Kit (Counterflow Heat Exchanger)

Kit (Counterflow Heat Exchanger)

Properties
Stacks	No
Paintable	Yes
Recipe
Created With	Hydraulic Pipe Bender Tier two
Cost	10g Steel, 10g Invar
Logic
Item Hash	6361127870
Item Name	ItemKitPassthroughHeatExchanger

Counterflow Heat Exchanger -
Gas + Gas Counterflow Heat Exchanger -
Gas + Liquid Counterflow Heat Exchanger -
Liquid + Liquid

Operation
Prefab Hash	Varies
Prefab Name	Varies
Construction
Placed with	Kit (Counterflow Heat Exchanger)
Placed on	Small Grid
Stage 1
Next Stage Construction
Constructed with tool	Welder
Constructed with item	Steel Sheets x1
Deconstruction
Deconstructed with	Hand Drill
Item received	Kit (Counterflow Heat Exchanger)
Stage 2
Deconstruction
Deconstructed with	Wrench
Item received	Steel Sheets x1

Description

Stationpedia

Exchange heat from one pipe network to another. By drawing down the pressure of the outputs with a pump or regulator and regulating input pressures, the temperatures of the two counterflowing networks can be effectively exchanged.
Balancing the throughput of both inputs is key to creating a good exchange of temperatures.

Swaps the temperature of two input fluids, how well it does this depends on the relative flow rate of each input.
Perfect temperature exchange is thermodynamically impossible, and doesn't happen in stationeers either. The two connections on the top are part of network 1, and the two on the bottom are part of network 2. A meter on the side displays the heat exchange rate in joules per tick as well as the throughput of input 1 and 2 in moles per tick.

Usage

1. The intended use case for a counterflow heat exchanger is when you have two fluids with the same thermal mass flowing at the same rate in opposite directions. In this condition the heat exchanger will swap the temperatures of the two input fluids and send them to their outputs, possibly off by a few degrees. See first example.

• This can be useful for phase change cooling loops to warm the evaporated phase before it is condensed and to cool the condensed phase before it is evaporated, improving efficiency.

2. They are also commonly used as a more effective heat exchanger that can take greater advantage of a coolant's thermal energy and keep a consistant temperature in a pipe network. In this case fluid properties and flow rate are not the same.

• Say you have a 20C coolant flow trying to cool down a trickle of hot waste gas down to 20C. As long as the flow (or thermal mass) of the coolant is much greater than the waste gas, the output temperature of the waste gas will always be very close to the coolant. If using the Direct heat exchanger instead, the temperature would spike every time more hot gas was introduced to the network before cooling down to the temperature of the coolant again. See second example.
  

Setup

• Example temperature differences are exaggerated, usually the input 1 and output 2 temperatures get very close, within tenths of a degree.

Example showing how the two inputs can effectively exchange their temperatures in ideal conditions.


Example showing how the initial temperature of network 1 determines the output temperature of network 2, when flowrate / thermal mass is skewed heavily in favor of network 1.

Mechanics

The top pipe pair is one flow path (top input → top output). The bottom pipe pair is the other flow path (bottom input → bottom output).

Passive flow

The counterflow heat exchanger is a passive structure. It does not pump by itself. Flow must be created by pumps, regulators, pressure differences, or liquid level differences.

For gas, each side moves the amount needed to equalize its own input and output pressure for that tick:

n_gas = max(0, Pin - Pout) / (8.3144 * Tin * (1/Vin + 1/Vout))

where:

• Pin and Pout are that side's current input and output pressures
• Tin is that side's input temperature
• Vin and Vout are the gas volumes of the connected atmospheres

This means:

• the top input/top output pressure difference controls gas throughput on the top side
• the bottom input/bottom output pressure difference controls gas throughput on the bottom side

For liquids, the exchanger moves liquid to equalize the liquid fill ratio between input and output.

Important: the exchanger has no built-in fixed throughput cap in mol/tick. Actual flow depends on the connected networks.

Minimum flow for heat exchange

Heat exchange only runs if both sides pass at least:

top side throughput    >= 0.008 mol/tick
bottom side throughput >= 0.008 mol/tick

If either side is below this threshold, fluid can still pass through, but it will do so with no heat exchange.

Heat exchange strength

The exchanger effectiveness is:

eta =
max( clamp(Ptop_input / 1 atm, 0, 1), clamp(TopInputLiquidVolumeRatio / 0.01, 0, 1) )
*
max( clamp(Pbottom_input / 1 atm, 0, 1), clamp(BottomInputLiquidVolumeRatio / 0.01, 0, 1) )

In practice:

• Pressure affects throughput on both sides.
• Pressure or liquid fill on both inputs affect heat exchange strength.
• Either input side reaches full effectiveness at about 1 atm or 1% liquid volume ratio.

Practical takeaway

For best performance:

• Maintain flow on both the top and bottom sides.
• Keep both sides above 0.008 mol/tick if you want any heat exchange at all.
• Similar thermal mass flow on both sides gives the best temperature swap.
• Very low pressure on either input side weakens the exchanger unless that side is carrying liquid.

Notes

• It has no logic port
• Requires frame support
• In older versions, heat exchangers had 2 inputs and 2 outputs intended for active liquid flow, but the heat swapping mechanic wasn't fleshed out. This eventually became the counterflow heat exchanger after the Airflow update.
• Passive device: it does not create flow on its own.
• There is no fixed throughput cap. Flow is determined by the connected networks.
• Heat exchange requires at least 0.008 mol/tick on both sides.
• Heat exchange strength depends on the top input and bottom input conditions.
• Either input side reaches full effectiveness at about 1 atm or 1% liquid volume ratio.

Prefab Information

	Prefab Hash	Prefab Name
Gas to Gas	-1674187440	StructurePassthroughHeatExchangerGasToGas
Gas to Liquid	1928991265	StructurePassthroughHeatExchangerGasToLiquid
Liquid to Liquid	-1472829583	StructurePassthroughHeatExchangerLiquidToLiquid