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Energy efficiency and the amount of refrigerant in heat exchangers used in cooling systems has recently been an important research subject. In this study, in order to compare and analyze different types of evaporators, industrial refrigerators were designed and in this context, test setups in accordance with TS EN ISO 23953-2 standard were produced. R290 (propane) was used as the refrigerant in the designed system. During the experiment, temperature-pressure measurements were taken at a certain point in the cooling system equipment of the products, which were cooled every minute, and test data were recorded. As a result of the data obtained from the experimental results, while the temperature difference of the air entering and leaving the evaporators was 6.797 in the first system using ½" tube diameter evaporator, it was calculated as 7.052 in the corrugated and hydrophilic coated second system using 3/8" tube diameter. In the experimental setups, the energy consumed in the first and second systems and the masses of R-290 refrigerant were measured as 24.64 kWh, 23.39 kWh and 700 grams, 430 grams, respectively. Consequently, it was calculated that the second system was 5.073% and 38.57% more efficient in terms of energy efficiency and the refrigerant mass used. Coefficient of performance values for the first and second systems were found as 2.807 and 3.013, respectively. [ABSTRACT FROM AUTHOR]

A miniature vapor compression refrigeration system included two heat sinks connected in series (indicated as series system) or in parallel (indicated as parallel system) was built. The performance of the series system was studied and compared with that of the parallel system. The results indicate that the largest cooling capacity of the two systems is about 160 W and the optimal refrigerant charge is about 0.6 M total in the miniature vapor compress refrigeration (VCR) system. There is no relation between the optimal refrigerant charge and the arrangement of the heat sinks. The coefficient of performance (COP) of the series system ranged from 1.81 to 3.22, while the COP of the parallel system was in the range of 1.51–2.92 under the cooling capacity of 100 W. The cooling of the heat sink 2 lag behind that of the heat sink 1 in the serial system, while the refrigerant is difficult to equally distribute in the parallel system. [ABSTRACT FROM AUTHOR]

In this paper, the Computational Fluid Dynamics (CFD) technique is used to investigate the influences of varying cooling loads on the ejector pressure recovery performance in an ejector-based multi-evaporator refrigeration system (EMERS) using R134a as the refrigerant. The performance of pressure recovery in the EMERS reflects the performance of the compression energy saving. The developed CFD model is first validated by actual experimental data from the EMERS. Turbulence model constants are carefully selected in order to minimize the model prediction error. Over 200 different cases are studied using the model to find the effects of varying cooling loads on pressure recovery ratio. The results indicate that pressure recovery ratio is very sensitive to the varying primary and secondary flow cooling loads. The maximum pressure recovery ratio can reach 60% as the cooling loads vary. It was found that in order to keep the system stable, the primary and secondary cooling loads should be maintained within ±5% and ±10%, respectively, in which case the pressure recovery ratio will have a maximum ratio of 32.8%. [ABSTRACT FROM AUTHOR]

Abstract: The effects of the subcooling heat exchanger (SCHX) on the performance of the multi-split variable refrigerant flow (VRF) system with long pipe were investigated in a field test during the cooling season. By varying the refrigerant mass flow rate via the electronic expansion valve, the degree of subcooling was controlled. It was found that VRF system with SCHX improved the cooling performance factor (CPF) about 8.5% under similar outdoor temperature profiles, as compared to the baseline without SCHX. However, when the fraction of total refrigerant that passes through the SCHX was higher than 5.27%, the CPF starts to decrease due to the decreased refrigerant mass flow rate through the evaporators. Employing a SCHX in a VRF system with long pipe was found to be an effective method for improving the system performance and reliability. [Copyright &y& Elsevier]

Abstract: This article presents the concepts of an air-source heat pump for simultaneous heating and cooling (HPS) designed for hotels and smaller residential, commercial and office buildings in which simultaneous needs in heating and cooling are frequent. The main advantage of the HPS is to carry out simultaneously space heating and space cooling with the same energy input. Ambient air is used as a balancing source to run a heating or a cooling mode. The second advantage is that, during winter, energy recovered by the subcooling of the refrigerant is stored at first in a water tank and used subsequently as a cold source at the water evaporator to improve the average performance and to carry out defrosting of the air evaporator using a two-phase thermosiphon. Unlike conventional air-source heat pumps, defrosting is carried out without stopping the heat production. A R407C HPS prototype was built and tested. The basic concepts of the HPS are detailed in part1 of this article . Its performance on defined operating conditions corresponds to the data given by the selection software of the compressor manufacturer. In the present part of this article, the operation of the high pressure control system, the transitions between heating, cooling and simultaneous modes and the defrosting sequence are analysed and validated experimentally. [Copyright &y& Elsevier]

Abstract: Refrigerant and airflow maldistribution in fin-and-tube evaporators for residential air-conditioning was investigated with numerical modeling. Fin-and-tube heat exchangers usually have a pre-defined circuitry. However, the objective in this study was to perform a generic investigation of each individual maldistribution source in an independent manner. Therefore, the evaporator and the condenser were simplified to be straight tubes for the purposes of this study. The numerical model of the R410A system, its verification and an investigation of individual maldistribution sources are presented in this paper. The maldistribution sources of interest were: inlet liquid/vapor phase distribution, feeder tube bending and airflow distribution. The results show that maldistribution reduced the cooling capacity and the coefficient of performance of the system. In particular, different phase distribution and non-uniform airflow distribution reduced the performance significantly. Different feeder tube bendings only caused a minor decrease in performance. [Copyright &y& Elsevier]

This technical note communicates the thermal performance of a modified ten-Ton Refrigerant Direct Expansion (10-TR DX) air conditioning unit into a chiller under actual operating conditions. The modified unit achieved higher COP and cooling capacity compared with conventional DX. The increase in the unit cooling capacity is basically attributed to the enhanced heat transfer coefficient of the Plate-and-Frame Heat Exchanger evaporator. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a novel cooling method of enhancing refrigeration capacity during short time (order of 1min) by storing low-temperature liquid refrigerant. This method actively controls the refrigerant mass flow rate for the evaporator. The compressor of the refrigerator, therefore, does not have to be oversized to cope with intermittent large cooling load of the system. During a short period of time, a higher cooling capacity than that of the steady operation is achieved by the increased mass flow rate of liquid refrigerant. An experimental apparatus was designed and fabricated to validate the proposed cooling methodology. Two reservoirs as temporary sequential storages of the refrigerant were set up before and after the evaporator. Several on/off solenoid valves were installed to control the refrigerant flow. From the experimental results, we confirmed a successful operation of rapid cooling process as designed. This rapid cooling methodology shall be useful for temporarily enhancing the refrigeration capacity in other low-capacity refrigeration systems. The practical system must optimize the design of refrigerant reservoirs to reduce the whole system size. [Copyright &y& Elsevier]

• Flow distribution in an evaporator with 52 circuits was studied experimentally. • Face split design with enlarging header size reduced header ΔP and maldistribution. • Choked flow design of extra capillary tubes avoided liquid sucked into compressor. • Improved system presented even refrigerant distribution with various mass flow rate. • Cooling capacity and COP of the improved system increased by 10.5% and 13.4%. In this paper, the design concept of the face split evaporator with a retrofitted suction header and choked flow in the capillary tubes was adopted to improve a direct expansion air-conditioning system with a designed air flow rate of 20,000 m3/h. The novel design of the direct expansion air-conditioning system was experimentally tested and validated. Face split evaporator reduced the refrigerant pressure drop in the suction header and the choked flow design limited the maximum flow rate across each branch circuit, which both contributed to the uniform refrigerant flow distribution of the improved system. Consequently, the cooling capacity and COP of the improved system was 10.5% and 13.4% higher than the original system. With the refrigerant mass flow rate of the improved system varying from 1.33 kg/s to 2.05 kg/s, the measured cooling capacity ranged 240–350 kW and the ratio of the system COP to the ideal COP of the reversed Carnot cycle with the same evaporating and condensing temperatures maintained at 0.72–0.74. The experimental results demonstrated that the improved system performed a relatively uniform refrigerant flow distribution among the branch circuit of the evaporator regardless of the refrigerant mass flow rate. This study is beneficial to the optimization design of the multi-circuit evaporator for a direct expansion air-conditioning system with a large air flow rate in engineering applications. [ABSTRACT FROM AUTHOR]

The efficient operation of a solar cooling system strongly depends on the chiller behavior under part load conditions, since driving energy and cooling load are never constant. For this reason, the performance of a single stage, hot water driven 30 kW H2O/LiBr-absorption chiller employed in a solar cooling system with a field of 350 m² evacuated tube collector has been analyzed under part load conditions with both simulations and experiments. A simulation model has been developed for the whole absorption chiller (Type Yazaki WFC-10), where all internal mass and energy balances are solved. The connection to the external heat reservoirs of hot, chilled, and cooling water is done by lumped and distributed UA values for the main heat exchangers. In addition to an analytical evaporator model-which is described in detail-experimental correlations for UA values have been used for the condenser, generator, and solution heat exchanger. For the absorber, a basic model based on the Nusselt theory has been employed. The evaporator model was developed, taking into account the distribution of refrigerant on the tube bundle, as well as the change in operation from a partially dry to an overflowing evaporator. A linear model is derived to calculate the wetted area. The influence of these effects on cooling capacity and coefficient of performance (COP) is calculated for three different combinations of hot and cooling water temperature. The comparison to experimental data shows a good agreement in the various operational modes of the evaporator. The model is able to predict the transition from partially dry to an overflowing evaporator quite well. The present deviations in the domain with high refrigerant overflow can be attributed to the simple absorber model and the linear wetted area model. Nevertheless, the results of this investigation can be used to improve control strategies for new and existing solar cooling systems. [ABSTRACT FROM AUTHOR]

The paper describes the successful amalgamation of the thermoelectric and the adsorption cycles into a combined electro-adsorption chiller (EAC). The symbiotic union produces an efficiency or COP (coefficient of performance) more than threefold when compared with their individual cycles. The experiments conducted on the bench-scale prototype show that it can meet high cooling loads, typically 120 W with an evaporator foot print of 25 cm², that is 5 W/cm² at the heated surface temperature of 22°C, which is well below that of the room temperature. The COPs of the EAC chiller vary from 0.7 to 0.8, which is comparable to the theoretical maximum of about 1.1 at the same operating conditions. With a copper-foam cladded evaporator, the high cooling rates have been achieved with a low temperature difference. In addition to meeting high cooling rates, the EAC is unique as (i) it has almost no moving parts and hence has silent operation, (ii) it is environmentally friendly as it uses a nonharmful adsorbent (silica gel), and (iii) water is used as the refrigerant. [ABSTRACT FROM AUTHOR]