79 results about "Ground heat exchanger" patented technology

A method of operating a thermal system implementing a ground-source heat pump includes receiving design parameters associated with a design of the thermal system and receiving one or more measurement inputs associated with a flow of a thermal fluid through a borefield of a ground heat exchanger. The method further includes, based on the measurement inputs and the design parameters, predicting one or more predicted thermal values of the thermal fluid using a forward model. The method further includes predicting one or more predicted borefield parameters of the borefield based on inverting the forward model. The method further includes monitoring the thermal system based on the predicted borefield parameters.

Controlling heating and cooling in a conditioned space utilizes a fluid circulating in a thermally conductive structure in fluid connection with a hydronic-to-air heat exchanger and a ground heat exchanger. Air is moved past the hydronic-to-air heat exchanger, the air having fresh air supply and stale air exhaust. Sensors located throughout the conditioned space send data to a controller. User input to the controller sets the desired set point temperature and humidity. Based upon the set point temperature and humidity and sensor data, the controller sends signals to various devices to manipulate the flow of the fluid and the air in order to achieve the desired set point temperature and humidity in the conditioned space. The temperature of the fluid is kept less than the dew point at the hydronic-to-air heat exchanger and the temperature of the fluid is kept greater than the dew point at the thermally conductive structure.

The invention relates to the technical field of ground source heat pumps, and discloses a buried pipe type heat exchanger temperature distribution determining method which is based on a U-shaped buried pipe heat exchange system and comprises the steps that an equilibrium equation is established, and initial conditions and boundary conditions are set; calculating thermal resistance of each part according to thermophysical parameters of rock soil and a system; determining an initial drilling wall temperature distribution and an initial fluid temperature distribution before the system begins to operate; determining the heat flux density of the rock soil converged outside the well in each small section of the U-shaped buried pipe; establishing a line source model equation set, and calculating drilling wall temperature distribution in a system operation process; well wall temperature distribution in the system operation process is substituted into the balance equation, and fluid temperature distribution and heat exchange amount in the system operation process are obtained; and performing cycle calculation according to the cycle index and the operation period. According to the method, the ground heat exchanger model is established through the virtual heat source method, the temperature distribution condition of rock soil and fluid in the well in the operation cycle is obtained, and the thermal behavior of the tube well in the drilled well is predicted.

The invention relates to a distributed cross-seasonal heat storage type ground source heat pump heating air-conditioning system group and a regulation and control method. The distributed cross-seasonal heat storage type ground source heat pump heating air-conditioning system group is composed of a plurality of distributed heating air-conditioning systems. Each distributed heating air-conditioning system is close to the served building and is provided with an independent ground heat exchanger, a heat pump, a circulating pump, a connecting pipeline, a heating air-conditioning user and an outdoor air heat exchanger; a plurality of distributed heating air-conditioning systems form a heating air-conditioning system group; the distributed heating air-conditioning systems in the group are subjected to centralized and unified power distribution, all the distributed heating air-conditioning systems are interconnected through a wireless communication network, operation data of all the distributed heating air-conditioning systems are shared, and centralized cooperative regulation and operation management are carried out. In spring and autumn, surplus wind, light and electric power are utilized to store heat or cold underground through a heat pump and a ground heat exchanger; in summer, the heat pump is used for air-conditioning refrigeration, and heat is discharged to the underground or air; in winter, heat of soil or air is extracted through the ground source heat pump to supply heat to a room.

The invention discloses a buried pipe temperature response calculation method considering underground water seepage and ground temperature gradient, and belongs to the field of building environment and energy application engineering.The buried pipe temperature response calculation method comprises the steps that a shallow buried pipe heat exchanger is regarded as a finite long-line heat source model, and when underground water seepage passes, the shallow buried pipe heat exchanger is regarded as a finite long-line heat source seepage model; an energy control equation containing a soil heat conduction item, an underground water seepage convection item and a ground temperature gradient correlation item at the same time is established, and initial temperature distribution based on ground temperature gradient, ground surface fixed wall temperature and boundary conditions of an underground limited boundary are set; and finally, obtaining an analytical solution expression of the change of the temperature at any position of the underground soil along with the time through analytical solution. According to the method, the defect that a traditional model ignores key environmental factors is overcome, the heat transfer process of heat conduction and convection coupling can be accurately simulated, the accuracy of temperature field prediction and the reliability of long-term performance evaluation are remarkably improved, meanwhile, the complexity of numerical calculation is avoided, and the calculation efficiency is improved.

The utility model discloses a soil source heat pump air conditioning system combining gravity assisted heat pipes with zoned pipe burying and cross-seasonal cold storage. The soil source heat pump air conditioning system comprises a first pipe burying area, a second pipe burying area and a soil source heat pump unit. Wherein the soil source heat pump unit communicates with the first ground heat exchanger and the second ground heat exchanger in a switchable mode, and the one-way heat exchanger is used for releasing heat from first soil to surface air in a one-way mode. In this way, when the ground air temperature is lower than the first soil temperature in the cold supply period (summer), heat absorbed by the first soil is released into the ground air through the gravity heat pipe, and then the refrigeration energy efficiency of the ground source heat pump unit can be improved; when the ground air temperature is lower than the first soil temperature in the non-cooling period of the air conditioner, the one-way heat exchanger can transmit heat in the first soil to the ground air in a one-way mode, cross-seasonal cold storage of the first soil can be achieved for a long time, and the refrigeration energy efficiency of the ground source heat pump air conditioning system is higher in the cooling period of the air conditioner in the next year.

The utility model discloses a heating system utilizing compressed air energy storage compression thermal coupling ground source heat pump, which belongs to the technical field of compressed air energy storage, and comprises a compressed air energy storage system and a ground source heat pump system, the water side of the steam-water cooler in each compressed air energy storage compression unit is connected with the cooling tower through a cooling water circulation pipeline, and the ground source heat pump system is connected with the cooling water circulation pipeline. According to the compressed air energy storage system, compression heat in the compressed air energy storage process can be stored in the soil in the non-heating season through comprehensive utilization of equipment such as the ground heat exchanger and the ground source heat pump unit arranged in the compressed air energy storage system and pipelines, the cross-seasonal heat storage mode is adopted, the ground source heat pump system is combined, and the energy storage efficiency is improved. The utilization efficiency of waste heat and the energy efficiency of the whole compressed air energy storage system are improved while heating is achieved.

A multi-source ground-to-air heat transfer system is configured to store thermal energy during a cooling / dehumidifcation mode of operation for future use during a heating mode of operation. The multi-source ground-to-air heat transfer system utilizes a ground loop that is configured under an enclosure, such as a greenhouse, and is in thermal communication with a thermal reservoir medium to conduct and store heat. A thermal exchange fluid is pumped through the ground loop and ground heat exchanger and may receive heat from a condenser during a cooling / dehumidification mode of operation and may liberate heat to the evaporator during a heating mode. The enclosure air may receive heat from the heat pump during a heating mode and may liberate heat to the evaporator during a cooling / dehumidification mode. The heat exchange system may employ a heat pump having a reversing valve to change the mode of operation.

The invention provides a PV / T coupling ground source heat pump heat supply method. The PV / T coupling ground source heat pump heat supply method comprises the steps that heat supply is achieved for users through a PV / T efficient coupling ground source heat pump heat supply system; the system comprises a heat storage water tank, a ground source heat pump unit, a ground heat exchanger, an electric heating device and a liquid storage tank, the method comprises the steps that the temperature of a heat storage water tank is detected, the user side circulating water trend and / or the ground source side circulating water trend of the ground source heat pump unit side are / is determined according to the temperature of the heat storage water tank, and heating of the user side is achieved according to the user side circulating water trend and / or the ground source side circulating water trend. According to the method provided by the invention, the energy consumption of the ground source heat pump unit can be effectively reduced.

Systems and methods using fluid flow through concentric channels for ground heat exchange. A heat exchange system may be installed by inflating a flexible tube in a borehole. An accessible subsurface adaptor provides connections between the heat exchange features and laterals, as well as the ability to measure and monitor performance of the system.

The utility model belongs to the technical field of tubular heat exchanger equipment, and particularly relates to a shallow sleeve type ground heat exchanger which comprises a straight pipe assembly, a U-shaped pipe assembly and a flange plate assembly, and the straight pipe assembly and the U-shaped pipe assembly are connected in a sealed mode through the flange plate assembly. The straight pipe assembly comprises an inner straight pipe and an outer straight pipe. The U-shaped pipe assembly comprises an inner U-shaped pipe and an outer U-shaped pipe. The flange assembly comprises a first flange and a second flange. The first flange plate and the second flange plate are detachably connected; two clamping blocks are installed at the side end of the first flange plate, inserting holes are formed in the side ends of the clamping blocks, a first gasket is installed at the bottom of the first flange plate, and a plurality of first through grooves are formed in the first gasket; an inserting groove is formed in the bottom of the second flange plate, a sliding groove is formed in the second flange plate, the inserting groove communicates with the sliding groove, a through hole is formed in the side end of the second flange plate, an inserting assembly is arranged at the position of the through hole, a second gasket is installed at the bottom of the second flange plate, and a plurality of second through grooves are formed in the second gasket.

The utility model discloses an open type buried pipe fresh air heat exchange system which comprises a plurality of buried pipe heat exchangers extending into deep soil in the longitudinal direction, the buried pipe heat exchangers are connected in series through communicating pipes, and the buried pipe heat exchangers connected in series form a buried heat exchange module. An air outlet of the buried heat exchange module is connected with the circulating fan, the circulating fan is connected with the air collection chamber, the air collection chamber is connected with an air feeder of the bidirectional flow fresh air ventilator, and the air feeder of the bidirectional flow fresh air ventilator is connected with the air supply pipeline; an exhaust fan of the bidirectional flow fresh air machine is connected with an air return pipeline and an exhaust pipeline, and the exhaust pipeline is connected with an air inlet of the buried heat exchange module. The indoor unit is ingenious and reasonable in structural design, ground source heat energy can be fully utilized by matching the ground heat exchanger with the circulating fan and the two-way flow fresh air fan, and alternate operation of two working conditions of internal circulation and external ventilation can be realized, so that fresh and clean air is always provided for the interior of a room, and the indoor unit is environment-friendly and energy-saving. And a relatively comfortable temperature and humidity state is kept indoors.

The present application belongs to the technical field of geothermal energy development and utilization, and relates to a hydrothermal type buried pipe heat exchanger optimization design method based on PINN, comprising: 1, numerical simulation and benchmark data set generation; 2, PINN construction and training: constructing a PINN neural network, converting the mass conservation equation and the energy conservation equation in the pore medium into a partial differential equation residual, and together with the discrete data error generated by the numerical simulation software to form a composite loss function; using the nonlinear fitting capability of the PINN neural network, and embedding the physical partial differential equation of fluid flow and heat transfer in the pore medium into the loss function as a soft constraint; 3, data-driven optimization based on the proxy model; the present application not only fundamentally solves the problems of poor generalization ability and easy non-physical interpretation of traditional pure data-driven models, but also breaks through the bottleneck of convergence difficulty and high training cost when solving complex engineering problems by pure PINN.

The present invention relates to a thermal management system and energy storage station for a sodium-electric energy storage device. The thermal management system includes: an above-ground heat exchanger disposed within the sodium-electric energy storage device; an above-ground temperature sensor disposed within the sodium-electric energy storage device; multiple underground heat exchangers that can be dispersedly buried underground at the site where the sodium-electric energy storage device is located; multiple underground temperature sensors that can be buried underground and adjacent to the multiple underground heat exchangers; a control pipeline that connects the above-ground heat exchanger and each underground heat exchanger and includes a control valve group and a drive pump; and a control unit that is electrically connected to the control valve group, the drive pump, the above-ground temperature sensor, and each underground temperature sensor. The thermal management system can effectively manage the thermal state of the sodium-electric energy storage device and has the advantages of energy saving, high efficiency, low cost, and compact size, which is conducive to promoting the popularization and application of sodium-electric energy storage devices.

A heat exchanger (20) for a heating network, in particular a cold district heating network or long-distance heating network, with at least one heat transfer surface for transferring heat from a network fluid of the heating network to a building heating fluid of a building heating system of a building (7), in particular a residential building, wherein at least one flow connection (5) for the building heating fluid and at least one return connection (5) for the building heating fluid are provided, is proposed, which is improved compared to the state of the art, in particular reducing the effort and / or increasing the energy efficiency and the economic efficiency and / or realizing new functionalities.This is achieved according to the invention by the heat exchanger (20) being designed as a ground heat exchanger (20), wherein the ground heat exchanger (20) has at least one ground contact surface for the ground and wherein the ground heat exchanger (20) has at least one heat network inlet (21) for receiving a heat network line (1), in particular a heat network pipe (1), of the heat network, wherein the heat network inlet (21) comprises at least the heat transfer surface.

The invention discloses a compressed air energy storage system coupled with a deep ground source heat pump, which comprises a compressed air energy storage system, a deep ground source heat pump system and a heat user side, an expansion end heat exchanger in the compressed air energy storage system is connected with an expansion end liquid storage tank and a ground heat exchanger in the deep ground source heat pump system; the compression end heat exchanger is connected with a compression end liquid storage tank and a heat user end intermediate heat exchanger, and meanwhile, a buried pipe heat exchanger of the deep ground source heat pump system is also connected with the heat user end intermediate heat exchanger and serves as a supplementary heat source of a compressed air energy storage system and a heat user end; and renewable heat energy is introduced to optimize and improve the heat energy distribution utilization and energy supply level of the compressed air energy storage system. Through a coupling mode, the utilization and consumption capability of the system for renewable energy sources is enhanced, peak shifting scheduling of low-grade energy sources in the system is realized, and the stability and continuity of system operation are improved; the defects that when a traditional compressed air system is coupled with the heat user side, the coincidence degree of the heat energy demand period is high, the heat source temperature is unstable, and the heat supply amount is insufficient are overcome, so that the energy distribution mode of the coupling system is more reasonable, and the operation mode is more diversified.

The invention belongs to the field of shallow geothermal resources, particularly provides a shallow geothermal energy multi-field coupling simulation experiment system, and aims to solve the problems that traditional numerical simulation lacks physical authenticity, and field test is high in cost, long in period and uncontrollable. An experiment platform box body integrated with a layered simulation geologic body is constructed, and systems such as groundwater runoff simulation, mesh temperature control, a heat interference source, buried pipe heat exchange and water pumping and filling wells and the like are cooperatively operated; a'heat-water-force 'multi-physical field coupling environment including underground water seepage, ground temperature field distribution and ground source / water source heat pump engineering activities is truly simulated, so that the development process of shallow geothermal energy is accurately simulated.

The invention belongs to the technical field of underground pipe geothermal heating, and relates to an asymmetric arrangement method and design method of a buried pipe group for an underground water seepage field, and the method comprises the following steps: in the flowing direction of underground water, the depth of buried pipes is non-uniformly distributed according to the gradient principle of'shallow upstream and deep downstream '; the horizontal distances between the buried pipes are non-uniformly distributed according to the principle that the upstream is dense and the downstream is sparse; in the three-dimensional space, the adjacent buried pipes are distributed in a stepped mode or a staggered mode through differential arrangement of the depth and the distance, so that the heat affected zones of all the wells are overlapped in a staggered mode in the vertical direction and the horizontal direction. The depth, the horizontal distance and the arrangement form of the buried pipes are differentially adjusted in the seepage direction, so that the heat extraction strength of a pipe group is matched with the heat-carrying recovery capacity of underground water in space, cold accumulation is restrained, and dynamic balance of a regional rock-soil thermal field and long-term efficient and stable operation of a system are achieved.

The present invention is a system for generating electricity using the temperature difference between the surface and underground of a planet in combination with solar energy. Utilizing the temperature difference between the surface and underground of a planet that has the opportunity to be exposed to sunlight, a uniquely structured ground heat exchanger is used on a planet that can be periodically exposed to sunlight to fully utilize its surface and underground heat and cold sources. The system then combines this with an organic Rankine cycle to perform heat-to-work conversion, thereby achieving thermoelectric power generation on the planet. To save costs, the present invention uses a reasonable structural design to enable the heat-to-work conversion system to operate in both forward and reverse directions. To adapt to different usage scenarios, the present invention can flexibly select different working fluids based on the specific temperature conditions of the planet, so that the system's power generation efficiency can always reach the optimal level for the current situation. This type of power generation method can largely get rid of dependence on solar radiation, and can also obtain relatively stable, high-quality electricity in places where sunlight cannot always be irradiated.

The invention relates to a thermal management system for a sodium electricity energy storage device and an energy storage station, and the thermal management system comprises an overground heat exchanger which is arranged in the sodium electricity energy storage device; the overground temperature sensor is arranged in the sodium electricity energy storage device; the underground heat exchangers can be dispersedly buried under the ground of a site where the sodium electricity energy storage device is located; the plurality of underground temperature sensors can be buried underground and are adjacent to the plurality of underground heat exchangers one by one; the control pipeline is connected with the ground heat exchanger and each underground heat exchanger, and comprises a control valve group and a driving pump; and the control unit is electrically connected with the control valve group, the driving pump, the overground temperature sensor and the underground temperature sensors. The thermal management system can perform effective thermal management on the sodium electricity energy storage device, has the advantages of energy conservation, high efficiency, low cost, compact size and the like, and facilitates promotion of popularization and application of the sodium electricity energy storage device.

The invention discloses a ground source heat pump electric heating power conversion calculation method considering variable flow buried pipe heat exchange characteristics, and belongs to the field of comprehensive energy and electric power system comprehensive dispatching, and the ground source heat pump electric heating power conversion calculation method comprises the steps that 1, a thermal model of a single U-shaped buried pipe under variable flow regulation is established, obtaining a linear relation between the temperature of an outlet and an inlet of the fluid and the temperature of a drill hole wall when the flow of the fluid in the single U-shaped buried pipe changes; 2, the method is popularized to a thermal model of a multi-U-shaped buried pipe system, the linear relation between the outlet and inlet fluid temperatures and the borehole wall temperature when the terminal fluid flow changes is obtained, and the extracted total heat is calculated through the flow of each branch and the temperature difference between the inlet and the outlet; and 3, establishing a variable-flow electric-thermal coupling model of the ground source heat pump to obtain an electric-thermal power conversion relation among the heating power of the ground source heat pump, the temperature of the starting end inlet and the output temperature of the drilling field. According to the invention, the fluid flow is used as a continuous regulation variable, so that the operation flexibility of the ground source heat pump system is improved.

The invention discloses a multi-stage ground source heat pump system based on a green building. The multi-stage ground source heat pump system comprises a ground heat exchanger, an atomizing pump, a ground source heat pump, an air compression pump, a solar auxiliary heating system and a control valve. According to the system, the ground heat exchanger is connected with the atomizing pump, and the atomizing pump is connected with the ground source heat pump and the air source heat pump in series, so that efficient heat energy conversion is realized. In addition, the solar auxiliary heating system in the system can be connected with the atomizing pump in parallel, so that energy utilization is more sufficient. Control valves such as a reversing valve and a flow control valve in the system can be adjusted according to needs. According to the multi-stage ground source heat pump system, on the basis that the basic heat energy requirement is met, heat can be supplemented to the ground through the ground heat exchanger, so that the temperature of underground rock soil is kept stable, and the system construction cost is reduced. Meanwhile, the air source heat pump and the solar auxiliary heating system are introduced to serve as supplementary energy, balance of the underground temperature field can be further optimized, and the overall energy efficiency is improved.

A system and method for in ground heat exchange, including at least one first array and one second array, each first and second array comprising a plurality of capped pipes; at least one temperature sensor; and at least one flow rate sensor, a plurality of flow rate valves connected to each first array and second array, the flow rate valves configured to facilitate flow of a liquid through the system; at least one pump attached to the flow rate valves for modulating the flow rate of the system; and a heat pump, wherein the system is configured to provide heating and cooling to a building.

The quincunx ground heat exchanger comprises an inner pipe, outer pipes and a bottom sealing section, the multiple outer pipes are arranged on the outer wall of the inner pipe at intervals, every two adjacent outer pipes are not in contact, the contact area of the outer pipes and the stratum is effectively increased, and the heat exchange amount and the heat exchange efficiency of the outer pipes are remarkably improved; the outer wall surface of the inner pipe is tangent to the contour line of the outer wall surface of the outer pipe, and the contact area is obviously reduced through point contact between the outer pipe and the inner pipe, so that heat loss caused by heat exchange of high-temperature fluid in the inner pipe to the outer pipe is reduced; in the construction process, the backfill material with low heat conductivity coefficient is filled between the outer part of the inner pipe and the adjacent outer pipe, so that the outward heat loss of the thermal fluid in the inner pipe is further reduced, the single well heat extraction efficiency of the buried pipe is greatly improved, and the construction cost of utilizing the geothermal energy in the middle-deep layer is saved.

The invention provides a solar middle-deep layer ground source heat pump flexible heat supply system and a design calculation method. The system comprises a solar heat collector, a middle-deep layer sleeve type buried pipe heat exchanger, a heat pump unit and a heat exchanger. The solar heat collector is connected with the heat exchanger; the heat exchanger is connected with the middle-deep layer sleeve type buried pipe heat exchanger and a user side through a three-way adjusting valve group; the middle-deep layer sleeve type ground heat exchanger is connected with the heat pump unit through the valve group, and the heat pump unit is connected with the user side through the valve group; the solar heat collector collects low-grade heat energy, and part of the low-grade heat energy is stored underground through the middle-deep layer sleeve type buried pipe heat exchanger and used for flexible regression of an underground temperature field deviating from an initial value under the influence of heat extraction. The ground source heat pump unit converts low-grade heat energy into high-grade heat energy. The invention further provides a design calculation method based on the system. On the basis of the heat transfer model, the quantitative regulation operation method of the heat supply system is provided to guide flexible and efficient operation of the composite system.

The application provides a ground source heat exchanger installation structure and a ground source heat exchanger installation method. The ground source heat exchanger installation structure comprises a ground buried pipe heat exchanger, a horizontal connecting pipe and a cantilever beam support. The ground buried pipe heat exchanger is arranged on the outside of a building body. The horizontal connecting pipe is connected with the ground buried pipe heat exchanger and extends horizontally from the outside of the building body. The cantilever beam support is installed horizontally on the outside of the building body. When the horizontal connecting pipe connected with the ground buried pipe heat exchanger extends along the outside of the building body, even if the outside of the building body still needs to be continuously constructed, such as pit backfilling and the like, the horizontal connecting pipe is not easily bent and damaged by the stress of the pit backfilling due to the support of the cantilever beam support on the lower side of the horizontal connecting pipe, the horizontal connecting pipe is effectively protected, the risk of gas collection after the horizontal connecting pipe is connected in an up-down bending manner is reduced, and the stable and efficient operation of the ground source heat exchanger system is ensured.

The invention belongs to the technical field of buried pipe heat exchange, and relates to a PINN-based shallow buried pipe heat exchanger optimization design method, which comprises the following steps of: 1, simulating a high-fidelity numerical value and generating a reference data set; 2, constructing a physical information neural network; 3, verifying the consistency of the training model and the physics; 4, performing multi-target automatic optimization based on the micro agent model; according to the method, the physical mechanism is generated in the data driving model, and the differentiable end-to-end optimization framework is constructed, so that the core defects of physical incredibility, low optimization efficiency, flow splitting and the like of an agent model in the prior art are fundamentally solved, and the crossing from'rapid simulation 'to'reliable optimization' is realized.

The invention provides a heating system for a long-period industrial waste heat storage area. The heating system comprises a ground heat exchanger; the first circulating cooling water waste heat recovery device is used for recovering heat in the cooling water; the first circulating cooling water waste heat recovery device and the absorption heat pump are connected to the ground heat exchanger in parallel through valves and pipelines; the heating terminal device is connected to the absorption heat pump through a heat exchanger and a valve; the steam waste heat recovery device is connected to a generator of the absorption heat pump to form a circulation loop, the steam waste heat recovery device serves as a high-level heat source of the absorption heat pump, and the first circulating cooling water waste heat recovery device is connected with the ground heat exchanger in the non-heating season through the state of the switching valve; in the heating season, the absorption heat pump is connected with the ground heat exchanger.

A geothermal heat storage intelligent regulation and control heat exchange device comprises a water injection section, a connecting section, a water outlet section and a ground heat exchanger, the connecting section is communicated with the water injection section and the water outlet section, a circulating medium is injected into the water injection section and circulates in the connecting section, the water outlet section and the ground heat exchanger, and a filtering assembly is rotationally installed in the water outlet section. A micro-electrostatic module is installed at the joint of the water outlet section and the ground heat exchanger, a plurality of reinforcing rings are installed on the peripheries of the water injection section and the water outlet section, suspended solids passing through the filtering assembly are adsorbed and removed, blockage of a heat exchange channel is avoided, through the reinforcing rings, the strength of the water injection section and the strength of the water outlet section can be improved, and the phenomenon that the water injection section and the water outlet section are damaged due to soil extrusion is avoided.