Experimental investigations on air side heat and mass transfer phenomena in evaporative condensers (original) (raw)
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Experimental performance comparison between circular and elliptical tubes in evaporative condensers
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For effective design of an air cooled condenser (ACC) the heat transfer coefficients on both sides must be known. The heat transfer coefficient on the air-side is lowest and therefore there is a huge potential for improving an efficiency of ACC. On the other hand the condensation in inclined non-circular tubes is not well documented and the potential of increasing of performance is not known there. This study experimentally examine the air-side heat transfer coefficient.
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In the phase change process, latent heat is transferred and the amount of heat transferred will be excessive high compared to the amount of sensible heat transfer. For that reason, condensation and evaporation processes are the main steps in the refrigeration cycle in order to increase the amount of heat transferred. The main objective of this study is to experimentally and analytically examine overall heat transfer coefficient and to present the effect of water flow and refrigerant pressure on condensation process. For this purpose, a refrigeration system where a water cooled condenser with a heat transfer surface area of 0.075 m 2 was installed. R134a was used as a refrigerant and condenses on the outer surface of the pipe that water circulates through. In this study, experiments were repeated for water mass flow rates of 15, 20, 25, 30 and 35 g/s at constant 7.0 bar condensation pressure. Then, condensation pressures were changed to 6.5, 6.75, 7.0, 7.25 and 7.5 bar at constant wa...
Air-side heat transfer and pressure drop characteristics of accelerated flow evaporators
International Journal of Refrigeration, 2011
Microchannels are likely to be the next heat transfer technology for household refrigerating applications, especially due to their compact design and high heat transfer rate per unit of volume. In contrast to the conventional tube-fin evaporators, the available heat transfer and pressure drop correlations are not well-stablished yet. This study introduces a new microchannel evaporator design to be used in 'nofrost' household refrigerators. The performance of sixteen evaporators prototypes with distinct geometric characteristics were evaluated experimentally in an open-loop wind-tunnel calorimeter facility coming up with data for the overall thermal conductance and the air-side pressure drop data as a function of the air flow rate. Empirical correlations for Colburn j-factor and friction f-factor were devised in terms of the Reynolds number and key compact heat exchanger parameters, being able to predict 90% of the experimental counterparts within ±10% and ±20% error bands, respectively. Furthermore, comparisons against a typical no-frost tube-fin evaporator was carried out with respect to air-side pressure drop and overall thermal conductance, which indicated a promising potentiality of application in household refrigeration appliances.
Evaluation of Evaporative Cooling for Heat Transfer in the Condenser of Window-Air Conditioners
2006
There is a demand for reduced power consumption in the vapor compression refrigeration cycle. Coefficient of performance of window-air conditioners considerably decreases and power consumption increases under very hot conditions. These problems have encouragecl studies aimed at improving the performance of window-air-conditioners by enhancing the heat transfer rate in the condenser. In this article, a new design for application of evaporative cooling in the condenser of * % D ow nl oa de d fr om jc m e. iu t.a c. ir at 1 8: 54 IR D T o n M on da y Ju ly 2 7t h 20 20
Heat Transfer Analysis of Refrigerant Flow in an Evaporator Tube
the paper aim is to presenting the heat transfer analysis of refrigerant flow in an evaporator tube is done. The main objective of this paper is to find the length of the evaporator tube for a pre-defined refrigerant inlet state such that the refrigerant at the tube outlet is superheated. The problem involves refrigerant flowing inside a straight, horizontal copper tube over which water is in cross flow. Inlet condition of the both fluids and evaporator tube detail except its length are specified. here pressure and enthalpy at discrete points along the tube are calculated by using two-phase frictional pressure drop model. Predicted values were compared using another different pressure drop model. A computer-code using Turbo C has been developed for performing the entire calculation
2006
Sensitivity analysis can be used to identify important model parameters, in particular, normalized sensitivity coefficients; by allowing a one-on-one comparison. Regarding design of evaporative coolers, the sensitivity analysis shows that all sensitivities are unaffected by varying the mass flow ratio and that outlet process fluid temperature is the most important factor. In rating evaporative coolers, effectiveness is found to be most sensitive to the process fluid flow rate. Also, the process fluid outlet temperature is most sensitive to the process fluid inlet temperature. For evaporative condensers, the normalized sensitivity coefficient values indicate that the condensing temperature is the most sensitive parameter and that these are not affected by the value of the mass flow ratio. For evaporative condenser design, it was seen that, for a 53% increase in the inlet relative humidity, the normalized sensitivity of the surface area increased 1.8 times in value and, for a 15 8C increase in the condenser temperature, the sensitivity increased by 3.5 times. The performance study of evaporative condensers show that, for a 72% increase in the inlet relative humidity, the normalized sensitivity coefficient for effectiveness increased 2.4 times and, for a 15 8C increase in the condenser temperature, it doubled in value.
International Journal of Thermofluids, 2020
This paper summarises a two dimensional numerical study of the performance of an evaporator of a window type air conditioner. The analysis of the performance of the heat exchanger is done using software ANSYS CFD with finite volume discretization. For the study a couple of commercially available sizes of copper pipes were considered. Six transverse pitch sizes with identical variation between them with an inlet velocity range of 1.5 to 4.0 m/s, the prevalent conditions for Indian window air conditioners were considered as the input data. The objective of the investigation is to understand the effects of transverse pitch variation on Nusselt number, heat transfer, pressure drop and friction factor in a tube bank of an evaporator with seven rows of tubes. The above study provides better understanding of the effect on heat transfer due to variation of transverse tube pitch and velocity of fluid flow under constant surface temperature of the tubes through simulation study. The outcome of the simulation revealed that for lower transverse pitch values heat transfer was lower and as the pitch increased the Nusselt number increased so also was the heat transfer. With the increase in tube size there was corresponding increase in Nusselt number and heat transfer. In the airflow direction, the larger diameter tube performed better as compared to inline smaller diameter tube. For the verification and validation of the outcome from this study were compared with the values derived from existing correlations of the earlier published literature. The simulation values of Nusselt number showed a deviation of 8% with the correlated values which are well within the acceptable range. The information from the study can be used to improve the design and operation of heat exchanger units in window air conditioners.