Transient Heat Transfer Of Solar Power
Author: Source: Datetime: 2016-09-21 15:04:35
Under transient conditions, with respect to the object of determining the quality, the first law of thermodynamics requires its heating rate must be equal to its internal energy zo (reactive power exchange between the object and the surrounding environment is assumed) acceleration rate. If the temperature of the object is uniform, can be obtained by the first law of thermodynamics is time varying heat input rate of children, depends on the solution of the differential equation «(in the form of objects and the initial temperature of zero. if only to consider the following simplified monk case, that is, objects the initial temperature Tw and the heat input rate is a constant, the object at any subsequent time, attention, with the constant input of heat, the temperature of the object will continue to rise linearly in many cases _ heat input rate in part by a child temperature of the object is determined. for example, in a thermal storage tank, the heat losses and gains, respectively, by the heating load, through the tank wall to the surrounding environment and the heat loss from the collector for heating hot water storage tank three part.
In all of the above discussion, assume that at any time an object is isothermal, but in many systems, including solar components, including, the actual situation is not the case. At any given moment, within the component temperatures throughout It is different. for example, the temperature of the hot water storage tank having a tendency to stratification, i.e., near the top of the water near the bottom of the water temperature is relatively high. Another example is a passive thermal storage wall, the exterior surface of the high temperature during the day on the interior wall surface, while at night the opposite. in order to obtain a temperature distribution inside the object, the object can usually be divided into small isothermal Bands. a correction method can be used to calculate the expected band for each temperature versus time.
Most collectors are liquid preclude the use of combination-type absorber tube plate and tubes in front back or the whole plate welded into a plate, sometimes use bent corrugated metal plate as a heat absorber air collector is the use of the channel between the absorber and the cover sheet or absorber behind the passage of the air and body heat in order to increase thermal contact with a heat transfer coefficient, but also by an agitator, fins and corrugated absorber as well as the porous absorber, etc. As to build a house, so that the two glass can also be used transparent plastic layers by the collector uses and i live on location at low latitudes, usually only one ; DA in latitude and longitude at Gao, you may need to use two or even three, to prevent excessive heat loss, the outermost layer must be able to withstand hail, snow, rain, and even the occasional stone impact, and within layer may be more vulnerable, but all of the cap must have a high transmittance of solar radiation, and thermal (infrared) radiation is a low transmittance.
Collector transmittance and absorption ratio of the product of people hitting the collector on the outermost layer of the cover solar radiation is absorbed by the body than the transmittance absorbed by the percentage referred to collectors and absorption ratio of the product ( Acronym product through absorption ratio) which is one of the main indicators characterizing the performance of the collector, in addition to capping and absorber coating material or relevant, it also depends on the direction of incidence and capping the number of direct radiation.
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