A Heat Transfer Analysis for Passively Cooled “Trumpet” Secondary Concentrators

1987 ◽  
Vol 109 (4) ◽  
pp. 289-297 ◽  
Author(s):  
D. Suresh ◽  
J. O’Gallagher ◽  
R. Winston
Keyword(s):  
Heat Transfer ◽  
Thermal Load ◽  
Flux Distribution ◽  
The Body ◽  
Heat Transfer Analysis ◽  
Normal Operation ◽  
Transfer Model ◽  
Simulation Experiments ◽  
Ray Trace ◽  
Solar Thermal Applications

Some practical questions associated with the use of hyperboloidal “trumpet” shaped terminal concentrators for use in solar thermal applications are addressed. Computer ray-trace calculations show that the flux distribution is strongly peaked over a small neck area at the exit of the trumpet, which will be subjected to a substantial thermal load. A quasi-transient heat transfer model has been developed to analyze the thermal behavior of passively cooled trumpets. The thermal analysis shows that simple techniques exist such that one can design passive secondary trumpets which will remain below safe temperature limits under normal operation for many applications. The wall thickness and its variation along the body of the bell-shaped shell from the exit are found to play an important role in controlling the temperature at all flux levels. As a check on the validity of the model, a set of electrical simulation experiments was conducted and excellent agreement was found.

The Thermo-Mechanical Couple Analysis Base on Assembly

2013 ◽  
Vol 467 ◽  
pp. 416-419
Author(s):  
Gui Chuan Hu ◽  
Jing Hua Liu
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Stress Intensity ◽  
Cylinder Head ◽  
Thermal Load ◽  
Tensile Force ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
Sealing Performance ◽  
Steady Heat

Finite element simulation technology was applied to the steady heat transfer and thermo-mechanical coupling analysis in order to investigate the influence of thermal load on stress intensity and sealing performance. An finite element heat transfer model of cylinder head joint assembly was set up, based on which the steady heat transfer analysis was performed subsequently by applying reasonable boundary conditions and loads. The influence on cylinder head sealing performance due to thermal field under the thermal stress conditions was evaluated by using the finite element method. The results showed that the thermal load increases the bolt tensile force and the gasket pressure, which help to improve the sealing performance. Compared to the mechanical load case, the thermo-mechanical stress of the liner and the cylinder head is obviously increased, so the thermal load is not neglect able when calculating the stress intensity of the cylinder head and the cylinder liner.

Applicability of Heat Mirrors in Reducing Thermal Losses in Concentrating Solar Collectors

2016 ◽  
Author(s):  
Prashant Mahendra ◽  
Vikrant Khullar ◽  
Madhup Mittal
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Solar Irradiance ◽  
Solar Collector ◽  
Flux Distribution ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
Solar Collectors ◽  
Parabolic Trough ◽  
Glass Envelope

Flux distribution around the parabolic trough receiver being typically non-uniform, only a certain portion of the receiver circumference receives the concentrated solar irradiance. However, radiative and convective losses occur across the entire receiver circumference. This paper attempts to introduce the idea employing transparent heat mirror to effectively reduce the heat loss area and thus improve the thermal efficiency of the solar collector. Transparent heat mirror essentially has high transmissivity in the solar irradiance wavelength band and high reflectivity in the mid-infrared region thus it allows the solar irradiance to pass through but reflects the infrared radiation back to the solar selective metal tube. Practically, this could be realized if certain portion of the conventional low iron glass envelope is coated with Sn-In2O3 so that its acts as a heat mirror. In the present study, a parabolic receiver design employing the aforesaid concept has been proposed. Detailed heat transfer model has been formulated. The results of the model were compared with the experimental results of conventional concentrating parabolic trough solar collectors in the literature. It was observed that while maintaining the same external conditions (such as ambient/initial temperatures, wind speed, solar insolation, flow rate, concentration ratio etc.) the heat mirror-based parabolic trough concentrating solar collector has about 3–12% higher thermal efficiency as compared to the conventional parabolic solar collector. Furthermore, steady state heat transfer analysis reveals that depending on the solar flux distribution there is an optimum circumferential angle (θ = θoptimum, where θ is the heat mirror circumferential angle) up to which the glass envelope should be coated with Sn-In2O3. For angles higher than the optimum angle, the collector efficiency tends to decrease owing to increase in optical losses.

Thermo-Mechanical Couple Analysis of Cylinder Head Joint with Quadratic Contact

2013 ◽  
Vol 871 ◽  
pp. 141-144
Author(s):  
Gui Chuan Hu ◽  
Jing Hua Liu
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Stress Intensity ◽  
Cylinder Head ◽  
Thermal Load ◽  
Tensile Force ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
Sealing Performance ◽  
Steady Heat

Finite element simulation technology was applied to the steady heat transfer and thermo-mechanical coupling analysis in order to investigate the influence of thermal load on stress intensity and sealing performance. An finite element heat transfer model of cylinder head joint assembly was set up, based on which the steady heat transfer analysis was performed subsequently by applying reasonable boundary conditions and loads. The influence on cylinder head sealing performance due to thermal field under the thermal stress conditions was evaluated by using the finite element method. The results showed that the thermal load increases the bolt tensile force and the gasket pressure, which help to improve the sealing performance. Compared to the mechanical load case, the thermo-mechanical stress of the liner and the cylinder head is obviously increased, so the thermal load is not neglectable when calculating the stress intensity of the cylinder head and the cylinder liner.

scholarly journals Safe Duration Of A Person Soaking Inside A Hot Tub: Theoretical Prediction of Temperature Elevations in Human Bodies Using A Whole Body Heat Transfer Model

2020 ◽  
Author(s):  
Myo Min Zaw ◽  
Manpreet Singh ◽  
Ronghui Ma ◽  
Liang Zhu
Keyword(s):  
Heat Transfer ◽  
Human Body ◽  
Energy Balance Equation ◽  
The Body ◽  
Whole Body ◽  
Equation Modeling ◽  
Transient Temperature ◽  
Transfer Model ◽  
Bioheat Equation ◽  
Arterial Blood

In this study, we first develop a whole body model based on measurements of a human body, with realistic boundary conditions incorporated before and after a person jumps into a hot tub. For the transient heat transfer simulation, the initial condition is the established steady state temperature field of the human body with appropriate clothing layer to ensure the thermal equilibrium of the body with its surroundings. Once the person is inside a hot tub, the Pennes bioheat equation is used to simulate the transient temperature elevations of the body, and the rising of the arterial blood temperature is solved by an energy balance equation modeling thermal exchange between body tissue and the blood in the body. The safe duration of soaking in hot tubs is then determined as affected by the hot tub water temperatures.

Numerical Simulation of Subcooled Flow Boiling Heat Transfer in Helical Tubes

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Jong Chull Jo ◽  
Woong Sik Kim ◽  
Chang-Yong Choi ◽  
Yong Kab Lee
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Steam Generator ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Transfer Analysis ◽  
Normal Operation ◽  
Phase Flow ◽  
Two Phase ◽  
Side Flow

This paper addresses the numerical simulation of two-phase flow heat transfer in the helically coiled tubes of an integral type pressurized water reactor steam generator under normal operation using a computational fluid dynamics code. The shell-side flow field where a single-phase fluid flows in the downward direction is also calculated in conjunction with the tube-side two-phase flow characteristics. For the calculation of tube-side two-phase flow, the inhomogeneous two-fluid model is used. Both the Rensselaer Polytechnic Institute wall boiling model and the bulk boiling model are implemented for the numerical simulations of boiling-induced two-phase flow in a vertical straight pipe and channel, and the computed results are compared with the available measured data. The conjugate heat transfer analysis method is employed to calculate the conduction in the tube wall with finite thickness and the convections in the internal and external fluids simultaneously so as to match the fluid-wall-fluid interface conditions properly. Both the internal and external turbulent flows are simulated using the standard k-ε model. From the results of the present numerical simulation, it is shown that the bulk boiling model can be applied to the simulation of two-phase flow in the helically coiled steam generator tubes. In addition, the present simulation method is considered to be physically plausible in the light of discussions on the computed results.

Overall Effectiveness of a Blade Endwall With Jet Impingement and Film Cooling

2013 ◽  
Vol 136 (3) ◽  
Author(s):  
Amy Mensch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Jet Impingement ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
Convective Cooling ◽  
Impingement Cooling ◽  
Internal Impingement ◽  
The Impact ◽  
Overall Effectiveness

Ever-increasing thermal loads on gas turbine components require improved cooling schemes to extend component life. Engine designers often rely on multiple thermal protection techniques, including internal cooling and external film cooling. A conjugate heat transfer model for the endwall of a seven-blade cascade was developed to examine the impact of both convective cooling and solid conduction through the endwall. Appropriate parameters were scaled to ensure engine-relevant temperatures were reported. External film cooling and internal jet impingement cooling were tested separately and together for their combined effects. Experiments with only film cooling showed high effectiveness around film-cooling holes due to convective cooling within the holes. Internal impingement cooling provided more uniform effectiveness than film cooling, and impingement effectiveness improved markedly with increasing blowing ratio. Combining internal impingement and external film cooling produced overall effectiveness values as high as 0.4. A simplified, one-dimensional heat transfer analysis was used to develop a prediction of the combined overall effectiveness using results from impingement only and film cooling only cases. The analysis resulted in relatively good predictions, which served to reinforce the consistency of the experimental data.

Co-Axial Laminar Multiphase Jet: A Novel Methodology for the Attainment Enhancement in Transition Boiling Regime

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Kashinath Barik ◽  
B. Swain ◽  
A.R. Pati ◽  
Susmit Chitransh ◽  
S.S. Mohapatra
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flux Distribution ◽  
Flow Behavior ◽  
Heat Transfer Analysis ◽  
Heat Flux Distribution ◽  
Low Mass ◽  
Multiphase Fluid ◽  
Thermal Diffusivities ◽  
The Comparative Study

Abstract In the current investigation, by using a very low mass flux co-axial laminar multiphase fluid jet, enhancement in heat transfer rate, uniformity in heat flux distribution, and reduction in coolant consumption rate characteristics are simultaneously tried to achieve in case of cooling from a very high initial temperature (900 °C). The information on quenching technology depicting all the above-mentioned advantages has not been reported in the literature. In the present work, kerosene–water, nanofluid (Al2O3 = 0.15%)–kerosene, and nanofluid (Al2O3 = 0.15%)–polyethylene glycol combinations were used for co-axial cooling experimentation. From the heat transfer analysis, it is observed that nanofluid (Al2O3 = 0.15%) and kerosene combination produces maximum critical heat flux due to the alteration of thermophysical and interfacial properties, which enhance the driving force and flow behavior defining momentum and thermal diffusivities in the favorable direction of heat transfer, respectively. In addition to the above, the comparative study ensures a significant reduction in coolant consumption and augmentation in uniformity in heat flux distribution.

One-Dimensional Zonal Model for the Unsteady Heat Transfer Analysis in an Open Volumetric Air Receiver

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Gurveer Singh ◽  
Vishwa Deepak Kumar ◽  
Laltu Chandra ◽  
R. Shekhar ◽  
P. S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Operating Conditions ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
High Heat Flux ◽  
Unsteady Heat Transfer ◽  
Volumetric Heating ◽  
One Dimensional ◽  
Zonal Model

Abstract The open volumetric air receiver (OVAR)-based central solar thermal systems provide air at a temperature > 1000 K. Such a receiver is comprised of porous absorbers, which are exposed to a high heat-flux > 800 Suns (1 Sun = 1 kW/m2). A reliable assessment of heat transfer in an OVAR is necessary to operate such a receiver under transient conditions. Based on a literature review, the need for developing a comprehensive, unsteady, heat transfer model is realized. In this paper, a seven-equations based, one-dimensional, zonal model is deduced. This includes heat transfer in porous absorber, primary-air, return-air, receiver casing, and their detailed interaction. The zonal model is validated with an inhouse experiment showing its predictive capability, for unsteady and steady conditions, within the reported uncertainty of ±7%. The validated model is used for investigating the effect of operating conditions and absorber geometry on the thermal performance of an absorber. Some of the salient observations are (a) the maximum absorber porosity of 70–90% may be preferred for non-volumetric and volumetric-heating conditions, (b) the minimum air-return ratio should be 0.7, and (c) the smallest gap to absorber-length ratio of 0.2 should suffice. Finally, suggestions are provided for extending the model.

Estimation and Use of the Radiation Distribution Factor Median for Predicting Uncertainty in the Monte Carlo Ray-Trace Method

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Mehran Yarahmadi ◽  
J. Robert Mahan ◽  
Kory J. Priestley
Keyword(s):  
Heat Transfer ◽  
Monte Carlo ◽  
A Priori ◽  
Heat Transfer Analysis ◽  
Distribution Factor ◽  
Recent Contribution ◽  
Radiation Distribution ◽  
Radiation Behavior ◽  
Ray Trace ◽  
Probability Density Function Pdf

In a recent contribution, the authors show that the uncertainty in heat transfer results obtained using the Monte Carlo ray-trace (MCRT) method is related to the median of the radiation distribution factor probability density function (PDF). The value of this discovery would be significantly enhanced if the median could be known a priori without first computing the distribution factors. This would allow the user to determine the number of rays required to achieve the desired accuracy of a subsequent heat transfer analysis. The current contribution presents a correlation for the median of the distribution factor PDF as a function of emissivity and the number of surface elements defining an enclosure. The correlation involves a single parameter whose value is unique for a given enclosure geometry. We find that the radiation behavior of a given enclosure can be classified on a scale ranging from reflection-dominated to geometry-dominated. The correlation is shown to work well for reflection-dominated enclosures but less well for geometry-dominated enclosures.

Numerical Simulation of Subcooled Flow Boiling Heat Transfer in Helical Tubes

2006 ◽  
Author(s):  
Jong Chull Jo ◽  
Woong Sik Kim ◽  
Chang-Yong Choi ◽  
Yong Kab Lee
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Steam Generator ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Heat Transfer Analysis ◽  
Normal Operation ◽  
Phase Flow ◽  
Two Phase ◽  
Pressurized Water

This paper addresses the numerical simulation of two phase flow heat transfer in the helically coiled tubes of an integral type pressurized water reactor steam generator under normal operation using a CFD code. The single phase flow which flow downward direction in the shell side is also calculated together. For the calculation of tube side two-phase flow the inhomogeneous two-fluid model is used. Both the RPI (Rensselaer Polytechnic Institute) wall boiling model and the bulk boiling model are implemented for the numerical simulation and the computed results are compared with the available measured data. The conjugate heat transfer analysis method is employed to calculate the conduction in the tube wall with finite thickness and the convections in the internal and external fluids simultaneously so as to match the fluid-wall-fluid interface conditions properly. Both the internal and external turbulent flows are simulated using the standard k-ε model From the results of present numerical simulation, it is shown that the bulk boiling model can be applied to the simulation of two-phase flow in the helically coiled steam generator tubes. The results also show that the present simulation method is considered to be physically plausible when the computed results are compared with available previous experimental and numerical studies.

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