This model demonstrates how the air path for a pusher fan can be modeled in KULI. The focus is on the high resistance of the hub, which influences the flow distribution. To take care of this effect, the air path is split in separate segments.
To model the high resistance of the hub, an equivalent area resistance located in the air path is modeled. Therefore the circular area of the hub must be converted in a rectangular area resistance. In our experience, the zeta value (dimensionless resistance) of the area resistance should be 3 times higher than the zeta value of the radiator next to the hub.
The air path is split into several segments. A part of the air mass flow passes the resistance, the rest flows by. Due to this uneven resistance characteristic, the resulting uneven air mass flow leads to a temperature distribution.Usable from release: KULI 9.1-0.01
To optimize the fuel consumption, new concepts like the Thermo Electric Generator (TEG) may show potential. To analyze the possibilities of such system, the layout can be modeled in KULI and different concepts can be compared.
The model consists of an exhaust gas system (hot side) and a water circuit (cold side), whereby the electric power is generated out of this temperature difference.
The modeling of new concept like the TEG is a challenging task for each engineer. This example shows how such a model can be easily created with KULI “on-board” components.
Therefore a combination of calculation controllers, maps and circuits is used to describe the behavior of such a component.
Basically the model consists of two circuits, whereby each of them contains a point mass (hot and cold side of the TEG). Both PM are connected by heat conduction, the area for the heat transfer is calculated by the overall number of elements, the area of such an element and the thickness.
For the calculation of the TEGs performance, the characteristic is provided by a 2D curve which is based on the temperature difference between hot and cold side.Usable from release: KULI 9.1-0.01
Due to the little loss heat of modern (diesel) engines during warm-up, PTC (Positve Temperature Coefficient) heaters are used to guarantee the fast warm up of the cabin. The inner resistance of the PTC increases for higher temperatures, therefore the heating power is automatically reduced for high temperatures (caused by high inlet temperatures, low mass flows, …).
Usually the PTC is positioned next to the conventional cabin heater and is mainly used during the warm up phase of the engine. To reduce the fuel consumption, the PTC is deactivated if the heating power of the engine is sufficient. Due to the characteristic of the inner resistance which will reduce the current and therefore also the heating power for higher temperatures, no additional emergency shut of system is required.
In this example the model of the PTC is reduced to an air-side point mass, including the thermal inertia and heat transfer coefficient. The amount of heat is calculated by the inner resistance (2D map) and a calculation controller.
Additionally the heater will be turned off if the cabin (air ducts) temperature exceeds 60 deg.Usable from release: KULI 9.1-0.01
For higher driving velocities, the fan acts like an additional resistance and reduces the effective cooling mass flow. To avoid that effect, air flaps are included in the shroud. These flaps open in case of an “overblown” fan and the cooling air flow can directly pass by this flaps.
The air flaps are modeled by area resistances, their pressure loss characteristic is defined by a velocity depended map. To adjust the mass flow distribution between the air flaps and the shroud (fan), additional Build in Resistances (BiR) were used for the lower part of the radiator. The ratio of the resistances will directly influence the mass flow distribution.
In case of a fan driven air mass flow, the air flaps are closed. Therefore the resistance of the flaps in comparison to the BiR is very high. In case of an overblown fan (usually at high driving speeds) the resistance of the BiR is very high, in contrast the resistance of the open air flaps (area resistance) is quite small.Usable from release: KULI 9.1-0.01
Due to its thermal inertia, the charge air cooler will show a special transient behavior. Especially if the volume flow or the temperature changes, this influence can lead to deviations in the temperatures, pressure losses, … The example demonstrates a possibility how the user can take care of this effect and easily include the model in an existing KULI model.
To take care of the charge air coolers (CAC) thermal inertia, point masses (PM) are included. Basically two different types of PM are used in the model:
- Point mass at the air side (mass ~ 40% of the CAC overall mass)
- Point mass in the circuit (mass ~ 60% of the CAC overall mass)
A separation of the CAC into two parts in combination with 3 point masses (inner side) and 2 point masses at the air side shows a very realistic behavior.
A separation of the inner circuits’ point mass of 10%, 70% and 20% (based on 60% of the overall mass) is recommended. The heat transfer area is calculated from the dimensions of the fins (inner side) and from the CACs’ net dimensions (air side). For the heat transfer coefficient a separation into inner and outer side is recommended.
This subsystem calculates the averaged consumption per 100 km. The input data is based on the current fuel consumption of the engine model and the track length. To convert the consumption from kg/s to a volume flow (liters per 100 km), it’s necessary to input the fuel density.
This subsystem demonstrates how easy the actual fuel consumption of the engine can be converted into fuel consumption in liters per 100 km. Therefore a PID controller containing an Integrator is used to get the overall consumption in kg. To convert the mass into a volume, the value is divided by the fuel density (user input). Also the track length – which is a necessary input for the simulation – can be calculated by integrating the driving velocity (if necessary this must be additionally added by the user).
The output of that subsystem is the overall fuel consumption [kg] and the fuel consumption per 100 km.Usable from release: KULI 9.1-0.01
This subsystem calculates the heat flows in the cabin model. The system provides the amount of heat to the outlet air, the effective cooling power and the Heat flow to the ambient.
The calculation is done in the subsystem, whereby some additional data like the heat transfer values to the ambient must be input by the user.
This subsystem demonstrates how the heat flow in a cabin can be calculated. Three different types of heat flow are calculated:
- Heat to outlet air: The amount of heat lost via the discharged air
- Effective cooling power: How much heat is effectively used for the cool down of the air flow
- Heat flow to ambient: The amount of heat exchanged between the cabin and the ambience
Due to the fact that some of the values are defined directly in the component, they are not available as sensor. Therefore external controller inputs can be used to set these values by user defined constants. All other necessary information is connected by using the sensor path.
Several calculation controllers (in combination with media components) are used to calculate the amount of exchanged heat.
In KULI the user can choose between different ways how to model a battery. They mainly differ in the necessary amount of input data, the effort for the creation of the model and also in the level of detail of the results.
This example shows in a detailed way how to model an energy storage. The battery contains cells & modules, as well as the multi-dimensional housing. The electric model is based on a cell level R-C model, which also considers the capacitive behavior.
This example demonstrates the advanced modeling concept for a thermal-electric battery model. Each of the 8 modules is housed in the battery and includes 12 cells (overall 96 li-Ion pouch cells including the cooling plates). Beside the thermal inertias of the cells themselves, also a multi-directional model of the housing is included. Each side of the housing as well as the cells can be connected by heat conduction. To simulate the electric behavior, a cell based R-C model is used. On the one hand this model describes the electric properties (like SOC, open cell voltage, ..), on the other hand the thermal behavior of the cells. Beside averaged values, each cell temperature can be accessed. For that reason the model shows excellent opportunities for battery layout design and of course also for the development of the battery cooling system.Usable from release: KULI 9.1-0.01
In KULI different ways how to model a battery exist. They mainly differ in the necessary amount of input data, the effort for the creation of the model and also in the level of detail of the results.
This example shows the most reduced way how to model a battery. Therefore all cells, modules and housings of the battery are reduced to one single lumped mass model for the use in KULIs cell model.
This example loosely describes a liquid cooled Li-Ion traction battery with around 290 cells and an overall weight of 180kg. By the reduction to a lumped mass / cell model, the whole battery is reduced to a single mass with an averaged thermal heat capacity (cp value). The heat transfer surface is the sum of all single heat transfer surfaces (each cell is in contact with a liquid cooling plate), the heat transfer coefficient is modeled as function of the flow velocity. To convert the mass flow to a flow velocity, the overall cross section must be defined in the component parameters window.
Due to simplicity, the electric properties are reduced to a constant value resistance model. The values are based on the battery characteristics.
This way of modeling a battery is very fast and effective, with the limitation of getting averaged values. Therefore it’s very useful for the estimation of the (transient) heat input in the cooling system and for simulating the influence of the batteries’ inertia, but not for designing the batteries’ inner layout.Usable from release: KULI 9.1-0.01
This example shows a quite simple way how hysteresis can be modeled. The calculation controller differs between two cases, with respect on the previous operating state. To avoid that the temperature / fan RPM is oscillating around a certain value, a function is used.
To avoid a highly oscillating fan RPMs, a hysteresis in the controlling strategy is included. This is modeled by a calculation controller. If the temperature exceeds a certain value, the fan switches to the maximum RPM mode. Additionally this high RPM mode is also used, if the temperature is between the two temperature limits and the high RPM cooling mode is already active. In case of underestimating the lower activation border or in case of an active min. RPM mode & actual temperature between the limits, minimal RPM mode is selected. To avoid a logical loop, a delay controller is used for sensing the input speed of the fan.Usable from release: KULI 9.1-0.01