NOVELTY - A flooded heat exchanger (24) has a vessel having a process portion and a heating fluid portion separated from the process portion, a heat fluid inlet (36), a heat fluid outlet, a process liquid inlet (28), a control valve (22), a process gas inlet (32), a process vapor outlet (40), and a level control device (26).    USE - In system for facilitating calculation of steam-carbon ratio in reformers or vaporizers (claimed), and for preheating steam and/or hydrocarbon gas for reformer or vaporizers.    ADVANTAGE - By introducing natural gas into heat exchanger in form of small bubbles, the area of contact between water and natural gas is maximized, thus the efficiency of humidification of natural gas is increased and efficiency of heat exchanger is also increased. The system for facilitating calculation of steam-carbon ratio, allows the operator to determine exact amount of water entering the reformer, regardless of temperature and pressure fluctuations in the heat exchanger. Since a level sensor is provided external to the heat exchanger, the system is less susceptible to minor fluctuations in water level caused by boiling or condensation of water. The level control system maintains water level in the heat exchanger at a constant level. Since the system maintains constant water level in the heat exchanger, the system facilitates accurate calculation of steam-carbon ratio in the reformer. By knowing the exact amount of water entering the reformer, the operator accurately calculates and controls the steam-carbon ratio. Thus, the efficiency of the system is increased and harmful emission from the reformer is decreased.    DETAILED DESCRIPTION - A flooded heat exchanger has a vessel portion having a process portion and a heating fluid portion separated from the process portion, a heat fluid inlet, a heat fluid outlet, a process liquid inlet, a control valve, a process gas inlet, a process vapor outlet, and a level control device. The vessel portion facilitates heat transfer between the process portion and the heating fluid portion. The heating fluid inlet directs the heating fluid to the heating fluid portion. The heating fluid outlet removes heating fluid from the heating fluid portion. The process liquid inlet directs the process liquid to the process portion. The control valve controls the amount of process liquid entering the process portion. The process gas inlet directs process gas to the process portion and is provided below a desired process liquid level in the process portion such that process gas entering the process portion bubbles through at least some process liquid. The process vapor outlet removes process vapor from the process portion and is provided above desired process liquid level. The level control device is fluidly coupled to the process portion. Portion (I) of level control device communicates with an upper location on vessel portion above desired process liquid level. Portion (II) of level control device communicates a lower location on vessel portion below desired process liquid level. The level control device operates a control valve to maintain an actual process liquid at least close to desired process liquid level.    INDEPENDENT CLAIMS are also included for:    (1) system (10) for facilitating calculation of steam-carbon ratio in reformer or vaporizer (12) which has the flooded heat exchanger. The heat exchanger further has a water meter for calculating amount of water entering the process portion. The level control device is operated with a control valve to maintain water level in process portion at constant level, such that reading on water meter provides amount of steam generated by the heat exchanger to facilitate calculation of steam-carbon ratio; and    (2) method of determining amount of steam entering reformer or vaporizer to facilitate calculation of steam-carbon ratio in the reformer or vaporizer which involves providing the heat exchanger to supply steam to reformer or vaporizer. A water meter is provided to register the amount of water entering the heat exchanger. Water level in heat exchanger is maintained constant during operation. A register on water meter is read to determine the amount of water entering the heat exchanger during operation. The steam-carbon ratio in reformer or vaporizer is calculated based on the reading of the water meter, knowing that amount of steam generated by heat exchanger during operation is equal to the amount of water provided to heat exchanger during same period.    DESCRIPTION OF DRAWING(S) - The figure shows the flow diagram of the system for facilitating calculation of steam-carbon ratio in the reformer.    system for facilitating calculation of steam-carbon ratio (10)    reformer or vaporizer (12)    control valve (22)    flooded heat exchanger (24)    level control device (26)    process liquid inlet (28)    process gas inlet (32)    heat fluid inlet (36)    process vapor outlet (40)    by-pass line (44)