Validation of a coupled multibody and TEHL simulation by a piston/cylinder component test rig

A tribological highly stressed contact in the actuating system of axial piston machines is located between the control piston and the control chamber. This paper presents a new type of component test rig for measuring the frictional force and the gap heights between piston and cylinder. For this purpose, the original system is reduced to the actuator system, whereby the real kinematics and the loading forces are maintained. The axial movement of the control piston and the pressure in the control chamber can be configured individually. The measurement results of different parameter variations are compared with the results of the simulation. The simulation based on a coupled multibody and TEHL simulation with a transient, three-dimensional, thermal elastohydrodynamic contact calculation.

A Thermally Actuated Microvalve for Irrigation in Precision Agriculture Applications

It is currently impossible to control irrigation at the level of a single plant. Even with drip irrigation, in which emitters could conceivably be placed on a plant-by-plant basis, there is no way to control the amount of water emitted according to the needs of the individual plants. If such a capability were practically available on farms, the result would be a step change in precision agriculture, such that the water input for every plant in a farm (or field) could be optimized. Therefore, we are exploring the possibility of developing a microfluidic system that could be controlled, capillary by capillary, to deliver the needed amount of water to individual plants in a large field. The principal aim is to show proof of concept by building and testing a prototype to produce data suggestive of the potential for multiple individually controllable microfluidic ports along a pressurized tube of water. Hence, in this study we perform experiments using a thermally actuated microvalve for irrigation in precision agriculture applications. The microvalve was manufactured using soft-lithography techniques, i.e., using polydimethylsiloxane (PDMS). The active microvalve was designed for a “normally open” configuration and consists of two layers: (1) a flow layer and (2) a control layer. The flow layer contains the water inlet, outlet, and the flow channels for passage of water. The control layer contains an enclosure (chamber) which expands upon heating, which in turn deforms a thin membrane into the flow layer and thus impedes (or reduces) the water flow rate in the flow layer. Both layers are bonded together and then on a glass substrate. The bonded PDMS microvalve and glass assembly is heated to different temperatures for enabling the actuation of the microvalve. Experiments were performed using two microvalves of identical design but with two different actuation fluids. The first design used the control chamber filled the air while the second design used the control chamber containing a Phase Change Material (PCM). Experiments were performed to determine the reduction of water flowrate as the membrane deforms with increase in temperature. Water flows into the inlet of the microvalve from a syringe barrel, with a hydrostatic pressure head of about 0.62 [m]. The water from the microvalve outlet was collected in a 10[ml] pipette. The results show that the water flowrate decreased as the temperature at the base of the microvalve was increased. There was a 60% and 40% reduction in the water flowrate through the microvalve design with control chamber containing air and PCM (phase change material) respectively.

Advanced Temperature-Control Chamber for Resistance Standards

Calibration services for resistance metrology have continued to advance their capabilities and establish new and improved methods for maintaining standard resistors. Despite the high quality of these methods, there still exist inherent limitations to the number of simultaneous, measurable resistors and the temperature stability of their air environment. In that context, we report progress on the design, development, and initial testing of a precise temperature-control chamber for standard resistors that can provide a constant-temperature environment with a stability of ± 6 m°C. Achieving this stability involved customizing the chamber design based on air-flow simulations. Moreover, microprocessor programming allowed the air flow to be optimized within an unsealed chamber configuration to reduce chamber temperature recovery times. Further tests were conducted to improve the stability of the control system and the efficiency of the chamber.

Dynamic modeling of a cabin pressure control system

Cabin pressure control system of an aircraft maintains cabin pressure in all flight modes as per the aircraft cabin pressurization characteristics by controlling the air flow from the cabin through the outflow valve of the cabin pressure control valve. The movement of outflow valve in turn depends on the air flow from the control chamber of cabin pressure control valve, which is controlled by the clapper and the poppet valves. These valves are actuated by absolute pressure and the differential pressure capsules, respectively depending upon the operating flight conditions. Mathematical models have been developed to simulate the air outflow rates from the cabin and the control chamber of cabin pressure control valve during steady-state and transient flight conditions. These mathematical models have then been translated into a MATLAB program to obtain plots of cabin pressures as a function of aircraft altitudes. The mathematical models are validated for standard cabin pressurization characteristics of a multirole light fighter/trainer aircraft. The model developed, thus can be used to produce a number of variants of cabin pressure control valve to suit different cabin pressurization characteristics.