Thermodynamic analysis of auto-cascade high-temperature heat pump cycle using low GWP refrigerant

doi:10.11949/0438-1157.20241362

Abstract

Abstract:

Addressing the issue of low energy efficiency in high-temperature heat pumps under large temperature difference heating conditions, a novel auto-cascade high-temperature heat pump cycle is proposed. The cycle employs a cascade heating strategy to achieve high-temperature water heating. The zeotropic mixed refrigerant with low GWP is selected due to temperature glide characteristics. The HCs refrigerant is chosen for the low-boiling composition. A thermodynamic mathematical model is constructed to analyze the energy and exergy performance of the modified cycle. The result indicates that within the range of outlet water temperature variation, the heating COP and heating capacity increase by an average of 49.36% and 44.30%. The mass flow rate of the refrigerant is reduced by an average of 50.53%. The exergy efficiency is enhanced by 3.47 times. Therefore, the modified cycle demonstrates potential for improvement in both energy and exergy performance.

Key words: auto-cascade heat pump cycle, zeotropic mixed refrigerant, energy analysis, exergy analysis

摘要：

针对大温差加热时高温热泵能效较低的问题，提出了一种级联加热式自复叠高温热泵循环，采用级联加热策略来实现水的大温升加热。采用低GWP的非共沸混合制冷剂作为工作介质，低沸点组分选用了碳氢化合物自然工质。改进循环的配置优化了流体的换热过程，减少了不可逆损失。热力学分析结果表明，级联加热式自复叠高温热泵循环在出水温度变化的范围内制热COP和制热能力分别平均提高了49.36%和44.30%，制冷剂的质量流量平均减少了50.53%，㶲效率增加了3.47倍。因此，级联加热式自复叠高温热泵循环在大温升条件下相比于基本循环具有显著提升潜力。

关键词: 自复叠热泵循环, 非共沸混合制冷剂, 能量分析, ?分析

CLC Number:

TB 61

Yuqing YANG, Yinlong LI, Gang YAN. Thermodynamic analysis of auto-cascade high-temperature heat pump cycle using low GWP refrigerant[J]. CIESC Journal, 2025, 76(S1): 43-53.

杨语晴, 李银龙, 晏刚. 采用低GWP制冷剂的级联加热自复叠高温热泵循环热力学分析[J]. 化工学报, 2025, 76(S1): 43-53.

Figures/Tables 13

Fig.1 Schematic diagram of cycles

Fig.2 The T-s diagram of MAHPC and BAHPC

Table 1 The mass and energy conservation equations for components in the MAHPC

部件	质量守恒方程	能量守恒方程
压缩机	$m 2 = m 1$	$W c o m = m 1 h 2 - h 1 = m 1 h 2 s - h 1 / η c o m$
冷凝器	$m 3 = m 2$	$Q h - c o n = m 2 h 2 - h 3$
蒸发器	$m 7 = m 6$	$Q e = m 6 h 7 - h 6$
相分离器	$m 3 = m 3 V + m 3 L$	$m 3 h 3 = m 3 V h 3 V + m 3 L h 3 L$
膨胀阀1	$m 4 = m 3$	$h 4 = h 3 L$
膨胀阀2	$m 6 = m 5$	$h 6 = h 5$
复叠换热器	$m 10 = m 9$ $m 5 = m 3 V$ $m 1 = m 8$	$m 3 V h 3 - h 5 = m 9 h 10 - h 9 + m 9 h 1 - h 8$

Table 1 The mass and energy conservation equations for components in the MAHPC

部件	质量守恒方程	能量守恒方程
压缩机	$m 2 = m 1$	$W c o m = m 1 h 2 - h 1 = m 1 h 2 s - h 1 / η c o m$
冷凝器	$m 3 = m 2$	$Q h - c o n = m 2 h 2 - h 3$
蒸发器	$m 7 = m 6$	$Q e = m 6 h 7 - h 6$
相分离器	$m 3 = m 3 V + m 3 L$	$m 3 h 3 = m 3 V h 3 V + m 3 L h 3 L$
膨胀阀1	$m 4 = m 3$	$h 4 = h 3 L$
膨胀阀2	$m 6 = m 5$	$h 6 = h 5$
复叠换热器	$m 10 = m 9$ $m 5 = m 3 V$ $m 1 = m 8$	$m 3 V h 3 - h 5 = m 9 h 10 - h 9 + m 9 h 1 - h 8$

Table 2 Exergy destruction of all components in the MAHPC

部件	㶲损失
压缩机	$E x c o m = E x 1 - E x 2 + W c o m$
冷凝器	$E x c o n = E x 2 + E x 10 - E x 3 - E x 11$
蒸发器	$E x e v a = E x 6 - E x 7 - E x Q e$
相分离器	$E x s e p = E x 3 - E x 3 V - E x 3 L$
EV1	$E x E V 1 = E x 3 L - E x 4$
EV2	$E x E V 2 = E x 5 - E x 6$
复叠换热器	$E x C H X = E x 3 V - E x 5 + E x 9 - E x 10 + E x 8 - E x 1$

Table 2 Exergy destruction of all components in the MAHPC

部件	㶲损失
压缩机	$E x c o m = E x 1 - E x 2 + W c o m$
冷凝器	$E x c o n = E x 2 + E x 10 - E x 3 - E x 11$
蒸发器	$E x e v a = E x 6 - E x 7 - E x Q e$
相分离器	$E x s e p = E x 3 - E x 3 V - E x 3 L$
EV1	$E x E V 1 = E x 3 L - E x 4$
EV2	$E x E V 2 = E x 5 - E x 6$
复叠换热器	$E x C H X = E x 3 V - E x 5 + E x 9 - E x 10 + E x 8 - E x 1$

Table 3 Input parameters for the simulation

参数	数值
蒸发温度t_e/℃	10
冷凝温度t_c /℃	90
冷水入口温度t_win/℃	15
冷水中间温度t_wmid/℃	55
冷水出口温度t_wout/℃	95
制冷剂1组分z₁	0.5
冷凝器出口质量干度q₃	0.5
蒸发器出口干度q₇	1
热负荷Q_h/W	100

Table 4 Validation of the calculation results with two studies［15，18］

t_am/℃	COP_h（本文）	COP_h^[15]	Relative error/%	COP_h^[18]	Relative error/%
-18	1.28	1.29	0.78	1.30	1.54
-13	1.43	1.46	2.05	1.47	2.72
-8	1.61	1.62	0.62	1.64	1.83
-3	1.82	1.80	1.11	1.81	0.55
2	1.95	1.98	1.52	2.00	2.50
7	2.17	2.18	0.46	2.19	0.91

Table 5 Thermophysical properties of selected refrigerants

Property	High-boiling		Low-boiling
Property	R1336mzz(Z)	R1233zd(E)	R1270	R290	R1234yf
t_NBP /℃	33.00	18.00	-47.70	-42.11	-26.11
t_crit/℃	171.30	166.50	90.10	96.74	36.30
P_crit/MPa	2.90	3.60	4.21	4.25	4.10
ODP	0	0	0	0	0
GWP	2	1	3	20	2

Fig.3 The variation of cycle performance with different mixed refrigerant

Fig.4 The variation of COPh, qh,v and mr with the mass fraction of the R1233zd(E)

Fig.5 The variations of the cycle performance

Fig.6 The variations of the exergy performance

Fig.7 Exergy destruction distributions of MAHPC and BAHPC

Fig.8 Temperature distribution of MAHPC and BAHPC

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