Apparatus and method for producing foamed cementitious slurries

Abstract

According to the present invention, there is provided an apparatus (100) for producing a foamed cementitious slurry, the apparatus comprising: a mixing chamber (101) for mixing a cementitious material with water to form a cementitious slurry; and a channel (103) fluidly connected to the mixing chamber (101) at a first end (111) for receiving the cementitious slurry from the mixing chamber (101). In the apparatus, the channel (103) extends from the first end (111) and terminates at least one second end (112). The channel (103) comprises a first foam inlet (106) for introducing foam into the channel (103), and the apparatus (100) is configured, during use, to introduce foam through the first foam inlet (106) at a velocity no greater than 5.4 times the velocity of the cementitious slurry in the channel (103). Methods of using the apparatus are also described.

Description

[Technical Field]

[0001] The present invention relates to an apparatus for producing a foamed cementitious slurry, and also to a method for producing a foamed cementitious slurry using the apparatus. [Background technology]

[0002] Gypsum occurs naturally as a raw material in the form of calcium sulfate dihydrate (CaSO42(H2O)). Gypsum-containing products, such as gypsum board, are prepared by forming a mixture of calcined or dehydrated gypsum, i.e., calcium sulfate hemihydrate (CaSO40.5(H2O)), with water to form a settable slurry that is then cast into a desired shape. The calcium sulfate hemihydrate reacts with water and rehydrates to form dihydrate crystals, which are then set or dried to a solid state.

[0003] Gypsum products are commonly found throughout buildings due to their versatility, desirable mechanical properties, and the possibility of achieving a high level of finish. Therefore, it is desirable to produce lightweight gypsum products. Reducing the amount of gypsum used significantly reduces the resource demands of the manufacturing process, thereby reducing material costs. Therefore, the weight of these gypsum products is very important.

[0004] To provide a lightweight gypsum product, foam can be added to the settable slurry. However, the introduction of foam into the slurry can result in shearing and dispersion of the foam. Such dispersion can lead to high foam loss, resulting in an inefficient process that can limit the degree of density reduction achieved using this method. Foam loss is particularly common when large amounts of foam are introduced into the slurry. Summary of the Invention

[0005] According to a first aspect of the present invention, there is provided an apparatus for producing a cementitious slurry comprising foam, the apparatus comprising: a mixing chamber for mixing a cementitious material and water to form the cementitious slurry; and a channel fluidly connected at a first end to the mixing chamber for receiving the cementitious slurry from the mixing chamber, the channel extending from the first end and terminating in at least one second end, the channel comprising a first foam inlet for introducing foam into the channel, the apparatus being configured, in use, to introduce foam via the first foam inlet at a velocity of no more than 5.4 times the velocity of the cementitious slurry in the channel.

[0006] The present invention provides an apparatus for efficiently and consistently combining foam into a cementitious slurry, such as a stucco or gypsum slurry. The foam experiences sufficiently low shear forces when combined with the slurry to maintain foam stability. In prior art systems, mixing means within a mixing chamber can impose very high shear rates within the slurry. These high shear rates can destroy bubbles and destabilize the foam within the mixing chamber. Therefore, introducing foam into a cementitious slurry within a mixing chamber can result in high levels of foam loss. The present invention addresses this problem of the prior art by controlling the rate of foam injection to ensure that foam is uniformly mixed throughout the cementitious slurry with low levels of foam loss.

[0007] Preferably, the apparatus is configured, in use, to introduce foam through the first foam inlet at a rate not more than four times the velocity of the cementitious slurry in the channel. More preferably, the apparatus is configured, in use, to introduce foam through the first foam inlet at a rate not more than three times the velocity of the cementitious slurry in the channel. Even more preferably, the apparatus is configured, in use, to introduce foam through the first foam inlet at a rate not more than two times the velocity of the cementitious slurry in the channel.

[0008] Preferably, the apparatus is configured, in use, to introduce foam through the first foam inlet at a rate that is at least twice the velocity of the cementitious slurry in the channel. More preferably, the apparatus is configured, in use, to introduce foam through the first foam inlet at a rate that is at least three times the velocity of the cementitious slurry in the channel. Even more preferably, the apparatus is configured, in use, to introduce foam through the first foam inlet at a rate that is at least four times the velocity of the cementitious slurry in the channel.

[0009] Preferably, the apparatus is configured, in use, to introduce foam through the first foam inlet at a rate of at least 1.8 and at most 5.4 times the velocity of the cementitious slurry in the channel. More preferably, the apparatus is configured, in use, to introduce foam through the first foam inlet at a rate of at least 1.8 and at most 3.4 times the velocity of the cementitious slurry in the channel. Even more preferably, the apparatus is configured, in use, to introduce foam through the first foam inlet at a rate of at least 2.4 and at most 3.4 times the velocity of the cementitious slurry in the channel. Most preferably, the apparatus is configured, in use, to introduce foam through the first foam inlet at a rate of 2.4 times the velocity of the cementitious slurry in the channel.

[0010] Preferably, the maximum opening dimension of the first foam inlet is 15 mm or more. More preferably, the maximum opening dimension of the first foam inlet is 17.5 mm or more. Most preferably, the maximum opening dimension of the first foam inlet is 20 mm or more.

[0011] Preferably, the maximum opening dimension of the first foam inlet is 25 mm or less. More preferably, the maximum opening dimension of the first foam inlet is 20 mm or less. Most preferably, the maximum opening dimension of the first foam inlet is 17.5 mm or less.

[0012] Preferably, the mixing chamber is a tangential mixer. Preferably, the tangential mixer comprises a single mixing element. Alternatively, the tangential mixer comprises multiple mixing elements.

[0013] Preferably, the first foam inlet is located on an outer wall of the channel, the outer wall extending tangentially from the mixing chamber. Preferably, if the mixing chamber is a tangential mixer, the first foam inlet is located on an outer wall of the channel, the outer wall extending tangentially from the tangential mixer.

[0014] Preferably, the device comprises a second foam inlet for introducing foam into the channel.

[0015] Preferably, the apparatus is configured, in use, to introduce foam through the second foam inlet at a rate of no more than 5.4 times the velocity of the cementitious slurry in the channel. More preferably, the apparatus is configured, in use, to introduce foam through the second foam inlet at a rate of no more than 3.4 times the velocity of the cementitious slurry in the channel. Even more preferably, the apparatus is configured, in use, to introduce foam through the second foam inlet at a rate of no more than 2.4 times the velocity of the cementitious slurry in the channel. Most preferably, the apparatus is configured, in use, to introduce foam through the second foam inlet at a rate of no more than 1.8 times the velocity of the cementitious slurry in the channel.

[0016] Preferably, the apparatus is configured, in use, to introduce foam through the second foam inlet at a rate that is at least twice the rate of the cementitious slurry in the channel. More preferably, the apparatus is configured, in use, to introduce foam through the second foam inlet at a rate that is at least three times the rate of the cementitious slurry in the channel. Even more preferably, the apparatus is configured, in use, to introduce foam through the second foam inlet at a rate that is at least four times the rate of the cementitious slurry in the channel.

[0017] Preferably, the apparatus is configured, in use, to introduce foam through the second foam inlet at a rate of at least 1.8 and at most 5.4 times the velocity of the cementitious slurry in the channel. More preferably, the apparatus is configured, in use, to introduce foam through the second foam inlet at a rate of at least 1.8 and at most 3.4 times the velocity of the cementitious slurry in the channel. Even more preferably, the apparatus is configured, in use, to introduce foam through the second foam inlet at a rate of at least 2.4 and at most 3.4 times the velocity of the cementitious slurry in the channel. Most preferably, the apparatus is configured, in use, to introduce foam through the second foam inlet at a rate of 2.4 times the velocity of the cementitious slurry in the channel.

[0018] Preferably, the maximum opening size of the second foam inlet is 15 mm or greater. More preferably, the maximum opening size of the second foam inlet is 17.5 mm or greater. Most preferably, the maximum opening size of the second foam inlet is 20 mm or greater. Again, the maximum opening size of the second foam inlet ensures that the foam is uniformly mixed throughout the cementitious slurry with a low level of foam loss.

[0019] Preferably, the maximum opening dimension of the second foam inlet is 25 mm or less. More preferably, the maximum opening dimension of the second foam inlet is 20 mm or less. Most preferably, the maximum opening dimension of the second foam inlet is 17.5 mm or less.

[0020] Preferably, the first foam inlet is located in the lower half of the channel, alternatively, the first foam inlet is located in the upper half of the channel, or alternatively, the first foam inlet is located at the vertical midpoint of the channel.

[0021] Suitably, the second foam inlet is located in a wall of the channel substantially opposite the outer wall, which extends tangentially from the mixing chamber. The wall of the channel may be continuous, as when the channel is circular, or segmented, as when the channel is rectangular or square.

[0022] Preferably, the first foam inlet is located on a channel wall substantially opposite the channel wall in which the second foam inlet is located. Preferably, the first foam inlet is located on an opposite side of the channel to the first foam inlet.

[0023] Preferably, the first foam inlet and the second foam inlet are located at the same vertical position within the channel. In such a configuration, the first foam inlet and the second foam inlet may be located on the same horizontal plane of the channel. When the first foam inlet and the second foam inlet are located at the same vertical position within the channel, the distance between the base of the channel and the first foam inlet and the distance between the base of the channel and the second foam inlet are the same, or the distance between the top of the channel and the first foam inlet and the distance between the top of the channel and the second foam inlet are the same.

[0024] Preferably, the first and second foam inlets are located at the vertical midpoints of the channel, with the distance between the top of the channel and the foam inlets being the same as the distance between the base of the channel and the foam inlets.

[0025] Preferably, the first foam inlet and the second foam inlet are offset along the length of the channel. Preferably, the offset is at least 30 mm. More preferably, the offset is at least 50 mm. Even more preferably, the offset is at least 100 mm. Even more preferably, the offset is at least 150 mm.

[0026] Preferably, the first foam inlet is closer to the first end of the channel than the second foam inlet, and preferably the distance between the first foam inlet and the first end of the channel is the same as the distance between the second foam inlet and the second end of the channel.

[0027] Preferably, the second foam inlet is located at least 200mm from the first end of the channel. Preferably, the second foam inlet is located less than 250mm from the first end of the channel.

[0028] Preferably, the second end of at least one of the channels is connected to a distribution hose. Preferably, the channel has a single second end.

[0029] Preferably, the second end of at least one of the channels is connected to a secondary chamber.

[0030] Preferably, the channels are substantially straight. In selected embodiments, the channels are substantially curved. Preferably, the channels have a substantially similar cross-sectional area along their length. Preferably, the channels have a substantially similar cross-sectional shape along their length. Even more preferably, the channels have a substantially similar cross-sectional area and a substantially similar cross-sectional shape along their length.

[0031] Preferably, the axis of at least one bubble inlet is perpendicular to the axis of the channel at the point where they join the channel. More preferably, the axes of both the first and second bubble inlets are perpendicular to the axis of the channel at the point where they join the channel, resulting in improved distribution of bubbles within the channel. Preferably, the axis of at least one bubble inlet intersects the axis of the channel at the point where they join the channel.

[0032] Preferably, the first foam inlet has a substantially circular cross section, in which case the maximum opening dimension is the diameter of the circle, or alternatively, the first foam inlet has a substantially square or rectangular cross section, in which case the maximum opening dimension is the diagonal.

[0033] Preferably, the second foam inlet has a substantially circular cross section, in which case the maximum opening dimension is the diameter of the circle. Alternatively, the second foam inlet has a substantially square or rectangular cross section, in which case the maximum opening dimension is the diagonal.

[0034] Preferably, the channels have a circular cross section. Alternatively, the channels have a square or rectangular cross section.

[0035] Preferably, the cementitious material comprises at least one of calcium sulfate hemihydrate and calcium sulfate dihydrate. More preferably, the cementitious material consists essentially of calcium sulfate hemihydrate.

[0036] According to a second aspect of the present invention, there is provided a method of producing a cementitious slurry containing foam, the method comprising providing an apparatus as described above; introducing cementitious material and water into the mixing chamber to form a cementitious slurry; and introducing foam into the cementitious slurry via the first foam inlet at a velocity not greater than 5.4 times the velocity of the cementitious slurry in the channel.

[0037] Thus, a method is provided for efficiently and consistently incorporating foam into a cementitious slurry, such as a stucco or gypsum slurry. The foam experiences sufficiently low shear forces when combined with the slurry to maintain foam stability. In prior art, mixing means within a mixing chamber can impose very high shear rates within the slurry. These high shear rates can destroy bubbles and destabilize the foam within the mixing chamber. Therefore, introducing foam into a cementitious slurry within a mixing chamber can result in high levels of foam loss. The present invention addresses this problem of the prior art by controlling the rate at which foam is introduced into the slurry via a foam inlet, ensuring that foam is uniformly mixed throughout the cementitious slurry with low levels of foam loss.

[0038] Preferably, the foam is introduced into the cementitious slurry at a velocity no greater than four times the velocity of the cementitious slurry in the channel, more preferably, the foam is introduced into the cementitious slurry at a velocity no greater than three times the velocity of the cementitious slurry in the channel, and even more preferably, the foam is introduced into the cementitious slurry at a velocity no greater than two times the velocity of the cementitious slurry in the channel.

[0039] Preferably, the foam is introduced into the cementitious slurry at a velocity greater than or equal to two times the velocity of the cementitious slurry in the channel. More preferably, the foam is introduced into the cementitious slurry at a velocity greater than or equal to three times the velocity of the cementitious slurry in the channel. Even more preferably, the foam is introduced into the cementitious slurry at a velocity greater than or equal to four times the velocity of the cementitious slurry in the channel.

[0040] Preferably, the foam is introduced into the cementitious slurry at a velocity of at least 1.8 and at most 5.4 times the velocity of the cementitious slurry in the channel. More preferably, the foam is introduced into the cementitious slurry at a velocity of at least 1.8 and at most 3.4 times the velocity of the cementitious slurry in the channel. Even more preferably, the foam is introduced into the cementitious slurry at a velocity of at least 2.4 and at most 3.4 times the velocity of the cementitious slurry in the channel. Most preferably, the foam is introduced into the cementitious slurry at a velocity 2.4 times the velocity of the cementitious slurry.

[0041] Preferably, the apparatus comprises a second foam inlet and the method further comprises introducing foam into the cementitious slurry via the second foam inlet.

[0042] Preferably, when the apparatus includes a second foam inlet, the foam is introduced into the cementitious slurry via the first and second inlets at a rate of at least 1.8 and at most 5.4 times the velocity of the cementitious slurry. Even more preferably, when the apparatus includes a second foam inlet, the foam is introduced into the cementitious slurry via the first and second inlets at a rate of at least 1.8 and at most 3.4 times the velocity of the cementitious slurry. Even more preferably, when the apparatus includes a second foam inlet, the foam is introduced into the cementitious slurry via the first and second inlets at a rate of at least 2.4 and at most 3.4 times the velocity of the cementitious slurry. Most preferably, when the apparatus includes a second foam inlet, the foam is introduced into the cementitious slurry via the first and second inlets at a rate of 2.4 times the velocity of the cementitious slurry.

[0043] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0044] [Figure 1] 1 shows an apparatus according to a first embodiment of the present invention; [Figure 2] 1 shows a schematic diagram of a method according to a second embodiment of the present invention. [Figure 3] 1 shows a theoretical Foam Efficiency Factor (FEF)-distance graph illustrating foam stability for various distances of the foam inlet along the device. [Figure 4] 1 shows a theoretical Foam Efficiency Factor (FEF)-diameter graph illustrating foam stability for various foam inlet diameters. [Figure 5] 1 shows a density deviation-diameter graph illustrating the mixing uniformity of foam and cementitious slurry mixtures for various foam inlet diameters. [Figure 6] 1 illustrates a bubble inlet configuration within the scope of the present invention. [Figure 7] 10 is a graph showing the effect of various foam inlet configurations on the density deviation measured in a slurry-foam mixture. [Figure 8] 1 shows shear rate-distance and density deviation-distance graphs illustrating the shear forces experienced by the foam and the mixing uniformity of the foam and cementitious slurry mixture for various distances of the foam inlet along the device. DETAILED DESCRIPTION OF THE INVENTION

[0045] 1 shows an apparatus 100 for producing a foamed cementitious slurry. The apparatus 100 comprises a mixing chamber 101 and a secondary chamber 102, the secondary chamber comprising a canister. The mixing chamber 101 is connected to the secondary chamber 102 by a channel 103.

[0046] The mixing chamber 101, here a tangential mixer, includes a cementitious material inlet 104 for introducing at least one cementitious material, such as calcium sulfate hemihydrate or stucco, into the mixing chamber 101, and a first water inlet 105 for introducing water into the mixing chamber 101. Thus, the cementitious material and water can be introduced into the mixing chamber 101. The mixing chamber includes a mixing element, which includes a plurality of blades or teeth. During use, the mixing element rotates within the mixing chamber 101, combining the water and the cementitious material to form a cementitious slurry. Once formed, the cementitious slurry exits the mixing chamber 101 and enters the channel 103 via the mixing chamber outlet 111. The mixing chamber outlet 111 ensures that the channel 103 is in fluid communication with the mixing chamber 101 so that the cementitious slurry can freely pass from the mixing chamber 101 to the channel 103. The mixing chamber outlet 111 represents a first end of the channel 103.

[0047] Channel 103 includes a foam inlet 106 for introducing foam into channel 103. Foam inlet 106 is in fluid communication with channel 103 to ensure that, during use, foam can freely enter channel 103 via foam inlet 106. During use, foam is injected into channel 103 via foam inlet 106. In this way, downstream of foam inlet 106, the channel contains a mixture of cementitious slurry and foam with increased uniformity.

[0048] In the illustrated embodiment, the foam is an aqueous foam generated in a foam generator 107. The foam generator includes a second water inlet 108 for introducing water into the foam generator 107, a soap inlet 109 for introducing soap into the foam generator 107, and an air inlet 110 for introducing air into the foam generator 107. The paths of the second water inlet 108 and the foam inlet 109 meet and combine before entering the foam generator 107. The air, water, and soap are introduced into the foam generator 107 to generate foam.

[0049] The channel 103 extends from the mixing chamber outlet 111 and is substantially linear. The channel 103 terminates at a second end, which is the secondary chamber inlet 112. Thus, the cementitious slurry exiting the mixing chamber 101 via the mixing chamber outlet 111 and the foam entering the channel via the foam inlet 106 are combined and mixed as they flow along the channel 103. The mixed foam and cementitious slurry then exit the channel 103 and enter the secondary chamber 102 via the secondary chamber inlet 112. In the secondary chamber 102, the cementitious slurry and the foam are further mixed. If the foam were injected directly into the mixing chamber 101, the stability of the foam would be reduced due to the movement of the mixing arm and the shear forces present in the mixing chamber 101. Therefore, to reduce foam loss, the foam inlet 106 is located within the channel 103 downstream of the mixing chamber outlet 111.

[0050] The foam inlet 106 is positioned such that the distance between the first end of the channel 103, i.e. the end located adjacent the mixing chamber outlet 111, and the foam inlet 106 is 100 mm. In this embodiment, the foam inlet is circular with a diameter of 15 mm.

[0051] The secondary chamber 102 is connected to a distribution hose 113. The cementitious slurry and foam streams exiting the channel 103 and entering the secondary chamber via the secondary chamber inlet 112 are further mixed as they pass through the secondary chamber 102 before exiting the secondary chamber 102 via the distribution hose 113. Thus, there is a continuous fluid connection between the mixing chamber 101 and the distribution hose 113, which continues through the mixing chamber outlet 111, the channel 103, the secondary chamber inlet 112, and the secondary chamber 102. In this embodiment, the distribution hose 113 bifurcates at points along its length to comprise a pair of elongated portions, each comprising a distribution hose outlet. In this embodiment, the distribution hose 113 is connected to the secondary chamber 102, although it is envisioned that in alternative embodiments, the distribution hose 113 may be connected directly to the channel 103, such that the secondary chamber 102 is omitted from the apparatus.

[0052] The present invention further relates to a method 300 for producing a cementitious slurry containing foam, as shown in Figure 2. The method comprises a step 301 of providing an apparatus, wherein the apparatus is provided as described above. This is followed by a step 302 of introducing a slurry additive, wherein cementitious material and water are introduced into the slurry chamber via respective inlets. Foam may then be introduced into the cementitious slurry in the channel via the foam inlet in a step 303 of introducing foam.

[0053] Computer modeling was performed to demonstrate the advantages of the above-described apparatus and method. shear rate

[0054] Foam stability is assessed by the Foam Efficiency Factor (FEF), which is calculated using the following formula:

number

[0055] Foam stability and intrafoam bubble breakup can also be expressed by the ratio of shear force to surface tension. Shear force acts to break the intrafoam bubbles, while surface tension provides resistance to shear force. Each foam stability depends on the shear rate and bubble size and can be defined by the capillary number (Ca).

number

number

[0056] The theoretical FEF can be calculated using the assumption that foam will be lost if exposed to a shear rate higher than a critical shear rate during the process of incorporation into a cementitious slurry.

[0057] To assess how the distance from the mixing chamber to the foam inlet affected the shear forces experienced by the foam and foam stability, computer simulations were performed considering a device with a channel and a single foam inlet. Figure 3 shows the estimated theoretical FEF (%) at the point where the foam enters the channel for multiple foam inlet locations.

[0058] In the case of a tangential mixer, a portion of the channel extends beyond the first end of the channel and is located within the mixing chamber. The first end of the channel is understood to be the point where the entire channel cross section exits the mixing chamber. Thus, a negative distance value indicates that the foam inlet is located in the portion of the channel that is located within the mixing chamber. To obtain the data in Figure 3, the channel was modeled as having a square cross section with dimensions of 39 mm x 39 mm.

[0059] Numerical modeling of the slurry-foam mixture was performed using a continuous single-phase model using the ANSYS Fluent computational mechanics software package. Within the model framework, the foamed cementitious slurry was modeled as an effectively incompressible fluid with non-Newtonian rheology that depends on the local air fraction. The cementitious slurry was modeled as an effective fluid with 0% air fraction, and the foam was modeled as an effective fluid with 100% air fraction. Herschel-Berkeley rheology was used in the model to describe the foam, slurry, and foamed slurry, and the coefficients used in the model were based on measurements made with a laboratory rheometer.

[0060] As can be seen in Figure 3, the foam entering through the inlet located within the channel experiences increased foam stability compared to the foam introduced into the mixing chamber. This increased FEF is beneficial because it reduces the amount of foam destroyed during the production of cementitious products. A higher FEF improves the overall efficiency of the production process. density deviation

[0061] The calculated variation in density of the slurry-foam mixture at various portions within the channel can be considered to assess the quality of the cementitious slurry-foam mixture by evaluating the uniformity of the slurry-foam mixture. In these calculations, greater variability in density measured at a given point indicates less uniformity of the slurry-foam mixture. Thus, less density variability is desirable because it indicates the device will provide a more consistent product.

[0062] To calculate the uniformity of the slurry-foam mixture, the flow of the cementitious slurry, foam, and slurry-foam mixture was modeled. Cross sections through the channel were obtained, and the average density and standard deviation of density at each cross section were calculated. The average density was obtained over a volume or cross-sectional area, not an average density over time. The density deviation was then calculated and defined as:

number

[0063] Computer modeling of bubble inlet diameter was performed to evaluate the effect of inlet diameter on density deviation.

[0064] When selecting the foam inlet diameter for the device, a compromise is made between mixing efficiency, where the foam requires high shear rates to mix with the cementitious slurry, and foam stability, which is adversely affected by high shear rates. The effect of foam inlet diameter on the average shear rate experienced by the foam at the point where it enters the slurry flow and the density deviation at the second end (outlet) of the channel is shown in Figures 4 and 5, respectively. To obtain the data in Figures 4 and 5, the channel was modeled as having a square cross section of 39 mm x 39 mm.

[0065] Here, numerical modeling of slurry foam mixing was performed using a continuous single-phase model using the ANSYS Fluent computational mechanics software package. Within the model framework, the foamed cementitious slurry was modeled as an effectively incompressible fluid with non-Newtonian rheology that depends on the local air fraction. The cementitious slurry was modeled as an effective fluid with 0% air fraction, and the foam was modeled as an effective fluid with 100% air fraction. Herschel-Berkeley rheology was used in the model to describe the foam, slurry, and foamed slurry, and the coefficients used in the model were based on measurements made with a laboratory rheometer.

[0066] In the model, the volumetric flow rate of the foam was kept constant at 0.004 m 3 s -1 The volumetric flow rate of the cementitious slurry after foam injection was 0.10 m 3 s -1 The slurry velocity is modeled as 6.6 ms -1 The model was modeled as follows. To inject foam into a cementitious slurry stream at a constant flow rate, varying the foam inlet diameter is necessary to vary the foam velocity as it enters the channel. As shown in Figures 4 and 5, there is a region A of high mixing efficiency and a region B of high foam stability.

[0067] Reviewing Figure 4, it can be seen that the theoretical FEF experienced by the foam increases as the foam inlet diameter increases from 5 mm to 31 mm, reaching a level acceptable for gypsum board manufacturing when the foam inlet diameter is equal to 15 mm. It was observed that when the foam inlet diameter is greater than 17.5 mm, the average shear rate experienced by the foam does not decrease any further and the theoretical FEF remains high. Thus, Region B of high foam stability is observed for foam inlet diameters of 15 mm or greater.

[0068] As shown in Figure 5, the density deviation at the second end (outlet) of the channel increased with increasing bubble inlet diameter, indicating that the smaller the inlet diameter, the better the bubbles penetrate and mix with the slurry flow. Region A of high mixing efficiency occurs up to an inlet diameter of approximately 17.5 mm.

[0069] The intersection of region A of high mixing efficiency and region B of high foam stability occurs at an inlet diameter of about 15 mm to about 17.5 mm. speed ratio

[0070] The ratio of the velocity at which the foam enters the cementitious slurry flow to the velocity of the cementitious slurry flow at the point at which the foam enters the slurry flow has been found to affect the FEF of the final cementitious product. [Table 1] From Table 1, it can be seen that acceptable foam stability (sufficiently high FEF) is obtained when the ratio of foam velocity to slurry velocity is 5.4 or less. It can also be seen that the smaller the ratio of foam velocity to slurry velocity, the higher the FEF, indicating high foam stability. Bubble inlet configuration

[0071] Further modeling was performed to evaluate density deviations in the slurry-foam mixture for devices with channels having one, two, and four foam inlets arranged in multiple configurations.

[0072] Three configurations were modeled: an aligned configuration where all bubble inlets are collinear along the length of the channel, a crossed configuration where the bubble inlets are directly across from each other, and an alternating configuration where the bubble inlets are alternately positioned on either side along the length of the channel.

[0073] In the aligned configuration, the foam inlets were spaced 35 mm apart from each other (between adjacent centers of each inlet), with the first foam inlet positioned adjacent to the first end of the channel at a distance of 136 mm from the first end. Aligned configurations with two and four foam inlets were modeled.

[0074] In the cross configuration, each foam inlet is located 136 mm from the first end of the channel. In the two-inlet cross configuration, a pair of opposing inlets is provided, with the inlets located on either side of the channel. In the four-inlet cross configuration, each inlet is located equidistant about the circumference of the channel, so that there are two pairs of opposing inlets.

[0075] In the alternating configuration, the foam inlets are spaced apart along the length of the channel. In the two-inlet alternating configuration, a pair of opposing inlets is provided, with a first foam inlet located 136 mm from the first end of the channel and a second foam inlet spaced 35 mm from the first inlet in a direction away from the mixing chamber.

[0076] In a four-inlet alternating configuration, each inlet is positioned equidistantly around the circumference of the channel. The first foam inlet is located 136 mm from the mixing chamber. The second, third, and fourth foam inlets are positioned along the channel away from the first end of the channel. The first through fourth foam inlets are positioned along the channel with a distance of 35 mm between each adjacent inlet.

[0077] During modeling, bubbles are initially pumped at a constant rate of 22 ms through a configuration with a constant total inlet area. -1 In the second round of modeling, bubbles were introduced into the channel at different velocities through a bubble inlet diameter of 15 mm. A constant total volumetric flow rate was used in all models.

[0078] The bubble inlet configuration is shown in Figure 6 and detailed in Table 2. [Table 2]

[0079] Figure 7 shows the modeled density deviation of the slurry-foam mixture at the second end (outlet) of the channel. To obtain the modeled data presented in Figure 7, the channel was considered to have a square cross section of 39 mm on each side in all models. The velocity of the cementitious slurry after injection of the foam was 6.6 m / s. -1 was modeled as.

[0080] Here, numerical modeling of slurry foam mixing was performed using a continuous single-phase model using the ANSYS Fluent computational mechanics software package. Within the model framework, the foamed cementitious slurry was modeled as an effectively incompressible fluid with non-Newtonian rheology that depends on the local air fraction. The cementitious slurry was modeled as an effective fluid with 0% air fraction, and the foam was modeled as an effective fluid with 100% air fraction. Herschel-Berkeley rheology was used in the model to describe the foam, slurry, and foamed slurry, and the coefficients used in the model were based on measurements made with a laboratory rheometer.

[0081] The calculated density deviation percentage is plotted for each scenario in Figure 7. The calculated density deviation for the control scenario is plotted across the graph as a dashed line.

[0082] As can be seen from Table 2 and Figure 7, the cross and alternating inlet configurations generally show improved slurry-foam mixture uniformity compared to the aligned configuration. In other words, the modeled density deviation is lower for the cross and alternating configurations when compared to the equivalent aligned configuration.

[0083] It can also be seen from Table 2 and Figure 7 that the alternating inlet configurations generally exhibit improved slurry-foam mixture uniformity compared to the crossed configuration. In other words, the modeled density deviation is lower for the alternating configurations when compared to the equivalent crossed configurations. It is noteworthy that all alternating configurations exhibit reduced slurry-foam mixture density deviation compared to the control scenario.

[0084] It can also be inferred from Table 2 and Figure 7 that increasing the number of foam inlets while maintaining the same total inlet area and foam injection rate increases the modeled density deviation. Such observations are consistent across all three configurations, as can be seen from the comparisons between scenarios 1 and 2, scenarios 5 and 6, and scenarios 9 and 10. Second entrance placement

[0085] Considering a configuration with multiple inlets, the presence of two or more inlets can reduce the velocity of foam entering the cementitious slurry while maintaining a constant volumetric flow rate of foam entering the slurry stream for a fixed foam inlet diameter. Furthermore, we investigated how the distance between the first end of the channel and the second foam inlet, i.e., the foam inlet distal to the mixing chamber, affected foam uniformity and stability. By positioning the second foam inlet farther from the mixing chamber, the rotation of the mixing chamber's mixing elements reduces the velocity of the slurry stream, reducing the shear rate experienced by the foam as it enters the slurry stream. As a result, the density deviation of the slurry-foam mixture increases with decreasing shear rate, but the foam efficiency factor can increase.

[0086] Figure 8 shows the average shear rate experienced by the foam at the point where it enters the slurry flow and the density deviation at the second end (outlet) of the channel versus the location of the second foam inlet from the mixing chamber for the Scenario 4 configuration. The velocity ratio was modeled as 1.7:1. The second foam inlet is understood to be the foam inlet distal to the mixing chamber. Again, a compromise is made between mixing efficiency, where the foam requires high shear rates to mix with the cementitious slurry, and foam stability, which is adversely affected by high shear rates.

[0087] If the second bubble inlet is located more than 200 mm from the first end of the channel, the bubble experiences a shear rate of 3700 s -1 It was found that the density deviation is below the critical value of . Therefore, locating the second foam inlet more than 200 mm from the first end of the channel helps improve the foam efficiency coefficient. However, because the shear rate experienced by the foam decreases as the second inlet moves away from the first end of the channel, the modeled density deviation becomes unacceptable when the second foam inlet is located more than 250 mm from the first end of the channel. As a result, locating the second foam inlet within this region of the channel may provide a good balance between density deviation and foam efficiency.

Claims

1. 1. An apparatus for producing a foamed cementitious slurry, comprising: a mixing chamber for mixing the cementitious material and water to form a cementitious slurry; a channel fluidly connected at a first end to the mixing chamber for receiving cementitious slurry from the mixing chamber; Equipped with the channel extends from the first end and terminates in at least one second end; the channel includes a first foam inlet for introducing foam into the channel; wherein the apparatus is configured, in use, to introduce foam through the first foam inlet at a velocity of no more than 5.4 times the velocity of the cementitious slurry in the channel. Device.

2. 2. The apparatus of claim 1, configured to, during use, introduce foam through the first foam inlet at a velocity no greater than four times the velocity of the cementitious slurry in the channel, more preferably no greater than three times the velocity of the cementitious slurry in the channel, and even more preferably no greater than two times the velocity of the cementitious slurry in the channel.

3. 3. The device of claim 1 or claim 2, wherein the maximum opening dimension of the first foam inlet is 17.5 mm or more, more preferably 20 mm or more, and even more preferably 25 mm or more.

4. 4. The apparatus of any one of claims 1 to 3, configured, in use, to introduce foam through the first foam inlet at a velocity that is at least twice the velocity of the cementitious slurry in the channel, more preferably at least three times the velocity of the cementitious slurry in the channel, and even more preferably at least four times the velocity of the cementitious slurry in the channel.

5. The device according to any one of claims 1 to 4, wherein the mixing chamber is a tangential mixer.

6. The device of any one of claims 1 to 5, wherein the first foam inlet is located on an outer wall of the channel, the outer wall extending tangentially from the mixing chamber.

7. An apparatus according to any preceding claim, comprising a second foam inlet for introducing foam into the channel.

8. 8. The apparatus of claim 7, configured to, in use, introduce foam through the second foam inlet at a velocity of no more than 5.4 times the velocity of the cementitious slurry in the channel, more preferably at a velocity of no more than 3.4 times the velocity of the cementitious slurry in the channel, even more preferably at a velocity of no more than 2.4 times the velocity of the cementitious slurry in the channel, and most preferably at a velocity of no more than 1.8 times the velocity of the cementitious slurry in the channel.

9. 9. Apparatus according to claim 7 or claim 8, wherein the maximum opening dimension of the second foam inlet is at least 15 mm, more preferably at least 17.5 mm, even more preferably at least 20 mm, and most preferably at least 25 mm.

10. The device according to any one of claims 1 to 9, wherein the at least one second end of the channel is connected to a distribution hose.

11. The device of any one of claims 1 to 10, wherein the second end of the at least one channel is connected to a secondary chamber.

12. 1. A method for producing a foamed cementitious slurry, comprising: Providing a device according to any one of claims 1 to 11; introducing cementitious materials and water into the mixing chamber to form a cementitious slurry; introducing foam into the cementitious slurry through the first foam inlet at a velocity no greater than 5.4 times the velocity of the cementitious slurry in the channel; A method comprising:

13. 13. The method of claim 12, wherein the foam is introduced into the cementitious slurry at a velocity no greater than 3.4 times the velocity of the cementitious slurry, more preferably at a velocity no greater than 2.4 times the velocity of the cementitious slurry in the channel, and even more preferably at a velocity no greater than 1.8 times the velocity of the cementitious slurry in the channel.

14. 14. The method of claim 12 or claim 13, wherein the foam is introduced into the cementitious slurry at a velocity greater than or equal to twice the velocity of the cementitious slurry, more preferably greater than or equal to three times the velocity of the cementitious slurry in the channel, and even more preferably greater than or equal to four times the velocity of the cementitious slurry in the channel.

15. 15. The method of claim 12, claim 13 or claim 14, wherein the foam is introduced into the cementitious slurry at a velocity of between 1.8 and 5.4 times the velocity of the cementitious slurry in the channel, more preferably between 1.8 and 3.4 times the velocity of the cementitious slurry in the channel, even more preferably between 2.4 and 3.4 times the velocity of the cementitious slurry in the channel, and most preferably at a velocity of 2.4 times the velocity of the cementitious slurry in the channel.

Images