scholarly journals Estimation of subsurface flow from high-resolution temperature profiles

Author(s):  
Bo Zhang ◽  
Kai Gu ◽  
Peter Bayer ◽  
Bin Shi ◽  
Fulin Xiang ◽  
...  

Subsurface flow rates are critical for hydrology and geothermal research, while field characterization remains a challenge. There are several analytical solutions for calculating the vertical water flux based on measured temperatures. Heat is a popular natural tracer to estimate subsurface flow rates. However, quantifying flow rates is impeded by insufficient sensors spacing during field investigations or simplifying assumptions for analysis such as sinusoidal temperature boundary. The objective of this study is to develop a convenient method to investigate subsurface flow on the sub-meter scale. Here, we present a program to estimate water fluxes based on temperature-depth profiles, so-called TempFlow. TempFlow is a numerical program written in MATLAB that calculates steady state flow in transient heat tracing based on the inversion of measured high-resolution temperature-depth series observed at a certain time. In this program, the Fiber Optic Distributed Temperature Sensing (FO-DTS) is recommended for temperature collection. FO-DTS techniques provide high-resolution temperature measurements with continuous temperature profiles that account for sub-meter scale and nonperiodic boundary conditions in saturated sediments. The estimated subsurface flow using TempFlow was validated in a medium-scale tank with a series of experiments, where the hydraulic and temperature boundary conditions were well-controlled. The results indicate that the estimation using TempFlow obtained similar results as the experiments. Thus, the method could potentially be used to determine the flow rate of the subsurface.

2002 ◽  
Vol 473 ◽  
pp. 201-210 ◽  
Author(s):  
ROBERTO VERZICCO

The effects of a sidewall with finite thermal conductivity on confined turbulent thermal convection has been investigated using direct numerical simulation. The study is motivated by the observation that the heat flowing through the lateral wall is not always negligible in the low-aspect-ratio cells of several recent experiments. The extra heat flux modifies the temperature boundary conditions of the flow and therefore the convective heat transfer. It has been found that, for usual sidewall thicknesses, the heat travelling from the hot to the cold plates directly through the sidewall is negligible owing to the additional heat exchanged at the lateral fluid/wall interface. In contrast, the modified temperature boundary conditions alter the mean flow yielding significant Nusselt number corrections which, in the low Rayleigh number range, can change the exponent of the Nu vs. Ra power law by 10%.


Author(s):  
Zhihang Song ◽  
Bruce T. Murray ◽  
Bahgat Sammakia

The integration of a simulation-based Artificial Neural Network (ANN) with a Genetic Algorithm (GA) has been explored as a real-time design tool for data center thermal management. The computation time for the ANN-GA approach is significantly smaller compared to a fully CFD-based optimization methodology for predicting data center operating conditions. However, difficulties remain when applying the ANN model for predicting operating conditions for configurations outside of the geometry used for the training set. One potential remedy is to partition the room layout into a finite number of characteristic zones, for which the ANN-GA model readily applies. Here, a multiple hot aisle/cold aisle data center configuration was analyzed using the commercial software FloTHERM. The CFD results are used to characterize the flow rates at the inter-zonal partitions. Based on specific reduced subsets of desired treatment quantities from the CFD results, such as CRAC and server rack air flow rates, the approach was applied for two different CRAC configurations and various levels of CRAC and server rack flow rates. Utilizing the compact inter-zonal boundary conditions, good agreement for the airflow and temperature distributions is achieved between predictions from the CFD computations for the entire room configuration and the reduced order zone-level model for different operating conditions and room layouts.


2021 ◽  
Author(s):  
Simon Schüppler ◽  
Roman Zorn ◽  
Hagen Steger ◽  
Philipp Blum

<p>The measurement of the undisturbed ground temperature (UGT) serves to design low-temperature geothermal systems, in particular borehole heat exchangers (BHEs), and to monitor shallow aquifers. Wireless and miniaturized probes such as the Geosniff (GS) measurement sphere, which are characterized by an autarkic energy supply and equipped with pressure and temperature sensors, are increasingly being used for the measurement of highly resolved vertical temperature profiles. The measurement probe sinks along the course of the BHE with a selectable measurement frequency to the bottom of the BHE and is useable for initial measurements as well as long term groundwater monitoring. To ensure quality assurance and further improvement of this emerging technology, the analysis of measurement errors and uncertainties of wireless temperature measurements (WTMs) is indispensable. Thus, we provide an empirical laboratory analysis of random, systematic, and dynamic measurement errors, which lead to the measurement uncertainty of WTMs using the GS as a representative device. We subsequently transfer the analysed uncertainty to measured vertical temperature profiles of the undisturbed ground at a BHE site in Karlsruhe, Germany. The precision and accuracy of 0.011 K and -0.11 K, respectively, ensure a high reliability of the GS measurements. The largest measurement uncertainty is obtained within the first five meters of descent resulting from the thermal time constant τ of 4 s. The measured temperature profiles are qualitatively compared with common Distributed Temperature Sensing (DTS) using fiber optic cables and punctual Pt-100 sensors. Wireless probes are also suitable to correct temperature profiles recorded with fiber optics with systematic errors of up to -0.93 K. Various boundary conditions such as the inclination of the BHE pipes or changes of the viscosity and density of the BHE fluid effect the descent rate of the GS of up to 40 %. We additionally provide recommendations for technical implementations of future measurement probes and contribute to an improved understanding and further development of WTMs.</p>


2011 ◽  
Vol 15 (3) ◽  
pp. 1081-1093 ◽  
Author(s):  
F. Suárez ◽  
J. E. Aravena ◽  
M. B. Hausner ◽  
A. E. Childress ◽  
S. W. Tyler

Abstract. In shallow thermohaline-driven lakes it is important to measure temperature on fine spatial and temporal scales to detect stratification or different hydrodynamic regimes. Raman spectra distributed temperature sensing (DTS) is an approach available to provide high spatial and temporal temperature resolution. A vertical high-resolution DTS system was constructed to overcome the problems of typical methods used in the past, i.e., without disturbing the water column, and with resistance to corrosive environments. This paper describes a method to quantitatively assess accuracy, precision and other limitations of DTS systems to fully utilize the capacity of this technology, with a focus on vertical high-resolution to measure temperatures in shallow thermohaline environments. It also presents a new method to manually calibrate temperatures along the optical fiber achieving significant improved resolution. The vertical high-resolution DTS system is used to monitor the thermal behavior of a salt-gradient solar pond, which is an engineered shallow thermohaline system that allows collection and storage of solar energy for a long period of time. The vertical high-resolution DTS system monitors the temperature profile each 1.1 cm vertically and in time averages as small as 10 s. Temperature resolution as low as 0.035 °C is obtained when the data are collected at 5-min intervals.


Author(s):  
Ali Pourfard ◽  
Esmaeel Khanmirza ◽  
Reza Madoliat

Simulation of a natural gas network operation is a prerequisite for optimization and control tasks. Treating gas in a transient manner is necessary for accurate simulation of gas networks. However, solving the governing nonlinear partial differential equations of pipe flows is a challenging task. In this paper, a novel approach is proposed based on using an intelligent algorithm called teaching–learning-based optimization. This approach simplifies transient simulation of gas networks with a specified type of boundary conditions. Teaching–learning-based optimization estimates different values for network inlet flow rates. Then by knowing the inlet boundary conditions of the network, the discretized flow equations become linear and the flow equations of each pipe can be solved independently. Thus, the network outlet flow variables can be easily obtained. The differences of obtained and actual network outlet flow rates are considered as a cost function or error. Finally, this intelligent algorithm determines the optimum inlet flow rates at each time level, which minimize the error. The proposed approach is implemented on the in-service gas network. To validate the simulation results, a conventional gradient-based method called trust region dogleg is also used for simulation of the gas network. The comparison of numerical results confirms the accuracy and efficiency of this approach, while it is more computationally efficient. Moreover, the substitution of teaching–learning-based optimization with another powerful intelligent optimization algorithm would not improve the performance of the proposed approach.


2020 ◽  
Vol 17 (24) ◽  
pp. 6423-6439
Author(s):  
Bart Schilperoort ◽  
Miriam Coenders-Gerrits ◽  
César Jiménez Rodríguez ◽  
Christiaan van der Tol ◽  
Bas van de Wiel ◽  
...  

Abstract. Complex ecosystems such as forests make accurately measuring atmospheric energy and matter fluxes difficult. One of the issues that can arise is that parts of the canopy and overlying atmosphere can be turbulently decoupled from each other, meaning that the vertical exchange of energy and matter is reduced or hampered. This complicates flux measurements performed above the canopy. Wind above the canopy will induce vertical exchange. However, stable thermal stratification, when lower parts of the canopy are colder, will hamper vertical exchange. To study the effect of thermal stratification on decoupling, we analyze high-resolution (0.3 m) vertical temperature profiles measured in a Douglas fir stand in the Netherlands using distributed temperature sensing (DTS). The forest has an open understory (0–20 m) and a dense overstory (20–34 m). The understory was often colder than the atmosphere above (80 % of the time during the night, >99 % during the day). Based on the aerodynamic Richardson number the canopy was regularly decoupled from the atmosphere (50 % of the time at night). In particular, decoupling could occur when both u*<0.4 m s−1 and the canopy was able to cool down through radiative cooling. With these conditions the understory could become strongly stably stratified at night. At higher values of the friction velocity the canopy was always well mixed. While the understory was nearly always stably stratified, convection just above the forest floor was common. However, this convection was limited in its vertical extent, not rising higher than 5 m at night and 15 m during the day. This points towards the understory layer acting as a kind of mechanical “blocking layer” between the forest floor and overstory. With the DTS temperature profiles we were able to study decoupling and stratification of the canopy in more detail and study processes which otherwise might be missed. These types of measurements can aid in describing the canopy–atmosphere interaction at forest sites and help detect and understand the general drivers of decoupling in forests.


2021 ◽  
Author(s):  
Mehmet Ilicak ◽  
Ivan Federico ◽  
Ivano Barletta ◽  
Nadia Pinardi ◽  
Stefania Angela Ciliberti ◽  
...  

&lt;p&gt;Marmara Sea including Bosphorus and Dardanelles Straits (i.e. Turkish Strait Systems, TSS) is the connection between the Black Sea and the Mediterranean. The exchange flow that occurs in the Straits is crucial to set the deep water properties in the Black Sea and the surface water conditions in the Northern Aegean Sea. We have developed a new high-resolution unstructured grid model (U-TSS) for the Marmara Sea including the Bosporus and Dardanelles Straits using the System of HydrodYnamic Finite Element Modules (SHYFEM). Using an unstructured grid in the horizontal better resolves geometry of the Turkish Straits. The new model has a resolution between 500 meter in the deep to 50 meter in the shallow areas, and 93 geopotential coordinate levels in the vertical. We conducted a 4 year hindcast simulation between 2016 and 2019 using lateral boundary conditions from CMEMS (https://marine.copernicus.eu/) analysis, in particular Black Sea Forecasting System (BS-FS) for the northern boundary and Mediterranean Sea Forecasting System (MS-FS) for the southern boundary. Atmospheric boundary conditions fare from the ECMWF dataset.&lt;/p&gt;&lt;p&gt;Mean averaged surface circulation shows that there is a cyclonic gyre in the middle of the basin due to Bosphorus jet flowing to the south and turning to west after reaching the southern Marmara coast. The U-TSS model has been validated against the seasonal in situ observations obtained from four different cruises between 2017 and 2018. The maximum bias occurs at around halocline depth between 20 to 30 meters. &amp;#160;We also found that root mean square error field is higher in the mixed layer interface. We conclude that capturing shallow mixed layer depth is very in the Marmara Sea due to the interplay of air-sea fluxes and mixing parametrizations uncertainties. Maximum salinity bias and rms in the new U-TSS model are around 3 psu which is a significant improvement with respect to previous studies. This new model will be used as an operational forecasting system and will provide lateral boundary conditions for the BS-FS and MS-FS models in the future.&lt;/p&gt;


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