(Pdf) effects of condensate and initial formation of thin frost layer on evaporator coil performance of room air-conditioners gas and sand

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This study investigated experimentally and theoretically, how condensate and initial formation of a thin frost layer on thesurface of the evaporator affects the evaporator performance of room air-conditioners compared to dry coil conditions. The theoretically obtained results were validated with the measured values in both wet and initial frost formation conditions and a good correlation t gas terengganu was found. The results indicated that, at the same range of change in face velocity value, the total conductivity of a dry coil (UA) dry is increased by 38.8%. However, when it is combined with an increase in latent heat to the evaporator total cooling capacity ratio value (Qlat/Q) of 10.6%, the total conductivity of wet coil (UA) wet is 45.4%. These results clearly indicate that the evaporator coil is characterized by higher performance under wet conditions compared to dry coil conditions. The results also show that the total conductivity after initial formation of a thin frost layer (UA) Fr has a higher value by about 8.2% than the dry coil condition. Moreover, the degradation in the evaporator coil performance underthin frost with a thickness up to one mm is only about 6.7%.

The present study proposes a new reduction method to calculate the heat and mass transfer characteristics of the wavy fin-and-tube heat exchangers gas vs electric water heater under dehumidifying conditions. For fully wet conditions, the sensible heat transfer and mass transfer characteristics are relatively insensitive to the inlet relative humidity. The heat gas emoji meaning and mass transfer performances show appreciable influence of fin spacing at 1-row configuration. Both the heat and mass transfer performances increase when the fin spacing is reduced. However, the difference becomes less noticeable when ReDc 3000. For 1-row configuration, larger wave height shows much larger difference with the fin spacing. However, the effect of inlet conditions and geometrical parameters on the heat and mass performance becomes less significant with the rise of number of tube rows. Test results show that the heat and mass transfer analogy is roughly applicable (the ratios of hc,o/hd,oCp,a are in the range 0.6–1.1, and is insensitive to change of fin spacing). The correlations are proposed to describe the heat gas turbine and mass transfer characteristics. These correlations can describe 94.19% of the jh factors within 15% and 83.72% of the jm factors within 15%. Correspondingly, 93.02% of the ratios of hc,o/hd,oCp,a are predicted by the proposed correlation within 15%.

The present study proposes a new reduction method to calculate the heat and mass transfer characteristics of the wavy fin-and-tube heat exchangers under dehumidifying conditions. For fully wet conditions, the sensible heat transfer and mass transfer characteristics are relatively insensitive to the inlet relative humidity. The heat and mass transfer performances show appreciable influence of fin spacing at 1-row configuration. Both the heat and mass transfer performances increase when the fin gas variables pogil spacing is reduced. However, the difference becomes less noticeable when ReDc 3000. For 1-row configuration, larger wave height shows much larger difference with the fin spacing. However, the effect of inlet conditions and geometrical parameters on the heat and mass performance becomes less significant with the rise of number of tube rows. Test results show that the heat and mass transfer analogy is roughly applicable (the ratios of hc,o/hd,oCp,a are in the range 0.6–1.1, and is insensitive to change of fin spacing). The correlations are proposed to describe the heat and mass transfer characteristics. These correlations can describe 94.19% of the jh factors within 15% and gas knife 83.72% of the jm factors within 15%. Correspondingly, 93.02% of the ratios of hc,o/hd,oCp,a are predicted by the proposed correlation within 15%.

The objectives of this study are to develop frost maps for two different surfaces having two different hydrophilic characteristics and to find ambient conditions associated with the formation of frost structures. Test samples with two different surfaces having dynamic contact angle (DCA) of 23° and 88° were installed in a wind tunnel and exposed to a humid airflow. Frost structure is observed with a visualization system in the operating conditions gas bloating pain of household refrigerator: airflow temperature in the range of +10–20 °C, humidity in the range of 2.64–9.36 g/kg′, Reynolds number in the range of 7000–17,000 and cold plate temperature in the range of −11.6 to −28.4 °C. As results of this study, frost structures are classified and frost maps are proposed for two different surface hydrophilicities. Surface with low DCA (23°) shows lower frost thickness and higher frost density than that with high DCA (88°). It was found that frost structures on surfaces with different DCA are similar. However, low DCA surface at low humidity provides 20–30% denser frost formation due to the shift of areas with different structures.

In this paper a model for compact evaporators and a gas has no volume condensers is presented. The flow along a channel of a compact HE is considered to be 2-D and split into separated 1-D paths. Then, every 1-D flow path is discretised in as many elements as required. First, both fluid flow evolution along the heat exchanger are calculated through the integration of the 1-D conservation equations for single or two phase flow, assuming that wall temperatures are known. This calculation is performed through an explicit finite volume scheme, following the flow path. Once the temperature field for both fluids is calculated, then, the wall temperatures are obtained from the integration of the wall energy equation by means of an explicit scheme again. Then a new iteration starts till convergence throughout the HE is obtained. The presented method has proven to be very robust and very fast, being able to take into account local variation of properties and coefficients, and also include the calculation of longitudinal conduction.

A quasi-steady finite-volume model was developed for modeling a plain-fin-round-tube heat exchanger under frosted conditions. It was validated grade 9 electricity test by comparing with the wet-and-dry surface experimental observations (medium and low temperature gas used in ww1 applications) of total, sensible and latent heat transfers, air-side pressure drop, and frost deposition. In general good agreement was obtained between the model predictions and experimental observations within the range of experimental uncertainty. The results demonstrate that at one time step correlations for frost density and conductivity can be combined with j and f-factor correlations and heat and mass transfer equations to predict frost distribution patterns which in turn can be used at the next time step to update the local fin thickness used to calculate heat and mass transfer and air-side pressure drop. The model could be further extended to simulate direct expansion evaporators with varying operating conditions and variable heat exchanger geometry.

An oxide electrode replacing Ni/YSZ anode for a solid oxide fuel cell (SOFC) is desirable to reduce the carbon deposition under carbonaceous fuel. If this oxide material can simultaneously work as cathode, it will increase the simplicity and stability of an SOFC stack as in a symmetrical SOFC. However, the current oxide electrodes for symmetrical SOFCs are mostly p-type oxides showing compromised … [Show full abstract] conductivity in reducing atmosphere, dictating a thin gas stoichiometry formula anode to reduce the ohmic loss. On the contrary, an n-type oxide showing superior electronic conduction in anode chamber will allow a thick anode support, giving room to a thin electrolyte and cathode to reduce the ohmic loss and the diffusion-related loss on the cathode side, respectively. A novel material Fe0.5Mg0.25Ti0.25Nb0.9Mo0.1O4–δ (FMTNM) with cations distributed randomly, based on n-type FeNbO4, is studied as both r gasquet tennis cathode and anode for an SOFC. This material synthesized in ambient air was stable in Ar-5% H2 at 750°C and showed higher electrical conductivity in reducing atmosphere than in air. It was the first demonstration using an n-type oxide for both cathode and anode due to the conductivity arising from Fe²⁺/Fe³⁺ and Mo⁵⁺/Mo⁶⁺ transition. Read more