scholarly journals Experimental Estimation of the Heat Transfer Coefficient of an Unglazed Solar Plate for Unsteady Humid Outdoor Condition

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Felix Uba ◽  
Eric Osei Essandoh ◽  
Gilbert Ayine Akolgo ◽  
Richard Opoku ◽  
Lawrence Oppong-Kyereh ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Mild Steel ◽  
Transfer Coefficient ◽  
Specific Heat ◽  
Steel Plate ◽  
Outdoor Environment ◽  
Empirical Equations ◽  
Outdoor Condition ◽  
The Heat Transfer Coefficient

This research presents a study on the heat transfer coefficient for an unglazed solar plate collector in an unsteady humid outdoor environment. The purpose for undertaking this research is to investigate the correlation between the heat transfer coefficient and air speed and also verify whether heat transfer from unglazed solar thermal collectors under outdoor conditions can be experimentally determined using a particular mathematical relationship for different locations. In estimating the heat transfer coefficient for an unglazed solar plate in an unsteady humid outdoor condition, an experiment was held using an outdoor setup that measured temperatures, wind speeds, and solar radiations from 11:00 A.M. to 2:00 P.M. The solar plate collector was placed on a flat bed of height 2.2 m and a collection area of 0743 m2. An average temperature of 45°C was recorded for a mild steel plate collector which was initially exposed to an ambient temperature which ranges from 25°C to 32°C. The interfacial temperature between the plate and an asbestos board ranges from 42°C to 52°C, and that of the asbestos and a plywood is 40°C to 46°C. The specific heat capacity of the mild steel plate and the asbestos board used for the construction of the experimental setup are 25.00 kJ/kg and 950.00 kJ/kg, respectively, while the thermal conductivity of these materials is 0.46 W/m·K and 0.25 W/m·K, respectively. The novelty of this work is the use of such a study to generate empirical equations for Ghana and to produce representative equations for determining the heat transfer coefficient for solar plate collectors in unsteady humid outdoor conditions in West Africa. This work is expected to contribute data alongside similar works done for different areas to help propose empirical equations for estimating global and not site-specific heat transfer coefficients.

Numerical Analysis on Heat Transfer Coefficient of Large Die Steel Quenching

2012 ◽  
Vol 487 ◽  
pp. 449-452
Author(s):  
Xin Xiao Bian ◽  
Chao Zhang ◽  
Lin Zhu Qian
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Process Simulation ◽  
Air Cooling ◽  
Empirical Equations ◽  
Surface Conditions ◽  
Die Steel ◽  
Quenching Process ◽  
The Heat Transfer Coefficient

Heat transfer coefficient is one of the most important boundary conditions for quenching process simulation. It depends on many factors, such as material, size, surface conditions of a part, and so on. It is, therefore, difficult to evaluate the heat transfer coefficient accurately. T In the environment for large modules P20 and the actual heat transfer conditions, the off-line air-cooling heat transfer coefficient of C are simulated by using empirical equations.

scholarly journals The Influence of Window-Wall Ratio on Heating Energy Consumption of Rural House in Severe Cold Regions of China

2020 ◽  
Vol 173 ◽  
pp. 03008
Author(s):  
Teng Shao ◽  
Hong Jin ◽  
Wuxing Zheng ◽  
Jin Wang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Energy Consumption ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Outdoor Environment ◽  
Shape Coefficient ◽  
Heating Energy Consumption ◽  
The Heat Transfer Coefficient ◽  
Large Shape

Rural houses in severe cold areas of China are mostly single-storey independent buildings with large shape coefficient. Compared with urban residential, it has larger contact area between envelope and outdoor environment of each household. Meanwhile, the heat transfer coefficient of window is usually greater than that of external wall and roof. The window-wall ratio is one of the important indicators affecting the energy consumption of rural house. This paper takes window-wall ratio as the main variable, building orientation, thermal performance of envelope and window heat transfer coefficient as the auxiliary variables, and applies DesignBuilder software to quantitatively analyse the mechanism of window-wall ratio on rural house’s heating energy consumption under the interactive influence of multiple factors. Results show that the influence rule of window-wall ratio with different orientations on heating energy consumption will change when the thermal performance of envelope or window heat transfer coefficient changed. The synthetic effect of various factors should be considered in the design to reasonably determine the windowwall ratio of rural house.

Heat Transfer Mechanisms of Propane Boiling on Horizontal Steel Tubes With Smooth and Enhanced Surfaces

2010 ◽  
Author(s):  
A. Luke ◽  
Bjo¨rn C. F. Mu¨ller
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Mild Steel ◽  
Transfer Coefficient ◽  
Steel Surface ◽  
Bubble Formation ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Mild Steel Surface ◽  
The Heat Transfer Coefficient

The trend towards a better understanding of the fundamentals of nucleate boiling in re-entrant cavities is supported by the variation of the heating surface’s characteristics and the identification of parameters influencing the heat transfer at enhanced tubes. The optimized surface of enhanced evaporator tubes supports the bubble formation by providing stable nucleation sites, which are cavities that trapped the necessary amount of vapor to generate the next bubble. The optimal size of the cavities for bubble formation depends on various thermodynamic properties of the fluid and the wall material. The knowledge of these physical mechanisms is important for the further optimization. The influence of micro- and macrostructures on the overall heat transfer coefficient is investigated with the refrigerant R134a and the hydrocarbon propane (R290) boiling in a wide range of reduced pressures (p* = ps/pc = 0.03 to 0.5) and heat fluxes (0.05 to 100 kW/m2). The measurements are carried out using a standard apparatus and a horizontally positioned, electrically heated surface with various wall materials. Two different materials — copper and mild steel — with the same surface preparation by polishing are investigated. Furthermore, heat transfer measurements are carried out on a plain mild steel tube and on an industrially manufactured surface of the GEWA-PB type. The polished surfaces demonstrate a deterministic microstructure, the roughness parameters depends strongly on the measurement direction. The heat transfer coefficient as function of the heat flux of the polished copper tube can be described by the correlation of the VDI Heat Atlas, while the mild steel surface differ from former investigations due to the deep re-entrant cavities remaining from the drawn surface. The onset of boiling is nearly the same of both materials because of these cavities on the mild steel surface. As presented in the recent years, the heat transfer of nucleate boiling at tubes with subsurface channels can be divided into different domains, each influenced by different parameters like wettability, the product of vapor density and evaporation enthalpy. The identification of parameters influencing the bubble formation is done by heat transfer measurements, high-speed-video recording and photographic documentation. The experimental results of this work are compared to results of the polished surfaces. The heat transfer coefficient increases drastically for the enhanced tube, especially for beginning nucleation. The same α-q-relationship as on plain tubes is observed for higher pressures and heat fluxes but for three times higher values of the heat transfer coefficient α.

Evaporation of lignin-lean black liquor

TAPPI Journal ◽  
2015 ◽  
Vol 14 (7) ◽  
pp. 441-450
Author(s):  
HENRIK WALLMO, ◽  
ULF ANDERSSON ◽  
MATHIAS GOURDON ◽  
MARTIN WIMBY
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Black Liquor ◽  
Salt Content ◽  
Solubility Limit ◽  
Lignin Removal ◽  
Kraft Black Liquor ◽  
Black Liquors ◽  
The Heat Transfer Coefficient

Many of the pulp mill biorefinery concepts recently presented include removal of lignin from black liquor. In this work, the aim was to study how the change in liquor chemistry affected the evaporation of kraft black liquor when lignin was removed using the LignoBoost process. Lignin was removed from a softwood kraft black liquor and four different black liquors were studied: one reference black liquor (with no lignin extracted); two ligninlean black liquors with a lignin removal rate of 5.5% and 21%, respectively; and one liquor with maximum lignin removal of 60%. Evaporation tests were carried out at the research evaporator in Chalmers University of Technology. Studied parameters were liquor viscosity, boiling point rise, heat transfer coefficient, scaling propensity, changes in liquor chemical composition, and tube incrustation. It was found that the solubility limit for incrustation changed towards lower dry solids for the lignin-lean black liquors due to an increased salt content. The scaling obtained on the tubes was easily cleaned with thin liquor at 105°C. It was also shown that the liquor viscosity decreased exponentially with increased lignin outtake and hence, the heat transfer coefficient increased with increased lignin outtake. Long term tests, operated about 6 percentage dry solids units above the solubility limit for incrustation for all liquors, showed that the heat transfer coefficient increased from 650 W/m2K for the reference liquor to 1500 W/m2K for the liquor with highest lignin separation degree, 60%.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

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