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KISSsys 03/2018 – Template

Thermal analysis, Efficiency Template

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General Information

This paper describes how to use the thermal analysis calculation in KISSsys, to be able to calculate the power

losses, efficiency, and heat dissipations of a given gearbox.

Several different methods are implemented in order to let the user select how the calculation should be

performed, according to the ISO/TR 14179 standard, part 1 and part 2 (combined with AGMA 6123-B06).

In some cases, results have to be treated with special care, because calculation methods used may not fully

support the type of geometry.

Additionally to these calculation methods, some extensions and combinations of them are introduced.

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Contents

1 Introduction ............................................................................................................................. 4

1.1 Thermal analysis ..................................................................................................................................... 4

1.1.1 Power losses ....................................................................................................................................... 4 1.1.2 Heat dissipations ................................................................................................................................. 4

1.2 Possible calculations ............................................................................................................................... 4 1.3 Flow chart ................................................................................................................................................ 5

2 Importing the template ............................................................................................................ 5

2.1 Default templates .................................................................................................................................... 5 2.2 Automatic creation of elements ............................................................................................................... 6

2.2.1 Gear churning losses .......................................................................................................................... 6 2.2.2 Gear meshing losses .......................................................................................................................... 6 2.2.3 Bearing losses .................................................................................................................................... 7 2.2.4 Seal losses .......................................................................................................................................... 7

2.3 User defined elements ............................................................................................................................ 7

3 Using the template .................................................................................................................. 7

3.1 Requested result ..................................................................................................................................... 8 3.2 Housing ................................................................................................................................................... 8 3.3 Settings ................................................................................................................................................. 10

3.3.1 ISO TR 14179-1 ................................................................................................................................ 10 3.3.2 ISO TR 14179-2 ................................................................................................................................ 11

3.4 Ventilation ............................................................................................................................................. 12

3.4.1 ISO TR 14179-1 ................................................................................................................................ 12 3.4.2 ISO TR 14179-2 ................................................................................................................................ 13

3.5 Lubrication ............................................................................................................................................. 13 3.6 Cooler .................................................................................................................................................... 14 3.7 Correction factors .................................................................................................................................. 15 3.8 Report ................................................................................................................................................... 16 3.9 Temperature Spectrum ......................................................................................................................... 16

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1 Introduction

1.1 Thermal analysis

The thermal analysis can be defined in two sections: power losses and heat dissipations. Additionally, an

external cooler can be taken into account. Power losses as well as heat dissipations can be separated in several

sections to consider the effect of all the different transmission components.

1.1.1 Power losses

Power losses can be separated in two main losses, load dependent losses and load independent losses.

Normally when a gear box is in operation, both losses will be present. Power losses can be also separated

between different gearbox elements like, gears, bearings and seals. For the gears, we consider the meshing

(according to Niemann, eventually Wech for bevel gears, Contact Analysis …) and churning losses (according to

ISO/TR 14179), for the bearings, the rolling, sliding, seal and drag friction (according to SKF), and for the seals,

the seal friction (according to ISO/TR 14179).

In some cases, the results have to be treated with special care, because the calculation methods used may not

fully support the type of geometry. For the churning losses for example, the standard propose a solution for

cylindrical gears that is extended to bevel gears. And the AGMA 6123-B06 propose a solution for planetary gear

sets with a fixed ring. All other types of gears or configurations are not considered.

1.1.2 Heat dissipations

Heat dissipation can be divided in heat dissipations via housing (with or without thermal finning), foundation,

outcoming parts (input/output shafts and couplings), and cooling oil flow.

1.2 Possible calculations

The user can then simply calculate independently the total efficiency and the total heat dissipation capacity of a

gearbox for a given lubricant temperature, cooler power and input power. Or he can also set two of these three

inputs and calculate the optimum third one, the one for which he gets the thermal balance of the gearbox,

meaning when the heat dissipated is equal to the heat generated through the power losses.

The difference between part 1 and part 2 of the standard is the way the different inputs for the calculations will be

set. The main advantage of the part 1 will be to let the user input his own heat transfer coefficient for the

dissipations through the housing (if it has a very specific shape), whereas in the part 2, this coefficient will be

calculated according to an approximation of the shape of the housing. The main advantage of this part will then

be to consider the fins, foundations and rotating parts in the calculation of the heat dissipations.

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1.3 Flow chart

2 Importing the template

2.1 Default templates

The efficiency template should be only added in an existing KISSsys model, because it is a calculation extension

for a “complete” model. The template is included in the default templates.

The administrator mode needs to be activated using “Extras/Administrator” as shown below to be able to add

new elements like this template in the model.

Figure 1. Changing to administrator mode

Then the template can be loaded on the root of the tree structure by using the corresponding default templates

button. The template contains a table element (standard name: “Efficiency”), which includes all the functionalities,

a two sub tab called “Losses” and “TemperatureSpectrum”.

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Figure 2. Importing "EfficiencyTemplate.ks"

If the user already have a model with the efficiency template integrated, to be able run the calculation using the corresponding button, the administrator mode doesn’t need to be activated anymore, but the specific license right k11h is mandatory. For any request concerning this feature, please contact info@kisssoft.ag.

2.2 Automatic creation of elements

When the table for thermal analysis is implemented in a KISSsys model, some functions automatically adapt the

model according to the needful variables and elements. But this action is always reversible by pressing the

button “Reset” from the template. By doing this, the user will remove all the additional elements added to the

model, and all the connection to other variables, to set the model exactly as it was before the integration of

template. When he presses the button to run the calculation again, all the elements and settings defined from the

efficiency table will be set back, and the calculation will run.

2.2.1 Gear churning losses

To be able to consider the churning losses of the gears, new elements for these are added in the model. These

elements, type “kSysPowerLoss”, are added to the shafts and connected to the corresponding gear elements on

the shafts. The elements are automatically named as “Losses+name_of_the_gear”. Churning loss components

are automatically created for different type of gears, and in case of planetary calculations, one element is also

created to consider the churning losses of the carrier.

2.2.2 Gear meshing losses

For the meshing losses, some functions will input the efficiency results from KISSsoft calculations directly in the

constraint elements. (When “Reset” is pressed, the original inputs/formulas for these values are set back).

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2.2.3 Bearing losses

For the roller bearing losses, some elements are created, type “kSysPowerLoss”, and called

“Losses+name_of_the_bearing”. For connection roller bearings, one element is created on each shaft to which

the bearing is connected (to get the relative speed for the calculation).

2.2.4 Seal losses

To be able to consider the losses of the seals, the user has the choice to let the template add some elements

automatically wherever the housing is crossing an outcoming shaft. The elements are automatically named as

“Losses_Seal_Ymax” or “Losses_Seal_Ymin” depending if the seal is created on the right or the left side of the

shaft on the Y axis. The user can then select what type of seal he wants to use according to the standard, and

depending on this selection the power losses will be calculated automatically.

2.3 User defined elements

In any case, the user can define additional power losses anywhere on the model by simply adding

“kSysPowerLoss” elements. He can then enter directly the power loss value inside the element.

If he wants to add a seal element using the standard power loss calculation, he can add and position a

“kSysPowerLoss” element on a shaft, and then add a variable type real called “seal” in this element. Then he

doesn’t need to enter a loss value but only to select the type of seal like for the automated ones (see after).

3 Using the template

All the inputs needed before performing the calculation are directly available in the template interface, under

“Calculation Setup” section (it is now possible to use the contact analysis instead of Niemann or Wech for the

meshing losses). The user can then use the Efficiency button to run the calculation. Under the section

“Specific functions”, the user can then see if the results are consistent or not, print a report, and reset the

variables and elements. In the two other sections, the user has a general overview of the different results in the

selected unit (under the section “Calculation Setup” as well). The “Efficiency (gear mesh)” result is displayed to

compare with the total efficiency, has it is the result that the user would get without using this specific template

considering the other losses (then more accurate).

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Figure 3. Interface for thermal rating calculations in KISSsys

3.1 Requested result

The first input we have to describe is the type of calculation the user wants to perform. In the field “Requested

result”, it is possible to select 5 different results:

- “Efficiency”, to calculate only the heat generated, and the corresponding efficiency of the complete

gearbox.

- “Heat transfer”, to calculate the heat generated and the heat dissipated (maximum capacity with this

housing and gearbox), plus the efficiency

- “Cooler power” *, to calculate the cooler power needed to get the thermal balance between the heat

generated and the heat dissipated for a certain oil temperature and input power

- “Oil temperature” *, to calculate the oil temperature needed to get the thermal balance between the heat

generated and the heat dissipated for a certain cooler power and input power

- “Input power” *, to calculate the input power needed to get the thermal balance between the heat

generated and the heat dissipated for a certain oil temperature and cooler power

- “Temperature/Time”, to calculate the oil temperature variations through the operating time and load,

according to the difference between the heat generated and the heat dissipated at a time t.

* For these calculations, the user will get the requested result in the corresponding field, section “Results

summary”. When the user runs the calculation with one of these selections, all the other results (losses,

efficiency …) will be displayed by taking into account this request result as an input. But for the input power

selection, the original value will be set back to the model input directly after the calculation.

3.2 Housing

To be able to consider heat dissipations through the housing, some settings regarding its geometry, material,

surface treatment must be done. The user can first select if the housing can be approximated by a rectangular or

cylindrical shape. Then he can define its wall thickness, material, extensions in every direction (value between

the extreme element in this direction and the inside of the housing). And finally he can integrate the coupling in

the housing or not (for the calculation of the minimum housing size required after).

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Figure 4. Dialog for housing dimensions

Then, depending on the shape selection, the user has a display of the external dimensions of the housing, taking

into account the extensions and wall thickness previously defined. Here it is possible to give some dimensions

and calculate the total surface area, or to input it directly (selection “Calculated” or “Own input”). It is also

possible to set a total surface and some dimensions in maximum two directions to get the other one(s). It is also

possible to switch back to the default (and minimum) values calculated by the template (button Sizing). After the

housing size definition, the surface treatment must be defined. It will have an influence on the heat emissivity (but

the value can be changed anyway afterwards), and it is dependent on the previous material selection.

Figure 5. General housing settings

In this dialog he will find also the input for the automatic creation of the seal losses elements. If the user select

“Yes”, or if he has created a user defined seal loss element with a variable “seal”, then he will have a third dialog

with the selection of the seal type for all these elements using the loss calculation from the standard.

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Figure 6. Seal type selection

If the user selects “Yes” for the fields “Draw housing” and “Draw oil level”, he will get the following display (if he

has at least one gear calculation with an oil bath lubrication, otherwise without oil level): display of the housing

with the wall thickness and the oil level in the 3DView (also the foundations if the user defined it).

Figure 7. Visualization of the housing and oil level in kSys3DView

Important note: The housing shapes (meant to be an approximation of an industrial gearbox housing) are really simple because they are just used mainly to calculate, with the material and surface treatment, the main heat transfer coefficient of the gearbox. If the user wants, he can anyway define it manually after.

3.3 Settings

With this button, the user will be able to give all the general inputs needed, depending on the calculation method

selected: ISO TR 14179 part 1 or part 2.

3.3.1 ISO TR 14179-1

When calculation method “ISO TR 14179-1” is selected, only the housing can be considered in heat dissipation.

Therefore housing with thermal fining, heat dissipation via foundation and outcoming parts will not be regarded.

With this calculation method, the heat dissipated will be calculated by taking into account these general

assumptions:

• Lubricant temperature of 95 °C

• Ambient temperature of 25 °C

• Air velocity smaller than 1.4 m/s

• Air density at sea level

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• Continuous operation

The user will then have to select the real operating conditions to apply some correction factors and get the

effective heat dissipation calculation.

Figure 8. Real operating condition for ISO TR 14179-1

3.3.2 ISO TR 14179-2

When calculation method “ISO TR 14179-2” is selected, the housing will be considered in heat dissipation, but

also thermal fining (result included in “Housing” on the interface is defined), foundations and outcoming parts if

the user wants to consider them. If he wants, the user can also select if he wants to define manually the heat

transfer coefficient instead of using the one calculated from the housing definition (value set later).

Figure 9. Additional heat dissipations for ISO TR 14179-2

If thermal fining should be considered in heat dissipation, the geometry for these needs to be set using the

following dialog.

Figure 10. Definition dialog for thermal finning

If the foundations should be considered in heat dissipation, the geometry for these needs to be set using the

following dialog.

Figure 11. Definition dialog for foundations

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If output shafts should be considered in heat dissipation, the geometry for these need to be set using the

following dialog.

Figure 12. Definition dialog for outcoming parts

In this dialog will appear all the shafts outcoming from the defined housing. Below the shaft inputs will appear the

coupling inputs if there is an outcoming coupling as well. For these elements, the output length, mean output

diameter as well as the thermal (or heat conduction) coefficient must be set. If the user press the button “Init all

values”, all the different values will be calculated and filled out automatically (for the thermal coefficient for both

shafts and couplings, the value is taken form the shaft material). If the user doesn’t want to consider a shaft or a

coupling, he can simply enter “0” in the field “Output length”.

Important note: all these different dialogs have some restrictions, and the user can’t input “0” in some fields. The

dialog will simply re-open if a field is not correctly defined.

3.4 Ventilation

With this button, the user will be able to give all the ventilation inputs needed, depending on the calculation

method selected, and on the “Ventilation method” selected in the “Settings” for ISO TR 14179-1.

3.4.1 ISO TR 14179-1

Depending on the selection for the “Ventilation method”, the user will get three different dialogs.

With “Own input”, he can define his own heat transfer coefficient, and apply or not an external ventilation

(auxiliary cooling) with a certain speed (with no ventilation, the speed can be different to zero, but must be inferior

or equal to 1.4 m/s). Ventilated air temperature is grayed out if no external ventilation is considered.

Figure 13. Own input

With “With auxiliary cooling”, he can define an air speed (this time it must be at least superior to 1.4 m/s), and the

different temperatures. The heat transfer coefficient is then calculated internally.

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Figure 14. With auxiliary cooling

With “Without auxiliary cooling”, he can select the space around the gearbox, and the speed, respecting the

restrictions indicated in the selection. The heat transfer coefficient will then be depending on this selection. And

no ventilated air temperature can be defined as there is no auxiliary cooling.

Figure 15. Without auxiliary cooling

3.4.2 ISO TR 14179-2

When this calculation method is selected, the user will have the following dialog. If the heat transfer coefficient is

set manually, he gets an additional field for the value here. The user can then select if he has an auxiliary cooling

or not. If yes, he has to select a plane (normal to the ventilated surface). Then he has to input air velocity, and the

temperatures as before (ventilated air temperature grayed out if no auxiliary cooling considered).

Figure 16. Ventilation input ISO TR 14179-2

3.5 Lubrication

For the lubrication setup, the user will have different dialogs, depending on the lubrication type for the gears.

The first important thing to know is that only oil bath and oil injection lubrications are considered in the standard.

For other types, no solution is provided for the churning losses of the gears.

In every dialog the user will have the possibility to connect the oil temperature to all the different KISSsoft

calculations in the model. This will be mandatory to use the different calculations possible with the template

expected “Efficiency” where you can input a different oil temperature for every different element if needed.

The oil type and lubrication types are to be defined separately, in each calculation or using a general external

table like the “Settings” one available in the “templates.ks”.

If the user has only oil bath lubrications defined he will get the following dialog. He can then select to calculate

(middle of the lowest tooth or roller from the highest gear or bearing) or input the oil level (defined in the global

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coordinate system of the gearbox). He can then connect the oil temperature and set the value. He can also

connect the oil level which will then be transferred locally to each shaft calculation for the bearing losses.

Figure 17. Only oil bath lubrication

If the user has also oil injection lubrications defined he will get an additional selection in the dialog to define the

oil injection properties. He can then select to define a global oil injection input or do it separately for each different

gear calculation.

Figure 18. Only oil injection lubrication

For the global oil injection input or for each gear calculation with oil injection lubrication, he will get the following

dialog, where he has to define the injection volume and velocity, and the point of injection.

Figure 19. Oil injection setup

Important note: for the bearings, the user can also define a separated oil level (the previous one will then only

be used to calculate the churning losses of the gears) in each shaft calculation, in the “Module specific settings”.

He can define there as well the calculation method (be careful, SKF 1994 doesn’t take into account the oil level),

lubrication type, and seals torque loss (for the bearings only). The user can also connect all this variables with

the latest version of the “Settings” template.

3.6 Cooler

For the cooler definition, the user will have to define the cooler needed cooler power and the temperature drop of the oil over the cooler from the starting point to the end.

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Figure 20. Cooler power setup

3.7 Correction factors

The user will also be able to adjust the different losses calculated according to his own measurements. For that he has two different entries possible. The first one will be the general correction factors input available from the main interface of the template.

Figure 21. General correction factors for heat generation

In this dialog, he will be able to apply a general correction factor for each group of losses (default value is “1”). Each time he opens this dialog, if he selects “Yes” for a specific losses group, the factor below is applied. If he already defined one before and/or defined individual corrections (see after), and he opens again this dialog, by pressing “OK”, he will overwrite all the values where “Yes” is selected. He should then select “No” if he doesn’t want it overwritten. This dialog is in fact just created to spare time when you have a lot of different individual losses to correct. It is also possible to input correction factors for the heat dissipation.

Figure 22. General correction factors for heat dissipation

The second entry will then be the “Losses” sub table.

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Figure 23. Individual losses and correction factors

In this table, the user can first have an overview of all the different losses from the model. He can then define individually all the different correction factors for each loss by doing a “right clic – Edit” on the “Correction factor” column. For the user defined loss elements, he can’t apply the general correction factors unless it is modified as a seal with the variable “seal” inside. But in any case it will appear in the individual losses sub table. If it is defined as a seal, it will have the “Calculated value” filled out, otherwise not as it is a user input (then “0” is set, but he can apply a correction factor anyway).

3.8 Report

The user will finally be able to print out a general report gathering all the inputs and outputs of his calculation.

The report file will be saved in the KISSsys project folder. After writing the report it will be automatically shown in

the editor.

Figure 24. General report

3.9 Temperature Spectrum

If the user wants to calculate the temperature variations (Temperature/Time), he can then define a temperature

spectrum in the same way as with the load spectrum template. The main difference here is that he needs to

define a real sequence to be able to see the evolution of the temperature through the time.

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Figure 25. Definition dialog of the temperature spectrum

Then the user can define the sequence. If you use some steps with a big duration, they are anyway cut in several steps to be able to calculate properly the temperature evolution. The user can then modify the maximum number of iteration and the maximum temperature variation from one step to the other by changing the default values in the variables below. In the variables TotalEfficiency, TotalHeat…,… he will get the actual results for each virtual step calculated (can then be 10 even if the user has only 2 steps defined in the temperature spectrum).

Figure 26. Additional useful variables in TemperatureSpectrum tab

The temperature start need then to be defined in the lubrication button. It can be set for example to the ambient temperature.

Figure 27. Definition of the initial temperature

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Then when the user presses the calculation button, a dialog pops up to enter mass and specific heat capacity for

the various elements which are dissipating heat. Depending on the selected calculation method and user

definitions the dialog changes dynamically.

These values can be calculated by pressing the update button, or each time the geometry is modified and the calculation is launched when setting the auto update selection to “yes”.

Figure 28. Definition of the mass and specific heat capacity of heat dissipating elements

When the calculation is finished, the user gets the results in the temperature spectrum tab, with additional columns for the temperature, efficiency, heat generated and heat dissipated for each step.

Figure 29. Display of the results

A good first approach is to use the nominal load on each step as on the example above, with a duration of 0.03h for each. Then you can see quite well the exponential increase of the temperature until the reach of the thermal balance.

When exporting the result from the table (or the virtual steps) in Excel, the user can then get a good overview of

the temperature evolution.

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Figure 30. Results for nominal load

Figure 31. Results for a load sequence variation