An Improved Thermal-Resistance-Capacitance Model for Vertical Single U-Tube Ground Heat Exchanger

2018 ◽  
Vol 11 (1) ◽  
Author(s):  
Quan Liao ◽  
Yongxiang Fan ◽  
Xiaobo Zhu ◽  
Jintang Li
Keyword(s):  
Heat Exchanger ◽  
Thermal Resistance ◽  
Finite Volume ◽  
Three Dimensional ◽  
Thermal Response ◽  
Data Interpretation ◽  
Physical Parameters ◽  
Ground Heat Exchanger ◽  
Cfd Model ◽  
Capacitance Model

Abstract Based on four-thermal-resistance-capacitance network within a borehole, an improved thermal-resistance-capacitance model (TRCM), which takes into account the effect of nonuniform temperature distribution along the borehole perimeter, is proposed for vertical single U-tube ground heat exchanger. For a given geometric and physical parameters of ground heat exchanger, the numerical simulations of the conventional TRCM based on three-thermal-resistance-capacitance network within borehole, the improved TRCM based on four-thermal-resistance-capacitance network within borehole and three-dimensional (3D) finite volume computational fluid dynamics (CFD) model by using fluent software were conducted, respectively. Through the comprehensive comparisons of simulation results between these above-mentioned three models for vertical single U-tube ground heat exchanger, it could be concluded that the proposed improved TRCM could not only provide relatively high accurate results, but also remarkably decrease the solving time as compared to the benchmark 3D finite volume CFD model. Since the proposed TRCM has better performance than the one based on three-thermal-resistance-capacitance network within borehole and 3D finite volume CFD model, a new reliable and feasible TRCM for vertical single U-tube ground heat exchanger could be available for the design and optimization of ground heat exchanger, the data interpretation of thermal response test (TRT) and other applications of ground heat exchanger in real industrial engineering.

scholarly journals Analysis on Thermal Performance of Ground Heat Exchanger According to Design Type Based on Thermal Response Test

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 651 ◽  
Author(s):  
Sang Bae ◽  
Yujin Nam ◽  
Jong Choi ◽  
Kwang Lee ◽  
Jae Choi
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Heat Exchange ◽  
Thermal Resistance ◽  
Heat Pump ◽  
Thermal Performance ◽  
Thermal Response ◽  
Ground Heat Exchanger ◽  
Thermal Response Test ◽  
Borehole Thermal Resistance

A ground source heat pump (GSHP) system has higher performance than air source heat pump system due to the use of more efficient ground heat source. However, the GSHP system performance depends on ground thermal properties and groundwater conditions. There are many studies on the improvement of GSHP system by developing ground heat exchanger (GHX) and heat exchange method. Several studies have suggested methods to improve heat exchange rate for the development of GHX. However, few real-scale experimental studies have quantitatively analyzed their performance using the same ground conditions. Therefore, the objective of this study was to evaluate the thermal performance of various pipe types of GHX by the thermal response test (TRT) under the same field and test conditions. Four kinds of GHX (HDPE type, HDPE-nano type, spiral fin type, and coaxial type) were constructed in the same site. Inlet and outlet temperatures of GHXs and effective thermal conductivity were measured through the TRT. In addition, the borehole thermal resistance was calculated to comparatively analyze the correlation of the heat exchange performance with each GHX. Result of the TRT revealed that averages effective thermal conductivities of HDPE type, HDPE-nano, spiral fin type, and coaxial type GHX were 2.25 W/m·K, 2.34 W/m·K, 2.55 W/m·K, and 2.16 W/m·K, respectively. In the result, it was found that the average borehole thermal resistance can be an important factor in TRT, but the effect of increased thermal conductivity of pipe material itself was not significant.

Combined Microstructure and Heat Transfer Modeling of Carbon Nanotube Thermal Interface Materials1

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Sridhar Sadasivam ◽  
Stephen L. Hodson ◽  
Matthew R. Maschmann ◽  
Timothy S. Fisher
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Finite Volume ◽  
Pressure Dependence ◽  
Matrix Material ◽  
Three Dimensional ◽  
Coarse Grain ◽  
Total Thermal Resistance ◽  
Thermal Interface ◽  
Cnt Arrays

A microstructure-sensitive thermomechanical simulation framework is developed to predict the mechanical and heat transfer properties of vertically aligned CNT (VACNT) arrays used as thermal interface materials (TIMs). The model addresses the gap between atomistic thermal transport simulations of individual CNTs (carbon nanotubes) and experimental measurements of thermal resistance of CNT arrays at mesoscopic length scales. Energy minimization is performed using a bead–spring coarse-grain model to obtain the microstructure of the CNT array as a function of the applied load. The microstructures obtained from the coarse-grain simulations are used as inputs to a finite volume solver that solves one-dimensional and three-dimensional Fourier heat conduction in the CNTs and filler matrix, respectively. Predictions from the finite volume solver are fitted to experimental data on the total thermal resistance of CNT arrays to obtain an individual CNT thermal conductivity of 12 W m−1 K−1 and CNT–substrate contact conductance of 7 × 107 W m−2 K−1. The results also indicate that the thermal resistance of the CNT array shows a weak dependence on the CNT–CNT contact resistance. Embedding the CNT array in wax is found to reduce the total thermal resistance of the array by almost 50%, and the pressure dependence of thermal resistance nearly vanishes when a matrix material is introduced. Detailed microstructural information such as the topology of CNT–substrate contacts and the pressure dependence of CNT–opposing substrate contact area are also reported.

Calculation and Design Method Study of the Coil-Wound Heat Exchanger

2014 ◽  
Vol 1008-1009 ◽  
pp. 850-860 ◽  
Author(s):  
Zhou Wei Zhang ◽  
Jia Xing Xue ◽  
Ya Hong Wang
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Exchanger ◽  
Design Method ◽  
Fluid Velocity ◽  
Exchange Process ◽  
Three Dimensional ◽  
Simulation Method ◽  
Physical Parameters ◽  
Numerical Result

A calculation method for counter-current type coil-wound heat exchanger is presented for heat exchange process. The numerical simulation method is applied to determine the basic physical parameters of wound bundles. By controlling the inlet fluid velocity varying in coil-wound heat exchanger to program and calculate the iterative process. The calculation data is analyzed by comparison of numerical result and the unit three dimensional pipe bundle model was built. Studies show that the introduction of numerical simulation can simplify the pipe winding process and accelerate the calculation and design of overall configuration in coil-wound heat exchanger. This method can be applied to the physical modeling and heat transfer calculation of pipe bundles in coil wound heat exchanger, program to calculate the complex heat transfer changing with velocity and other parameters, and optimize the overall design and calculation of spiral bundles.

scholarly journals A new three-dimensional CFD model for efficiency optimisation of fluid-to-air multi-fin heat exchanger

2020 ◽  
Vol 19 ◽  
pp. 100658 ◽  
Author(s):  
Miftah Altwieb ◽  
Krzysztof J. Kubiak ◽  
Aliyu M. Aliyu ◽  
Rakesh Mishra
Keyword(s):  
Heat Exchanger ◽  
Three Dimensional ◽  
Cfd Model

An Experimental Study on the Thermal Performance Evaluation of SCW Ground Heat Exchanger

2017 ◽  
Vol 25 (01) ◽  
pp. 1750006 ◽  
Author(s):  
Keun Sun Chang ◽  
Min Jun Kim ◽  
Young Jae Kim
Keyword(s):  
Thermal Conductivity ◽  
Performance Evaluation ◽  
Heat Exchanger ◽  
Effective Thermal Conductivity ◽  
Thermal Performance ◽  
Thermal Response ◽  
High Heat ◽  
Injection Rate ◽  
Operating Parameters ◽  
Ground Heat Exchanger

In recent years, application of the standing column well (SCW) ground heat exchanger (GHX) has been noticeably increased as a heat transfer mechanism of ground source heat pump (GSHP) systems with its high heat capacity and efficiency. Determination of the ground thermal properties is an important task for sizing and estimating cost of the GHX. In this study, an in situ thermal response test (TRT) is applied to the thermal performance evaluation of SCW. Two SCWs with different design configurations are installed in sequence to evaluate their effects on the thermal performance of SCW using a single borehole. A line source method is used to derive the effective thermal conductivity and borehole thermal resistance. Effects of operating parameters are also investigated including bleed, heat injection rate, flow rate and filler height. Results show that the effective thermal conductivity of top drawn SCW (Type A) is 11.7% higher than that of bottom drawn SCW (Type B) and of operating parameters tested bleed is the most significant one for the improvement of the thermal performance (40.4% enhanced in thermal conductivity with 10.9% bleed).

Numerical Assessment of Thermal Response Associated With In Vivo Skin Electroporation: The Importance of the Composite Skin model

2006 ◽  
Vol 129 (3) ◽  
pp. 330-340 ◽  
Author(s):  
S. M. Becker ◽  
A. V. Kuznetsov
Keyword(s):  
Three Dimensional ◽  
Thermal Response ◽  
Physical Parameters ◽  
Damage Potential ◽  
Electric Pulses ◽  
Large Molecules ◽  
Composite Layers ◽  
Thermal Tissue Damage ◽  
Pass Through

Electroporation is an approach used to enhance transdermal transport of large molecules in which the skin is exposed to a series of electric pulses. The structure of the transport inhibiting outer layer, the stratum corneum, is temporarily destabilized due to the development of microscopic pores. Consequently agents that are ordinarily unable to pass into the skin are able to pass through this outer barrier. Of possible concern when exposing biological tissue to an electric field is thermal tissue damage associated with Joule heating. This paper shows the importance of using a composite model in calculating the electrical and thermal effects associated with skin electroporation. A three-dimensional transient finite-volume model of in vivo skin electroporation is developed to emphasize the importance of representing the skin’s composite layers and to illustrate the underlying relationships between the physical parameters of the composite makeup of the skin and resulting thermal damage potential.

scholarly journals Borehole Thermal Analysis for a Closed Loop Vertical U-Tube DX Ground Heat Exchanger

2021 ◽  
Vol 8 (4) ◽  
pp. 501-509
Author(s):  
Ali H. Tarrad
Keyword(s):  
Heat Exchanger ◽  
Thermal Resistance ◽  
Thermal Design ◽  
Ground Heat Exchanger ◽  
Total Thermal Resistance ◽  
Steady State Condition ◽  
Tube Heat Exchanger ◽  
Cooling Unit ◽  
Geometry Configuration ◽  
Borehole Thermal Resistance

The borehole geometry configuration and its sizing represent great challenges to the thermal equipment designer in the field of geothermal energy source. The present work represents a piece in that direction to avoid elaborate mathematical and computation schemes constraints for the preliminary design of the U-tube ground heat exchanger operates under a steady-state condition. A correlation was built for the prediction of the borehole thermal resistance. The U-tube diameter, leg spacing, borehole diameter, and the offset configuration with respect to the center of the borehole were introduced in the present correlation. An equivalent tube formula and borehole configuration were postulated to possess the same grout volume as the original loop. A variety of geometrical configurations were tested at different U-tube and borehole sizes. The predicted total thermal resistance of the borehole was implemented into the thermal design of the (DX) ground condenser to sizing the borehole U-tube heat exchanger. A hypothetical cooling unit of (1) ton of refrigeration that circulates R410A refrigerant was chosen for the verification of the present model outcomes. The predicted thermal resistance revealed an excellent agreement with other previously published work in this category.

scholarly journals UNSTEADY HEAT TRANSFER IN A HORIZONTAL GROUND HEAT EXCHANGER

2018 ◽  
Vol 40 (4) ◽  
pp. 34-40
Author(s):  
B.I. Basok ◽  
B.V. Davidenko ◽  
I.K. Bozhko ◽  
M.V. Moroz
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Three Dimensional ◽  
Heat Transfer Agent ◽  
Ground Heat Exchanger ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Unsteady Heat Transfer ◽  
Pump System ◽  
Heat Pump System

By the three-dimensional model of heat transfer in the system "ground - horizontal ground heat exchanger - heat transfer agent", an analysis of the efficiency of the horizontal multi-loop heat exchanger, which is an element of the heat pump system, was carried out. Based on the results of numerical simulation, the time dependence of the heat transfer agent temperature at the outlet from the ground heat exchanger and the amount of heat extracted from the ground is determined. The results of calculations by the presented model are satisfactorily agree with the experimental data.

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