Docstoc

ANNEX 7 (DOC download)

Document Sample
ANNEX 7 (DOC download) Powered By Docstoc
					CONFIDENTIAL                 NOTRE             Annex 7 to Progress Report n.01




                             ANNEX 7
               Simplified approach for refrigerated trucks
CONFIDENTIAL                              NOTRE                    Annex 7 to Progress Report n.01




In the meeting in Paris, DIPTEM has discussed theoretical results obtained by means of a
simulation program regarding the frost forming on cooling coils in trucks with tA about 5°C.
The model solves the vapour mass balance of a refrigerated cell with the following assumptions:
isothermal conditions, internal air recycle constant, perfect air mixing, fixed CC surface
temperature. The scheme of the cell is depicted in fig 3 .


                                                                            R. A.




          C. C.     -




                                                               M




                                 VE1

.   Fig. 3: Schematic cell mathematical model ( C.C. cooling coils; VE1 membrane contactor; M
           mass of product; R.A. renewal air)

The ice forming process on CC is represented in fig. 4 on the psychometric chart; in it ts: coil surf.
temp.; te: air temp. at the outlet of CC; tF: air temp. at the inlet of CC; E: air state at the outlet of
CC; F’: air state at the inlet of CC.
CONFIDENTIAL                                 NOTRE              Annex 7 to Progress Report n.01




                            ASHRAE
                            PSYCROMETRIC CHART

                            tS tE          tF'
                                    0 °C




                                                      i
                                                 F'

                               E



Fig. 4 Air dehumidification process on CC owing to the frost forming

As example, ice forming on CC (ts = -5 °C, BF = 0.3) has been evaluated for a refrigerated cell
having a volume of 100 m3, at a cell air temperature of 4°C and with a 7000 m3/h of total recycled
air flow of which 700 m3/h are handled by the membrane contactor (8 m2). The desiccant solution
is saturated CaCl2 at - 3°C inlet temperature.




Fig. 5 Ice forming on CC as a function of time in presence and absence of membrane contactor


Results reported in fig. 5 show that a significant reduction of frost formed on CC versus simulation
time can be obtained, by dehumidificating only a part of the air flow recycled in the cell.

				
DOCUMENT INFO