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44 Nicolae Bara and Marin Bica There are many types of vaporizers, depending on their destination: vaporizers for air cooling; vaporizers for liquids cooling. Correct design and choice of vaporizers are very important for refrigeration systems proper operation and for their efficiency. A wrong sized vaporizer may produce an excessive decrease of the vaporization temperature, and reducing it with every degree corresponds to a reduction in cooling power with approx. 3…4%. This is why the vaporizer can not be dissociated from its liquid supply system. In practice, often a proper rebound refrigerant corresponds to each type of vaporizer. 2. Experimental Research For the chosen vaporizer represented in Fig. 1, measurements were made on the air flow at different velocities. The results are presented in Table 1. In this case the air flow velocity variation was performed with the help of the car speed variator. In this case the air flow velocity variation was performed with the help of the car speed variator. Fig. 1 – The air conditioner vaporizer from a baby-car. Table 1 Variation of the cooled air temperature depending on the flow (tair: 28.4 ° C and 22 o C) Nr. mair [kg/s] t 2 ′ [°C] t 2 ′ [°C] Number of plates Channel width 1 0.081 28.4 21.1 14 0.002 2 0.110 28.4 18.2 14 0.002 3 0.127 28.4 17.1 14 0.002 4 0.142 28.4 15.4 14 0.002 5 0.089 22 18 14 0.002 6 0.117 22 16.2 14 0.002 7 0.132 22 14.3 14 0.002 8 0.147 22 12.8 14 0.002 where t 2 – ambient temperature, ′ t 2 ′ – air temperature at vaporizer outlet. The graph shown in Fig. 2 highlights the known decreasing trend of the temperature at vaporizer outlet, when air velocity (air flow) increases. There are confirmed the conclusions from the specialty literature that the flow becomes turbulent when velocity increases, causing an intensification of heat transfer on
Bul. Inst. Polit. Iaşi, t. LVIII (LXII), f. 4, 2012 45 the air. Taking into account the large differences of values between αair and αlf coefficients and the lowest values obtained on the air flow, research has to be focused on increasing their values in order to increase the overall heat transfer coefficient. The research performed on the vaporizer turns out that an air flow velocity increasing is a solution up to a certain value and then the increasing slope of the heat exchange is negligible. Fig. 2 – Cooled air temperature variation depending on flow. The two curves were built for different ambient conditions, respectively 28.4 and 22 o C. Measurements to determine the air flow were performed using a Kimo-type thermo-anemometer provided by ICMET Craiova. There were measured air temperatures at the vaporizer entry and exit, and the air flow
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