scholarly journals Thermal Fluxes and Solar Energy Storage in a Massive Brick Wall in Natural Conditions

Energies ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 8093
Author(s):  
Mariusz Owczarek
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Energy Storage ◽  
Solar Radiation ◽  
Solar Energy ◽  
Transfer Coefficient ◽  
Internal Surface ◽  
Transient State ◽  
Wave Radiation ◽  
Brick Wall

The thermal state of building elements is a combination of steady and transient states. Changes in temperature and energy streams in the wall of the building in the transient state are particularly intense in its outer layer. The factors causing them are solar radiation, ambient temperature and long-wave radiation. Due to the greater variability of these factors during the summer, the importance of the transient state increases at this time. The study analysed heat transfer in three aspects, temperatures in the outer, middle and inner parts of the wall, heat fluxes between these layers and absorption of solar energy, heat transfer coefficient on the wall exterior was also calculated. The analysis is based on temperature measurements at several depths in the wall and measurements of solar radiation. The subject of research is a solid brick wall. The results show that the characteristics of heat flow in winter and summer for the local climate show distinct differences. In the winter, the maximum temperature difference between the external and internal surface of the wall was 10 °C and in summer, 20 °C. In the winter, the negative flux on the internal surface reached 10 W/m2 and on the external 40 W/m2 and was constant throughout the day. The mean heat transfer coefficient on the exterior surface for winter week was 8 W/(mK). A Nusselt and Biot number for dimensionless convection analysis was calculated. The research contributes to the calculation of the variability of heat or cold demand in a daily period and to learn about the processes of energy storage in the wall using sensible heat.

Analysis on Non-Balance Insulation in Lhasa

2011 ◽  
Vol 243-249 ◽  
pp. 6990-6996
Author(s):  
En Li ◽  
Jia Ping Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Solar Radiation ◽  
Solar Energy ◽  
Transfer Coefficient ◽  
Heat Loss ◽  
Thermal Environment ◽  
Climate Data ◽  
Overall Heat Transfer Coefficient ◽  
Local Test

In Lhasa city, because of the abundant solar radiation, different direction walls absorb very different amount of solar energy. For the more efficient using of solar radiation, this difference should be reflected in the insulation design. By analysis on the typical year climate data, the absorption of solar radiation of different direction walls is clear. Compared with the inland city, Lhasa has more abundant solar energy and the bigger difference of direction, which means, the non-balance insulation is meaningful. The local test verifies the result of south and north room’s big difference thermal environment in the target building. By analyzing the permissible value of net heat loss by the envelope, the suggested limited value of overall heat transfer coefficient is proposed.

scholarly journals Experimental Determination of the Heat Transfer Coefficient of Real Cooled Geometry Using Linear Regression Method

Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 180
Author(s):  
Asif Ali ◽  
Lorenzo Cocchi ◽  
Alessio Picchi ◽  
Bruno Facchini
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Linear Regression ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
External Surface ◽  
Internal Surface ◽  
Regression Method ◽  
Thermal Transient

The scope of this work was to develop a technique based on the regression method and apply it on a real cooled geometry for measuring its internal heat transfer distribution. The proposed methodology is based upon an already available literature approach. For implementation of the methodology, the geometry is initially heated to a known steady temperature, followed by thermal transient, induced by injection of ambient air to its internal cooling system. During the thermal transient, external surface temperature of the geometry is recorded with the help of infrared camera. Then, a numerical procedure based upon a series of transient finite element analyses of the geometry is applied by using the obtained experimental data. The total test duration is divided into time steps, during which the heat flux on the internal surface is iteratively updated to target the measured external surface temperature. The final procured heat flux and internal surface temperature data of each time step is used to find the convective heat transfer coefficient via linear regression. This methodology is successfully implemented on three geometries: a circular duct, a blade with U-bend internal channel, and a cooled high pressure vane of real engine, with the help of a test rig developed at the University of Florence, Italy. The results are compared with the ones retrieved with similar approach available in the open literature, and the pros and cons of both methodologies are discussed in detail for each geometry.

scholarly journals Heat-Up Performance of Catalyst Carriers—A Parameter Study and Thermodynamic Analysis

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 964
Author(s):  
Thomas Steiner ◽  
Daniel Neurauter ◽  
Peer Moewius ◽  
Christoph Pfeifer ◽  
Verena Schallhart ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Surface Area ◽  
Internal Surface ◽  
Installation Space ◽  
Parameter Study ◽  
Thin Wall ◽  
Primary Role ◽  
Internal Surface Area

This study investigates geometric parameters of commercially available or recently published models of catalyst substrates for passenger vehicles and provides a numerical evaluation of their influence on heat-up behavior. Parameters considered to have a significant impact on the thermal economy of a monolith are: internal surface area, heat transfer coefficient, and mass of the converter, as well as its heat capacity. During simulation experiments, it could be determined that the primary role is played by the mass of the monolith and its internal surface area, while the heat transfer coefficient only has a secondary role. Furthermore, an optimization loop was implemented, whereby the internal surface area of a commonly used substrate was chosen as a reference. The lengths of the thin wall and high cell density monoliths investigated were adapted consecutively to obtain the reference internal surface area. The results obtained by this optimization process contribute to improving the heat-up performance while simultaneously reducing the valuable installation space required.

scholarly journals Experimental and Theoretical Investigation of the Natural Convection Heat Transfer Coefficient in Phase Change Material (PCM) Based Fin-and-Tube Heat Exchanger

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 716
Author(s):  
Saulius Pakalka ◽  
Kęstutis Valančius ◽  
Giedrė Streckienė
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Energy Storage ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Convection Heat Transfer Coefficient

Latent heat thermal energy storage systems allow storing large amounts of energy in relatively small volumes. Phase change materials (PCMs) are used as a latent heat storage medium. However, low thermal conductivity of most PCMs results in long melting (charging) and solidification (discharging) processes. This study focuses on the PCM melting process in a fin-and-tube type copper heat exchanger. The aim of this study is to define analytically natural convection heat transfer coefficient and compare the results with experimental data. The study shows how the local heat transfer coefficient changes in different areas of the heat exchanger and how it is affected by the choice of characteristic length and boundary conditions. It has been determined that applying the calculation method of the natural convection occurring in the channel leads to results that are closer to the experiment. Using this method, the average values of the heat transfer coefficient (have) during the entire charging process was obtained 68 W/m2K, compared to the experimental result have = 61 W/m2K. This is beneficial in the predesign stage of PCM-based thermal energy storage units.

Heat Transfer in Vertically Aligned Phase Change Energy Storage Systems

1999 ◽  
Vol 121 (2) ◽  
pp. 98-109 ◽  
Author(s):  
H. T. El-Dessouky ◽  
W. S. Bouhamra ◽  
H. M. Ettouney ◽  
M. Akbar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Energy Storage ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Storage Systems ◽  
Flow Direction ◽  
Vertically Aligned ◽  
Bottom To Top

Convection effects on heat transfer are analyzed in low temperature and vertically aligned phase change energy storage systems. This is performed by detailed temperature measurements in the phase change material (PCM) in eighteen locations forming a grid of six radial and three axial positions. The system constitutes a double pipe configuration, where commercial grade paraffin wax is stored in the annular space between the two pipes and water flows inside the inner pipe. Vertical alignment of the system allowed for reverse of the flow direction of the heat transfer fluid (HTF), which is water. Therefore, the PCM is heated from the bottom for HTF flow from bottom to top and from the top as the HTF flow direction is reversed. For the former case, natural convection affects the melting process. Collected data are used to study variations in the transient temperature distribution at axial and radial positions as well as for the two-dimensional temperature field. The data is used to calculate the PCM heat transfer coefficient and to develop correlations for the melting Fourier number. Results indicate that the PCM heat transfer coefficient is higher for the case of PCM heating from bottom to top. Nusselt number correlations are developed as a function of Rayleigh, Stefan, and Fourier numbers for the HTF flow from bottom to top and as a function of Stefan and Fourier numbers for HTF flow from top to bottom. The enhancement ratio for heat transfer caused by natural convection increases and then levels off as the inlet temperature of the HTF is increased.

scholarly journals Determination of long-term permissible currents in wires of power supply systems of railways

2019 ◽  
Vol 78 (2) ◽  
pp. 90-95 ◽  
Author(s):  
E. P. FIGURNOV ◽  
Yu. I. ZHARKOV ◽  
V. I. KHARCHEVNIKOV
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Solar Radiation ◽  
Transfer Coefficient ◽  
Surface Area ◽  
Meteorological Conditions ◽  
The Body ◽  
Additional Heating ◽  
The Heat Transfer Coefficient

In the standard for contact wires made from copper and its alloys, the values of long-term permissible temperatures have significantly decreased. This requires recalculation of previously valid values of long-term permissible currents. Authors considered revised method for calculating the long-term permissible currents, based on a more rigorous consideration of the laws of heat transfer and experimental studies of the conditions of heating and cooling of shaped (contact) and stranded wires. Technique is based on heat balance conditions, using which the sources of greatest inaccuracies become such quantities as cooled surface area, influence of wind direction, meteorological conditions, laws of change in heat transfer coefficient, effect on additional heating of solar radiation. Deviations when these indicators are taken into account by existing methods can cause errors of 40 % or more. Formulas for calculating the actual outer surface of stranded and shaped wires are given. The inadmissibility of calculating the surface area of the wires by their reference diameter is noted. Updated law of the change in heat transfer coefficient for stranded and shaped wires, as well as the degree of its dependence on wind speed and cooled surface, is given based on a summary of extensive domestic and foreign research. It is shown that with the longitudinal direction of the wind, the reduction of this coefficient occurs to a lesser extent than has been assumed so far. Authors propose method for taking into account an increase in the heat transfer coefficient under meteorological conditions characteristic of ice formation. The heat transfer coefficient of shaped and stranded wires in no case can not be taken as for round pipes with smooth surface. Existing method of accounting for solar radiation, which influences the additional heating of wires, leads to an unjustified and repeated exaggeration of this effect, since previously only the radiation incident on the wire was taken into account in the calculations. According to the laws of heat transfer, the temperature of the irradiated body does not depend on the incident, but on the resulting radiation, defined as the difference between the radiations incident on the body and emitted by it in accordance with its temperature. A formula for accounting for such heat transfer is proposed. The above methodology and calculation formulas allow performing reasonable calculations to determine the long-term permissible currents of individual stranded and shaped wires, as well as the contact network as a whole.

Experiment Study on Thermodiode and Energy Storage Material

2011 ◽  
Vol 225-226 ◽  
pp. 1028-1031
Author(s):  
Shi Dong Li ◽  
Ren Yuan Zhang ◽  
Liang De Liu ◽  
Hao Yuan Zhong
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Energy Storage ◽  
Transfer Coefficient ◽  
Inclination Angle ◽  
Myristic Acid ◽  
Heat Storage ◽  
Charge Ratio ◽  
Working Fluid ◽  
Storage Material

To research for application of thermodiode in energy storage solar water heater, experimental research on heat transfer of thermodiode using myristic acid as heat storage material was made, starting characteristics of thermodiode using acetone and R134a was compared. Especially for working fluid of R134a, influence of thermodiode on heat storage process of myristic acid was tested for under different working conditions such as thermodiode’s positions, liquid charge ratios, etc. Test result shows, thermodiode charged with R134a was quicker in start-up than the case of myristic acid; with liquid charge ratio of 80% , heat transfer coefficient was the highest; with an inclination angle η=30°C of thermodiode plane to horizontal plane, an inclination angle α=10°C of heating-evaporating section to horizontal line, 25W power input and a liquid charge ratio of 80%, average heat transfer coefficient was 113 W/(m2·K).

scholarly journals Thermodynamic Analysis of Compressed Air Energy Storage (CAES) Reservoirs in Abandoned Mines Using Different Sealing Layers

2021 ◽  
Vol 11 (6) ◽  
pp. 2573
Author(s):  
Laura Álvarez de Prado ◽  
Javier Menéndez ◽  
Antonio Bernardo-Sánchez ◽  
Mónica Galdo ◽  
Jorge Loredo ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Rock Mass ◽  
Energy Storage ◽  
Transfer Coefficient ◽  
Abandoned Mines ◽  
Compressed Air ◽  
Concrete Lining ◽  
The Heat Transfer Coefficient ◽  
Sealing Layer

Million cubic meters from abandoned mines worldwide could be used as subsurface reservoirs for large scale energy storage systems, such as adiabatic compressed air energy storage (A-CAES). In this paper, analytical and three-dimensional CFD numerical models have been conducted to analyze the thermodynamic performance of the A-CAES reservoirs in abandoned mines during air charging and discharging processes. Unlike other research works, in which the heat transfer coefficient is considered constant during the operation time, in the present investigation a correlation based on both unsteady Reynolds and Rayleigh numbers is employed for the heat transfer coefficient in this type of application. A tunnel with a 35 cm thick concrete lining, 200 m3 of useful volume and typical operating pressures from 5 to 8 MPa were considered. Fiber-reinforced plastic (FRP) and steel were employed as sealing layers in the simulations around the fluid. Finally, the model also considers a 2.5 m thick sandstone rock mass around the concrete lining. The results obtained show significant heat flux between the pressurized air and the sealing layer and between the sealing layer and concrete lining. However, no temperature fluctuation was observed in the rock mass. The air temperature fluctuations are reduced when steel sealing layer is employed. The thermal energy balance through the sealing layer for 30 cycles, considering air mass flow rates of 0.22 kg s−1 (charge) and −0.45 kg s−1 (discharge), reached 1056 and 907 kWh for FRP and steel, respectively. In general, good agreements between analytical and numerical simulations were obtained.

scholarly journals Evolution of global heat transfer coefficient on PCM energy storage cycles

2017 ◽  
Vol 136 ◽  
pp. 188-195 ◽  
Author(s):  
Luís Pedro Esteves ◽  
Ana Magalhães ◽  
Victor Ferreira ◽  
Carlos Pinho
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Energy Storage ◽  
Transfer Coefficient
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