Heat liquid side

The apparatus consists of a tube T (Fig. 76) usually of total height about 75 cm. the upper portion of the tube has an internal diameter of about I cm., whilst the lower portion is blown out as shown into a bulb of about 100 ml. capacity. Near the top of T is the delivery-tube D of coarse-bored capillary, bent as shown. The tube T is suspended in an outer glass jacket J which contains the heating liquid this jacket is fitted around T by a split cork F which has a vertical groove cut or filed m the side to allow the subsequent expansion of the air in J. The open end of the side-arm D can be placed in a trough W containing water, end a tube C, calibrated in ml. from the top downwards, can be secured ts shown over the open end of D. 

Sinek and Young present a design procedure for predicting liquid-side falling film heat transfer coefficients within 20% and overall coefficients within 10%. 

The impact process of a 3.8 mm water droplet under the conditions experimentally studied by Chen and Hsu (1995) is simulated and the simulation results are shown in Figs. 16 and 17. Their experiments involve water-droplet impact on a heated Inconel plate with Ni coating. The surface temperature in this simulation is set as 400 °C with the initial temperature of the droplet given as 20 °C. The impact velocity is lOOcm/s, which gives a Weber number of 54. Fig. 16 shows the calculated temperature distributions within the droplet and within the solid surface. The isotherm corresponding to 21 °C is plotted inside the droplet to represent the extent of the thermal boundary layer of the droplet that is affected by the heating of the solid surface. It can be seen that, in the droplet spreading process (0-7.0 ms), the bulk of the liquid droplet remains at its initial temperature and the thermal boundary layer is very thin. As the liquid film spreads on the solid surface, the heat-transfer rate on the liquid side of the droplet-vapor interface can be evaluated by... 

The heats of main and side reactions are calculated by Equation 6 for the whole liquid inventory. For the main reaction the heat is about 300 J/g. The formation of propionic acid gives the maximum heat of side reaction which is about 1000 J/g. The most dangerous chemical in this process is carbon monoxide which appears in the reaction section. As a construction material stainless steel and Hastelloy are both needed. Hastelloy gives the score value 2. Most dangerous chemical interaction may appear between methanol and hydriodic acid in the reaction section resulting heat formation and even a fire, which gives the score 4. 

The gas film coefficient is dependent on turbulence in the boundary layer over the water body. Table 4.1 provides Schmidt and Prandtl numbers for air and water. In water, Schmidt and Prandtl numbers on the order of 1,000 and 10, respectively, results in the entire concentration boundary layer being inside of the laminar sublayer of the momentum boundary layer. In air, both the Schmidt and Prandtl numbers are on the order of 1. This means that the analogy between momentum, heat, and mass transport is more precise for air than for water, and the techniques apphed to determine momentum transport away from an interface may be more applicable to heat and mass transport in air than they are to the liquid side of the interface. 

The values of the film coefficient for liquids without phase change are usually larger than those for gases, by one or two orders of magnitude. Nonetheless, the liquid-side heat transfer resistance may be the major resistance in an equipment heated by saturated steam. Film coefficient for liquids without phase change can be predicted by correlations such as those in Equations 5.8a, 5.12a, or 5.13. 

Note that in a kettle reboiler, the bottoms product level control valve does not control the level in the tower it controls the level on the product side of the reboiler only. The liquid level on the boiling or heat-exchanger side of the kettle is controlled by the internal overflow baffle. But what controls the tower-bottom liquid level ... 

On heating the bent side-arm, the heated liquid circulates and raises the temperature of the sample in such a way that no stirring of the bath liquid is required. 

What Controls Mass/Heat Transfer Liquid or Gas Transfer or Bypassing Either gas side or liquid side of the interface can be controlling. 

Absorption of hypochlorous acid into water, a liquid-side mass transfer-limited process, showed HTU values as low as 4 cm, with a strong dependence on liquid-flow rate. Heat of absorption removal was identified as a potential issue with absorption in rotating beds (9). 

The type of heat exchanger to be selected depends primarily on the type of fluids involved, the size and weight limitations, and the presence of any phase-change pmetsses, For example, a heat exchanger is suitable to cool a liquid by a gas it the surface area on the gas side is many limes that on the liquid side. On tile other hand, a plate or shell-and-tube heat exchanger is very suitable for cooling a liquid by another liquid. 

In Figure 3, heat transfer coefficients are shown for n-pentane--C02 at 8.9 MPa and bulk fluid CO2 mole fractions of 0.830 on the liquid side of the LOST, 0.865 precisely at the LOST, and 0.876 on the vapor side. For comparison, we also show results for pure carbon dioxide at the same bulk temperature and pressure. A similar set of results is shown for n-decane--C02 for each of two pressures in Figures 4 and 5. In Figure 4, at 10.4 MPa, the LOST of 325 K occurs at a CO2 mole fraction x of 0.93 0.02 according to our Peng-Robinson fit of the phase equilibrium data. Thus, only the results for x - 0.973 are clearly on the vapor side of the LOST and only those for x - 0.867 are on the liquid side. In Figure 5, for 12.2 MPa, the LOST has shifted slightly to x - 0.91 + 0.02 and T -335 K. Therefore, we expect the data for x - 0.940 to now be on the vapor side. 

The most striking feature of these results is the steep rise in the heat transfer coefficient for the n-decane--CO2 results at x -0.973 at both pressures. This rise coincided in both cases with the onset of the condensation process as we observed droplets or streamers falling from the test section. In all but the n-decane-CO2 mixture of x - 0.867 we saw some form of dense material falling from the test section, but it was not always clear whether this was an immiscible phase the appearance was often more like that of density schlieren. We offer no explanation for the fact that, in the n-pentane--C09 results, the liquid side heat transfer coefficients are greater than for the vapor side in contrast to the n-decane--CO2 system, but we stress that the vapor side condensation results for the former are still "enhanced in the sense described below. 

The heat-transfer coefficient expresses the facihty of heat flow for a particular design and operation. The overall resistance (l/U) is the sum of the resistances to heat transfer on the steam side, on the liquid side, and across the tube wall ... 

The method has been applied to absorbers (Khoury, 1980), where all heat duties, side draws, and all feeds except the liquid feed at the top of the column and the vapor feed at the bottom are set to zero. The rates of change of the component molar holdup and total energy on a stage may be broken down into liquid and vapor contributions (subscripts j and i are dropped in the rates of change terms for simplicity) ... 

A wall separates a gas from a liquid. The temperature of the gas, Tg, is different from that of the fluid, T,. It is proposed to increase the heat transfer between the gas and the liquid by adding fins to either the gas side or the liquid side. To which side must the fins be added for the best result Data Brass wall, k = 100 W/m-K, rectangular brass fins, 1 mm thick, 2.5 cm long, and spaced 2 mm apart. The gas-side and the liquid-side coefficients of heat transfer are hg = 10 and hi = 1,000 W/m2 K, respectively. 

Liquid-side coefficients. The liquid-side coefficient depends to a large extent on the velocity of the liquid over the heated surface. In most evaporators, and especially those handling viscous materials, the resistance of the liquid side controls the overall rate of heat transfer to the boiling liquid. In natural-circulation evaporators the liquid-side coefficient for dilute aqueous solutions is between 1500 and 3000 W/m -°C (300 and 600 Btu/ft -h- F). The heat flux may be conservatively estimated for nonfouling solutions from Fig. 15.13. 

Forced circulation gives high liquid-side coefficients even though boiling inside the tubes is suppressed by the high static head. The liquid-side coefficient in a forced-circulation evaporator may be estimated by Eq. (12.32) for heat transfer to a nonboiling liquid if its constant 0.023 is changed to 0.028. ... 

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