Miquel Nogués

Industrial heat recovery by absorption/compression heat pump using TFE–H2O–TEGDME working mixture

Abstract The thermodynamic performance of a single-stage absorption/compression heat pump using the ternary working fluid Trifluoroethanol–Water–Tetraethylenglycol dimethylether (TFE–H2O–TEGDME) for upgrading waste heat has been studied. A simulation program has been developed using a mathematical model based on mass and energy balances in all components of the cycle and thermodynamic equilibrium considerations. In order to establish the optimum operating conditions of the cycle for various thermal conditions, sensitivity studies of the coefficient of performance (COP), the flow rate of the weak solution and the compressor volumetric displacement, both per unit of upgraded energy, were carried out versus of water content in the vapour phase. The results obtained show that the operation of the cycle with this ternary system is still more advantageous than the TFE–TEGDME binary working pair. So, it is possible to upgrade thermal waste heat from 80 to 120°C, with a COP of about 6.4, with a compression pressure ratio of 4 at a low pressure of 100 kPa, the water mole fraction in the vapour being 42%. At these operating conditions, the necessary weak solution mass flow rate is about three times lower than the corresponding binary one. The performance comparison of such a cycle with other absorption cycles like the heat transformer or the single-effect heat pump, both of them using the ternary system, shows its interest and potential.

Comparison of Stratification in a Water Tank and a PCM-Water Tank

Most of the storage systems available on the market use water as storage medium. Enhancing the storage performance is necessary to increase the performance of most systems. The stratification phenomenon is employed to improve the efficiency of storage tanks. Heat at an intermediate temperature, not high enough to heat up the top layer, can still be used to heat the lower, colder layers. There are a lot of parameters to study the stratification in a water tank such as the Mix Number and the Richardson Number among others. The idea studied here was to use these stratification parameters to compare two tanks with the same dimensions during charging and discharging processes. One of them is a traditional water tank and the other is a PCM-water (a water tank with a Phase Change Material). A PCM is good because it has high energy density if there is a small temperature change, since then the latent heat is much larger than the sensible heat. On the other hand, the temperature change in the top layer of a hot water store with stratification is usually small as it is held as close as possible at or above the temperature for usage. In the system studied the Phase Change Material is placed at the top of the tank, therefore the advantages of the stratification still remain. The aim of this work is to demonstrate that the use of PCM in the upper part of a water tank holds or improves the benefit of the stratification phenomenon.Copyright

Influence of the transmission configuration of a multiple axle vehicle on the obstacle surmounting capacity

Conventional wheeled vehicles have serious mobility limitations in rough terrain while walking vehicles have inherent drawbacks such as a high number of DOF and actuators, control complexity and low-energy efficiency. Vehicles that passively adapt the position of multiple wheels to maintain contact with the ground can be a good compromise between both conventional wheeled and walking vehicles. One way to increase the number of wheels in contact with the ground is using bogies. However, the kinematics of a multiple axle vehicle moving on irregular terrain is quite complex since every wheel can require different angular speed to avoid slippage. The present work aims to quantify the obstacle surmounting capacity of a four axle, double-bogie vehicle depending on the transmission configuration, since it can provoke the slippage of some of its wheels. Some results are presented corresponding to the vehicle moving on a straight upward slope of different angles and facing variable obstacles in any of its axles. It can be observed that as more restricted the transmission is, more wheels are forced to slip and less traction the vehicle has, and, as a consequence, less obstacle surmounting capacity.

Surgical dynamometer to simultaneously measure the tension forces and the distance between wound edges during the closure of a laparotomy

The closure of the abdominal wall after making a laparotomy is a major challenge for surgeons, since a significant percentage of closures fail and incisional hernias rise. The suture has to withstand the forces required to close the incision, while not hindering the adequate wound healing progression. Currently, there is no surgical measuring device that could be used to determine the required closing forces, which can be very different depending on the patient. This paper presents a dynamometer to measure the tension forces to be applied while closing a surgical incision, and it simultaneously measures the distance between wound edges. It is a compass-like instrument. A mechanism between the two legs incorporates a load cell, whose signal is read by an electronic device that computes the values of the tension forces between wound edges. An angular position sensor at the pin joint between legs provides the distance between both sides of the incision. Measuring capabilities of the instrument prototype were verified at the laboratory. Thereafter, its functionality was demonstrated in experimental surgery tests. Therefore, the instrument could be very useful in clinical applications, assisting personalized surgical techniques.

Efficiency analysis of a multiple axle vehicle with hydrostatic transmission overcoming obstacles

ABSTRACT Transmission configurations in off-road vehicles with multiple driven axles can be a determining factor in the obstacle surmounting capacity and also in the vehicle efficiency. An off-road articulated vehicle with four driven axles, four bogies and two modules has been considered for the global hydrostatic transmission efficiency analysis and for the vehicle functional efficiency analysis. The power flow through the transmission system has been quantified from the combustion engine shaft to each axle of the wheels. It has been done for different the operating conditions and taking into account the wheel–terrain interaction and the transmission configuration, that could lead to a forced slippage of some of the wheels. Results show the influence of the different wheels’ requirements, the transmission configuration limitations and the considered control strategy on the global transmission and vehicle functional efficiencies.