Why is the expansion valve modeled as h4 = h3?

A throttling valve is approximately adiabatic with no shaft work, so the steady-flow energy equation gives an isenthalpic process. Pressure drops sharply while part of the liquid flashes to vapor.

Why does higher condensing temperature lower COP?

A higher condenser temperature raises the high-side pressure and compressor pressure ratio, so more work is needed for roughly the same evaporator heat pickup.

Vapor-Compression Refrigeration Cycle

Compressor, condenser, expansion valve, evaporator: COP, cooling capacity, pressure ratio, and p-h sketch with states 1-2-3-4.

The cycle shows the four ideal components and the energy balances. Real systems require refrigerant property tables, pressure drops, heat-exchanger approach temperatures, compressor maps, oil return, and two-phase details.

Live graphs

About this model

A vapor-compression refrigerator circulates refrigerant through four idealized components: the evaporator absorbs heat at low pressure, the compressor raises pressure and temperature, the condenser rejects heat at high pressure, and the expansion valve throttles liquid back to the evaporator pressure. This simulator uses a simple refrigerant-like property model to expose the energy bookkeeping: COP_R = (h1 − h4)/(h2 − h1), compressor efficiency raises h2 above the isentropic endpoint, and the expansion valve is treated as isenthalpic with h4 = h3. The p-h sketch marks states 1-2-3-4 and the component schematic shows heat and work flows. It is not a property-table solver: real design needs refrigerant data, two-phase quality, pressure drops, heat-exchanger approach temperatures, compressor maps, superheat control, oil return, and safety limits.

Who it's for: HVAC, refrigeration, thermodynamics, heat-pump, and mechanical engineering introductions.

Key terms

Vapor-compression cycle
COP
Evaporator
Condenser
Expansion valve
p-h diagram

How it works

Vapor-compression refrigeration cycle with compressor, condenser, expansion valve, evaporator, COP, cooling capacity, pressure ratio, and p-h sketch.

Key equations

COP_R = q_evap / w_comp = (h1 − h4)/(h2 − h1)

Compressor: h2 = h1 + (h2s − h1)/ηis; valve: h4 = h3

Frequently asked questions

Why is the expansion valve modeled as h4 = h3?: A throttling valve is approximately adiabatic with no shaft work, so the steady-flow energy equation gives an isenthalpic process. Pressure drops sharply while part of the liquid flashes to vapor.
Why does higher condensing temperature lower COP?: A higher condenser temperature raises the high-side pressure and compressor pressure ratio, so more work is needed for roughly the same evaporator heat pickup.

Continue with similar topics in this category — or all 46 in Thermodynamics.

View category →

NewSchool

Otto Cycle

Launch Simulator

PV diagram: adiabatic compression/expansion and isochoric heat; η = 1 − r^{1−γ}.

NewSchool

Rankine Cycle (Steam)

Launch Simulator

T–s with vapor dome + schematic P–v: pump, boiler, turbine, condenser; x₄ and pressure sliders.

NewSchool

Brayton Cycle (Gas Turbine)

Launch Simulator

PV: isentropic compress, isobaric heat in, isentropic expand, isobaric cool — jet/GT core cartoon.

NewSchool

Refrigeration Cycle (Reverse Carnot)

Launch Simulator

PV loop like Carnot but reversed; COP_R & COP_HP; T_C/T_H in K; symbolic fridge sketch.

NewSchool

Diesel Cycle (PV)

Launch Simulator

Air-standard: adiabat compress, isobaric heat, adiabat expand, isochoric out; η(ρ_c, β).

NewSchool

Wet Steam (T–s sketch)

Launch Simulator

Vapor dome, horizontal isobar in two-phase region, quality x and superheat sketch.

Vapor-Compression Refrigeration Cycle

Live graphs

About this model

How it works

Key equations

Frequently asked questions

Related simulators

Otto Cycle

Rankine Cycle (Steam)

Brayton Cycle (Gas Turbine)

Refrigeration Cycle (Reverse Carnot)

Diesel Cycle (PV)

Wet Steam (T–s sketch)

Vapor-Compression Refrigeration Cycle

Live graphs

About this model

How it works

Key equations

Frequently asked questions