To address the issue of temperature rise induced by refrigerant pump operation in solar ejector refrigeration systems, this study employs a multistage centrifugal pump. Through a combination of theoretical analysis and experimental investigation, using R142b as the working fluid, a test platform was constructed to simulate a flow range of 50%-100%, assessing the thermal rise characteristics under varying rotational speeds and inlet pressures. By applying energy balance principles and dimensionless analysis, a predictive model for temperature rise was developed. The results reveal that lower flow rates and increased speeds lead to greater internal energy dissipation within the pump, significantly elevating the refrigerant temperature and compromising both pump efficiency and overall system stability. The proposed model accurately predicts over 95% of the data within a ±5% margin of error, demonstrating its applicability in engineering design and pump selection optimization.

The effect of refrigerant charge on the system performance of quasi-two-stage compression heat pump (QCHP) with replacement refrigerant of R32/R1270 (15/85 wt.%) (B for short) for district heating was studied under nominal conditions based on the self-designed QCHP test system and the feasibility of replacing R22 with B was discussed under variable evaporation temperature conditions. The results indicated that the refrigerant charge showed distinct impact on the COPh, heating capacity and discharge temperature of the system using B. The system with B at the optimal charge of 1.2 kg (B-opt) achieved the maximum heating capacity of 7.455 kW and the maximum COPh of 3.35 at nominal conditions. The COPh and heating capacity of both systems with B-opt and R22 had similar trends with the change in evaporating temperature, while their discharge temperatures showed different changes from the heating capacity. Compared to those of R22 system, B-opt system showed improvement in COPh and heating capacity of 9.73%similar to 17.54% and 50.84%similar to 53.40% respectively in the evaporating temperature of -15 similar to-5 degrees C, with the distinctly lower discharge temperature. Thus, B-opt has remarkable replacement advantages in the QCHP. The lower discharge temperature highlights the outstanding benefits of B-opt system in the reliable heating at lower ambient temperature and longer service life. This study provides reliable reference data for refrigerant replacement in heat pumps and low-carbon heating.

The promotion of heat pump heating technology is one of the important means to achieve carbon neutrality in the construction field. Seeking more efficient heat pump systems and green alternative refrigerants is the focus of current research. The concentration optimization experiment of R32/R1270 was carried out using the quasi-two-stage compression heat pump (QCHP) test device, and its potential to replace R410A in the QCHP for producing hot water was experimentally evaluated. The results showed that R32/R1270 with an optimal concentration of 15/85 (MRopt for short) can be used as a promising green alternative refrigerant, mostly because the MRopt system obtained a 12.30 %similar to 16.07 % rise in coefficient of performance (COPh) compared with the R410A system under the condition of evaporation temperature of-30 degrees C similar to-5 degrees C,with the discharge temperature reduced by 12.40 degrees C similar to 15.71 degrees C, and the heating capacity was increased by 1.87 %similar to 5.24 % at-30 degrees C similar to-25 degrees C, while its was decreased by 2.00 %similar to 6.00 % at -20 degrees C similar to-5 degrees C. The lower discharge temperature and clearly higher suction pressure than the standard atmospheric pressure meant that the MRopt system had the outstanding advantages in safely operating at lower ambient temperature and providing higher temperature hot water. Under standard heating conditions, the optimal refrigerant charge required by the MRopt system was about 40% less than that of the R410A system, which would significantly reduce the indirect greenhouse effect. The refrigerant concentration had distinct effect on COPh, heating capacity and discharge pressure. Both the COPh and heating capacity of the system decreased as the evaporation temperature decreased, while the impact of evaporation temperature on the system's discharge pressure was not significant.The effects of refrigerant concentration and evaporation temperature on discharge temperature both showed conditional dependence.

The effects of the charge and concentration of mixed refrigerant (MR) on start-up characteristics of instantaneous heating heat pump water heater (IHHPWH) with R744/R290 were investigated by utilizing the IHHPWH test device. The results indicated that both the augmentations in charge and R290 concentration led to substantial reduction in the start-up time of transient exit temperature of heat sink (TETHS) and transient mixed refrigerant temperatures and its transient pressures. The system start-up time decreased considerably with increasing charge, from 1370 s to 1225 s to 1030 s, and also decreased prominently with decreasing R744 concentration, from 1370s to 1225 s to 1020 s. The former and the latter were respectively mainly due to the substantial reduction in the durations of rapid increment segment and slow increment segment (SIS) of TETHS. Both the charge and concentration of mixed refrigerant had negligible impact on the trend of the same transient parameter. Under the conditions studied, all TETHS exhibited two evolution stages, but the transient temperatures and transient pressures of mixed refrigerant manifested four or five evolution stages, with all exhibiting fluctuation segments. The SIS of TETHS consumed 51.0 %similar to 61.1 % of system starting time at the conditions studied, while they only caused temperature rise of 2.77 similar to 4.15 degrees C. Thus, the system rapid start was notably influenced by the SIS. The minimum transient suction pressure increased slowly and rapidly with the rises of charge and R744 concentration respectively.

This study presents an integrated experimental–modeling investigation of the thermal behavior of a multistage centrifugal refrigerant pump in solar ejector refrigeration systems (SERS). A temperature-rise prediction model is formulated strictly from energy conservation with viscous dissipation and validated on a closed-loop test rig under variable flow rates, inlet pressures, and operating frequencies. Experiments show that the outlet temperature rise (ΔT) decays approximately exponentially with increasing flow rate, while higher operating frequency intensifies viscous-dissipation heating. The pressure difference (Δp) increases with both flow rate and frequency, whereas the overall efficiency (η) exhibits a parabolic trend, peaking at 32.6% at 37.5 Hz. The model achieves high predictive accuracy, with errors within ±0.4 °C at 25–37.5 Hz and about ±1.1 °C at 50 Hz. By constructing Δp–Q–f operating maps and coupling them with cavitation-risk analysis, safe and optimal operating zones (“best zone” and “caution zone”) are identified. These results provide quantitative guidance for pump thermal management, frequency scheduling, and system integration, enabling energy-efficient and reliable operation of solar-driven ejector refrigeration systems.

Based on the test set-up of instant heat pump water heater (IHPWH), the performances of system operating with zeotropic natural mixture (ZNM) (R744/R290) (12/88)) and system operating with R22 refrigerant were compared under variable entry temperature of heat sink (ETHSK) and variable entry temperature of heat source (ETHSC) conditions, aiming to comprehensively evaluate the replacement potential of ZNM in the IHPWH. The results revealed that ZNM had an obvious alternative advantage, mainly attributed to that system operating with ZNM refrigerant achieved the comparable or markedly superior heating capacity and COP and markedly lower discharge temperature compared to those of system operating with R22 refrigerant under two conditions. The discharge temperature of system operating with ZNM refrigerant was reduced by 5.4 similar to 26.7 degrees C compared to that of system operating with R22 refrigerant, thus system operating with ZNM refrigerant can produce higher temperature domestic hot water. Compared with those of system operating with R22 refrigerant, both heating capacity and COP of system operating with ZNM refrigerant had markedly different trends with the change of ETHSK, while they had slightly different trends with the change of ETHSC. Compared to the ETHSK, the ETHSC has a more conspicuous impact on the heating capacity, COP and discharge temperature of system operating with ZNM refrigerant.

The effect of refrigerant charge on the system performance of quasi-two-stage compression heat pump (QCHP) with replacement refrigerant of R32/R1270 (15/85 wt%) (B for short) for district heating was studied under nominal conditions based on the self-designed QCHP test system and the feasibility of replacing R22 with B was discussed under variable evaporation temperature conditions. The results indicated that the refrigerant charge showed distinct impact on the COPh, heating capacity and discharge temperature of the system using B. The system with B at the optimal charge of 1.2 kg (Bopt for short) achieved the maximum heating capacity of 7.455 kW and the maximum COPh of 3.35 at nominal conditions. The COPh and heating capacity of both systems with Bopt and R22 had similar trends with the change in evaporating temperature, while their discharge temperatures showed different changes from the heating capacity. Compared to those of R22 system, Bopt system showed improvement in COPh and heating capacity of 9.73%~17.54% and 50.84%~53.40% respectively in the evaporating temperature of -15~-5 ?, with the distinctly lower discharge temperature. Thus, Bopt has remarkable replacement advantages in the QCHP. The lower discharge temperature highlights the outstanding benefits of Bopt system in the reliable heating at lower ambient temperature and longer service life. This study provides reliable reference data for refrigerant replacement in heat pumps and low-carbon heating.

The feasibility of R1270 and R290 replacing R22 in an instant heat pump water heater was evaluated experimentally and the temperature distribution characteristics of heat sinks and refrigerants were discussed under different conditions. The results indicated that R1270 was preferred as an alternative to R22, mainly because compared to those of R22 system, R1270 system achieved an increase of 5.28 %similar to 8.39 % in heating capacity and 3.08 %similar to 7.14 % in coefficient of performance (COP) and a decrease in the discharge temperature of 10.89 similar to 14.19 degrees C under studied conditions, but R290 system experienced a decrease in heating capacity of 7.19 %similar to 9.91 %. R290 could be used as an alternative to R22, but the compressor with slightly greater displacement needed to be replaced. Both R1270 system and R290 system could produce high-temperature hot water, especially the latter. Compared with heat sink inlet temperature (HSIT), the heat sink outlet temperature had marked effect on all operation performances of both systems except heating capacity. The heat sinks of both systems did not exhibit the second slow temperature rise zone only under low HSIT condition. Both the outlet and inlet temperatures of heat sink had no apparent impact on the first temperature rise transformation tube length of both systems, but had apparent impact on the second temperature rise transformation tube length. The positions of the two heat transfer pinch points and the two maximum heat transfer temperature differences of both systems did not shift regularly with the variations in the outlet and inlet temperatures of heat sink.

This study evaluates two low-global warming potential (low-GWP) refrigerants—R1233zd(E) and R1234ze(Z)—for use in solar ejector refrigeration systems. A steady-state thermodynamic model is developed to compare their performance with baseline R134a across representative operating conditions. Key metrics include refrigerant pump power, system coefficient of performance (COP), and energy efficiency ratio (EER). At a 10 kW cooling load, pump energy demand drops by 73.2% and 68.2% for R1233zd(E) and R1234ze(Z), yielding EER values of 27.11 and 22.64—over four times that of R134a. Though COPs (0.19 and 0.20) are modestly lower than R134a (0.25), markedly reduced saturation pressures translate to improved electrical efficiency and safer operating envelopes.To validate pumping feasibility under low-pressure refrigerant conditions representative of these fluids, a closed-loop multistage centrifugal pump test platform was constructed. Variable-frequency trials confirmed stable subcooled liquid delivery and identified a peak measured overall pump efficiency near 30%, consistent with model expectations. The combined simulation–experiment evidence indicates that R1233zd(E) and R1234ze(Z) are strong candidates for small- to medium-scale solar ejector cooling in low-carbon buildings.

To solve the problem of poor heat transfer effect in the subcooled region of integrated condenser, a combined condenser for instant heat pump water heater (IHPWH) was proposed and designed based on the condenser design model, aiming at obtaining an optimal design method of condenser. The off-design performances of heat pump water heater (HPWH) with a combined condenser (HPWHCC) and HPWH with an integrated condenser (HPWHIC) were investigated and compared based on the Mopt IHPWH test unit, aiming at verifying the feasibility of using a combined condenser replacement of an integrated condenser in the IHPWH. The results show that the heat transfer area of combined condenser is only 83.33 % of that of integrated condenser. Compared with the HPWHIC, the HPWHCC achieves basically equivalent COP and heating capacities and slightly higher discharge temperatures under variable heat sink outlet temperature (HSOT) condition and variable heat sink inlet temperature (HSIT) condition. Therefore, the combined condenser has the obvious potential to replace the integrated condenser in the IHPWH. The HSOT has a remarkable influence on the COP of HPWHIC and HPWHCC but a small influence on their heat capacities, while the HSIT has a small influence on their COP and heat capacities.

The present study aims to further understand the effect of surface properties of vertical textiles indoors on the particle deposition. A 512 L cubic aluminum experimental chamber was built to obtain the deposition loss rate coefficients for 0.37, 0.54, 0.75, 0.9, 1.3, and 1.6 µm particles under three different airflow conditions. Eight curtain fabrics—four window voile fabrics and four curtain cloths—were selected as the deposition surfaces in investigating the effect of fabric porosity on particle deposition. The total fabric porosity can be roughly divided into inter-yarn porosity and inter-fiber porosity. The experimental results reveal that both the near-surface airflow velocity and the particle size affect the deposition loss rate coefficient. The trend of the deposition loss rate coefficient with increasing inter-yarn porosity differs from that with increasing inter-fiber porosity.

The effects of an expansion valve opening on the robustness and system performance of an R32 heat pump system under variable heat source inlet temperatures and hot-water inlet temperatures are studied.The results show that the system has different superheat oscillation ranges under different operating conditions,and the heat source inlet temperature has a significant effect on the initial oscillation superheat,whereas the hot water inlet temperature has no obvious effect on it.Under the variable heat source inlet temperature(15-25℃)conditions,the heating capacities show different variation trends with the superheat,whereas the COP shows the same changing trends,and the maximum COP of the system is obtained within the superheat oscillation range.Under the variable hot water inlet temperature(30-40℃)conditions,the heating capacities and COP show the same trends with the superheat,and both of them reach the maximum values in the superheat oscillation range.Both the increase in the heat source inlet temperature and the decrease in the hot water inlet temperature can increase the maximum heating capacity and the maximum COP,which are 9.287 kW and 4.646,respectively when the heat source inlet temperature is 25℃,and 9.148 kW and 5.665,respectively,when the hot water inlet temperature is 30℃.

The effects of starting mode and outlet temperature of heat sink (OTHS) on the starting performances of direct-heated heat pump water heater using natural blend were investigated experimentally. The results indicated that both starting mode and OTHS had notable impact on starting time of transient performance parameters. Both warm start and lower OTHS helps to quickly obtain hot water at the target temperature, mainly because the system startup time in the warm start was 16.73 % shorter than that in the cold start and the system gained the shortest startup time (1015 s) in low temperature condition. The transient heat sink outlet temperature had a rapid temperature rise section and a slow temperature rise section (STRS), and the STRS consumed 56.58 %–66.67 % of the system starting time, so the improvement of STRS is the key to realize the fast startup. The effects of startup mode on the trends of transient performance parameters were memorably different, but the OTHS had no apparent effect on their trends. The transient refrigerant pressures and transient refrigerant temperatures had the fluctuations. The transient suction pressures had the minimum values (0.3925–0.5575 MPa), and both cold start mode and higher OTHS resulted in a decrease in the minimum value.

为了寻找用于热泵热水器的低GWP替代工质,构建了基于EES软件的热泵热水器系统性能预测模型,并对其可靠性进行了验证.通过对比分析循环性能,理论评价了6 组R744 环保混合工质在直热式热泵热水器中替代R22 的可行性.结果表明:工质浓度对R744 混合工质热泵热水器的循环性能具有显著的影响,且所有R744 混合工质均存在最优质量浓度使其系统分别获得最大COPth;相比于R22 系统,R744/R290 和R744/R1270 系统在最优质量浓度14/86 下均获得了显著提升的COPth和制热量以及较低的排气温度,因此 R744/R290(14/86)和 R744/R1270(14/86)在直热式热泵热水器中均具有显著的替代优势;其余4 组混合工质均不适宜在直热式热泵热水器中作为替代工质.本研究拓宽了热泵热水器用环保工质的选择范围,并为其工质替代提供参考依据.

The influence of flow step ratio (FSR) on the startup characteristics of instant heat pump water heaters (IHPWHs) with natural mixture M (R744/R290 (12/88)) under nominal conditions was studied experimentally to verify the feasibility of a new quick startup method. The results show that the FSR had a marked effect on the startup time of system performance parameters. Under the optimal FSR of 0.6, the shortest system startup time and available hot water supply time were 700 s and 250 s, respectively, which were markedly shorter than those in the conventional startup. Therefore, rapid startup of the system and rapid production of usable domestic hot water can be realized by controlling the flow step. The influence of flow step on the variation trend of system performance parameters was obviously different, and there was no slow warming section for the heat sink outlet temperature (HSOT) under three FSRs. The HSOT, heating capacity, and high pressure side pressures had the maximum values in the quick startup, and the maximum values were obviously affected by the FSR. The FSR had no marked effect on the minimum suction pressure. The refrigerant pressures and refrigerant temperatures fluctuated markedly in both rapid and conventional starts.

Based on the visualization experimental system of refrigerant/lubricating oil flow pattern, the effects of the superheat on the flow patterns of R134a/lubricating oil in the horizontal tube and vertical tube at the evaporator outlet under the different conditions were compared and analyzed and the variation law of the system cycle performances of heat pump with the superheat under the working condition 2 was studied experimentally in order to obtain the corresponding relationship between the system performances and the flow patterns of refrigerant/lubricating oil. The results show that in the range of about 0～15 ℃ superheat, the same four flow patterns of R134a/lubricating oil will appear in the horizontal tube under three working conditions, while the same three flow patterns will appear in the vertical tube; The heat source inlet temperature has a significant effect on the corresponding superheat ranges of the flow patterns（except for the stratified annular flow）of R134a/lubricating oil in the horizontal tube and vertical tube and the flow pattern transition superheat（except for the first horizontal flow pattern transition superheat）; Under the condition 2, the system obtains the higher COP and heating capacity in the transition state, and the maximum COP and heating capacity are 5.348 and 4.386 kW at the first horizontal flow pattern transition superheat（0.2 ℃）, respectively.

A bench performance test for a refrigerant pump was built to analyze the variations among parameters such as flow rate, head, rotational speed, efficiency/total efficiency and power consumption of a multistage centrifugal pump under different working conditions. The study showed that the outlet pressure, differential pressure and power consumption of the pump increased with increasing frequencies at the rated flow rate of 1 m3/h and inlet pressure pc = 0.454 MPa. The total pump efficiency showed a trend toward first increasing and then decreasing, and the maximum value was approximately 27.7%. When the refrigerant pump was at a frequency of 37.5 Hz and the inlet pressure was between 0.338 and 0.523 MPa, the pump outlet pressure and differential pressure decreased with increasing flow rates, and the pump outlet pressure increased with increasing inlet pressures. While the pump differential pressure increased with the increase in suction pressure, the pump power consumption increased with the increase in flow and increased slowly with the pump inlet pressure. With the increase in the flow rate, the total efficiency of the pump showed a tendency toward first increasing and then slowly declining. The total efficiency of the pump was between 4.0% and 30.2% at flow rates between 0 and 1.8 m3/h. Under the same conditions, when the pump operated under low flow rate and high pressure differential conditions, and the refrigerant pump efficiency was low.

基于搭建的直热式热泵热水器系统实验研究和分析了充注量对M(R744/R290(12/88))热泵系统的循环性能和冷凝器中换热流体的温度分布的影响.实验结果表明:在两种实验工况下,M热泵系统存在相同的最优充注量使COP分别达到最大值;不同充注量下冷凝器中均会出现两个传热窄点,且充注量的变化会导致第一传热窄点的出现位置发生迁移;充注量是影响M热泵系统的循环性能和冷凝器中换热流体的温度分布的显著因素.

基于搭建的直热式水源热泵实验装置,实验研究了R744/R600a和R600a系统变工况循环性能,分析了热汇出口温度对冷凝器内换热流体温度分布的影响.结果 表明:随着热汇出口温度升高,R744/R600a和R600a热泵系统的COPh和制热量Qh均呈降低趋势,而相应的冷凝压力、压比和排气温度等均呈升高趋势;在45 ～ 60℃的热汇出口温度范围内,R744/R600a系统的COPh和制热量Qh均明显优于R600a系统;与R600a系统相比,显著的温度滑移导致R744/R600a系统冷凝器内换热流体间的温度匹配水平明显提高,相应的冷凝器不可逆损失显著降低;热汇出口温度的升高导致了R744/R600a系统冷凝器内换热流体间的温度匹配水平降低及不可逆损失增大.

提出一种太阳能喷射-压缩复合蓄冷新系统,设计并搭建系统性能实验研究平台,以R134a为制冷剂,实验分析得出太阳能喷射-压缩复合蓄冷系统的最优运行工况.结果 表明:系统能效比整体随蒸发温度的升高而升高;在不同的蒸发温度阶层内,系统能效比均呈先增加后降低的变化规律,系统功耗均呈先降低后上升的变化规律;在冷凝温度为32℃及中间温度为15℃时,存在最优的发生温度,最优发生温度介于76～78℃之间,此时能效比最高,可达2.65;总功耗最低,可达330W.同样,系统在研究工况范围内存在最优的中间温度,当冷凝温度为35℃时,最优中间温度介于12～16℃之间,此时系统能效比最高,最高能效比可达2.6,总功耗呈不断减少的趋势,系统的总功耗最低为300 W.