Development of an Experimental Apparatus for Studying High-Temperature Heat and Mass Transfer in Soils

2021 ◽  
Author(s):  
Mohsen Hedayati-Dezfooli
Keyword(s):  
Heat Flux ◽  
Temperature Profile ◽  
Heat Fluxes ◽  
Temperature Level ◽  
Experimental Assessment ◽  
Linear Temperature ◽  
Experimental Apparatus ◽  
The Difference ◽  
Bottom Heat ◽  
Heat And Moisture

The objective of this study was to design and build an experimental apparatus for studying heat and moisture transport phenomena in soils at temperatures greater than 40°C up to 90°C. An experimental soil cell was designed and constructed for experimental studies of one-dimensional heat and moisture transfer within a vertical soil column. The interference effect between two proximate TDR probes was examined for three types of soils and it was found that parallel TDR probes can interfere with each other if the distance between them is around 1 cm. Also, for the samples with higher water contents, the effect of interference on the electromagnetic waveform signals is more prominent, which can result in 15% uncertainty in the measurement of water content. Through the numerical study, four stages of design analysis were carried out to eventually reach a satisfactory design which was deemed to meet the research objective, i.e. less than 5% variation of heat fluxes in the radial direction along the soil cell. The experimental assessment of the final soil cell was first performed using dry Matilda soil. The temperature profile along the soil cell deviated from the linear temperature profile by 18.6% when the temperature level and gradient was high at 82.6°C and 90°C/m, respectively. At this condition, the difference of heat fluxes between the top and bottom heat flux meters was recorded to be 34%. This case is the worst case due to the low thermal conductivity of the dry soil. The experimental assessment of the final soil cell was also done for a wet Matilda soil at a degree of saturation of about 65%. The temperature profile along the soil cell had a maximum deviation of 7.7% from the linear temperature profile even when the temperature level of the soil cell was high at 82.1°C. At this condition, the difference of heat fluxes between the top and bottom heat flux meters was recorded to be 4.2%. After the reliability of the apparatus was assessed, nine cases of the wet soil were studied. The results show that the temperature gradient is the main driving force to cause moisture migration.

scholarly journals Development of an Experimental Apparatus for Studying High-Temperature Heat and Mass Transfer in Soils

2021 ◽  
Author(s):  
Mohsen Hedayati-Dezfooli
Keyword(s):  
Heat Flux ◽  
Temperature Profile ◽  
Heat Fluxes ◽  
Temperature Level ◽  
Experimental Assessment ◽  
Linear Temperature ◽  
Experimental Apparatus ◽  
The Difference ◽  
Bottom Heat ◽  
Heat And Moisture

The objective of this study was to design and build an experimental apparatus for studying heat and moisture transport phenomena in soils at temperatures greater than 40°C up to 90°C. An experimental soil cell was designed and constructed for experimental studies of one-dimensional heat and moisture transfer within a vertical soil column. The interference effect between two proximate TDR probes was examined for three types of soils and it was found that parallel TDR probes can interfere with each other if the distance between them is around 1 cm. Also, for the samples with higher water contents, the effect of interference on the electromagnetic waveform signals is more prominent, which can result in 15% uncertainty in the measurement of water content. Through the numerical study, four stages of design analysis were carried out to eventually reach a satisfactory design which was deemed to meet the research objective, i.e. less than 5% variation of heat fluxes in the radial direction along the soil cell. The experimental assessment of the final soil cell was first performed using dry Matilda soil. The temperature profile along the soil cell deviated from the linear temperature profile by 18.6% when the temperature level and gradient was high at 82.6°C and 90°C/m, respectively. At this condition, the difference of heat fluxes between the top and bottom heat flux meters was recorded to be 34%. This case is the worst case due to the low thermal conductivity of the dry soil. The experimental assessment of the final soil cell was also done for a wet Matilda soil at a degree of saturation of about 65%. The temperature profile along the soil cell had a maximum deviation of 7.7% from the linear temperature profile even when the temperature level of the soil cell was high at 82.1°C. At this condition, the difference of heat fluxes between the top and bottom heat flux meters was recorded to be 4.2%. After the reliability of the apparatus was assessed, nine cases of the wet soil were studied. The results show that the temperature gradient is the main driving force to cause moisture migration.

The effects of thermal conditions on the cell sizes of two-dimensional convection

1994 ◽  
Vol 281 ◽  
pp. 33-50 ◽  
Author(s):  
Masaki Ishiwatari ◽  
Shin-Ichi Takehiro ◽  
Yoshi-Yuki Hayashi
Keyword(s):  
Heat Flux ◽  
Lower Boundary ◽  
Thermal Conditions ◽  
Heat Fluxes ◽  
Internal Cooling ◽  
Two Dimensional ◽  
Numerical Integrations ◽  
The Difference ◽  
Convective Cells ◽  
Upper Boundary

The effects of thermal conditions on the patterns of two-dimensional Boussinesq convection are studied by numerical integration. The adopted thermal conditions are (i) the heat fluxes through both upper and lower boundaries are fixed, (ii) the same as (i) but with internal cooling, (iii) the temperature on the lower boundary and the heat flux through the upper boundary are fixed, (iv) the same as (iii) but with internal cooling, and (v) the temperatures on both upper and lower boundaries are fixed. The numerical integrations are performed with Ra = 104 and Pr = 1 over the region whose horizontal and vertical lengths are 8 and 1, respectively.The results confirm that convective cells with the larger horizontal sizes tend to form under the conditions where the temperature is not fixed on any boundaries. Regardless of the existence of internal cooling, one pair of cells spreading all over the region forms in the equilibrium states. On the other hand, three pairs of cells form and remain when the temperature on at least one boundary is fixed. The formation of single pairs of cells appearing under the fixed heat flux conditions shows different features with and without internal cooling. The difference emerges as the appearance of a phase change, whose existence can be suggested by the weak nonlinear equation derived by Chapman & Proctor (1980).

Dissimilarity of Turbulent Fluxes of Momentum and Heat in Perturbed Turbulent Flows

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
H. D. Pasinato
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Direct Numerical Simulation ◽  
Turbulent Flows ◽  
A Priori ◽  
Heat Fluxes ◽  
Reynolds Stresses ◽  
Interaction Terms ◽  
The Difference ◽  
Velocity Pressure

The dissimilarity between the Reynolds stresses and the heat fluxes in perturbed turbulent channel and plane Couette flows was studied using direct numerical simulation. The results demonstrate that the majority of the dissimilarity was due to the difference between the wall-normal fluxes, while the difference between the streamwise fluxes was lower. The main causes for the dissimilarity were the production terms, followed by the velocity-pressure interaction terms. Further insights into the importance of the velocity-pressure interaction in the origin of the dissimilarity are provided using two-point correlation. Furthermore, an octant conditional averaged dataset reveals that not only the wall-normal heat flux but also the streamwise heat flux is strongly related to the wall-normal gradient of the mean temperature. A simple Reynolds-averaged Navier–Stokes (RANS) heat flux model is proposed as a function of the Reynolds stresses. A comparison of the direct numerical simulation data with an “a priori” prediction suggests that this simple model performs reasonably well.

scholarly journals Revising the definition of anthropogenic heat flux from buildings: role of human activities and building storage heat flux

2021 ◽  
Author(s):  
Yiqing Liu ◽  
Zhiwen Luo ◽  
Sue Grimmond
Keyword(s):  
Heat Flux ◽  
Energy Consumption ◽  
Energy Balance ◽  
Human Activities ◽  
Building Energy ◽  
Heat Emission ◽  
Heat Fluxes ◽  
Anthropogenic Heat ◽  
Anthropogenic Heat Flux ◽  
The Difference

Abstract. Buildings are a major source of anthropogenic heat emissions, impacting energy use and human health in cities. The difference between building energy consumption and building anthropogenic heat emission magnitudes and time lag and are poorly quantified. Energy consumption (QEC) is a widely used proxy for the anthropogenic heat flux from buildings (QF,B). Here we revisit the latter’s definition. If QF,B is the heat emission to the outdoor environment from human activities within buildings, we can derive it from the changes in energy balance fluxes between occupied and unoccupied buildings. Our derivation shows the difference between QEC and QF,B is attributable to a change in the storage heat flux induced by human activities (∆So-uo) (i.e., QF,B = QEC − ∆So-uo). Using building energy simulations (EnergyPlus) we calculate the energy balance fluxes for a simplified isolated building (obtaining QF,B, QEC, ∆So-uo) with different occupancy states. The non-negligible differences in diurnal patterns between QF,B and QEC caused by thermal storage (e.g. hourly QF,B to QEC ratios vary between −2.72 and 5.13 within a year in Beijing, China). Negative QF,B can occur as human activities can reduce heat emission from building but are associated with a large storage heat flux. Building operations (e.g., open windows, use of HVAC system) modify the QF,B by affecting not only QEC but also the ∆So-uo diurnal profile. Air temperature and solar radiation are critical meteorological factors explaining day-to-day variability of QF,B. Our new approach could be used to provide data for future parameterisations of both anthropogenic heat flux and storage heat fluxes from buildings. It is evident that storage heat fluxes in cities may also be impacted by occupant behaviour.

Preliminary Investigation of Boiling and Transpiration of Water in a Porous Media Cooled With an Air Flow

2004 ◽  
Author(s):  
Alexis Schubert ◽  
John Keffler ◽  
Alfonso Ortega
Keyword(s):  
Heat Flux ◽  
Porous Media ◽  
Porous Structure ◽  
Heated Surface ◽  
Preliminary Investigation ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Foam Sample ◽  
Porous Sample ◽  
Experimental Apparatus

This paper describes a study focused on heat and mass transfer through various porous media involving both boiling and transpiration. Heat was supplied to a porous structure immersed in water. Water was boiled at the base of the porous material and in some cases advected from the porous structure by air blown over its surface. The porous media was expected to provide higher heat fluxes than those attained during pool boiling by providing additional surface area and by increasing the number of nucleation sites. The behavior was studied from just below the boiling point and into the nucleate boiling regime. The experimental apparatus consisted of a 2.5 cm square jet impinging onto a 2.5 cm square porous sample. A total of four copper foam samples and one carbon graphite foam sample were tested. The foam sample was placed in contact with a 2.5 cm square heated surface. Water was supplied through the sides of the porous sample and was able to leave the system as a vapor through the top surface of the sample, where it was advected away. It was determined that the presence of an impinging jet had no noticeable effect on heat flux. Up to 60% enhancement in heat flux was observed, compared to boiling of the plain surface. Contact resistance was significant and mitigated the affects of sample thermal conductivity.

Thermal instability in a horizontal fluid layer: effect of boundary conditions and non-linear temperature profile

1964 ◽  
Vol 18 (4) ◽  
pp. 513-528 ◽  
Author(s):  
E. M. Sparrow ◽  
R. J. Goldstein ◽  
V. K. Jonsson
Keyword(s):  
Heat Flux ◽  
Rayleigh Number ◽  
Boundary Conditions ◽  
Temperature Profile ◽  
Fluid Layer ◽  
Bounding Surface ◽  
Fixed Temperature ◽  
Linear Temperature ◽  
Lower Bounding ◽  
Horizontal Fluid Layer

An investigation is carried out to determine the conditions marking the onset of convective motion in a horizontal fluid layer in which a negative temperature gradient occurs somewhere within the layer. In such cases, fluid of greater density is situated above fluid of lesser density. Consideration is given to a variety of thermal and hydrodynamic boundary conditions at the surfaces which bound the fluid layer. The thermal conditions include fixed temperature and fixed heat flux at the lower bounding surface, and a general convective-radiative exchange at the upper surface which includes fixed temperature and fixed heat flux as special cases. The hydrodynamic boundary conditions include both rigid and free upper surfaces with a rigid lower bounding surface. It is found that the Rayleigh number marking the onset of motion is greatest for the boundary condition of fixed temperature and decreases monotonically as the condition of fixed heat flux is approached. Non-linear temperature distributions in the fluid layer may result from internal heat generation. With increasing departures from the linear temperature profile, it is found that the fluid layer becomes more prone to instability, that is, the critical Rayleigh number decreases.

Critical Heat Flux in Helically Coiled Tubes

1981 ◽  
Vol 103 (4) ◽  
pp. 660-666 ◽  
Author(s):  
M. K. Jensen ◽  
A. E. Bergles
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Velocity ◽  
High Heat ◽  
Heat Fluxes ◽  
Tube Diameter ◽  
Coiled Tube ◽  
Coil Diameter ◽  
The Difference

A study of boiling R-113 in electrically heated coils of various diameters is reported. Subcooled critical heat flux (CHF) is lower with coils than with straight tubes. The difference increases as mass velocity and ratio of tube diameter to coil diameter (d/D) increases. On the contrary, quality CHF is enhanced and increases with d/D; CHF initially increases with increasing mass velocity, but decreases after a maximum is reached. Operational problems, in particular upstream dryouts, can occur if a coiled tube is operated with low to moderate subcooling near the inlet and with moderately high heat fluxes.

scholarly journals Groundwater flow, heat flux, and permeability inferred from borehole temperature profile in Izu-Oshima volcano, Japan – Implications for subsurface hydrothermal system

2020 ◽  
Author(s):  
Shin'ya Onizawa ◽  
Nobuo Matsushima
Keyword(s):  
Heat Flux ◽  
Groundwater Flow ◽  
Temperature Profile ◽  
Hydrothermal System ◽  
Heat Fluxes ◽  
Total Heat ◽  
Conductive Heat ◽  
Upward Flow ◽  
Total Heat Flux ◽  
Layer Formation

Abstract Groundwater flow velocity as well as conductive and convective heat fluxes were estimated using temperature profile data from a 1000 m–deep borehole in the central part of the Izu-Oshima volcano, Japan. Two depth intervals below groundwater level with upward groundwater flow patterns were examined assuming a one-dimensional vertical steady flow. The groundwater velocity and total heat flux were estimated to be 5.0–5.4×10-10 m/s and 0.54–0.59 W/m2, respectively, for the basement layer (Formation 4). For the shallower layer (Formation 2), both the upward velocity and heat flux were higher, indicating greater contributions of convective mass and heat transfer compared to those in the deeper layer. Furthermore, assuming that the upward flow was buoyancy-driven, vertical permeabilities of 2.8–5.1×10-15 and 1.7–3.1×10-16 m2 , respectively, were estimated for Formations 2 and 4. The temperature patterns of the lava-dominant region (Formation 3), sandwiched between Formations 2 and 4, suggested the occurrence of lateral cooler groundwater inflow in fractures. These results were used for understanding a hydrothermal system beneath the volcano. The total heat flux estimated for Formation 4 (0.54–0.59 W/m2) was nearly three times higher than the conductive heat flux in the northwestern coastal area, suggesting a higher heat supply below the central part of the volcano. A hydrothermal free convection system was inferred in Formations 2 and 3. In Formation 2, buoyancy-driven upward flow was enhanced because of the heat below and the higher permeability. Cooler groundwater was laterally supplied in lava fractures in Formation 3 to compensate for the mass loss by the upward flow at the bottom of Formation 2.

Critical Heat Flux Limits for a Heated Surface Impacted by a Stream of Liquid Droplets

1994 ◽  
Vol 116 (3) ◽  
pp. 679-685 ◽  
Author(s):  
P. J. Halvorson ◽  
R. J. Carson ◽  
S. M. Jeter ◽  
S. I. Abdel-Khalik
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Heated Surface ◽  
Droplet Impact ◽  
Heat Fluxes ◽  
Liquid Droplets ◽  
Impact Frequency ◽  
Experimental Apparatus ◽  
Key Factor ◽  
Wetted Area

An experimental apparatus has been constructed to allow investigation of heat transfer from a horizontal, upward facing, heated surface impacted by streams of monodisperse water droplets of varying size and impact frequency. Droplet diameters between 2.3 and 3.8 mm were used, with drop frequencies varying from 2 to 15 droplets per second. The droplet impact velocity was 1.3 m/s. Critical heat flux, surface superheat, droplet size, and frequency were the primary measured data. Heat fluxes as high as 325 W/cm2 were achieved with wall superheats of only 24°C. The liquid film thickness produced upon droplet impact is shown to be a key factor in these experiments, and the importance of investigating the wetted area is highlighted. The effectiveness of droplet impact cooling using droplets with diameters on the order of millimeters is shown.

scholarly journals Technical Note: Is radiation important for the high amplitude variability of the MOC in the North Atlantic?

2007 ◽  
Vol 4 (5) ◽  
pp. 699-707
Author(s):  
D. Nof ◽  
L. Yu
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Air Temperature ◽  
North Atlantic ◽  
High Amplitude ◽  
Technical Note ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Ocean Temperature ◽  
The Difference

Abstract. Radiation is of fundamental importance to climate modeling and it is customary to assume that it is also important for the variability of North Atlantic Deep Water (NADW) formation and the meridional overturning cell (MOC). Numerous articles follow this scenario and incorporate radiation into the calculation. Using relatively old heat-flux maps based on measurements taken in the nineteen sixties, Sandal and Nof (2007) recently suggested that, even though the radiation terms are of the same order as the other heat-flux terms, they are not important for the variability of the NADW and the MOC. They proposed that only sensible and latent heat fluxes are important for the long-term variability of the convection, i.e., for processes such as Heinrich events, which supposedly correspond to turning convection on-and-off in the Atlantic. Here, we place this suggestion on a firmer ground by presenting new and accurate up-to-date heat flux maps that also suggest that the radiation is of no major consequence to the NADW variability. Also, we attribute the relative importance of sensible and latent heat fluxes and the contrasting negligible role of radiation to the fact that the latent and sensible heat fluxes are primarily proportional to the difference between the sea surface and the air temperature whereas the radiation is primarily proportional to the sea surface temperature, i.e., radiation is approximately independent of the atmospheric temperature. Due the small heat capacity ratio of air/water (1/4), the difference between the ocean temperature and the air temperature varies dramatically between the state of active and inactive MOC, whereas the ocean temperature by itself varies very modestly between a state of active and inactive convection.

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