| The magnetic refrigerator (MR) has drawn worldwide attention as a promising technology to replace the conventional vapor compression cooling cycle. The MR is based on magnetocaloric effect (MCE), which is the temperature change as a function of the applied magnetic field. The maximum adiabatic temperature change induced by MCE for most materials is limited to 2-3 K/Tesla. Thus, to generate more than 20 K temperature span in a single device with a practical magnetic field, i.e.1～2 Tesla, the active magnetic regenerator (AMR) is required.As fluid flows through an AMR bed in which a temperature gradient is established, each section of the regenerator undergoes its own sub-cycle at the local temperature. The series of all these sub-cycles account for the large temperature span by the use of AMRs. However, the sub-cycles in which the temperature of the hot end and the cold end changes constantly, influence each other when they are series-coupled, so it is difficult to realize the calculation with an analytical method. Recently, many works for modeling and calculating the cooling power for the MR near room temperature have been done, but almost all the studies were carried out with numerical method which did not reveal the relation between the performance and parameters of the AMR device. Thus an analytic study for the cooling power of AMR device is necessary to instruct the design of MRs.In this paper, the author made an analytical calculation on the AMR room temperature MRs by building a proper physical model for AMRs. From the result of the numerical study, there is a platform in the temperature field of the AMR bed. For the research of the cooling power of the AMR with temperature platform, the author did the research on the linear temperature distribution which connects the cold end and the hot end firstly, and then calculated the cooling power of the condition in which the platform exists. The contents and the results of the two parts are as follows:1. Assuming the temperature field within AMR is a linear distribution, and the temperature of the liquid flowing from the cold end and the hot end is also a linear distribution. By calculating the cooling power of the condition it is found that the cooling power of MR is proportional to the square of adiabatic temperature change induced by the MCE, which means that the magnetic field plays a very important role to improve the cooling power of an device based on the AMR type, although the MCE is not exactly proportional to magnetic field strength. Secondly, the pore ratio and total heat capacity of magnetic refrigerant affect the cooling power. At last, the cooling power is in inverse proportion to temperature span across the whole device.2. Assuming the temperature field is formed by the platform with a certain length and the linear region, using the method of the linear temperature field to calculate the cooling power, it is found that the cooling power is in inverse proportion to temperature span between the cold end and hot end, and is related to the adiabatic temperature change induced by the MCE and the temperature span of the working temperature range of the material, and the general formula of the cooling power is also found, in which the temperature field is with a platform or not.3. whether there is a platform or not, the cooling power is always the production of the flux of the liquid and the adiabatic temperature change induced by the MCE, so increasing the flux will lead to a larger cooling power, but the flux is in inverse proportion to temperature span, which means there is a restrict factor to increase the cooling power. |
PDF Full Text Request