1. Flow mal-distribution study in cryogenic counter-flow plate fin heat exchangers Geet Jain1, Sharad Chaudhary1, Prabhat Kumar Gupta2, P.K. Kush2 1Institue of Engineering and Technology, DAVV, Indore (MP), India 2CCDD,Raja Ramanna Centre for Advanced Technology (RRCAT), Indore (MP), India
Poster ID - 8-P1-11
ICEC
Abstract
Cryogenic compact heat exchanger are well known for their high effectiveness. They are mainly Counter flow type plate fin heat exchanger which are used in various cryogenic applications. Due to their complex operating conditions, geometry and the effects of some physical phenomena such as flow mal-distribution, variable fluid properties, heat leakage, longitudinal heat conduction through wall etc, various losses are there. Conventional design procedure does not takes these effects. Even very small non uniformity in flow may result in huge reduction in thermal performance of heat exchanger. In order to accommodate such performance reduction due to mal-distribution in flow a numerical model is developed and results are compared with conventional method results. If, higher the deviation of mass flow rate for a layer from the average value of mass flow rate for each layer, It will result in more degradation of heat exchanger performance. Temperature limit is K.
Introduction
Helium liquefiers/refrigerators are the energy intensive systems and require very
highly effective(>95%) and compact heat exchanger. The stringent requirement
from these heat exchangers are,
High effectiveness
Low pressure drop
High degree of compactness
These requirements led to the development of compact heat exchangers. Brazed
plate fin heat exchangers are the most suitable heat exchangers in this category.
Figure 1. Different components of heat exchanger core
In header/nozzle combination, the nozzle could be placed at two locations either
center of header or top of the header as shown in figure 2a and figure 2b.
Figure2. (a) Linear weighted distribution (b) Center weighted distribution
Mathematical Modeling and Solution Procedure
It is assumed that one side either hot or cold flow is mal-distributed in different
layers of heat exchanger. When flow is distributed uniformly among different
layers the average mass flow rate can be calculated by following expression:
For linear weighted distribution, the mass flow rate among different layers, is
linearly distributed and can be expressed as,
Mean outlet temperature :
Effectiveness :
Simulation Results and Discussion
Table 1: Process data and some geometric data for case study
Operating parameters Values
Hot and cold fluid mass flow rates (g/s)
Hot fluid inlet temperature (K)
Cold fluid inlet temperature (K)
Process Fluid Helium
No. of hot fluid layer
No. of cold fluid layer
One of the main technical challenges to achieve the required higher effectiveness of plate fin heat exchanger
Minimize the flow mal-distribution
Flow - Uniform
Outlet temperature - Same for all the layers.
Temperature Profile - Same
Flow - maldistributed
Outlet temperature - Different for different layers.
Temperature Profile - Different
This figure shows that the outlet hot fluid temperature of each layer significantly varies with mal-distribution parameter.
Effects of linear weighted maldistribution condition are more severe than the center weighted maldistribution condition.
Performance degradation is 2-3% more in linear weighted than center weighted distribution.
Maximum degradation of performance will occur when only one of the fluid is mal-distributed with highest diviation parameter and the other one flow uniformly throughout all the layers.
Conclusions :
Model developed can evaluate the temperature profiles of different layers of plate fin heat exchanger in presence of flow maldistribution.
Study concludes that center weighted distribution is more preferable and therefore most industrially produced heat exchanger fitted with the nozzle in center position.