International Journal of Refrigeration-revue Internationale Du Froid最新文献

Indirect evaporative cooling (IEC) technology is an energy-efficient approach for regulating the indoor thermal environment of buildings. The conventional tubular indirect evaporative cooler (TIEC) may have a relatively low cooling efficiency due to poor wettability issues. The application of moisture-conducting fibers provides a feasible way to solve the above problem. However, the integration of moisture-conducting fibers with TIEC is still in the exploratory stage. This study proposed a novel moisture-conducting fiber-assisted TIEC and conducted a multi-objective optimization. An experimental facility and theoretical model of the proposed moisture-conducting fiber-assisted TIEC were developed. Based on the numerical model validated by experiments and response surface methodology (RSM), the regression models for performance prediction of the cooler were established. Eight input parameters including inlet air parameters, operating parameters and geometric parameters were selected, and four performance evaluation indicators were chosen as output responses. The parameter sensitivity of the regression models was analyzed. The multi-objective optimization was performed by considering the influence of different relative weights assigned to the output responses. Furthermore, the performance of the optimized cooler applied in different climate zones was predicted. The results showed that the product air temperature drop could achieve 8.8–11.3 °C after cooling by the cooler. The established regression models can predict the performance of the moisture-conducting fiber-assisted TIEC conveniently and effectively, which is expected to guide the design and optimization of engineering practices.

Wettability may have significant influence on jet impingement boiling on metal foam, but the effect mechanism of metal foam wettability remains unclear. In this study, the boiling heat transfer characteristics of distributed jet array impingement on hydrophobic and hydrophilic metal foam covers were experimentally researched and compared with those on uncoated metal foam covers to analyze the influence of wettability. The experimental conditions cover contact angles of 14.0–158.7°, pore densities of 20–40 PPI, porosities of 92 %-97 %, thicknesses of 3.0–5.0 mm, and jet velocities of 0.5–4.0 m·s⁻¹. The results show that, the obtained maximum heat flux and maximum heat transfer coefficient are up to 538.1 W cm⁻² and 57.9 Kw m⁻² K⁻¹, respectively; the hydrophobic metal foam cover has a 4.8 K lower surface superheated degree at the onset of nucleate boiling, but a 7.5 % lower maximum heat transfer coefficient compared with the uncoated one; the hydrophilic metal foam cover shows a less deterioration after the departure from nucleate boiling but a 5.3 K higher surface superheated degree at the onset of nucleate boiling than those of the uncoated one. A new correlation for boiling heat transfer coefficients was developed with a mean relative error of 9.75 %.

Defining the required trackability level of the target condition for the testing facility reconditioning unit represents an unresolved challenge in improving the reproducibility of load-based tests and corresponding performance rating standards development. To enhance the reproducibility of such testing methodology, this paper presents and discusses a new feed-forward compensation technique based on the development of a transfer function model for the delay and offset characteristics of the psychrometric room's air temperature and humidity modulations with reference to the target signal from the room emulator. It is demonstrated that the proposed methodology enables offset and delay reduction in the trackability of the return air condition within 60 s at different testing conditions, enhances the reproducibility of the test results to limit performance deviations to within 2 %, and achieves closely matched controlled parameter modulations during load-based tests.

Spiral blast freezing is a common unit operation used in food processing facilities for rapidly freezing a variety of foodstuffs. The purpose of a blast freezer is to generate high velocity, low temperature air flow over food products being conveyed within refrigerated enclosures to accomplish the freezing process. However, air flow patterns observed within field operating blast freezers are often suboptimal, resulting in diminished system performance. This paper applies a Monte Carlo simulation technique to a food product freezing simulation in order to identify velocity profiles that optimize the freezing process. A one-dimensional food product model is used to evaluate the interplay between the time variation in the magnitude of the air velocity over food products conveyed through the freezing system and the resulting dwell time needed to achieve a target product core temperature at the blast freezer exit. Temporal heat transfer coefficients derived from field measurements made in a newly installed spiral blast freezer serve as a basis to calibrate the one-dimensional product model.

The results of the Monte Carlo analysis show freezing system performance is improved when high and stable air velocities over the product are achieved early in the freezing process dwell time. Air flow patterns within a freezing system that result in high air velocity later in the freezing process dwell time are suboptimal. Field-measured data on a newly installed spiral blast freezer showed this suboptimal air flow pattern and the use of baffling within the spiral enables improved airflow leading to an estimated 10 % increase in production throughput.

Air cooler is a critical heat dissipation equipment applied in the field of oil and gas storage, which is mainly used to control the temperature during oil and gas storage and ensure the safety of oil and gas storage. After the installation of the spray cooling system on the skid-mounted compressed natural gas (CNG) air cooler Suqiao gas storage, the inlet air temperature of the air cooler decreases, resulting in reduced compressor power consumption. This effectively addresses the issue of unit shutdown due to high temperatures during the summer. However, the actual spray effect on-site reveals the impact of crosswinds, which poses a challenge. In this study, the flow field and causes of the skid-mounted CNG air cooler equipped with a spray cooling system under the influence of crosswinds are analyzed. Additionally, a solution involving the installation of a baffle is proposed. The results highlight that crosswinds have an adverse effect on outdoor spray cooling. With the installation of the baffle, the low-temperature area expands, resulting in lower temperatures. The cooling range is approximately 2 K, effectively counteracting the negative effects of crosswinds.

Thermal link is an important carrier used to transfer the cooling capacity and suppress the temperature fluctuation in cryostat. To balance these two points, it is usually necessary to find the optimum thermal link parameters. This paper establishes a model for the cryocooler cold head-thermal link-second flange based on a cryostat. Utilizing the response surface method, response equations correlating thermal link parameters with the temperature and its fluctuations of the second stage flange are developed at the lowest temperature of cryocooler. Through dual-objective optimization of cooling capacity transfer and temperature fluctuations at the second flange, the optimal thermal link parameters are determined and experimentally validated based on predicted results. The experimental and predicted values show good agreement with an error of 2 %. The optimized thermal link led a minor temperature increase and a significant temperature fluctuation reduction, decreasing from 230mK at the cold head to 2.900mK at the second flange, achieving a 98.74 % reduction. Furthermore, compared with non-optimization structure, the optimization one has further lowered the temperature fluctuation at the second flange from 4.000mK to 2.900mK with 27.5 % improvement. These results show that the present methods are reliable and useful to help to realize highly stable low-temperature environment in cryostat.

This review provides a comprehensive summary of research pertaining to the purge section within desiccant wheels featuring multi-sector configurations. Additionally, it encompasses discussions on innovative wheel designs such as non-adiabatic desiccant wheels and the achievement of two-stage dehumidification from a single wheel employing multi-sector approaches. The review begins by providing a concise historical overview of the desiccant wheel, followed by a systematic classification of the research conducted in this area. Subsequently, various categorizations are presented in a logical sequence, offering a structured understanding of the subject matter. Central to the critical findings of this review is the identification of an optimal purge wheel sector angle, which not only decreases the energy consumption of the desiccant wheel but also significantly reduces the exit temperature of process air. Moreover, the review highlights the potential of achieving isothermal dehumidification through the utilization of non-adiabatic rotary desiccant wheels. Furthermore, the introduction of a multi-sector desiccant wheel is one of the key successes in obtaining two-stage dehumidification and getting multi-output like cooling, heating with dehumidification, and heating with humidification. These are all efficiently derived from a single wheel.

Sorption heat transformers and thermal energy storage systems are emerging technologies that utilize and store low-grade waste heat for heating and cooling applications. The performance of sorption systems is not only affected by systems’ operating conditions, and overall systems’ design but also by sorption material or composite parameters such as thermal diffusivity, composition, and pore structure, among others. In this study, CaCl₂-based salt-in-porous-matrix composites of different compositions and coating thicknesses were synthesized. During synthesis, salt to silica gel and polyvinyl alcohol to silica gel ratios were fixed and the thermal additive (expanded natural graphite) to silica gel ratio was varied with care from 0 to 0.26 (or 0 to 20.5 wt.%, additive to silica gel ratio). The thickness of samples varied from 2.3 to 8.3 ± 0.1 mm. The composites were characterized by a transient plane source (thermal conductivity and thermal diffusivity), nitrogen adsorption porosimetry (specific surface area and total pore volume), and thermogravimetric sorption analysis (water sorption equilibrium) methods. A custom-built gravimetric large pressure jump (G-LPJ) testbed was used to study water sorption kinetics (water uptake vs. time) for selected samples. The thermal conductivity and diffusivity of the studied composite samples have shown significant enhancements, e.g., 240% (0.11 W/(m·K) vs. 0.37 W/(m·K)) and 310% (0.21 mm²/s vs. 0.87 mm²/s), respectively, by adding 12.5 wt.% expanded natural graphite (additive to silica gel ratio is 0.14) as a thermally conductive additive (additive to silica gel ratio) because of thermal percolation effect. This ratio of expanded natural graphite to silica gel was found to be optimal for studied composition. The results indicate that sorption composites with higher thermal diffusivity offer notably higher specific cooling power and improved sorption kinetics, compared to the composites without expanded natural graphite of the same thickness (850 W/kg vs. 480 W/kg at 70% water conversion for samples with thickness of 5.3 mm).