You need to select or design a heat exchanger for a waste heat recovery system in cars.
The assignment requires to be submitted in a MS Word or pdf file with 2200-2500 words limit and at least 10 references in Harvard style.
Part 1 – Heat Exchanger selection/design:
Assume that you are part of a product development team that is developing a novel waste heat recovery system to make cars more efficient. One feature of the system is to transfers wasted exhaust heat to the engine oil through a heat exchanger to decrease the friction of the oil, particularly during warm up, however as well during steady state operation at engine loads below wide open throttle. Your task is to choose and source an existing heat exchanger which will be suitable for this application. Even although most driving patterns in a car are highly dynamic you are given most operating conditions as average over the legal fuel consumption drive cycle. In the assignment you require to justify the decisions based on you engineering judgment and by applying the concepts you learned in the heat transfer unit.
The priorities for the new product are as shown below:
1) Safe operation beneath all possible operating conditions at ambient temperatures between - 30 °C and + 50 °C
2) Maximum efficiency of the heat exchanger to be able to realize the maximum possible fuel economy enhancement.
3) Durability of 150,000km (legal necessity for emission relevant components).
4) Low weight to minimize the negative impact of additional weight towards the fuel economy.
5) Small external volume to make it simple to package it in the packed and tight engine compartment.
6) Low cost.
7) Low external temperatures to avoid deterioration, aging or long term damage of close by plastic components.
8) Long term resistance against the fouling.
Operating conditions:
The given operating conditions must be considered in your selection or design process:
A) The test condition is the New European Drive Cycle (NEDC), the duration is 1180 sec.
B) The exhaust gas comprises of corrosive combustion products. The average water content is around 10%.
C) The average exhaust temperature to the heat exchanger is 434 °C throughout the NEDC.
D) The maximum exhaust gas temperature is 625 °C throughout the NEDC.
E) The ambient air temperature is 24 °C throughout the NEDC; this doesn’t change over the test cycle.
F) The start temperature of all engine components inclusive the exhaust gas heat exchanger and the engine oil is as well 24 °C.
G) The average flow rate of exhaust gas is 6.9 g/s.
H) The average oil flow rate is 10 l/min.
I) The average oil temperature is 60 °C.
J) The average vehicle speed is 35km/h; the wind speed is simulated proportionally to the vehicle speed through a vehicle cooling fan.
K) The average exhaust heat flow throughout the NEDC is 4kW.
L) The target exhaust gas temperature after the heat exchanger is to be below 90 °C throughout most parts of the NEDC to be able to utilize the condensation enthalpy of the water as much as possible.
Deliverables:
The given deliverables are needed as the outcome of your development work, independent if you selected an existing heat exchanger or if you designed your own. When some numerical values that might be needed for your calculations are not given in the assignment, you require estimating them and you need to justify such estimations. Whenever you make assumptions you need to clearly articulate the assumptions, cite the source of your assumptions and add up a comment regarding the potential effect of the uncertainty of your assumptions.
a) Material specification that will be used and material thickness.
b) Average efficiency or effectiveness.
c) Overall weight.
d) Outside dimensions.
e) Package volume.
f) Maximum average outside surface temperature throughout NEDC.
g) Maximum average inside surface temperature throughout NEDC.
h) Oil volume in the heat exchanger.
i) Heat needed to warm up the heat exchanger (a lump sum analysis is sufficient).
j) Average heat rejected to the ambient.
k) Effective heat transfer surface.
l) Layout with definition of inlet and outlet for oil and exhaust.
m) Sketch the cross section.
n) Cost (single unit prototype and if mass generated at 100,000 units per year).