Question

#1. To reduce nitrogen oxide emissions from a diesel engine, one commonly used strategy is exhaust gas recirculation (EGR). In a stack-type EGR cooler, exhaust gases flow through tubes with a rectangular cross-section (4 mm x 6 mm). In each tube, the mass flow rate of exhaust gases is 0.0001 kg/s; the gases enter at 140°C while the inner surface of each tube is maintained at 80°C due to water being circulated as a coolant. The length of the tube is 135 mm. In this preliminary analysis, assume that the exhaust gases can be modeled using air properties at 1 atm. d) a) Is the flow in the tube laminar or turbulent? Is the boundary layer developing or fully developed? Justify your answers. (Re = 883) b) Estimate the convection heat transfer coefficient between the exhaust gases and the inner surface of the tube. (32-36 W/m²-K) c) What is the exit temperature of the exhaust gases leaving the EGR cooler? (103-105°C) Because the exhaust gas temperature changes along the tube length, the driving force for convection heat transfer is not constant. What is the log mean temperature difference? (39. 40°C) e) Fouling can be a problem in an EGR cooler due to the formation of particulate matter and hydrocarbon deposits on the tube surfaces. What will happen to the exit temperature of the exhaust gases as the deposits accumulate (e.g. Te will be less than, equal to, or greater than 103-105°C)? No calculations are necessary, but explain your answer.

Answer 1

In this solution i have using the standard properties of Air at 1 atm pressure , T = 140 degree celcius from trusted sites. Therefore the answer i found after calculation has slightly different values as compared to the answer mentioned behind the above questions .

so kindly considered it during review of given anwer.
Rp = 4.8778 X 0.0048 2.745x10-5 852,9486 = 2300 So, laminage flow It is fully developed laminace flow through pipes as the < 2800). In felly developed claninas flow 6x + fac for damnar Pipe flow ñz 0.664 Rella bella for all at larm 2140°C z pe= 0.7041 ñ z 0.664 x(852-9486)*x (0-2011) " 1ñ 17.252 61 mod ke 7 © considering consta wall Mempercetare conditions- oz hA (Tw-Tbi) z in GP (Too-Tbi) whore, Az Scoface Area of Rectangular pipe ₂ berimeter x lengin of Pipe » 0.0d x 0.135 = 0.0027 m² 1 hut this value in above equation 17.254 x 0.0007x (80-140) = 0.000181.014 (760-14) using cp Value 1:014 kolage at 140°c jou air trit fempereroe T6. z 112.4376 of exhaust gat

d) for dog mean temp difference 140°C 1 12.437°C Boto 2 32.437 077260°C * 276 - 80 sich IMTD z logarthnic Mean temperesheree difference IMTD : антр ? ATS Is ATO ATIN » (то) ATD Go - 32:437 Un / bo 32.433 - 44.8150 C IMTD