Potential application of vacuum insulated tubing for deep borehole heat exchangers

The photovoltaic module temperature depends on many parameters and becomes an important parameter from the system efficiency point of view. For this reason, in this research, a comprehensive analys...

An Experimental and Numerical Investigation of Photovoltaic Module Temperature Under Varying Environmental Conditions

Knowledge of the temperature of the ground in time and space as well as its thermal properties gives basic information about physical phenomena concerning the transfer and accumulation of heat in the ground. It can be also used for evaluation of the heating possibilities of heat pumps; to proper design the size of the ground exchangers and the depth, at which they should be installed. For this purpose, a mathematical model based on the heat balance equation on the ground surface was developed. The basis of the model is the Carslaw-Jaeger equation regarding the temperature profile in the ground. The model was verified using experimental results for two different locations (different climatic conditions, moderate and arid climate)—the standard deviation is equal 0.62 K and 0.92 K, respectively. In this work, the impact of several parameters on the ground temperature profiles and thermal fluxes was determined. It was found that among the examined parameters the amplitude of the daily average solar radiation flux strongly effects on the total amount of heat transferred between the ground and the environment during the year, wherein the other parameters have a negligible effect.

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Heat Transfer Model to Predict Temperature Distribution in the Ground

Evaluation of temperature profiling quality in determining energy efficiencies of borehole heat exchangers

Research on borehole heat exchangers is described on the development of a method for the determination, based on thermal response tests, of the effective thermal conductivity and the thermal resistivity for borehole heat exchangers. This advance is important, because underground thermal energy storage increasingly consists of systems with a large number of borehole heat exchangers, and their effective thermal conductivities and thermal resistivities are significant parameters in the performance of the system (whether it contains a single borehole or a field of boreholes). Borehole thermal energy storages provide a particularly beneficial method for using ground energy as a clean thermal energy supply. This benefit is especially relevant in cities with significant smog in winter. Here, the authors describe, in detail, the development of a formula that is a basis for the thermal response test that is derived from Fourier’s Law, utilizing a new way of describing the basic parameters of the thermal response test, i.e., the effective thermal conductivity and the thermal resistivity. The new method is based on the resistivity equation, for which a solution giving a linear regression with zero directional coefficient is found. Experimental tests were performed and analyzed in support of the theory, with an emphasis on the interpretation differences that stem from the scope of the test.

A New Method Based on Thermal Response Tests for Determining Effective Thermal Conductivity and Borehole Resistivity for Borehole Heat Exchangers

The estimation of the ground temperature profile with respect to the depth and time is the key issue in many engineering applications which use the ground as a source of thermal energy. In the present work, the influence of the model components on the calculated ground temperature distribution has been analysed in order to develop an accurate and robust model for the prediction of the ground temperature profile. The presented mathematical model takes into account all the key phenomena occurring in the soil and on its top surface. The impact of individual model elements on the temperature of the soil has been analysed. It has been found that the simplest models and the most complex model result in a similar temperature variation over the simulation period, but only at a low depth. A detailed analysis shows that a larger depth requires more complex models and the calculation with the use of simple models results in an incorrect temperature and a theoretical COP estimation.

An analysis of the numerical model influence on the ground temperature profile determination

The high (HTGR) and very high (VHTR) temperature nuclear reactors are the most innovative designs and belong to the most advanced fourth generation gas-cooled reactor technology. These types of reactors are designed to have an outlet temperature between 800-1000° C for the HTGR and the VHTR respectively. Such systems are able to generate electrical energy and supply process heat in a broad spectrum of high-temperature and energy-intensive non-electric and thermal processes. In this paper, a numerical analysis of the high temperature HTGR/VHTR combined cycle with co-production of hydrogen and electricity is conducted. The presented cycle consists of three subsidiary circuits with gas turbine and two steam turbines for electric energy generation, and two heat exchangers for hydrogen production at high or medium temperature. The results show that such a combination allows a significant increase of thermal efficiency to about 50% at the reactor outlet temperature of 1273 K and a decrease in cost of hydrogen production.

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Thermodynamic modeling of high-temperature combined cycle for hydrogen and electricity co-production

In this work, the influence of boundary conditions model (environmental model) on the ground temperature profile is analyzed. A numerical model for transport phenomena in the area above the top ground surface and below in the ground is presented. The results of simulation- ground temperature profile and mean seasonal temperature which estimate the energy potential of the ground are presented. In addition, the results of implementation of five different environmental models for the area above the top ground surface are presented. It is found that none of the models is able to reproduce the temperature variation similar to the reference (most complex) model accuracy. On the other hand, it is found that with a slight error a similar result for low ground depth can be obtained using the simplest Model 1.

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An analysis of the boundary conditions model influence on the ground temperature profile determination

The ground surface temperature and the temperature with respect to depth are one of the most important issues for geotechnical and environmental applications as well as for plants and other living organisms. In geothermal systems, temperature is directly related to the energy resources in the ground and it influences the efficiency of the ground source system. The ground temperature depends on a very large number of parameters, but it often needs to be evaluated with good accuracy. In the present work, models for the prediction of the ground temperature with a focus on the surface temperature at which all or selected important ground and environmental phenomena are taken into account have been analysed. It has been found that the simplest models and the most complex model may result in a similar temperature variation, yet at a very low depth and for specific cases only. A detailed analysis shows that taking into account different types of pavement or a greater depth requires more complex and advanced models.

https://iopscience.iop.org/article/10.1088/1742-6596/745/3/032007/pdf

Inga Polepszyc

Papers

An analysis of the numerical model influence on the ground temperature profile determination

Thermodynamic modeling of high-temperature combined cycle for hydrogen and electricity co-production

An analysis of the boundary conditions model influence on the ground temperature profile determination

A numerical model for ground temperature determination