Benefit is claimed under 35 U.S.C. 119(a)-(d) to Foreign application Serial No. 1784/CHE/2015 filed in India entitled “ESTIMATING FROST MASS FORMED IN A DESIGN COMPONENT OF A MULTI-COMPONENT STRUCTURE”, on Apr. 3, 2015, by AIRBUS GROUP INDIA PRIVATE LIMITED, which is herein incorporated in its entirety by reference for all purposes.
Embodiments of the present subject matter generally relate to frost formed in a design component of a multi-component structure, and more particularly, to estimating frost mass formed in the design component of the multi-component structure.
Typically, during operation a design component of a multi-component structure encounter humid air and the humid air may condense due to surrounding low temperatures. This can result in forming frost in and around the design component and reducing efficiency of the design component. Example multi-component structure is a vehicle, an air conditioning system and so on. Exemplary vehicle is an aircraft, an automobile and the like. The design component may be a duct or a bend having uniform or non-uniform cross sections. Generally, ambient air may come and go out of an aircraft cabin based on ventilation systems and passenger comfort needs. When humid ambient air gets stagnated in insulation near an aircraft door, humidity in the air may condense on cold walls of design components in the aircraft door, forming frost in and around the design components. The accumulated frost can decrease the performance and also substantially increase the weight of the aircraft which may result in increasing fuel consumption.
A technique for estimating frost mass formed in a design component of a multi-component structure is disclosed. According to one aspect of the present subject matter, the frost mass formed in the design component may be iteratively estimated using a porosity parameter associated with a fluid medium, a height of a frost layer and/or a density of the frost layer in the design component.
According to another aspect of the present subject matter, the system includes a processor and a memory coupled to the processor. The memory includes a frost modeling tool. In one embodiment, the frost modeling tool iteratively estimates frost mass formed in a design component of a multi-component structure using a porosity parameter associated with a fluid medium, a height of a frost layer and/or a density of the frost layer in the design component.
According to yet another aspect of the present subject matter, a non-transitory computer-readable storage medium of estimating frost mass formed in a design component of a multi-component structure, having instructions that, when executed by a computing device causes the computing device to perform the method described above.
The system and method disclosed herein may be implemented in any means for achieving various aspects. Other features will be apparent from the accompanying drawings and from the detailed description that follow.
Various embodiments are described herein with reference to the drawings, wherein:
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
In the following detailed description of the embodiments of the present subject matter, references are made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the present subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present subject matter, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present subject matter. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present subject matter is defined by the appended claims.
Embodiments described herein provide methods, techniques, and systems for estimating frost mass formed in a design component of a multi-component structure. For example, the multi-component structure includes a vehicle (e.g., an aircraft, an automobile and the like), an air conditioning system and so on. The design component may include ducts or bends having uniform or non-uniform cross-sectional areas. In an embodiment, the fluid medium in the design component is modeled as a porous medium and a porosity parameter (i.e., a porosity value) is updated as per growth of a frost layer. Further, a heat transfer rate at an interface between the fluid medium and the frost layer in the design component is computed based on the porosity parameter inside the porous medium (representing the frost layer). Also, a height and density of the frost layer is determined based on a condensation rate which is determined by the heat transfer rate at the interface. Frost mass is then estimated based on the determined height and density of the frost layer. Thus, the frost mass is reliably estimated as the frost layer is modeled inside the fluid medium.
At block 106, the initial porosity parameter associated with each of the cells is updated based on an initial height and initial density at each shell corresponding to a frost layer, in a first cycle. For example, the initial height and the initial density of the frost layer are guessed or assumed height and density of the frost layer when the frost mass estimation process is started. The first cycle can be a first cycle after the frost mass estimation process is started. In an embodiment, cells for each wall face (i.e., shells) in the design component are selected using semi hemispheres having a diameter equal to the initial height of the frost layer. Further, the porosity parameter associated with each of the selected cells is updated based on the initial density of the frost layer at each wall face (shells). For example, a porosity value at a normal fluid region is 1.0 and in regions of a domain near a cold wall or surface where the frost exists, porosity values are varied (i.e., in between 0 to 1) to incorporate frost modelling in the fluid medium. In an example, a porosity value of 0.4 at a cell indicates 40% of solid medium is present at the cell which is partially blocking the fluid.
As shown in a schematic diagram 200A of
At block 108, a CFD simulation is performed to compute a heat transfer rate at the interface in the design component based on the updated or initial porosity parameter and/or other properties of the cells associated with each of the wall faces (shells). The heat transfer rate computation in the fluid domain is performed by a CFD tool. In an embodiment, heat transfer through the porous medium can be represented with or without assumption of thermal equilibrium between the porous medium and the fluid flow. In this embodiment, the porous medium is assumed as isotropic and an effective conductivity is estimated by using the porosity parameter which is a weighted average of fluid and solid regions as shown below.
wherein,
ρ=a density,
Cp=a specific capacity of the fluid,
U=a flow field convention,
Tpm=a temperature, and
Keff=an effective thermal conductivity.
Further, the effective thermal conductivity in the porous medium, keff, is computed as a volume average of a fluid medium thermal conductivity and a solid medium thermal conductivity using a below example equation:
keff=kfγ+ks(1−γ)
wherein,
kf=a fluid medium thermal conductivity,
ks=a solid medium thermal conductivity, and
γ=a porosity parameter of the medium.
Furthermore, a product of the density and the specific capacity of the fluid in the porous medium is obtained using a below example equation:
(ρCp)pm=(ρCp),(1−γ)+(ρCp)fγ
wherein,
(ρCp)s=a product of the density and the specific capacity of the fluid in the solid medium, and
(ρCp)f=a product of the density and the specific capacity of the fluid in the fluid medium.
At block 110, condensation mass at each of the shells corresponding to the frost layer in the design component is determined using the computed heat transfer rate at the interface. In an example implementation, a condensation rate at each shell corresponding to the frost layer is determined using the determined heat transfer rate at the interface and then the condensation mass at each shell corresponding to the frost layer is determined using the condensation rate. In this example implementation, the condensation rate is governed by a rate of diffusion of water vapour towards a cold wall of the design component. For example, the condensation mass can be represented through use of a mass (continuity) source term in a near-cell wall as shown in below equation:
wherein,
{dot over (m)}m=a total condensation rate per unit volume at a wall face,
ρ=a density of fluid adjacent to the wall,
v=a velocity of the fluid,
Acellwall=an area of the wall face, and
Vcell=a volume of a cell.
At block 112, an updated height and density at each shell corresponding to the frost layer, in the first cycle, are determined based on the determined condensation mass. In an example implementation, a change in the initial height and initial density at each shell corresponding to the frost layer is determined based on the determined condensation mass. This is explained in more detail with reference to
After each iteration, the frost interface is calculated in the fluid medium based on the porosity parameters of the cells. Once the frost interface is calculated, the frost mass estimations are performed where the heat transfer rate on the frost interface is accessed from the CFD tool. Once the frost mass at all shells on the frost interface are estimated, this data is transferred to the respective wall faces (shells) where these values are used to update the frost height and frost density and hence the other parameters like frost density and calculation of hemisphere radius for application of porosity in updated frost layer cells. Porosity at normal fluid region is 1.0 and the regions of domain near the wall where frost exists, the porosity value is varied as per frost modeling.
At block 114, frost mass formed in the design component is estimated using the determined height and density at each shell corresponding to the frost layer, in the first cycle. At block 116, the process steps from block 106 to block 114 are repeated for estimating frost mass formed in the design component for a predefined number of cycles. If the frost mass is estimated during a design phase or manufacturing of the structure, then design of the structure is changed such that the frost formation is reduced. If the frost mass is estimated after design and before use of the structure (i.e., before flight in case of an aircraft), then the structure is sent for maintenance (i.e., cleaning) or a ventilation system is changed to maintain efficiency of the structure.
Referring now to
wherein,
ρf=a density of the frost layer,
ρice=a density of ice or a solid medium,
Xs=a height of the frost layer,
kf=a thermal conductivity or frost conductivity,
Fvap=a frost densification factor,
Deff=a molecular diffusivity,
TS=a temperature at the interface,
R=a universal gas constant,
Mv=molecular mass,
Pv=a vaporization pressure,
HS=Heat of sublimation,
Ta=an atmospheric temperature,
hH=a heat transfer co-efficient, and
qtot=total heat.
Further, changes in the density and height of the frost layer are obtained using below equations, respectively:
Referring now to
In one embodiment, the CFD tool 406 generates a volume mesh having shells on walls inside the design component and cells in the fluid medium of the design component. Further, the CFD tool 406 models the fluid medium in the design component as a porous medium having an initial porosity parameter associated with each of the cells. Furthermore, the CFD tool 406 updates the initial porosity parameter associated with each of the cells based on an initial height and initial density of the frost layer, in a first cycle. In addition, the CFD tool 406 performs a simulation to compute a heat transfer rate at an interface between the fluid medium and the frost layer in the design component based on the updated initial porosity parameter associated with each of the cells.
The frost modeling tool 408 then determines condensation mass at each shell corresponding to the frost layer using the computed heat transfer rate at the interface. Further, the frost modeling tool 408 determines an updated height and density at each shell corresponding to the frost layer, in the first cycle, based on the determined condensation mass. Furthermore, the frost modeling tool 408 estimates frost mass formed in the design component using the determined height and density at each shell corresponding to the frost layer, in the first cycle.
Moreover, the CFD tool 406 repeats the steps of updating the porosity parameter associated with each of the cells based on the determined height and density at each shell corresponding to the frost layer and performing a simulation to compute a heat transfer rate at the interface in a next cycle. Also, the frost modeling tool repeats the steps of determining condensation mass at each shell corresponding to the frost layer, determining an updated height and density at each shell corresponding to the frost layer and estimating frost mass formed in the design component based on the determined height and density at each shell corresponding to the frost layer in the next cycle. This is explained in more detail with reference to
The machine-readable storage medium 504 may store instruction 506. In an example, instruction 506 may be executed by processor 502 to iteratively estimate the frost mass formed in the design component using a porosity parameter associated with a fluid medium, a height of a frost layer and/or a density of the frost layer in the design component.
For the purpose of simplicity of explanation, the example method of
Although certain methods, systems, apparatus, and articles of manufacture have been described herein, the scope of coverage of this patent is not limited thereto. To the contrary, this patent covers all methods, apparatus, and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.
Number | Date | Country | Kind |
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1784/CHE/2015 | Apr 2015 | IN | national |
Number | Name | Date | Kind |
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9546004 | Safai | Jan 2017 | B1 |
Entry |
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Luer et al. Frost Deposition in a Parallel Plate Channel Under Laminar Flow Conditions Int. J. Therm. Sci., 2000 39 pp. 85-95. |
Ellgas et al. Modeling Frost Formation Within a Commercial 3-D CFD Code Numerical Heat Transfer, Part A, 53 2008 pp. 485-506. |
Huang et al. The Effects of Frost Thickness on the Heat Transfer of Finned Tube Heat EXchanger Subject to the Combined Influence of Gan Types Applied Thermal Engineering 28, 2008 pp. 728-737. |
Gall et al. Modeling of Frost Growth and Densification Int. . Heat Mass Transfer, vol. 40, No. 13, pp. 3177-3187, 1997. |
Silva et al. Experimental Study of Frost Accumulation on Fan-Supplied Tube-Fin Evaporators Applied Thermal Engineering 31, pp. 1013-1020 (Year: 2011). |
Number | Date | Country | |
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20160292328 A1 | Oct 2016 | US |