Type Heat Exchanger Research Articles

Design and optimization of heat exchanger in coaxial pulse tube cryocooler working above 100 K

The coaxial pulse tube cryocooler (PTC) has the advantages of without moving parts at the cold end, compactness and high-efficiency, it shows great application potential in many fields. The present work numerically and experimentally investigated a coaxial PTC working at temperature range from 90 K to 260 K. To improve its efficiency, the exergy analysis method was used to study the distribution of available energy loss in the coaxial PTC. To reduce one of the main available energy losses coming from the heat exchanger, three types of heat exchanger, slit, circular hole (CH) and copper mesh (CM), were analyzed and optimized based on the law of conservation of energy. Finally, two different cold end and hot end heat exchangers are designed respectively in the experiment. The results show the optimized pulse tube cooler can supply 50 W cooling power at 185.3 K with 200 W input power. To the best of our knowledge, its relative Carnot efficiency (16% at 165 K) lies one of the best results in the world. The experimental results also show that the refrigeration efficiency of the present PTC could be much improved by optimizing its operating parameter. In summary, the present PTC can work efficiently at a wide temperature range from 90 K to 260 K, which shows great potential candidate for small refrigerators such as vaccine preservation, organ freezing transportation and outdoor preservation of wildlife samples.

Correlation to predict conditions that lead to liquid-flooding at compressor start-up as a function of evaporator size and fluid properties

Refrigeration cycles with fixed speed compressors cycle on and off to modulate their time averaged cooling capacity. While the cycles are turned off, refrigerant can migrate from the condenser into the colder evaporator. The next start-up process can then pull liquid refrigerant out of the evaporator and into the compressor causing liquid flooding. This phenomenon results in a loss of latent heat for cooling, can undercool the lubricant, and may cause damage to the compression mechanism. The geometric and thermophysical conditions that lead to liquid flooding are poorly understood. Experimental data collected for four refrigerants and three heat exchangers was analyzed for flooding conditions. A correlation was fitted to the experimental data, predicting the experimentally determined charge threshold for flooding with an average deviation of 6.6% and a maximum deviation of 16.7%. Repeating the tests with other heat exchanger types and smaller or larger compressors is suggested as important future work.

Enhanced of fluids mixing and heat transfer in a novel SSK static mixer Organic Rankine Cycle direct contact heat exchanger

In this study, new gas-liquid-liquid three phase direct contact heat exchangers based on SSK mixing elements and annular ribs are proposed to improve the thermal efficiency of the Organic Rankine Cycle. Three types of heat exchangers, including hollow tube heat exchanger, SSK heat exchanger and SSK annular rib combined heat exchanger, are established to compare their heat transfer performance. The heat transfer performance, turbulence intensity, turbulence kinetic energy and pressure drop of three heat exchangers are numerically investigated. The results show that the volumetric heat transfer coefficient, outlet temperature of gaseous working medium, turbulence intensity and turbulent kinetic energy of the combined heat exchanger are significantly higher than those of the SSK heat exchanger and the hollow tube heat exchanger. In addition, the pressure drops of the SSK heat exchanger and the combined heat exchanger are basically the same, which are slightly larger than the pressure drop of the empty tube heat exchanger. In summary, the combined heat exchanger has improved heat transfer performance without causing excessive pressure drop.

Development and performance measurements of a 2.5 kW-class free-piston stirling converter with detailed design and fabrication processes

This study presents the development and performance measurement of a 2.5 kW class free-piston Stirling engine with detailed design and fabrication processes, considering flexure spring stiffness effects on the engine dynamics and performance. The development of the test engine includes tube type heat exchangers and planar flexure springs. In particular, the flexure springs are designed via finite element analyses and verified through stiffness measurements and fatigue life tests. For the performance measurements, an engine test rig is constructed with an LNG combustion heat supply. The thermal efficiency is evaluated in terms of combustion gas components based on the reaction formula of methane. As a result, the electric output and efficiency of the test engine were measured to be 2.46 kW and 19.46%, respectively. Furthermore, the effects of displacer spring stiffness are experimented with a stack design of flexure springs by varying the number of springs. As a result, increases in displacer stiffness increased engine operating frequency and decreased both the piston amplitudes, while power piston velocity remained relatively constant as well as the engine power output. The experimental results are analyzed through a simple linear dynamic model, which showed reasonable agreements.

Simulation of gasketed-plate heat exchangers using a generalized model with variable physical properties

In this article, we present a new generalized model for the steady-state simulation of gasketed-plate exchangers handling single-phase fluids with properties varying with temperature. The model is based on differential balance equations that are discretized using a finite-difference scheme. The set of equations of the proposed model can simulate gasketed-plate heat exchangers with any configuration, encompassing any number of passes for each stream and including the variation of the streams’ physical properties with temperature. The selection of a given configuration is provided by a set of model parameters, without the need to modify the system of equations. Comparisons of the simulation results with closed-form relations valid for an infinite number of plates and with a numerical solution indicate average differences equal to 0.17 % and 0.075 %, respectively. The comparison with experimental data available in the literature indicates mean deviations smaller than 2 °C. The analysis of the simulation results of a typical heat exchanger shows that the models usually employed in the design optimization problems, based on uniform physical properties, may present large departures from the results of our detailed modeling, based on varying properties with temperature, which for its nature is considered more accurate. Moreover, when used in a design, we show that uniform physical properties may yield exchangers that are either oversized or undersized as compared to the use of our model. Therefore, the capacity of the proposed model to provide more accurate simulation results for any gasketed-plate heat exchanger configuration using a unique set of equations is an important contribution to future works involving heat exchanger design optimization.

Development of tin copper alloys in shell and tube evaporator heat exchanger systems in ocean thermal energy converse power plant

A case study of the manufacture of an OTEC factory on a floating ship has been carried out using 100 MW Titanium material at a fairly expensive cost, so the OTEC system was researched using a copper-tin alloy. The behavior of the tin-copper heat exchanger between the Aspen Plus simulation and the Computational Fluid Dynamics (CFD) simulation on Shell And Tube evaporators of Bonnet Divided Flow fixed and Bonnet One-pass Shell fixed (BEM) types is investigated. The difference in temperature between water at sea level of 29 °C and water at a depth of 1000 meters at a temperature of 5 °C is assumed to produce electricity. A marine thermal energy conversion power plant is a continuous source of energy sourced from nature an evaporator heat exchanger with ammonia working fluid will produce power that can drive a turbine forwarded to a generator. The simulation results of CFD of a Bonnet Divided Flow fixed type Heat Exchanger on the hot water inlet line has a temperature of 29.9 °C, when exiting the evaporator shell the temperature decreases to 26.4 °C. At the inlet line, the working fluid of ammonia enters the evaporator at 7.9 °C and when it leaves the tube, the temperature rises to 26.3 °C. The best results of the simulation of Aspen Plus Heat Exchanger type BEM Inlet Ammonia temperature 8 °C and at CFD 7.99 °C. Meanwhile, at the ammonia outlet at 28 °C and in the CFD simulation, the ammonia outlet temperature was 28.21 °C. Aspen Plus Inlet heating water temperature is 30 °C, and in CFD simulation, the temperature is 29.99 °C. While the heating water outlet is 28 °C, and in the CFD simulation, the heating water outlet is 28.15 °C. The conclusion from the simulation results is that the BEM-type heat exchanger is very good and suitable for experimental prototyping.

Cooling performance of Joule Thomson coolers with straight heat exchangers for space science missions

Space-qualified Joule Thomson coolers with significant cooling power below 5K enable a variety of missions, which include large infrared space telescopes, superconducting detectors for astrophysics, and quantum applications. In JAXA, a 4K-class Joule–Thomson cryocooler (4K-JT) and a 1K-class Joule–Thomson cryocooler (1K-JT) have been developed with the required cooling power of 40mW at 4.5K and 10mW at 1.7K respectively, for upcoming next-generation space missions. This paper reports the results of cooling performance tests of these JT coolers with straight heat exchangers. A straight heat exchanger is desirable in several space science missions, including the Space Infrared Telescope for Cosmology and Astrophysics (SPICA), while the coiled type of heat exchanger was used in past missions. The effectiveness of the heat exchanger is strongly affected by its shape and length, and the effectiveness significantly influences the cooling power and the cooling efficiency of the Joule–Thomson cooler. This study designed, fabricated and measured several types of heat exchanger test models. The effect of gravity and the thermal environment on cooling performance are also reported.

Numerical investigation of heat transfer characteristics of spiral, helical, and conical tubes

A tube type heat exchanger is generally used in many industrial applications due to its high heat exchange property and compact structure. Due to the formation of turbulence in a curved section of pipe dean vortices are formed which leads to an increase in heat transfer coefficient. Heat transfer characteristics such as heat transfer coefficient and heat rate for spiral, helical and conical tubes are studied by using ANSYS Fluent. Additionally, pressure drop, temperature distribution, and velocity distribution are also shown for three different tubes. The outlet temperature of fluid flowing through tubes is predicted using a steady-state numerical simulation utilizing a Fluent solver. Similar tube diameter and length are considered for all CFD trials. The outlet temperature of heat transfer fluid is varied with the mass flow rate for all shapes of tubes. A maximum outlet temperature of 338.39 K is observed for the spiral tube for a 0.04 kg/s mass flow rate. For a 0.04 kg/s mass flow rate, the heat transfer coefficient of a spiral tube is 0.44 percent higher than that of a helical tube and 2.57 percent higher than that of a conical tube. Additionally, pressure drop through the spiral tube is 2 % greater than the helical and conical tube.

Experimental and numerical investigation on conjugate performance of fan and heat exchanger of helicopter oil cooling system

• The overall performance of axial fan was studied with two flowrate adjusting modes. • HEs with different fin structures and flow lengths were designed and fabricated. • Coupling performances of fan and different HEs were studied experimentally. • The flow field of oil cooling system at different air flow rate was simulated. • The performance curves obtained by two modes form a hysteresis region. In this article, a combined experimental and numerical study has been performed to investigate the operating performance of axial fan and oil cooling system. A test rig was established, and six types of plate-fin heat exchangers (HEs) with offset strip and rectangular fins and three different flow lengths of 30 mm, 60 mm and 90 mm at side were designed and manufactured. The performance of an axial fan with front guide vane was experimentally studied by two different adjusting modes: gradually increasing and decreasing air flow rate. The conjugate performances of the axial fan and different HEs were discussed in detail. Moreover, a three-dimensional (3D) model was developed to investigate the flow distribution of the system including fan and 30 mm offset strip fins HE at different flow rates. The results show that: (1) the total pressure performance curve of the axial fan under two adjusting modes could form a hysteresis region near the stall boundary. In the hysteresis region, the fan performance curves showed significant difference under both adjusting modes; (2) when the offset strip fins HE with large flow resistance is considered, the system could have two theoretical working points in the hysteresis region. For the case of HE with 90 mm offset strip fins, the flow rates of the system at two theoretical working points were 25.1 m 3 /min and 34.2 m 3 /min, and the heat transfer capacity of the HE were 23.1 kW and 27.5 kW, respectively. In the current experiment, it was found that the system operated at the point with smaller flow rate; (3) when the HE flow resistance exceeded a certain value, the boundary layer separation of the airflow could occur at the rotor blade. The separation had a small effect on the inlet airflow due to its turbulence kinetic energy was low and basically the same at each blade passage. Therefore, the system did not surge or stall at small flow rate.

A comparative study to critically assess the designing criteria for selecting an optimal adsorption heat exchanger in cooling applications

• Adsorption heat exchanger (AdHEx) type, fin dimension and body material are studied. • Different design criteria for comparing AdHExs are employed. • Rectangular finned-flat tube and annular finned-tube AdHExs are compared. • The AdHEx superiority in terms of chiller performance and compactness is examined. • A powerful numerical tool for designing the most efficient AdHExs is provided. In an adsorption cooling system (ACS), it is essential to design the most efficient AdHEx in terms of compactness, heaviness, and ACS performance parameters. For this purpose, the coupled effects of structural type, body material, and fin geometrical specifications of its adsorber heat exchanger (AdHEx) need to be investigated. Therefore, a three-dimensional distributed-parameter model is developed and validated to conduct a comprehensive parametric study on finned flat-tube and annular finned-tube AdHExs. In this regard, two different design criteria of AdHEx heat transfer area to adsorbent mass ratio (S/m ads ) and inter-particle mass transfer resistance are adopted as common bases of the comparisons. The results indicate that for any given bed geometrical configurations, there exists a certain threshold value for the thermal conductivity of AdHEx body material. For values greater than it, the specific cooling power (SCP) and volumetric cooling power (VCP) are approximately invariant. In contrast, the coefficient of performance (COP) is mainly influenced by the volumetric heat capacity (VHC) of the AdHEx body material such that it steadily decreases by increasing VHC. Independent of body material, utilizing the smallest fin dimensions for an AdHEx leads to the highest SCPs at the cost of lowering COP, dramatically. However, maximizing VCP is more complicated because the variations of VCP with fin height show entirely distinct behaviors for different body materials and AdHEx type. It is found that estimating the superiority of an AdHEx over another is beyond the ability of common rules of thumb because of complicated transport phenomena within the adsorber beds. In light of this, the approach and results of this study properly bridge the gap between the scientific and practical aspects of designing an AdHEx based on application constraints.

Spirally wound tubular heat exchanger optimisation using Genetic Algorithm

• Spirally coiled (Giauque-Hampson) type heat exchanger optimization. • Thermal analysis of optimum tube geometry predicted by Genetic Algorithm. • Design aimed at minimum exchanger weight under pressure drop constraints. • Design aimed at minimum exchanger height under pressure drop constraints. • Effect of different process parameters on the optimum heat exchanger design. A Genetic Algorithm based optimization of spirally wound two-fluid stream exchanger is presented. The proposed method elaborates a design methodology consistent with the user-defined specifications while simultaneously fulfilling a design objective linking optimization of either weight, height or thermo-hydraulic performances, etc., depending on the customer requirement. Optimization variables include tube material, tube size, normalized transverse and longitudinal pitches, number of tubes in the innermost layer, increment in the number of tubes with each successive layer, and the total number of tube layers. The effectiveness-NTU approach is adopted for design calculations, including fluid property variations with temperature. This paper explores the effect of optimization criteria like minimum weight or height and variation in pressure drop constraints on the optimized design. A compromise in exchanger effectiveness can substantially reduce its weight. Among the exchangers of the same effectiveness, the one handling 10 times larger flow could be 35 times heavier (subjected to other constraints). Exchanger designed with the minimum height criterion is nearly two times shorter than the one created on a minimum weight basis, while the shorter unit could be two times heavier. The optimum design is a trade-off between achievable minimum mass and maximum allowable pressure drop.

Heat exchangers with fluidization of bulk material (Design review)

A classification of heat exchangers with fluidization of bulk material for use in enterprises of the chemical, mining, construction, food, metallurgical and processing industries has been developed. A critical review of the most characteristic designs of heat exchangers with a fluidized bed, proposed by scientists, designers and inventors of the leading countries of the world, has been carried out. The designs of heat exchangers are analyzed depending on the method of fluidization, the role of bulk material in the heat exchange process, the nature of the heat exchange process over time, the nature of fluidization (in continuous heat exchangers), the mechanism of heat exchange of bulk material, the number of fluidized beds, the presence of additional heat exchange devices in the heat exchanger, the presence of movable structural elements, as well as the type of bulk material of the fluidized bed.
 An analysis of the designs of heat exchangers with a fluidized bed indicates their considerable diversity, however, the most simple to manufacture and operate reliable devices with fixed structural elements and one fluidized bed remain in demand by the industry. The most promising direction for improving fluidized bed heat exchangers is the development of specialized (for processing bulk material or fluid coolant) designs of apparatuses.
 In the future, it is planned to analyze the designs of other types of heat exchangers, as well as ways to improve their efficiency.

Thermo-hydraulic rating of a shell and tube heat exchanger for methanol condensation

Shell and tube heat exchangers are the most common type of heat exchangers, and are applicable for a wide range of operating temperatures and pressures. In the present work the thermo-hydraulic rating of a shell and tube heat exchanger was carried out, in order to perform the condensation of a methanol stream using water as coolant. The overall heat transfer coefficient for both the sensible-heat and latent-heat zone had values of 166.41 W/m2.K and 1,198.39 W/m2.K, respectively; while the required total heat transfer area and percent excess area had values of 38.08 m2 and 3.05 %, respectively. The pressure drops of methanol and water streams reached the values of 51,490.84 Pa and 2,890.50 Pa, respectively. The proposed shell and tube heat exchanger can be employed satisfactorily for the demanded heat transfer service, since the calculated percent excess area does not exceed 25%, and the pressure drop of the water stream does not exceed the value of 80,000 Pa.

Hydrogen preheating in a PEMFC system employing a heat exchanger equipped with an innovative turbulator

Membrane electrodes are the essential parts of a proton exchange membrane fuel cell (PMFC), and they have a significant impact on the shelf life of the stack. Under the influence of prolonged low-temperature conditions, the gas diffusion layer will not be able to remove liquid water and gas transport because of the ruined micro-porous structure. Therefore, hydrogen preheating of the PEMFC anode side is critical. In the present work, a new type of heat exchanger as hydrogen preheater is presented in which an innovative turbulator is inserted at the entrance of the hydrogen side. The proposed turbulator consists of two sections; (i) the finned part with spiral blades, and (ii) the conical part with lateral outputs. A commercial CFD code has been employed to perform a series of numerical simulations based on finite volume method. The impacts of four efficient geometrical parameters on the hydrothermal behavior of hydrogen inside the proposed preheater are investigated numerically. The considered geometrical parameters are the number of the blades, turbulator's length, turbulator's diameter, and blade's angle. All simulations have been performed in any case for four various Reynolds numbers, including Re = 40,000, 60,000, 80,000, and 100,000. The obtained numerical outcomes depicted that employing the proposed hydrogen preheater of PEMFC leads to better performance of the PEMFC by increasing the durability of membrane electrodes.

Dynamic Heat Transfer Characteristic of Heat Exchanger for Sensible Heat Recovery of Raw Coke Oven Gas

Abstract A simplified hybrid-dimensional unsteady heat transfer model for the ascension-pipe heat exchanger with a helically coiled tube embedded in the jacket and supported by high conductivity particles is established based on the non-thermal equilibrium theory of porous medium. This idea can also be used in the design of other heat exchange devices involving the helically coiled tube. According to calculations, the wall temperature of the ascension-pipe heat exchanger periodically varies due to the periodic variations of flow rate and temperature of raw coke oven gas. A great thermal stress will be produced due to this reason. The coal tar precipitation mainly occurs in the late stage of the coking period due to the continuous cooling of molten salt. Based on the detailed analysis, thermal conductivity of packing layer, heat capacity per unit volume of packing layer, volume of packing layer, flow rate of molten salt and inlet temperature of molten salt are important factors that should be scientifically designed in the design of this type of heat exchanger to reduce thermal stress and coal tar precipitation. Cutting off molten salt in the late stage of the coking period is an effective measure to control the wall temperature of the ascension pipe above the dew point of coal tar vapor.

Upgrading the performance of shell and helically coiled heat exchangers with new flow path by using TiO2/water and CuO–TiO2/water nanofluids

Along with the developing technologies, the need for energy has increased day by day and negative environmental effects of fossil energy based systems increased the importance of efficient energy systems. In the recent years, shell and helically coiled type heat exchangers (SHCHEs) are extensively used in various applications because of their superior specifications in comparison with other heat exchangers. In the present work, it is targeted to raise the thermal performance of recently developed shell and helically coiled heat exchangers using single and hybrid type nanofluids. The main aim of this research is specifying the impact of hybrid CuO–TiO2/water nanofluid in comparison with single TiO2/water nanofluid. Also, the effect of adding fins as turbulators on performance enhancement of nanofluids was analyzed. In this regard, TiO2/water and CuO–TiO2/water nanofluids with 1% (wt./wt.) concentration was prepared and circulated in the hot side of both heat exchangers. TiO2/water working nanofluid application in finless and finned SHCHEs averagely upgraded overall heat transfer coefficient as 7.5% and 8.6%, respectively. CuO–TiO2/water working nanofluid application in finless and finned SHCHEs averagely upgraded overall heat transfer coefficient as 10.8% and 12%, respectively. Generally, it was observed that utilizing TiO2/water and CuO–TiO2/water nanofluid in unmodified and modified SHCHEs importantly raised the thermal performance. However, utilization of hybrid type nanofluid presented better performance than single nanofluid in both SHCHEs. Moreover, the outcomes exhibited further positive impacts of integrating fins on performance enhancement of both single and hybrid nanofluids.

Flow and heat transfer in a plain fin-and-hexagonal tube heat exchanger with different side ratios

Improving the thermo-hydraulic performance of heat exchangers (HEs) can considerably manage the energy requirements in various engineering processes. The fin-and-tube heat exchangers (FTHEs) are extensively utilized in recent decades, and they provide substantial benefits over the typical HEs such as high heat transfer surface. The shape and geometry of the tubes remarkably affect the thermal efficiency and pressure drop of these devices. There are many experimental and numerical investigations relating to improving the thermo-hydraulic performance of FTHEs with circular and elliptical tubes in the literature. In the current research, five various hexagonal tubes with different side ratios were utilized to enhance the performance of an FTHE. The impact of various hexagon side ratios on heat transfer capacity and fluid flow characteristic of the FTHE at different Reynolds numbers has studied numerically. According to the obtained results, the plain-fin-and hexagonal tube HE with the side ratio of 0.25 had the best performance. Although the lowest values of the Colburn factor and the weakest heat transfer belong to the FTHE with the side ratio of 0.25, it is preferred to circular tube HEs due to the lower pressure drop they cause.

Numerical simulation on heat transfer and flow of supercritical methane in printed circuit heat exchangers

The printed circuit heat exchanger (PCHE) is a novel type of heat exchanger in liquefied natural gas (LNG) industry. The gasification pressure of LNG in PCHE could exceed the critical pressure of methane, the main component of LNG. This paper established a series of three-dimensional models of PCHE units. The effects of structural parameters and channel shapes on the thermal hydraulic performance are studied. And new correlations to calculate the Nusselt number and Fanning factor of supercritical methane in straight and zigzag PCHEs are developed. For straight PCHE, the most influential geometrical parameters are the spacing between two adjacent channels in the plate and the diameter of the semicircle, which have been taken into account in the new correlation. For zigzag PCHE, the inclined angle has impact on both heat transfer coefficient and pressure drop while the pitch number only influences the pressure drop. Considering these factors, the new correlations for zigzag PCHE are modifications from the new straight PCHE correlations.

Numerical and experimental study on thermal performance of a novel shell and helically coiled tube heat exchanger design with integrated rings and discs

Shell and Helically Coiled Tube Heat Exchangers (SHCTHEXs) are utilized in energy conversion applications in industry and in various engineering systems. They are generally composed of a helically coiled tube and a shell covering it. This coiled structure of tubes, provides better heat transfer and takes less space. There is an ongoing interest in research on this type of heat exchangers. In this study, a new design was created modifying a simple type of conventional shell and helically coiled heat exchanger, by integrating discs and rings. These rings and discs were attached to the helically coiled tubes with the aim of performing as baffles restricting the shell side flow and creating turbulence. The thermal performance of a conventional heat exchanger was improved by this modification. The study was carried out both numerically and experimentally. At first step, two SHCTHEXs, one conventional; one modified, were designed with same overall geometric dimensions. Then created solid models were numerically simulated with same boundary conditions using ANSYS Fluent. Simulations were performed with various flow rates and the results were reported. According to the simulations, compared to the conventional one, with the modified heat exchanger 7.1% increase in average amount of heat transfer rate and around 20% increase in overall heat transfer coefficient were obtained. With the promising results taken by simulations, the modified heat exchanger was fabricated with the same dimensions and it was experimentally tested with same conditions in laboratory to verify the simulation results. Experimental results were in harmony with the simulations with little differences. The average differences between simulation and experimental values in terms of average amount of heat transfer rate were obtained as 2.4% for 3 l/min hot fluid flow rate and 3.5% for 4 l/min hot fluid flow rate. Overall heat transfer coefficient of modified SHCTHEX with circular baffles achieved in the range of 1050–1400 W/m2K. General outcomes of this study exhibited successful design of baffled SHCTHEX.

Group Performance of Energy Piles under Cyclic and Variable Thermal Loading

Energy piles, a new type of heat exchanger that serves dual purposes, have gained increasing attention due to the growing energy demand and corresponding carbon emissions. Depending on intended operational requirements or by accident, energy pile groups may be subjected to cyclic and variable thermal loadings. This study presents the results from a series of full-scale field tests of a 2×2 energy pile foundation. The energy pile group was operated partially or fully during the tests to investigate the potential effects of cyclic nonuniform thermal loadings. The results indicated that the cyclic thermal loadings could induce an increase in compressive stress of piles at the end of the experiments. Further comparative analysis showed that the residual compressive stress was attributed mainly to the drag-down effects of the surrounding soil. The compressive stress induced by drag-down effects will overlap with the thermally induced stress, and thus lead to a more significant effect on the energy piles. If the drag-down effects are presented, the stress change may exceed the theoretical upper bound of thermal stress and may be underestimated. In addition, cyclic nonsymmetrical thermal loadings could induce accumulation of differential settlement and group tilt in the energy pile group. It was shown that the group tilt caused by cyclic and variable thermal loadings can be acceptable for general engineering structures. The group tilt will not accumulate further when subjected to symmetrical thermal loadings. A reasonable arrangement of operational piles still can be used to avoid unwanted group tilt generation.