$2.$ Consider an Electrolux refrigerator using NH$3-$H$2$ system. Close to the evap$-$ orator some hydrogen leaks in the pipeline carrying ammonia at the rate $0\mathrm{.}08$ kg$/$s$.$ Comment on the effect on the performance of the evaporator based on the flow regime present as ammonia reaches the evaporator. Take pipe diameter as d $36$ mm$,$ system pressure as $20$ bar and temperature as$15$C and mass flow rate of ammonia as $0\mathrm{.}4$ kg$/$s$.$

$3.$ Water$$air mixture flows in a $2\mathrm{.}5$ cm diameter pipe, vertically upwards at $80$ bar and $250$C$.$ Mass flow rate of water is $0\mathrm{.}13$ kg$/$s and that of air is $0\mathrm{.}02$ kg$/$s$.$ At

a certain point, the air in the pipeline is completely evacuated and the engineer says that since only water must be present, the pressure can be lowered to $39$ bar. Check till what point he is allowed to do so$,$ if the flow regime in the pipeline has to be maintained as before.

$4.$ At low volumetric fluxes of liquid phase, the critical gas velocity at flow reversal point is given by the relation Jg$=0\mathrm{.}9,$ i$.$e$.,$ volumetric flux of gas reaches the value of $0\mathrm{.}9$ m$3/$s$.$ This is also the limit for churn flow. Verify the above statement from Hewitt$$s map for water at $100$C and specify the limits for the volumetric flux of liquid. Take tube diameter as $56$ mm$.$

$5.$ Consider annular flow in horizontal helical coils. It has been observed that two$-$ flow patterns are obtained: one where the liquid phase is forced to the outside of the coil and another where the liquid phase travels on the inside surfaces of the coil. Develop a crude flow map using explanations from the momentum flux considerations for the liquid and the gas phase. Also, illustrate its applicability using an example.

$6.$ Flow maps for liquid metal$-$gas two$-$phase flows are extremely important in Nuclear applications. Consider a nuclear reactor system with NaK$-78$ and nitro$-$ gen flow in the tube of diameter $22$ mm$.$ Mass flow rate is $0\mathrm{.}4$ kg$/$s and the quality is $0\mathrm{.}1.$ Comment on the heat transfer capability under these circumstances. Take

temperature as $700$C$.$

$7.$ In a process heat transfer application $0\mathrm{.}01$ kg$/$s of water at $100$C is required. The quality is $0\mathrm{.}03$ and water flows through a horizontal pipe. Under these conditions, the flow regime is observed to be intermittent which is not desirable. A malfunction in the tube locators lowers the tube by $5$C$.$ Check from Barnea$$s map if it will affect the system seriously. Verify from Taitel and Dukler$$s Map. Take the diameter of the pipe as $1$ in$.$

$8.$ In a pressurized water heater reactor $($PWR$)$ cooling system, light water flows through an $1$ in$.$ diameter pipe at $155$ bar and $315$C with a mass flow rate of $0\mathrm{.}0996$ kg$/$s and quality of $0\mathrm{.}909.$ Obstructions are intended to be used to enhance

the flow heat transfer. However, whether to use central obstructions or peripheral obstructions is to be decided so as to keep the design calculations for the earlier flow regime intact since it affects the whole system. Hence, determine the type of obstruction to be used.

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$9.$ mass flux In hydrogen liquefier, hydrogen is compressed to $100$ bar at $300$ K$.$ As a result, the hydrogen undergoes a phase change and is liquefied. After this, heat needs to be taken away. At a certain point, the quality is $0\mathrm{.}08.$ Determine if this is the right place to take away heat. Take mass flow rate in the tube as $0\mathrm{.}01$ kg$/$s and diameter of tube as $1$ in