DF Research project meeting 21/7/10

Desert Fridge Research Project meeting minutes 21/7/10

Attendance (Skype): Muddassar Rashid (MR), Qasid Safir (QS).

Discussion:

· Heat transfer in 1D model of DF

o MR: Why does area term not appear in any equation? QS: Because we are using heat flux (i.e W/m2)

o MR: For heat transfer across composite wall you have not used overall resistance as in methods seen previously. QS: instead we have used overall heat transfer coefficient which is reciprocal of resistance.

· Mass transfer in 1D model of DF

o QS: unable to use ficks law in form presented here to determine mass of vapourising water as this requires knowledge of diffusion length term. Instead we could try using mass transfer driving force approach as used in other examples of sweat cooling analysis. However do not understand how this equation used for mass transfer driving force is derived. Exmplained in convective heat and mass transfer by W Kays but includes 14 pages of differential equation. Need to read. MR: agreed.

· Mass Transfer by Wesselingh and Krishna

o MR: This book explains that there are three factors which influence mass transfer driving force: chemical (mole fraction) gradients, temperature gradients and gravity. But temperature and gravity are negligible.

· MR: Forward to discussion about forced/free convection in last meeting, found section in page Transport Phenomenon (2^nd edition) by Bird and Lightford on page 317 which addresses this issue. Need to read this.

· Continuous operation of solar ammonia absorption ice maker.

o MR: instead of evaporating water (which may be a scarce resource), why not use evaporation of ammonia which already occurs in cooled chamber to cool the generator.

o QS: will consider this option bearing in mind we don’t want to waste all the heat extraction from evaporation of ammonia in cooling generator so much so that primary objective of cooling chamber is overseen.

· Research by Marzan Rahman:

o MR: confirm evaporation is defined as specific case of vapourisation (see wiki).

o QS: is it preferable to add cold water to DF as suggested by M Rahman? MR: cold water would absorb more heat but would take longer to start vapourising. Need to experiment.

· 2^nd law of thermodynamics and net heat transfer

o Agreed that cooling of DF across against temperature gradient does not break 2^nd law of thermodynamics as work driving process is provided by heat removal by evaporation

o Agreed that net heat transfer in our 1D model of DF should be constant but not zero.

Actions

· QS, MR: to understand derivation of mass transfer driving force.

· QS: to run experiment o investigate the effect of temperature of water added

Next meeting Thursday 22/7/10 at 9pm on Skype (to join add skype ID: qasidsafeer)