Study On Thermophysical Properties Of Novel Working Pairs For A Solar-driven Absorption Refrigeration Cycle And Their Applications

In summer,the solar-driven absorption refrigeration is an optimal method to utilize solar energy.Currently,the solar-driven absorption refrigeration cycle uses LiBr/H₂O as its working pair.A single-stage solar-driven absorption refrigeration cycle based on LiBr/H₂O needs a driving heat source temperature,that is,the solar collecting temperature as high as 88.0?,which is too high for the commonly used flat plate collectors or vacuum glass tube collectors.So far,there are two technical approachs to encounter this problem,one is to apply high temperature solar collectors in the solar collecting sub-system,and another one is to adopt a two-stage absorption refrigeration cycle.As the costs of high temperature solar collectors such as the heat pipe vacuum glass tube collectors and CPC collectors,and the complexity and low COP of the two-stage absorption refrigeration system,the solar-driven absorption refrigeration technology has not yet achieved large-scale engineering application so far.On another hand,some industrial low-grade waste heat cannot be effectively used as the driving heat source of absorption refrigeration cycle,because of the required generation temperature for the single-stage absorption refrigeration cycle based on LiBr/H₂O being too high.As a typical example,in the iron and steel industry,the heat of the blast furnace melting slag is carried away by the blast furnace slag flushing water.Since the temperature of the blast furnace slag flushing water is usually lower than 85.0 ?,the waste heat is difficult to be used for absorption refrigeration.On the other hand,we know that the dehumidification of blast furnace air can bring many benefits such as reducing the coke ratio,reducing the power consumption of the air blower,and increasing the output of the blast furnace.That is to say,if the required temperature of the driving heat source is reduced,the waste heat of the slag can be effectively utilized for the absorption refrigeration,and by combining the refrigeration with the dehumidification of the blast furnace air,the energy saving and efficiency improvement can be achieved.An innovative technical approach has been proposed to solve the problem that a single-stage absorption refrigeration cycle using LiBr/H₂O is hardly driven by the solar energy colected with flat plate collectors or vacuum glass tube collectors,due to the required solar collecting temperature being too high.That is,from the point of changing the absorption characteristics of working pairs,this approach is to explore some new working pairs,the refrigeration absorption characteristics of which are superior to LiBr/H₂O.Good refrigeration absorption characteristics refer to,in the diagram of the saturated vapor pressure against the absorption temperature for absorption solutions,at the same saturated vapor pressure of 0.872 kPa?corresponding to the evaporator and absorber pressure of a conventional absorption refrigeration cycle?,the new working pair absorption solution has the same or higher absorption temperature as the LiBr/H₂O absorption solution?corresponding to the absorber temperature of a conventional absorption refrigeration cycle?,and at the same saturated vapor pressure of 6.290 kPa?corresponding to the conventional absorption refrigeration cycle condenser and generator pressure?,the new working pair absorption solution has a lower absorption temperature than the LiBr/H₂O absorption solution?corresponding to the generator temperature of a conventional absorption refrigeration cycle?.In this thesis,through experimental research it is found that CaCl₂/H₂O has a good refrigeration absorption characteristic,and based on the refrigeration absorption characteristic of CaCl₂/H₂O,two new working pairs with the refrigeration absorption characteristics significantly better than that of LiBr/H₂O,and using cheap CaCl₂ as their main component have been selected.They are CaCl₂-LiNO₃-KNO₃?15.5:5:1?/H₂O and CaCl₂-LiNO₃-LiBr?8.72:1:1?/H₂0.The crystallization temperature,saturated vapor pressure,density,viscosity,specific heat capacity,and specific enthalpy of two novel working pairs were systematically measured.The measured values of these thermophysical properties were fitted with Antoine equation and the least-squares method,and the experimental equations between the thermophysical properties and the absorption solution's mass fraction and temperature were obtained and compared with LiBr/H₂O.Results showed that under the same refrigeration conditions,the required solar collecting temperature of the single-stage absorption refrigeration cycle based on CaC12-LiNO₃-KNO₃?15.5:5:1?/H₂0 and CaCl₂-LiNO₃-LiBr?8.72:1:1?/H₂O were 7.1? and 7.7? lower than that based on LiBr/H₂O,respectively.Thus.the inexpensive flat plate collectors or vacuum glass tube collectors are able to be used to improve the economy of the solar-driven absorption refrigeration system.In order to investigate the corrosion behaviors of structural materials and heat exchanger materials of absorption refrigeration system in the absorption solutions of CaCl₂-LiNO₃-KNO₃?15.5:5:1?/H₂O and CaCl₂-LiNO₃-LiBr?8.72:l:1?/H₂O.the corrosion rates of Q235 carbon steel.316L stainless steel and T6 copper were measured by a weight loss method,and the effects of temperature,mass fraction,pH,and corrosion inhibitor on the corrosion rates were studied and compared with that in the absorption solution of LiBr/H₂O with the same absorption ability.Results showed that over a temperature range of 70.0 to 100.0?,the corrosion rate of each metal material reaches its lowest value when the pH is 9.7 and no corrosion inhibitor is added.Except that the corrosion rate of Q235 carbon steel in CaCl₂-LiNO₃-LiBr?8.72:1:1?/H₂O absorption solution was too large to be used,the corrosion rates of each metal material in the two novel working pairs absorption solution could meet the practical requirements of engineering applications.The performances of the single-stage solar-driven absorption refrigeration cycle based on CaCl₂-LiNO₃-KNO₃?15.5:5:1?/H₂0 and CaCl₂-LiNO₃-LiBr?8.72:1:1?/H₂O were analyzed and compared with LiBr/H₂O.Results showed that under the same refrigeration conditions,the refrigeration COPs of the single-stage solar-driven absorption refrigeration cycle based on CaCl₂-LiNO₃-KNO₃?15.5:5:1?/H₂0 and CaCl₂-LiNO₃-LiBr?8.72:1:1?/H₂0 were 0.04 higher than that based on LiBr/H₂O,indicating that through applying the two novel working pairs in the solar-driven absorption refrigeration system,not only the requirement for the solar collecting temperature can be reduce,but also the energy utilization efficiency can be effectively improved.