Design And Research Of Adiabatic Temperature Change Measuring Device Under High Frequency And Wide Temperature Range

Magnetic refrigeration has the advantages of low refrigeration power,high efficiency,compact structure of the refrigerator,and no pollution.In today’s global depletion of resources and the gradual deterioration of the environment,magnetic refrigeration,as a new type of lowenergy,environmentally-friendly refrigeration technology,has attracted the attention of many scientific research institutions and university research groups around the world,as well as a large amount of government funding.Isothermal magnetic entropy change(ΔSM)and adiabatic temperature change(ΔTad)are important parameters to measure the magnetocaloric performance of magnetic refrigeration materials.However,most of the current research work only depends on the ΔSM,which is usually calculated indirectly from the isothermal magnetization curve using Maxwell’s equation.However,the larger the ΔTad,the more heat can be transferred from the cold end to the hot end of the magnetic refrigeration prototype,which directly determines the refrigeration capacity of the magnetic refrigeration prototype.Existing measuring devices still have disadvantages such as the inability to adjust the magnetic field strength,the narrow measuring temperature range,or the inability to frequency conversion.Therefore,it is necessary to develop a new type of device that directly measures the magnetocaloric effect(also known as measuring adiabatic temperature change).In summary,this article has designed and developed two devices that can directly measure the adiabatic temperature change of materials,and conducted structural design,performance testing and theoretical analysis of the devices,and studied the performance of magnetocaloric materials under high frequency and large magnetic fields.Therefore it aims to develop a device with high accuracy and high reliability,laying a foundation for the development of magnetic refrigeration technology.The high-frequency adiabatic temperature change measurement device developed in this work is designed based on the permanent magnetic field generated by the permanent magnet.The device uses a measurement method in which the sample cavity is fixed and the magnet system is driven by a stepper motor to rotate.The sample cavity is fixed to avoid the interference of the measurement caused by the vibration of the sample rod when the sample rod is quickly moved in and out of the magnetic field in the previous device.The frequency of the measurement can be adjusted by adjusting the rotation speed of the motor.The device was completely modeled using three-dimensional software and the magnet system was simulated using finite element software.The strength of the magnet system’s working gap was 0.72 T.The structure of the device was optimized several times,and then the device processed assembling and performance test.The device was used to measure the adiabatic temperature change of Gd under variable temperature and variable frequency,and the measurement of ΔTad at a frequency of up to 9.0 Hz was achieved.At the theoretical level,the data obtained by the mathematical theoretical model we established and the measurement data of the device also achieved a good agreement,indicating that the device can achieve reliable measurement of the adiabatic temperature change of the material under the conditions of variable temperature and variable frequency.Secondly,this article has developed a wide temperature range and large magnetic field adiabatic temperature change measurement device,which is based on the comprehensive physical property measurement system(PPMS)for research and development.With the help of the sample cavity,temperature field and magnetic field of PPMS,the measurement environment of 0～9 T and 6～380 K can be realized.The sample stage and sample rod module for placing the sample,the driving module for driving the sample rod in and out of the magnetic field,and the recording sample are designed.Temperature recording module for temperature and vacuum module to ensure the measurement environment.Next,the influence of factors such as residence time in the magnetic field,sample quality,sample rod moving speed,sample type and state on the measurement of the device was tested,and the best test parameters were explored.When the device measures the adiabatic temperature change of the sample,the measurement method of slowly rising temperature is adopted.Therefore,the error correction of the measurement result is carried out.The corrected ΔTad value is 0.11%～0.4%higher than the directly measured value.Then the measurement results are theoretically analyzed.The secondary phase change material(such as Gd)satisfies the power function relationship of ΔT～H2/3;the primary phase change material(such as Mn1.15Fe0.8P0.5Si0.5C0.05)is due to the discontinuity during phase transition does not satisfy the above relationship.This kind of material satisfies the power function relationship of ΔTad～Hn,where n can be calculated by the formula n=dln|ΔTad|/d ln H.The adiabatic temperature change data of Gd and Mn1.15Fe0.8P0.5Si0.5C0.05 were measured using this device,which satisfies the above-mentioned two power function relationships well,respectively,indicating the accuracy of the device measurement.Finally,this article analyzes the influencing factors of the adiabatic temperature change measuring device,and explores the influence of adiabatic conditions,excitation rate,and temperature acquisition rate on the performance of the device,and provides guidance for the design and development of the adiabatic temperature change measuring device in the future.