Comprehensive Study of Heat Transfer and Pressure Drop in Regenerator and Optimization of Solid-state Caloric Cooling Cycles Using Realistic Hydraulic Diameter of Regenerator

Many researchers have used very small hydraulic diameters in regenerators of solid-state caloric cooling cycles, because smaller diameters can generate higher cooling capacity and system COP. However, using very small diameters hardly represent the real performance of the caloric cooling cycle, because they cannot be manufactured for a real system. Therefore, this paper has used more realistic hydraulic diameter which is used in commercial heat exchangers. To get the more accurate heat transfer coefficient and friction factor, the model used in this paper incorporates hydrodynamic and thermal developing regions which are usually neglected in other papers. This paper shows that COP is a function of heat transfer coefficient, pressure drop and displacement ratio. Higher heat transfer coefficient, lower pressure drop and the optimal displacement ratio can generate higher COP in magnetocaloric refrigeration cycle. From simple analytical comparison, it is expected that plate type regenerators can generate the highest cooling capacity and COP. The regenerator with smaller hydraulic diameter has higher performance, but 0.3mm hydraulic diameter has been chosen in this paper due to manufacturing limitation. In addition, this paper has investigated the effect of the length of the regenerator, the cycle frequency and the regenerator’s porosity on heat transfer phenomena in the regenerator. The cycle frequency has a large effect on cooling capacity and system efficiency while the effects of length and porosity of the regenerator are marginal. For the plate-type regenerator with 0.3mm hydraulic diameter, the system with 0.2m length of the regenerator, 0.45Hz cycle frequency and 0.5 porosity has the highest COP of 2.3 to generate 100W kg-1 cooling capacity for a temperature lift of 20°C. This paper provides detailed information of heat transfer phenomena in the solid-state cooling cycles, which need to be understood thoroughly in order to efficiently utilize caloric effects

Performance Analysis of Active Magnetic Regenerative Refrigeration Cycle using Transient Modeling

This paper evaluates the performance of an active magnetic regenerative refrigeration cycle (AMRRC) by using a transient modeling tools. While theoretical COPs of magnetic refrigeration systems are quite promising, parasitic losses inherent to the cycle can substantially reduce the energy efficiency that can be achieved in reality. For solid state refrigeration systems, such as the AMRR cycle, the regenerator undergoes cyclic heating and cooling, making the thermal capacitance of the component a critical parameter during no flow periods. Additional performance reductions are experienced due to additional temperature differences required to convect heat into and out of the magnetic regenerator through the use of a secondary heat transfer fluid. Therefore, this paper combines transient modeling of the magnetic regenerator and the heat exchangers that connect the system to the heat source and sink. The model is then used to study the effects of relevant parameter variations, including magnetic cycling and fluid flow frequencies, mass flow rate of the secondary fluid stream, and geometric variations of the regenerator design, on parasitic losses, cooling capacity and COP. In addition, the model is used to assess the COP reduction caused by these inherent parasitic losses, which allow for a more fair comparison to standard vapor compression systems

Applying Two-phase Zeotropic Heat Transfer Fluids to Solid-state Cooling Cycle and Comparison with Baseline using Single Phase Water

Solid-state caloric cooling cycles are considered to be a promising alternative to conventional cooling technology. Theoretically, they can compete with the conventional vapor compression cycle and are much more efficient. However, this technology does have one problem: its performance decreases rapidly if the temperature difference between the condenser and evaporator gets larger. The environment where cooling technology is used often has large temperature differences between condenser and evaporator. For instance, in a typical automotive system, the condenser operates at 45°C and the evaporator at 5°C. Thus, the temperature difference between the condenser and evaporator reaches 40°C. The cooling load of the caloric cycle decreases by 86% when the temperature difference increases from 5°C to 20°C. This weakness prevents the magnetic refrigeration cycle from becoming commercialized and competing with vapor compression cycle. To solve this issue, the authors have applied two-phase zeotropic blends as heat transfer fluid in the caloric cycles. There are two reasons. First, using two-phase flow can increase the Nusselt number. The flow is laminar when the system uses single phase water, so the Nusselt number cannot be improved in the regenerator. Second, two-phase zeotropic mixture can generate a temperature gradient in the regenerator to overcome the large temperature difference. Therefore, an ethane/isobutane mixture has been chosen due to its high temperature glide (~ 40°C). This selection is different from that of the vapor compression cycle which normally prefers small glide zeotropic mixture. This paper shows that using two-phase zeotropic mixture through the entire regenerator has much better performance than using single and two-phase flow together in the caloric cooling cycle. Optimized zeotropic refrigerant system was chosen to compare with a water system. As a result, the system using two-phase zeotropic blend can increase temperature difference between cold and hot side of the regenerator because Nusselt number increases and lower mass flow rate is required to reach the optimal displacement ratio. Therefore, the amount of heat transfer in the cold heat exchanger significantly increases and the system\u27s efficiency ultimately gets much better. This is first time to use two-phase flow zeotropic mixture in the caloric refrigeration system and this paper expands the application of two-phase zeotropic blends to caloric cooling systems

Novel regenerator design for caloric cycles using artificial neural network — Genetic algorithm method and additive manufacturing

The regenerator is a key component to determine the performance of the active regenerative caloric cycle. Although the geometry of the regenerator is an important factor, very limited geometries have been used in prototypes due to the limitations of conventional manufacturing. Therefore, this study proposed a new type of regenerator with a high heat transfer rate for the caloric cycle, which is a packed rod bed, using additive manufacturing. In order to ensure a systematic approach for the new design of the regenerator, a new design optimization using an artificial neural network — genetic algorithm with the help of computational fluid dynamics was introduced. Artificial neural network models were used to predict the j and f factors of the packed rod bed and showed a mean relative error of less than 2.0% for the j factor, and a mean relative error of less than 7.5% for the f factor. The accurate results of artificial neural networks contribute to improving the optimization process. The regenerator optimized through the artificial neural network — genetic algorithm method increased the system efficiency by 4.7% and the cooling capacity by 13.0% compared to the baseline caloric cycle using a parallel plate matrix. Considering that caloric cycles are still in the development stage due to the lack of performance of the magnetocaloric cycle, this eventually may contribute to the commercialization and energy saving of the magnetic refrigeration cycle while the design optimization might also help to improve the performance of other caloric cycles

Late presentation of hepatitis B among patients with newly diagnosed hepatocellular carcinoma: a national cohort study

Abstract Background Recently, the concept of “late presentation with viral hepatitis” was introduced to help quantify the proportion of patients missing timely diagnosis and treatment for viral hepatitis. The clinical implications of late presentation of hepatitis B at the population level, however, are largely unexplored. Methods Using newly-diagnosed hepatitis B related hepatocellular carcinoma (HCC) patients (N = 1276) from the Korean National Health Insurance Service-National Sample Cohort, a nationally representative cohort study was conducted between 2002 and 2013. HCC patients were classified into 3 groups: late presentation of hepatitis B (no prior clinic visits for hepatitis B before HCC diagnosis), irregular visits (irregular pattern of outpatient clinic visits), and regular visits (regular pattern of outpatient clinic visits). Results The proportion of patients with late presentation decreased from 50.8% in 2003 to 23.1% in 2013. In multivariable analysis compared with patients in the regular visits group, patients with late presentation were more likely to be younger and to be in lower income percentiles. After adjusting for age, sex, year of HCC diagnosis, income percentile, and initial treatment, the hazard ratios (95% confidence intervals) for all-cause mortality comparing the late presentation and irregular visits groups to the regular visits group were 1.76 (1.42–2.18) and 1.31 (1.06–1.61), respectively. Conclusion Timely diagnosis and treatment for hepatitis B related HCC was suboptimal at the population level. More intensive strategies to minimize late presentation for hepatitis B are needed, with special attention to younger people and lower income levels

Graphical user interface design to improve understanding of the patient-reported outcome symptom response.

BackgroundSymptom monitoring application (SMA) has clinical benefits to cancer patients but patients experience difficulties in using it. Few studies have identified which types of graphical user interface (GUI) are preferred by cancer patients for using the SMA.MethodsThis is a cross-sectional study aimed to identify preferred GUI among cancer patients to use SMA. Total of 199 patients were asked to evaluate 8 types of GUIs combining text, icon, illustration, and colors using mixed-methods. Subgroup analyses were performed according to age and gender.ResultsThe mean age of the patients was 57 and 42.5% was male. The most preferred GUI was "Text + Icon + Color" (mean = 4.43), followed by "Text + Icon" (mean = 4.39). Older patients (≥ 60 years) preferred "Text + Icon" than younger patients (p for interaction ConclusionSimple and intuitive text and icons were the most useful GUI for cancer patients to use the SMA. Researchers need to be careful when applying realistic face drawings to cancer symptom monitoring applications because they can recall negative images of cancer

Survival in untreated hepatocellular carcinoma: A national cohort study.

This study aimed to analyze the proportion, characteristics and prognosis of untreated hepatocellular carcinoma (HCC) patients in a large representative nationwide study. A cohort study was conducted using the National Health Insurance Service (NHIS) database in Korea. A total of 63,668 newly-diagnosed HCC patients between January 2008 and December 2013 were analyzed. Patients were categorized into treatment group and no treatment group using claim codes after HCC diagnosis. The proportion of untreated HCC patients was 27.6%, decreasing from 33.4% in 2008 to 24.8% in 2013. Compared to treated patients, untreated patients were more likely to be older (P < 0.001), female (P < 0.01), to have a distant SEER stage (P < 0.001), severe liver disease (P < 0.001), and lower income (P < 0.001). The fully-adjusted hazard ratio for all-cause mortality comparing untreated to treated patients was 3.11 (95% CI, 3.04-3.18). The risk of mortality was higher for untreated patients in all pre-defined subgroups, including those with distant SEER stage and those with severe liver disease. About one fourth of newly diagnosed HCC patients did not receive any HCC-specific treatment. Untreated patients showed higher risk of mortality compared to treated patients in all subgroups. Further studies are needed to identify obstacles for HCC treatment and to improve treatment rates