Yin Liu

The heat pipe (HP) is widely applied in the thermal management field at present. In order to make use of the low-grade and renewable energies to maintain building thermal comfort in the heating season, more and more studies with respect to improving the thermal performance of the building heating system integrated with the HP (BHSIHP), such as the floor heating system integrated with the HP (FHSIHP), the thermal storage wall heating system integrated with the HP (TSWIHP), conventional wall integrated with the HP (WIHP) and radiator heating system integrated with the HP (RHSIHP), are conducted. This paper aims to summarize different types of HPs applied in the building heating system and offers an overview of the thermal performance improvement for the BHSIHP. The thermal response, thermal conductivity, thermal resistance, heat capacity, heat transfer coefficient, temperature distribution, thermal storage and heat release capacity are always selected to investigate characteristics of the BHSIHP. Results show that the thermal performance of the FHSIHP, the TSWIHP, the WIHP and the RHSIHP is more outstanding than that of the conventional heating system. The thermal performance of the BHSIHP is affected by heat source temperature, installation tilt angle, working fluid, and filling ratio of the HP. The heat source temperature, which positively affects the performance of the BHSIHP, is crucial for the selection of the working fluid and filling ratio. However, the performance of the BHSIHP is increased first and then decreased with the increase of the installation tilt angle. The optimal filling ratio of the working fluid has been proven not to be a fixed value.

This article proposes an effective thermal management solution for electric vehicles by incorporating a low global warming potential (GWP) hybrid refrigerant R1234ze(E)/R134a/R32 (with a mass percentage of 85/10/5). By integrating R1234ze(E), the potential of substituting R134a with this mixed refrigerant in electric vehicle air conditioning for thermal analysis was analyzed. The findings are that R1234ze(E) exhibits a COP reduction of 0.51% compared to R134a, while R1234ze(E)/R134a/R32 showcases a coefficient of performance (COP) enhancement of 1.53% over R134a. The compressor exhaust temperatures of R1234ze(E) and R1234ze(E)/R134a/R32 are, respectively, 7.4°C and 5.2°C lower than those of R134a. R1234ze(E) demonstrates a volumetric cooling capacity ~26.3% smaller than that of R134a. However, the volumetric cooling capacity of R1234ze(E)/R134a/R32 aligns closely with R134a, facilitating convenient direct charging. R1234ze(E)/R134a/R32 proves to be an excellent refrigerant for applications in the thermal management of electric vehicles.

In this paper, the thermal performance of three low-global warming potential refrigerants R1224yd(Z), R1223zd(E) and R1336mzz(Z) were studied to replace R245fa in the high-temperature heat pump system. The results showed that the heating capacity of R1224yd(Z), R1223zd(E) and R1336mzz(Z) was 6, 12 and 88% less than that of R245fa, respectively. The coefficient of performance (COP) of R1224yd(Z) and R1223zd(E) was 2 and 1% higher than that of R245fa, respectively. However, the COP of R1336mzz(Z) was 5% less than that of R245fa. The difference in compressor discharge temperature between R1224yd(Z), R1223zd (E), R1336mzz(Z) and R245fa was about ±5°C. R1224yd(Z) is the best refrigerant to replace R245fa. R1223zd(E) is the second. R1336mzz(Z) cannot be directly replaced unless the original system is modified.

The performance of an enhanced vapor-injection heat-pump drying system was designed and theoretically studied in cold areas. According to the simulation findings, the ideal vapor-injection charge of the system ranges from 12.3 to 13.9%, and its ideal intermediate pressure is between 1.278 and 1.498 MPa when the evaporation temperature is above 0 °C. The ideal vapor-injection charge of the system ranges from 13 to 20%, and its optimal intermediate pressure ranges from 1.078 to 1.278 MPa when the evaporation temperature is −15–0 °C. The ideal vapor-injection charge of the system ranges from 20 to 24%, and the intermediate pressure ranges from 0.898 to 1.078 MPa when the evaporation temperature is below −15 °C. The heat and humidity exhausted air source heat-pump drying (HHE–ASHPD) system has higher dehumidification efficiency than the closed heat-pump drying (CHPD) system under the same air temperature, humidity, and volume parameters.