طراحي عملگر حرارتي از جنس آلياژ حافظه دار براي كنترل دماي جاذب هاي انرژي خورشيدي

چكيده انگليسي :

Design of an SMA thermal actuator for temperature control in solar collectors Nazita Taghavi n taghavi@me iut ac ir April 14 2010 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Dr Mahmood KadKhodaei kadkhodaei@cc iut ac ir Abstract The dependence of industrial societies to energy sources leads the renewable energies such as sun energy to be noticeable Nowadays various solar systems are designed and used But the thermal and refrigerating solar systems usually have some problems with temperature control With all solar water heating systems there is the potential for the solar collectors to reach very high temperatures particularly during power failures or periods when there is minimal hot water consumption Under these conditions the solar collectors may reach stagnation temperatures exceeding 170 If exposed to these high temperatures the heat transfer fluid may rapidly degrade or even boil and excessive pressures may be produced in the solar collector heat transfer loop The problem is particularly acute in climates where there is a potential for freezing temperatures during part of the year Solar systems designed for these climates typically use an anti freeze solution to transport heat from the solar collectors to a load The most common anti freeze fluids used in solar systems are propylene glycol water mixtures that typically subject to deterioration at elevated temperatures greater than approximately 120 Under these conditions the heat transfer fluid may become corrosive resulting in accelerated fouling and corrosion of the solar system components Having recognized the harmful effects of stagnation a mechanism for limiting the temperature of solar collectors was developed Also heat transfer and thermal analysis was conducted to obtain a suitable design It was concluded that the most practical and reliable means of increasing the heat loss characteristics of a solar collector during stagnation was to incorporate cooling channel under the absorber plate This channel would be used to introduce ambient air between the absorber plate and the back insulation thereby allowing the natural convection cooling of the collector absorber plate Based on heat transfer analysis in this thesis a cooling channel of 17 mm depth was found to be adequate if the interior of the channel was coated with a high emissivity coating For the proposed design a thermal actuator at the upper periphery of the collector opens under stagnation conditions allowing hot air to exhaust from the top of the collector and cool ambient air to enter at the bottom of the collector This air is heated in the venting channel behind the collector absorber thereby removing excess heat from the back of the absorber plate The movement of the air is driven passively by a temperature induced density gradient that exists in the air in the venting channel At collector temperature below a prescribed control point the thermal actuator closes restricting the circulation of air through the solar collector Under these conditions the air in the venting channel is thermally stratified and remains stationary acting as an insulating layer to heat loss from the back of the solar collector An important feature of the implemented design is that it operates passively requiring no user intervention or external power source As well the operation of the solar collector is not affected during normal conditions For designing thermal actuator shape memory alloys were investigated These alloys are a class of smart materials with special characteristics which allow them to be used as thermal actuators Shape memory alloy actuators can be divided in two categories First category is one way shape memory effect OWSME actuators usually produce small force and stroke Other category is two way shape memory effect TWSME actuators which can be produced large force and stroke In the solar collector temperature control appar

تقوي، نازيتا

طراحي عملگر حرارتي از جنس آلياژ حافظه دار براي كنترل دماي جاذب هاي انرژي خورشيدي

كلكتور خورشيدي , اثرات يك سويه حافظه داري , اثرات دو سويه حافظه داري , معادلات ساختاري