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heat transfer across a nanoscale pressurized air gap and its application in magnetic recording

by:Mingfa Tech     2020-01-01
In this study, we investigate how the hot drive air bearing slider can be heated quickly
In the magnetic recording system, the storage disk is rotated through the high-pressure nano-air gap. A Eulerian-description-
Based on the calculation method, the consideration is developed by pressurized air film and near
Field radiation through the gap.
A set of field equations that control the dynamics of the air bearing, the heat of the slider
Both mechanics and disk heat dissipation are solved by iterative method.
It was found that the temperature field in the same order as the hot slider surface was established in the disk.
It is found that the effective local heat transfer coefficient varies greatly with the change of disc material and linear velocity.
This method quantifies the amplitude of different heat transfer schemes and verifies the accuracy by good agreement with our experiment, which measures the local slider temperature rise with a resistance temperature sensor.
It also shows an effective calculation method for dealing with transient thermal processes in component systems with relatively fast speed and different length scales.
Finally, the thermal transmission mechanism studied has resulted in a large number of pitch changes, which have a significant impact on the spacing margin of today\'s magnetic storage systems.
The heat transfer of nano-gap is crucial in the thermal management of micro-devices and nano-devices.
For example, in the magnetic recording system, the slider built with the magnetic read and write sensor is fast-
Rotate the storage disk by forming a high-pressure air gap (air bearing).
Tight magnetic spacing (i. e.
, The distance between the magnetic sensor and the record layer of the storage disk)
It is necessary for higher data storage capacity.
Hot flight for this purpose-Height control (TFC)
It has been invented that the Joules heater is embedded near the magnetic sensor in the slider body.
The heater causes thermal expansion so that the bottom surface of the slider (the so-
Called air bearing surface or ABS)
Highlight to the disk and reduce the local magnetic spacing.
The pressure in the air gap can accumulate to more than 100 kbps atm, resulting in a strong heat conduction flow from the slider to the disk.
Due to the strong coupling between the process and the slider, it has been widely studied.
Mechanics and air bearing dynamics have a significant impact on key performance such as recording spacing, data storage density, and power consumption.
With the rapid growth of storage capacity, the minimum gap size is now close to 1 nm or even sub-nanometer.
This nano-scale gap provides an opportunity for research by very small (10u2009nm)
Air gap, but when the minimum gap size is reduced to below, a key challenge is encounterednanometer.
In fact, experiments have shown that the disk material has a significant impact on the temperature field of the slider measured locally by the embedded contact sensor (ECS)
This challenges the ideal radiator assumption.
However, so far, there is no modeling method to quantify this disk temperature field and its subsequent effects on the recording system.
A particular difficulty is that rotating the disc heats up when it moves below the slider and cools when it moves out of the slider --
Covers the region, which makes it a transient process that is difficult to adaptadopted steady-state approach.
In this study, we developeddescription-
Methods for characterizing disk heat dissipation based on contributions from a variety of nanothermal transport schemes, including air film conduction and near-field radiation.
Then integrate the model into multiple
Physical system and solve simultaneously with other field equations that control the dynamics of the air bearing and the heat of the slider
Mechanics of iterative methods.
The accuracy of the numerical model is confirmed by good agreement with the experimental data.
The temperature field of the disk establishes heat
The drive slider is quantified in the same order as the heat source surface.
Disk configuration and relative linear velocity contribute greatly to the effective heat transfer coefficient of the interface and the resulting temperature field on both sides of the interface.
This method verifies the size of the different heat transfer schemes in the pressurized narrow gap maintained by the dynamics of the air bearing.
It also shows an effective calculation method for dealing with transient thermal processes in component systems with relatively fast speed and different length scales.
It is also shown that for the magnetic recording system, the thermal transmission mechanism studied has resulted in a large amount of spacing changes at several angles, which accounts for a large part of today\'s working spacing (
Usually around 1 nm).
As shown in the figure, the problem is formed in this way. .
The rotating disc brings airflow below the patterned ABS at the bottom of the slider, forming a pressure field that keeps the slider in the desired posture, usually quantified by the flight of the slider
Height, spacing, and scrolling.
The resistance heater built in the slider body partially heats the slider and forms a bump on the rear edge of the slider, making the recording sensor closer to the disk.
The minimum gap size between the slider and the disk can reach 1 nm or even sub-nanometer.
As mentioned earlier, by the heat-
The mechanical deformation of the slider will be affected and affected by the lower pressure field.
Now, if the disk is hot, the temperature field will not
Negligible, the heat flow between the slider and the disc is expected to have an impact on the pressure field in the slider body, the attitude of the slider and the temperature/stress/strain field.
Although the thermal process inside the disk is only a thermal conduction problem controlled by the thermal equation, it is not trivial to integrate the disk temperature field into this coupled field analysis.
For a separate material point on the disk, it is heated when it rotates under the slider and cools when it moves out of the slider --covered area.
The temperature changes periodically every turn, and the transient process is not balanced.
Considering that the size of the slider is less than a hundred times the circumference of the disk, the calculation of the complete simulation of this temperature field is expected to be huge, because it is crucial to accurately characterize the temperature field on the surface of the slider.
However, although the size of the disk is very large, but in the whole-plane.
So if we change our viewing angle from disk to slider, that is, this disk temperature field does reach a stable state if we fix the coordinates with the slider (i. e.
The temperature field under this coordinate does not change with time)
As shown in the figure. .
So we need to re-
The heat equation of the disk temperature field is formulated using the Euler method coordinates.
We first use the control volume formula combined with Fourier\'s law,
The thermal equation controlling the temperature field of the disk is expressed as stable-State convection-diffusion-
Type equation: Here is the disk temperature represented by the Euler method coordinates, respectively, the volume heat capacity and thermal conductivity of the disk material, which is downTrack and crossover
Track the linear speed separately.
The disk vibration in the direction is ignored here.
Solving the equation ()
We have developed a limitedvolume-
Numerical code based on transverse adaptive grid (and )and vertical ()directions.
In the landscape, the mesh in the area directly below the slider matches the mesh on the ABS to capture the lateral pressure gradient (
Closely related to heat transfer coefficient)
The numerical error caused by interpolation is avoided.
Due to no material movement, the temperature gradient in is expected to drop sharply in the top solid layer.
Therefore, the grid size can adapt to the temperature gradient, from the top of the disk ~ 1 nm to the bottom of the disk ~ Ranges from 100nm in order to improve accuracy and efficiency (
Supplementary Mapdetails).
Instead of solving the temperature of the entire disk, we limit our solution domain to a disk block of size 1. 7u2009mmu2009×u20090. 7u2009mmu2009×u20090.
8mm, starting at the front of the slider, to the end of the space positionslider-length down-
Trace from the trailing edge of the slider to keep the problem moderately sized.
The boundary of the solution domain is determined by a series of simulations of different domain sizes, which confirm that the dilikelite boundary conditions at ambient temperature apply to the side and bottom surfaces of the disk block.
From the equation ()
Coupling with the whole system through the heat flow boundary condition is determined by the temperature field of the slider and the dynamics of the air bearing.
The pressure field between the slider and the disk is solved by the generalized Reynolds equation, which is an adaptive form of the classical Reynolds equation derived from the linear boertzman equation, in order to adapt to the situation of highly sparse air flow, for example, the pressurized thin film air bearing in our problem.
Given the load applied on the slider and the ABS geometry design, the pressure field and the slider pose are solved using the CML Air from the coupled Renault equation and the slider static equation.
These two solutions (
Spacing and pressure)
Then the heat flow boundary condition through ABS is related to the deformation of the slider under the Joules heating: as shown in the equation ()
There are three main heat transfer schemes, including conduction, radiation and viscous heating of air bearings.
Generally considered as the main heat transfer scheme, and has been studied in depth, can be obtained by solving continuous energy equations with jump boundary conditions, a very similar treatment, like the generalized Reynolds equation, write in the following form: the position and position of the spatial coordinates along the downTrack and crossover
As shown in the figure, track the direction separately. .
Is the air thermal conductivity, is the thermal adaptation coefficient, is the specific heat ratio, Pr is the Prandtl number, is the local temperature of the slider at the ABS, is the local temperature of the disk surface, from the equation ()
, Is the local spacing between the slider and the disk, solved from the CML Air.
The average free range of local air is proportional to the film temperature and inversely proportional to the film pressure (, ).
Solve from Renault equation and calculate the mean value of I as sume. , u2009=u2009(+u2009)/2.
With the size of the nano-gap, the contribution of viscous heating becomes insignificant, while the radiation thermal guide may become a significant contribution.
To evaluate, we used a theoretical model to extend the classical Planck law to near-field radiation states and demonstrated qualitative consistency with experiments performed using a real head.
In the temperature range studied, the model shows the radiation heat transfer coefficient (defined by /(−u2009))
Is a strong function of spacing d, contrary to its weak dependence on and.
Therefore, in order to reduce the cost of iteration, only linear terms are included in the calculation. A fixed-
Using the point iteration strategy in the main program, the thermal deformation of the slider is first solved in the commercial software ANSYS.
Displacement solutions are used to calculate the dynamics of air bearings using CML air, and temperature solutions are used to simulate the disk temperature field using our finite volume solver.
The obtained pressure and disk temperature field are then applied to the equation ()
Define a new set of heat flow boundary conditions to be applied in the ANSYS model.
This simulation strategy is then applied to test the two common clearance heating effects.
The type of disk used in the magnetic recording industry, that is, the disk with aluminum and glass substrates.
The material properties of the sliders and disks used in this analysis can be found from recent literature.
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