DEHUMIDIFY AND RECYCLE A GAS FROM A 3D PRINTER

A 3D printing apparatus to dehumidify and recycle a gas from a 3D printer is disclosed herein. The apparatus comprises: a gas inlet to receive a gas flow from a 3D printer, the gas flow comprising gas with evaporated solvents to be cleaned; a heat exchanger to dehumidify the gas flow from the evaporated solvents, the heat exchanger to cool the gas flow by heat transfer to a cold liquid stream from a chiller to saturate and condensate the solvents from the gas flow; a gas outlet to output the dehumidified gas flow back to the 3D printer; and a controller. The controller is to receive a humidity and temperature measurements from a sensor located downstream from the heat exchanger; compare the humidity and temperature measurements with a target humidity and a target temperature respectively; and control a chiller valve from the chiller based on the comparison to adjust the temperature of the gas flow to set an absolute humidity of the gas flow to a predeterminable value.

BACKGROUND

Some additive manufacturing or three-dimensional printing systems generate 3D objects by selectively solidifying portions of a successively formed layers of build material on a layer-by-layer basis.

DETAILED DESCRIPTION

The following description is directed to various examples of additive manufacturing, or three-dimensional printing, apparatus and processes involved in the generation of 3D objects. Throughout the present disclosure, the terms “a” and “an” are intended to denote at least one of a particular element. In addition, as used herein, the term “includes” means includes but not limited to, the term “including” means including but not limited to. The term “based on” means based at least in part on.

For simplicity, it is to be understood that in the present disclosure, elements with the same reference numerals in different figures may be structurally the same and may perform the same functionality.

3D printers generate 3D objects based on data in a 3D model of an object to be generated, for example, using a CAD computer program product. 3D printers may generate 3D objects by selectively processing layers of build material. For example, a 3D printer may selectively solidify portions of a layer of build material, e.g. a powder, corresponding to a slice of 3D object to be generated, thereby leaving the portions of the layer un-solidified in the areas where no 3D object is to be generated. The combination of the generated 3D objects and the un-solidified build material may also be referred to as build bed.

The volume in which the build bed is generated may be referred to as a build chamber.

Suitable powder-based build materials for use in additive manufacturing include polymer powder, metal powder or ceramic powder. In some examples, non-powdered build materials may be used such as gels, pastes, and slurries. Some types of build materials may be used under normal atmospheric conditions, whereas some build materials may be used in an inert atmosphere (e.g., due to oxidation risk, or explosion risk). Some inert gases suitable for the generation of a 3D object may include, for example, nitrogen or carbon dioxide.

Some 3D printers selectively solidify portions of a build material layer corresponding to the geometry of the object to be generated through the ejection of a printing fluid onto the build material layer, the printing fluid may be a curable binder liquid, an energy absorbing fusing liquid, a detailing agent or any printing fluid suitable for the generation of a 3D object. Additionally, the chemical composition of some printing fluids may include, for example, a liquid vehicle and/or solvent to be evaporated once the printing fluid have been applied to the build material layer. For simplicity, the liquid vehicle and/or solvents may be referred hereinafter as solvents. The evaporated solvents may mix with the gas in the build chamber (e.g., ambient air, inert gas). The mix of the gas with the evaporated solvents is further removed from the build chamber.

To avoid part quality defects during the generation of the 3D objects, the build chamber may contain a gas with specific temperature and humidity values. For example, the gas may be present in the build chamber, and may be present between particles of build material in the build chamber. The gas may be supplied to the build chamber in an airflow manner. The composition of the build chamber airflows may also influence the part quality of the 3D objects to be generated. For example, an excessive amount of evaporated solvents in a sealed build chamber may have an impact on the build material in which the 3D objects are to be generated. Thus, it is useful to remove the evaporated solvents from the build chamber using an exhaust gas airflow. Furthermore, some types of build material may require to be in contact with an oxygen free gas, for example an inert gas, to remove any risk of explosion or oxidization. In these examples, a mix of the inert gas and the evaporated solvents are exhausted from the build chamber. In some examples, the inert gas may be recycled. However, a removed gas with evaporated solvents mixed therein may not be suitable for recycling as such solvents may modify the temperature, humidity and composition of the gas and have an associated effect in the part quality of the 3D objects.

Referring now to the drawings,FIG.1is a schematic diagram showing an example of a 3D printing apparatus100to dehumidify and recycle a gas from a 3D printer. Additionally, the 3D printing apparatus100is to control the humidity and temperature of the recycled gas in a 3D printer build chamber. In some examples, the apparatus100may be an integral part of the 3D printer. In other examples, however, the apparatus100is an independent entity fluidically couplable with the 3D printer by means of conduits. In the present disclosure, a conduit may be understood as any channel for conveying a fluid (e.g., ambient air, inert gas). An example of a conduit is a rigid or semi-rigid tube that may have a circular section, or any other section.

The apparatus100comprises a gas inlet115couplable to a first conduit (not shown) that fluidically connects the build chamber of the 3D printer with the gas inlet115. The gas inlet115is to receive a relatively hot gas flow110from the 3D printer. The gas flow110from the 3D printer comprises a gas mixed with evaporated solvents to be cleaned. In the present disclosure, the terms “to clean” and “to dehumidify” may be understood as to separate the evaporated solvents from the gas. The evaporated solvents may be generated from water, alcohol, or other liquid evaporated in the build chamber during the generation of the 3D object.

The apparatus100further comprises a heat exchanger130to separate (e.g., dehumidify) the gas flow110from the evaporated solvents. The heat exchanger130may be implemented as a liquid-to-gas heat exchanger, thereby enabling heat exchange between the relatively hot gas flow110with a relatively cold liquid stream147from a chiller140. The chiller140may be any machine suitable for removing heat from a liquid via a vapor-compression or absorption refrigeration cycle, for example. In some examples, the chiller140is an external element from the apparatus100that interacts with the heat exchanger130. In other examples, the chiller140is an integral part of the apparatus100.

The heat exchanger130is, therefore, to cool the gas flow110by heat transfer135to a cold liquid stream147from the chiller140to saturate and condensate, and thereby separate, the solvents from the gas flow. After the heat transfer135, the liquid stream149warms up due to the absorption of heat from the gas flow110and is recirculated back to the chiller140to cool it down as the cold liquid stream147. The condensed solvents may be collected in a collection tank or a collection tray190for further removal.

The chiller140additionally comprises a chiller valve145to control the flow rate of cold liquid stream147inputted to the heat exchanger130. Therefore, the chiller valve145controls the magnitude of the heat transfer135and may be used to regulate the amount of condensed liquid including the solvents. The chiller valve145is controlled by a controller150. Additionally, or alternatively, the chiller140may control the temperature of the cold liquid stream145to further regulate the amount of condensed liquid including the solvents.

The apparatus100further comprises a gas outlet125couplable to a second conduit that fluidically connects the gas output port of the heat exchanger130with the gas outlet125. The gas outlet125is therefore to receive the dehumidified gas flow120from the heat exchanger130. The dehumidified gas flow120may be totally dehumidified, partially dehumidified of dehumidified below a predeterminable level. In some examples, the gas outlet125is to output the dehumidified gas flow120back to the 3D printer through, for example, an external output conduit to recycle the gas.

Additionally, a sensor160may be installed downstream from the heat exchanger130to measure the temperature and the humidity of the dehumidified gas flow120. In some examples, the sensor160may be a device integrating a thermometer and a hygrometer. In other examples, the sensor160may comprise a first sensor to measure the temperature and a second independent sensor to measure the humidity of the gas flow120. In an example, the sensor160may be part of the apparatus100and may be installed in the second conduit; i.e., between the heat exchanger130and the gas outlet125. In another example, however, the sensor may be an external element from the apparatus100and may be installed in the external output conduit; i.e., between the gas outlet125and the 3D printer. The sensor160is coupled to the controller150.

The controller150comprises a processor155and a memory157with specific control instructions to be executed by the processor155. The controller150is coupled to the chiller valve145and the sensor160. The controller150may control some of the operations of the elements that it is coupled with. The functionality of the controller150is described further below with reference toFIG.2.

In the examples herein, the controller150may be any combination of hardware and programming that may be implemented in a number of different ways. For example, the programming of modules may be processor-executable instructions stored in at least one non-transitory machine-readable storage medium and the hardware for modules may include at least one processor to execute those instructions. In some examples described herein, multiple modules may be collectively implemented by a combination of hardware and programming. In other examples, the functionalities of the controller150may be, at least partially, implemented in the form of an electronic circuitry. The controller150may be a distributed controller, a plurality of controllers, and the like.

FIG.2is a flowchart of an example method200of dehumidifying and recycling a gas from a 3D printer, for example using apparatus100ofFIG.1. The method200may involve previously disclosed elements fromFIG.1referred to with the same reference numerals. In some examples, method100may be executed by the controller150.

The method200starts when a gas flow110with evaporated solvents from a 3D printer is received through the gas inlet115and transferred to the heat exchanger130, where the solvents are condensed and thereby separated from the dehumidified gas flow120. The dehumidified gas flow120may be then recycled and transferred back to the 3D printer.

At block220, the controller150controls the sensor160to receive from the sensor160the temperature and the humidity of the dehumidified gas flow120. The controller150may then receive the temperature and humidity measurements. The received temperature and humidity measurements may be indicative of the conditions in which the build chamber is generating the 3D objects. The sensor160may measure the humidity of the gas flow which may include the absolute humidity and/or the relative humidity.

In the examples herein, the absolute humidity may be understood as the quantity of evaporated solvent (e.g., water) dispersed in a kilogram of the gas (e.g., ambient air, inert gas). The relative humidity may be understood as the amount of evaporated solvent present in the gas expressed as a percentage of the amount needed for saturation at the same temperature.

At block240, the controller150compares the humidity and temperature measurements with a target humidity and a target temperature respectively. In some examples herein, the target humidity and the target temperature may be a range of target humidity and a range of target temperatures.

If the measured humidity and/or temperature are above the target humidity and/or target temperature respectively, it may be indicative that the gas flow110from the 3D printer has not condensed enough solvents, being thereby indicative that the recycled gas flow120may not be completely dehumidified and may potentially affect the part quality of the 3D objects to be generated. Contrarily, if the measured humidity and/or temperature are below the target humidity and/or target temperature respectively, it may be indicative that the gas flow120from the 3D printer may have condensed excessively.

At block260, the controller150controls the chiller valve145to set an absolute humidity of the gas flow to a predetermined value. In an example, the controller150may control the valve145to open and close. In another example, the controller150may control the chiller valve145to fully open, fully close, partially open, or partially close, where the partial positions may comprise any position ranging from the fully opened and fully closed positions.

If the measured humidity and/or temperature are above the target humidity and/or target temperature respectively, the controller150may control the chiller valve145to open or partially open so that a larger cold liquid stream147flow reaches the heat exchanger130, thereby increasing the heat transfer135from the gas flow110from the 3D printer to the cold liquid stream147, and therefore condensing a larger amount of solvents. Contrarily, if the measured humidity and/or temperature are below the target humidity and/or target temperature respectively, the controller150may control the chiller valve145to close or partially close so that a smaller cold liquid stream147flow reaches the heat exchanger130, thereby reducing the heat transfer135from the gas flow110from the 3D printer to the cold liquid stream147, and therefore condensing a smaller amount of solvents.

FIG.3is a schematic graph300of an example of a psychrometric chart to illustrate the thermodynamic cycle of the examples of the present disclosure.

Graph300illustrates the behavior of different relative humidity values of a gas, for example ambient air, an inert gas, water vapor, or any vaporized solvent. Graph300shows the different relative humidity, temperature and absolute humidity values for a given pressure.

As mentioned above, absolute humidity is the quantity of evaporated solvent (e.g., water) dispersed in a kilogram of the gas (e.g., ambient air, inert gas). Relative humidity is the amount of evaporated solvent present in the gas expressed as a percentage of the amount needed for saturation at the same temperature. Therefore, a 100% relative humidity is indicative that the gas is saturated with vapour so that if it is further cooled down, part of the vapour may start to condense. The more the saturated gas is cooled down, the more the evaporated solvents mixed therein may condense. The condensation may involve transforming part of the gas (e.g., the evaporated solvents) into liquid form, thereby enabling the separation between the condensed liquid solvents from the dehumidified gas.

Some thermodynamic states are illustrated in graph300which correspond to the thermodynamic cycle of the gas in the apparatus100fromFIG.1. State A may correspond to the gas in the gas flow110with evaporated solvents from the 3D printer. In some examples, the gas at state A comprises a high absolute humidity, high temperature, and a relative humidity below saturation. The gas flow110enters to the heat exchanger130where the gas is cooled. In the heat exchanger130the gas experiences the transition from state A to state B (illustrated through arrow320) where the gas saturates. The gas at state B has substantially the same absolute humidity as the gas at state A but with a lower temperature and a relative humidity corresponding to saturation. The heat exchanger130may further cool down the saturated gas so that the vaporized solvents condense, thereby transitioning the gas from state B to state C (illustrated through arrow340). At state C, the gas has a lower absolute humidity and temperature than the gas at state B, but the gas is still at a saturation point. During the condensation phase, solvent vapours are removed from the saturated gas and, therefore, the saturated gas experiences a reduction of the absolute humidity. The saturated gas is saturated (i.e., is at 100% relative humidity) throughout the solvent vapour condensation process. The resulting dehumidified gas120is then transferred to the 3D printer.

In the 3D printer, the dehumidified gas120may be heated by a heating element (e.g., gas heater) before entering back again to the print chamber. This heating process may increase the temperature of the dehumidified gas, which may transition from state C to state D (illustrated through arrow360). In some examples, the gas at state D has substantially the same absolute humidity as the gas at state C, but the gas has a higher temperature and a lower relative humidity (i.e., the gas is no longer saturated). This heated gas at state D may then enter to the print chamber and be used during the generation of a 3D object.

The controller150may control the elements of apparatus100so that the gas at state D has an intended temperature and humidity value, for example that may be optimal for the generation of 3D objects in the build chamber of the 3D printer. In an example, the gas at state D has a temperature from 20° C. to 45° C., for example 30° C. or 35° C.; and a relative humidity from 20% to 70%, for example 40% or 50%. In another example, the gas at state D has a temperature from 10° C. to 60° C., for example 25° C. or 50° C.; and a relative humidity from 10% to 80%, for example 30% or 60%. In yet another example, the gas at state D has a temperature from 30° C. to 40° C.; and a relative humidity from 25% to 30%.

This thermodynamic cycle completes during the generation of the 3D object where some solvents are evaporated into the gas (i.e., gas flow110from the 3D printer). The gas with the evaporated solvents is transferred to the apparatus100. The energy sources from the build chamber may heat the gas and the solvents evaporate into the gas, thereby increasing the temperature and absolute humidity of the gas. This may cause the transition from state D to state A (illustrated through arrow380).

This aforementioned thermodynamic cycle (i.e., states A, B, C and D) may repeat throughout the generation of a print job by the 3D printer.

FIG.4is another schematic diagram showing another example of a 3D printing apparatus400to dehumidify and recycle a gas from a 3D printer (not shown). Additionally, the 3D printing apparatus100is to control the humidity and temperature of the recycled gas in the build chamber. The apparatus400may comprise previously disclosed elements fromFIG.1referred to with the same reference numerals. The apparatus400comprises the gas inlet115, the heat exchanger130, the gas outlet125and the controller150. The apparatus400may additionally comprise or may be engageable with the chiller140and the sensor160. The controller150is coupled to the sensor160and the chiller valve145from the chiller140.

The apparatus400additionally comprises a recuperator470. The recuperator470is a gas-to-gas heat exchanger. The dehumidified gas flow435, resulting from the liquid-to-gas heat exchanger130, is intended to be used to heat the gas flow110from the 3D printer. The heated gas flow with evaporated solvents is illustrated with reference to arrow475. Similarly, the gas flow110from the 3D printer is intended to be used to cool the dehumidified gas flow435resulting from the liquid-to-gas heat exchanger130, thereby outputting dehumidified gas flow120which may be transferred to the 3D printer.

The recuperator470enables the gas flow with evaporated solvents475to enter to the heat exchanger130at a higher temperature. In the graph300ofFIG.3, the recuperator470may heat the gas flow with evaporated solvents475at a thermodynamic state within the length of arrow320and up to state B of the graph300. In some examples, there may not be condensation of the solvents in the recuperator. By installing the recuperator470in the apparatus400, the heat exchanger130may have to exchange a lower quantity of energy to condensate the evaporated solvents.

FIG.5is another schematic diagram showing another example of a 3D printing apparatus500to dehumidify and recycle a gas from a 3D printer (not shown). Additionally, the 3D printing apparatus500is to control the humidity and temperature of the recycled gas in the build chamber. The apparatus500involves previously disclosed elements fromFIG.4referred to with the same reference numerals.

In addition to the elements of apparatus400fromFIG.4, apparatus500comprises a bypass conduit580between an exit port? of the recuperator, and a bypass valve585within the bypass conduit580. The controller150is coupled with and may control the bypass valve585. In an example, the controller150may control the bypass valve585to open and close. In another example, the controller150may control the bypass valve585to fully open, fully close, partially open, or partially close, where the partial positions may comprise any position ranging from the fully opened and fully closed positions. The bypass conduit is to selectively allow at least part of the dehumidified gas flow435to bypass the recuperator470.

In an example, the bypass valve585may be in its closed position, so that all of the dehumidified gas flow435passes through the recuperator. In this example, the controller150may detect through the sensor160that the temperature of the dehumidified gas flow120(i.e., gas flow after the recuperator) that is transferred to the 3D printer is above a predeterminable temperature threshold. In this example, the controller150may instruct the bypass valve585to open or partially open so that a part of the dehumidified gas flow435passes through the bypass conduit580(arrow587A) and the remaining part of the dehumidified gas flow435passes through the recuperator (arrow587B). The part of the dehumidified gas flow435that passes through the bypass conduit does not heat up, and similarly, is not used to cool the gas flow110from the 3D printer. Therefore, the temperature of the resulting gas flow120(combination of flow587A and587B) after opening or partially opening the bypass valve585may be reduced.

FIG.6is another schematic diagram showing another example of a 3D printing apparatus600to dehumidify and recycle a gas from a 3D printer (not shown). Additionally, the 3D printing apparatus600is to control the humidity and temperature of the recycled gas in the build chamber. The apparatus600may involve previously disclosed elements fromFIG.1referred to with the same reference numerals. The apparatus600comprises the gas inlet115, the heat exchanger130, the gas outlet125and the controller150. The apparatus600may additionally comprise or may be engageable with the chiller140and the sensor160. The controller150is coupled to the chiller valve145from the chiller140and the sensor160. Additionally, apparatus600may further comprise elements from apparatus400and500fromFIGS.4and5respectively.

The controller150from apparatus600may be coupled with and may control a supply valve695A. In some examples, the supply valve695is external from the apparatus600. In other examples, the supply valve is an integral element of the apparatus600. The supply valve695A is fluidically connectable with a gas source690A comprising the gas (e.g., gas reservoir). In some examples, the gas source690A is external but couplable with the apparatus600. In other examples, the gas source690A is a removable supply that once installed, it is part of the apparatus600.

The controller150may control a pressure sensor (e.g., sensor160) to receive from the pressure sensor a measure of a pressure indicative of the pressure within the apparatus600conduits. If the controller150detects that the pressure within the conduits is below the atmospheric pressure, it may be indicative that a leak may have occurred, and atmospheric air may have entered the system. In order to address this situation and to stop atmospheric gas from entering to the system, the controller150may instruct the supply valve695A to open or partially open to let an amount of gas from the gas source690A to enter the apparatus600and therefore increase the pressure within the apparatus? to a pressure above atmospheric pressure. Once the pressure within the system conduits is above a predeterminable threshold above the atmospheric pressure, the controller150may instruct the supply valve695A to close.

In the examples in which the gas is an inert gas, the atmospheric air that entered the apparatus600conduits may have to be removed to avoid potential issues in the build chamber. In order to address this situation, a large amount of inert gas from the gas source690A may be supplied to the apparatus600conduits to purge the small amount of atmospheric air that may have entered to the conduits within the apparatus600. In an example, the amount of inert gas to be supplied may be multiple times the amount of atmospheric air that may have entered to the conduits.

Additionally, the controller may further control an additional supply valve695B fluidically connectable with a gas source690B comprising a gas. In some examples, the gas of the gas source690B is a different gas than the gas from the gas source690A. The supply valve695B and the gas source690B may be similar to and may be controlled in a similar way than the supply valve695A and the gas source690A respectively. Some 3D printers may print different print jobs under different gas environment conditions, for example a first print job with air and a second print job with an inert gas. The apparatus600may comprise an independent gas source for each gas to assist in the purge of a first gas corresponding to the previous print job in virtue of the filling of a second gas corresponding to the following job. In some examples, instead of a gas source, the apparatus600may capture ambient air from the surrounding environment.

FIG.7is a schematic diagram showing an example of a 3D printer700that dehumidifies and recycles a gas. Additionally, the 3D printer700is to control the humidity and temperature of the recycled gas in the build chamber710. The apparatus600may involve previously disclosed elements fromFIG.1referred to with the same reference numerals. The 3D printer700comprises the heat exchanger130, the sensor160and the controller150. The 3D printer700may additionally comprise or may be engageable with the chiller140. The controller150is coupled to the chiller valve145. Additionally, 3D printer700may further comprise elements from apparatus400,500and600fromFIGS.4,5and6respectively.

The 3D printer700comprises a build chamber710where 3D objects745are generated on a build platform720from build material740. During the generation of the 3D objects745, the build chamber710is subject to a gas flow780(e.g., atmospheric air, inert gas) at a specific temperature and humidity. In order to selectively solidify or selectively bind the portions of the build material740which are intended to be part of the 3D objects745, an agent distributor730is to selectively deposit a printing fluid735with liquid solvents to the build material740uppermost layer and an energy source (not shown) is to evaporate part of the liquid solvents into the gas flow (i.e., mix of gas flow and evaporated solvents illustrated as arrow110).

A first conduit fluidically connects the build chamber710to a first end of the heat exchanger130and a second conduit fluidically connects a second end of the heat exchanger130back to the build chamber710. The mix of gas and evaporated solvents is transferred from the build chamber710to the heat exchanger where the solvents may condense (see, e.g., arrow320and340ofFIG.3) to thereby dehumidify the gas. The dehumidified gas120is transferred to the build chamber710though the second conduit.

The 3D printer700further comprises a build chamber sensor760to measure the temperature and humidity values of the gas flow that is to be recirculated back to the build chamber710. The build chamber sensor760is coupled to and controlled by the controller150.

The 3D printer700further comprises a gas heater750and/or a humidifier770at the second conduit between the second end of the heat exchanger130and the build chamber sensor760. An example of gas heater750may be a resistive heating element. An example of a humidifier770may be a vaporizer.

The gas heater750and/or the humidifier770are coupled to and controlled by the controller150. The gas heater750and/or the gas dehumidifier770may be controlled to set the dehumidified gas flow120at a build chamber target humidity and a build chamber target temperature based on the measurements of the build chamber sensor760. The build chamber target humidity and build chamber target temperature may be the same as or similar to the state D examples described above with reference toFIG.3. The resulting air flow780may then enter the build chamber710.

The above examples may be implemented by hardware, or software in combination with hardware. For example, the various methods, processes and functional modules described herein may be implemented by a physical processor (the term processor is to be implemented broadly to include CPU, SoC, processing module, ASIC, logic module, or programmable gate array, etc.). The processes, methods and functional modules may all be performed by a single processor or split between several processors, reference in this disclosure or the claims to a “processor” should thus be interpreted to mean “at least one processor”. The processes, method and functional modules are implemented as machine-readable instructions executable by at least one processor, hardware logic circuitry of the at least one processor, or a combination thereof.

The drawings in the examples of the present disclosure are some examples. It should be noted that some units and functions of the procedure may be combined into one unit or further divided into multiple sub-units. What has been described and illustrated herein is an example of the disclosure along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration. Many variations are possible within the scope of the disclosure, which is intended to be defined by the following claims and their equivalents.

There have been described example implementations with the following sets of features:

Feature set 1: A 3D printing apparatus to dehumidify and recycle a gas from a 3D printer, the apparatus comprising:a gas inlet to receive a gas flow from a 3D printer, the gas flow comprising gas with evaporated solvents to be cleaned;a heat exchanger to dehumidify the gas flow from the evaporated solvents, the heat exchanger to cool the gas flow by heat transfer to a cold liquid stream from a chiller to saturate and condensate the solvents from the gas flow;a gas outlet to output the dehumidified gas flow back to the 3D printer; anda controller to:receive a humidity and temperature measurements from a sensor located downstream from the heat exchanger;compare the humidity and temperature measurements with a target humidity and a target temperature respectively; andcontrol a chiller valve from the chiller based on the comparison to adjust the temperature of the gas flow to set an absolute humidity of the gas flow to a predeterminable value.

Feature set 2: A 3D printing apparatus with feature set 1, wherein the gas comprises an inert gas.

Feature set 3: A 3D printing apparatus with any preceding feature set 1 to 2, wherein the gas comprises Nitrogen.

Feature set 4: A 3D printing apparatus with any preceding feature set 1 to 3, further comprising a recuperator to cool the gas flow from the 3D printer and to heat the dehumidified gas flow through gas heat exchange means.

Feature set 5: A 3D printing apparatus with any preceding feature set 1 to 4, further comprising a bypass conduit between the ends of the recuperator to selectively allow the dehumidified gas flow to bypass the recuperator; a bypass valve within the conduit; and the controller to control the bypass valve position based on the comparison between the measured temperature and the target temperature so that the temperature of the dehumidified gas flow is below a temperature threshold.

Feature set 6: A 3D printing apparatus with any preceding feature set 1 to 5, further comprising a supply valve to fluidically connect the 3D printing apparatus with a gas source comprising the gas; and the controller to control the supply valve to input an amount of gas to the gas flow so that that the gas flow pressure within the 3D printing apparatus is above an atmospheric pressure.

Feature set 7: A 3D printing apparatus with any preceding feature set 1 to 6, w wherein the gas source is an air source, the apparatus further comprising: an additional supply valve to fluidically connect the 3D printing apparatus with an inert gas source comprising the inert gas; and the controller to control the additional supply valve to input an amount of the inert gas to the gas flow so that the gas flow pressure within the 3D printing apparatus is above the atmospheric pressure.

Feature set 8: A 3D printing apparatus with any preceding feature set 1 to 7, wherein the controller is further to control a gas heater and/or a humidifier from the 3D printer to set the dehumidified gas at a build chamber target humidity and a build chamber target temperature.

Feature set 9: A 3D printer comprising:a build chamber subject to a gas flow to receive a build material layer to be used in the generation of a 3D object;an agent distributor to selectively deposit a printing fluid with liquid solvents to the build material layer;an energy source to evaporate the liquid solvents to the gas flow;a first conduit to fluidically connect the build chamber to a first end of a heat exchanger;the heat exchanger to dehumidify the gas flow with solvents from the build chamber, the heat exchanger to cool the gas flow with solvents by heat transfer to a cold liquid stream from a chiller to saturate and condensate the solvents from the gas flow;a second conduit to fluidically connect a second end of a heat exchanger back to the build chamber;a sensor to measure a humidity and temperature from the dehumidified gas flow within the second conduit; anda controller to:receive a humidity and temperature measurements from the sensor;compare the humidity and temperature measurements with a target humidity and a target temperature respectively; andcontrol a chiller valve from the chiller based on the comparison to adjust the temperature of the gas flow to set an absolute humidity of the gas flow to a predeterminable value.

Feature set 10: A 3D printer with feature set 9, wherein the gas is an inert gas.

Feature set 11: A 3D printer with any preceding feature set 9 to 10, further comprising a recuperator to cool the gas flow from the 3D printer and to heat the dehumidified gas flow

Feature set 12: A 3D printer with any preceding feature set 9 to 11, further comprising: a bypass conduit between the ends of the recuperator to selectively allow the dehumidified gas flow to bypass the recuperator; a bypass valve within the conduit; and the controller to control the bypass valve position based on the comparison between the measured temperature and the target temperature so that the temperature of the dehumidified gas flow is below a temperature threshold.

Feature set 13: A 3D printer with any preceding feature set 9 to 12, further comprising a humidifier to set the dehumidified gas at a build chamber target humidity and a build chamber target temperature.

Feature set 14: A 3D printer with any preceding feature set 9 to 13, further comprising a gas heater to set the dehumidified gas at a build chamber target humidity and a build chamber target temperature.

Feature set 15: A method to dehumidify and recycle a gas within a 3D printer, the method comprising:inputting a gas flow with solvents from a 3D printer to a heat exchanger;inputting a cold liquid stream from a chiller to the heat exchanger;cooling the gas flow with solvents by heat transfer to the cold liquid stream to saturate and condensate the solvents and thereby dehumidifies the gas flow from the solvents;measuring a humidity and temperature of the dehumidified gas flow;comparing the humidity and temperature measurements with a target humidity and a target temperature respectively; andoperating a chiller valve from the chiller based on the comparison to adjust the temperature of the gas flow to set an absolute humidity of the gas flow to a predeterminable value.