• Energy Research

Abstract In an adsorption chiller, the refrigerant (water) operating pressure is low (0.5–5 kPa) and the cooling power generation of a flooded evaporator is affected by the height of water column. To resolve this issue, we experimentally investigate the performance of a flooded evaporator as a function of water height. The results show an optimum water height equal to 80% of the tube diameter leading to achieve the highest cooling power. Under this condition, the internal and external thermal resistances on the inside and outside of the evaporator tubes account for up to 73% of the overall thermal resistance. To reduce the internal thermal resistance, twisted and Z-type turbulent flow generators are incorporated into the evaporator tubes. The evaporator cooling power shows an increase by 12% and 58% when twisted tape and Z-type turbulators are used at a cost of an increase in the internal pressure drop by 2.5 and 14.5 times, respectively. The twisted tape and Z-type turbulators improve the average specific cooling power of the adsorption chiller by 9% and 47%, respectively. To reduce the external thermal resistance, the outside surface of the evaporator tubes is coated with porous copper. The coated evaporator increases the overall heat transfer coefficient by 1.4 times and improves the specific cooling power of the adsorption chiller by 48% compared to the uncoated tubes.

Abstract In an adsorption chiller, the refrigerant (water) operating pressure is low (0.5–5 kPa) and the cooling power generation of a flooded evaporator is affected by the height of water column. To resolve this issue, we experimentally investigate the performance of a flooded evaporator as a function of water height. The results show an optimum water height equal to 80% of the tube diameter leading to achieve the highest cooling power. Under this condition, the internal and external thermal resistances on the inside and outside of the evaporator tubes account for up to 73% of the overall thermal resistance. To reduce the internal thermal resistance, twisted and Z-type turbulent flow generators are incorporated into the evaporator tubes. The evaporator cooling power shows an increase by 12% and 58% when twisted tape and Z-type turbulators are used at a cost of an increase in the internal pressure drop by 2.5 and 14.5 times, respectively. The twisted tape and Z-type turbulators improve the average specific cooling power of the adsorption chiller by 9% and 47%, respectively. To reduce the external thermal resistance, the outside surface of the evaporator tubes is coated with porous copper. The coated evaporator increases the overall heat transfer coefficient by 1.4 times and improves the specific cooling power of the adsorption chiller by 48% compared to the uncoated tubes.

Abstract This study investigates the performance of a low-operating pressure evaporator using capillary-assisted tubes for adsorption cooling systems (ACS). When using water as a refrigerant in an ACS, the operating pressure is low (

Abstract This study investigates the performance of a low-operating pressure evaporator using capillary-assisted tubes for adsorption cooling systems (ACS). When using water as a refrigerant in an ACS, the operating pressure is low (

Abstract Adsorption cooling systems (ACS) are a viable alternative to vapor compression refrigeration cycles (VCRCs) where low-grade waste heat is readily available. In an ACS, which works with water as a refrigerant, the operating pressure is quite low (∼1 kPa). Under such low evaporation pressures, the height of a water column affects the water saturation pressure and, consequently, its saturation temperature, which can severely affect the performance of an ACS. This makes the design of evaporators of ACS different from those of conventional VCRCs. One practical solution in low pressure (LP) evaporators is to use capillary-assisted tubes. In this study, three enhanced tubes with different fin geometries (fin spacing and fin height), and a plain tube as a benchmark, are tested for different chilled water inlet temperatures. The results show that enhanced tubes have 9.8–21 times lower external convective heat transfer resistances compared to the plain tube. In addition, the enhanced tube with the highest fin height (Turbo Chil-26 FPI) has 33% lower external convective resistance than that with lower fin height (GEWA-KS-40 FPI). The major finding of this study is that up to 89% of the overall thermal resistance in the enhanced tubes is due to the internal convective resistance. This clearly indicates that the main bottleneck in the performance of a LP evaporator is the convective heat resistance inside the tube. Therefore, the internal heat transfer coefficient and internal surface area of enhance tubes should be increased to enhance the performance of the LP evaporator and overall specific cooling power (SCP) of ACS.

Abstract Adsorption cooling systems (ACS) are a viable alternative to vapor compression refrigeration cycles (VCRCs) where low-grade waste heat is readily available. In an ACS, which works with water as a refrigerant, the operating pressure is quite low (∼1 kPa). Under such low evaporation pressures, the height of a water column affects the water saturation pressure and, consequently, its saturation temperature, which can severely affect the performance of an ACS. This makes the design of evaporators of ACS different from those of conventional VCRCs. One practical solution in low pressure (LP) evaporators is to use capillary-assisted tubes. In this study, three enhanced tubes with different fin geometries (fin spacing and fin height), and a plain tube as a benchmark, are tested for different chilled water inlet temperatures. The results show that enhanced tubes have 9.8–21 times lower external convective heat transfer resistances compared to the plain tube. In addition, the enhanced tube with the highest fin height (Turbo Chil-26 FPI) has 33% lower external convective resistance than that with lower fin height (GEWA-KS-40 FPI). The major finding of this study is that up to 89% of the overall thermal resistance in the enhanced tubes is due to the internal convective resistance. This clearly indicates that the main bottleneck in the performance of a LP evaporator is the convective heat resistance inside the tube. Therefore, the internal heat transfer coefficient and internal surface area of enhance tubes should be increased to enhance the performance of the LP evaporator and overall specific cooling power (SCP) of ACS.