Efficiency of the Cooling System

st is small enough and heat losses play a significant role. In this case the growth of t/L.st with d takes place. 

The total energy, which is supplied to the liquid from the wall, is equal to the heat flux multiplied by the lateral area of the micro-channel The energy, 

The effect of the heat losses to the inlet on the thermal states of the micro-channel depends mainly on the meniscus position, which is determined by the flow parameters. To characterize this effect, the coefficient of efficiency is introduced it may be defined as the ratio of the energy expended to the liquid vaporization and the total energy supplied to the micro-channel. 

Since the coefficient of efficiency depends on the location of the meniscus, it is different for semi-filled and filled regimes. 

In a steady state two-phase flow in a heated capillary, there is the balance of forces, which act on the liquid and its vapor. The analysis of this balance shows that there are two stable states of the flow. They correspond to the different locations of the meniscus, which separates the liquid and the vapor. The existence of such states 

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Thus, there are two meniscus positions near the edges of the micro-channel, where the heat losses are significant. Between them there is some position, in which these losses are minimal and the evaporation is the most intense. This corresponds to the optimal efficiency of the cooling system. 

The thermal stagnation zone can happen in the lower part of the droplet layer, over which t(z) has almost reached its possible limit, and so there is no cooling of droplets over the lower part of their trajectories. This means that the density of droplets is too high, and the efficiency of the cooling system can be improved by arranging the spraying nozzles to reach a lesser density of droplets. 

Visualizing efficiency makes it possible to dispense with cooling channels that contribute little to heat dissipation from the tool. At other points, repositioning the cooling channels can increase the efficiency of the cooling system. The objective is to achieve uniform temperature distribution at the surface of the mold. 

Vapor-phase coohng reduces the cost of the cooling system, increases heat recovery, and may result in improved engine efficiency. 

Also, the unit costs of electricity and natural gas are 0.09/kWh and 0.45/lherm (1 thenti = 105,500 kJ), respectively. If the coefficient of performance of the cooling system is 3.2 and the efficiency of the furnace is 0.90, determine the net annual cost savings due to installing reflective coating on the windows. Also, determine the simple payback period if the installation cost of reflective film is 20/m . 

The cost of insulation, including installation, is 120/m. Capital charges (see Chapter 6) are 20% per year. The cost of fuel, allowing for the efficiency of the heating system is 8/GJ. The cost of cooling is 5/GJ. Average... 

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