Advanced exergy analysis of heat pump performance affected by heat transfer matching characteristics of non-azeotropic refrigerants

doi:10.11949/0438-1157.20201015

Abstract

Abstract:

This work is aimed at the non-azeotropic working fluid nonlinear and complex phase change heat transfer process, based on the advanced exergy analysis method, deduced the evaluation index model that characterizes the heat pump system performance—temperature matching degree (TMD), the heat transfer matching characteristics between the non-azeotropic working fluid and the heat exchange fluid are discussed, the accuracy and applicability of the model are verified by experiments. Three representative non-azeotropic working fluids with different temperature slip degrees (M1, M2, M3) are selected as objects, the relationship between TMD and heat exchange pinch point, system COP, exergy efficiency η and actual exergy loss ratio of heat exchanger ε were investigated. The results show that the smaller the TMD, the better the temperature matching between the heat exchange fluids, the greater the COP and exergy efficiency η of the system, the smaller the actual exergy loss of the heat exchanger, and vice versa; and when the TMD is the smallest, the pinch point in the heat exchanger always appears at the saturated gas point .

Key words: heat pump, advanced exergy analysis, non-azeotropic working fluid, temperature matching degree, exergy

摘要：

针对非共沸工质非线性复杂相变传热过程，基于高级分析方法，推导出表征热泵系统性能的评估指标模型——温度匹配度（TMD），探讨了非共沸工质与换热流体之间的换热匹配特性，实验验证了模型的准确性与适用性。选用了三组不同温度滑移程度的非共沸工质（M1、M2、M3）为对象，探究了TMD与换热夹点、系统COP、效率η以及换热器实际损占比ε之间的关系。结果表明：TMD越小，换热流体间的温度匹配越好，系统COP、效率越大，换热器实际损占比越小，反之亦然；且当TMD最小时换热器内夹点总是出现在饱和气态点处。

关键词: 热泵, 高级分析, 非共沸工质, 温度匹配度

CLC Number:

TB 61⁺1

LIANG Kunfeng, FENG Changzhen, WANG Moran, DONG Bin, WANG Lin, LIU Ruijian. Advanced exergy analysis of heat pump performance affected by heat transfer matching characteristics of non-azeotropic refrigerants[J]. CIESC Journal, 2021, 72(4): 2038-2046.

梁坤峰, 冯长振, 王莫然, 董彬, 王林, 刘瑞见. 非共沸工质换热匹配特性影响热泵性能的高级分析[J]. 化工学报, 2021, 72(4): 2038-2046.

Figures/Tables 12

Fig.1 Temperature distribution of non-azeotropic working fluids on heat exchange side

Fig.2 Schematic diagram (a) and T-S diagram (b) of heat pump system with non-azeotropic working fluids

Table 1 Operating conditions

工况	冷却水进口温度（T_w,in）/℃	冷却水出口温度（T_w,out）/℃
工况1	25	40
工况2	25	60

Table 2 Temperature glide of three non-azeotropic mixtures

第一组分的质量分数	滑移温度/℃
第一组分的质量分数	R600/R32 (M1)	R600/R134a(M2)	R245fa/R290(M3)
0.1	0.48	0	0.35
0.2	6.67	1.85	0.96
0.3	17.95	7.43	2.02
0.4	27.58	12.89	3.85
0.5	35.71	16.74	6.95
0.6	42.39	18.66	11.65
0.7	46.96	18.33	17.38
0.8	47.24	15.29	23.05
0.9	36.42	9.15	25.55

Fig.3 COP variation curve of three working fluids under different working fluid mass fractions in condition 1

Table 3 TMD and COP corresponding to different mass fraction of working fluids

参数	M1				M2				M3
参数	0.78	0.88	0.98	1.00	0.66	0.76	0.86	0.96	0.79	0.89	0.99	1.00
TMD	3.56	3.32	2.38	2.62	2.43	2.35	2.14	2.49	2.88	2.92	2.39	2.62
COP	3.35	3.69	4.88	4.28	4.56	4.75	5.17	4.53	3.64	3.74	4.80	4.29

Fig.4 Variation curves of TMD, COP and cyclic temperature difference under different working fluid mass fractions in condition 1

Fig.5 Variation curves of TMD and COP under different working fluid mass fractions in two conditions

Fig.6 Variation curves of TMD, η and heat transfer temperature difference under different working fluid mass fractions in condition 1

Fig.7 Variation curves of TMD and η under different working fluid mass fractions in two conditions

Fig.8 Variation curves of TMD and ε under different working fluid mass fractions in two conditions

Table 4 The parameters in the literature and corresponding TMD

文献	工作流体	P_c/MPa	P_e/MPa	COP	TMD
[28]	W1	1.69	0.60	5.36	2.51
		1.88	0.59	4.68	2.65
		2.09	0.59	4.20	2.76
	W2	1.33	0.46	5.41	2.56
		1.48	0.45	4.77	2.69
		1.65	0.45	4.29	2.89
[29]	Z1	1.160	0.420	5.09	2.13
		1.292	0.420	4.51	2.29
		1.434	0.416	4.01	2.45
	Z2	1.716	0.654	4.97	2.02
		1.898	0.648	4.37	2.16
		2.094	0.642	3.87	2.32
[30]	R134a/R245fa (0.1/0.9)	1.51	0.41	3.94	2.79
	R134a/R245fa (0.2/0.8)	1.76	0.48	3.92	2.83
	R134a/R245fa (0.3/0.7)	2.00	0.56	3.88	2.84
	R134a/R245fa (0.4/0.6)	2.26	0.64	3.77	2.86

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