Heat pipes and two‐phase thermosyphon systems are passive heat transfer systems that employ a two‐phase cycle of a working fluid within a completely sealed system. Consequently, heat exchangers based on heat pipes have low thermal resistance and high effective thermal conductivity, which can reach up to the order of (105 W/(m K)). In energy recovery systems where the two streams should be unmixed, such as air‐conditioning systems of biological laboratories and operating rooms in hospitals, heat pipe heat exchangers (HPHEs) are recommended. In this study, an experimental and theoretical study was carried out on the thermal performance of an air‐to‐air HPHE filled with two refrigerants as working fluids, R22 and R407c. The heat pipe heat exchanger used was composed of two rows of copper heat pipes in a staggered manner, with 11 pipes per row. Tests were conducted at different airflow rates of 0.14, 0.18, and 0.22 m3/h, evaporator inlet‐air temperatures of 40, 44, and 50°C, filling ratios of 45%, 70%, and 100%, and ratios of heat capacity rate of the evaporator to condenser sections (Ce/Cc) of 1 and 1.5. For HPHE's steady‐state operation, a mathematical model for heat‐transfer performance was set and solved using MATLAB. Results illustrated that the heat transfer rate was in direct proportion with the evaporator inlet‐air temperature and flow rate. The highest HPHE's effectiveness was obtained at a 100% filling ratio and (Ce/Cc) of 1.5. The predicted and experimental values of condenser outlet‐air temperature were in good agreement, with a maximum difference of 3%. HPHE's effectiveness was found to increase with the increase in evaporator inlet‐air temperature and number of transfer units (NTU) and with the decrease in airflow rate, up to 33% and 20% for refrigerants R22 and R407c, respectively. Refrigerant R22 was the superior of the two refrigerants investigated.

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Background: Bronchial asthma is characterized by lower respiratory tract inflammation associated with bronchial hyper responsiveness with variable and reversible airflow obstruction. The majority of asthmatics are sensitized to at least one common allergen. Aim of the study: The aim of this study is to determine the association of high-risk asthma with allergy-related parameters (total serum IgE levels, serum levels of allergen-specific IgE, eosinophil count, eosinophil percentage) and pulmonary functions in children. Subjects and methods: 50 Children aged 8-15 years diagnosed with atopic asthma were enrolled in the study. Pulmonary function tests, total leukocyte count (TLC), eosinophil count, and eosinophil percentage were estimated. Total serum immunoglobulin E (IgE) levels and serum IgE levels specific to antigens from 1 to 9 allergens with class 1 or higher, namely, Dermatophagoides pteronyssinus (D. pteronyssinus) , Dermatophagoides farina (D. farina), cat dander , dog dander, cockroach, egg white, milk, Aspergillus fumigatus, and fish, were measured using UniCAP fluoroenzyme immunoassay (FEIA). Results: This study includes 50 participants, 20 (40%) belonged to the high-risk and 30 (60%) to the low-risk groups. This study revealed no significant association in peak expiratory flow rate (PEFR, ％) values between high-risk and low-risk asthma groups (p ˃ 0.05). There was no significant association in forced expiratory volume in first second [ FEV1 (L)] values between high-risk and low-risk asthma groups (p ˃ 0.05), whereas there was significant association in FEF 25-75% (forced expiratory flow 25-75%) values between high-risk and low-risk asthma groups (p ˂ 0.05). There was a significant association between total serum IgE level and high-risk asthma, but TLC, eosinophil count, and eosinophil percentage showed non significant association with high-risk asthma. Serum levels of IgE specific to D. pteronyssinus, D. farina, cat dander, and dog dander were significantly associated with high-risk asthma. The high-risk group had higher serum levels of IgE specific to D. pteronyssinus (p < 0.0001), D. farina (p < 0.0001), cat dander (p < 0.0001), and dog dander antigens (p < 0.0001) compared with those in the low-risk group. There was no significant association between high-risk asthma and the serum levels of IgE specific to antigens from other allergens (including cockroach, egg white, and milk). Serum levels of IgE specific to Aspergillus fumigatus and fish were both negative (class level < 1) in both the high-risk group and the low-risk group. Conclusion Children with higher serum levels of IgE specific to D.pteronyssinus, D. farina, cat dander and dog dander antigens, and total serum IgE levels, and lower FEF25-75% values belong to the high-risk asthma group. The characterization of risk factors has enabled us to identify high-risk asthma in children , leading to better treatment options.

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