# Gas Foil Bearing Technology Enhanced with Smart Materials
## 6 Applications of Thermoelectric Modules and Thermoouples to Gas Foil Bearings  
TEMs (also referred to as Peltier modules) are devices made of n- and p-type semiconductors that allow one to impose heat energy flow [42]. The amount of transported energy is controlled with the electric current supplying the device. The energy flow is governed by the Peltier effect. TEMs are solid components, hence, they do not require any refrigerants and do not exhibit mechanical wear due to lack of moving parts. One of the major disadvantages of using TEMs is limited energy efficiency. Specifically, exceeding the consumption of a given specific current leads to a reduction in both heat energy transport efficiency and the ability to maintain the demanded temperature difference between the module's hot and cold sides (junctions).  
A TC is constructed as an electrical connection of two conductors (the hot junction) [43]. The remaining two free ends of the conductors compose the so-called cold junction which should be maintained at the referential temperature (ambient temperature). If the temperatures of the two junctions differ, the electromotive force \(E\) is adequately generated thanks to the thermoelectric effect, i.e., the Seebeck effect. The measured electric potential drop \(E\) can be considered as a quantity proportional to the temperature difference.  
As referenced in Sections 1 and 2, thermal management (heat flow management) is critical for the operation of a GFB. Hence, both TEMs and TCs may be advantageously used to provide effective means to control the flow and dissipation of heat energy within the body of the bearing. The former components allow one to guide the heat flow by acting as the active energy sources and sink, whereas the latter devices can measure the temperatures at the demanded localizations in a GFB. The work [37] reports the results of experimental investigation on the GFB installation equipped with TEMs and TCs. The authors propose an active cooling method, making use of TEMs installed in the GFBs' bushing. TCs have been applied to measure the temperature on the outer surface of the top foil. The conducted measurements confirm the capability of reducing the bearing's average temperature as well as its gradient without affecting the dynamic properties of the shaft's journal.  
The recent work [8] extends the scope of the above-presented study. Specifically, numerical simulations are employed to assess various scenarios for GFBs' thermal management. The obtained results have been experimentally confirmed. Based on the theoretical and experimental findings, the authors have proposed strategies for effective reduction in undesired temperature gradients that should lead to a considerable decrease in the risk of thermal stability loss for an operating GFB.  
An innovative method dedicated to temperature measurements in a GFBs' top foil is presented in [38]. The authors propose to extend the standard functionality of this foil, i.e., assurance of a smooth surface for developing the air film, also to become a sensingcomponent via integration of TCs. For the experimentally tested approach, platinum wires are soldered to the outer surface of the top foil and establish a matrix of TCs with a common electrode which is a part of the foil.