Application

Question 1

All 2 eq needed to solve HX problems

Answer 1

1. dQ = USdT
2. dQ = Mh C,p,h dTh
3. dQ = Mc C,p,c dTC

(1) - cross flow heat transfer
(2), (3) - infinitesimal heat gained/lost in stream

Question 2

How to solve for total SA of a heat exchanger

Answer 2

1. start with combining X-flow, same flow dQ to find an expression for dS
2. find an expression for Th-Tc where it is only dependent on either Th or Tc
   A+BTc
3. sub into the integral
4. Define the system - where 1 , 2 are each side of HX
5. integrate
6. eliminate 1/B - dividing top and bottom
7. Should use side 2 as final boundary condition
   * T2,T1
   * ΔTh, ΔTc

Should end up with ΔTLm

Question 3

How to get the temperature profile of a heat exchanger either stream.

Answer 3

1. Start with the same process for finding total SA
2. Don’t sub in the boundary condition for side 2
3. Instead, define the S, Th and Tc as a function of x, position along the heat exchanger

Question 4

Assumptions made when doing haemodialysis

Answer 4

Quasi-steady state
1. conc. of blood is well mixed and constant throughout
2. steady state clearance, K

Question 5

What is E

in dialysis

Answer 5

Extraction ratio = actual / max removed

Question 6

What is clearance, K

in Dialysis

Answer 6

vol. of blood fully cleaned / sec

Question 7

How to express rate of removal of solute in blood

dialysis

Answer 7

= K * Ci,b

i.e. vol. cleaned * how much it’s cleaned by

Question 8

How did they deduce the max. removable in E expression

Answer 8

Assume max : Conc. in blood = conc. in dialysate

= Fb * (Ci,b - Ci,d)

Question 9

Mass balance of species in blood

dialysis

Answer 9

Body centred CV
assume conc. in dialysate = 0

Question 10

How to find the rate of transfer (mass/time)

Answer 10

flux(mass/Area time) * SA

mass