsidized renewable energy especially affects the operational strategy of conventional power plants. In pursuit of flexibility improvements, extension of life cycle, in addition to a reduction in start-up time, General Electric has developed a product to warm-keep high/intermediate pressure steam turbines using hot air. In order to optimize the warm-keeping operation and to gain knowledge about the dominant heat transfer phenomena and flow structures, detailed numerical investigations are required. Considering specific warm-keeping operating conditions characterized by high turbulent flows, it is required to conduct calculations based on time-consuming unsteady conjugate heat transfer (CHT) simulations. In order to investigate the warm-keeping process as found in the presented research, single and multistage numerical turbine models were developed. Furthermore, an innovative calculation approach called the Equalized Timescales Method (ET) was applied for the modeling of unsteady conjugate heat transfer (CHT). The unsteady approach improves the accuracy of the stationary simulations and enables the determination of the multistage turbine models. In the course of the research, two particular input variables of the ET approach — speed up factor (SF) and time step (TS) — have been additionally investigated with regard to their high impact on the calculation time and the quality of the results. Using the ET method, the mass flow rate and the rotational speed were varied to generate a database of warm-keeping operating points. The main goal of this work is to provide a comprehensive knowledge of the flow field and heat transfer in a wide range of turbine warm-keeping operations and to characterize the flow patterns observed at these operating points. For varying values of flow coefficient and angle of incidence, the secondary flow phenomena change from well-known vortex systems occurring in design operation (such as passage, horseshoe and corner vortices) to effects typical for windage, like patterns of alternating vortices and strong backflows. Furthermore, the identified flow patterns have been compared to vortex systems described in cited literature and summarized in the so-called blade vortex diagram. The comparison of heat transfer in the form of charts showing the variation of the Nusselt-numbers with respect to changes in angle of incidence and flow coefficients at specific operating points is additionally provided.

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Numerical analysis of heat exchange process in the biomass carbonisation reactor

MATEC Web of Conferences ◽

10.1051/matecconf/201925205019 ◽

2019 ◽

Vol 252 ◽

pp. 05019 ◽

Cited By ~ 1

Author(s):

Robert Zarzycki ◽

Justyna Jędras

Keyword(s):

Heat Transfer ◽

Heat Exchange ◽

Numerical Analysis ◽

Exchange Process ◽

Geometrical Model ◽

Heating Time ◽

Heating Process ◽

Hot Air ◽

Cyclic Operation ◽

Heat Exchange Process

The study presents the problem of heat exchange in the biomass carbonisation reactor with cyclic operation. Based on the actual parameter of the biomass carbonisation reactor, a geometrical model was developed, and the computation of the heating process was conducted for two cases: an empty reactor and a filled reactor. Its result demonstrated that for the analysed configuration of the reactor, the process of heating biomass in the containers is limited by the capability of heat transfer to the biomass in the container. The results suggest opportunities for the improved heat exchange in the reactor and, accordingly, shortening heating time through installation of the system that forces circulation of hot air inside the reactor.

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Study on Sewage Sludge Drying System With Built-in Solar Drying Bed

E3S Web of Conferences ◽

10.1051/e3sconf/202123701041 ◽

2021 ◽

Vol 237 ◽

pp. 01041

Author(s):

Zhipan Gu ◽

Jichun Yang ◽

Jing Liu ◽

Leren Tao ◽

Ye Zhang ◽

...

Keyword(s):

Heat Transfer ◽

Sewage Sludge ◽

Radiation Heat Transfer ◽

Middle Layer ◽

Bottom Layer ◽

Mass Transfer Process ◽

Hot Water ◽

Solar Drying ◽

Hot Air ◽

Air Supply

In this paper, the renewable energy solar energy is used as the heat source. The combination of solar drying bed and traditional hot air drying can effectively reduce energy consumption and operation cost. The drying chamber is divided into three layers. The top air supply outlet supplies hot air, the middle layer places wet sludge, and the bottom layer uses hot water coil to dry the sludge. The whole drying process is a heat and mass transfer process with convective heat transfer and radiation heat transfer. After analysis and comparison with traditional energy drying, it is found that drying 97.5kg of sewage sludge will save 79% energy, save 12.84 kg of standard coal, reduce 32 kg of carbon dioxide and 1.284 kg of sulphur dioxide.

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Evaluation and Optimisation of Processes Time for the Hot Air Oven Containing Sleeves

International Journal for Research in Applied Science and Engineering Technology ◽

10.22214/ijraset.2021.38109 ◽

2021 ◽

Vol 9 (11) ◽

pp. 404-410

Author(s):

Bandaru Nithin Kumar Varma

Keyword(s):

Heat Transfer ◽

Mixed Convection ◽

Epoxy Resin ◽

Latent Heat ◽

Air Flow ◽

Whole Process ◽

Hot Air

Abstract: The Hot air producing Oven is used to heat the sleeves which are used as raiser in casting purpose. The sleeves that are being manufactured are made of epoxy resin which consists of approximately 75% water and 25% mineral mix before heating and once the processes are complete i.e. the sleeves getting heated in the oven the product would turn into 35% water + 65% mix. The whole process would estimate the time around 4.5 hours. The first 2.5 hours the water is being removed from the sleeves in form of latent heat vaporization. The next 2 hours is use as the time for curing the them because of the flow of hot air through the sleeves. The processes time is evaluated keeping in mind that the heat transfer is happening in mixed convection. As they are placed vertically to the direction of air flow. The amount of heat transfer in terms of energy is evaluated for 4.5 hours in actual practise. The energy which is utilised in 4.5 hours is found and the same amount is consumed in 2.5 hours which is a solution solved theoretically by considering datum values. Keywords: epoxy resin, sleeves, latent heat, heat transfer, mixed convection.

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Thermal performance of a packed bed double pass solar air heater with a latent heat storage system: an experimental investigation

World Journal of Engineering ◽

10.1108/wje-08-2019-0221 ◽

2019 ◽

Vol 17 (2) ◽

pp. 203-213 ◽

Cited By ~ 2

Author(s):

Chaitanya Dosapati ◽

Mohan Jagadeesh Kumar Mandapati

Keyword(s):

Heat Transfer ◽

Solar Energy ◽

Solar Air Heater ◽

Transfer Coefficients ◽

Absorber Plate ◽

Content Type ◽

Heat Transfer Coefficients ◽

Hot Air ◽

Sunshine Hours ◽

Poultry Farms

Purpose Solar energy applications are limited because of its intermittent and discontinuous availability with respect to time. Hence, solar energy thermal conversion systems need integration with thermal storage units (TSUs) to use solar energy in off sunshine hours. This paper aims to perform thermal analysis of a solar air heater (SAH) integrated with a phase change material (PCM)-based TSU to supply hot air during night period. Design/methodology/approach An experimental setup with TSU as main component was prepared with SAH at its upward side, food chamber at its downward side as subcomponents. In TSU, paraffin wax was used as thermal energy storage material. Mass flow rate of air considered as an input parameter in the experiment. Two different absorber plates, namely, plane and ribbed absorber plates were used for the experimentation. Each day for a fixed mass flow of air, observations were made during charging and discharging of PCM. Findings Nusselt number and convection heat transfer coefficients were analytically calculated by considering flow through TSU as external flow over bank of tubes in a rectangular duct. A temperature drop of around 7-8°C during charging of PCM and temperature rise of around 4-5°C during discharging of PCM was observed from the experimental results. The average practical efficiency of TSU with ribbed absorber plate SAH during charging and discharging of PCM was 22 and 6 per cent, respectively, higher than that of TSU with plane absorber plate SAH. Research limitations/implications There are no limitations for research on SAH integrated with TSU. Different PCM including paraffin wax, Glauber’s salt, salt hydrates and water are used for thermal storage. Only limitation is lower efficiency of SAH integrated with TSU because of lower heat transfer coefficients with air as working medium. If it can improve heat transfer coefficients of air then heat transfer rates with these units will be higher. Practical implications There are no practical limitations for research on SAH integrated with TSU. Sophisticated instrumentation is needed to measure flow rates, temperatures and pressure variations of air. Social implications In poultry farms during night, chicks cannot survive at cold climatic conditions. Hence, hot air should be supplied to poultry farms whenever the atmospheric temperature drops. It is proposed that, in combination with TSUs, heat produced by SAH is stored in day time in the form of either sensible or latent heat and is retrieved to provide hot air in the night times. This will reduce total operating costs in poultry farms. Originality/value Conventionally, people are producing hot air by combusting coal in poultry forms. This cost around Rs. 75,000 per month for a batch of 225 to 250 chicks in a poultry form. Hot air could be produced economically during off sunshine hours from SAH integrated with TSU compared to the conventional method of coal burning. Present experimental investigations conducted to fill the literature gap in this area of research and to design a SAH integrated with TSU to produce hot air for poultry forms.

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