scholarly journals A Simplified Thermal Design Model for a Single Vertical U-Tube Borehole Utilized in Ground-Coupled Source Heat Pumps

2020 ◽  
pp. 151-162
Author(s):  
Ali H. Tarrad
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Heat Pumps ◽  
Tube Diameter ◽  
Thermal Design ◽  
Test Range ◽  
New Development ◽  
Ground Coupled Heat Pump ◽  
Conductivity Range ◽  
Borehole Thermal Resistance

The present work dealt with the thermal assessments of the ground-coupled heat pump heat exchangers utilized in the field of geothermal energy source. A model was performed to predict the overall thermal resistance of a single vertical heat exchanger embedded in the borehole. The philosophy of the U-tube replacement with a single equivalent tube size was implemented with new development. Four tube sizes were used to build several borehole geometry configurations, they were (9.53) mm, (12.7) mm, (15.88) mm, and (19.05) mm accommodated in borehole sizes of (65) mm, (75) mm, (90) mm, and (100) mm respectively. Twelve borehole geometry configurations were examined as DX condensers circulate R410A refrigerant. These geometry assemblies produced a range of (0.29-0.57) for tube spacing to borehole ratio tested at (0.73) W/m K to (1.9) W/m K filling thermal conductivity range. The results of the present correlation showed good agreement with previously published correlations in the open literature. A mean temperature difference between the condensed vapor refrigerant and soil was assumed to have existed as (14) °C. Increasing the tube spacing from (2) to (3) times the tube diameter exhibited an augmentation in the heat loading of the borehole. This rise in the heat loadings of the U-tube was (8-10) % and (13-17) % for the geometry configurations of (9.53) mm and (12.7) mm tube sizes respectively. The tube diameter has also shown its importance in the thermal process of the borehole. At (75) mm borehole size and tube spacing of (2) times tube outside diameter, the predicted borehole thermal resistance for (9.53) mm tube diameter was higher than that of (19.05) mm one by (78-80) % for the test range of grout thermal conductivity.

An Investigation of Hydrological Effects on the Thermal Performance of Standing Column Well Using the in-situ Thermal Response Test

2019 ◽  
Vol 27 (02) ◽  
pp. 1950015 ◽  
Author(s):  
Keun Sun Chang ◽  
Young Jae Kim ◽  
Min Jun Kim
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Flow Rate ◽  
Large Scale ◽  
Thermal Response ◽  
Thermal Response Test ◽  
Response Test ◽  
Geological Conditions ◽  
Wide Range ◽  
Borehole Thermal Resistance

The standing column well (SCW) for ground source heat pump (GSHP) systems is a highly promising technology with its high heat capacity and efficiency. In this study, a large-scale thermal response tester has been built, which is capable of imposing a wide range of heat on the SCW ground heat exchangers and measuring time responses of their thermal parameters. Two standing column wells in one site but with different well hydrological and geological conditions are tested to study their effects on the thermal performances. Borehole thermal resistance ([Formula: see text]) and the effective thermal conductivity ([Formula: see text]) are derived from data obtained from the thermal response test (TRT) by using a line source method. Results show that the influence of groundwater movement on the thermal conductivity of the SCW is not very significant (3.6% difference between two different geological conditions). This indicates that results of one TRT measurement can be applied to other SCWs in the same site, with which considerable time and cost are saved. The increase of circulation flow rate enhances the ground thermal conductivity moderately (4.5% increase with flow rate increase of 45%), but the borehole thermal resistance is substantially lowered (about 25.9%).

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.

Research on the Thermal Property of Lightweight-Aggregate-Concrete Hollow-Block Wall

2011 ◽  
Vol 250-253 ◽  
pp. 2970-2974
Author(s):  
Dan Li ◽  
Jun Lin Tao ◽  
Jiang Yu
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Thermal Property ◽  
Lightweight Aggregate ◽  
Thermal Design ◽  
Lightweight Aggregate Concrete ◽  
Key Factor ◽  
Hollow Block ◽  
Block Wall ◽  
Heat Flux Law

The Theoretical calculation and the finite element method (FEM) are used for studying the thermal property of hollow-block and hollow-masonry. The method of appendix in the standard for Thermal Design of Civil Buildings is adopted to calculate the thermal resistance and the average thermal conductivity of hollow-block and hollow-masonry. ANSYS is used for simulating temperature distribution and heat flux law under connective loads. The conduction and convection phenomena are taking into account in this study for four different values of the mortar conductivity and four different values for the bricks. The thermal resistance and the average thermal conductivity of hollow-block and hollow-masonry is the key factor for reference.

Thermal Resistance of Particle Laden Polymeric Thermal Interface Materials

2003 ◽  
Author(s):  
Ravi S. Prasher ◽  
Jim Shipley ◽  
Suzana Prstic ◽  
Paul Koning ◽  
Jin-Lin Wang
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Volume Fraction ◽  
Applied Pressure ◽  
Electronics Cooling ◽  
Thermal Design ◽  
Thermal Interface Materials ◽  
Particle Volume ◽  
Thermal Interface ◽  
Interface Materials

Particle laden polymers are one of the most prominent thermal interface materials (TIM) used in electronics cooling. Most of the research has primarily dealt with the understanding of the thermal conductivity of these types of TIMs. For thermal design, reduction of the thermal resistance is the end goal. Thermal resistance is not only dependent on the thermal conductivity, but also on the bond line thickness (BLT) of these TIMs. It is not clear which material property(s) of these particle laden TIMs affects the BLT and eventually the thermal resistance. This paper introduces a rheology based semi-empirical model for the prediction of the BLT of these TIMs. BLT depends on the yield stress of the particle laden polymer and the applied pressure. The BLT model combined with the thermal conductivity model can be used for modeling the thermal resistance of these TIMs for factors such as particle volume faction, particle shape, base polymer viscosity, etc. This paper shows that there exists an optimal filler volume fraction at which thermal resistance is minimum. Finally this paper develops design rules for the optimization of thermal resistance for particle laden TIMs.

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.

scholarly journals Evaluation of Subsurface Heat Capacity through Oscillatory Thermal Response Tests

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5791
Author(s):  
Nicolò Giordano ◽  
Louis Lamarche ◽  
Jasmin Raymond
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Resistance ◽  
Thermal Response ◽  
Heat Diffusion ◽  
Observation Well ◽  
Pump System ◽  
In Situ Conditions ◽  
Radial Depth ◽  
Borehole Thermal Resistance

Two methods are currently available to estimate in a relatively short time span the subsurface heat capacity: (1) laboratory analysis of rock/soil samples; (2) measure the heat diffusion with temperature sensors in an observation well. Since the first may not be representative of in-situ conditions, and the second imply economical and logistical issues, a third option might be possible by means of so-called oscillatory thermal response tests (OTRT). The aim of the study was to evaluate the effectiveness of an OTRT as a tool to infer the subsurface heat capacity without the need of an observation well. To achieve this goal, an OTRT was carried out in a borehole heat exchanger (BHE). The total duration of injection was 6 days, with oscillation period of 12 h and amplitude of 10 W m−1. The results of the proposed methodology were compared 3-D numerical simulations and to a TRT with a constant heat injection rate with temperature response monitored from a nearby observation well. Results show that the OTRT succeeded to infer the expected subsurface heat capacity, but uncertainty is about 15% and the radial depth of penetration is only 12 cm. The parameters having most impact on the results are the subsurface thermal conductivity and the borehole thermal resistance. The OTRT performed and analyzed in this study also allowed to evaluate the thermal conductivity with similar accuracy compared to conventional TRTs (3%). On the other hand, it returned borehole thermal resistance with high uncertainty (15%), in particular due to the duration of the test. The final range of heat capacity is wide, highlighting challenges to currently use OTRT in the scope of ground-coupled heat pump system design. OTRT appears a promising tool to evaluate the heat capacity, but more field testing and mathematical interpretation of the sinusoidal response is needed to better isolate the subsurface from the BHE contribution and reduce the uncertainty.

Thermal Resistance of Particle Laden Polymeric Thermal Interface Materials

2003 ◽  
Vol 125 (6) ◽  
pp. 1170-1177 ◽  
Author(s):  
Ravi S. Prasher ◽  
Jim Shipley ◽  
Suzana Prstic ◽  
Paul Koning ◽  
Jin-lin Wang
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Volume Fraction ◽  
Applied Pressure ◽  
Electronics Cooling ◽  
Thermal Design ◽  
Thermal Interface Materials ◽  
Semiempirical Model ◽  
Thermal Interface ◽  
Interface Materials

Particle laden polymers are one of the most prominent thermal interface materials (TIM) used in electronics cooling. Most of the research has primarily dealt with the understanding of the thermal conductivity of these types of TIMs. For thermal design, reduction of the thermal resistance is the end goal. Thermal resistance is not only dependent on the thermal conductivity, but also on the bond line thickness (BLT) of these TIMs. It is not clear which material property(s) of these particle laden TIMs affects the BLT and eventually the thermal resistance. This paper introduces a rheology based semiempirical model for the prediction of the BLT of these TIMs. BLT depends on the yield stress of the particle laden polymer and the applied pressure. The BLT model combined with the thermal conductivity model can be used for modeling the thermal resistance of these TIMs for factors such as particle volume faction, particle shape, base polymer viscosity, etc. This paper shows that there exists an optimal filler volume fraction at which thermal resistance is minimum. Finally this paper develops design rules for the optimization of thermal resistance for particle laden TIMs.

In-Situ Thermal Response Test for Ground Source Heat Pump Application

2011 ◽  
Author(s):  
Wenzhi Cui ◽  
Quan Liao ◽  
Guiqin Chang ◽  
Qingyuan Peng ◽  
Tien-Chien Jen
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Heat Pump ◽  
Thermal Response ◽  
Ground Source Heat Pump ◽  
Thermal Response Test ◽  
Response Test ◽  
Ground Source ◽  
Borehole Thermal Resistance

The design and performance optimization of ground source heat pump (GSHP) systems need the exact thermal properties of the soil, such as ground thermal conductivity and capacity, and the borehole thermal resistance of borehole heat exchanger (BHE). In-situ thermal response test (TRT) is the most widely used method to determine the overall thermal physical properties of the geological structure around the borehole. A TRT experimental apparatus has been developed and thermal response test was performed in Chongqing, southwest China. Both single-U and double-U borehole heat exchangers are studied in this work. The test duration is about 70 hours. Data direct fitting and parameter estimate method are both used to determine the soil thermal conductivity and the borehole thermal resistance. The results showed that the average ground thermal conductivity of the test region for single U and double U BHE conditions are 2.55 and 2.51 Wm−1K−1, and borehole thermal resistance are 0.116 and 0.066 mKW−1, respectively.

scholarly journals Development of Analytical Model for a Vertical Single U-Tube Ground-Coupled Heat Pump System

2020 ◽  
pp. 1-14
Author(s):  
Ali H. Tarrad
Keyword(s):  
Thermal Resistance ◽  
Analytical Model ◽  
Heat Pump ◽  
Diameter Ratio ◽  
Thermal Design ◽  
Pump System ◽  
Heat Pump System ◽  
Ground Heat Exchangers ◽  
Borehole Thermal Resistance ◽  
Outside Diameter

An analytical model was built to study the thermal design of a single vertical U-tube coupled heat pump under steady-state conditions. It was based on the philosophy of U-tube replacement by an equivalent thermal resistance situated between the heat transfer medium that flows inside the tube and the borehole boundary. An obstruction factor was introduced to account for the reduction of heat flow from or to a tube in the borehole due to the presence of the second leg of the U-tube. Two Copper U-tubes with wall factors of (12.5) and (14.29) were implemented to comprise several borehole configurations to verify the present work. The shank spacing was ranged between (2) and (4) times the U-tube outside diameter producing shank spacing to borehole diameter ratio range of (0.29-0.59). The model was utilized for the assessment of DX ground heat exchangers works as a condenser for cooling purposes. Reducing of the tube spacing to tube outside diameter ratio from (3.3) to (2) for both tube wall factors showed a rise for the borehole thermal resistance in the range of (22-54)% and (26.5-28)% predicted at wall factors of (12.5) and (14.29) respectively.

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