Performance Analysis of Domestic Refrigerator with Forced and Natural Convection (original) (raw)
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Heat transfer by natural convection in domestic refrigerators
Journal of Food Engineering, 2004
This paper analyses heat transfer by natural convection in domestic unventilated refrigerators. A literature review of natural convection in an empty cavity, between vertical plates and air, and between a cylinder and air, was conducted in order to gain an insight into the mechanism of heat transfer. A model is proposed in order to quantify heat exchange by convection, conduction and radiation in a typical refrigerator; the predicted mean air temperature and refrigerating capacity are close to the experimental values. Another numerically solved model was carried out in order to estimate the time required to cool warm food which is placed inside the refrigerator. Good agreement was obtained when calculated and experimental temperatures were compared.
Study of House Hold Refrigerator
Domestic refrigerators and freezers are among the most energy demanding appliances in a household due to their continuous operation. Worldwide the no. of consumers is constantly increasing. Refrigerators consume about ¼ th of the total energy consumption in a house. It also accounts to about 1/6 th of greenhouse gas emission. Although, the recent technologies use hydrocarbon as a refrigerant to reduce the greenhouse gas emission; the overall performance enhancement of domestic refrigerator is mandatory to reduce the indirect emissions and the amount of energy consumption. Most of the household refrigerator commonly used, works on vapor compression refrigeration cycle with cop around 1.7. However, some refrigerators use absorption systems, and, in some cases, thermoelectric (Peltier-effect) refrigeration with COP of 0.2 and 0.1 respectively. The refrigerant vapor is compressed by means of compressor to a pressure at which temperature obtained at the end of compression will be more than atmosphere, so that at this high temperature it will reject heat and will get condensed. This condensate is then allowed to pass through a capillary so that the pressure and temperature are lowered. Capillary device acts as throttle. A portion of the capillary tube is usually soldered to the suction line to form a heat exchanger. Whirlpool's insulated capillary technology surrounds the capillary with the super cold gas. Cooling refrigerant in the capillary tube with the suction gas increases capacity and efficiency. The discharge from evaporator will be either dry and saturated or super-heated, which then is sucked by compressor or cycle is completed. Along with above components there is liquid line filter drier [between condenser and capillary] and accumulator [between evaporator and compressor] so that the former will dry the refrigerant so as to remove moisture if at all present to avoid freezing in capillary. The later will not allow liquid refrigerant to pass to the compressor. Classification of Refrigerators-i. Depending upon usage Blood bank refrigerator-Used for storage of blood. [Temp. range 2 to 6 o c.] Mortuary Refrigerator-Used for Storage of dead bodies. [Temp. range 0 to 4 o c] House hold refrigerator-Used for storage of food items and in preparation of ice. Biological refrigerator-Used in hospitals, pharmacies, medical laboratories and serum preservation [ Temp. range 1 to 3 o c ]
Numerical simulation of air flow and heat transfer in domestic refrigerators
This work was carried out in order to study heat transfer by natural convection in domestic refrigerators without ventilation. Only the refrigerating compartment was studied for three configurations: empty refrigerator, refrigerator equipped with glass shelves and refrigerator loaded by product. Both experimental and numerical approaches were used.
International Journal of Refrigeration, 2006
In almost all domestic refrigeratorsefreezers all components are assembled in the same relative position since several years ago. It is also known that the condenser releases heat at high temperatures (first law of thermodynamics) as well as the compressor. This heat is rejected to the environment in almost all practical situations partially by natural air convection. However, part of it is due to thermal radiation that causes an overheating of the refrigeratorefreezer surfaces adjacent to those equipments. As a consequence there are more heat gains to the refrigeratorefreezer through these surfaces and hence higher air temperatures inside. This paper describes how a simple technique can be very useful in order to minimize that part of heat transfer by radiation. The improvement is achieved by placing a radiation shield e a sheet of aluminium foil e over the surfaces close to the condenser and the compressor. For validating this technique a refrigeratorefreezer was monitored with thermocouples for the measurements of the inside air temperatures in two situations: with and without the radiation shield. Results show that with this practice the average inside air temperatures in the refrigeratorefreezer could decrease to about 2 K. An available commercial code was used in order to simulate the air temperature distribution and air velocities inside the refrigerator cabinet in both situations. Results from the experimental apparatus and from simulations show that there is a good agreement between them which validates the experiments carried out.
Heat & Air Flow - Inside a Refrigerator
Epidemiological data from Europe, North America, Australia and New Zealand indicate that a substantial proportion of foodborne disease is attributed to improper food preparation practices in consumers’ homes. Product temperature is a quality and safety-determining factor. It is therefore necessary to fully understand the mechanism of heat transfer and airflow inside a refrigerator. Several numerical studies have been carried out on heat transfer in empty domestic refrigerators (Pereira and Nieckele, 1997; Silva and Melo, 1998; Deschamps et al, 1999). The numerical studies provide knowledge on the temperature and velocity inside the cavity of the refrigerator. Laguerre et al (2007) carried out CFD simulation (Fluent software) on empty and static refrigerator (without a fan). In this study, airflow along the refrigerator walls and temperature stratification along the height are shown. In spite that CFD is a powerful simulation tool; its use is limited because of calculation time and geometry assumptions
Thermal management of machine compartment in a built-in refrigerator
MATEC Web of Conferences
In general a multi-door refrigerator machine compartment comprises of fan, condenser, compressor, control box, drain tray, and drain tubes. The performance of machine compartment depends upon the efficiency of heat extraction or heat exchange from heat generating components such as condenser and compressor. The efficiency of heat exchange can be improved by addressing two major factors, namely (1) Air bypass and (2) Hot air recirculation. The hot air recirculation in the machine compartment for builtin multi-door refrigerator configuration is the focus of this study. The results from Computational Fluid Dynamics (CFD) simulations show that efficiency of heat exchange for built-in application is lower than that for free-standing configuration. Recirculation of hot air and reduction in airflow are the two major factors which contribute towards the variation in machine compartment performance. The CFD simulations were coupled with Partial Factorial Design of Experiment (DoE) approach to systematically investigate the effect of variables such as (a) side gap and top gap between kitchen cabinetry and the refrigerator, (b) the baffle/flap (i.e. back and bottom of machine compartment) on the performance effectiveness of machine compartment. The results of the simulation provided critical design improvement directions resulting in performance improvement. Furthermore, the CFD simulation results were also compared to test data and the results compared favourably.
In-Situ Evaporator Heat Transfer Experiments for Domestic Refrigerators
2000
This paper describes a specially prepared experimental set-up to measure the heat transfer characteristics of evaporators placed inside a domestic refrigerator or freezer. The evaporators can either be of the forced air or natural convection type (optionally integrated into the cabinet wall). The paper discusses the special arrangements needed in this experimental set-up to accurately determine the very low heat flows occurring (from 20 to 80 W). Special attention will be paid to the refrigerant flow control needed to set a certain superheat at the evaporator outlet. It will be shown that the same apparatus can also be used to measure the heat transmission through the cabinet walls. Trial experiments, in which the radiation coefficients of the cabinet walls were varied, influencing the heat transmission coefficients, give an example of the capabilities ofthe system.
Numerical Study of Air Inside Refrigerating Compartment of Frost-free Domestic Refrigerators
2010
This paper is focussed on the study of the temperature and air distribution inside household frost-free refrigerators. It is well known that the correct air and temperature distribution inside the refrigerated chamber is the most important factor that affects refrigerator efficiency. In frost-free refrigerators the cooled air is supplied directly inside the fresh food and vegetable cabinets. Therefore, studies intended to establish the actual air flow and temperature distributions inside these cabinets are relevant in order to improve temperature homogeneity and to reduce energy consumption. The proposed methodology is based on the numerical simulation of the cabinets by means of computational fluid dynamics. Turbulence is solved by means of LES models. Unsteady three-dimensional numerical studies are carried out, simulating the cooling process starting from a uniform warm temperature inside the refrigerator. Furthermore, the influence of inlet and outlet ports location is also investigated.