scholarly journals Borehole Resistance and Heat Conduction Around Vertical Ground Heat Exchangers

2012 ◽  
Vol 6 (1) ◽  
pp. 32-40 ◽  
Author(s):  
Zoi Sagia ◽  
Athina Stegou ◽  
Constantinos Rakopoulos
Keyword(s):  
Heat Conduction ◽  
Heat Exchanger ◽  
Thermal Resistance ◽  
Heat Exchangers ◽  
Borehole Diameter ◽  
Working Fluid ◽  
Geometrical Parameters ◽  
Conductive Heat ◽  
Ground Heat Exchanger ◽  
Borehole Thermal Resistance

Borehole thermal resistance in Ground Heat Exchanger (GHE) installations is affected by several parameters such as geometrical attributes of heat exchanger in the borehole, pipes' characteristics and grout’s thermal conductivity. A study is carried out to compare the values computed by Ground Loop Design (GLD) Software, GLD 2009, with three ana-lytical solutions for U-shaped tubes. The analysis is focused on dimensionless ratios of borehole geometrical parameters (borehole diameter to outside pipe diameter and shank spacing to borehole diameter) and pipes according to Standard Di-mension Ratio (SDR) and on eight common grouts. Finally, the effect of heat conduction in the borehole is examined by means of finite element analysis by Heat Transfer Module of COMSOL Multiphysics. A two-dimensional (2-D) steady-state simulation is done assuming working fluid temperatures for winter and summer conditions and typical Greek undis-turbed ground temperature in a field of four ground vertical U-tube heat exchangers surrounded by infinite ground. The temperature profile is presented and the total conductive heat flux from the pipe to the borehole wall per meter of length of ground heat exchanger is computed for pipes SDR11 (the outside diameter of the pipe is 11 times the thickness of its wall), SDR9 and SDR17 for summer working conditions and three different configurations. It is attempted to reach to comparative results for borehole thermal resistance value through different types of analysis, having considered the major factors that affect it and giving trends for the influence of each factor to the magnitude of its value.

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.

Thermal Simulation of Plate-Fin Heat Exchangers

2013 ◽  
Vol 291-294 ◽  
pp. 1623-1626 ◽  
Author(s):  
Jin Jin Tian ◽  
Zhe Zhang ◽  
Yong Gang Guo
Keyword(s):  
Heat Conduction ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Temperature Response ◽  
Process Industry ◽  
Geometrical Parameters ◽  
Fluid Temperature ◽  
Recent Past ◽  
Plate Heat ◽  
Transfer Data

Plate-fin heat exchangers are playing an important role in the power and process industry in the recent past. Hence, it has become necessary to model their temperature response accurately. A new mathematical model of plate-fin heat exchanger is proposed, considering the heat conduction resistance along the fins and the separating plates. The effects of fin geometrical parameters and spacer thickness on the performances of the heat exchanger have been numerically calculated. It is found that the heat conduction resistance of fins has significant influence on the outlet fluid temperature variation. The analysis presented here suggests a better method of heat-transfer data analysis for plate heat exchangers.

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.

Comparison of Borehole Thermal Resistance Values of Ground Heat Exchanger Obtained by Several Methods

2013 ◽  
Vol 732-733 ◽  
pp. 103-108 ◽  
Author(s):  
Han Byul Kang ◽  
Seok Yoon ◽  
Gyu Hyun Go ◽  
Seung Rae Lee
Keyword(s):  
Heat Exchanger ◽  
Thermal Resistance ◽  
Heat Pump ◽  
Heating System ◽  
Geothermal System ◽  
Ground Heat Exchanger ◽  
Ubiquitous System ◽  
Borehole Thermal Resistance ◽  
Quantity Of Heat ◽  
Emission Of Greenhouse Gases

The Ground-Coupled or Source Heat Pump (GCHP/GSHP) system is increasingly being considered as an alternative to traditional cooling/heating system because it can reduce the emission of greenhouse gases. The GCHP/GSHP system uses sustainable ground temperature to emit heat during the summer and to extract heat during the winter. It is a ubiquitous system because it can be used at any time or place and semi-permanent energy. The geothermal system is composed of Ground Heat Exchanger (GHE), heat pump and load facilities. The GHE is embedded in a borehole, which is made up of GHE and grout. The borehole thermal resistance is the most important parameter in designing the geothermal system because it shows the quantity of heat transfer in the borehole. There are many methods to estimate the borehole thermal resistance. Thermal Performance Tests (TPTs) were conducted to directly measure the borehole thermal resistance of several kinds of GHEs. Then the experiment results and analytical results were compared in order to select the most accurate methods to evaluate the borehole thermal resistance.

scholarly journals Evaluation of Borehole Thermal Resistance in Ground Heat Exchanger

2013 ◽  
Vol 29 (10) ◽  
pp. 49-56 ◽  
Author(s):  
Seok Yoon ◽  
Seung-Rae Lee ◽  
Han-Byul Kang ◽  
Gyu-Hyun Go ◽  
Min-Jun Kim ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Thermal Resistance ◽  
Ground Heat Exchanger ◽  
Borehole Thermal Resistance

The Effect of Longitudinal Heat Conduction on Periodic-Flow Heat Exchanger Performance

1964 ◽  
Vol 86 (2) ◽  
pp. 105-117 ◽  
Author(s):  
G. D. Bahnke ◽  
C. P. Howard
Keyword(s):  
Heat Conduction ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Zero Element ◽  
General Purpose ◽  
Periodic Flow ◽  
Gas Streams ◽  
Flow Heat ◽  
Area Use ◽  
Significant Figures

A numerical finite-difference method of calculating the effectiveness for the periodic-flow type heat exchanger accounting for the effect of longitudinal heat conduction in the direction of fluid flow is presented. The method considers the metal stream in crossflow with each of the gas streams as two separate but dependent heat exchangers. To accommodate the large number of divisions necessary for accuracy and extrapolation to zero element area, use was made of a general purpose digital computer. The values of the effectiveness thus obtained are good to four significant figures while those values for the conduction effect are good to three significant figures. The exchanger effectiveness and conduction effect have been evaluated over the following range of dimensionless parameters. 1.0⩾Cmin/Cmax⩾0.901.0⩽Cr/Cmin⩽∞1.0⩽NTU0⩽1001.0⩾(hA)*⩾0.251.0⩾As*⩾0.250.01⩽λ⩽0.32

THE EFFECT OF LIQUID SUCTION HEAT EXCHANGER SUB-COOLER ON PERFORMANCE OF A FREEZER USING R404A AS WORKING FLUID

2015 ◽  
Vol 76 (11) ◽  
Author(s):  
Muhammad Nuriyadi ◽  
Sumeru Sumeru ◽  
Henry Nasution
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Cooling Capacity ◽  
Experimental Results ◽  
Working Fluid ◽  
Liquid Line ◽  
Cabin Temperature

This study presents the effect of liquid-suction heat exchangers (LSHX) sub-cooler in a freezer. The LSHX sub-cooler is a method to increase the cooling capacity of the evaporator by lowering temperature at the condenser outlet. The decrease in temperature of the condenser outlet will cause a decrease in the quality refrigerant entering the evaporator. The lower the quality of the refrigerant entering the evaporator, the higher the cooling capacity produced by the evaporator. The LSHX sub-cooler utilizes a heat exchanger to transfer heat from the outlet of the condenser (liquid line) to the suction of the compressor. In the present study, three different LSHX sub-coolers in the freezer with cabin temperature settings of 0, -10 and -20oC were investigated. The results showed that the lowest and the highest of effectiveness of the heat exchanger were 0.28 and 0.58, respectively. The experimental results also showed that EER reduction is occurred at the cabin temperature setting of 0oC and -10oC, whereas the EER improvements were always occurred at the cabin temperature settings of -20oC.

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