Phase-changing Plate Research Articles

Experimental study of the effect of high humidity on the phase change plate thermal storage under natural convection

Phase change materials (PCMs) play a significant role in energy storage and temperature regulating, but the traditional researches failed to accurately consider the influence of high humidity on the thermal performance of phase change-unit, leading to a fallible guide, especially in humid region. This research fills in an important research gap by designing a novel experiment to clarify the influence of high humidity environment on the melting process of phase change plate (PCP). Further, the improved momentum equation and the similarity number Grd caused by humidity ratio difference are derived in theoretical method. Finally, the heat and mass transfer criterion equations of PCP under natural convection are fitted. The results show that the melting process of PCP is significantly affected by high temperature and humidity environment in different ways. Under the experimental condition, the melting rate of PCP can be increased by more than 60%, and the proportion of latent heat transfer can reach more than 80%. The heat and mass transfer criterion equations adopt the same form but different coefficients. The results would provide valuable design guidelines for engineers regarding the estimation of the energy release process of phase change-unit used in a humid climate zone at the design stage.

Study of temperature uniformity and thermal storage performances of a shell-and-tube type phase change plate

In this paper, a phase change plate composed of shell-and-tube latent heat storage units was investigated for air conditioning application. A mathematic model of one shell-and-tube unit was built in COMSOL software, which was then validated with experimental results. Numerical and theoretical analysis results show that the improvement of temperature uniformity and better heat transfer performances are highly related, which can be improved with larger void fraction and smaller fluid channel diameter. Optimal void fraction and fluid channel diameter were proposed for the longest effective cooling time of heat transfer fluid, which is influenced by the critical temperature of outlet air. Design parameters of phase change plate were suggested to have the fluid channel diameter less than 0.5 cm and void fraction between 0.5 and 0.7. Then, optimal phase change temperature was suggested to secure relatively long effective cooling time in a large range of air inlet temperature.

Preparation and Properties of Paraffin/PMMA Shape-stabilized Phase Change Material for Building Thermal Energy Storage

The composite phase change material (PCM) consisting of phase change paraffin (PCP) and polymethyl methacrylate (PMMA) was prepared as a novel type of shape-stabilized PCM for building energy conservation through the method of bulk polymerization. The chemical structure, morphology, phase change temperature and enthalpy, and mechanical properties of the composite PCM were studied to evaluate the encapsulation effect of PMMA on PCP and determine the optimal composition proportion. FTIR and SEM results revealed that PCP was physically immobilized in the PMMA so that its leakage from the composite was prevented. Based on the thermo-physical and mechanical properties investigations, the optimal mass fraction of PCP in the composite was determined as 70%. The phase change temperature of the composite was close to that of PCP, and its latent heat was equivalent to the calculated value according to the mass fraction of PCP in the composite. For estimating the usability in practical engineering, thermal stability, reliability and temperature regulation performance of the composite were also researched by TG analysis, thermal cycling treatments and heating-cooling test. The results indicated that PCP/PMMA composite PCM behaved good thermal stability depending on the PMMA protection and its latent heat degraded little after 500 thermal cycling. Temperature regulation performance of the composite before and after thermal cycling was both noticeable due to its latent heat absorption and release in the temperature variation processes. The PCP/PMMA phase change plate was fabricated and applied as thermal insulator in miniature concrete box to estimate its temperature regulation effect under the simulated environmental condition. It can be concluded that this kind of PCP/PMMA shape-stabilized PCM with the advantages of no leakage, suitable phase change temperature and enthalpy, good thermal stability and reliability, and effective temperature regulation performance have much potential for thermal energy storage in building energy conservation.

Energy conservation analysis of regenerative radiator for low-temperature heating

Abstract In this paper, the phase change plate is made of the organic phase change material (PCM) with the phase change temperature of about 30°C. The PCM is installed in the capillary natural convection radiator with the water supply temperature of 30–60°C. A low-temperature natural convection radiator with heat storage function is formed. The mathematic model is established by enthalpy method and solved by line-by-line iteration method. The applicability and economy of the equipment in Shanghai area are calculated. Taking the time ratio and average temperature of the target domain as the limiting parameters, the operation schemes suitable for three representative days are determined, and the optimum thickness of the phase change plate is 0.05 m for use in Shanghai. The regenerative low-temperature heating radiator provides a new idea for the application of PCMs in the field of low-temperature heating. The conclusions obtained provide a basis for further research and application of the equipment.

Thermal performance of a 10-kW phase-change plate heat exchanger with metal foam filled channels

Compact-sized organic Rankine cycle (ORC) power generators call for small-scale heat exchangers to work with them. Since the heat transfer area plays a direct role in the performance of heat exchangers, micro-cellular structures such as metal foams are proposed to increase the heat duty of heat exchangers by increasing the surface area while maintaining their small size. In this experimental study, the performance of a 10-kW heat exchanger with channels filled with copper metal foam was investigated. A hot water loop was designed for heat input. The cold side of the heat exchanger works with R245fa as the working fluid. Single-phase and two-phase experiments were performed with different mass fluxes ranging from 180 to 600 kg/m2s. The effect of the pores per inch (PPI), working pressure, and different arrangements of metal foams was also investigated. Although the metal foam increases the pressure drop in the channel, it increases the recovered waste heat from the heat source and overall heat transfer coefficient of the heat exchanger by up to 2.3 times compared to a conventional heat exchanger without metal foams.

Novel Measurement Method of Small Phase with Interference Phase Contrast

A novel method to measure small phase in micro-holography is discussed. It originated from Zernike phase contrast imaging technique, which has been a successful linear phase-to-intensity mapping approach toward phase object. Instead of phase-changing plate, an interference phase contrast technique that is based on in-line holography is utilized to obtain a hologram in the proposed method. The intensity distribution of hologram presents a monotone function with respect to phase distribution of phase object. Thus, the phase can be directly detected through hologram without phase unwrapping. In the work, the contrast of hologram is analyzed toward various phase difference between object wave and reference wave. An optimal solution to measure small phase of phase object is developed, which extends the measuring range of phase. Simulation on a computer is performed to validate theoretically the proposed method.

Study on Wheat Straw/ Sodium Sulfate /Water Glass Shaped Phase Change Plate for Walling Material

Novel shaped phase change plate was made of wheat straw impregnated with Na2SO4solution and water glass as cementing agent. The plate was subsequently inserted into the concrete bricks with rectangular holes, assembled as phase change bricks. The latent heat of phase change of the plate was measured by DSC, the microstructure of the plate was observed by SEM, and the performance of the plate was also measured. In addition, the heat insulating property of the brick was investigated. The results are as follows. The wheat straws can encapsulate 1.86 times Na2SO4•10H2O in mass,and the phase change heat of the plate is 113 J/g. The microstructure shows that the straws and hardened water glass play an encapsulating action for Na2SO4•10H2O. The weight loss of the plate was 1.8% after 30 times of phase change cycles. For the concrete bricks (size: 240×240×115 mm) inserted with phase change plates, when the heated surface temperature was 80 oC for 5 h or 8 h , the cold surface temperature increased by only 1.8 oC and 4.4 oC respetively ,that is, the temperature difference between the cold with hot surface was 63.7 oC and 61.1 oC. This study reflects that if the brick is used as walling material, interior temperature does not fluctuate, even in extreme heat summer. It has dramatically saving energy and the effect of improving inhabited environment.

Complex-valued acquisition of the diffraction imaging by incoherent quasimonochromatic light without a support constraint

A scheme for complex-valued acquisition of the diffraction imaging with quasimonochromatic incoherent light is theoretically proposed. The main idea is to project the real and the imaginary parts of a Fraunhofer diffraction field on intensity distributions, respectively, with the use of a $\ensuremath{\pi}/2$ phase-changing plate. The whole procedure is iterative algorithm free and needs no a priori knowledge of an arbitrary object. A numerical experiment and a quantitative confirmation are also given. To our knowledge, it was the first physical proposal for the complex-valued acquisition of a diffraction imaging by two-dimensional coherent patterns with thermal illumination.

Study on Inorganic Phase Change Materials Encapsulated by Rice Straws

Na2SO4 solution was impregnated into rice straws, then the straws impregnated with Na2SO4 was cemented using water glass and molded to shaped phase change plate. The plate was subsequently inserted into the concrete bricks with rectangular holes, assembled as phase change bricks. The latent heat of phase change of the plate was measured by DSC, the microstructure of the plate was observed by SEM, and the heat insulating property of the brick was investigated. The results are as follows. The rice straws can encapsulate 2 times Na2SO4•10H2O in mass and the phase change heat of the plate is 121 J/g. The microstructure shows that the rice straws and hardened water glass play an encapsulating action for the package of Na2SO4•10H2O. The weight loss of the plate was 0.9% after 30 times of phase change cycles. For the concrete bricks (size: 240×240×115 mm) inserted with phase change plates, when the heated surface temperature was 80 oC and the initial cold surface temperature was 14.5 oC, the needed time that the cold surface temperature rose to 25 oC was 17 h, which was 6.5 h and 9 h longer than the concrete bricks inserted with rice straw plates and the original concrete bricks, respectively. When the heating was maintained for 5 h and 8 h, the cold surface temperature increased by only 1.4 oC and 3.9 oC and the temperature difference between the cold surface and hot surface was 64.1 oC and 61.6 oC. This study provides a new way for the encapsulation of phase change materials and its application in construction.

Phase-only optical encryption based on the zeroth-order phase-contrast technique

A phase-only encryption/decryption scheme with the readout based on the zeroth-order phase-contrast technique ZOPCT, without the use of a phase-changing plate on the Fourier plane of an optical system based on the 4f optical correlator, is proposed. The encryption of a gray-level image is achieved by multiplying the phase distribution ob- tained directly from the gray-level image by a random phase distribution. The robustness of the encoding is assured by the nonlinearity intrinsic to the proposed phase-contrast method and the random phase distribution used in the encryption process. The experimental system has been implemented with liquid-crystal spatial modulators to generate phase- encrypted masks and a decrypting key. The advantage of this method is the easy scheme to recover the gray-level information from the de- crypted phase-only mask applying the ZOPCT. An analysis of this de- cryption method was performed against brute force attacks. © 2009 Society