More Ideas for Compact Double Pipe HXs P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Ideas for Creation of Compact HX!!!

Helical Double-tube HX

Secondary Flow in Helical Coils The form of the secondary flow would depend on the ratio of the tube diameters and other factors. A representative secondary flow pattern is shown below: Thirdly, this configuration should lead to a more standard approach for characterizing the heat transfer in the exchanger. The ratio of the two tube diameters may be one of the ways to characterize the heat transfer.

Heat Transfer in Helical Tubes Acharya et al. (1992, 2001) developed the following two correlations of the Nusselt number, for Prandtl numbers less than and greater than one, respectively.

Heat Transfer in Helical Annulus  Nusselt numbers for the annulus have been calculated and correlated to a modified Dean number.  The modified dean number for the annulus is calculated as it would be for a normal Dean number, except that the curvature ratio used is based on the ratio of the radius of the outer tube to the radius of curvature of the outer tube, and the Reynolds number based on the hydraulic radius of the annulus.  Thus the modified Dean number is:

Helical Coils: Laminar flow De is Dean Number. De=Re (a/R) 1/2. Srinivasan et al. (7 < R/a < 104): Manlapaz and Churchill: Correction for vp:

Helical coils: turbulent flow

Classification of Heat Exchangers Creation of Variety in Anatomy of Heat Exchanger!!!

Creative Ideas for Techno-economic Feasibility of a HX. For a viable size of a HX: How to maximize Effective area of heat communication?. How to maximize Overall Heat transfer coefficient? How to modify the effective temperature difference?

Heat Exchanger : An Effective Landlord Creates a housing for both donor and Receiver. How to accommodate both in a single housing? Space Sharing & Time sharing Space sharing: Donor and Receiver are present always. Develop partition(s) in the house(HX). Time Sharing : Donor And Mediator for sometime and Mediator and Receiver for sometime : Repeat! Time Sharing : Regenerators Space Sharing : Recuperators Central Limit Theorem : It is impossible to have time and space sharing in one system.

A Train of External HXs in A Power Plant

S A B 0 D i i-1 C T T-s Diagram of A Modern Power Plant

Train of Shell & Tube HXs.

DCGSC DC GSC

Sequence of Energy Exchange from Flue Gas to Steam FLUE GAS PLATEN SH PENDENT SH COVECTIVE SH ECONOMIZER RH EVAPORATOR

Fuel Power Furnace absorption Platen SH Final SH LTSH Reheater Economizer Combustion LossesC & R losses Hot Exhaust Gas losses ~400 0 C

Gas Temperatures Platen Super Heater: Inlet Temperature: C Outlet Temperature: C Final Super Heater: Inlet Temperature: C Outlet Temperature: C Reheater: Inlet Temperature: C Outlet Temperature: C Low Temperature Super Heater: Inlet Temperature: C Outlet Temperature: C Economizer: Inlet Temperature: C Outlet Temperature: C Steam Temperatures Platen Super Heater: Inlet Temperature: C Outlet Temperature: C Final Super Heater: Inlet Temperature: C Outlet Temperature: C Reheater: Inlet Temperature: C Outlet Temperature: C Low Temperature Super Heater: Inlet Temperature: C Outlet Temperature: C Economizer: Inlet Temperature: C Outlet Temperature: C

Design Calculate d 1Adiabatic Flame Temp (K) FEGT ( 0 C) Platen SH-I Outlet ( 0 C) Platen SH-II Outlet-I outlet ( 0 C) RH 3rd & 2nd outlet ( 0 C) RH 1st Stage outlet ( 0 C) Economiser outlet ( 0 C) APH Outlet ( 0 C) Flue Gas Temperature At different regions of Furnace:210 MWe)

The concept of Time Sharing At any time: The overall heat transfer coefficient, U OR At stead operation: OR

Stockholm 1920 The Ljungström Air Preheater

Economic Impact of the Landmark The use of a Ljungström Air Preheater in a modern power plant saves a considerable quantity of fuel. So much that the cost of the preheater is generally recovered after only a few months. It has been estimated that the total world-wide fuel savings resulting from all Ljungström Air Preheaters which have been in service is equivalent to 4,500,000,000 tons of oil. An estimate shows that the Ljungström Air Preheaters in operation annually saves about $30 Billion US. The distribution of thermal power capacity in which Ljungström Air Preheaters are installed over the world is shown in the table below.