Knowledge of PHE Condenser

Knowledge of PHE Condenser

19 Feb 2019

Pressure drop of PHE condenser
1. Refrigerants usually operate under forced pressure, which makes enough pressure drop available.
2. The allowable pressure drop under large temperature difference is higher than that under small temperature difference (large flow rate), but the temperature difference should not be less than 1-2 ℃.
3. The pressure drop at the nozzle should be less than 20% of the total pressure drop, otherwise uneven distribution will occur from the first to the last passage.

PHE condenser
Condensation pressure of PHE condenser
The design condensation pressure should be kept as low as possible. Reducing the condensation pressure means reducing the energy consumption of the compressor under a given refrigeration capacity, or increasing the refrigeration capacity when the energy consumption of the compressor is constant. It is most appropriate to control the difference between condensation temperature and inlet water temperature between 5 and 10 ℃.
During the operation of compressor, the pressure should be kept unchanged. When the cooling water temperature decreases, the condensation pressure should not be reduced to the limit value at least. If too much reduction is made, the thermal expansion valve will not have enough pressure difference to give the required capacity.

Direction of flow
Because the load of the condenser cycle (the amount of condensation) is greater than that of the evaporator cycle (the amount of refrigeration). So it is better to make the condenser cycle countercurrent (heat pump cycle), and the evaporator cycle downstream (refrigeration cycle).

Pressure drop
1. From an economic point of view, pressure drop can be adjusted to a reasonable value.
2. When the pressure drop is less than 0.2-0.3 MPa, there is no risk of erosion in brazed heat exchanger.
3. Flow rate and pressure drop must be calculated at the same time in order to get the best value.
4. Shell-and-tube or tube heat exchangers are conducive to large flow rate and low pressure drop, while brazed heat exchangers are the opposite. The optimum flow rate is generally to make the pressure drop of the length of the runner per meter greater than 0.04 MPa.
5. The total pressure drop at the nozzle is less than 30%.

Fault Diagnosis of PHE condenser
Insufficient capacity
1. Check flow rate, temperature and pressure drop. Determine what causes abnormal pressure drop.
2. Check water flow obstruction, abnormal sound, etc.
3. Check the temperature change on the outside surface of the condenser. Large temperature difference may be inert gas blockage or water side blockage or refrigerant flow blockage.
4. If it's not pure water, check the cooling fluid. In the case of ethylene glycol aqueous solutions or similar substances, their concentration and/or viscosity can be checked. High concentration will weaken heat transfer.
5. Check fouling in liquid side of condenser and lubricating oil in refrigerant side.

Does the evaporator match the compressor?
1. Check the compressor. Whether the compressor discharges enough refrigerant to the condenser at rated pressure.
If more refrigerant is discharged than inhaled, the excess refrigerant can not condense in the condenser, which reduces the capacity. Is the internal leakage of refrigerant caused by compressor wear? Is the speed and current consumption consistent with its capacity?

Low capacity, but the supercooling degree of the condensate is too high, which means that the condensate level is too high, blocking the heating surface of the condenser used for condensation. This phenomenon may be that there is too much refrigerant charge in the system.

The large distance between the pressure control valve of the reservoir and the condenser means that the condensate has to be filled with condensate tube before its liquid level rises, that is, the response time is long. On the contrary, the response time is short when the condenser discharges liquid.

2. Check the mechanical properties of various valves. Especially expansion valves, impurities in water or metal debris due to wear and tear, it is easy to block flow and damage valves. If the flow reduction is caused by blockage, its capacity will also be reduced. The blocked valve is exposed through its irregular control operation and/or abnormal sound.