Cooling Coefficient Of Performance Research Articles

Experimental Analysis of a Polygeneration System: Assessment of the Thermal Sub-System

In this paper, the experimental results of the thermal sub-system of a reliable and cost-effective polygeneration solar system are presented. This polygeneration system produces heating, cooling, and electricity from solar energy, which is used in an existing test building. Heat is generated in four evacuated tube solar collectors (ETCs). The heat may be used for space cooling through a variable geometry ejector (VGE) heat pump. In order to reduce the mismatches between generation and consumption, two thermal storage tanks were added. The performance of a new thermal storage, with 400 L, able to store both sensible and latent heat, was tested. The heating performances of the test building were assessed. Ejector cycle tests were also performed, and the variation of the cooling coefficient of performance (COP) was calculated for different flow rates. For heating, the results showed that the heat storage was capable of heating the test building for 8 h, with temperatures between 22 °C and 26 °C. All results showed that this polygeneration prototype could be capable of meeting the heating and cooling needs when applied to a real building.

Topologically optimized manifold microchannel heat sink with extreme cooling performance for high heat flux cooling of electronics

The manifold microchannel heat sink (MMCHS) has become one of the most promising cooling solutions for high heat flux electronics due to its lower pressure drop and higher temperature uniformity compared to the traditional microchannel heat sink (MCHS). However, the microchannel configurations in previous MMCHS are dominated by parallel, straight microchannels, which would limit their further enhancement in cooling performance. In this work, we designed the microchannel configuration in the MMCHS using a topology optimization method and proposed a manifold microchannel heat sink with a topologically optimized microchannel substrate (MMCHS-TOMS). The thermohydraulic performance of the MMCHS-TOMS was experimentally and numerically studied. The results showed that the microchannel configuration with optimal cooling performance is achieved at a width ratio of inlet to outlet (Win/Wout) = 0.5 and inlet pressure (Pin) = 10 Pa. The MMCHS-TOMS demonstrates a uniform flow distribution in adjacent arrays, and the discrepancies of volumetric flow rate (V̇d) among all inlets are less than 6 %. The MMCHS-TOMS is capable of removing 1570 W/cm2 heat flux under a footprint area of 42 × 10.5 mm2 with a pressure drop of 11.9 kPa, in which the volumetric flow rate and inlet temperature are 3 L/min and 293 K, respectively. With a volumetric flow rate of 1 L/min and a heat flux of 687 W/cm2, the MMCHS-TOMS achieved a maximum cooling coefficient of performance (COP) of 78273, which is the highest value reported up to date. Moreover, oscillations in temperature (mild) and pressure drop (large) are observed in the MMCHS-TOMS when violent boiling occurs; the system stability caused by those oscillations can be suppressed via increasing the volumetric flow rate, although the COP would thus be reduced.

Optimum pressure control with three controllable ejectors of a CO2 multi-ejector refrigeration system

The strict regulations on traditional synthetic refrigerants prompted a strong focus on eco-friendly working fluids including carbon dioxide. Nevertheless, a large throttling loss in CO2 refrigeration leads to an inefficient operation. The introduce of ejector allows for recovering part of expansion work and has positive effect on system efficiency, whereas performance deterioration may be found at off-design conditions. In this study, the design of multi-ejector with three controllable ejectors was proposed to improve the system off-design performance. A detailed experimental analysis on the CO2 multi-ejector refrigeration system was investigated. The impact of various operating conditions on multi-ejector performances including pressure lift, entrainment ratio and multi-ejector efficiency was evaluated. In addition, a comparative study was carried out taking the single-stage compression system with an expansion valve as the baseline. A maximum pressure lift of 656 kPa could be provided. An optimum pressure control (OPC) strategy was proposed and could be used to instruct the practical application in order to maximize the cooling coefficient of performance (COP) at different operating conditions. The cooling COP of multi-ejector system could be improved by 30.69 % by adopting the OPC strategy compared with the baseline.

Numerical study on temperature distribution uniformity and cooling performance of manifold microchannel heat sink

The manifold microchannel heat sink (MMCHS) is a promising design for cooling electronic devices due to its ability to effectively dissipate high heat flux. The structural changes of the heat sink play a crucial role in achieving uniform heat dissipation and optimal cooling performance. In order to enhance temperature distribution uniformity and cooling performance, this study conducted numerical simulations by introducing flow-regulating baffles between the manifold channels and microchannels. Additionally, two different types of diverging/converging manifold channels, namely horizontal (z direction) and vertical (y direction) diverging/converging manifold channels, were examined. The simulations were performed under single-phase conditions with varying coolant mass flow rates, and various parameters such as flow distribution, pressure drop, thermal resistance, temperature uniformity, and overall heat transfer performance were analyzed. The findings indicate that the modified MMCHS with baffles exhibited improved temperature distribution uniformity at the base of the heat sink and reduced average thermal resistance. However, it was observed that the pressure drop increased in all cases. The MMCHS with baffles demonstrated an average increase of 70.68% in microchannel flow distribution uniformity, an average increase of 44.55% in temperature distribution uniformity at the base of the heat sink, and an average increase of 7.67% in cooling coefficient of performance (COP). On the other hand, the MMCHS with diverging/converging manifold channels in the z and y directions showed an average increase of 81.44% and 83.65% in microchannel flow distribution uniformity, and an average increase of 57.71% and 62.13% in temperature distribution uniformity. However, it was noted that the COP decreased by an average of 14.58% and 29.81% for these cases.

Ammonia Adsorption Performance of Zeolitic Imidazolate Frameworks for Cooling.

Promoting the cooling performance of adsorption chillers (ACs) greatly relies on the exploration of high-performance adsorbent/refrigerant working pairs. Ammonia is not only an environmentally friendly refrigerant but also favorable for heat and mass transfer in ACs owing to its large vapor pressure and enthalpy of evaporation. Zeolite imidazolate frameworks (ZIFs) with excellent ammonia stability are identified as a class of potential adsorbents for practical ammonia-based ACs. However, high-performing ZIF/ammonia working pairs with excellent AC performance are still to be developed. In this work, the cooling performance including the coefficient of performance for cooling (COPC) and the specific cooling effects (SCEs) of 26 ZIFs with the same composites but different topologies was evaluated by combining molecular simulation and mathematical modeling. Five high-performing ZIFs with COPC > 0.45 and SCE > 250 kJ/kg were identified, among which gis-ZIF with the highest COPC of 0.51 and lta-ZIF with the highest SCE of 354 kJ/kg both are promising to be synthesized and applied further. Besides, the quantitative structure-performance relationship (QSPR) was extracted that can help quickly identify and design high-performing ZIFs according to their ammonia adsorption isotherms and structural characteristics. Moreover, "S"-shaped adsorption isotherms with high saturation adsorption capacity (>0.2 g/g), suitable step position (0.2-0.4), and relatively low Henry's constant (<1 × 10-5 mol/(kg·Pa)) are more favorable for excellent COPC and SCE. From the perspective of structure characteristics, ZIFs possessing low crystal density (<0.9 g/cm3), high accessible surface area (>2000 m2/g), balanced largest cavity diameter (∼15 Å), and accessible pore volume (∼0.65 cm3/g) are beneficial for high-efficient cooling performance.

Experimental analysis of an integrated system using photovoltaic–thermal and air source heat pump for real applications

To realize zero energy buildings, photovoltaic-thermal (PVT)–ground source heat pump (GSHP) systems are being developed. However, the PVT–GSHP system faces challenges in urban areas or in existing buildings owing to the complicated installation process and high initial cost. To address this problem, this study devised an integrated PVT–air source heat pump (ASHP) system that allows installation in a limited space and reduces the initial cost. Particularly, a real-scale experimental plant was constructed based on a small-scale building to evaluate the performance of the PVT–ASHP system. The measurement data of the PVT–ASHP system was collected using a monitoring system, and the heating and cooling coefficients of performance (COPs) were evaluated. The average heating and cooling COPs of the PVT–ASHP system were 3.54 and 3.31, respectively. The COP of the system improved by approximately 52% compared to the ASHP. The PVT–ASHP system indicated a performance difference of approximately 9% compared to the PVT-GSHP system. Moreover, the initial cost of the PVT–ASHP system was reduced by 44% compared to the PVT–GSHP system. PVT–ASHP systems have economic benefits and are a suitable alternative to PVT–GSHP systems.

Numerical study on thermal and hydraulic performances of a hybrid manifold microchannel with bifurcations for electronics cooling

The rapid growth in heat flux of electronic devices demands effective and energy-saving cooling solutions. A hybrid manifold microchannel (MMC) with bifurcations is proposed in this study to improve thermal performance. Flow and heat transfer characteristics of the hybrid MMC are numerically investigated. Deionized water is used as the coolant and the Reynolds number ranges from 20 to 200. The effects of geometric parameters such as bifurcation length, bifurcation width, secondary channel width, and the ratio of manifold inlet and outlet are studied respectively. The results show that the thermal performance can be improved due to the additional heat transfer area brought by the bifurcation. The shape of the bifurcation was optimized to enhance the overall performance, and the best inlet-to-outlet ratio of the manifold is found to be 3. The thermal resistance of the optimized MMC can be reduced by 43.2 % when compared to the common one at the same pumping power. Besides, a heat flux of 2500 W/cm2 can be removed by the hybrid MMC at a maximum temperature rise of 60 K. Compared to other ones, the proposed hybrid MMC possesses a higher cooling coefficient of performance (COP), and it is proven to be a more energy-saving solution for electronics cooling as the COP of the hybrid MMC can reach beyond 10,000 at the heat flux of 1500 W/cm2.

When Polymorphism in Metal-Organic Frameworks Enables Water Sorption Profile Tunability for Enhancing Heat Allocation and Water Harvesting Performance.

The development of thermally driven water-sorption-based technologies relies on high-performing water vapor adsorbents. Here, polymorphism in Al-metal-organic frameworks is disclosed as a new strategy to tune the hydrophilicity of MOFs. This involves the formation of MOFs built from chains of either trans- or cis- µ-OH-connected corner-sharing AlO4(OH)2 octahedra. Specifically, [Al(OH)(muc)] or MIP-211, is made of trans, trans-muconate linkers, and cis-µ-OH-connected corner-sharing AlO4(OH)2 octahedra giving a 3D network with sinusoidal channels. The polymorph MIL-53-muc has a tiny change in the chain structure that results in a shift of the step position of the water isotherm from P/P0≈ 0.5 in MIL-53-muc, to P/P0≈ 0.3 in MIP-211. Solid-state NMR and Grand Canonical Monte Carlo reveal that the adsorption occurs initially between two hydroxyl groups of the chains, favored by the cis-positioning in MIP-211, resulting in a more hydrophilic behavior. Finally, theoretical evaluations show that MIP-211 would allow achieving a coefficient of performance for cooling (COPc) of 0.63 with an ultralow driving temperature of 60°C, outperforming benchmark sorbents for small temperature lifts. Combined with its high stability, easy regeneration, huge water uptake capacity, green synthesis, MIP-211 is among the best adsorbents for adsorption-driven air conditioning and water harvesting from the air.

Enhanced Water Adsorption of MIL-101(Cr) by Metal-Organic Polyhedral Encapsulation for Adsorption Cooling

Metal-organic frameworks (MOFs) are one of the most promising adsorbents in the adsorption cooling system (ACS) for their outstanding water adsorption performance. Notwithstanding that fact, numerous reports pay more attention to the ACS performance improvement through enhancing equilibrium water uptake of MOFs. However, adsorption cooling performance, including specific cooling power (SCP) and coefficient of performance for cooling (COPC) of MOF/water working pairs, always depends on the water adsorption kinetics of MOFs in ACS. In this work, to increase the water adsorption rate, the preparation of MOP/MIL-101(Cr) was achieved by encapsulating hydrophilic metal-organic polyhedral (MOP) into MIL-101(Cr). It was found that the hydrophilicity of MOP/MIL-101(Cr) was enhanced upon hydrophilic MOP3 encapsulation, resulting in a remarkable improvement in water adsorption rates. Furthermore, both SCP and COPC for MOP/MIL-101(Cr)-water working pairs were also improved because of the fast water adsorption of MOP/MIL-101(Cr). In brief, an effective approach to enhance the water adsorption rate and cooling performance of MOF-water working pairs through enhancing the hydrophilicity of MOFs by encapsulating MOP into MOFs was reported in this work, which provides a new strategy for broadening the application of MOF composites in ACS.

Experimental study on the performance and control strategy of a water-cooled subcooler-assisted carbon dioxide heat pump for combined cooling and heating

Carbon dioxide heat pump is considered a potential low-carbon combined cooling and heating solution. However, there is a strong need for simple methods to improve the energy efficiency of the carbon dioxide heat pump due to the larger throttling losses that result in poor performance. Given this, a compact water-cooled subcooler-assisted carbon dioxide heat pump for combined cooling and heating is designed in this paper. An experimental test platform is built, where experimental investigations are performed to reveal the working performance. Furthermore, a matching control strategy is developed and verified as well. The experiments demonstrated that the adoption of the water-cooled subcooler has significantly improved the cooling performance. The cooling capacity (Q̇c) and cooling coefficient of performance (COPc) are increased by up to 20.2% and 31.5%, respectively. Moreover, the optimal discharge pressure is lowered by 0.5 MPa. However, the heating performance is somewhat degraded, for which the control strategy with the synergistic variation of subcooling degree and compressor rotation speed is developed. The deteriorated heating performance is thus mitigated. The developed control strategy has been verified in practice, and the carbon dioxide heat pump performance could be maintained at the highest possible level. Q̇c and COPc are further improved by a maximum of 40.7% and 37.7%, respectively. The heating and overall coefficient of performance could reach 2.55 and 5.10 at the return water and outlet water temperatures of 40 °C and 75 °C, respectively.

Experimental Study on Effects of Different Water Flow Rates on Heat Transfer Characteristics of Evaporator

Since China set forth the goal of “dual carbon”, studies on heat transfer characteristics of evaporators have been one of the hot spots in the field of refrigeration and heating. This paper conducts an experimental study on the heat transfer performances of evaporators under different flow rates by changing the water flow of the evaporator and condenser. The results shows that on the premise of unchanged water flow of condenser, cooling coefficient of performance (COP) and heat transfer coefficient (HTC) grow with the increases in flow rates of evaporator and temperatures of inlet and outlet water. However, the changes in HTC are relatively smooth; the compressor’s inhalation and expulsion temperatures grow with the increases in water flow rates of the evaporator, and the changes are quite evident. The paper also discusses and analyzes deeply those manifestations, which provides experimental evidence for the experiments and improvement of the evaporator, optimization of evaporator design, and the enhancement of the economic performance of the system.

Numerical and experimental analysis of refrigerating performance for hybrid nanolubricants with sepiolite additives

The use of nanomaterials in various forms and compositions provides the basis for the creation of high-performance structures in their application in many heating and cooling systems. In this study, the lubrication properties of rod-shaped Sepiolite (SP) and its various carbon composites Carbon Black (CB), Multi-Walled Carbon Nanotubes (MWCNT), and reduced Graphene Oxide (rGO) were investigated for the first time in a vapor compression cooling system. The cooling heat transfer performance was compared by analyzing the rheological and thermal behaviors using nanolubricants. The best improvement in cooling Coefficient of Performance (COP) was obtained by using SP-rGO nanoparticles. Compared to Polyol Ester (POE), the cooling performance COP increased by 23.6 % with the addition of SP-rGO. The strategy proposed here is simple and has great potential for producing high-efficiency cooling systems. In addition, the single-phase compressor motor was modeled with Finite Element Analysis (FEA) simulation in the experimental studies, and the simulation results were reported. According to the power loss data obtained from FEA simulation results, a total power loss of 119 W is determined as core losses of 44 W, winding losses of 65 W and frictional losses of 10 W for a 1 HP single-phase compressor motor. Thus, the electrical energy efficiency of the motor is approximately 86 %.

Comprehensive study on EEVs regulation characteristics of vapor-injection CO2 heat pump for electric vehicles

The regulation characteristics of electronic expansion valves (EEVs) are critical to improving the comprehensive energy efficiency of the heat pump system for electric vehicles. In this paper, a vapor-injection transcritical CO2 heat pump system for electric vehicles was first established to experimentally study the impacts of EEV1 and EEV2 openings on the overall system performance. The results show that the cooling capacities of the vapor-injection system are respectively increased by 3.13% / 5.75% with the EEV1’s opening of 15% / 25% and injection ratio of 0.0975 / 0.8305, compared against these of the basic system without vapor injection. As the injection ratio rises, the cooling capacity increment tends to increase while the cooling coefficient of performance (COP) declines from 1.7 to 1.51. Then, the regulation characteristics of EEV1 and EEV2 were quantitively analyzed, indicating that the evaporation pressure is mainly determined by EEV2’s openings. By adjusting EEV1’s opening, the COP of the CO2 vapor-injection heat pump can be maximized at 1.9, with EEV1’s opening at 20% and outdoor/indoor ambient temperature at 0°C / 20°C. When adjusting EEV2’s opening, the maximum injection pressure corresponds to the maximum COP of 1.84, with EEV2’s opening at 65% under 35°C/ 27°C. When the COP reaches the maximum, the refrigerant at the outlet of EEV1 is just saturated liquid under cooling conditions, while it is located in the two-phase region under heating conditions. Besides, the optimal COP regulation strategy of the CO2 vapor-injection heat pump was further formulated based on two modes, as the strategy in the cooling mode differs from that in the heating mode.

An assessment of the potential effect of climate change on renewable hybrid heating and cooling systems

Combating climate change requires a significant reduction of energy use, in particular that used for heating and cooling of buildings. Innovative solutions, such as the hybridization of ground-source heat pump (GSHP)-based heating, ventilation and air conditioning (HVAC) systems with personal comfort systems (PCS) and natural ventilation (NV) can be employed to improve energy efficiency. However, although climate change will alter the need for HVAC and the efficacy of passive solutions, most building energy simulations use historical weather data, and thus, do not consider the effects of climate change. This study focused on the impact of warmer future weather on the performance of eight heating and cooling scenarios, which result from different combinations of heat pump, either air-source (ASHP) or ground-source (GSHP), and PCS and/or NV, in an office building in fourteen cities across the Iberian Peninsula.Building energy simulations confirm that, while heating loads decrease in most cities, cooling thermal demand increases significantly as a consequence of warming due to climate change. The resulting increased energy imbalance increased heat build-up in the ground, reducing the thermal load satisfied by the GSHP. The warmer outdoor air and ground led to lower cooling coefficients of performance (COP) for the ASHP and GSHP, respectively, which, with the increased need for cooling, resulted in electricity needs for heating and cooling increasing significantly.Revised simulations based on decreasing the internal heat load generated by equipment and lighting were carried out to explore measures that could be used to mitigate these climate change impacts. The reduction in internal loads resulted in a noticeable shift in the thermal loads towards the heating demand. This reduced imbalance resulted in a decrease in cooling demand, as well as a lower build-up of heat in the ground, which consequently improved the coverage of the load by the GSHP and increased the cooling COP, resulting in a decrease in electricity needs for heating and cooling of up to 71%, relative to standard internal loads.

Experimental Study on Operating Characteristic of a Combined Radiant Floor and Fan Coil Cooling System in a High Humidity Environment

The combined radiant floor and fan coil cooling (RFCAFC) system is widely used due to its high comfort and large energy saving potential. In this study, as an example, the combined RFCAFC system was studied in a high humidity environment in Jinan, Shandong Province, China. The novelty of the combined RFCAFC system lies in its ability to automatically adjust the water supply temperature of the radiant floor and fan coil in real time according to outdoor meteorological conditions, achieving thermal comfort while eliminating the likelihood of condensation on the radiant floor surface. Days with similar outdoor meteorological conditions were grouped, and the comfort level and hourly cooling performance coefficient (EERh) of different operating strategies for different outdoor meteorological conditions were monitored along with other evaluation indicators. The RFCAFC had good energy efficiency and comfort in a high humidity room environment. This study showed that the indoor vertical air temperature difference ranged from 1.6 to 1.8 °C, which met the ASHRAE55-2017 standard. The radiant floor surface temperature uniformity coefficient (S) fluctuated between 0.7 and 1.0, and the time it took the radiant floor surface temperature to reach 63.2% of the total variability range (τ63) for different operation strategies based on different outdoor meteorological conditions ranged between 4.4 and 4.7 h, which was within the normal range. The proportion of the total cooling capacity contributed by fan coil cooling under low temperature and high humidity (LH), high temperature and low humidity (HL), and medium temperature and medium humidity (MM) were 68.0%, 73.8%, and 71.7%, respectively. Based on this study, the following recommendations for the combined cooling system can be made: (1) When the outdoor humidity is high, the radiant floor system should be turned on early to provide cooling capacity. When the outdoor temperature is high, the fan coil system should be turned on early to reduce the indoor temperature. (2) To reduce energy consumption and achieve efficient operation of the system, the radiant floor system should be continuously operated to maximize its contribution to the cooling capacity, while the fan coil can be operated intermittently. Natural cooling can be integrated to provide additional cooling capacity to the room in the hours preceding occupation (i.e., 7:00–9:00). (3) The operation strategy of the combined cooling system must be able to respond in real time to changes in outdoor meteorological conditions to prevent discomfort in times of extreme heat or humidity.

ANALISA KOEFISIEN UJUK KERJA MESIN PENDINGIN (CHILLER) UNIT 1 PADA POWER HOUSE

Each refrigerant has different characteristic properties which affect the refrigeration effect and the resulting coefficient of performance (COP). A refrigeration machine that works by cooling water is called a refrigeration machine chillers. Chiller is an air conditioner with no cooling system direct. In this indirect cooling system, the refrigeration engine does not instantly cools the air in every room. Refrigeration machine cools water demin first, then this cold demin water is used for cool the air in the room. Cold demin water as cooling medium to reduce the temperature of a wide room at power house (PH) PLTA Musi. The method used in working on this practical work report is:by making observations or observations in the field, conducting interviews (interview) with supervisors and practical work supervisors regarding theoretical data (specification data). In this study, the Cooling Performance Coefficient (COP) was analyzed On Power House (PH) PT PLN (PERSERO) UL PLTA Musi The results of this study get the conclusion, namely: The coefficient of performance (COP) on the machine chiller unit 1 in Power House PLTA Musi by 4.22 is smaller than specification coefficient. This indicates that the cooling system is working properly optimal.

Experimental Study to Analyze Feasibility of a Novel Panelized Ground-Source Thermoelectric System for Building Space Heating and Cooling

A thermoelectric module is a device that converts electrical energy into thermal energy through a mechanism known as the Peltier effect. A Peltier device has hot and cold sides/substrates, and heat can be pumped from the cold side to the hot side under a given voltage. By applying it in buildings and attaching it to building envelope components, such as walls, as a heating and cooling device, the heating and cooling requirements can be met by reversing the voltage applied on these two sides/substrates. In this paper, we describe a novel, panelized, ground source, radiant system design for space heating and cooling in buildings by utilizing the Peltier effect. The system is equipped with water pipes that are attached to one side of the panel and connected with a ground loop to exchange heat between the cold/hot sides of the thermoelectric module and the underground region. The ground loop is inserted in boreholes, similar to those used for a vertical closed-loop Ground Source Heat Pump (GSHP) system, which could be more than a hundred meters deep. Experiments were conducted to evaluate the feasibility of the developed panel system applied in buildings. The results show that: (1) the average cooling Coefficients Of Performance (COP) of the system are low (0.6 or less) even though the ground is used as a heat sink, and thus additional studies are needed to improve it in the future, such as to arrange the thermoelectric modules in cascade and/or develop a new thermoelectric material that has a large Seebeck coefficient; and (2) the developed system using the underground region as the heat source has the potential of meeting heating loads of a building while maintaining at a higher system coefficient of performance (up to ~3.0) for space heating, compared to conventional heating devices, such as furnaces or boilers, especially in a region with mild winters and relatively warm ground.

Increasing the Performance of an Adsorption Chiller Operating in the Water Desalination Mode

The intensive development of the world economy and the expected population growth mean that demand for cooling and water will continue to rise. The use of conventional technologies to meet this demand is associated with an enormous expenditure of electricity, which still comes mainly from non-renewable sources. With the increasing demand for energy, the increasing scarcity of drinking water, and the negative impact of humankind on the environment due to global warming and ozone depletion, intensive research has been carried out to find modern desalination technologies Most of the technologies use electricity for the process of desalination, and over 6% of the world’s electricity is generated from non-renewable sources, thus increasing the emissions of harmful pollutants into the atmosphere. One possibility to reduce emissions is the use of adsorption chillers with desalination function, which allow the production of cooling simultaneously with the process of water desalination. These systems can be powered by low-temperature waste heat from industrial processes or from renewable sources (solar panels) and require little electricity to operate. This paper presents options to improve their performance and increase the production of condensate in the process of desalination of saline water. Moreover, also presented are the results of tests carried out on a two-bed adsorption chiller with desalination function. The aim of the study was to determine the effect of cycle time on the cooling coefficient of performance (COP) and on the production of condensate from water desalination. The obtained results confirmed that increasing the adsorption and desorption cycle time leads to an increase in the COP value of the adsorption chiller, but the efficiency of the desalination process and condensate production decreases with increasing cycle time.

Effect of Metal Additives in the Bed on the Performance Parameters of an Adsorption Chiller with Desalination Function

Adsorption chillers with desalination functionality, being devices characterised by very low electricity consumption, provide an alternative to conventional sources of cooling and water. The option of desalinating water means that the use of a single device enables obtaining two useful products. Adsorption chillers are not widely used at present. due to their low performance characteristics; these are, however, constantly being improved. This paper presents a verification of the possibility of increasing the cooling coefficient of performance (COP) and specific cooling power (SCP) of a laboratory adsorption chiller by optimising the length of cycle times and using a copper additive to silica gel with a mass fraction of 15% to increase heat transport in the bed. The choice of copper among other considered additives was determined by the conclusions from the research on the sorption kinetics of various mixtures, price and availability, and a high thermal conductivity. The device was operated in a two-bed mode aimed at producing cooling. The adsorbate was distilled water. The results were compared with those obtained under similar conditions when the beds were only filled with silica gel. As a result of the testing, it was found that the use of the copper additive with the sorbent increased both the COP and SCP. The tests were performed for different cycle times, of 100, 200, 300 and 600 s. With increasing cycle time COP also increased. In contrast, the specific cooling power increased only up to a certain point, whereafter its value decreased.

Flow thermohydraulic characterization of hierarchical-manifold microchannel heat sink with uniform flow distribution

• Flow uniformity of manifold microchannel (MMC) heat sink is analyzed. • Flow difference between adjacent microchannels is less than 7% in hierarchical-MMC. • Pressure drop of hierarchical-MMC is reduced by 28–32% compared to typical-MMC. • Heat dissipation of 450 W/cm 2 is achieved under heated area of 9 cm 2 in experiment. • Maximum value of cooling coefficient of performance (COP) is obtained to be 19,480. The manifold microchannel (MMC) heat sink has been used for thermal management of high heat flux electronics. Flow maldistribution among microchannels is one of the major hindrances that affect the proper functioning of the typical-MMC ( i.e. , a coplanar design of the manifolds and the inlet/outlet ports) cooling system, which is attributed to the Z-shaped flow of fluid between the microchannels and the manifolds. Herein, a novel hierarchical-MMC heat sink with stacked configuration is proposed, which mitigates flow maldistribution by optimizing the flow path. First, the fluid flow and heat transfer characteristics of the typical-MMC and the hierarchical-MMC are compared through single-phase conjugate simulation. Next, experimental tests are performed on the hierarchical-MMC heat sink fabricated by Selective Laser Melting (SLM) technology under single-phase and subcooled flow boiling conditions. The numerical results indicated that the hierarchical-MMC exhibits a uniform flow distribution, and the difference of percentage of volumetric flow rate in the section plane of the parallel microchannels is less than 5%. Compared with the typical-MMC, the total pressure drop and overall thermal resistance of the hierarchical-MMC are reduced by 28–32% and 7–13% at the volumetric flow rate of 0.12–1.17 L/min, respectively. Moreover, the experimental results verified the accuracy of the numerical simulation and the feasibility of fabricating the hierarchical-MMC through SLM technology. Under subcooled flow boiling condition, a heat dissipation of 450 W/cm 2 is achieved under a footprint area of 30 × 30 mm at the volumetric flow rate of 1 L/min. The maximum value of cooling coefficient of performance (COP) for hierarchical-MMC heat sink is obtained to be 19,480 at the volumetric flow rate of 0.6 L/min and heat flux of 260 W/cm 2 .