Free & Forced Convection Heat Transfer

Experiment 8 - Free & Forced Convection Convection Heat Transfer.doc

EXPERIMENT ON FREE AND FORCED CONVECTION HEAT TRANSFER 8.1 OBJECTIVES To study experimental data for heat transfer in order to evaluate the overall heat transfer coefficients and heat balances for the following cases of heat transfer in a .shell and tube heat exchanger. (a) Natural convection and (b) Forced convection. 8.2 THEORY A basic diagram of a shell and tube heat exchanger is shown in Figure 8.1. Here steam at a temperature of Tv is sent to the shell side at the port A at a rate of W kg/s. The steam transfers heat to a fluid at the tube side .The steam condenses during this process and leaves the shell side at the port B at a temperature Ts. The tube side fluid enters the heat exchanger at C with a flow rate of M kg/s at a temperature Ti and leaves at D at a temperature To. The heat loss QH from the steam can be expressed as QH = W(λ + CpH.(Tv-Ts)) Similarly, the heat gained by the tube side fluid QC can be expressed as QC= M.CpT. (Ti-To) The heat transfer coefficient for the shell side and tube side hH and hc can be estimated using QH = hH .ΔTM and QC = hC. ΔTM .

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Experiment 8 - Free & Forced Convection Convection Heat Transfer.doc

STEAM AT TV ENTER AT PORT A

TUBE SIDE FLUID ENTERS AT Ti

TUBE SIDE FLUID LEAVES AT To

CONDENSED STEAM LEAVES PORT B AT TEMPERATURE TS

FIGURE 8.1 BASIC LAY-OUT OF A SHELL AND TUBE HEAT EXCHANGER
Calculation of the individual heat transfer coefficients involves the following dimensionless numbers: The Nusselt number, Nu . where α= individual heat transfer coefficient [W/m2·K] d = characteristic length [m] (e.g. tube diameter) λ = thermal conductivity [W/m·K] cp = specific heat [J/kg·K] μ = dynamic viscosity [Pas] v = velocity [m/s] ρ = density [kg/m3] The Prandtl number, Pr

The Reynolds number, Re

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Experiment 8 - Free & Forced Convection Convection Heat Transfer.doc

For natural convection one

References: 1. Brodkey, R.S. and H.C. Hershey, Transport Phenomena: A Unified Approach, McGraw-Hill, 1988. 2. Kern, D.Q., Process Heat Transfer, McGraw-Hill, 1950. 3. Levenspiel, O., Engineering Flow and Heat Exchange, Revised Edition, Plenum Press, 1998. 4. McCabe, W.L., J.C. Smith, and P. Harriott, Unit Operations of Chemical Engineering, 5th Edition, McGraw-Hill, 1993. 5. McCabe, W.L., J.C. Smith, and P. Harriott, Unit Operations of Chemical Engineering, 6th Edition, McGraw-Hill, 2001. 6. Mehra, D.K., "Shell-and-Tube Heat Exchangers", Chemical Engineering, July 25, 1983. 7. Standards of Tubular Exchanger Manufacturers Association, 6th Edition, 1978. Page 15 of 15