MIL-101(Cr) and water were applied to adsorption refrigeration technology. MIL-101(Cr) was prepared by hydrothermal synthesis method and characterized by X-ray diffraction patterns (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption–desorption measurement at 77 K, thermal gravimetric analysis (TGA) and scanning electron microscope (SEM). The adsorption isotherms of water vapor on MIL-101(Cr) were investigated by using a gravimetric water sorption analyzer. This study established the basic adsorption cycle mathematical model and used MATLAB/Simulink for the simulation. The control variable method was used to simulate the effect on the cooling capacity and coefficient of performance (COP) when the desorption temperature changed. When the adsorption temperature was 35 °C, the evaporation temperatures were 15 °C and 20 °C, and the amount of water vapor equilibrium adsorption on MIL-101 (Cr), Cooling power per unit adsorbent mass (SCP), and COP were measured by using the adsorption performance test rig on the basis of a new type of powder adsorbent filling method.

An MIL-101(Cr) powder material was successfully prepared using the hydrothermal synthesis method, and then the original MIL-101(Cr) was combined with different mass fractions of CaCl2 using the immersion method to obtain a MIL-101(Cr)/CaCl2 composite material. The physical properties of the adsorbent were determined by X-ray powder diffraction (XRD), an N2 adsorption desorption isotherm test, and thermogravimetric analysis (TG). The water vapor adsorption performance of the metal-organic frameworks MOFs was tested with a gravimetric water vapor adsorption instrument to analyze its water vapor adsorption mechanism. Based on the SIMULINK platform in the MATLAB software, a simulation model of the coefficient of performance (COP) and cooling capacity of the adsorption refrigeration system was established, and the variation trends of the COP and cooling capacity of the adsorption refrigeration system under different evaporation/condensation/adsorption/desorption temperatures was theoretically studied. MIL101-(Cr)/CaCl2-20% was selected as the adsorption material in the adsorption refrigeration system through the physical characterization of composite materials with different CaCl2 concentrations by means of adsorption water vapor test experiments. A closed adsorption system performance test device was built based on the liquid level method. The cooling power per unit and adsorbent mass (COP and SCP) of the system were tested at different evaporation temperatures (288 K/293 K/298 K); the adsorption temperature was 298 K, the condensation temperature was 308 K, and the desorption temperature was 353 K. The experimental results showed that COP and SCP increased with the increase in the evaporation temperature. When the evaporation temperature was 298 K, the level of COP was 0.172, and the level of SCP was 136.9 W/kg. The COP and SCP of the system were tested at different adsorption temperatures (293 K/298 K/303 K); the evaporation temperature was 288 K, the condensation temperature was 308 K, and the desorption temperature was 353 K. The experimental results showed that the levels of COP and SCP decreased with the increase in the adsorption temperature. When the adsorption temperature was 293 K, the level of COP was 0.18, and the level of SCP was 142.4 W/kg.

Summary At present, all types of large–medium‐sized supermarkets with aquatic products adopt ice preservation to ensure freshness. The traditional method of ice preservation needs to make a large amount of thick ice and thus wastes manpower and freshwater. A new ice preservation system with cold storage (IP&CS) is designed, and its performance is tested. The use of a cold storage tank to replace the thick ice laid achieves a repeated cold storage and discharge. This experiment uses NaCl solution as the cold storage phase change material (PCM). The phase change temperature of the cold storage PCM and the optimum temperature of the secondary refrigerant during the cold storage process are determined. Results show that the center temperature of aquatic products, water loss rate, color of aquatic products, power consumption, and electricity cost of the IP&CS system are better than those of the traditional ice preservation system.

No abstract

Nonlinear dynamic response with stability analysis of a sandwich structure with flexible core are investigated by integration of variational asymptotic method (VAM) and the first-order shear deformation theory. A simply supported sandwich structure is subjected to an harmonic transverse excitation in thermal environments. Generalized 2 D Reissner-Mindlin type stiffness matrices including an equivalent transverse shear matrix are obtained based on through-the-thickness analysis using VAM without invoking any ad hoc kinematic assumptions. The governing equation is derived using Hamilton’s principle taking into account von K[Formula: see text]rm[Formula: see text]n geometric nonlinearity. Galerkin’s method is employed to develop a nonlinear differential equation of the problem with quadratic and cubic nonlinearities, which are associated with the coupling of the in-plane stretching and transverse deflection due to thermal moments. Periodic solutions are determined using the incremental harmonic balance (IHB) method and incremental arc-length technique. The stability is evaluated by Routh-Hurwitz theory. The effects of the temperature variation, geometric parameters and material properties on the resonance as well as amplitude of steady state vibration are investigated through a detail parametric study.

Five commonly used thawing methods include water immersion (WT), lotic water (LT), ambient temperature (AT), refrigerator (RT), and microwave (MT) thawing. WT, LT, and AT cannot maintain a specified constant temperature during thawing, whereas MT consumes substantial energy. On the basis of the shortcomings of the above methods, a constant temperature water immersion thawing system using fixed-frequency refrigerator compressor casing heat storage (CWT-CCTS) is designed. The CWT-CCTS recycles the waste heat of the compressor casing and uses the heat to thaw frozen food in constant temperature water. The new system not only provides a new heat source for thawing but also reduces the overall energy consumption and noise of the system during operation. Under a stable full-load operating condition of the refrigerator, CWT-CCTS can reduce the compressor casing and discharge temperatures by 3.8°C and 2.5°C, respectively. The water loss rate of CWT-CCTS is only 15.9% of MT, demonstrating a decrease of 84.1%. In terms of thawing, the maximum power consumption saved by the device is 516.79 kW·h per year in comparison with MT, and the cost of the device can be recovered after 178 days of use KEYWORDS compressor casing, constant temperature water, heat storage, phase change material, water immersion thawing | INTRODUCTIONOwing to the improvement of living standard and the fast pace of life, customers not only require a variety of food types but also gradually start to pay attention to the preservation quality, flavor, and nutritional ingredients of food. Food-freezing technology has rapidly developed in recent years to meet the requirements of people. Frozen food must be thawed before processing. At present, the most common methods of thawing are MT, WT, LT, RT, and AT. The thawing speeds of WT, LT, RT, and AT are low. Although the thawing speed of MT is high, this approach consumes an enormous amount of power. 1 A common shortcoming of WT, LT, and AT is that they cannot accurately control the thawing temperature, thereby leading to the decline of food quality. Therefore, many researchers have conducted in-depth research on various thawing methods.Li 2 investigated the effect of various freezing and thawing combinations on the quality preservation of Pleurotus eryngii (king oyster mushroom). MT showed the most rapid thawing time, followed by LT and AT for

The commonly used normal-temperature air-thawing method is time-consuming and cannot achieve constant temperature thawing. Furthermore, microwave thawing consumes a considerable amount of electricity. These two common thawing methods cannot guarantee food quality. Thus, a new type of constant air-temperature thawing system (CATT) that uses compressor casing thermal storage is designed and tested in this study. Results show that the CATT has faster speed than the air-thawing method.Furthermore, although the thawing speed of CATT is slower than that of microwave thawing, food with 274.25 g thawing quality can save 0.2 kW h of electricity per iteration. The weight loss of CATT at 34 C was 64.6% of that of microwave thawing. The weight loss of CATT at 46 C was 40.8% of that of microwave thawing. When thawing at a constant temperature of 46 C, the thawing time required for the central temperature of chicken meat to increase from −8 to 10 C is 2 hr. The thermal storage material can decrease compressor noise effectively by 17.65%. Practical ApplicationsThe thawing of frozen food is a common problem. Hence, this paper proposes a new thawing method based on the residual heat of the refrigerator compressor casing. This method does not need to consume other energy and instead uses directly waste heat generated by the compressor casing to thaw frozen food. Frozen food can be thawed naturally at a constant temperature by controlling the temperature of the thawing chamber, and consequently, the disadvantages of long-term air thawing and poor quality of microwave thawing are improved. The application of this method can increase the thawing function of the refrigerator and has considerable application prospects.

No abstract