A two-stage deep freezing chemisorption cycle driven by low-temperature heat source

Abstract

A two-stage chemisorption cycle suitable for deep-freezing application driven by low- temperature heat source was proposed. Through two-stage desorption processes, the two-stage cycle can break through the limitations of the heating temperature and ambient cooling temperature. The two-stage cycle based on CaCl₂/BaCl₂-NH₃ working pair can utilize the heat source with a temperature of above 75°C, and simultaneously realize deep-freezing all the year round. Experimental results and performance prediction show that the adsorption quantity of calcium, theoretical coefficient of performance (COP) and optimized specific cooling power (SCP) of the CaCl₂/BaCl₂-NH₃ chemisorption system are 0.489 kg/kg (salt), 0.24 and 120.7 W/kg, when the heating temperature, ambient cooling temperature, pseudo-evaporating temperature and mass ratio of reacting salt and expanded graphite are 85, 30, -20, and 4∶1, respectively.

Key words： adsorption; freezing; desorption; heat source

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Grant No. 50806043) and National 100 Outstanding Ph.D. thesis Foundation in China.

Notations

COP	Coefficient of performance
mba	Mass of BaCl2/kg
mca	Mass of CaCl2/kg
p	Equilibrium reacting pressure/Pa
pc	Condensing pressure/Pa
pe	Evaporating pressure/Pa
peq	Equilibrium pressure for desorption process between CaCl2 and BaCl2 reactors/Pa
pm	Equilibrium pressure for two-stage desorption processes/Pa
SCP	Specific cooling power per kilogram of adsorbent within each adsorber/(W·kg-1)
T	Temperature of adsorbent/K(°C)
Ta	Adsorption temperature/K(°C)
Tac	Adsorption temperature of chemical adsorbent/K(°C)
Tc	Ambient cooling temperature, condensing temperature/K(°C)
Te	Pseudo-evaporating temperature/K(°C)
Tg	Desorption temperature/K(°C)
Tgc	Desorption temperature of chemical adsorbent/K(°C)
Th	Heating temperature/K(°C)
Δxca	Adsorption quantity of CaCl2/(kg·kg-1)
Δxba	Adsorption quantity of BaCl2/(kg·kg-1)

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