To optimize the performance of the transcritical CO2 two-stage compression refrigeration system, the energy analysis and the exergy analysis are conducted. It is found that higher COP, lower compression power, and less exergy destruction can be achieved when the auxiliary gas cooler is applied. Moreover, the discharge temperature of the compound compressor (HPS) can be reduced by decreasing the temperature at the outlet of the auxiliary gas cooler (Tagc,out). When the Tagc,out is reduced from 30 to 12 ℃, the discharge temperature of the compound compressor (HPS) can be decreased by 13.83 ℃. Furthermore, the COP and the exergy efficiency can be raised by enhancing the intermediate pressure. Based on these results, the optimizations of system design and system operation are put forward. The application of the auxiliary gas cooler can improve the performance of the transcritical CO2 two-stage compression refrigeration system. Operators can decrease the discharge temperature of the compound compressor (HPS) by reducing the Tagc,out, and increase the COP and the exergy efficiency by enhancing the intermediate pressure.
The single-tube heat transfer experiment rig is composed of various equipment and devices connected through pipelines. This paper adopts Siemens PLC as the main controller and cooperates with WEINVIEW HMI MT6000 series HMI to design the experimental measurement and control platform of a single-tube heat transfer experiment rig. In the single-tube heat transfer experiment measurement and control platform, the PLC communicates with the HMI through an RS-485 cable, and the HMI can display the experimental data changes in real-time and has a separate control interface. The-single tube heat transfer experiment measurement and control platform is safe and reliable, with functions such as real-time monitoring and acquisition, real-time fault alarm, parameter change, and remote control, which simplifies the steps of data acquisition, reduces the difficulty of equipment control, and realizes the automatic acquisition and control.
In this paper, the effect of different forms of electric heating wire forms
on the anti-icing performance of the refrigerated container was studied
based on numerical simulation. The heat transfer and the thermal
conductivity of the refrigerated container door wall, and the uniformity of
airflow distribution in the refrigerated container are analyzed. The heating
wire form 2 has the best anti-icing performance and meets the anti-icing
requirement When the thermal conductivity is from 0.005 W/(m?K) to 0.01
W/(m?K). The electric heating wires nearest to the inner wall surface is the
optimal anti-icing solution. The spare electric heating wires placement can
be determined according to the thickness of the refrigerated container door.
The specific layout of electric heating wires in the future can be further
optimized in combination with carbon emissions.
By means of the porous media theory, computational fluid dynamic models of heat transfer and fluid flow at different pack stacking modes in a refrigerated room are elaborated. A practical case is simulated, where brick-shaped packs with aquatic products, partially frozen to 261.15 K, are loaded in the room to complete the freezing process down to 255.15 К, followed by long-term frozen food storage at the latter standard temperature. The best freezing completion effect (defined as the maximum reduction of the highest product temperature during a certain residence time) is achieved by using the pyramidal stacking mode whose upper package is in the center of four lower packages (UPF-PSM) with two piles. The highest temperature of aquatic products at a two-pile-UPF-PSM can be reduced from 261.15 to 255.60 K for a residence time of 24 h. Within the same time, the product temperature becomes most uniform at a UPF-PSM. Simultaneously, the best uniformity of flow distribution and highest efficiency of air circulation in a refrigerated room are obtained by using the neat stacking mode (NSM) during the long-term frozen storage. Furthermore, a comprehensive stacking mode is proposed (using UPF-PSM for freezing completion and NSM for long-term frozen storage), which enhances both the freezing completion effect and the efficiency of air circulation in the studied refrigerated room.
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