The friction clutch is considered a very important element of machines, as it plays a major role in transferring power from the driving part to the driven part. A common application of the friction clutch is in vehicles to connect between the gearbox and the engine. Fast wear occurs as a result of frictional heating that is generated when the clutch is starting to engage. This wear, in addition to the high thermal stresses, will lead to premature failure in the contacting surfaces. The present review highlights the most important studies of the thermal and thermoelastic problems of friction clutches during the last 10 years to show the challenges that were overcome and also the other challenges that needed to find solutions. The present paper will discuss in detail the influence of the frictional heat generated between contact surfaces during slipping and the main factors affecting the thermal behavior of dry friction clutches, such as sliding speed, friction materials, applied pressure, and so on. Furthermore, significant conclusions and remarks based on the available solutions to the thermal problem of the clutch are presented.
An experimental and theoretical study for heat transfer through thermoelectric cooling system in this paper was presented. An experimental work was conducted to evaluate the performance of a thermoelectric module fitted to a sun flower heat sink with a similar sized heat source. The experimental investigation was done to evaluate the effect of TE input voltage, flow rates of cooling air and heat source (heating element) power input on the performance of a thermoelectric cooling system. Four low heating load (1.7, 2.4, 3.6 and 5 W) were used and hot side was fitted to a sunflower heat sink with forced convection. Experimental results show that the increasing of cooling air flow rates improves system performance, while increasing in applied TE voltage leads to deterioration it. The COPmax obtained is about 4.7 at 2V TE voltages and 5W heating load, and then decreased sharply as voltage further increased and reaches 0.13 at 12V. The results of the current study show that all Thermo-electric Cooling system recorded temperatures increase with increasing in heating load at a constant TE voltage and air flow rate. In addition to that the Tc
decreases and Th
increases with the increment of input voltage and that can lead to increase of the air temperature passing over heat sink. TE performance is highly affected by air flow rate. The theoretical result validated experimentally and shows an acceptable agreement between them.
Several parameters affect the properties of Portland cement and one of these parameters is the cooling rate of the clinker. If the effectiveness of the cooling method of the clinker increases, a good enhancement in the properties of Portland cement will be found. Depending on the new cooling method suggestion by Nasr et. al. [20], the counter pattern of air clinker flow was studied using (FLUENT 6.3.26). The dimensions of the cooling room in grate cooler, the constant mass flow rate of both clinker and air, different height ratios, and different clinker porosity were considered in this numerical work. The results show that the heat transfers in the first half of the cooling room (0 < X < 0.9 m) is larger than that in the second half (0.9 < X < 1.8 m), and this leads to an increase in the temperature of outlet air so can benefits from it in the heating of furnace. When the clinker and air are flowing in the counter direction, the cooling method is more beneficial when compared with that of parallel flow because the exiting clinker has a great rate of cooler and the air exits from the grate cooler is loaded with large thermal energy. Finally, it can design the best length of gate according to the required clinker temperature at the outlet side, and this results to reduce the cost of the cooling process according to the temperature distribution results at (0 < X > 1.8m) for different porosity and H.R values.
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